Compendium Type: I
METHODS AND KEY TO RATINGS
Preferred Practice Pattern® guidelines should be clinically relevant and specific enough to provide useful information to practitioners. Where evidence exists to support a recommendation for care, the recommendation should be given an explicit rating that shows the strength of evidence. To accomplish these aims, methods from the Scottish Intercollegiate Guideline Network1 (SIGN) and the Grading of Recommendations Assessment, Development and Evaluation2 (GRADE) group are used. GRADE is a systematic approach to grading the strength of the total body of evidence that is available to support recommendations on a specific clinical management issue. Organizations that have adopted GRADE include SIGN, the World Health Organization, the Agency for Healthcare Research and Policy, and the American College of Physicians.3
All studies used to form a recommendation for care are graded for strength of evidence individually, and that grade is listed with the study citation.
To rate individual studies, a scale based on SIGN1 is used. The definitions and levels of evidence to rate individual studies are as follows:
High-quality meta-analyses, systematic reviews of randomized controlled trials (RCTs), or RCTs with a very low risk of bias
Well-conducted meta-analyses, systematic reviews of RCTs, or RCTs with a low risk of bias
Meta-analyses, systematic reviews of RCTs, or RCTs with a high risk of bias
High-quality systematic reviews of case-control or cohort studies
High-quality case-control or cohort studies with a very low risk of confounding or bias and a high probability that the relationship is causal
Well-conducted case-control or cohort studies with a low risk of confounding or bias and a moderate probability that the relationship is causal
Case-control or cohort studies with a high risk of confounding or bias and a significant risk that the relationship is not causal
Nonanalytic studies (e.g., case reports, case series)
Further research is very unlikely to change our confidence in the estimate of effect
Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate
Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate
Any estimate of effect is very uncertain
Used when the desirable effects of an intervention clearly outweigh the undesirable effects or clearly do not
Used when the trade-offs are less certain-either because of low-quality evidence or because evidence suggests that desirable and undesirable effects are closely balanced
The Highlighted Findings and Recommendations for Care section lists points determined by the PPP Panel to be of particular importance to vision and quality of life outcomes. A good practice point may emphasize the importance of patient preferences in decision making or feature a practical point for which there is not, nor is there likely to be, any research evidence.4
Literature searches to update the PPP were undertaken in February, March, and December 2011 in PubMed and the Cochrane Library. Complete details of the literature search are available in Literature Search Details under Related Links.
HIGHLIGHTED FINDINGS AND RECOMMENDATIONS FOR CARE
Overnight wear, regardless of contact lens type (including the newest highly gas-permeable silicone hydrogel lenses), increases the likelihood of corneal infection.5-11 (good evidence) Although there are lenses approved by the Food and Drug Administration (FDA) for extended wear, this and other risks, benefits, and alternatives should be presented to patients for whom this mode of contact lens wear is being considered.(strong recommendation)
Patients should be instructed that rubbing is an important part of the cleaning step before disinfection for any lens that is to be reworn. Rubbing the contact lens enhances the cleaning performance of the solution, likely by removing loosely bound deposits. Hydrogen peroxide systems may be superior to preserved disinfecting solutions in reducing pathogen bindingand cysticidal disinfection, but they require more complex care regimens.12-18 (strong recommendation, good evidence)
Environmental risk factors and hygiene practices, such as no-rub cleaning, topping off (reuse) of solutions, contaminated lens cases, exposure to tap water, wearing contact lenses in hot tubs, and changes in water supply are emerging as possible risk factors for the increases in Acanthamoeba and fungal keratitis in association with contact lens use in the past decade.12,13,15,19-37(moderate evidence)
Presbyopia can be managed by using eyeglasses or contact lenses (soft, rigid gas-permeable, aspheric bifocal or multifocal). These can be used bilaterally or for monovision and modified monovision. Modified monovision is the use of a bifocal or multifocal contact lens in one eye and a distance contact lens in the fellow eye. Surgical management of presbyopia includes keratorefractive surgery for monovision or intraocular lens implantation (monofocal lenses for monovision, multifocal lenses, or accommodative lenses).(good evidence)
Preoperative assessment of the potential refractive surgery patient should address expectations for postsurgical vision and emphasize potential adverse events or complications that may occur, explaining which may be transient and which may be permanent. (good practice point)
Before refractive surgery, corneal topography should be evaluated for evidence of irregular astigmatism, corneal warpage, or abnormalities suggestive of keratoconus or other corneal ectasias. All of these conditions may be associated with unpredictable refractive outcomes, and keratoconus and the ectasiasmay be associatedwith ectasia progression following keratorefractive surgery.38-41 When considering intraocular refractive surgery, measurement ofcorneal topography is important to assess the optical characteristics of the cornea. It is also relevant if akeratorefractive surgical procedure is necessary to optimize the refractive result after the lens surgery or for toric intraocular lens implantation. (strong recommendation, moderate evidence)
Patients should be informed that there is a risk for night-vision symptoms afterkeratorefractive surgery. (good evidence, strong recommendation) Most studies of conventional and wavefront-guided laser in situ keratomileusis (LASIK) have not shown a relationship between the diameter of the low-light pupil and night-vision symptoms postoperatively.42-46(moderate evidence)
The preferred approaches for LASIK retreatment are relifting the original flap or performing photorefractive keratectomy (PRK) with or without mitomycin-C (off-label use) on the original flap. If a new flap is cut, the intersection of the surgical planes can result in displaced stromal fragments, which can cause irregular astigmatism and loss of best-corrected visual acuity (BCVA).47,48 (strong recommendation, moderate evidence)
It is recommended that refractive surgery patients be provided with a record or that the ophthalmologist maintains a record that lists information about the patient's eye condition, including preoperative keratometry readings and refraction, as well as stable postoperative refraction, so that it will be available if the patient requires cataract surgery or additional eye care. (See Appendix 7.) (good practice point)
Because there is a potential compromise in quality of vision with some intraocular lenses (IOLs), such as multifocal, compared with spheric monofocal IOLs49 (good evidence), surgeons should understand the individual patient's lifestyle and expectations so that the best IOL option can be selected for patients undergoing a refractive lens exchange. (strong recommendation)
Refractive error (ametropia) is present when parallel rays of light entering the nonaccommodating eye do not focus on the retina. The visual effect is a blurry image. Myopia is a common optical aberration in which the eye has too much optical power and parallel light rays from a distant image are focused on a point anterior to the retina. Hyperopia is also a common aberration and is one in which the eye does not have enough optical power and distant light rays strike the retina before converging on the retina. Astigmatism and other forms of optical aberrations occur when incident light rays do not converge at a single focal point. Total refractive astigmatism can be divided into corneal (or keratometric) astigmatism, lenticular astigmatism, and retinal astigmatism. Most astigmatism is corneal in origin. Lenticular astigmatism is a result of uneven curvature, lens tilt, and differing refractive indices within the lens.50
In regular astigmatism, the refractive power varies successively from one meridian to the next, and each meridian has a uniform curvature at every point across the entrance pupil. The meridians of greatest and least power, the so-called principal meridians, are located 90 degrees apart.51
In irregular astigmatism, the magnitude and the axis of astigmatism vary from point to point across the entrance pupil (e.g., following keratoplasty, radial keratotomy [RK], or complicated keratorefractive surgery).52 This can be clinically significant in conditions such as keratoconus and other corneal ectasias, corneal epithelial basement membrane and stromal dystrophies, corneal scarring, and postsurgical corneas. Irregular astigmatism is one example of a type of optical aberration termed higher order aberration (HOA). Higher order aberrations cannot be fully corrected by spherocylindrical eyeglass lenses. Methods for describing HOAs include Zernike polynomials and Fourier analysis.
In this document, low to moderate refractive errors are defined as less than 6.00 diopters (D) of myopia, less than 3.00 D of hyperopia, and less than 3.00 D of regular astigmatism. High refractive errors are defined as 6.00 D or more of myopia, 3.00 D or more of hyperopia, and 3.00 D or more of regular astigmatism.
Presbyopia is a condition that develops with aging and results in insufficient accommodation for near work in a patient whose distance refractive error is fully corrected. Although not truly a refractive error, presbyopia will be considered in this document because its correction has similarities to the correction of refractive errors. The correction of presbyopia is also discussed in the Cataract in the Adult Eye PPP.53
This PPP addresses refractive errors in patients who are beyond the age at which amblyopia may develop, and Table 1 lists the International Classification of Diseases codes for refractive errors.
TABLE 1. International Classification of Diseases and Related Health Problems Codes
Individuals who are beyond the amblyogenic age and have refractive errors
Determine the patient's visual needs
Identify and quantify any refractive errors
Discuss with the patient the nature of the refractive error, appropriate alternatives for correction, and the risks and benefits of each approach
Inform patients, especially those with high refractive errors, about the potentially increased incidence of associated pathologic conditions
Correct symptomatic refractive errors with eyeglasses, contact lenses, or surgery, as desired by the informed patient and as deemed appropriate by the physician
Provide the patient with follow-up care and management of any side effects or complications resulting from the correction provided
PREVALENCE AND RISK FACTORS
Over half of Americans older than 40 have ametropia of sufficient magnitude to require refractive correction.54 Currently, an estimated 93 million Americans aged 12 years and older use some form of eyewear to correct refractive errors at distance.55 About 36 million people in the United States used contact lenses in 2005.56 It is estimated that over 8.5 million people in the United States have undergone refractive surgery since 1995.57
The prevalence of myopia (0.75 D or more) is estimated to be 9% in children in the United States aged 5 to 17 years.58 A meta-analysis of population-based studies found a prevalence of myopia (1.00 D or more) of 25% in persons over age 40 in the United States59; a study based on a sample representative of the US population found a prevalence of 31% in those aged 40 and older and of 36% in those aged 20 and older.54 A number of population-based studies have shown that the prevalence of myopia is lower in older persons than in younger persons. The prevalence is about 35% to 40% among persons in their 20s to 40s and decreases to about 15% to 20% among those in their 60s, 70s, and 80s.54,60-62 Myopia was found to be significantly more prevalent among non-Hispanic white persons than among persons of non-Hispanic black or Mexican American race/ethnicity.54
Both hereditary and environmental factors appear to play a role in the development of myopia. Studies suggest a higher concordance of myopia between monozygotic than dizygotic twins63 and between children and parents.64-66 Studies have identified links between several gene regions, particularly chromosome 18p, and myopia,67-72 although other studies have either found no association,73 more complex relationships,74 or in studying Asian populations, have found other genetic variations associated with high myopia.75-80 More years of formal education have been strongly associated with a higher prevalence of myopia.81-85 Some studies have reported that a higher level of near work is associated with a higher prevalence and progression of myopia,86-89 but subsequent studies have not, especially with respect to middle distance activities such as those that involve video display terminals.84,90-93 The use of night lights for children under age 2 years has been reported as a strong risk factor for myopia94; however, other studies that were able to adjust for parental refractive status did not find such an association.87,95 Several studies have reported that myopia was associated with less time spent outdoors.92,96-98 Studies in Israel and England have found an association between higher prevalence of myopia and birth during the summer months.99,100
Studies of ethnic Chinese in Taiwan documented an increase in the prevalence and severity of myopia over two generations.101-104 Genetics alone are unlikely to account for such a rapid change, although one study has speculated that genetic factors do not preclude such a change.105 A study of successive cohorts of enlistees in the Israeli army showed a marked increase in prevalence of myopia over a 13-year period.106 A study in Finland showed that the prevalence of myopia doubled among teenagers and young adults over the course of the 20th century.107 A study comparing U.S. population-based estimates in 1971 to 1972 and 1999 to 2004 also found a marked increase in the prevalence of myopia, although the reasons for this increase could not be identified.108
A meta-analysis of population-based studies found the prevalence of hyperopia was 10% in the United States and increased with increasing age.59 Another study, based on a sample representative of the U.S. population, found that the prevalence of hyperopia in those aged 40 and older was 5%, with little variation by race/ethnicity.54 Population-based studies of Caucasians aged 40 and older report that the prevalence of hyperopia increases from about 20% among those in their 40s to about 60% among those in their 70s and 80s.60,61,109 A similar pattern of higher prevalence of hyperopia in older ages was observed in a U.S. population-based study.54 A similar prevalence and changes with age were seen among African Americans in Baltimore.61 In contrast to myopia, hyperopia was associated with fewer years of formal education in the same populations.60,61
Kleinstein et al58 found that 28% of their U.S.-based study population aged 5 to 17 years had astigmatism of 1.00 D or more. In a multiethnic pediatric eye disease study, the prevalence of astigmatism in African American and Hispanic children aged 6 to 72 months was 12.7% and 16.8%, respectively.110 Astigmatism of 1.00 D or more is common among older adults (31% in persons aged 40 and older), and the prevalence is higher in older age groups.54 In adult Americans, the prevalence of astigmatism has been reported to be 20% higher among men than women but was not associated with number of years of formal education and did not vary substantially by race/ethnicity.54,61 There have been conflicting data about the association of astigmatism with prematurity or low birth weight, and with retinopathy of prematurity.111-114
Further discussion of the epidemiology of refractive errors is presented in Appendix 2.
The distribution of refractive errors changes with age. Newborns average 3.00 D of hyperopia.115 This may increase slightly in the first few months, but then it declines toward an average of 1.00 D of hyperopia by 1 year of age.115 Fewer than 5% of infants have more than 3.00 D of hyperopia at age 1 year.115,116 This shift toward emmetropia is a complex process that involves changes in the power of the refractive components of the eye, including thinning of the crystalline lens.117 Visual stimulation appears to play a role in this process.118,119
Myopia typically appears between 6 and 12 years of age, and the mean rate of progression is approximately 0.50 D per year, based on studies of mostly Caucasian children.120-122 A study reported that progression of myopia varied by ethnicity and by age of the child.123 For ethnic Chinese children, the rate of progression is higher.124-129
Astigmatism in children is commonly oriented with the steep axis vertical ("with the rule"). In older adults, astigmatism oriented with the steep meridian horizontally is more common ("against the rule")130,131 and remains relatively stable in older adults,132 although one study found that the axis of astigmatism tended to shift against the rule over a 5-year period.133
Individuals with high refractive errors are more likely to develop pathologic ocular changes over time. Highly myopic patients have an increased incidence of progressive elongation of the eye with progressive retinal thinning, peripheral retinal degeneration, retinal detachment,134 cataract,135 and glaucoma.136-139 An increased risk of glaucoma and visual field defects with myopia has also been found.140,141 An increased risk of developing primary angle-closure glaucoma among individuals with hyperopia has been reported.142
RATIONALE FOR TREATMENT
The major reasons for treating refractive errors are to improve a patient's visual acuity, visual function, and visual comfort. It may be desirable to correct a very small error in one patient, whereas another patient may function well with no ill effects when the same very small refractive error is not corrected. Patients with moderate to high refractive errors generally require correction to achieve satisfactory vision. Other reasons for treatment include enhancing binocular vision (e.g., for driver safety), controlling strabismus (e.g., accommodative esotropia), and, on a societal level, preventing economic productivity loss associated with uncorrected refractive error.143 In patients beyond visual maturity (see Amblyopia PPP144), uncorrected refractive errors do not result in amblyopia. At any age, uncorrected refractive errors do not lead to structural ocular damage or to worsening of the refractive status.
Treatments have been reported that aim to prevent progression of refractive errors, particularly myopia. Evidence reported in the peer-reviewed literature, including from randomized clinical trials and a 2011 Cochrane review is currently insufficient to recommend any intervention to prevent progression of refractive errors.145,146(See Appendix 3.)
PATIENT OUTCOME CRITERIA
Outcome criteria vary depending on the individual's needs, lifestyle, and overall medical condition. The goal is to provide vision that meets the patient's functional needs with minimal and tolerable side effects.
The evaluation of refractive errors requires an assessment of both the refractive status of the eye, the patient's current mode of correction, symptoms, and visual needs. Refraction is often performed in conjunction with a comprehensive medical eye evaluation.147
The history should incorporate the elements of the comprehensive adult medical eye evaluation to consider the patient's visual needs and any ocular pathology. (See Appendix 4.)
Measuring Visual Acuity
Distance visual acuity is usually measured in a dimly lit room, typically at 20 feet (6 meters), as the patient looks at a chart with lines of high-contrast characters. Distance acuity should be measured separately for each eye with current correction. Near acuity is usually measured while the patient looks at a well-lit reading card of high-contrast characters held at a specified near working distance, typically 14 inches or 36 centimeters.
Each eye should be evaluated independently. The refraction may be performed objectively by retinoscopy, an autorefractor, or a wavefront analyzer; or it may be done subjectively. In cooperative patients, subjective refinement of refraction using a phoropter or trial lens set is preferred. Determination of vertex distance and precise astigmatic axis is especially important in patients with high refractive errors.
The reproducibility of subjective refraction has been found to be within 0.50 D for spherical equivalent, spherical power, and cylindrical power.148,149
Distance refraction should be performed with accommodation relaxed. This may be accomplished by using manifest (noncycloplegic) refraction with fogging or other techniques to minimize accommodation with care not to provide excess minus power correction to the patient. In some cases, especially in younger patients,150 a cycloplegic refraction can be useful.
Near vision should be measured in each eye before cycloplegia for patients with high hyperopia, presbyopia, or complaints about near vision. If the patient is presbyopic, the near- vision add is determined at the reading or working distance preferred by the patient.
Cycloplegic refraction is indicated for patients in whom accommodation cannot be relaxed and for patients whose symptoms are not consistent with the manifest (noncycloplegic) refractive error. It is advised for patients when the accuracy of the refraction is in question for any reason. In adults, the most frequently used cycloplegic agents are tropicamide and cyclopentolate. Tropicamide provides a more rapid onset of action and a shorter duration of effect while cyclopentolate provides greater cycloplegia that can allow a more accurate refraction but a longer duration of effect.151 A significant difference between manifest and cycloplegic refraction is observed frequently in children; in adults, a substantial difference between manifest and cycloplegic refraction may require a postcycloplegic refraction on a subsequent day when the cycloplegic refraction is used to guide the final manifest prescription. The postcycloplegic refraction is performed after full accommodation has returned.
Although most normal eyes should have a corrected acuity of 20/20 to 20/25 or better, it may not be possible to achieve this level of acuity in patients with high refractive errors, even with optimal refraction. For a subset of patients, this might be due to the minification produced by high myopic correction at the spectacle plane. In other cases, refractive amblyopia may be the cause. However, a pathologic basis for reduced best-corrected visual acuity (BCVA) should be sought. A suddenly acquired refractive change may signal a systemic or local disease, or a drug or medication effect. Excellent visual acuity does not preclude serious eye disease; therefore, all patients should have a comprehensive medical eye evaluation at the recommended intervals.147,150
The need to correct refractive errors depends on the patient's symptoms and visual needs. Patients with low or monocular refractive errors may not require correction; small changes in refractive corrections in asymptomatic patients are generally not recommended. Correction options include eyeglasses, contact lenses, or refractive surgery. Various occupational and recreational requirements as well as personal preferences affect the specific choices for any individual patient.
Presbyopia can be managed by eyeglasses or contact lenses (soft, rigid gas-permeable, aspheric bifocal or multifocal). These can be used bilaterally or for monovision and modified monovision. Modified monovision is the use of a bifocal or multifocal contact lens in one eye and a distance contact lens in the fellow eye. Surgical management of presbyopia includes keratorefractive surgery for monovision or intraocular lens implantation (monofocal lenses for monovision, multifocal lenses, or accommodative lenses).(good evidence)
Eyeglasses are the simplest and safest means of correcting a refractive error; therefore, eyeglasses should be considered before contact lenses or refractive surgery. A patient's eyeglasses and refraction should be evaluated whenever visual symptoms develop. Optimal eyeglass correction for higher refractive errors requires precision in fitting, especially with respect to the position of the optical center of each lens relative to the pupil. High-index lenses, which reduce the lens thickness and weight, are useful in correcting high refractive errors and providing increased comfort and better cosmetic appearance. The principles and guidelines for correcting specific refractive errors with eyeglasses are outlined in Appendix 5.
When hyperopia is accompanied by esotropia, eyeglasses may be required to control the strabismus or to improve fusion.152 If minus lenses improve fusion in intermittent exotropia, eyeglass correction may be indicated even if the patient is not myopic.
A nonrefractive, yet important, indication for eyeglasses is to protect the eyes from accidental injury. Safety glasses or eye protectors are strongly recommended for individuals involved in certain sports (e.g., racquetball, squash) and hazardous activities in which there is risk of flying particles (e.g., using hammers, saws, weed trimmers).153 They are also recommended for all individuals with good vision in only one eye. When ocular protection is the foremost consideration, polycarbonate plastic is the material of choice because it is much more impact resistant than regular plastic or hardened glass.154 Depending on the activity, frames with side protection may be important.
A contact lens can correct a wide range of refractive errors by acting as the initial refractive surface of the eye. Soft hydrogel contact lenses, silicone hydrogel contact lenses with greater oxygen transmissibility, or rigid gas-permeable contact lenses are used most commonly. Polymethylmethacrylate (PMMA) contact lenses are now rarely used because that material is not permeable to oxygen. Approximately 36 million individuals in the United States successfully used contact lenses for visual correction in 2010, and in 2007 there were an estimated 125 million contact lens wearers globally.155 Although contact lenses are of great visual benefit, their use does carry some risk of ocular complications.
Patients who do not wish to wear eyeglasses most frequently use contact lenses. Many patients who use contact lenses note better field of vision, greater comfort, and/or an improved quality of vision. Some patients have special occupational needs that cannot be met by eyeglasses, and others prefer their appearance without eyeglasses. Some patients achieve optimal visual function only with contact lenses. This may include patients with high refractive errors, symptomatic anisometropia or aniseikonia, or an irregular corneal surface or shape.
The use of contact lenses to correct refractive errors may not be advisable when there is significant eyelid, tear film, or ocular surface abnormalities related to any of the following:
Other corneal abnormalities
Other relative contraindications include the following:
Use of topical corticosteroids
Inflammation of the anterior segment
Presence of a filtering bleb
Certain environmental or work settings (e.g., dust, volatile chemicals
History of corneal complications related to contact lense
Inability to understand the risks and responsibilities involved
The risks of complications associated with contact lenses should be weighed against the protective benefit of eyeglasses for monocular or functionally monocular patients.
The most serious risk of contact lens use is the development of microbial keratitis, which can lead to visual loss even if properly treated. Other complications with all types of contact lens use include hypersensitivity reactions such as giant papillary conjunctivitis, problems of the ocular surface such as surface breakdown, superficial keratitis, recurrent erosions, Salzmann nodules, subepithelial fibrosis, subepithelial opacification, and limbal stem cell deficiency, as well as corneal neovascularization, sterile infiltrates, and corneal warpage.156-161 Transient subclinical stromal edema frequently occurs, and corneal thinning of the epithelium and stroma during contact lens wear has also been reported.161,162 Endothelial changes can occur, including polymegethism, pleomorphism, and, rarely, reduction of endothelial cell density.163-165 The clinical significance of transient edema, thinning, and endothelial changes is uncertain.
Microbial keratitis as a complication of contact lens use is most frequently caused by bacteria, but it can also be caused by more unusual organisms that are difficult to diagnose and treat such as Acanthamoeba and fungi.166-172
When soft contact lenses were introduced for extended wear in the early 1980s, Pseudomonas aeruginosa became a frequently identified pathogen in cases of keratitis in individuals using extended-wear soft contact lenses.166,168 Investigations into the pathogenesis of Pseudomonas keratitis showed that Pseudomonas aeruginosa adhered readily to contact lens deposits.173 This was of concern because contact lenses develop more deposits as duration of use increases. Other investigations demonstrated that the relative risk of microbial keratitis was 10 to 15 times greater in patients using soft contact lenses on an extended-wear basis compared with patients using soft lenses for daily wear174 and that extended-wear soft contact lens users had an annualized incidence five times that of daily-wear patients (21 vs. 4 per 10,000 persons).11
Disposable soft contact lenses for extended wear were introduced in the late 1980s in an attempt to improve the safety of extended wear by allowing more frequent contact lens replacement. Disposable soft contact lenses for extended wear were eventually found to have the same incidence of microbial keratitis as conventional reusable soft lenses for overnight wear.5,6 It was the pattern of contact lens wear (overnight vs. daily) rather than the type of contact lens (disposable vs. nondisposable) that appeared to be the overriding risk factor for microbial keratitis.5,6 Despite the increased risk of microbial keratitis associated with overnight wear, there are contact lenses approved by the FDA for extended (including overnight) wear. Although the incidence of microbial keratitis is similar whether disposable or conventional soft contact lenses are used for overnight wear, disposable lenses are more often associated with relatively benign peripheral infiltrates than with the aggressive central microbial keratitis that is common with conventional soft lenses used for overnight wear.6,175,176 In cases where microbial keratitis does occur, disposable contact lenses for extended wear are more often associated with gram-positive organisms than with gram-negative organisms.177-179 Patients using disposable soft contact lenses for overnight wear are also less likely to be symptomatic in terms of discomfort or red eye complaints than patients using conventional reusable lenses for overnight wear.175
Although disposable contact lenses were initially introduced for extended wear, they have become popular for daily wear as well. Patients who use disposable soft contact lenses on a daily-wear basis tend to be less symptomatic in terms of lens-related complaints when compared with conventional soft daily-wear lens users.180 Disposable soft contact lenses intended for one day of use only (daily disposables) were introduced in 1995. Their use currently represents the safest method of soft contact lens wear.181 However, the parameters available for daily disposable contact lenses are somewhat more limited than those for disposable lenses intended for longer use or conventional reusable soft lenses.
Investigators have shown that contact lenses of lower oxygen transmission are more likely to be associated with corneal epithelial binding of Pseudomonas aeruginosa than are higher oxygen transmissible lenses.182-185 Soft silicone hydrogel contact lenses with extremely high gas transmission have now been developed for extended wear, but the anticipated reduction in rate of microbial keratitis has not occurred.7-9 These materials meet central and peripheral oxygen transmissibility thresholds to avoid corneal swelling during open-eye soft contact lens wear.186 The delivery of adequate oxygen to the cornea is of particular concern when contact lenses are used to correct high refractive errors because of increased contact lens thickness combined with increased likelihood of inadequate movement to achieve subjective tolerance.
A small percentage of patients who are fitted with silicone hydrogel contact lenses for 7-day or 30-day continuous wear developed sterile inflammatory peripheral corneal infiltrates with 1 year of use.187 Another study showed a 10% probability of developing an infiltrate at the end of 3 years when silicone hydrogel contact lenses were worn for up to 30 nights continuously.188 Smoking and a substantial lens bacterial bioburden pose prominent risks for a corneal infiltrative event.189 In addition to hypoxia, tear stagnation may play a role in alterations of corneal epithelium associated with overnight contact lens wear.190 Neither of the more recently introduced contact lens modalities, daily disposable or silicone hydrogel material, reduced the overall risk of acute nonulcerative events.191 The exact relationship between corneal infiltrative events and microbial keratitis remains unclear.
A study of patients using silicone hydrogel contact lenses continuously for up to 30 days concluded that the overall rate of microbial keratitis in these lenses with very high oxygen transmissibility was similar to that of conventional extended-wear soft lenses.7 A 2008 case-control study from London found that the risk of microbial keratitis had not been reduced for users of daily disposable and silicone hydrogel lenses, and that different brands of contact lenses may be associated with significantly different risks of keratitis. Their findings suggest that lens and ocular surface interactions may be more important in the development of corneal infection than oxygen levels and contact-lens-case contamination.8 A population-based surveillance survey in Australia published at the same time found that the incidence of microbial keratitis was not reduced with the introduction of new lens types, and that overnight use of any contact lens is associated with a higher risk than daily use.9
Overnight wear of a soft lens may be indicated on a therapeutic basis for ocular surface problems; there are highly gas-permeable silicone hydrogel lenses that are FDA-approved for extended wear on that basis. Overnight use of any contact lens is associated with a higher risk of infectious keratitis, and daily wear of a rigid gas-permeable lens is associated with the lowest rate of microbial keratitis of any lens type and wearing schedule.9
Overnight wear, regardless of contact lens type (including the newest highly gas-permeable silicone hydrogel lenses), increases the likelihood of corneal infection.5-11 (good evidence)Although there are lenses approved by the Food and Drug Administration (FDA) for extended wear, this and other risks, benefits, and alternatives should be presented to patients for whom this mode of contact lens wear is being considered.(strong recommendation)
There have been outbreaks and reports of increases in Acanthamoeba and fungal keratitis in association with contact lens use in the past decade.12,13,15,19-33,192 This trend predates the association with the use of certain multipurpose solutions with reduced antimicrobial efficacy that are no longer on the market,34-37 and it is associated with all lens types. Environmental risk factors and hygiene practices, such as no-rub cleaning, topping off (reuse) of solutions, contaminated lens cases, exposure to tap water, and changes in water supply are emerging as possible risk factors. A study of Fusaria isolates from the U.S. outbreaks of 2005 and 2006 found a high degree of phylogenetic diversity consistent with multiple sources of contamination.193
MedWatch (www.fda.gov/medwatch) is the Safety Information and Adverse Reporting Program for drugs and other medical products regulated by the FDA. Adverse experiences of contact lens wear should be reported to MedWatch.
Environmental risk factors and hygiene practices, such as no-rub cleaning, topping off (reuse) of solutions, contaminated lens cases, exposure to tap water, wearing contact lenses in hot tubs, and changes in water supply are emerging as possible risk factors for the increases in Acanthamoeba and fungal keratitis in association with contact lens use in the past decade.12,13,15,19-37 (moderate evidence)
Selection and Fitting
Before fitting a patient for contact lenses, an ocular history including past contact lens experience should be obtained and a comprehensive medical eye evaluation should be performed.147,150 During this examination, particular attention should be directed at evaluating the patient's hygiene and ability to adhere to proper contact lens care, as well as to ocular parameters such as lid function, lid margins, meibomian glands, tear film, conjunctival surface, and the corneal surface. General principles for selecting and fitting contact lenses are described in Appendix 6.
Patient Education and Contact Lens Care
The FDA has made the following recommendations for contact lens wearers regarding proper lens care practices:194
Wash hands with soap and water, and dry (lint-free method) before handling contact lenses
Wear and replace contact lenses according to the schedule prescribed by the doctor
Follow the specific contact lens cleaning and storage guidelines from the doctor and the solution manufacturer
Keep the contact lens case clean and replace it every 3 to 6 months
Remove the contact lenses and consult your doctor immediately if you experience symptoms such as redness, pain, tearing, increased light sensitivity, blurry vision, discharge, or swelling
These recommendations apply to contact lenses prescribed for refractive error and for contact lenses that alter the appearance of the eye (decorative contact lenses).195,196
When contact lenses are initially prescribed and dispensed, patients should be trained and supervised in contact lens insertion and removal. Contact lens cleaning and disinfection should be carefully explained, because improper care may be associated with complications of contact lens wear.6,24,197,198 Patients should be instructed that rubbing is an important part of the cleaning step before disinfection for any lens that is to be reworn. Hydrogen peroxide systems may be superior to preserved disinfecting solutions in reducing pathogen binding and cysticidal disinfection, but they require more complex care regimens.16-18 Patients should be instructed to use only sterile products that are commercially prepared specifically for contact lens care and to replace these at the intervals recommended by the manufacturers.199 (good practice point) Specifically, patients should be instructed not to rinse contact lenses or lens cases with nonsterile water (e.g., tap water, bottled water).198(strong recommendation, moderate evidence) Patients should also be instructed to clean and replace contact lens cases frequently, because they can be a source of lens contamination.31,198,200 (strong recommendation, good evidence) Patients should be instructed to replace the solution in contact lens cases each time the lenses are disinfected (i.e., the old solution should not be topped off).201
Patients should be made aware that using contact lenses can be associated with the development of ocular problems, including corneal infections that may threaten vision, and that overnight wear of contact lenses is associated with an increased risk of these corneal infections.8-11,202 This increased risk of corneal infections with overnight contact lens wear should be discussed with patients who are considering this modality of vision correction. If patients choose overnight wear, they should be instructed to use only lenses specifically approved for extended wear.
Swimming with contact lenses has been associated with the development of Acanthamoeba keratitis,202 and showering with lenses seems to be part of a pattern of risk.24 Patients should be instructed to minimize water contact when wearing contact lenses and informed of the risks of wearing contact lenses while swimming, in a hot tub, or showering.
For additional information about contact lens selection, fitting, and care, see Appendix 6.
Patients should be instructed that rubbing is an important part of the cleaning step before disinfection for any lens that is to be reworn. Rubbing the contact lens enhances the cleaning performance of the solution, likely by removing loosely-bound deposits. Compared to preserved disinfecting solutions, hydrogen peroxide systems may be superior as far as reducing pathogen bindingand cysticidal disinfection are concerned, but require more complex care regimens.12-18 (strong recommendation, good evidence)
Follow-up Examination and Contact Lens Replacement
The initial contact lens fitting process should include follow-up examinations to assess visual acuity, comfort, contact lens fit, and the effect of the contact lens on the health of the ocular surface. First-time daily-wear or extended-wear contact lens users should be checked soon after the contact lenses are initially dispensed. Experienced contact lens users should generally be examined annually. Routine follow-up examinations are important to promote safe contact lens wear. Patients should be questioned about problems such as irritation, redness, itching, discharge, decreased vision, or spectacle blur upon contact lens removal. The patient's wear schedule and contact lens care regimen should be reviewed, and any deviations from recommended practice addressed. Of note, patient noncompliance with recommended hygienic practices in contact lens wear is often considered a significant risk factor for microbial keratitis and adverse contact-lens-related events. One study found that 86% of patients believed that they were compliant with hygienic practices; however, an interview about their lens care practices revealed that only 34% of those who reported themselves as compliant exhibited good lens care practices.203 Patient-reported compliance does not indicate appropriate patient behavior, as a large proportion of patients remain noncompliant despite being aware of risk.203,204 Visual acuity with the contact lenses should be checked, and the cause of any changes should be determined. The contact lenses themselves should be examined to make certain that they fit and wet well and are free of deposits or defects.
The external eye and cornea should also be evaluated in the follow-up examination. Findings of conjunctival injection, corneal edema, staining, infiltrates, changes at the superior limbus, or tarsal papillary conjunctivitis all indicate possible problems with contact lens wear. The practitioner should examine patients for signs of corneal hypoxia, including epithelial microcysts, epithelial edema, stromal thickening, corneal folds, corneal vascularization, and corneal warpage. If findings of corneal hypoxia are recognized, the contact lens fit, material, or wearing time should be adjusted to allow for better oxygenation of the cornea. Keratometry or corneal topography as well as refraction without the contact lenses should be compared with initial readings for patients suspected of having corneal warpage.
The length of time a particular pair of contact lenses can be used will vary among individual patients. Rigid gas-permeable contact lenses are generally useful for 18 to 24 months, although the surface quality of these lenses may deteriorate more rapidly for some individuals. Conventional daily-wear soft contact lenses usually require replacement at least annually. Conventional extended-wear soft contact lenses often require replacement more frequently than once a year. Disposable soft contact lenses and silicone hydrogel lenses for daily wear or extended wear should be replaced according to the manufacturers' guidelines, which vary from 1 day to several months. The frequency of contact lens replacement should also be adjusted based on patient symptoms and findings at eye examinations. If a particular contact lens shows excessive deterioration or deposits, it should be replaced regardless of the length of wear.
Rigid gas-permeable corneal lenses continue to have the lowest rate of adverse events of any lens type,8,9,205 but initial patient discomfort and resources required for fitting and supplying these lenses compared with soft lenses has resulted in a continued decline in their use.206 Of soft lens options, daily disposable lenses worn on a daily-wear basis remains the safest regimen.8,181 Extended (overnight) wear, regardless of lens type (including the newest highly gas-permeable silicone hydrogel lenses), increases the likelihood of infection,8,9 and discussion of this increased risk should be undertaken with patients who are considering that modality of vision correction. Patients should be instructed that rubbing is an important part of the cleaning step before disinfection for any lens that is to be reworn. Finally, hydrogen peroxide disinfection has the lowest rate of adverse events compared with any other disinfection system regardless of lens type.
Rigid gas-permeable contact lenses can be prescribed as a nonsurgical and reversible method of refractive error reduction for the treatment of mild to moderate myopia with less than 1.50 D of corneal astigmatism. The technique of corneal reshaping is also known as corneal refractive therapy (CRT), or orthokeratology.
Orthokeratology, as originally described, utilized the application of sequentially flatter PMMA hard contact lenses to flatten the cornea and thereby reduce the myopic refractive error. When patients stop wearing contact lenses after undergoing orthokeratology, their corneas tend to revert to their original shape.207,208 Earlier attempts to predict which patients would respond to orthokeratology based on ocular biomechanical or biometric parameters were not successful,209 and the effects of orthokeratology were unpredictable and poorly controlled.207 In the 1990s, there was a resurgence using highly gas-permeable rigid contact lenses for temporary corneal reshaping. In this technique, patients with myopia are fitted with reverse-geometry rigid gas-permeable contact lenses that are used only during sleep. The center of the contact lens is deliberately fitted flatter than the central corneal curvature to transiently induce central corneal flattening, which will reverse myopia during the day when the lens is not worn. The contact lens must be used every one to two nights in order to maintain the effect. Food and Drug Administration approval has been granted for the use of this technique, often referred to as overnight orthokeratology (OOK), for temporary reduction of up to 6.00 D of myopia (in eyes with up to 1.75 D of astigmatism). Average uncorrected visual acuity ranges from 20/19 to 20/24 with a refractive error ranging from +0.27 to -0.41 D after 1 to 6 months of wearing reverse-geometry contact lenses.210-214
The complications of OOK overlap those of rigid contact lens wear. As with any overnight contact lens modality, orthokeratology is associated with an increased risk of microbial keratitis.213,215,216 Corneal pigmentation rings have been reported, but these are reversible. Patients may also note a decreased quality of vision, especially under low-illumination conditions due to an increase in HOAs. The most serious complication that has been associated with OOK is microbial keratitis, first reported in 2001.217,218 Most of these cases originated in Asia, particularly in China and Taiwan, and were reported during a relatively short period, when regulation of orthokeratology was limited.219 A high incidence of cases of Acanthamoeba keratitis reported with this modality emphasizes the importance of eliminating the use of tap water in care regimens for overnight orthokeratology.219,220 There is insufficient evidence to support the use of orthokeratology for the prevention of myopia progression in children.221,222,223
Refractive Surgery for Myopia, Astigmatism, and Hyperopia
The term "refractive surgery" describes various elective procedures that modify the refractive status of the eye. Procedures that involve altering the cornea are collectively referred to as keratorefractive surgery, refractive keratoplasty, or corneal refractive surgery. Other refractive surgery procedures include the placement of an intraocular lens (IOL) implant, either in front of the crystalline lens (phakic IOL) or in place of the crystalline lens (refractive lens exchange). Refractive surgery may be considered when a patient wishes to be less dependent on eyeglasses or contact lenses, or when there are occupational or cosmetic reasons not to wear eyeglasses. Keratorefractive surgery can be applied to a broad range of refractive errors, but in some circumstances, the surgeon may consider an intraocular procedure.
The ophthalmologist who is to perform the refractive surgery has the following responsibilities:224,225
To examine the patient preoperatively
To ensure that the record of the evaluation accurately documents the symptoms, findings, and indications for treatment
To obtain informed consent from the patient (see Informed Consent sections)
To review the results of presurgical diagnostic evaluations with the patient
To formulate a surgical plan
To formulate postoperative care plans and inform the patient of these arrangements (e.g., setting of care, individuals who will provide care)
To give the patient the opportunity to discuss the costs associated with surgery
The best interest of the patient is served by having the operating ophthalmologist perform the preoperative evaluation, because this will allow the surgeon to formulate the surgical plan and to establish a relationship with the patient prior to surgery. Although the ophthalmologist is responsible for the examination and review of the data, certain aspects of data collection may be conducted by another trained individual under the ophthalmologist's supervision and with his or her review.224,225
A comprehensive medical eye evaluation should be performed before any refractive surgery procedure.224 Visual acuity determination and refraction require particular attention. In addition to the elements listed in the comprehensive adult medical eye evaluation147 (see Appendix 4), the refractive surgery examination should include the following elements:
Distance visual acuity with and without correction
Manifest and, when appropriate, cycloplegic refraction
Computerized corneal topography
Central corneal thickness measurement
Evaluation of tear film and ocular surface
Evaluation of ocular motility and alignment226
Although the data from published studies fail to demonstrate a relationship between pupil size and the quality of postoperative vision, the importance of pupillometry in the preoperative workup remains controversial. Most studies of conventional and wavefront-guided laser in situ keratomileusis (LASIK) have not shown a relationship between the diameter of the low-light pupil and disturbing visual symptoms postoperatively.42-46 A benefit of more complex aspheric ablations relative to conventional ablations may be found under low-light conditions when the pupil is dilated, because this is when a reduction, or less induction, of HOAs, particularly spherical aberration, should be most apparent. Some studies comparing conventional and wavefront-guided LASIK have reported fewer postoperative complaints of glare or halo under mesopic conditions with wavefront-guided procedures.227,228 Irrespective of pupil size, it is important for potential patients to understand that there is a risk for night-vision problems after surgery. In conclusion, measurement of pupil size is not required in the preoperative examination.
Patients should be informed that there is a risk for night vision symptoms afterkeratorefractive surgery. (strong recommendation, good evidence) Most studies of conventional and wavefront-guided LASIK have not shown a relationship between the diameter of the low light pupil and night vision symptoms postoperatively.42-46(moderate evidence)
Because of the possibility of contact-lens-induced corneal warpage and corneal edema, patients who use contact lenses should discontinue their use before the preoperative examination and procedure.229 As a general guideline, spherical soft contact lenses should be discontinued for at least 3 days to 2 weeks.229,230 Toric soft contact lenses and rigid contact lenses should be discontinued for a longer period because they are associated with a greater potential for corneal warpage and refractive instability, which takes longer to resolve upon contact lens discontinuation. Particular attention should be paid to establishing refractive stability for these patients, which may require multiple visits.
When astigmatism determined by subjective refraction differs significantly from astigmatism found by corneal topography, lenticular astigmatism may be a possible cause. Keratorefractive surgery is intended to correct total astigmatism identified on refraction. Caution should be taken to identify early cataract formation in the presence of significant lenticular astigmatism. In this situation, lenticular refractive surgery may be a better option for the patient than keratorefractive surgery.
The patient should be evaluated using corneal topography to look for evidence of irregular astigmatism, corneal warpage, or signs of keratoconus or other corneal ectasias, because these may be associated with unpredictable outcomes of keratorefractive surgery and a decrease in best spectacle-corrected visual acuity (BSCVA). Caution should be taken to ensure that any irregular astigmatism, typically identified on corneal topography, is not a sign of keratoconus or another corneal ectatic condition before proceeding with any keratorefractive surgery.
Corneal topography is also important when considering intraocular refractive surgery to assess any contour abnormalities as well as to measure keratometry.
Measurement of the central corneal thickness should be obtained during the preoperative evaluation to identify unusually thin corneas and estimate residual stromal bed thickness. Corneal tomographic imaging systems measure the shape of the anterior and posterior surface of the cornea, allowing for assessment of abnormal pachymetric distribution across the entire cornea. Pachymetric maps demonstrating abnormal pachymetric distribution may be helpful in identifying the presence of keratoconus.231
Excimer ablations that result in very thin residual stroma increase the risk for ectasia. In the case of LASIK procedures, 250 μm has been suggested as a safe residual stromal bed thickness,232 but there is no absolute value that guarantees that ectasia will not occur. While surgeons do not agree on a particular figure, they do agree that when ectasia risk is assessed, many factors should be considered. Abnormal topography is the most significant risk factor for postoperative ectasia. Other risk factors may include thin preoperative central corneal thickness, younger patient age, thin postoperative stromal bed thickness, and higher attempted corrections.38-40
Before refractive surgery, corneal topography should be evaluated for evidence of irregular astigmatism, corneal warpage, or abnormalities suggestive of keratoconus or other corneal ectasias. All of these conditions may be associated with unpredictable refractive outcomes, and keratoconus and the ectasiaswith ectasia progression following keratorefractive surgery.38-41 When considering intraocular refractive surgery, measurement ofcorneal topography is important to assess the optical characteristics of the cornea. It is also relevant if akeratorefractive surgical procedure is necessary to optimize the refractive result after the lens surgery or for toric intraocular lens implantation. (strong recommendation, moderate evidence)
Research is ongoing to determine if personality characteristics can affect patients' satisfaction with the quality of their vision following refractive surgery. Until more information for patient selection is available, an assessment of the motivations and expectations of patients who wish to have refractive surgery and an assessment of mental health status and history may be helpful. Patients' preoperative expectations and psychological characteristics have been shown to affect satisfaction with LASIK.233 Depressive symptoms have been associated with decreased patient satisfaction with visual quality after LASIK.234 This study is consistent with studies from the cosmetic surgery literature, which identified the presence of a personality disorder or a history of depression or anxiety as predictors for poor psychological or psychosocial outcome following surgery.235
The most frequently performed procedures for low to moderate myopia utilize the excimer laser, which was first approved for this purpose by the FDA in 1995. A surface ablation technique, photorefractive keratectomy (PRK), was the first procedure performed; subsequently, LASIK has become the most commonly performed keratorefractive surgery. Other keratorefractive procedures to correct low to moderate myopia include variations of PRK called laser epithelial keratomileusis (LASEK) and epi-LASIK, insertion of intrastromal corneal ring segments,236 and RK.237
An advantage of surface ablation techniques over LASIK is that more residual posterior stromal tissue is preserved and there are no flap-related complications. Disadvantages of surface ablation techniques when compared with LASIK include more discomfort and slower recovery of vision due to the longer re-epithelialization time and potential development of subepithelial haze.238,239
High myopia is less likely to be fully corrected by keratorefractive surgery than low to moderate myopia.240 Because of the greater functional impairment experienced by highly myopic patients, however, the potential limitations of keratorefractive surgery may be more acceptable. Alternative procedures to correct high myopia include refractive lens exchange and phakic IOL implantation.
Surgery to correct hyperopia is performed less commonly than surgery to correct myopia. A hyperopic ablation profile is a peripheral annular ablation around the central optical zone, which results in steepening of the central cornea relative to the periphery. The FDA first approved use of the excimer laser to correct hyperopia in 1998.
Photorefractive keratectomy was the first refractive laser procedure to address astigmatism.241,242With the excimer laser, a spheroelliptical ablation is made in the corneal stroma to correct both the spherical and astigmatic refractive error. The laser ablation either flattens the steep meridian, steepens the flat meridian, or both (bitoric or cross-cylinder ablation), depending on the laser and its algorithm for the specific refractive error. In general, cross-cylinder and bitoric ablations remove less tissue and change the spherical equivalent less than ablations that only steepen the flat meridian or only flatten the steep meridian.243 Different laser platforms use different proprietary ablative patterns, which may affect the outcomes of long-term stability of the refractive procedures.
Excimer Laser Systems
By varying the ablation pattern, the excimer laser can alter the anterior corneal curvature to modify a particular refractive error described by sphere and cylinder. The laser delivery methods currently being utilized to achieve the ablation pattern are broad-beam, scanning-slit, or flying-spot systems. Eye-tracking technology is integrated into all the current commercially available excimer laser systems and permits the ablation to remain centered on the pupil in the presence of small ocular movements.
Wavefront-guided or customized ablation patterns are available on several commercially available excimer laser systems for LASIK. Wavefront analysis makes use of a detailed map of the optical system of the entire eye, measured across an entrance pupil aperture. This map is unique to the individual eye measured and can be described by varying degrees of standard optical aberration terms. Lower order aberrations consist of regular astigmatism and defocus. Higher order aberrations consist of an infinite series of increasingly complex optical imperfections that characterize what was previously known as irregular astigmatism (i.e., astigmatism not correctable with spherocylindrical lenses). Wavefront-guided and aspheric ablation techniques are commercially available and attempt to maintain a more prolate corneal shape, thus reducing induced spherical aberration. Compared with conventional LASIK, both wavefront-guided and aspheric laser ablations may lead to improved quality of vision under dim lighting conditions.244 Wavefront-guided or customized ablation techniques generally remove a greater volume of tissue than conventional procedures.245-252
A customized excimer ablation, using the wavefront aberrometry information, is able to limit the induction of HOAs and, in some instances, reduce pre-existing HOAs.253,254 Eyes that are otherwise healthy and have not had previous refractive surgery typically have very low levels of irregular astigmatism that do not significantly affect visual function. Some evidence exists that even healthy eyes, with relatively low levels of existing HOAs, may benefit from wavefront-guided excimer ablation due to the technology's ability to reduce the induction of HOAs, particularly spherical aberration.255
Procedures used to treat regular astigmatism include PRK and its variants (collectively termed "surface ablation"), LASIK, and astigmatic keratotomy (AK). Customized treatments based on wavefront or topographic information to reduce irregular astigmatism in eyes with high degrees of aberration have been studied, although they are not FDA-approved for these indications.256 Photorefractive keratectomy using wavefront-guided technology is considered an off-label use of an FDA-approved device.
Table 2 lists the excimer lasers for PRK and LASIK that have been approved by the FDA for the correction of myopia, hyperopia, astigmatism, and combinations thereof, and are commercially available.
MedWatch (www.fda.gov/medwatch) is the Safety Information and Adverse Reporting Program for drugs and other medical products regulated by the FDA. Adverse experiences of refractive surgery should be reported to MedWatch.
TABLE 2. FDA-Approved Indications for Excimer Lasers for PRK and LASIK
Certain abnormalities of the cornea (e.g., keratoconus or other corneal ectasias, thinning, edema, interstitial or neurotrophic keratitis, extensive vascularization)
Insufficient corneal thickness for the proposed ablation depth
Uncontrolled external disease (e.g., blepharitis, dry eye syndrome, atopy/allergy)
Uncontrolled autoimmune or other immune-mediated disease
Unrealistic patient expectations
Ocular conditions that limit visual function
Excessively steep or flat corneas (e.g., increased risk of mechanical microkeratome complications)
Abnormal corneal topography indicating forme fruste of keratoconus
Significant irregular astigmatism
Visually significant corneal stromal or endothelial dystrophies
History of herpes simplex virus (HSV) or varicella zoster virus (VZV) keratitis
Inadequately controlled dry eye
History of uveitis258
Pregnancy or lactation260
Autoimmune or other immune-mediated diseases261
Certain systemic medications (e.g., isotretinoin, amiodarone, sumatriptan, levonorgestrel implants, colchicine)
Under 21 years of age (FDA labeling should be consulted for each laser)
Although there is a high probability of successful outcomes for keratorefractive surgery, care should be taken to emphasize potential adverse events or complications that may occur, explaining which may be transient and which may be permanent. The patient should be informed of the potential risks, benefits, and alternatives to and among the different refractive procedures before surgery. The informed consent process should be documented, and the patient should be given an opportunity to have all questions answered before surgery. The surgeon is responsible for obtaining the patient's informed consent.224,225 Elements of the discussion may include the following:
Range of expected refractive outcomes
Residual refractive error
Reading and/or distance correction postoperatively
Loss of BCVA
Side effects and complications (e.g., microbial keratitis, sterile keratitis, keratectasia)
Changes in visual function not necessarily measured by visual acuity testing, including glare and function under low-light conditions
Night vision symptoms (e.g., glare, haloes) developing or worsening; careful consideration should be given to this issue for patients with high degrees of ametropia or for individuals who require a high level of visual function in low-light conditions
Effect on ocular alignment
Dry eye symptoms developing or worsening
Recurrent erosion syndrome
The limitations of keratorefractive surgery with respect to presbyopia and the potential loss of uncorrected near visual function that accompanies myopia correction
Monovision advantages and disadvantages (for patients of presbyopic age)
Conventional and advanced ablations advantages and disadvantages
Advantages and disadvantages of same-day bilateral keratorefractive surgery vs. sequential surgery. Because vision might be poor for some time after bilateral same-day PRK, the patient should be informed that activities such as driving might not be possible for weeks.
May influence predictive accuracy of IOL calculations for subsequent cataract surgery
Postoperative care plans (setting of care, providers of care)
GOOD PRACTICE POINT
Preoperative assessment of the potential refractive surgery patient should address expectations for post-surgical vision and emphasize potential adverse events or complications that may occur, explaining which may be transient and which may be permanent. (good practice point)
Patients should be informed that there is a risk for night vision symptoms afterkeratorefractive surgery. (strong recommendation, good evidence) Most studies of conventional and wavefront-guided LASIK have not shown a relationship between the diameter of the low light pupil and night vision symptoms postoperatively.42-46(moderate evidence)
Surface Ablation Techniques
In PRK, the central corneal epithelium is removed and the excimer laser is used to ablate Bowman's layer and superficial corneal stroma centered over the entrance pupil.
All instrumentation must be checked and calibrated before the procedure.262 The surgeon should confirm the identity of the patient, the operative eye, and that the parameters are correctly entered into the laser's computer.262 In the setting of significant astigmatism or a wavefront-guided treatment, the surgeon should take appropriate steps to ensure torsional alignment.Axis alignment is crucial in the treatment of higher astigmatic errors because there can be a large reduction in effect if the astigmatic ablation is not aligned with the true axis of astigmatism. Because there can be ocular cyclotorsion when the patient changes from the seated to supine position, it may be useful to place reference marks on the operative eye before the laser procedure while the patient is seated upright.263 These marks are then aligned intraoperatively with the laser reticle, thus compensating for ocular cyclotorsion. The use of a tracker or in some cases, a fixation ring, may help to stabilize the eye and increase the accuracy of the placement of the astigmatic ablation.
For customized ablations, registration of the acquired wavefront information with the patient's eye during surgery is essential to provide the most accurate and predictable results. Some laser platforms utilize iris landmarks to align the wavefront measurement acquired in the seated position to the patient's eye when lying supine for the surgery. Future wavefront registration techniques may utilize scleral vessels as landmarks and dynamic intraoperative registration. All wavefront-guided laser platforms make use of eye-tracking systems to account for small translational eye movements that occur during the ablation.
A topical antibiotic or antiseptic may be applied preoperatively to the operative eye, and a topical nonsteroidal anti-inflammatory drug (NSAID) drop may also be applied to help ameliorate postoperative pain. The nonoperative eye should be occluded. Sterile instruments must be used for each patient.The operative eye is anesthetized topically, the surrounding skin and eyelashes are cleansed and/or isolated, and a lid speculum is placed to optimize corneal exposure.
The epithelium can be removed mechanically (by brush, blade, or epikeratome), chemically (most often with approximately 20% alcohol), or by laser.264-269 Expeditious removal minimizes nonuniform drying of the stroma. Enough epithelium should be removed to permit placement of the full, planned laser optical zone diameter onto the stroma. The excimer laser ablation is performed centered on the entrance pupil. Care should be taken to maintain a proper head position so that the facial/corneal planes are parallel to the floor and orthogonal to the laser beam. In an off-label application, mitomycin-C is sometimes used to reduce the chance of corneal subepithelial haze developing, particularly in the setting of a high correction (i.e., deep ablation) or in eyes that have undergone prior corneal surgery such as RK, LASIK, or penetrating keratoplasty.270-272 Long-term studies of the effect of mitomycin-C on corneal physiology are not yet available. Most studies show no significant effect on endothelial cell counts when mitomycin-C is used at a concentration of 0.02% (0.2 mg/ml) for a brief period (e.g., 15 seconds).273,274 Topical antibiotics should be administered. A bandage contact lens is usually applied, and the lid speculum is removed. An NSAID drop may also be instilled.
Judicious short-term use of dilute topical anesthetics can help to control postoperative pain.
Laser Epithelial Keratomileusis and Epi-LASIK
Laser epithelial keratomileusis is a modification of PRK that attempts to preserve the epithelium. After 20% alcohol is applied to the corneal epithelium, an epithelial trephine and spatula are used sequentially to score, loosen, and roll up the epithelium, which remains attached at a nasal or superior hinge. Photoablation is then performed, and the epithelium is unrolled back over the central corneal stroma.275 A bandage contact lens is used for several days until the surface re-epithelializes.
An alternative surface ablation procedure to LASEK is epi-LASIK. Instead of using alcohol to loosen the epithelium, an epikeratome is used to dissect an epithelial sheet from Bowman's membrane. The epikeratome is similar in design to a mechanical microkeratome used for LASIK. Instead of using an oscillating sharp blade to incise the corneal stroma beneath Bowman's membrane, the epikeratome uses a blunt oscillating separator that moves across the cornea held under high pressure with a suction ring. This separator lifts a sheet of epithelium from Bowman's membrane. The laser ablation is then performed and the epithelial sheet is either replaced or discarded. It is unclear whether patient discomfort and subepithelial haze formation is reduced with LASEK or epi-LASIK when compared with PRK.276-278 Visual recovery and discomfort with LASEK and epi-LASIK are similar to PRK and are prolonged relative to LASIK. Epi-LASIK should be used only in eyes in which Bowman's membrane is intact. Breaks in Bowman's membrane (e.g., from previous PRK, LASIK, or even some corneal scars) increase the risk of the epi-LASIK blade separating stromal tissue and not just epithelium.279 In an off-label application, mitomycin-C is sometimes used to reduce the chance of corneal subepithelial haze developing, particularly in the setting of a high correction (e.g., deep ablation) or in eyes that have undergone prior corneal surgery such as RK, LASIK, or penetrating keratoplasty.280-282 Because LASEK and epi-LASIK are modifications of PRK, the potential for corneal haze to develop remains a concern.283-286
Photorefractive keratectomy reduces myopia, is most predictable for low to moderate myopia, and is less predictable for high myopia.240 A systematic review of data from over 2000 eyes with 1.00 D to 14.00 D of myopia reported that 70% and 92% of participants had an uncorrected visual acuity (UCVA) of 20/20 and 20/40, respectively, at 12 or more months following PRK.240 After 12 or more months of follow-up, 86% of eyes treated for myopia and myopic astigmatism were within 1.00 D of the expected correction.240 Loss of BCVA of 2 lines or more after PRK for low to moderate myopia varies between 0% and 1% at 1 year following surgery.240 Following PRK for high myopia, 6% of eyes lost 2 or more lines of BCVA.240
In a study of wavefront-guided PRK for myopia and myopic astigmatism, 81% of patients achieved a UCVA of 20/20 or better.287 In a contralateral eye study comparing wavefront-guided PRK with wavefront-guided LASIK, visual recovery was faster with LASIK than with PRK (88% vs. 48% were 20/20 or better at 1 month). At 6 months, however, visual acuities were similarly excellent in both groups (LASIK: 92% 20/20 or better; PRK: 94% 20/20 or better).288 Using wavefront-guided PRK, 1% of eyes lost 1 line of BCVA at 1 year (relative to pre-LASIK BCVA).289
Regression of the surgical effect was more common in patients with higher degrees of preoperative myopia.240 Long-term studies examining 10- to 12-year results demonstrated excellent safety and efficacy of PRK for the treatment of myopia.289-292 Two studies published together looked at 10-year follow-up of PRK in eyes with less than -6.00 D of myopia (lower myopic group) and more than -6.00 D of myopia (higher myopic group). While the long-term results were excellent, there was more regression of effect in the higher myopic group (-1.33 D over 10 years) compared with the lower myopic group (-0.10 D over 10 years).291,292
A study of the incidence of retreatments following wavefront optimized PRK and LASIK found no difference in the retreatment rates between the two procedures (6.3%).293 The efficacy and predictability of PRK retreatment are less than for primary procedures.294-298
Photorefractive keratectomy for hyperopia (H-PRK) reduces hyperopic refractive errors. Lower degrees of hyperopia (0 to +3.50 D) can be corrected with better predictability than higher hyperopic errors.240 A systematic review with data from more than 300 eyes treated with H-PRK reported that 79% of eyes achieved within 1.00 D of their intended refractive correction at 12 months after surgery.240 In one study, 85% of eyes with a mean preoperative correction of 2.88 D of hyperopia achieved corrections of ±1.00 D of the attempted correction.300 In eyes with more than 3.50 D of hyperopia, 79% were within 1.00 D of the intended correction.300 In another study 79% of eyes with a mean preoperative refraction of 3.03 D of hyperopia achieved ±0.50 D of emmetropia at 12 months.301 Following H-PRK, 5% of patients with mild to moderate hyperopia (3.50 D or less of hyperopia) and 20% of those with high hyperopia (3.50 D or more of hyperopia) lost 2 or more lines of BCVA relative to the preoperative BCVA, respectively.240 In a study of wavefront-guided PRK for hyperopia (mean preoperative refraction +2.90 ± 0.80 D), 100% of eyes achieved within 1.00 D of the intended correction and 12% of patients lost 2 or more lines of BCVA at 6 months of follow-up, primarily due to increases in higher order aberrations.302 Ninety percent of eyes were 20/40 or better 6 months following surgery.
Although overall corneal haze was generally mild, there were more-significant haze problems in the midperipheral ring, usually sparing the entrance pupil.303 Achievement of best postoperative vision is slower with H-PRK than with myopic PRK. Centration of the ablation is more critical in hyperopic treatments due to the smaller effective optical zone. The use of excimer lasers with eye trackers may reduce decentrations.
In a study comparing hyperopic PRK and LASIK outcomes at 2 years, refractive outcomes were less stable with PRK, as evidenced by a statistically significant regression at 2 years in the PRK group compared to no significant regression in the LASIK group.304 Higher regression in the PRK group was present even though there was a higher treated hyperopic spherical equivalent in the LASIK group (4.49 D vs. 2.85 D).
In three studies of PRK to correct astigmatism with 6 months of follow-up, less than 2% of patients lost 2 or more lines of BCVA. In these reports, 63% to 86% of patients were within 1.00 D of their intended correction and 82% to 94% had a UCVA of 20/40 or better.305-307
A systematic review of LASEK studies reported that loss of 2 or more lines of BCVA ranged from 0% to 8%; loss of 2 or more lines was more frequent in studies of high myopia and astigmatism.240 Outcomes for accuracy and UCVA were similar to those for PRK. A study comparing outcomes of LASEK and LASIK for low to moderate myopia reported clinically insignificant differences in the results obtained.308
Postoperative management is integral to the outcome of any surgical procedure and is the responsibility of the operating surgeon.225,309 Topical antibiotics are administered to minimize the risk of postoperative infection. Topical corticosteroids are generally started immediately after surgery and tapered over a period of days to weeks, and in some cases, months. If corticosteroid treatment is prolonged, the intraocular pressure (IOP) should be monitored. Mild transient elevations of IOP can most likely be managed with topical therapy, but close monitoring is essential because IOP control can easily be lost with prolonged corticosteroid use.310,311
Although postoperative pain may be reduced by using a bandage contact lens and NSAID drops, patients may still require prescription oral analgesics. Because NSAID drops may delay corneal epithelialization, they should be prescribed judiciously. Sterile corneal infiltrates associated with the use of NSAID drops without the concomitant use of topical corticosteroids have been described.312 Microbial keratitis, however, must be considered whenever a corneal infiltrate is seen.
Postoperative examination, including slit-lamp biomicroscopy of the cornea, is advisable on the day following surgery and every 2 to 3 days thereafter until the epithelium is healed. Epithelialization usually is complete within 5 days after surgery. If a bandage contact lens is used, it usually can be discontinued once significant re-epithelialization has occurred. Stable vision and refraction might not be achieved for many months. Periodic examinations are necessary to monitor ocular status and to check for corticosteroid-related side effects such as elevated IOP.
GOOD PRACTICE POINT
It is recommended that patients be provided with a record or that the ophthalmologist maintains a record that lists information about the patient's eye condition including preoperative keratometry readings and refraction, as well as stable postoperative refraction, so that it will be available if the patient requires cataract surgery or additional eye care. (See Appendix 7.) (good practice point)
Retreatments should generally not be performed until refraction, corneal haze, and corneal topography have stabilized, which usually requires at least 6 months after primary PRK surgery. Retreatment in the presence of any but mild corneal haze should be carefully considered.296 The off-label application of mitomycin-C at the time of retreatment has been reported to reduce the recurrence of haze.313,314
Side Effects and Complications
Surface ablation procedures are associated with side effects and complications that are uncommon, sometimes permanent and rarely debilitating. These side effects and complications include the following:
Symptomatic undercorrection or overcorrection315-318
Partial regression of effect319
Loss of BCVA315-318,320-326
Visual aberrations, including transient or permanent glare or starburst/halo effect, especially at night319,327
Decreased contrast sensitivity328-330
Induced regular or irregular astigmatism315,318
Premature need for reading correction315-318
Corneal haze or scarring (early or delayed onset)331
Corneal infiltrates, ulceration, melting, or perforation (sterile or microbial)312,325,332
Corneal ectasia (progressive corneal steepening)333
Development or exacerbation of dry eye symptoms
Decreased corneal sensitivity334
Recurrent corneal erosion335
Reactivation of HSV keratitis336
Corticosteroid-induced complications (e.g., ocular hypertension, glaucoma, cataract) 318
Adverse effect on ocular alignment226
Artifactual reduction of measured IOP (due to corneal thinning)
Mitomycin-C-related complications (e.g., endothelial cell decrease)337
Although there are case reports of retinal abnormalities that have been recognized following PRK, it is unclear if the incidence is any different in a comparable myopic population.338,339
Patient satisfaction depends on both patient expectations and surgical outcome. Patients have generally been satisfied with the results of PRK.340-342 Some individuals who achieve the intended correction, however, may be unhappy because of visual aberrations.
The most frequent complaints of patients dissatisfied with refractive surgery are blurred distance or near vision, glare, dry eyes, and night-vision problems. In many cases, dissatisfied patients had relatively good UCVA.343,344
Questionnaires have been developed to assess the functional and psychological impact of refractive error and its correction.345,346 Subjective visual function and patient satisfaction do not always correlate with objective measurements.347
Laser in Situ Keratomileusis
Laser in situ keratomileusis is a surgical procedure in which a hinged flap consisting of corneal epithelium, Bowman's membrane, and superficial stroma is created. The corneal flap is reflected, a tissue-ablating excimer laser is used to reshape the exposed corneal stroma, and the flap is repositioned. The anterior corneal surface can be altered to modify a patient's refractive error by varying the pattern of corneal tissue removal beneath the flap.
Special considerations when evaluating patients for LASIK include the following:
Abnormal corneal topography indicating forme fruste of keratoconus
Orbital, lid, or ocular anatomy that precludes proper function of the mechanical microkeratome or femtosecond laser
Corneal thickness calculation of estimated stromal bed thickness
Poor epithelial adherence, epithelial basement membrane dystrophy, or recurrent erosion syndrome
Significant occupational or recreational risk for corneal trauma
Significant dry eye
If one or more of these conditions are present, PRK or other surface ablation procedures may be considered.
All instrumentation must be checked and calibrated before the procedure. The surgeon must confirm the identity of the patient, the operative eye, and that the parameters are correctly entered into the laser's computer.262 In the setting of significant astigmatism or a wavefront-guided treatment, the surgeon should take appropriate steps to ensure torsional alignment. Axis alignment is crucial in the treatment of higher levels of astigmatic errors because there can be a large reduction in effect if the astigmatic ablation is not aligned with the true axis of astigmatism. Because there can be ocular cyclotorsion when the patient changes from the seated to supine position, it may be useful to place reference marks on the operative eye before the laser procedure while the patient is seated upright.263 These marks are then aligned intraoperatively with the laser reticle, thus compensating for ocular cyclotorsion. The use of a tracker or in some cases, a fixation ring, may help to stabilize the eye and increase the accuracy of the placement of the astigmatic ablation.
For customized ablations, registration of the acquired wavefront information with the patient's eye during surgery is essential to provide the most accurate and predictable results. Many laser platforms utilize iris landmarks to align the wavefront measurement acquired in the seated position to the patient's eye when lying supine for the surgery. Future wavefront registration techniques may utilize scleral vessels as landmarks, and dynamic registration. All wavefront-guided laser platforms make use of eye tracking systems to account for small translational eye movements that occur during the ablation.
In addition to microkeratome-based LASIK procedures, femtosecond lasers can be used to create a flap prior to excimer laser ablation. Femtosecond lasers refer to a group of solid-state lasers that operate in the infrared spectrum. Photodisruption occurs when the laser beam is absorbed by the target tissue, free electrons are released, and plasma (electrically charged particles) is created.348,349 Plasma ignition occurs and creates cavitation and gas bubbles. Femtosecond (10-15 second) lasers have a short pulse duration, which allows them to be useful for corneal applications by reducing the size of the cavitation bubble formation and resultant shock wave.
Femtosecond LASIK may offer a safety advantage over microkeratome-based LASIK procedures, because the corneal tissue does not need to be separated if an abnormal flap is made. The femtosecond lasers can also be programmed to vary flap width, flap depth, hinge width, and side cut angles, and they can perform other corneal procedures. Table 3 lists femtosecond lasers that have been approved by the FDA and indications for their use.
TABLE 3. FDA-Approved Indications for Femtosecond Lasers
A topical antibiotic or antiseptic may be applied preoperatively to the operative eye, and a topical NSAID eyedrop may also be applied to help ameliorate postoperative pain. The nonoperative eye should be occluded. Sterile instruments must be used for each patient. The operative eye is anesthetized topically, the surrounding skin and eyelashes of the operative eye are cleansed and/or isolated, and a lid speculum is placed to optimize corneal exposure. Marking the cornea facilitates flap reorientation at the end of the procedure, particularly in the event of a free cap.
The surgeon should confirm proper settings on the mechanical microkeratome or femtosecond laser. If a mechanical microkeratome is used to create the flap, a suction ring is placed on the eye to elevate the IOP and guide the mechanical microkeratome; the surgeon should confirm adequately elevated IOP.
The mechanical microkeratome is then passed across the corneal surface to produce a hinged corneal flap. If a femtosecond laser is used to create the flap, a suction ring is used to fixate the eye, the cornea is applanated, and the laser energy is applied intrastromally. Different hinge locations can be created using different mechanical microkeratomes.
In LASIK procedures, careful attention needs to be given to ensure that the stromal bed diameter beneath the LASIK flap is large enough to accommodate the entire ablation.
The flap should be inspected and reflected, and the flap and stromal bed should be examined for size and regularity. Intraoperative central corneal thickness measurements may be performed to estimate residual corneal bed thickness. The advantages include rechecking the accuracy of the microkeratome and confirming adequate residual stromal bed thickness. Disadvantages include prolonged surgical time with potential drying of the stromal bed and possible introduction of antigens or microbes from the tip of the pachymeter. If the quality of the flap and stromal bed are adequate, the excimer laser ablation is performed centered on the entrance pupil. However, if there is inadequate stromal exposure or an irregular bed or flap, it may not be possible to perform the laser treatment safely. If the flap is noted to be visibly defective or grossly decentered after withdrawing the mechanical microkeratome, it may be more appropriate to abort surgery with as little flap manipulation as possible. The flap should be repositioned and allowed to heal. In many cases, after a period of months, surface ablation with or without mitomycin-C can be performed. In some cases, a recut and ablation after a period of months can be considered, although there can be significant complications.
An ablation of the stromal bed is performed in a manner similar to the way it is performed for PRK. Following ablation, the flap is repositioned; the interface is usually irrigated with a balanced salt solution, and flap alignment is confirmed. The flap is given sufficient time to adhere and the eyelid speculum is removed, avoiding contact with the cornea. Before discharging the patient, the operative eye(s) should be examined in order to confirm flap position and appearance.
A systematic review of 64 studies of LASIK published since 2000 found 17 studies that reported 75% to 100% (median, 92%) of eyes with myopia or myopic astigmatism were within 1.00 D of the intended correction. Low to moderate myopia was corrected with a greater degree of predictability than higher degrees of myopia.350 A study with 10-year follow-up of patients who received LASIK for less than 10.00 D of myopia reported that 73% of eyes were within 1.00 D of the expected correction and 54.6% of eyes demonstrated an increase in BSCVA.351 In data from 22 studies, the systematic review reported that a median 94% of eyes had a postoperative UCVA of 20/40 or better. Uncorrected visual acuity of 20/40 or better was achieved in 94% to 100% (median, 98%) of eyes with low to moderate myopia, and in 76% to 97% (median, 89%) of eyes with high myopia. In three studies of myopic astigmatism, 94% to 100% (median, 99%) of eyes achieved UCVA of 20/40 or better. In 25 studies that reported eyes with a loss of 2 or more lines of BCVA from pre-LASIK BCVA, a median rate of 0.6% (range 0% to 3%) of eyes with myopia or myopic astigmatism lost 2 or more lines of BCVA.240
Laser in situ keratomileusis for hyperopia (preoperative refraction, 0.50 D to 6.00 D of hyperopia) was reported to achieve within 1.00 D of the intended refraction in 86% to 91% (median, 88%) of eyes.240 In hyperopic eyes, 94% to 100% had a postoperative UCVA of 20/40 or better. For eyes with hyperopic astigmatism, 88% to 89% (median, 88%) were within 1.00 D of the intended correction and 94% had UCVA of 20/40 or better.240 A systematic review of LASIK found two studies of eyes with hyperopia or hyperopic astigmatism, and in these reports 2% to 5% (median, 3%) lost 2 or more lines of BCVA.240
Hyperopic LASIK (H-LASIK) has also been used successfully to treat overcorrected myopic LASIK.352 A study353 of H-LASIK and H-PRK reported that they were comparable in efficacy and safety for low to moderate hyperopia. However, H-PRK was associated with more postoperative pain, an initial and temporary myopic overshoot, and delayed refractive stability than H-LASIK.
Laser in situ keratomileusis is associated with more regression in hyperopic procedures than in myopic procedures.354-356 The mechanisms of H-LASIK regression are not clearly defined but epithelial hyperplasia may be one of the causes. Apparent regression after refractive surgery can be due to natural age-related hyperopic shift, or to the emergence of residual or incompletely treated hyperopia as latent hyperopia becomes manifest.357
As with myopic LASIK, many of the more serious complications of H-LASIK are associated with the creation of the corneal flap. Most microkeratomes are capable of making the larger flaps needed for hyperopic corrections, but thin flaps may be more difficult to create and larger flaps can be associated with more bleeding if limbal vascularization is present.358,359 There is a greater rate of loss of BCVA reported following H-PRK and H-LASIK compared with myopic corrections.240
In one study of LASIK for mixed astigmatism, 95% of eyes were within 1.00 D of the intended postoperative refraction and 94% had postoperative UCVA of 20/40 or better.360
Postoperative management is integral to the outcome of any surgical procedure and is the responsibility of the operating surgeon.361,362 Mild to moderate discomfort can be expected in the first postoperative day. Topical antibiotics are administered to minimize the risk of postoperative infection. Corticosteroids are generally used for a short time postoperatively. Lubrication is typically used in the postoperative period and short-term use of a protective eye shield is recommended.
In the absence of complications, a postoperative examination should be performed within 36 hours following surgery. Visual acuity should be checked and the cornea should be evaluated with slit-lamp biomicroscopy. Specific features that should be noted include the presence of epithelial irregularity or staining, epithelial ingrowth into the flap interface; interface debris; corneal edema; diffuse or focal infiltrates in the flap, bed, periphery or interface; and the presence of microstriae or macrostriae. In the presence of corneal inflammation, the anterior chamber should also be evaluated. Patients with UCVA that has not yet met preoperative BCVA should be re-examined. The frequency of follow-up visits is individualized depending on the findings at the first postoperative visit. For the routine patient following uncomplicated LASIK, the second visit should be performed 1 to 4 weeks postoperatively and thereafter as appropriate.
GOOD PRACTICE POINT
It is recommended that patients be provided with a record or that the ophthalmologist maintains a record that lists information about the patient's eye condition including preoperative keratometry readings and refraction, as well as stable postoperative refraction, so that it will be available if the patient requires cataract surgery or additional eye care. (See Appendix 7.) (good practice point)
A stable refraction is usually achieved by 3 months after surgery, but more time may be required for higher corrections. Symptomatic residual refractive error may prompt consideration of retreatment (enhancement), but it should not be considered until refractive stability has been documented by repeat measurements. Before retreatment, an eye evaluation that includes all relevant elements of the preoperative evaluation should be performed. It should be determined that residual refractive error is not due to accommodation or to pathologic conditions such as developing cataract or corneal ectasia. Computerized corneal topography and central corneal thickness measurement should be performed before retreatment, and postretreatment residual stromal bed thickness should be calculated. Anterior segment optical coherence tomography may be used to measure the residual stromal bed thickness. Intraoperative central corneal thickness measurement may also be used to measure the stromal bed before repeat ablation to ensure sufficient residual stromal bed.
The preferred options for retreatment are relifting the original flap47 or PRK with or without mitomycin-C (off-label use).48 If the original flap is lifted, care should be taken to preserve epithelium of the flap and to avoid incorporating epithelium in the interface to minimize the risk of epithelial ingrowth. If PRK is performed, care should be taken during epithelial removal to minimize the risk of flap disruption. If a new flap is cut, the intersection of the surgical planes can result in displaced stromal fragments, which can result in irregular astigmatism and loss of BCVA.
The preferred approaches for LASIK retreatment are re-lifting the original flap or performing photorefractive keratectomy (PRK) with or without mitomycin-C (off-label use) on the original flap. If a new flap is cut, the intersection of the surgical planes can result in displaced stromal fragments, which can cause irregular astigmatism and loss of best-corrected visual acuity (BCVA).47,48 (strong recommendation, moderate evidence)
Side Effects and Complications
Laser in situ keratomileusis procedures are associated with side effects and complications that are uncommon, sometimes permanent and, on rare occasion, debilitating. These side effects and complications include the following:
Symptomatic undercorrection or overcorrection363,364
Partial regression of effect
Loss of BCVA
Visual symptoms, including transient or permanent glare or starburst/halo effect, especially at night
Decreased contrast sensitivity
Induced regular or irregular astigmatism
Premature need for reading correction
Corneal haze or scarring (early or delayed onset)
Corneal infiltrates, ulceration, melting, or perforation (sterile or microbial)
Corneal ectasia (progressive corneal steepening)
Development or exacerbation of dry eye symptoms
Decreased corneal sensitivity
Recurrent corneal erosion
Reactivation of HSV keratitis
Corticosteroid-induced complications (e.g., ocular hypertension, glaucoma, cataract)
Adverse effect on ocular alignment226
Artifactual reduction of IOP measured by applanation tonometry
Interface fluid accumulation and artifactual underestimation of IOP
Early or late onset diffuse lamellar keratitis (DLK)
Pressure-induced sterile keratitis
Transient-light sensitivity associated with femtosecond laser365,366
Rainbow glare associated with femtosecond laser367,368
Persistent flap edema
Striae (microstriae and macrostriae)
Traumatic flap dislocation
Although there are case reports of retinal abnormalities that have been recognized following LASIK, it is unclear if the incidence is different from that in a comparable myopic population.338,369
In some cases, residual refractive error might be accompanied by a reduction in BCVA, often due to induced irregular astigmatism, and caution should be exercised when considering retreatment under these circumstances. Irregular astigmatism can be caused by LASIK flaps that are irregular, fragmented, truncated, buttonholed, or avulsed. There may be an increased risk of flap striae with thinner flaps compared with thicker flaps. Excessive flap hydration or flap-bed contour mismatch can cause microstriae, and poor alignment or postoperative flap shift can cause macrostriae. Late-onset irregular astigmatism can result from corneal ectasia.
The quality of vision under low-light conditions can be reduced after LASIK. Smaller treatment-zone sizes, especially in high refractive corrections, may be associated with an increased likelihood of visually disturbing halo formation in low-light conditions.319,370
Reduced BCVA, fluctuating vision, foreign-body sensation, and discomfort can be caused by post-LASIK epitheliopathy. Multiple factors have been implicated in this problem, including aqueous tear deficiency, accelerated tear-film break-up, and neurotrophic changes. Symptoms typically improve with time, but in certain cases they may persist for months or years. Supplemental lubrication, topical cyclosporine eyedrops, and punctal occlusion may be helpful in such cases.371,372
If striae are present but are not visually significant, conservative management is appropriate. However, if visually significant striae are present postoperatively, the flap should be refloated and repositioned. Antitorque or interrupted 10-0 nylon sutures can be considered in cases of recalcitrant striae.373 Flap dislocation has been observed most commonly within the first 24 hours following surgery, but it can also be seen many months to years after surgery as a consequence of trauma to the cornea.
Epithelial ingrowth can follow primary LASIK procedures, but it is more common following retreatments or trauma. While minor peripheral epithelial ingrowth can be followed without intervention, more extensive epithelial ingrowth might require lifting the flap and debriding the interface. For persistent epithelial ingrowth, suturing the flap or placing tissue glue can be considered.374 Other indications for lifting a flap with epithelial ingrowth include increasing astigmatism, increased growth towards the entrance pupil, flap melt, decreased BCVA, irregular astigmatism, or staining at the flap edge, which indicates active epithelial cell migration.
Diffuse Lamellar Keratitis. A characteristic pattern of interface inflammation can arise following LASIK, most commonly in the first few days after surgery. The eye shows little or no conjunctival hyperemia or anterior chamber inflammation, and the patient will generally have no discomfort.375 Diffuse lamellar keratitis is a noninfectious aggregation of inflammatory cells confined to the lamellar interface in an otherwise uninflamed eye. It is characterized by a fine white granular reaction in the lamellar interface, is frequently more prominent in the periphery, and does not extend anteriorly into the flap or posteriorly into the stroma. Potential triggers include, but may not be limited to, interface debris from the mechanical microkeratome blade, gloves, drapes, cleaning solutions, meibomian gland secretions, bacterial antigens, endotoxins, or epithelial disruption, as well as energy-related diffuse lamellar keratitis after femtosecond laser flap creation.376
The treatment of DLK is commonly guided by the severity of the inflammation.377,378 The mildest forms of inflammation are probably self-limited and of little visual consequence. Nevertheless, most surgeons will treat such cases by increasing the frequency of topical corticosteroid administration and with closer follow-up. More severe DLK may be treated by one or more of the following: more frequent and/or higher concentrations of topical corticosteroids, the administration of systemic corticosteroids, lifting of the flap with irrigation of the interface, or direct application of corticosteroids to the exposed stromal interface. Eyes with significant central involvement, rapidly progressing DLK, or at risk of stromal tissue loss should be considered for flap lift and irrigation. Data are not available to make an evidence-based treatment recommendation.
Persistent DLK that is unresponsive to corticosteroids should prompt consideration of microbial keratitis or interlamellar fluid due to increased IOP, intraocular inflammation, or endothelial decompensation.379 In these cases, the IOP should be measured peripheral to the flap edge to avoid a falsely low IOP reading.
The long-term complications of DLK are also related to the severity of inflammation. Interface opacification, tissue loss, and epithelial ingrowth can result in refractive shifts and irregular astigmatism. For moderate to extensive DLK, the interface should be irrigated sooner rather than later to minimize stromal loss and changes in refractive correction.
Postoperative Infection. Infection following LASIK is uncommon, but it has been reported following both initial procedures and retreatments. In contrast to DLK, clinical symptoms and signs of microbial keratitis after LASIK generally include pain, redness, and photophobia. Corneal infiltrates are usually focal in nature and often extend beyond the lamellar interface into deeper or more superficial stroma. An anterior chamber reaction is frequently present. Infection can present either early or late in the postoperative period. The time of onset and clinical severity vary greatly depending on the causative organism, especially if intensive topical corticosteroids have been used.
Scrapings should be obtained from the involved area and submitted for microbiological investigation. If the flap interface is involved but no surface ulceration is observed, the flap should be elevated to allow access for scrapings. Intensive broad-spectrum topical antibiotic therapy should be initiated and modified as appropriate. If the infiltrate involves the interface and prompts elevation of the flap, antibiotics can be applied directly to the flap interface. Severe infection of the flap or of the deep stroma may require flap amputation to control the infection. In addition to common bacterial isolates, unusual organisms such as atypical mycobacteria, methicillin-resistant Staphylococcus aureus, nocardia, fungi, and HSV have been reported in these cases.380-386 The microbiology of infections associated with LASIK is different from corneal infections associated with other risk factors.
Corneal Ectasia. Although the actual incidence of progressive corneal ectasia after LASIK remains undetermined, estimates range from 0.04% to 0.6%.387-389 This variation may be due to differences in patient selection and detection of those who are at risk. Management options for ectasia after LASIK include contact lenses and intrastromal corneal ring segments. In severe cases, corneal transplantation may be required.
A study showed that cross-linking induced by topical riboflavin and ultraviolet irradiation arrested and/or partially reversed keratectasia over a postoperative follow-up of up to 25 months, as demonstrated by preoperative and postoperative corneal topography and a reduction in maximum keratometric readings.390 Collagen cross-linking therapy continues to be studied for treatment of postrefractive corneal ectasia but at present does not have FDA approval.391
Ectasia after refractive surgery can often be treated with soft toric, rigid gas-permeable, scleral, piggyback, and hybrid (gas-permeable center with soft surround) contact lenses. Specialty lenses can be helpful for these patients who may have been intolerant of contact lens before refractive surgery.389,392-395
Intrastromal corneal ring segments (ICRS) are FDA-approved for use in keratoconus and have been used off-label for ectasia after LASIK.396-400 Reported techniques vary in the size, number, and symmetry of the implants as well as the location of the incision. Long-term efficacy for this procedure remains to be determined.
Corneal transplantation is also an option for treatment of post-LASIK ectasia in patients who cannot be visually rehabilitated with any of the previously described treatments.
Patient satisfaction depends on both patient expectations and surgical outcomes.233 Most patients are satisfied with the results of LASIK.401-403 A review of 309 peer-reviewed LASIK articles published between 1988 to 2008 revealed that, on average, 95% of patients were satisfied with their outcome after LASIK surgery.404 Well-informed candidates who understand normal biologic variability, the effect of lighting conditions on visual function, and presbyopia are more likely to be pleased with the outcome of surgery. Patients generally prefer the more rapid, less painful recovery that follows LASIK when compared with PRK.405 Questionnaires have been developed and may be helpful to assess the functional and psychological impact of refractive error and its correction.345,346 Subjective visual function and patient satisfaction do not always correlate with objective measurements.347 The most frequent complaints of patients dissatisfied with refractive surgery are blurred distance and/or near vision, glare, dry eyes, and night-vision problems. In many cases, dissatisfied patients had relatively good UCVA.343,344 Because a subset of patients have substantial and persistent symptoms after LASIK, studies are continuing to explore patient-satisfaction issues.234
Intrastromal Corneal Ring Segments
The ICRS procedure involves placing plastic arcuate segments into channels created in the stroma of the midperipheral cornea. The central corneal shape is altered by the configuration of the segments and their location in the cornea. Intrastromal corneal ring segment technology has FDA approval in the United States for the correction of -1.00 to -3.00 D of spherical equivalent at the spectacle plane, with 0 to 1.00 D of astigmatism. Approval by the FDA is for the thickness of the ring segments, which, as of 2010, ranges from 210 to 450 micrometers. This narrow range of approved correction and the inability to correct astigmatism have limited the application of this technology. Its advantages are that it spares the central cornea and that the segments can be removed.406,407 Intrastromal corneal ring segment technology is approved by the FDA for reducing the irregular astigmatism of keratoconus.408-410 There are reports on the use of ICRS for correcting ectasia after keratorefractive surgery.396-400
The implant technique of ICRS requires a partial thickness corneal incision followed by the application of a suction ring and the use of a stromal separator, a circular instrument designed to create an arcuate intralamellar channel for the placement of the segments. Femtosecond laser dissection can also be used to create the incisions and channels.411
Arcuate plastic segments of prescribed thickness are then positioned within the channels and the incision is closed.412 Side effects and complications of the ICRS procedure include fluctuation of vision; under- or overcorrection; induced regular or irregular astigmatism; glare; haloes; anterior or posterior corneal perforation; segment malposition, migration or extrusion; corneal melting of the overlying stroma; pain; microbial keratitis; and lamellar channel deposits.236,412 A single retrospective within-patient comparison of topography after either LASIK or ICRS insertion reported that ICRS-treated eyes showed more corneal surface irregularity than LASIK-treated eyes.413 Intrastromal corneal ring segments are now rarely utilized to correct myopia.
Radial keratotomy is a surgical procedure that has been performed infrequently since the advent of PRK and LASIK. The procedure utilizes 4 or 8 radial paracentral corneal incisions placed outside a central optical zone to flatten central corneal curvature.414 The amount of central corneal flattening can be controlled by variations in surgical technique (e.g., the number, depth, and length of incisions; and the diameter of the central optical zone).237 The amount of correction also varies with patient characteristics, especially age. Reoperations (enhancements) are often used to improve the refractive result.415,416 Potential complications include glare, starburst, fluctuation of vision, regression, progression of refractive effect with subsequent hyperopia, corneal perforation into the anterior chamber, microbial keratitis, and endophthalmitis.237
Thermal keratoplasty is an old concept in refractive surgery that dates to the work of Lans in 1898.417 This technique steepens the central corneal curvature by heat-induced shrinkage of collagen fibers in the midperiphery of the cornea. Treatment can be applied by a noncontact laser or by contact probes. The amount of change depends on a number of variables including the total amount of energy delivered, number of pulses, pulse energy, spot size, and optical zone.
Conductive keratoplasty uses a contact probe to deliver radio frequency energy by inserting the tip sequentially in multiple locations of the peripheral cornea. The energy produces shrinkage of collagen lamellae that leads to steepening of the central cornea. Surgical technique appears to be an important variable in minimizing induced astigmatism.418 Conductive keratoplasty has FDA approval for patients aged 40 years or older for the temporary reduction of 0.75 D to 3.25 D of hyperopia and treatment of presbyopia, with a spherical equivalent of 0.75 D to 3.00 D and 0 to 0.75 D of astigmatism. All refractive measurements are specified as being obtained under cycloplegia. Two-year results indicated that while 43% of the effect noted at 1 month was lost, the regression rate was approximately 0.25 D per year after 1 year.419 Disadvantages include early overcorrection, regression, and induced astigmatism. Conductive keratoplasty has replaced noncontact holmium laser thermokeratoplasty.
Incisional Astigmatic (Transverse or Arcuate) Keratotomy
Astigmatic keratotomy (AK) procedures are those in which either transverse or arcuate incisions are made in the paracentral cornea to change its curvature to reduce or eliminate corneal astigmatism. Limbal relaxing incisions are a variant of AK in which incisions are placed just inside the vascular limbal arcade in one or both hemimeridians of steepest astigmatic power to treat low to moderate degrees of astigmatism.420 Limbal relaxing incisions have been performed alone or combined with phakic IOLs or cataract extraction and IOL implantation to reduce preoperative corneal astigmatism and to reduce surgical astigmatism following keratoplasty.420,421 Astigmatic keratotomy makes use of the coupling effect in that a transverse or arcuate incision in the cornea flattens the meridian in which it is made and steepens the meridian 90 degrees away.422,423 These incisions are usually single or paired, typically maintaining an optical zone between 6.0 mm and 7.0 mm. Astigmatic keratotomy using smaller optical zones has been associated with a higher incidence of adverse visual symptoms.424 This procedure may be performed alone or in conjunction with other refractive procedures.425 Clinical experience suggests that the effect can be modulated by the depth and length of the incision and the distance from the corneal center. Incisions can be created with blades designed to achieve consistent depth. Femtosecond lasers have been used to create arcuate incisions to achieve a refractive effect.426
Although there are numerous reports of AK performed in animal eyes, in cadaver eyes, and in patients,427-431 there are few well-controlled prospective clinical studies available on AK, either performed alone or in conjunction with other keratorefractive procedures. A prospective evaluation of AK demonstrated that it was capable of reducing 1.00 D to 6.00 D of astigmatism but with limited predictability.424 One study retrospectively examined
LASIK versus AK to treat astigmatism.432 The vector-corrected change and visual acuity achieved by LASIK and by AK were not significantly different, except that in eyes with compound myopic astigmatism over 2.00 D, 40% of LASIK patients compared with 7% of AK patients achieved UCVA of 20/20 or better. Both methods had low rates of loss of BCVA.432
Complications of AK include corneal perforation, regression or progression of effect, incision gape or dehiscence, microbial keratitis,433 irregular astigmatism, and fibrous scarring.424 Incision healing problems are more common if AK and RK incisions intersect.424
Automated Lamellar Keratoplasty
Automated lamellar keratoplasty (ALK) was an antecedent of LASIK and was used to create a corneal cap or flap mechanically and then mechanically remove a lenticule of stromal tissue. Automated lamellar keratoplasty had only fair predictability. Complications included irregular astigmatism, thin flaps, free or displaced caps, corneal perforation, interface opacities, microbial keratitis, and epithelial ingrowth.434 With the advent of LASIK, ALK using mechanical microkeratomes has been largely abandoned.
In epikeratoplasty, a lathed donor corneal lenticule is sutured on top of a de-epithelialized recipient cornea, changing its anterior curvature.435,436 Refractive results are variable and significant complications can occur.437 These include poor incision healing, irregular astigmatism, interface haze, lenticule necrosis, and microbial keratitis. The procedure has been largely abandoned for refractive correction.
Intracorneal Alloplastic Inlays
Implantation of intracorneal alloplastic inlays to treat presbyopia is under investigation. The original use of this procedure for myopia and hyperopia was abandoned due to complications. The development of newer materials that may avoid the complication of corneal melting associated with earlier inlays438 has led to renewed interest.
Numerous strategies are being pursued to improve near and intermediate function in the setting of presbyopia through the implantation of corneal devices that either enhance depth of focus or establish corneal multifocality. One particular device under investigation is a corneal implant of less than 4 mm with a central pinhole of less than 2 mm that creates a pinhole effect, thereby increasing depth of focus. Another approach is to create a multifocal cornea by implanting a transparent lens of appropriate curvature so that it creates focal elevation over the center of the pupil. Yet another approach to achieve multifocality is to implant a lens within the intracorneal stroma that increases the refractive index of the center of the pupil.
These devices are potentially limited optically and mechanically by the theoretical compromise in contrast sensitivity and the disadvantages of multifocality, as well as by the historical instability of intracorneal implants over time.
Intraocular Refractive Surgery
Intraocular refractive surgery is the elective use of an IOL in a phakic eye, or in the case of elective refractive lens exchange, to allow use of a pseudophakic IOL, to achieve a particular refractive outcome. Refractive IOLs used in conjunction with cataract surgery are discussed in the Cataract in the Adult Eye PPP.53
Intraocular refractive surgery can be considered for patients who desire to reduce their dependence on eyeglasses or contact lens wear. Table 4 lists the phakic IOLs that have been approved by the FDA for the correction of myopia. The FDA has not approved use of a pseudophakic IOL for the sole purpose of correction of refractive error in the absence of visually significant cataract.
MedWatch (www.fda.gov/medwatch) is the Safety Information and Adverse Reporting Program for drugs and other medical products regulated by the FDA. Adverse experiences of refractive surgery should be reported to MedWatch.
TABLE 4. FDA-Approved Indications for Phakic Intraocular Lenses
Contraindications for intraocular refractive surgery are as follows:
Visually significant cataract in the case of phakic IOLs
Corneal endothelial disease, including Fuchs dystrophy
Uncontrolled external diseaseActive or recently active uveitis, or uveitis that requires ongoing treatment or is recurrent in nature
Uncontrolled autoimmune or other immune-mediated disease
Unrealistic patient expectations
The use of intraocular refractive surgery to correct refractive errors may not be advisable when there are pre-existing systemic or ocular conditions that may increase the relative risk of intraocular surgery, including the following:
Significant eyelid, tear film, or ocular surface abnormalities related to keratoconjunctivitis sicca, blepharoconjunctivitis, acne rosacea, conjunctival cicatrization, corneal exposure, neurotrophic keratitis, or other corneal abnormalities
Inflammation of the anterior segment
Presence of a filtering bleb
History of uveitis
Autoimmune or other immune-mediated disease
Pregnancy or lactation260
A comprehensive medical eye evaluation should be performed before any refractive surgery procedure.224 In addition to the elements listed in the comprehensive adult medical eye evaluation147 (see Appendix 4), the intraocular refractive surgery examination includes the elements listed in Table 5.
TABLE 5. Elements of the Intraocular Refractive Surgery Preoperative Evaluation
Computerized corneal topography is important to assess the optical state of the cornea. It is also relevant if akeratorefractive surgical procedure is necessary to optimize the refractive result after the lens surgery or for toric IOL implantation.
Before refractive surgery, corneal topography should be evaluated for evidence of irregular astigmatism, corneal warpage, or abnormalities suggestive of keratoconus or other corneal ectasias. All of these conditions may be associated with unpredictable refractive outcomes, and keratoconus and the ectasiaswith ectasia progression following keratorefractive surgery.38-41 When considering intraocular refractive surgery, measurement ofcorneal topography is important to assess the optical characteristics of the cornea. It is also relevant if akeratorefractive surgical procedure is necessary to optimize the refractive result after the lens surgery or for toric intraocular lens implantation. (strong recommendation, moderate evidence)
The patient should be informed of the potential risks, benefits, and alternatives to and among the different refractive procedures before surgery. The informed consent process should be documented, and the patient should be given an opportunity to have all questions answered before surgery. The surgeon is responsible for obtaining the patient's informed consent.224,225Elements of the discussion include the following:
Range of expected refractive outcomes and possible residual refractive error
Procedures for possible reduction of residual refractive error (i.e., enhancement procedures)
Loss of accommodation following refractive lens exchange and the possible need for reading and/or distance correction postoperatively
Corneal endothelial damage leading to corneal edema
Loss of BCVA
Side effects and complications (e.g., microbial keratitis, endophthalmitis, intraocular inflammation, cystoid macular edema)
Retinal detachment (especially with myopic refractive lens exchange)
Changes in visual function not measured by visual acuity testing (e.g., glare and function under low-light conditions)
Night-vision symptoms (e.g., glare, haloes) developing or worsening. Careful consideration should be given to this issue for patients with high degrees of ametropia or for individuals who require a high level of visual function in low-light conditions.
Monovision advantages and disadvantages (for patients of presbyopic age)
Postoperative care plans (setting of care, providers of care)
Intraocular refractive surgery may be performed using a variety of anesthesia techniques that include general and local (regional) anesthesia (e.g., retrobulbar, peribulbar, sub-Tenons injection, topical, and intracameral). The planned mode of anesthesia should be discussed with the patient so that she or he will know what to expect in terms of pain, discomfort, consciousness level, visual experiences, and complications.
Depending on the type of implant, topical or local (regional) anesthesia, along with sedation, is generally used. Intravenous access is generally recommended to treat potential adverse events when sedation/analgesic agents are administered.439 Given the lack of evidence for an optimal anesthesia strategy during anterior segment intraocular surgery, the type of anesthesia management should be determined by the patient's needs and the preferences of the patient and surgeon.440
Issues for Decision
Intraocular refractive surgery is one of several alternatives for the correction of ametropia. Phakic IOLs allow correction of up to 20.00 D of myopia and are approved for reduction of myopia up to 20.00 D. They have optical and structural advantages compared with keratorefractive surgery at high levels of intended refractions.441 Patients with thin corneas or atypical topography may be at increased risk of corneal complications with keratorefractive surgery. In these situations, intraocular refractive surgery may be considered as an alternative to keratorefractive surgery. Risks include those complications generally associated with intraocular surgery and must be considered carefully. Retinal detachment following refractive lens exchange in the setting of high myopia has been described to occur in 2% to 8% of eyes, and the risk is cumulative over time.442,443 Phakic IOLs have not been associated with increased risk of retinal detachment compared with other intraocular interventions in highly myopic patients.339,444,445 In highly myopic eyes, the relative risk of loss of BCVA was less for phakic IOLs than for refractive lens exchange in patients between the ages of 30 and 50.446
Phakic Intraocular Lens Implantation
Specially designed IOLs may be surgically placed in the anterior chamber, attached to the iris, or placed in the posterior chamber anterior to the crystalline lens in the phakic eye to correct refractive error.447-452 Advantages include rapid visual recovery, stability of achieved correction, preservation of accommodation, and the ability to correct high myopic refractive errors. Potential complications include endophthalmitis, endothelial cell loss, chronic iridocyclitis, cataract formation, iris distortion, pigment dispersion, elevated IOP, glaucoma, and IOL dislocation.453,454 Two styles of phakic IOLs have been approved by the FDA for use in the United States and other designs are in clinical trials. Prototypes of multifocal phakic IOLs have demonstrated potential for treatment of presbyopia.455,456
Posterior chamber phakic IOLs require a peripheral iridectomy or iridotomy to prevent pupillary block. The iridectomy may be performed either before surgery or at the time of lens insertion. Neodymium yttrium-aluminum-garnet (Nd:YAG) laser iridotomy is most frequently performed 7 to 14 days before surgery. Single or paired iridotomies, approximately 0.2 mm to 0.5 mm in size, are placed superiorly, with care to avoid straddling the lid margin to lessen the risk of postoperative glare and ghosting.
The IOL power is determined using standard optical calculations similar to IOL power calculation methods for cataract surgery. The surgical setting and sterile preparation for insertion of a phakic IOL are similar to cataract surgery. In the case of posterior chamber phakic IOLs, adequate dilation is required. Anterior-chamber-style, iris-fixated, or angle-supported phakic IOLs are inserted with a nondilated pupil with or without the use of pharmacologic miosis. The FDA-approved iris-supported lens is held in place through a process called enclavation in which a knuckle of iris is brought anteriorly within the haptic portion of the IOL on either side.
A Cochrane review presented a meta-analysis of three clinical trials that compared keratorefractive surgery and phakic IOL implantation for patients with myopia ranging from -6.00 D to -20.00 D with up to 4.00 D of astigmatism.457,458 At 1 year, the authors found that the percentage of eyes with UCVA of 20/20 was not significantly different between the groups and that there was significantly less loss of BSCVA for the group receiving phakic IOLs. In a long-term study of anterior chamber iris-fixated phakic IOLs, the mean spherical equivalent after 10 years was -0.70 ± 1.00 D (range, -4.00 to +2.00 D), with no significant change in mean spherical equivalent at 1, 6, or 10 years. At 10 years, 68.8% of all eyes were within 1.00 D of the intended correction. The mean IOP remained stable and the mean endothelial cell loss was -8.90 ± 16.00% at 10 years.459
Higher order aberrations and contrast sensitivity changes were similar for phakic IOLs and LASIK in one study.460 However, another study reported that eyes undergoing LASIK had three times more induced spherical aberration and two times more induced coma than phakic IOL eyes with similar preoperative corrections.461
Toric anterior and posterior chamber phakic IOLs have shown improved clinical results in European trials compared with spherical phakic IOLs.462 The term bioptics has been used to describe the combination of a phakic or pseudophakic IOL with LASIK for residual refractive error.463,464
Postoperative management following phakic IOL implantation is similar to cataract surgery. (See Appendix 8.)
Side Effects and Complications
Symptomatic undercorrection or overcorrection
Loss of BCVA
Visual aberrations, including transient or permanent glare or starburst/halo effect, especially at night
Corticosteroid-induced complications (e.g., ocular hypertension, glaucoma, cataract)
Adverse effect on ocular alignment
Endothelial cell loss
Acute angle-closure glaucoma
Lens dislocation with subsequent need for repositioning, exchange, or removal
Information on complications compiled from the manufacturers' submissions to the FDA is in Table 6.
TABLE 6. Incidence of Complications with Phakic IOLs in FDA Submissions
Cataract formation has been identified as a potential risk of phakic IOLs.465-467 Additional factors such as intraoperative trauma and patient age greater than 50 at the time of implantation have been associated with an increased risk of lens opacification following posterior chamber implantation.468 The incidence of cataract formation with posterior chamber phakic IOLs has been linked to surgeon experience.469 Most lens opacities are observed in the early postoperative period and are thought to be due to surgical trauma.469 Posterior chamber phakic IOLs are designed to vault over the natural crystalline lens, but peripheral contact between the posterior chamber phakic IOL and crystalline lens has been demonstrated by ultrasound biomicroscopy in 72% of cases.470 Subtle changes in lens design can influence the incidence of cataract formation.471 Iris-fixated phakic IOLs have been associated with a transitory increase in IOP.472 Anterior location of the crystalline lens apex relative to the plane of the iris may predispose the eye to this complication.473 Endothelial cell loss and pigment dispersion remain a concern for both anterior- and posterior-chamber-style phakic IOLs.474 Long-term loss of endothelial cells has been reported for angle-, iris-, and sulcus-supported phakic IOL styles.441 Pupil ovalization has been associated with various styles of phakic IOLs.475-477 Slower pupil reaction and decreased resting pupil diameter have been reported following posterior chamber phakic IOL implantation.478
Indefinite long-term follow-up is recommended for all phakic IOL patients.
Subjective assessment of patient satisfaction with visual quality has been evaluated as part of the Phase III clinical trials conducted for the FDA-approval process.479,480 In general, a high proportion of patients rate their visual acuity as good to excellent. Rapid recovery of visual acuity with phakic IOLs was typical. Similar rates of patient satisfaction have been reported with both anterior and posterior chamber phakic IOLs.
Refractive Lens Exchange
Removal of a clear crystalline lens without visually significant cataract, with or without IOL implantation, has been performed to correct refractive errors.481 Advantages include rapid rehabilitation and predictability of refractive outcome. Disadvantages include loss of accommodation in younger patients and the risk of complications inherent to any intraocular procedure. These include endophthalmitis and the increased risk of retinal detachment, particularly in patients with high axial myopia.442
Biometry and Intraocular Lens Power Calculation
The accurate measurement of axial length and central corneal power, combined with an appropriate IOL selection based on a power-calculation formula, is the minimal requirement to achieve the targeted postoperative refraction. A-scan ultrasonography or optical biometry is used to measure axial length. Formulas for calculating IOL power rely on keratometry to determine the net refractive contribution of the cornea. These measurements can be obtained by either manual or automated keratometry, or through corneal topography. Following keratorefractive surgery, the determination of central corneal power is particularly difficult. All devices that measure corneal power by standard methods are unable to determine the central corneal power accurately following keratorefractive surgery. The Cataract Surgery in the Adult Eye PPP contains further information on techniques and formulas. (See Appendix 8).
The surgical technique of refractive lens exchange is functionally indistinguishable from cataract surgery. The preferred method to remove the lens is extracapsular extraction by phacoemulsification.
The ideal technical elements of a successful refractive lens exchange procedure currently include the following:
Capsular bag fixation of an appropriate posterior chamber IOL
Minimization of trauma to the corneal endothelium, iris, and other ocular tissues
A secure, watertight incision that minimizes surgically induced astigmatism or reduces pre-existing corneal astigmatism
Special considerations relevant to conditions typically encountered during refractive lens exchange include the following:
In eyes with high axial myopia, the depth and stability of the anterior chamber are abnormal during phacoemulsification
In short hyperopic eyes, there is an increased risk of choroidal effusion
In eyes with high axial length, there is an increased risk of perforation with retrobulbar injections
Control of astigmatism is important in achieving the UCVA desired by the refractive lens exchange patient. Control of astigmatism can include:
Strategic placement of the corneal incisions
Use of limbal relaxing incisions
Secondary keratorefractive surgery
Posterior chamber lenses are the most frequently used implants and the implant of choice. If there is inadequate capsular or zonular support, a suture-fixated or appropriately sized anterior chamber IOL may be required.
The surgeon should have access to a variety of styles to select an appropriate IOL for an individual patient. Variations in the preoperative state of the eye, the surgical technique, patient expectations, and surgeon experience and preference affect the decision.
Multifocal or accommodative IOLs may increase functional near vision when used with refractive lens exchange. Toric IOLs may be used to correct preoperative regular keratometric astigmatism.482
Because there is a potential compromise in quality of vision with some IOLs, such as multifocal, compared to spheric monofocal IOLs49 (good evidence), surgeons should understand the individual patient's lifestyle and expectations so that the best IOL option can be selected for patients undergoing a refractive lens exchange (strong recommendation).
Refractive lens exchange for myopia and hyperopia has been demonstrated to be predictable and effective, with studies reporting that from 68% to 100% of eyes were within ± 1.00 D of the intended refraction,481,483-486 and 58% to 70% of eyes within ± 0.50 D.483,485,486 Postoperative UCVA of 20/40 or better was reported in 77% to 100% of eyes.481,485,486 Loss of BSCVA was reported in 0% to 10% of eyes.483-486
Postoperative management following refractive lens exchange is similar to cataract surgery. (See Appendix 8.)
Side Effects and Complications
No large-scale investigations on complications of refractive lens exchange have been reported. Complications that may result in a permanent loss of vision are rare. Major complications of lens extraction that are potentially sight threatening include infectious endophthalmitis, intraoperative suprachoroidal hemorrhage, cystoid macular edema, retinal detachment, corneal edema, and IOL dislocation.
REFRACTIVE SURGERY FOR PRESBYOPIA
Techniques that have been utilized for the surgical correction of presbyopia include keratorefractive surgery (PRK, LASIK, or conductive keratoplasty) for monovision or multifocal ablation, IOLs (monofocal lenses for monovision, multifocal lenses, or accommodative lenses), anterior ciliary sclerotomy (ACS), and scleral expansion band segments.
Presbyopia can be managed by eyeglasses or contact lenses (soft, rigid gas-permeable, aspheric bifocal or multifocal). These can be used bilaterally or for monovision and modified monovision. Modified monovision is the use of a bifocal or multifocal contact lens in one eye and a distance contact lens in the fellow eye. Surgical management of presbyopia includes keratorefractive surgery for monovision or intraocular lens implantation (monofocal lenses for monovision, multifocal lenses, or accommodative lenses).(good evidence)
At present, the most widely used surgical approach to compensate for presbyopia is excimer laser photoablation to create monovision. Conductive keratoplasty has been used to treat presbyopia by achieving a monovision result (see Thermal Keratoplasty).487 The best candidates for monovision are patients over 40 years old who place a high premium on maximizing their freedom from optical aids and are willing to sacrifice uncorrected distance stereoacuity to achieve this goal. Larger degrees of anisometropia produce better visual function at near, but smaller degrees of anisometropia may be better tolerated and are a viable option for some patients willing to accept a compromise.488,489 Distance correction is usually performed for the dominant eye and near correction is performed for the nondominant eye.490 Evidence exists to suggest that near correction in the dominant eye may also be successful and even preferable in some patients.490,491Caution should be used in considering monovision in patients who have had previous strabismus surgery, phorias, or intermittent tropias, as these patients may develop postoperative diplopia. A preoperative trial with contact lenses is a useful test to see if a patient will adapt to the intended refractive outcome.
Patients with monovision who function well for most of their daily activities may still benefit from the use of eyeglass correction, especially in dim-light conditions while driving. Many patients with a low degree of monovision will be able to drive without difficulty. Patients with monovision may experience a decrease in contrast sensitivity and stereopsis compared with bilateral distance correction.492 When the eye corrected for near vision is corrected for distance vision using eyeglasses, distance visual acuity and depth perception are optimized.
Multizone excimer photoablation to create a multifocal effect in the cornea is being investigated to treat presbyopic patients with preoperative myopia or hyperopia. Excimer laser software is not approved by the FDA for multifocal ablation for presbyopia. In order to achieve a multifocal cornea, the central cornea can either be flatter or steeper than the midperipheral cornea. The ablation profile is designed to achieve either center distance/periphery near vision or center near/periphery distance vision. Early reports with small numbers of presbyopic patients with myopia or hyperopia treated with multifocal LASIK have shown variable results.493,494 Additional studies to refine ablation profiles, improve predictability, and assess the role of pupil size are ongoing.
A variety of intraocular surgeries can be used to address presbyopia. After crystalline lens removal, IOLs can be used to provide functional distance vision as well as near vision by means of a number of approaches. There are advantages and disadvantages to each of these modalities, and the choice for any one of these methods depends on the patient's visual needs, expectations, motivation to be less dependent on eyeglasses, and willingness to accept certain compromises.
One approach is the use of monofocal IOLs to achieve postoperative monovision. It can be difficult, however, to assess which eye is the dominant eye in a preoperative patient who has blurred vision due to cataracts. Before cataract surgery, it is also difficult to demonstrate the proposed results of monovision IOLs using contact lenses. Patients who have demonstrated success with monovision contact lenses before the development of cataracts may be well suited for this modality.
Multifocal IOLs are another option to provide distance, intermediate, and near vision without eyeglasses. Multifocal IOLs achieve their effect by dividing incoming light into two or more focal points and can be classified as refractive or diffractive. A Cochrane systematic review concluded that multifocal IOLs were effective at improving near vision when compared with monofocal IOLs and that unaided distance visual acuity was similar in the two groups.49 Multifocal IOLs did result in reduced contrast sensitivity and an increased incidence of haloes, however.49
Accommodative lenses have been designed to change position in the eye with near-focusing effort. The amplitude of lens movement varies among lens designs and patients.495 Biometric studies of IOL shift in response to accommodative effort have shown little if any lens movement with single-optic designs.496 These lenses may offer an alternative to allow patients to see well at distance with a modest improvement in near and intermediate vision when compared with monofocal lenses. The mechanism of improved distance and intermediate vision may involve pseudoaccommodation (increased depth of focus) and possibly a small degree of lens-position shift.497
In ACS, a series of 8 to 12 deep radial scleral incisions approximately 2.5 mm long are made posterior to the limbus in the area overlying the ciliary muscle, but stop short of the pars plana.498 The proposed mechanism of this procedure is the creation of additional space in the region of the ciliary body, thus increasing the distance between the ciliary body and the equatorial lens to allow greater zonular tension and potentially allow a greater accommodative effect during ciliary muscle contraction. No peer-reviewed data exist to support the efficacy of ACS, and a prospective comparative study of ACS in one eye and using the contralateral eye as a control showed no statistically significant increase in accommodation after surgery.499 This procedure has been largely abandoned due to lack of efficacy and complications such as anterior segment ischemia, regression, intraoperative anterior chamber perforation, and decreased ocular integrity.4998-502
To increase the effect of scleral expansion surgery, some researchers have proposed implanting a silicone expansion plug within the scleral incision, but no peer-reviewed data have been published to show improved results. Another approach has been the use of scleral expansion band segments. In this surgery, four PMMA segments measuring about 1.4 x 0.9 x 5.5 mm in size are inserted beneath partial-thickness scleral incisions (scleral belt loops) in each of the oblique quadrants. One prospective, multicenter trial showed a modest improvement in near vision in about half of the patients using subjective testing methods.503 Many investigators dispute the proposed mechanism of scleral expansion to treat presbyopia, and the results of these various surgeries have not shown predictable or consistent effects on distance corrected near acuity or accommodative amplitude.502,504
PROVIDER AND SETTING
Patients with refractive errors should be examined and evaluated for treatment by an ophthalmologist or an optometrist. If refractive surgery is considered, the operating ophthalmologist is responsible for the preoperative evaluation.224 Trained individuals under the supervision of the ophthalmologist or optometrist may collect certain data. Only an appropriately trained ophthalmologist should perform surgical treatment of refractive errors, including excimer and femtosecond laser surgery. Postoperative management is integral to the outcome of any surgical procedure and is the responsibility of the operating surgeon.361,362
COUNSELING AND REFERRAL
Any decisions about surgical correction of a refractive error should be made by an informed patient and an ophthalmologist familiar with refractive surgery.224 Information and discussion about the planned procedure should be available sufficiently in advance of the proposed surgical date so that the patient can carefully consider the risks, benefits, and alternatives to the procedure.224,361,362
Global Burden of Uncorrected Refractive Error
Uncorrected refractive error is a common cause of visual impairment and blindness throughout the world. The World Health Organization estimates that 153 million people have vision worse than 20/60 due to uncorrected refractive error, with the burden of disease greatest in developing countries.505 Globally, uncorrected refractive error accounts for 42% of persons with visual impairment worse than 20/60 and 18% of persons with vision worse than 20/400, making it the leading cause of visual impairment and second leading cause of blindness.506 The global burden of refractive error increases when presbyopia is taken into account. An estimated 1.04 billion people are estimated to have presbyopia, and nearly half of these do not wear presbyopic correction.507 Uncorrected presbyopia causes visual impairment for 410 million people worldwide, with the vast majority of cases (94%) occurring in developing countries.
Quality of Life
Refractive error reduces vision-related quality of life. In a British study, persons with myopia of 10.00 D or more had significantly worse vision-related quality of life compared with persons with less severe myopia.508 An Australian study found that individuals with myopia of 0.50 D or more reported worse vision-related quality of life measures compared with emmetropes.403 In a European study, more than half of pseudophakic patients who wore eyeglasses after cataract surgery would be willing to pay more than €0.50 per day to be free from wearing eyeglasses.509
Vision-related quality of life has been assessed for several refractive error treatments. In one study, contact lens wearers had a higher vision-related quality of life than eyeglass wearers.510 Patients undergoing refractive surgery are generally pleased with their decision, and a systematic review estimated that 95% of patients undergoing LASIK were satisfied with their outcome.404 In several nonrandomized studies of patients undergoing LASIK, vision-related quality of life was higher postoperatively compared with preoperatively.511-514 Persons willing to pay for refractive surgery are likely a biased group, with several studies showing that preoperative vision-related quality of life scores in patients having refractive surgery are lower than in patients with equivalent refractive error who wear eyeglasses or contact lenses.514,515 Worsening of vision-related quality of life metrics has been observed in roughly 5% of respondents.511,514 Several quality-of-life questionnaires have been designed specifically for refractive error, including the Refractive Status and Vision Profile (RSVP), the National Eye Institute Refractive Quality of Life (NEI-RQL), and the Quality of Life Impact of Refractive Correction (QIRC).511,516,517
Each year, over 27 million outpatient visits in the United States are devoted to assessment and treatment of refractive error.518 Moreover, refractive error accounts for one-third of the $16.24 billion in direct medical costs spent on vision disorders each year in the United States.518 Worldwide, the burden of uncorrected refractive error has substantial economic repercussions, with conservative analyses estimating a societal cost of $121.4 billion in lost productivity.143 A net economic gain would result from treatment of uncorrected refractive error if eyeglasses could be provided to each individual for less than $1000. At the individual level, several cost-effectiveness studies have compared refractive surgery to contact lenses. Although the results depend on the assumptions used in the models, these studies have generally found that refractive surgery has higher up-front costs compared with contact lenses but becomes more cost-effective in the long term.519,520 The long-term cost savings for refractive surgery results from fewer doctors' appointments and fewer prescriptions for contact lenses or eyeglasses. Similarly, toric IOLs were shown to be more cost-effective than conventional IOLs, mostly because toric lenses reduced long-term costs of postoperative contact lenses or eyeglasses.521 More research on the cost-effectiveness of various treatments for refractive error would be helpful for insurers as well as for clinicians counseling their patients on services not covered by health insurance.
APPENDIX 1. QUALITY OF OPHTHALMIC CARE CORE CRITERIA
Providing quality care
is the physician's foremost ethical obligation, and is
the basis of public trust in physicians.
AMA Board of Trustees, 1986
Quality ophthalmic care is provided in a manner and with the skill that is consistent with the best interests of the patient. The discussion that follows characterizes the core elements of such care.
The ophthalmologist is first and foremost a physician. As such, the ophthalmologist demonstrates compassion and concern for the individual, and utilizes the science and art of medicine to help alleviate patient fear and suffering. The ophthalmologist strives to develop and maintain clinical skills at the highest feasible level, consistent with the needs of patients, through training and continuing education. The ophthalmologist evaluates those skills and medical knowledge in relation to the needs of the patient and responds accordingly. The ophthalmologist also ensures that needy patients receive necessary care directly or through referral to appropriate persons and facilities that will provide such care, and he or she supports activities that promote health and prevent disease and disability.
The ophthalmologist recognizes that disease places patients in a disadvantaged, dependent state. The ophthalmologist respects the dignity and integrity of his or her patients, and does not exploit their vulnerability.
Quality ophthalmic care has the following optimal attributes, among others.
- The essence of quality care is a meaningful partnership relationship between patient and physician. The ophthalmologist strives to communicate effectively with his or her patients, listening carefully to their needs and concerns. In turn, the ophthalmologist educates his or her patients about the nature and prognosis of their condition and about proper and appropriate therapeutic modalities. This is to ensure their meaningful participation (appropriate to their unique physical, intellectual, and emotional state) in decisions affecting their management and care, to improve their motivation and compliance with the agreed plan of treatment, and to help alleviate their fears and concerns.
- The ophthalmologist uses his or her best judgment in choosing and timing appropriate diagnostic and therapeutic modalities as well as the frequency of evaluation and follow-up, with due regard to the urgency and nature of the patient's condition and unique needs and desires.
- The ophthalmologist carries out only those procedures for which he or she is adequately trained, experienced, and competent, or, when necessary, is assisted by someone who is, depending on the urgency of the problem and availability and accessibility of alternative providers.
- Patients are assured access to, and continuity of, needed and appropriate ophthalmic care, which can be described as follows.
- The ophthalmologist treats patients with due regard to timeliness, appropriateness, and his or her own ability to provide such care.
- The operating ophthalmologist makes adequate provision for appropriate pre- and postoperative patient care.
- When the ophthalmologist is unavailable for his or her patient, he or she provides appropriate alternate ophthalmic care, with adequate mechanisms for informing patients of the existence of such care and procedures for obtaining it.
- The ophthalmologist refers patients to other ophthalmologists and eye care providers based on the timeliness and appropriateness of such referral, the patient's needs, the competence and qualifications of the person to whom the referral is made, and access and availability.
- The ophthalmologist seeks appropriate consultation with due regard to the nature of the ocular or other medical or surgical problem. Consultants are suggested for their skill, competence, and accessibility. They receive as complete and accurate an accounting of the problem as necessary to provide efficient and effective advice or intervention, and in turn they respond in an adequate and timely manner.
- The ophthalmologist maintains complete and accurate medical records.
- On appropriate request, the ophthalmologist provides a full and accurate rendering of the patient's records in his or her possession.
- The ophthalmologist reviews the results of consultations and laboratory tests in a timely and effective manner and takes appropriate actions.
- The ophthalmologist and those who assist in providing care identify themselves and their profession.
- For patients whose conditions fail to respond to treatment and for whom further treatment is unavailable, the ophthalmologist provides proper professional support, counseling, rehabilitative and social services, and referral as appropriate and accessible.
- Prior to therapeutic or invasive diagnostic procedures, the ophthalmologist becomes appropriately conversant with the patient's condition by collecting pertinent historical information and performing relevant preoperative examinations. Additionally, he or she enables the patient to reach a fully informed decision by providing an accurate and truthful explanation of the diagnosis; the nature, purpose, risks, benefits, and probability of success of the proposed treatment and of alternative treatment; and the risks and benefits of no treatment.
- The ophthalmologist adopts new technology (e.g., drugs, devices, surgical techniques) in judicious fashion, appropriate to the cost and potential benefit relative to existing alternatives and to its demonstrated safety and efficacy.
- The ophthalmologist enhances the quality of care he or she provides by periodically reviewing and assessing his or her personal performance in relation to established standards, and by revising or altering his or her practices and techniques appropriately.
- The ophthalmologist improves ophthalmic care by communicating to colleagues, through appropriate professional channels, knowledge gained through clinical research and practice. This includes alerting colleagues of instances of unusual or unexpected rates of complications and problems related to new drugs, devices, or procedures.
- The ophthalmologist provides care in suitably staffed and equipped facilities adequate to deal with potential ocular and systemic complications requiring immediate attention.
- The ophthalmologist also provides ophthalmic care in a manner that is cost effective without unacceptably compromising accepted standards of quality.
Reviewed by: Council
Approved by: Board of Trustees
October 12, 1988
2nd Printing: January 1991
3rd Printing: August 2001
4th Printing: July 2005
APPENDIX 2. EPIDEMIOLOGY OF REFRACTIVE ERRRORS
Over half of Americans over the age of 40 have ametropia of sufficient magnitude to require refractive correction.54 It has been estimated that 93 million Americans aged 12 years and older use some form of eyewear to correct refractive errors in distance.55 About 36 million people in the United States used contact lenses in 2005.56 Current estimates indicate that over 8.5 million persons in the United States have undergone refractive surgery since 1995.57
The prevalence of myopia in the U.S. population was estimated in the early 1970s to be 25% in persons aged 12 to 54 years.522 A meta-analysis of population-based studies found a prevalence of 25% in persons over age 40.59 A study based on a sample representative of the U.S. population found a prevalence of 31% in those 40 and older and of 36% in those 20 and older.54 A number of population-based studies have shown that the prevalence of myopia is lower in older than in younger persons, ranging from about 35% to 40% among persons in their 20s to 40s to about 15% to 20% among persons in their 60s, 70s, and 80s.60-62 Individuals who develop nuclear sclerosis, however, tend to undergo a myopic shift over time.523-525
There is some evidence that the prevalence of myopia is increasing in more recent generations. Studies of ethnic Chinese in Taiwan document an increase in the prevalence and severity of myopia over two generations.101-104 Genetics alone are unlikely to account for such a rapid change, although one study has speculated that genetic factors do not preclude such a change.105 A study of successive cohorts of enlistees in the Israeli army showed a marked increase in prevalence of myopia over a 13-year period.106 A study in Finland showed that the prevalence of myopia doubled among teenagers and young adults over the course of the 20th century.107 A study comparing U.S. population-based estimates in 1971-1972 and 1999-2004 also found a marked increase in the prevalence of myopia, although the reasons for this increase could not be identified.108
In the United States, myopia was found to be significantly more prevalent among non-Hispanic white persons than among persons of non-Hispanic black or Mexican American race/ethnicity.54 Two population-based studies in the United States have reported that the prevalence of myopia in Latino persons aged 40 and older was 17% to 18%.59,526 A similar pattern was reported in Australia109,527 and in populations of African descent in Baltimore and Barbados.61,528 The prevalence of myopia in individuals of Asian ethnicity in the United States has not been published to date; however, there have been a number of population-based studies in different East Asian countries that indicate that the prevalence of myopia varies considerably. In elderly Taiwanese persons, the prevalence was 19% (≥65 years)529; in Indonesia, the prevalence was 26%530; in Beijing, the prevalence was 23% (≥40 years).531 In Chinese people aged 30 years and older, the prevalence was 26.7%,532 and the prevalence was 9.5% in persons living in southern China aged 50 years and older.533 A study of Japanese persons aged 40 years and older found a prevalence of myopia (0.50 D or more of myopia) of 41.8%.534 Other studies of young adult East Asian populations indicate that the prevalence of myopia is much higher than in their U.S. counterparts, ranging from 56% in 15- to 19-year-old Singaporean students535 to 85% in 19- to 23-year-old medical students in Singapore,536 to 30.7% in persons of Malay ethnicity aged 40 to 80 years.537 Studies in South Asian countries found prevalences of 13% for persons aged 30 or older living in rural India,538 37% for persons living in Andhra Pradesh state (India),539 and 36% for persons aged 30 and older in Pakistan.540
The prevalence of myopia in American children aged 12 to 17 was estimated at around 25% in the early 1970s.522 In one study, myopia (0.75 D or more of myopia) was found in 9% of children aged 5 to 17 years.58 Data from the Orinda, California, Longitudinal Study found that the prevalence of 0.50 D or more of myopia was about 3% among 5- to 7-year-olds, 8% among 8- to 10-year-olds, and 14% among 11- to 12-year-olds.117 Data suggest that ethnic Chinese children have much higher rates of myopia at all ages. A national survey in Taiwan found the prevalence was 12% among 6-year-old children and 84% among those 16 to 18 years old.101 In a series of studies using similar methodology and definitions for myopia (0.50 D or more of myopia) in children aged 7 to 15 years, prevalences of myopia varied widely by country and ethnicity: 4% in India541; 10% to 34% in Malaysia542; 5% to 17% in southern China543; 7% in New Delhi544; and 9% to 40% in Malaysia and Singapore.545 Similar rates have been found in Singapore (12% among 6- to 7-year-olds to 79% among 18-year-old males), and in Japan (44% among 12-year-olds to 66% among 17-year-olds).81,102,546,547 A survey in Nigeria found that the prevalence of myopia in persons aged 40 years or older was 16.2%.548
Less is known about the epidemiology of hyperopia and astigmatism than about myopia. Population-based studies of Caucasians aged 40 and older report that the prevalence of hyperopia increases from about 20% among those in their 40s to about 60% among those in their 70s and 80s.60,61,109 A meta-analysis of population-based studies found the prevalence of hyperopia was 10% in the United States and increased with increasing age.59 Another study, based on a sample representative of the U.S. population, found that the prevalence of hyperopia in those aged 40 and older was 5%, with little variation by race/ethnicity.54 A similar pattern of higher prevalence of hyperopia in older ages was observed in a U.S. population-based study.54 In a population of rural Chinese persons aged 50 and older, the prevalence of hyperopia was 8.9%533 and in another rural Chinese population aged 30 and older, the prevalence was 15.9%.532 A similar prevalence and association with age were seen among African Americans in Baltimore.61 In Australian children aged 6 years and 12 years, the prevalence of hyperopia was 13.2% and 5.0%, respectively.549 In a multiethnic pediatric eye disease study, the prevalence of hyperopia was found to be significantly higher in African American and Hispanic children aged 6 to 72 months than in non-Hispanic white children.550 Data from a 5-year follow-up of residents of Beaver Dam, Wisconsin, documented a hyperopic shift in individuals under age 70 but a myopic shift in individuals who were developing nuclear sclerosis even if under age 70.523 A study in Salisbury, Maryland, also found that nuclear sclerosis was associated with myopia,551 consistent with a report from a Latino population.525 In contrast to myopia, hyperopia was associated with fewer years of formal education in the same populations.60,61 African American men in Baltimore, Maryland, had half the prevalence of hyperopia that women had61 and female Mexican American participants in the Proyecto Ver study were more likely than their male counterparts to have hyperopia,59 but this gender difference was not observed among individuals of European descent.59-61 A study of persons aged 30 or older in rural India found a prevalence of hyperopia (0.50 D or more of hyperopia) of 18% 538 and a study of persons of similar age in Pakistan found a prevalence of 27%.540 A study of persons of Malay ethnicity in Singapore, aged 40 to 80, found a prevalence of hyperopia of 27%.537 In Japanese persons aged 40 and older the prevalence of hyperopia was 28%.534
Population-based data document the prevalence of astigmatism in children or young adults. In a multiethnic pediatric eye disease study, the prevalence of astigmatism in African American and Hispanic children aged 6 to 72 months was 12.7% and 16.8%, respectively.110 Kleinstein et al58 found that 28% of their U.S.-based study population aged 5 to 17 years had at least 1.00 D of astigmatism. A study of Australian 6-year-olds found a prevalence of astigmatism of nearly 5%.552 A series of studies carried out in children aged 7 to 15 from different countries but using similar methodology found a wide range of prevalences of astigmatism, varying from approximately 3% in Andhra Pradesh, India,541 to 7% in New Delhi,544 to 6% in Chinese children.129 The prevalence of high astigmatism in Native American children was reported as 23% to 29% in those aged 2 to 7 years.553 In Taiwanese preschoolers, the prevalence of astigmatism was 13.3%.554 One or more diopters of astigmatism is common among older adults (31% in persons aged 40 and older) and the prevalence is higher in older-age groups.54,61 This increase with age was also seen among African Americans, although the prevalence was about 30% lower than among Caucasians at every age.61 In adult Americans, the prevalence of astigmatism has been reported to be 20% higher among men than women but was not associated with number of years of formal education.54,61 Astigmatism was found in 7.6% of Chinese subjects aged 50 and older533 and in 24.5% of subjects aged 30 and older.532 A study of persons of Malay ethnicity aged 40 to 80 living in Singapore reported a prevalence of astigmatism of 33%.537 In Japanese persons aged 40 and older the prevalence of astigmatism was 54%.534 A study of persons aged 30 and older in Pakistan found a prevalence of astigmatism of 37%.540 There have been conflicting data about the association of astigmatism with prematurity or low birth weight, and with retinopathy of prematurity.111-114
These studies cannot be directly compared because the definitions of myopia, hyperopia, and astigmatism vary.
APPENDIX 3. PREVENTION OF MYOPIA PROGRESSION
Most myopic refractive errors develop and progress during childhood and adolescence.122 Treatments proposed to prevent or reduce the progression of myopia include optical correction, use of cycloplegic eyedrops, pressure-lowering eyedrops, contact lenses, and visual training. A Cochrane review of interventions to slow progression of myopia in children found positive effects of antimuscarinic eyedrops, which have undesirable side effects or are not commercially available, and lesser effect of multifocal eyeglasses.146 Reduction of peripheral hyperopic defocus may be the mechanism by which these interventions are effective.
Information about the effects of nutritional changes on the progression of myopia is largely anecdotal and no scientifically valid studies are available.
Optical correction in the form of bifocal eyeglasses, multifocal eyeglasses, or removal of distance eyeglasses when performing close work has been recommended in an attempt to reduce accommodation, since accommodation has been implicated in the progression of myopia. Studies examining distance eyeglasses alone have failed to demonstrate any overall effects on the progression of human myopia.555
Randomized, controlled clinical trials have compared the use of bifocal eyeglasses (with add powers ranging from +1.00 D to +2.00 D) with single-vision distance eyeglasses in myopic children, and have failed to demonstrate any significant differences in myopic progression.120,122,556,557 One study of 75 esophoric children, approximately half of whom used +1.50 D add bifocals, did show a slight reduction in the progression of myopia compared with controls.558 Among the children completing the 30 months of follow-up, myopia progression was statistically significantly lower for bifocals than for single-vision eyeglasses (1.00 D to 1.24 D).558 In a study comparing the use of multifocal eyeglasses to single-vision distance eyeglasses in myopic children, there was no statistically significant difference in the rate of myopia progression.128 One study of 469 children ages 6 to 11 years reported that progressive addition lenses compared to single-vision lenses slowed the progression of myopia by a small, statistically significant amount only during the first year.559 The authors concluded that the small magnitude of the effect does not warrant a change in clinical practice. Another study of 138 Hong Kong children ages 7 to 10.5 years found no evidence of retardation of myopia progression by wearing progressive addition lenses after 2 years.560 Thus, with the exception of one small trial, optical correction has not been shown to prevent progression of myopia.120,122,556,557
TOPICAL CYCLOPLEGIC AGENTS
Administration of atropine eyedrops has long been proposed as a treatment to prevent progression of myopia. Atropine inhibits accommodation, which may exert forces on the eye that result in axial elongation. In animal studies, atropine also appears to inhibit growth factors acting to elongate the eye independent of accommodation.561-563
The results of randomized, controlled clinical trials conducted in Taiwan and Singapore (three of which were masked) provide reasonable evidence that administration of atropine eyedrops retards the progression of myopia in school children.127,128,564,565 In one study, a range of atropine concentrations was utilized; 0.1%, 0.25%, and 0.5%. All reduced progression of myopia compared with the control group. The 0.5% concentration was the most effective.127
It has also been shown that atropine eyedrops are effective in populations in the West where children generally have less rapid rates of progression of myopia than in Taiwan.566-568 It is now also known that the beneficial effects remain once the use of atropine is discontinued.568 Potential risks of long-term atropine use are uncertain and include the risk of light toxicity to ocular structures, the potential for local allergic and systemic reactions, and the effect on accommodative amplitudes following discontinuation of atropine. However, it has been reported that daily atropine usage over 2 years for the treatment of myopia has no significant effect on retinal function as demonstrated by recordings of multifocal electroretinograms in children.569 Other potential disadvantages include the possible need for bifocal or multifocal eyeglasses (depending on the concentration of atropine administered), photosensitivity and glare, and the inconvenience of using daily eyedrops.
Cyclopentolate 1% administered nightly was evaluated in one study in school children in Taiwan. It was found to slow the rate of progression of myopia compared with controls (mean myopic progression of -0.60 D/year compared with -0.90 D/year, which is statistically significant), but not as much as atropine did (mean myopic progression of -0.20 D/year).564 Tropicamide 1% was evaluated in a study of monozygotic twins, and no significant difference in progression of myopia was noted compared with controls.570
Pirenzepine hydrochloride has been evaluated in two multicenter, double-masked, placebo-controlled parallel studies to slow the progression of myopia in school-aged children. Unlike atropine, which affects both accommodation and mydriasis, pirenzepine has a relatively selective effect on accommodation. The U.S. study examined 174 children ages 8 to 12 years,571 and the Asian study examined 353 children ages 6 to 13 years.572 Both studies found 2% pirenzepine ophthalmic gel effective and relatively safe in slowing myopia progression over a 1-year treatment period.
Because of uncertainty about long-term safety and optimal dosage, administration of atropine eyedrops or pirenzepine hydrochloride to reduce myopic progression in children is recommended only in research trials.564,571,572
Lowering IOP has been suggested as a pharmacologic intervention that might reduce progression of myopia, presumably by reducing internal pressure on the ocular wall. One prospective clinical trial comparing administration of 0.25% timolol maleate with the use of single-vision eyeglasses failed to show any retardation of progression of myopia.556,573 Therefore, this treatment is not recommended.
Soft contact lens use was evaluated in a randomized clinical trial in the U.S.574 No statistically significant difference in the rate of myopia progression could be demonstrated between the contact lens group and the group using single-vision eyeglasses.
It has long been postulated that rigid contact lens use could slow the progression of myopia in children.575,576 Previous studies published were limited by methodological difficulties.577-582 A 2-year randomized clinical trial evaluating the effect of rigid contact lenses on myopia progression in school children was conducted in Singapore,222 and another study concurrently in the U.S.583 The study of 428 Singaporean children ages 6 to 12 years found that rigid gas-permeable contact lenses did not slow the rate of myopia progression over 2 years, even among children who used them regularly and consistently.222 The U.S. study compared the effects of rigid gas-permeable contact lenses and soft contact lenses on myopia progression in 116 children ages 8 to 11 years. They found that rigid contact lens wearers experienced less myopia progression than soft contact lens wearers, and that the corneal curvature of the soft lens group steepened more than the rigid lens group, but the axial growth was not statistically significantly different between the groups. Because some of the effect was likely influenced by transient corneal curvature changes, the authors concluded that the results indicate that rigid gas-permeable contact lenses should not be prescribed primarily for myopia control.584
Although it has been suggested that orthokeratology can slow the progression of myopia in children, there is no randomized controlled-trial evidence to support this.221,222 A 2-year pilot study was conducted to determine whether orthokeratology can effectively reduce and control myopia in children. Thirty-five Hong Kong children ages 7 to 12 years undergoing orthokeratology treatment were compared with 35 children wearing single-vision eyeglasses from an earlier study (control). The study found a statistically significant change in axial length for the orthokeratology group and the control group (0.29 ± 0.27 mm and 0.54 ± 0.27 mm, respectively). However, there are substantial variations in changes in eye length among children and there is no way to predict the effect for individual subjects.221 Another orthokeratology myopia progression study (SMART, Stabilizing Myopia by Accelerating Reshaping Technique) began enrolling participants in 2007 and is due for final analysis in 2012. Participants (n=300) were ages 8 to 14 years old at enrollment. There is insufficient evidence to support the use of orthokeratology for the prevention of myopia progression in children.221,222
Visual training purported to reduce myopia includes exercises such as near-far focusing change activities.585-587 There are no scientifically acceptable studies that document that these treatments are clinically effective, and, therefore, this therapy is not recommended.585,588,589
APPENDIX 4. ELEMENTS OF THE COMPREHENSIVE ADULT MEDICAL EYE EVALUATION PPP
A comprehensive medical eye evaluation includes history, examination, diagnosis, and initiation of management. Included within each part of the evaluation is a series of items particularly effective for the detection, diagnosis, and choice of appropriate therapy for ocular, visual, and systemic disease. The items listed are basic areas of evaluation or investigation and are not meant to exclude additional elements when appropriate. For example, because history taking is an interactive process, additional questions and evaluation may be suggested by the patient's responses.
In general, a thorough history may include the following items, although the exact composition varies with the patient's particular problems and needs.
- Demographic data (e.g., name, date of birth, gender, and where appropriate, ethnicity or race)
- The identity of the patient's other pertinent health care providers
- Chief complaint and history of present illness
- Present status of visual function (e.g., patient's self-assessment of visual status, visual needs, any recent or current ocular symptoms, and use of eyeglasses or contact lenses)
- Ocular history (e.g., prior eye diseases, injuries, surgery, including refractive surgery, or other treatments and medications)
- Systemic history: pertinent medical conditions and previous surgery
- Medications: ophthalmic and systemic medications currently used, including nutritional supplements
- Allergies or adverse reactions to medications
- Family history: pertinent familial ocular and systemic disease
- Social history (e.g., occupation, smoking history, alcohol use, family and living situation as appropriate)
- Directed review of systems
The comprehensive eye examination consists of an evaluation of the physiologic function and the anatomic status of the eye, visual system, and its related structures. This usually includes the following elements:
- Assessment of relevant aspects of patient's mental and physical status
- Visual acuity with current correction (the power of the present correction recorded) at distance and when appropriate at near
- Measurement of best-corrected visual acuity (with a refraction) when indicated
- External examination (e.g., lids, eyelashes, and lacrimal apparatus; orbit; and pertinent facial features)
- Ocular alignment and motility
- Pupillary function
- Visual fields by confrontation
- Slit-lamp biomicroscopic examination: eyelid margins and eyelashes, tear film, conjunctiva, sclera, cornea, anterior chamber, and assessment of peripheral anterior chamber depth, iris, lens, and anterior vitreous
- Intraocular pressure measurement preferably with a contact applanation method (typically a Goldmann tonometer)
- Examination of the fundus: vitreous, retina (including posterior pole and periphery), vasculature, and optic nerve
Examination of anterior segment structures routinely involves gross and biomicroscopic evaluation before and after dilation. Evaluation of structures situated posterior to the iris requires a dilated pupil. Optimal examination of the peripheral retina requires the use of the indirect ophthalmoscope or slit-lamp fundus biomicroscopy. Optimal examination of the macula and optic nerve requires the use of the slit-lamp biomicroscope and accessory diagnostic lenses.
APPENDIX 5. EYEGLASSES
Guidelines for correcting specific refractive errors with eyeglasses are outlined below.
Individuals with asymptomatic myopia do not need eyeglass correction except for visually demanding activities like driving or school work. Overcorrecting myopic patients will cause excessive accommodation, which may create symptoms. Some patients may become symptomatic from an increased degree of myopia that occurs at low levels of illumination (night myopia), and they may require increased minus correction for clearer vision at night.
Because of the progressive nature of myopia in childhood and adolescence, screening examinations that include visual acuity are recommended every 1 to 2 years (see Pediatric Eye Evaluations PPP125).
Slight undercorrection may be desirable in young and middle-aged individuals with hyperopia because there is some physiologic accommodative tone. As the patient ages, full correction may be necessary to provide optimal distance vision and to minimize difficulties with near vision.
Full correction may not be needed for individuals with regular astigmatism. Adults with astigmatism may not accept full cylindrical correction in their first pair of eyeglasses or in subsequent eyeglasses if their astigmatism has been only partially corrected. In general, substantial changes in axis or power are not well tolerated.
Patients with presbyopia have several options for eyeglass correction: bifocals, trifocals, progressive addition lenses, or separate eyeglasses for distance and reading. Individuals with myopia must exert more accommodative effort when using contact lenses, or after refractive surgery, than when using eyeglasses. Individuals with hyperopia must exert more accommodative effort when using eyeglasses than contact lenses.
Bifocals come as flat-top, round-top, and executive styles. Flat top is the most popular but can induce a base-up prism effect while round top can create a base-down prism effect. The height of the segment is more critical than its width. The top of the segment is generally set about 3 to 5 mm below the optical center of the distance lens and is usually positioned to align with the level of the lower limbus, but it may need to be higher or lower for certain occupations or depending on individual preference. Individuals who use computers may find a modified bifocal helpful; the upper segment is selected for the computer monitor distance and the lower segment is selected for reading.
Trifocals should be considered for patients with specific intermediate-vision needs, and they may also be very helpful for individuals who use computers. Identifying the specific working distances allows the trifocal powers to be prescribed most accurately.
Progressive Addition Lenses
Progressive addition lenses can be useful to increase the range of vision, and they are cosmetically well accepted. A good candidate for this type of lens is an individual with early presbyopia who has not worn bifocals before and who does not require an especially wide field of vision at near. The disadvantages of progressive lenses are peripheral distortion inherent in the lens design, the smaller size of the reading zone compared with bifocals, higher cost, and the difficulty in properly fitting the lenses. The positioning of the optical centers and progressive add corridors are critical if the visual advantages of these lenses are to be appreciated. Problems with reading zone size and peripheral distortion increase with stronger addition lenses.
The majority of adults can tolerate up to 3.00 D of difference in eyeglass refractive correction between the two eyes. Occasionally, individuals may tolerate more than 3.00 D of difference. Reduction of symptomatic aniseikonia may be accomplished either by undercorrecting at the expense of acuity or modifying the lens base curve or lens thickness to alter relative image size.590
Vertical prism-induced diplopia can be a problem in presbyopic patients who wear bifocals. Small amounts of induced prism can be corrected by either slabbing-off or slabbing-on the bifocal segment.590 Dissimilar segment types can also be used. A separate pair of reading eyeglasses, although less convenient, will avoid the problem of vertical anisophoria.
DIFFICULTIES AND COMPLICATIONS OF EYEGLASS WEAR
A variety of factors related to lenses and frames may cause difficulties in wearing eyeglasses. These include:
- Incorrect prescription
- Base curve and location of the cylinder on the front or back surface
- Bifocal power and segment position (height and size)
- Anisometropia (if large)
- Prisms or prism effects
- Pantoscopic tilt
- Centration of lenses with respect to the pupil
- Vertex distance
- Size of frame and fit
- Contact sensitivity to frame material
- Change in lens material
In addition, the lenses in the eyeglasses can cause spherical and chromatic aberrations as well as lens distortions, including magnification (hyperopic lenses) and minification (myopic lenses).
APPENDIX 6. CONTACT LENSES
CONTACT LENS FITTING
Careful attention should be directed towards optimizing contact lens fit, including size, centration, and movement in order to minimize contact lens interference with normal ocular function.
Keratometry or corneal topography is usually performed to assist in the fitting process. The refractive error can also be compared with keratometry or corneal topography readings to assess the relative contributions of the cornea and the natural lens to astigmatism and to help determine what type of contact lens will provide the best vision and fit. These readings also provide baseline information for future comparison.
Once a contact lens that provides good vision has been selected, the contact lens should be evaluated to ensure good movement on the eye.
CONTACT LENS SELECTION
The type of contact lens selected (soft hydrogel, rigid gas-permeable, silicone hydrogel, or hybrid) and the method of wear (daily or overnight) depend on the needs of an informed patient. Additionally, contact lenses can be replaced at various intervals ranging from daily disposable soft lenses to replacing certain rigid gas-permeable lenses every 1 to 2 years.
Type of Contact Lens
Spherical refractive errors can be corrected with soft hydrogel, rigid gas-permeable, or silicone hydrogel contact lenses.591 Low to moderate astigmatism can be corrected with soft toric contact lenses or with rigid gas-permeable contact lenses. Rigid gas-permeable, soft hydrogel, and silicone hydrogel contact lenses with varying abilities to transmit oxygen are available for patients with different corneal metabolic demands, and some are approved for extended wear.
High astigmatic errors can be corrected effectively with rigid gas-permeable and hybrid contact lenses. In cases of greater amounts of corneal astigmatism, it may be preferable to use a bitoric or back-surface toric contact lens design in order to minimize corneal bearing and improve centration. Custom-designed soft toric contact lenses provide another means to correct high astigmatic refractive errors. These contact lenses offer good centration when properly fitted, a flexible wear schedule, and improved comfort in some patients. The piggyback modality, in which a rigid gas-permeable lens is worn on top of a soft lens, may have utility in some of these circumstances. Aspheric and reverse geometry designs may also be useful for high astigmatism or postoperative refractive error. Regardless of the design chosen, adequate contact lens movement is essential for comfortable wear and maintenance of corneal integrity.
Rigid gas-permeable scleral lenses (diameter >17 mm) are an option for the correction of high and/or irregular astigmatism particularly if combined with anisometropia. These lenses do not contact the cornea and are not designed to rely on movement for physiologic tolerance.
Contact lenses used to correct high refractive errors place increased physiologic demands on the cornea and anterior segment. The thickness and weight of some of these contact lenses may adversely affect delivery of oxygen to the cornea, leading to hypoxia, pannus, neovascularization, and opacification.
Soft hydrogel and rigid gas-permeable bifocal or multifocal contact lenses can be used to address presbyopia. Another option for the management of presbyopia with contact lenses is monovision. Generally, the dominant eye is corrected for distance and the nondominant eye for near. Patients wearing monofocal contact lenses may benefit from eyeglasses worn over the contact lenses while driving, especially at night, or for critical visual needs to correct the near eye for distance and thereby improve depth perception. Modified monovision is the use of a bifocal or multifocal contact lens in one eye and a distance contact lens in the fellow eye.
Polymethylmethacrylate hard contact lenses are now rarely fitted to correct refractive errors because they have a very limited ability to transmit oxygen to the corneal surface.
Method of Wear
Disposable soft contact lenses, rigid gas-permeable contact lenses, and silicone hydrogel contact lenses are available for either daily or overnight wear.
Several FDA-mandated clinical studies carried out into the late 1990s have confirmed that overnight wear of contact lenses is the most important risk factor for microbial keratitis. Fifty to seventy-five percent of the risk of microbial keratitis can be attributed to overnight wear. Generally speaking, the longer the duration of continuous wear, the greater chance of developing an infiltrate. The risk for those who used daily-wear contact lenses and sometimes wore them overnight was estimated to be approximately 12 times the risk for those who used daily-wear lenses and did not wear them overnight. Extended-wear users who wear their contact lens overnight have a 10- to 15-fold risk over conventional daily-wear lens users who do not sleep in their contact lens.5Reports from the United Kingdom8 and Australia9 in 2008 confirmed substantial increased risk of microbial keratitis, with overnight wear, regardless of lens type.
The increased risk of corneal infections with overnight contact lens wear should be discussed with patients who are considering this modality of vision correction. If patients choose overnight wear, they should be instructed to use only lenses specifically approved for extended wear.
CONTACT LENS CARE
Proper contact lens care involves a combination of cleaning, disinfecting, rinsing, and wetting solutions.201 Surfactant cleaning solutions act like detergents to solubilize debris that is not chemically bonded to the contact lens. Rubbing the contact lens enhances the cleaning performance of the solution, likely by removing loosely bound deposits.12-14 Enzymatic cleaners remove deposits that are chemically bonded to the surface. Disinfecting solutions reduce the number of microorganisms carried on the contact lens. Wetting solutions make a water-repellant lens surface hydrophilic. Many manufacturers combine these agents into multipurpose solutions.
Patients should also be instructed to clean and replace contact lens cases frequently, because they can be a source of lens contamination,31,198,200 and damaged or cracked cases should be discarded.
The American Academy of Ophthalmology (www.aao.org/store) and the Contact Lens Association of Ophthalmologists (www.clao.org/Publications/Products/tabid/87/Default.aspx) have patient information brochures for contact lens care.
Daily-Wear Soft Contact Lenses
Daily disposable soft contact lenses should not be worn longer than manufacturers' recommendations, nor should they be reused. At the time of removal of all other daily-wear soft contact lenses, a contact lens cleaner or multipurpose solution should be used daily to remove biofilm and deposits from the lens surface. Rubbing the contact lenses during cleaning and rinsing with contact lens solution is necessary for removal of deposits.13-15 Contact lenses should be disinfected using either a chemical or peroxide system. The frequency of adverse events varies with silicone hydrogel contact lens and lens-solution combinations, with nonpreserved (hydrogen peroxide) systems having the lowest incidence of corneal infiltrates.592 Hydrogen peroxide systems may be superior to preserved disinfecting solutions in reducing pathogen binding and cysticidal disinfection, but they require more complex care regimens.16
Periodic enzymatic cleaning may be useful for some patients. Manufacturers' recommendations for contact lens care and replacement should be followed.
Extended-Wear Soft Hydrogel Contact Lenses and Silicone Hydrogel Contact Lenses
The FDA recommends that overnight-wear soft hydrogel contact lenses be removed at least once a week for overnight cleaning and disinfection.591 Disposable contact lenses for extended wear should also be discarded on a regular basis consistent with manufacturers' recommendations or the specific instructions of their Eye Care Professional. Silicone hydrogel contact lenses are now FDA-approved for up to 30 days of continuous wear. Extended-wear soft hydrogel and silicone hydrogel contact lenses worn on a daily basis are cared for in the same way as daily-wear soft lenses.
Rigid Gas-Permeable Contact Lenses
After rigid gas-permeable contact lenses are removed, they should be surface cleaned and rinsed; nonsterile water such as tap or bottled water should not be used. The lenses should be stored overnight in a disinfecting solution. Tap water should be eliminated from the care regimen, as its use is thought to be associated with the prevalence of Acanthamoeba keratitis, particularly in cases associated with overnight orthokeratology.219 Rigid gas-permeable contact lenses may also require periodic enzymatic cleaning. Rigid gas-permeable contact lenses that are approved for overnight wear should be cared for according to the above guidelines for daily-wear rigid gas-permeable contact lenses.
APPENDIX 7. THE K CARD
A fillable PDF form for downloading is available at www.aao.org/ppp. Click on K Card in the Academy Resources box.
APPENDIX 8. CATARACT IN THE ADULT EYE PPP EXCERPT
BIOMETRY AND INTRAOCULAR LENS POWER CALCULATION
The accurate measurement of axial length and central corneal power, combined with an appropriate intraocular lens (IOL) selection based on a power calculation formula, is the minimal requirement to achieve the targeted postoperative refraction. A-scan ultrasonography or optical biometry is used to measure axial length. A-scan ultrasonography is performed using either an applanation or immersion technique. In A-scan ultrasonography by applanation, the ultrasound probe compresses the cornea by variable amounts and there is both a variable and artificial shortening of axial length; the accuracy and overall consistency of this method are highly dependent on the skill and experience of the operator.593-595 When the immersion technique is used, the ultrasound probe does not come in direct contact with the cornea, making the measurements more consistent.
Optical biometry is a high-resolution noncontact method for measuring axial length that uses a specialized light source rather than ultrasound. It is significantly more accurate and consistent than contact (applanation) A-scan biometry.593,596,597 Optical biometry was initially considered to be comparable to immersion A-scan biometry, but it has since been shown to produce improved refractive outcomes; the patient's spherical equivalent is more likely to be closer to the target refraction.598-600 Optical biometry has also been shown to give user-independent results.601 Other advantages over A-scan ultrasonography include ease and speed of automated operation and the ability to measure to the center of the macula when proper fixation is achieved. Because optical biometry measures the refractive axial length rather than the anatomic axial length, this method is more accurate than standard forms of ultrasound A-scan biometry when the fovea is located on the sloping wall of a posterior staphyloma.602 Additionally, it is easier to use optical biometry than ultrasound when the patient has silicone oil in the posterior segment.603,604 Despite recent advances in optical biometry that now allow the measurement of axial length through increasingly dense cataracts,605 A-scan biometry may be necessary to measure the axial length in certain cataracts or when patients are unable to fixate properly.606,607 The measurement and comparison of axial length for both eyes is advisable, even if surgery is not planned for the other eye.
Formulas for calculating IOL power rely on keratometry to determine the net refractive contribution of the cornea. These measurements can be obtained by either manual or automated keratometry, or through corneal topography. Following keratorefractive surgery, the determination of central corneal power is particularly difficult. All devices that measure corneal power by standard methods are unable to accurately determine the central corneal power following keratorefractive surgery. The use of standard keratometry in this setting without a compensatory adjustment will typically result in an unanticipated refractive outcome.
Recent-generation theoretical IOL power calculation formulas such as Hoffer Q, Holladay, and SRK/T should be used in the IOL selection process.608-613 Some newer-generation formulas, such as Haigis, Holladay 2, and Olsen, incorporate additional measurements such as anterior chamber depth, lens thickness, and horizontal corneal diameter in an attempt to predict more accurately the effective lens position of the IOL to be implanted. Theoretical formulas rely on numerical constants that allow the formula to predict the effective lens position within the eye. The Haigis formula uses three separate constants that are highly specific to the individual characteristics of a specific IOL model across its power range. Although the IOL manufacturer supplies lens constants to be used with calculation formulae, these numbers are generally considered to be only a recommendation and may not correspond to the biometry method being used. The eventual optimization of lens constants for a specific IOL based on an individual surgeon's actual refractive outcome is recommended.
The surgeon should consider the patient's individual desires and needs in selecting an appropriate postoperative refractive target. Depending on the manufacturer, a limited number of extended-range high plus and high minus IOL powers is available. For the patient with extreme myopia, very low-power IOLs that straddle both sides of plano may require unique lens constants for plus (+) and minus (-) powers that are quite different than those recommended by the manufacturer.614 For a patient with extreme hyperopia requiring an IOL power in excess of the available range, piggybacking two posterior chamber IOLs has been used.615 When this is required, it is preferable to use lens optics of different materials in different locations rather than inserting both IOLs within the capsular bag. This will reduce the risk of interlenticular (between the IOLs) membrane formation.616,617 Intraocular lens power calculations for piggybacked IOLs as a primary procedure may be less accurate than for a single IOL, because it is difficult to predict the combined effective IOL position.618 Refractive results with piggybacking IOLs have been favorable in two small case series.619,620
The ophthalmologist who performs the cataract surgery has a unique perspective and thorough understanding of the patient's intraoperative course, postoperative condition, and response to surgery. The operating ophthalmologist is responsible for the care of the patient during the postoperative interval, the time in which most complications occur and within which stable visual function is achieved, as well as an ethical obligation to the patient that continues until postoperative rehabilitation is complete.
The operating ophthalmologist should also provide those aspects of postoperative eye care that are within the unique competence of the ophthalmologist. These do not necessarily include those aspects of postoperative care permitted by law to be performed by auxiliaries. If such follow-up care is not possible, the operating ophthalmologist must make arrangements before surgery to refer the patient to another ophthalmologist for postoperative care with the prior approval of the patient and the ophthalmologist.224,309,621 In rare special circumstances, such as emergencies or if no ophthalmologist is available, the operating ophthalmologist may make different arrangements for the provision of those aspects of postoperative eye care within the unique competence of the ophthalmologist, as long as the patient's rights and welfare are the primary considerations.
The ophthalmologist who performs surgery has an obligation to inform patients about appropriate signs and symptoms of possible complications, eye protection, activities, medications, required visits, and details for access to emergency care. The ophthalmologist should also inform patients of their responsibility to follow advice and instructions provided during the postoperative phase and to notify the ophthalmologist promptly if problems occur. Patients should always have access to an ophthalmologist for appropriate care if serious problems arise.
Most ophthalmologists provide all postoperative care in their offices. Other members of a team of eye care professionals may also participate in the comanagement of postoperative care. The operating ophthalmologist is responsible to the patient for those aspects of postoperative care delegated to other eye care professionals.225
Postoperative regimens of topically applied antibiotics, corticosteroids, and nonsteroidal anti-inflammatory drugs (NSAIDs) vary among practitioners. There are no controlled investigations that establish optimal regimens for the use of topical agents; therefore, it is the decision of the operating surgeon to use any or all of these products singly or in combination. Complications of postoperative medications include elevated intraocular pressure (IOP) with corticosteroids and allergic reactions to antibiotics. Significant corneal reactions, including epithelial defects and stromal ulceration and melting, have rarely been reported with topical ocular NSAIDs.622-624
The frequency of postoperative examinations is based on the goal of optimizing the outcome of surgery and swiftly recognizing and managing complications. This requires prompt and accurate diagnosis and treatment of complications of surgery, providing satisfactory optical correction, educating and supporting the patient, and reviewing postoperative instructions. Table A8-1 provides guidelines for follow-up based on consensus in the absence of evidence for optimal follow-up schedules. Prospective studies from the United Kingdom have reported that omitting an examination on the day after uncomplicated cataract surgery for the routine patient was associated with a low frequency of serious ocular complications.625-628
TABLE A8-1. Postoperative Follow-up Schedule
Patients should be instructed to contact the ophthalmologist promptly if they experience symptoms such as a significant reduction in vision, increasing pain, progressive redness, or periocular swelling, because these symptoms may indicate the onset of endophthalmitis.
In the absence of complications, the frequency and timing of subsequent postoperative visits depend largely on the size or configuration of the incision; the need to cut or remove sutures; and when refraction, visual function, and the medical condition of the eye are stabilized. More frequent postoperative visits are generally indicated if unusual findings, symptoms, or complications occur, and the patient should have ready access to the ophthalmologist's office to ask questions or seek care.
Components of each postoperative examination should include the following:
Interval history, including use of postoperative medications, new symptoms, and self-assessment of vision
Measurement of visual function (e.g., visual acuity, including pinhole testing or refraction when appropriate)
Measurement of IOP
Counseling/education for the patient or patient's caretaker
A dilated fundus examination is indicated if there is a reasonable suspicion or higher risk of posterior segment problems. In the absence of symptoms or surgical complications, no study has demonstrated that a dilated fundus examination results in earlier detection of retinal detachment.
When postoperative visual improvement is less than anticipated, the ophthalmologist may perform additional diagnostic testing to evaluate the cause. For example, if maculopathy is suspected, optical coherence tomography (OCT) or fluorescein angiography would be appropriate to diagnose cystoid or diffuse macular edema, epiretinal membranes, or age-related macular degeneration (AMD). Likewise, corneal topography could diagnose irregular corneal astigmatism. Automated visual fields may diagnose a neuro-ophthalmic abnormality. Other testing may be conducted if appropriate.
A final refractive visit should be made to provide an accurate prescription for eyeglasses to allow for the patient's optimal visual function. The timing and frequency of refraction will depend on patient needs and the stability of the measurement. Sutures, if used, may be cut or removed by the ophthalmologist to reduce astigmatism. Optical correction can usually be prescribed between 1 and 4 weeks after small-incision surgery629 and between 6 and 12 weeks after sutured large-incision cataract extraction surgery.
RELATED ACADEMY MATERIALS
Basic and Clinical Science Course
- Clinical Optics (Section 3, 2012-2013)
- Refractive Surgery (Section 13, 2012-2013)
Clinical Statement -
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- Appropriate Management of the Refractive Surgery Patient (2012)
- Extended Wear of Contact Lenses (2008)
- Laser Surgery (2011)
- Use of Unapproved Lasers and Software for Refractive Surgery (2009)
- Summary Recommendations for Photorefractive Keratectomy (PRK) Surgery (2012)
- Summary Recommendations for LASIK (2012)
Available at http://one.aao.org/femtocenter; scroll down to Journals & News; enter required login.
- AAO Guidance on Femtosecond Laser Billing for Medicare (January 31, 2012)
- Innovations in Advanced Surface Laser Refractive Surgery (2010)
- Surgical Treatment of Presbyopia (2009)
- Wavefront-Guided LASIK (2008)
Ophthalmic Technology Assessment -
Published in Ophthalmology, which is distributed free to Academy members; links to abstracts and full text available at www.aao.org/ota.
- Intrastromal Corneal Ring Segments for Low Myopia (2001; reviewed for currency 2009)
- LASIK for Hyperopia, Hyperopic Astigmatism, and Mixed Astigmatism (2004; reviewed for currency 2009)
- Laser In-Situ Keratomileusis (LASIK) for Myopia and Astigmatism: Safety and Efficacy (2002; reviewed for currency 2009)
- Wavefront-Guided LASIK for the Correction of Primary Myopia and Astigmatism (2008)
Patient Education Brochure
- Contact Lenses (2011)
- Laser Surgery of the Eye (2011)
- LASIK (2012)
- Photorefractive Keratectomy (PRK) (2012)
- Refractive Errors (2011)
- Refractive Surgery (2012)
Patient Education Downloadable Handout
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- Refractive Procedures: Digital-Eyes Ophthalmic Animations for Patients (subscription) (also available in Spanish) (2009)
- What is Presbyopia?: Ophthalmic Animations for Patients (subscription) (also available in Spanish) (2009)
Preferred Practice Pattern® Guidelines - Free download available at www.aao.org/ppp.
- Cataract in the Adult Eye (2011)
- Comprehensive Adult Medical Eye Evaluation (2010)
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