The quality of a patient’s tear film has a significant impact on both the subjective and objective experience of refractive surgery. Postoperative dry eye symptoms have made the experience of refractive surgery an unpleasant memory for too many patients, and we realize now that the quality of the tear film also affects visual outcomes.
The tear film is the eye’s first refracting surface. If a refractive surgery patient’s tear film is compromised—if there is insufficient tear volume or the tear film breakup time is shorter than the interval between blinks—the patient’s quality of vision will suffer, particularly in the first 6 months following surgery.
In addition, the tear film is an important element of the eye’s antimicrobial defenses. A compromised tear film is a less effective antimicrobial barrier.
A Compromised Tear Film Compromises Results
Patients with preexisting tear film conditions (eg, dry eye, meibomitis, severe blepharitis) risk suboptimal visual outcomes if the underlying problems are not treated prior to surgery. Patients who experience postoperative tear film problems typically complain of visual fluctuations, and their subjective reports are confirmed by wavefront and topographic analyses. In such patients, wavefront examination reveals acuity that fluctuates from moment to moment, increased aberration, and intermittent periods when the patient must exert greater effort to achieve focus.
The preoperative status of the ocular surface also influences the quality of the topography and wavefront data collected. It is ironic and frustrating that the exquisitely accurate wavefront measuring device can be thrown off by a poor quality tear film. Distorted wavefront data can affect visual outcomes in custom surgery.
Patient Selection is Key
Screening for ocular surface disease prior to refractive surgery is almost as important as identifying topographic abnormalities. The ocular surface screening classifies patients as either ready for surgery or in need of treatment before surgery can be considered.
In a subset of patients, even 6 months of treatment with cyclosporine (Restasis®; Allergan), artificial tears, and/or other measures will not significantly ameliorate the underlying condition.
Ocular Surface Evaluation Protocol
Unless the patient begins by describing symptoms indicative of an ocular surface condition, my refractive surgery evaluation commences with a slit lamp examination. The experienced surgeon can detect corneal punctate epithelial erosions at the slit lamp even without staining. Rose bengal or lissamine green will, of course, enhance visibility of these and reveal other signs of conjunctival distress that, in the absence of staining, might escape detection.
Next, I will assess the tear film break up time. Schirmer testing is not part of my routine evaluation because the results are notoriously imprecise. (Schirmer testing is most useful in patients with consistently low scores; and once dry eye is identified, the Schirmer test provides a useful benchmark to measure the success of treatment. I find Schirmer testing far more useful for followup than screening.)
In recent months we have taken to using the Ocular Surface disease Index (OSDI) questionnaire for screening. The standardized 12-question instrument asks whether the patient has experienced dry eye symptoms during the prior week. I find it useful to review the OSDI results prior to commencing the exam.
If signs or symptoms of dry eye are present during the initial screening, I start treatment rather than conduct the full preoperative evaluation. Pretreatment typically consists of nonpreserved artificial tears and topical cyclosporine twice a day for 1 month. Meibomitis or blepharitis, if present, are also treated.
If, at 1 month, the signs and symptoms are completely resolved and the Schirmer score is greater than 5 mm, the preoperative evaluation for LASIK will commence. I default to PRK if, despite the absence of other signs and symptoms, the Schirmer score is less than 5 mm or the patient shows some conjunctival staining with lissamine green or rose bengal.
If signs or symptoms are still present at the 1-month reevaluation, therapy continues with further reevaluations at 2-month intervals. This patience is warranted because, the response to cyclosporine can take place slowly over time.
At 6 months, if dry eye signs persist (with or without symptoms), the patient will not be considered a candidate for excimer laser refractive surgery. While it can be difficult to break this news to an individual who has undergone months of pretreatment in order to be operated, the practitioner who isn’t turning away some patients due to irresolvable ocular surface problems may not be exercising sufficient vigilance.
Other Treatment Options
Since the advent of topical cyclosporine, my use of punctal plugs has declined dramatically. I do not use plugs as a first-line of treatment because, as Pflugfelder has demonstrated, the dry eye patient’s tear film contains high levels of proinflammatory cytokines, and punctal occlusion simply increases ocular exposure to these mediators. I limit punctal plug use to the period after the patient’s ocular surface has been stabilized and the quality of the patient’s tears has improved. Thus, if a patient continues to exhibit signs or symptoms after cyclosporine treatment, I will occlude the puntca. However, this is rarely necessary.
During the Procedure
To protect the ocular surface during surgery, it is important to keep the eye moist and to limit unnecessary exposure by ensuring the surgery proceeds expeditiously. Once the lid speculum is in place, the cornea dehydrates rapidly. This not only affects the ocular surface but can compromise the correction as well. It is essential, therefore, to avoid activities (eg, calibrating the laser) that increase the time the speculum is in place. At the end of the procedure, we typically administer balanced salt solution along with the dose of topical antibiotic and corticosteroid.
Ocular Surface Health after Surgery
Patients who require preoperative optimization of the ocular surface are instructed to take their cyclosporine the morning of surgery but to then discontinue its use for 2 days, before resuming twice-a-day dosing on postop day 3. Our concern is that oils present in the drug’s vehicle may get underneath the flap. There have been no reports of issues with this, so our approach is a conservative one. Cyclosporine treatment, along with non-preserved artificial tears, is typically continued for at least 6 months.
It is important to impress upon patients that only preservative-free tears should be used. This point needs to be made emphatically—and repeated. Patients who ignore doctor’s orders and purchase the cheapest available tears may find their dry eye exacerbated by the very drop they take to reduce symptoms! In fact, if a postop patient presents with an ocular surface problems, the first question I ask is: “Are you using nonpreserved artificial tears?” If the patient has not brought the product to the examination for me to inspect it, I will ask him to describe it and, if necessary, bring it to the next appointment.
Patients who had no dry eye signs or symptoms prior to surgery typically have an event-free postoperative course. Occasionally, however, an individual without preoperative symptoms or signs will present a week after surgery with corneal punctate epitheliopathy and fluctuating vision. Symptoms such as ocular dryness, stinging, burning, etc, may also be present. Such patients have LASIK-induced neurotrophic epitheliopathy (LINE).
Fortunately, cyclosporine treatment in conjunction with an ocular steroid, such as prednisolone acetate, has proven highly effective for LINE. I was initially surprised to find this was the case. If the etiology is neurotrophic, resulting from the severing of corneal nerves during the resection, why does an immunomodulating drug help?
However, as first shown by Marguerite McDonald, LINE patients do indeed respond to cyclosporine therapy. It is my hypothesis that these individuals were borderline dry eye patients whose symptoms and signs were subclinical prior to surgery. The added stress of denervation pushed them over the edge into signs and symptoms.
I do not see the possibility that a few borderline dry eye patients will slip through prescreening as an argument for pre-treating all refractive surgery patients. The percentage of patients who develop LINE without preoperative symptoms or signs is small and, with treatment, these patients do extremely well. For me, the risks, such as they are, simply do not justify the additional expense to patients whose ocular status is to all appearances normal.
That said, I am closely watching ongoing research into the possible relationship between preoperative cyclosporine treatment and refractive outcome. Some preliminary studies suggest patients pretreated with topical cyclosporine achieve better overall vision in the early postoperative period. If further study bears this out, I am willing to reconsider my position but, at present, we pre-treat only those patients who exhibit signs and/or symptoms of ocular surface distress.
Dr. Wilson is a consultant and speaker for Allergan, Irvine, CA. Steven E. Wilson, MD, is professor of ophthalmology and director of corneal research at the Cole Eye Institute, Cleveland, OH.
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