- Key to effective presbyopia treatment lies in understanding how the natural lens functions
- Autologous serum eye drops may be effective in treating post-LASIK dry eye
- New index for calculating IOL power after LASIK appears effective
- Limbal relaxing incisions appear more effective in reducing corneal astigmatism during cataract surgery
- Long-term study shows photorefractive keratectomy is effective in treating severe anisometropic amblyopia in children
- Wavefront-guided LASIK appears better than standard LASIK for re-treatments
- VisThesia use during phacoemulsification surgery doesn’t appear toxic to the cornea
- Preservative-free eye drops in multiple application containers are at risk for microbial contamination
- Early registration for the 2006 ISRS/AAO meeting in Istanbul ends March 1
- Housing and tour information for the 2006 ISRS/AAO meeting now live
- ISRS/AAO now accepting applications to join in 2006
- Review the latest news on the business side of refractive surgery
- Indian company wins FDA approval to produce ophthalmic drugs for US market
- Femtosecond laser used successfully in all-laser corneal transplant surgery
Key to effective presbyopia treatment lies in understanding how the natural lens functions
In this month’s feature Deepak K. Chitkara, FRCOphth, argues that a greater understanding of the mechanism of accommodation, particularly lenticular sclerosis, holds the greatest possibility for true reversal of presbyopia, provided we can replace the crystalline lens with a lens that responds to ciliary body contraction. Despite the promise surrounding multifocal IOLs, they will always remain a compromise. A truly accommodating IOL will be universal in its application, without compromising quality of vision. Chitkara describes his experience with the Tetraflex lens, a hydrophilic acrylic intraocular lens developed by Robert Kellan, MD. It is designed to maximize the effects of the ciliary muscle forces. Chitkara says it is now his lens of choice for all cataract and refractive lens exchange procedures.
Autologous serum eye drops may be effective in treating post-LASIK dry eye
This prospective study randomized 27 male patients (54 eyes) to receive either autologous serum eye drops or artificial tears after LASIK surgery. Using the Schirmer test with anesthesia, tear break-up time and rose bengal and fluorescein, the ocular surface was evaluated before surgery and at one, three and six months postop. Tear break-up time and vital staining improved significantly in autologous serum eye drops group. No difference was observed before and after LASIK in the artificial tears group. The authors conclude that autologous serum eye drops are also effective patients with pre-existing dry eye undergoing LASIK. The authors theorize that the drops may help regenerate nerve fibers and accelerate normalization of the epithelium, resulting in an improvement of dry eye after LASIK. The authors call for more study, particularly prospective, randomized trials of right and left eyes treated with autologous serum eye drops or artificial tears in the same patient, or prospective autologous serum eye drop trials for patients with pre-existing dry eye. Journal of Refractive Surgery, January/February 2006
New index for calculating IOL power after LASIK appears effective
This new formula calculates the K-reading after LASIK by subtracting the relative change of anterior radius of curvature induced by LASIK from the preoperative K-reading and does not account for the assumed index of refraction, which might vary between devices. The authors say this formula has proven to be simple, objective, non refraction-dependent and as accurate as the clinical history method formula. Journal of Refractive Surgery, January/February 2006
Limbal relaxing incisions appear more effective in reducing corneal astigmatism during cataract surgery
In this prospective study, 71 patients with 1.5 D or more of keratometric astigmatism were randomly assigned to two surgical techniques: on-axis incisions, consisting of a single clear corneal cataract incision centered on the steepest corneal meridian (33 eyes), or limbal relaxing incisions, consisting of two arcuate incisions straddling the steepest corneal meridian and a temporal clear corneal incision (38 eyes). At six weeks postop, the flattening effect was 0.41 D (median and interquartile range 0.15 to 0.78 D) in the on-axis incision group and 1.21 D (range 0.43 to 2.25 D) in the limbal relaxing incision group (P = .002). This effect was consistent throughout the follow-up period. At six months postop, the flattening effect was 0.35 D (range 0.00 to 0.96 D) and 1.10 D (range 0.25 to 1.79 D), respectively (P = .004). Journal of Cataract & Refractive Surgery, December 2005
Long-term study shows photorefractive keratectomy is effective in treating severe anisometropic amblyopia in children
This prospective, interventional case-control study treated 11 children (aged 2 to 11) who were noncompliant with conventional therapy. The control groups, treated with traditional therapy, consisted of 13 compliant and 10 noncompliant children with refractive errors similar to those of the PRK group. At last follow-up (mean 31 months), the mean final refractive error for both myopic and hyperopic PRK groups was significantly better that that of the control groups (P = 0.007 and P<0.0001, respectively). The mean final visual acuity of the PRK group was significantly better than that of the noncompliant control group (P = 0.003). Subepithelial corneal haze remained negligible throughout follow-up. Ophthalmology, February 2006
Wavefront-guided LASIK appears better than standard LASIK for re-treatments
This study compared 20 eyes (20 consecutive patients with SE of -2.01±1.36 D) treated with wavefront-guided Zyoptix Ablation Refinement software (ZAR) LASIK for both initial surgery and re-treatment with 20 eyes (20 consecutive patients with SE of -1.81±1.21 D) treated with standard Planoscan LASIK, for both initial surgery and re-treatment. Efficacy indexes were 1.09 for ZAR patients and 0.95 for Planoscan patients. At six months postop, no eye lost more than one line of BCVA, but in the ZAR group, two eyes gained one line and six eyes gained two lines or more. In the Planoscan group, three eyes gained one line. Also, wavefront-guided LASIK did not increase higher-order aberrations and did not modify contrast sensitivity compared with preoperative values. Ophthalmology, February 2006
VisThesia use during phacoemulsification surgery doesn’t appear toxic to the cornea
One full ampoule of this ophthalmic viscosurgical device, which incorporates lidocaine to the sodium hyaluronate to make patients under topical anesthesia more comfortable, was applied over the corneal surface of 50 eyes (50 patients). A non-contact endothelium microscope was used to examine the endothelium of the central cornea before surgery and at three months postop. Based on results from published studies using similar viscosurgical devices, researchers observed no increased endothelial cell loss or additional toxicity to the cornea. Journal of Cataract & Refractive Surgery, November 2005
Preservative-free eye drops in multiple application containers are at risk for microbial contamination
Of the 95 eye drop bottles collected and tested (on day three for inpatients and day seven for outpatients) and colleagues tested, significant bacterial growth was observed in eight, for an overall incidence of 8.4 percent. Contamination did not occur in any of the 53 antibiotic eye drop bottles. For the 42 non-antibiotic bottles, the overall incidence of contamination was 19 percent. Seven different types of organisms were identified from the eye drop bottles, including Staphylococcus aureus, a type of bacteria that is increasingly becoming resistant to standard antibiotics. Some of the contaminated bottles grew more than one type of contaminant. Researchers suggest the design of multiple application containers is to blame, since the pipette attached to the cap of the bottle comes completely out of the container during administration, exposing the open contents of the bottle directly. They add that content spillage and poor technique may also increase the risk of contamination. The authors suggest caution when prescribing these drops to patients with compromised ocular surface defenses. British Journal of Ophthalmology, February, 2006
Back to Top
Early registration for the 2006 ISRS/AAO meeting in Istanbul ends March 1
Registering by March 1 allows you to take advantage of reduced registration fees for this year’s meeting, International Refractive Surgery: Art and Science (May 26 to 28). Among the highlights: a live feed of surgeries performed at two Turkish hospitals beamed to the convention center, allowing attendees to ask questions of physicians in the surgery suites.
Housing and tour information for the 2006 ISRS/AAO meeting now live
To reserve your hotel room, complete the online housing form and return it to United Expo at +90-232-4650086. United Expo is also organizing half day, full day and pre/post meeting tours. To reserve your spot on a tour, complete the online order form and it fax to United Expo at +90 232 465 00 86. Find all the latest information on this year’s meeting in Istanbul, including recent updates to the program and faculty listing, from our Web site.
ISRS/AAO now accepting applications to join in 2006
Membership in ISRS/AAO provides many opportunities to keep up with the latest in clinical and research developments in refractive surgery, as well as access to the world’s leading refractive surgeons for specific clinical case questions and issues. You can either apply online or download and application and send it in.
Review the latest news on the business side of refractive surgery
Read the December issue of Irving Aron’s Refractive Highlights, now live on the ISRS/AAO Web site.
Back to Top
|Upcoming Meetings || || |
| || || |
|March 9-11, 2006 |
VIII Alicante Refractive International 2006
| ||May 25-28, 2006|
19th Congress of German Ophthalmic Surgeons (DOC)
| || || |
May 26- 28, 2006
2006 ISRS/AAO Meeting: International Refractive Surgery: Art and Science
| ||July 8-9, 2006|
Indian Intraocular Implant and Refractive Society Convention
| || || |
|Nov. 10-11, 2006 |
ISRS/AAO Subspecialty Day Meeting
Sands Expo at the Venetian Hotel
Las Vegas, Nevada, USA
| || |
Indian company wins FDA approval to produce ophthalmic drugs for US market
Indoco has signed an agreement with two US generic companies to supply them with sterile ophthalmic preparations from its facility in Goa. ''For the US market, we have adopted a partnering model with local companies,” said Suresh Kare, Indoco’s chairman and managing director. “In the coming months, we will file more ANDAs (abbreviated new drug applications) and increase our business from this important pharma market. The U.S. FDA approval is a step in our quest to be global players.”
Femtosecond laser used successfully in all-laser corneal transplant surgery
IntraLase Corp. announced the first corneal transplant cases using its IntraLase FS laser, which it says marks the first major technology advancement in corneal transplant surgery in more than five years. The high-speed laser is used to create a contoured, full-thickness corneal resection in preparation for corneal transplant. Physicians involved in these early surgeries say the FS laser is programmed to create a stepped-edged incision that may enhance the sealing and stability of the transplanted tissue and allow for faster healing. Full global launch of this new therapeutic application is expected in Fall 2006.
Back to Top
Accommodating IOLs – Beginning of the End for Presbyopia?
Deepak K. Chitkara, FRCOphth
Presbyopia ultimately affects 100 percent of the population during the normal human life span and yet no universally accepted treatment is available. It is no wonder that presbyopia and its correction are regarded as the Holy Grail of ophthalmology and more recently of refractive surgery. The loss of accommodative amplitude that characterizes presbyopia is still not completely understood. Current evidence points to lenticular sclerosis together with changes in geometry of zonular attachments or loss of ciliary muscle excursion as the main contributory factors in presbyopia. Despite some loss of ciliary muscle efficacy, significant ciliary body function persists in the very elderly.
Compensatory options to alleviate presbyopia include bifocal reading glasses and/or contact lenses, monovision correction either with contact lenses or surgical procedures such as LASIK, CK and intraocular lenses. There is much hype recently with the arrival and approval of two new multifocal IOL designs. No doubt this has given surgeons a vastly expanded option menu to offer their cataract and refractive surgery patients. However, by design, all multifocals sacrifice quality of vision at some distance by losing or splitting light and are more prone to glare and haloes.
A greater understanding of the mechanism of accommodation, particularly lenticular sclerosis, affords possibilities for true reversal of presbyopia, provided we can replace the crystalline lens with a lens that responds to ciliary body contraction. Such a lens would preserve quality of vision at all distances, ranging from near, far and all points in between. Before we discuss the accommodating lenses, it is pertinent to remember that any lens that attempts to restore accommodation need only achieve 3 D of accommodation to give adequate patient satisfaction.
Currently, only the Crystalens (Eyeonics, Inc. Aliso Viejo, Calif.) is approved by the FDA as an accommodating lens. It is a monofocal lens made of silicon. The hinged haptic is vaulted backwards within the capsule against the vitreous face. On contraction of the ciliary muscle, its volume increases and the resulting rise in vitreous pressure pushes the IOL and the hinge allows the optic to vault forward. It is claimed that this action can generate up to 1 D to 2 D of accommodation. This theory of function however has generated a great deal of skepticism because basic geometric optics and observed IOL movements suggest that it is impossible for the lens to move forward sufficiently to explain the quality of reading vision patients experience.
The Crystalens displays other characteristics that are inconsistent with a theory based purely on a rise in vitreous pressure. It is well documented that the lens sometimes shows no movement, can even move backwards and sometimes even tilt (the so called Z phenomenon). To understand these effects, it is important to understand natural accommodation.
In normal accommodation, contraction of the ciliary muscle makes the anterior capsule of the lens bow forward and the posterior capsule bow backward – in other words the lens gets fatter due to the compressive force acting at its equator. In fact there is very little forward movement of the natural lens. A lens that is vaulted backwards against the capsule may indeed move backwards during accommodation if this compressive force is greater than the force of vitreous pressing forward. Similarly, differential forces circumferentially around the equator may lead to the ‘Z’ phenomenon, where the balance between compressive force and vitreous pressure changes.
To make maximal use of these two forces acting on the lens substance during ciliary muscle contraction, an IOL must be vaulted forwards. This would make maximal use of the two forces generated during accommodative effort and eliminate the backward movement observed with the Crystalens.
The Tetraflex, a hydrophilic acrylic intraocular lens developed by Robert Kellan, MD, is one such lens. It is designed to maximize the effects of the ciliary muscle forces. It is vaulted 5 degree anteriorly. The haptics are tapered to allow the large 5.75mm optic to move with the ciliary muscle contraction. The forward vault eliminates any backward movement of the lens and the ‘Z’ phenomenon. The one-piece, square-edged lens can be injected through a 1.8mm incision and requires no atropinization.
I was the first surgeon worldwide to implant the Tetraflex lens, which received CE Marking in January 2003. To date, I have implanted well over 200 lenses. It is now my lens of choice for all cataract and refractive lens exchange procedures. An audit of my latest results show that approximately 80 percent of my patients show functional near vision of J5 or better with excellent distance vision. There is no loss of visual quality at any distance and 95 percent of patients achieve greater than 1.5 D of accommodative amplitude.
Wavefront analysis with Tracey system has demonstrated consistent objective assessment of accommodative amplitude. These results will be presented at the ASCRS meeting in March 2006 in San Francisco. The data also shows that during accommodation, there is a shift toward myopia in the refraction and an increase in the amplitude of refraction within the pupil area, thereby increasing the depth of field. In addition, there are changes in the curvature of the lens providing greater than 10 D of accommodation in some areas within the pupil. This raises questions about the accommodating mechanism itself and whether accommodating IOLs do indeed mimic natural phenomenon.
Many challenges must be addressed before accommodating lenses can provide truly consistent results. First and foremost, surgeons must understand that they have to adopt refractive surgery skills to obtain the best results. Meticulous biometry and a consistent surgical technique is essential in achieving postoperative emmetropia. If this fails, then access to an excimer laser is vital. It is also essential to understand that accommodation is a bilateral process and that the best results will always be achieved after bilateral implantation. Variations in the volume or diameter of the capsular bag, the ciliary muscle tone and the state of the vitreous are other factors that may affect the outcomes.
Tetraflex technology is owned by Advanced Ocular Systems Ltd. The lens is manufactured under license by Lenstec Inc. (St Pete’s, Fla.). It received CE Marking in Europe in 2003 and has since been available worldwide. To date, more than 3,500 lenses have been implanted worldwide. The U.S. FDA trials began in September 2005, with seven sites conducting the IDE study in the United States.
Other lens designers point to the limitations of a single-piece IOL in terms of movement within the capsular bag, and theorize that a dual-optic lens connected together would maximize the potential for movement. The Synchrony lens is the first dual-optic accommodating IOL to be inserted in human eyes. The two optics are linked by a spring system. The separation of the optics decreases significantly within the capsular bag due to its compressive tension. As the ciliary muscle contracts, the capsular tension is released and the optic separation increases. In theory, a high-powered anterior converging lens combined with a compensatory posterior diverging lens should produce a significantly greater change in object distance compared to a similar movement in a single-optic lens. Clinical trials using this lens are under way. Preliminary results are encouraging, showing accommodation up to 2.5 D. Much work remains to optimize the results, which will undoubtedly require modifications to the original design.
The ultimate IOL will mimic the natural lens in its ability to change shape during the accommodative process. If we do not yet fully understand how the natural lens functions, then how can we expect to mimic it? But we are making significant strides in understanding the changes that occur in the lens during accommodation. Ongoing studies with accommodating IOLs are highlighting the subtle changes within the lens geometry that contribute to accommodative process. On the whole, accommodating lenses show more promise and have many advantages over multifocal IOLs. A multifocal IOL will always remain a compromise and this will always affect the quality of vision. A truly accommodating IOL will be universal in its application without compromising quality of vision.
Deepak K. Chitkara, FRCOphth, is in private practice and is the director of Viewpoint Vision Services in Manchester, England. Phone: +44-161-848-0811, e-mail: Deepak@viewpointvision.com.
Back to Top