Refractive surgeon Stephen S. Lane, MD, has a vision for the future, and it includes much more than LASIK. “I think that, despite all of the hype surrounding LASIK, IOL implantation to correct refractive errors will increasingly become the technique of choice for many patients. This is a technology that will catch on. And while there are safety issues that need to be studied and overcome, it is only a matter of time until phakic IOLs emerge in the mainstream of refractive surgery,” he said.
“The intriguing aspect about phakic IOLs is that the surgery involves the ‘addition’ of a lens, whereas LASIK is a ‘subtraction’ procedure that involves removing tissue,” noted Dr. Lane, clinical professor of ophthalmology at the University of Minnesota and in private practice with Associated Eye Care in St. Paul. “Thus, phakic IOLs do not carry some of the inherent problems related to cornea surgery where you are changing the shape of the cornea. The subtraction of tissue can have a dramatic effect on quality-of-vision issues. These issues are all negated with phakic IOLs because, by adding a lens, the optical system remains intact.”
And with two different phakic IOL designs awaiting FDA approval and various safety issues being addressed, this is one of the hottest topics in refractive surgery today.Three Different Locations
Phakic IOLs can be placed in either the anterior or posterior chamber of the eye.Angle-supported anterior chamber phakic IOLs.
These have been in existence for a number of years and provide effective and stable refractive correction. Dr. Lane noted that U.S. clinical trials are slated to begin soon for Alcon’s angle-supported anterior chamber lens, which is made of a foldable hydrophobic acrylic material. The lens has been studied extensively in Europe, with early studies indicating good visual results for moderate to high myopia.
Two other types of phakic IOLs recently received FDA panel approval and now await final FDA approval:Artisan/Verisyse phakic IOL
(designed by Ophtec and distributed by AMO). The lens, which has been used in Europe for almost two decades, features an iris-fixation method that enables the lens to attach to the periphery of the iris in a way that does not inhibit the iris’ function. Once anchored, the lens vaults slightly forward, occupying the space between the iris and the corneal endothelium. This design thus provides for the free flow of aqueous from the posterior to the anterior chamber. Among the conditions recommended by the panel was an anterior chamber depth of more than 3.2 millimeters, as well as a postmarket study.Implantable Contact Lens (ICL)
(Staar Surgical). This phakic refractive lens is a posterior chamber implant that is situated behind the iris and in front of the natural crystalline lens. The FDA panel recommended the use of this lens in correcting myopia in the range of –3 D to –15 D and reducing myopia in the range of –15 D to –20 D. The conditions recommended by the panel primarily concerned postmarket surveillance of the patients currently enrolled in the study cohort, as well as labeling recommendations that will be further defined by the FDA.
According to Dr. Lane, “One key strength of phakic IOLs is that while the surgical implantation techniques differ from one lens design to another, in general, they are techniques that surgeons are familiar with because of their previous experience with cataracts. “Thus, it should not be a steep learning curve when surgeons begin to implant these lenses.”Safety ConcernsLess aberration.
In contrast to refractive surgery, phakic IOLs hold promise because they offer “good optics,” said Jack T. Holladay, MD, founder of the Holladay LASIK Institute in Houston and clinical professor of ophthalmology at Baylor College. “While we are moving in the right direction with wavefront technology, which induces less spherical aberration than most standard treatments, LASIK and PRK are still reducing the quality of the visual performance of the eye because the human eye is an off-axis system.”
However, several significant safety issues must be overcome before phakic IOLs enter the mainstream:Anterior chamber issues.
For instance, the placement of certain phakic IOLs in the anterior chamber has been associated with risks of pupil ovalization and endothelial cell loss. “In addition, this anterior chamber angle placement can be problematic for the trabecular meshwork in terms of reducing the trabecular outflow. Any time you put a lens against uveal tissue, you can run into problems,” Dr. Holladay said. Iris-fixation issues.
With the iris-fixated Artisan/Verisyse phakic IOL, chronic iritis and inflammation can be a problem, Dr. Holladay pointed out. In addition, earlier designs of iris-fixated IOLS were linked to cataract, glaucoma and endothelial cell loss. However, the manufacturers of the Artisan/Verisyse product have maintained that because of the unique design of this lens, the risk of both endothelial cell loss and cataract formation (which is associated with crystalline lens trauma) has been minimized.
There’s no question that safety concerns will drive the phakic IOL market, Dr. Lane said. “They will all work in terms of correcting vision, but the one that will eventually be successful is the one that proves the safest.”Best Candidates
Given the current state of technology for phakic IOLs, who should be considered for this surgery? Richard L. Lindstrom, MD, conducted a “selective meta-analysis” of the literature looking at clinical trials data on both LASIK and phakic IOLs to determine the most appropriate candidates for these procedures. LASIK or an IOL?
“Through this evidence-based comparison of efficacy and safety of phakic IOLs vs. LASIK, we came to the following conclusions: –1 D to –8 D, LASIK wins; –8 D to –12 D, it’s a horse race; and –12 to –20, IOLs win,” said Dr. Lindstrom, adjunct professor emeritus of the University of Minnesota and founder and managing partner of Minnesota Eye Consultants.
“I personally chaired two panels composed of surgeons from all over the world, and the consensus of both of them indicated that patients should start to consider a phakic IOL at –8 D exactly, and that is what the data supported,” Dr. Lindstrom said.
Based on these conclusions, treating patients who are either below –8 D or above –12 D is fairly straightforward. Patients who fall within this range should be informed about both options, Dr. Lindstrom said. “Surgeons should also take an individualized approach to determine the most appropriate technique, with decisions based on such factors as corneal thickness and anterior chamber depth.”Refractive Lens Exchange
Drs. Lane and Lindstrom both stressed that one cannot discuss phakic IOLs without talking about refractive lens exchange, which is another hot topic in refractive surgery.The presbyopia population.
“Phakic lenses are designed for patients who are prepresbyopic—who have the natural accommodating ability of their own lens,” Dr. Lane said. “And when they do reach middle age, they have the same options as other presbyopic individuals: wearing reading glasses, undergoing a LASIK procedure for monovision or having a multifocal or true accommodating IOL implant. They haven’t burned any bridges in terms of undergoing alternative future procedures.”
Dr. Lindstrom added, “The average patient who presented in the FDA trials of the phakic IOLs was prepresbyopic—about 39 to 40 years old. Yet the presbyopic patient must also be considered, and this is a complex population. For these individuals, who are mostly in their late 40s and 50s and ideally want to have their near vision corrected, we have multifocal and accommodating lenses.”
Dr. Lindstrom added, “I am comfortable doing clear lens extraction for patients in the range of –1 D to –6 D. However, for extreme myopes over –6 D with presbyopia, I tell them to avoid LASIK and refractive IOL implants. Just wait to develop cataract—and many don’t have to wait very long.”
_____________________________Dr. Holladay is a consultant for AMO, Dr. Lane is a medical monitor and consultant for Alcon and Dr. Lindstrom has received support from AMO and Staar.