A Closer Look at an Accommodative IOL
BY SETH A. BISER, MD
The Crystalens (Eyeonics, Inc.), which the FDA approved in late 2003, is an intraocular lens (IOL) that can not only correct ametropias, but can also restore accommodation in aging presbyopes and in patients who have cataracts. As such, the Crystalens offers an option to many patients for whom conventional refractive surgery procedures can't fully meet their vision needs.
I believe Eyeonics has set high standards for post-cataract refractive results that should have a positive effect, even for cataract patients who opt for conventional IOLs. In this article, I'll discuss the potential benefits of the Crystalens as well as the criteria by which I select Crystalens candidates.
Design and Performance
The Crystalens is a flexible IOL with hinged haptics (see figure). It's made of a third-generation silicone called Biosil (which has ultraviolet-blocking properties) that makes the Crystalens IOL soft and pliant.
Once implanted into the capsular bag, it vaults posteriorly and centers well. Experts believe that its effect on accommodation results from a shifting mass effect from the contracting ciliary muscle. The mass effect may increase vitreous pressure and push the lens anteriorly, thus increasing the lens's effective plus power. Whatever the mechanism of action, a multicenter FDA trial that looked at 425 Crystalens implants demonstrated the IOL's accommodating power.
In one study, researchers compared the Crystalens (124 patients) to the performance of a standard IOL (64 patients). Table 1 shows the results with patients reading through their distance correction.
These results show the positive effects of the Crystalens. Note that these results are based on distance-corrected near acuity (DCNA), which is likely to become the standard measure of performance for accommodative IOLs because correcting for distance vision neutralizes the effect of any ametropias on near vision. In my own practice, a review of 20 recent conventional IOL patients showed that 13 percent achieved J3, 13 percent achieved J2 and the average DCNA was J8.
Approaching the Procedure
Because the ultimate goal is patient happiness, achieving a plano distance refraction is ideal for the Crystalens. For this reason, it's critical for Crystalens surgeons to have a completely "refractive" mindset when approaching even routine cataract surgery -- they need to perform accurate biometry, manage astigmatism and track refractive outcomes closely.
Both Eyeonics and Stuart Cumming, MD, the inventor of the lens, have taken steps to ensure proper use of the product. Dr. Cumming visited me to watch me perform cataract surgery before I attended the first U.S. Crystalens certification course, and he's been responsive to questions and issues that I've raised about the new technology.
Study Shows Promising Results
The net results for Crystalens patients are satisfying. In the FDA trial, for example, the one-year analysis showed that 100 percent of the study patients achieved J3 or better binocular DCNA, 84 percent saw J2 or better and 52 percent saw J1 or better. Even more remarkable was that 100 percent of the study patients saw J1 at the intermediate distance (such as for computer use).
During the weeks to months following implantation, patients must learn to retrain their eyes for accommodation. Once they succeed, the majority can perform most common activities entirely without eyeglasses. Tasks requiring exceptional near vision (such as embroidery, reading fine-print books at length or reading in dim lighting) will typically require some reading add.
What about the downsides of the Crystalens? An optometrist friend asked me whether the lens stops working over time as the eye develops progressive fibrosis over the haptics. This misconception seems widespread.
In fact, the FDA results suggest that fibrosis doesn't affect the accommodative effect. Remember that most eyes that have intraocular implants develop haptic fibrosis within weeks to months of implantation. By one year, the fibrosis is complete or nearly so. Yet researchers measured all of the results from the FDA trial at one year.
Moreover, in 25 eyes from the FDA trials that reached the two-year mark, the DCNA was identical to the one-year results. Internationally, eyes that underwent Crystalens implantation nearly four years ago also demonstrate a sustained result.
One troubling factor with the Crystalens is an increased rate of posterior capsule opacification (PCO) compared to conventional IOLs. However, Yag capsulotomy doesn't diminish the accommodative effect of the Crystalens. The reason for this phenomenon remains unclear, but it may have to do with relaxation of posterior tension on the haptics. I've observed similar phenomena in conventional IOL patients.
Studies have carefully monitored patients for numerous other possible downsides with the Crystalens. In the FDA group, postoperative contrast sensitivity and glare were equivalent to conventional IOLs, despite the smaller (4.5mm) Crystalens optic. Experts believe that this results from the Crystalens's posterior vaulting. DCNA didn't diminish with increasing patient age (including in the 80+ group) nor with lower IOL power or higher axial lengths.
Halos and other visual complaints that have occurred with pseudo-accommodative IOLs haven't occurred with the Crystalens.
TABLE 1 Crystalens vs. Conventional IOL
READING THROUGH DISTANCE CORRECTION
Choosing Crystalens Candidates
Who are the best candidates for the Crystalens? Certainly any patient who needs cataract surgery is an excellent surgical candidate, as long as his correction falls within the available Crystalens powers (high myopes may be out of range); the alternative is a conventional IOL.
What about patients aged 55 and over? Mild myopes aren't good candidates because many are accustomed to removing their distance correction and reading well up close. Moderate to high hyperopes are clearly the best candidates in this group. Yet before considering the Crystalens on any patient, I evaluate both uncorrected distance acuity (UCDA) and the DCNA.
For example, when a 55+-year-old hyperope asks me about LASIK, I ask him to consider the Crystalens if he has a relatively poor UCDA (about 20/60 or worse) and DCNA (about J6 or worse). If the UCDA is poor, but the DCNA is good (about J3 or better), then bifocal lenses or monovision may prove a good nonsurgical option for that time.
Understate and Overdeliver
It's always good practice to give patients more than they expect. I tell all my cataract patients that their uncorrected distance vision will likely be mediocre after surgery and they'll probably want some thin eyeglasses to fine-tune their vision for driving or going to the movies.
For Crystalens candidates, I explain that over time, they'll be able to perform an increasing range of intermediate tasks without glasses. For small print, they'll depend significantly less on reading glasses than will a patient who has conventional lens implants. With this understated approach, patients are better prepared to enjoy the benefits of a remarkable new technology.
Dr. Biser is an ophthalmologist in private practice in Fleetwood, NY and New York, NY. He's also a clinical assistant professor for the Department of Ophthalmology, New York University School of Medicine and is a resident instructor at Manhattan Eye, Ear, and Throat Hospital. His Web site is www.drbiser.com.