A couple of years ago, corneal implants for presbyopia came onto the scene, whetting surgeons' appetites for the possibility of a reversible treatment for presbyopia, at least in some patients. One of these devices, the Presbylens (ReVision Optics), posted some preliminary results but had to return to the drawing board to remedy some issues. Now, the lens is back, redesigned and involved in a study in Mexico with an eye toward starting a U.S. Food and Drug Administration trial by the end of 2009. Here's a look at the modifications that were made and how they may be contributing to the lens's current outcomes.

 


The Design

The lens is made of a piece of proprietary polymer that's 2 mm in diameter and designed to fit beneath a corneal flap in the non-dominant eye of a plano presbyope. There, it changes the curvature of the cornea enough to enhance near vision while, the company hopes, minimizing any decrease in the distance vision.


The 2-mm diameter is a recent alteration, as the original diameter was 1.5 mm, but this caused issues with the size of the area that the patient could view accurately. "With the smaller lens design, some patients complained that the image area was small," explains Greenwood Village, Colo., surgeon Jon Dishler, a consultant and investigator for ReVision Optics. "For instance, the sentence the person was looking at might be clear but the area outside wasn't sharp. But, since the company has gone to 2 mm, patients don't complain about that any longer."


There were also some initial issues with haze postop. "One of the issues early on was the eyes developed a little haze sometimes," says Dr. Dishler. "It was a little bit of fibrocyte activation from the lens. But, due to an improved manufacturing process and a postop drug regimen, that problem has been solved and none of the patients in the current study developed haze." Though Dr. Dishler says he can't detail the exact drug regimen, he says it doesn't involve any unapproved medications, and instead consists of readily available FDA-approved agents. "Giving the right medications in the right combination allows the eye to heal without any haze," he adds. He also says tackling ocular surface issues preop has made a difference in the results. "A lot of presbyopic patients, especially women, have dry eyes," Dr. Dishler says. "So successfully treating or controlling any dry-eye problems was very important in making this a successful product. Avoiding any dry-eye problems and treating the condition appropriately when necessary has improved the lens's clinical performance."

 


The Surgery

The lens is situated beneath what is essentially a LASIK flap, though plans are in the works to create a lamellar space for it that will allow it to sit even more snugly.


"Surgically, it's a fairly straightforward, quick implantation," explains Dr. Dishler. "The flap is usually 120 to 130 µm thick, and you can create it with either a microkeratome or a femtosecond laser. When the lens comes from the manufacturer, it's already loaded into a delivery device. So, it's then a matter of sliding the lens off in the center of the pupil, letting it dry for a few seconds, then folding the flap back over top of the lens. Most of the procedure time is spent making the flap, and it's got the same postop risk profile as a LASIK."

Dr. Dishler says there hasn't been a problem with the implant migrating beneath the flap, and, if anything, the opposite is true. "You have to make sure you get it onto the right spot right away, because it's so small and so thin it's like a little piece of Saran wrap," he says. "As soon as you put it on there it wants to stick. At the end of the procedure, it's invisible because it's got the same index of refraction as the cornea, so it's hard to see through the flap. You can instill fluorescein at the end of the procedure, and it's actually recommended that you look at the patient under the slit lamp afterward to make sure it's well-centered. However, it's extremely unusual for it to move or decenter."


Dr. Dishler says there are definitely strategies that the surgeon needs to use to implant a Presbylens, including the use of mainly a "dry" technique. "It probably wouldn't be advisable to flush a lot of fluid under the flap once it's down or you could potentially dislodge the lens or wash it away," he warns. "So, the technique is to use very little fluid to float the flap back down and not do a lot of irrigation after that." In the future, there may be software for femtosecond lasers such as the IntraLase that will allow the surgeon to create a pocket in the cornea for the implant rather than a flap. The surgeon would then make a tiny incision in the cornea to slip the lens in, avoiding healing issues involved with severing the corneal nerves and the dangers of eye rubbing. It would also make the procedure less invasive. "In addition, it would help ensure that it's centered perfectly and can't move or be washed out," says Dr. Dishler. "It wouldn't be as technique-dependent."

 


The Study

The current pre-FDA study is being done in Monterrey, Mexico, by Enrique Barragan, MD. He's implanted the device in 18 patients, with a goal of 30 total. All patients are the target population for the implant: plano presbyopes between 45 and 65 years of age.


There's currently one-month follow-up on 14 patients. So far, Dr. Dishler says it appears that the lens, though it decreases distance vision to achieve better near vision, doesn't decrease distance acuity as much as monovision, the current gold standard for presbyopia treatment. "With contact lens monovision, for example, it's more of an even trade," says Dr. Dishler. "For every line you increase near vision, you lose distance vision by the same amount." In the study, before lens implantation all patients saw 20/30 or better uncorrected at distance, and had, on average, 20/60 near vision. Postop, near vision improved to 20/25 or better in all the patients, with 86 percent seeing 20/20 or better, while at worst distance vision was decreased to 20/40, with 72 percent of the patients seeing 20/30 or better at distance. There has been no haze or lens explantations thus far.




The lens is dependent on pupil size for its effect. "The tradeoff of getting this reading benefit without much of a loss of distance vision is that, when you do read, you need fairly bright light," says Dr. Dishler. "You can't expect to get this lens and be in a really dim restaurant and read some tiny print on a wine bottle."


As to how the lens achieves its effect, it appears that the draping of the cornea over the lens is a factor. "The lens has a varying radius of curvature," explains Dr. Dishler. "It has a certain amount of thickness to it. So you get the most power over the central 2 mm, and within that area you get the most power from the central 1 mm. But there's a transition from 2 mm out to 3 or 3.5 mm that gives some power due to the draping effect of the flap as it lies over the lens and goes back to conform to the original shape of the cornea.
When you look at topographies, for example, the refractive effect is over a larger diameter than the diameter of the lens itself. When the pupil's small, say around 3 mm during reading in bright light, the patient's getting 80 percent of his vision through the lens. In normal or dim light, he's getting up to 80 percent of his vision from the cornea outside the lens. That's why it works well in assisting reading vision without hurting distance vision so much." He says there haven't been any photic phenomena such as multiple images or halos postop.


The company plans to finish up the Mexican study and, if the follow-up data looks acceptable, it will begin a U.S. FDA trial of 100 patients at five sites by the end of 2009.


Reflecting on why the Presbylens may fill a niche, Dr. Dishler says, "If a patient's already in contacts, he might go to monovision contact lenses or something along those lines.
But for the presbyope who never had to wear contacts or glasses, he's more interested in having something done and just having it work. He just wants to do something and be done with it."