New lens will add another element of sophistication to the surgeon’s armamentarium.
For the past 7 years, we have had an array of premium IOLs designed for presbyopia correction, each with its own limitations well-known to those of us who use them.
The factor most strongly correlated with patient satisfaction with regard to these lenses is uncorrected distance visual acuity, and postoperative enhancements are frequently necessary to achieve the desired refraction, which is within 0.5 D of the target.
Although we tend to achieve that goal in more than 90% of cases in laser refractive surgery, the same cannot be said for IOLs. In fact, we may only reach that mark in about 40% of IOL cases. Thus, the Light Adjustable Lens (Calhoun Vision) was designed to address that need.
The lens involves complex chemistry and a light delivery device that have been developed over a 10-year period. We are only just now getting close to approval for this technology, however, because those developing this lens have had to cross a number of hurdles that other technologies simply have not had to address, including a new lens material and the creation of a device to deliver curvature-altering light to the lens after surgery.
In its current form, the three-piece lens has a 6-mm optic with Prolene haptics and is made from partially polymerized silicone, unlike the majority of silicone lens implants, which are made from fully polymerized silicone. It also contains ultraviolet-blocking materials and a photo initiator inside the material, which reacts to light. This creates more covalent bonds in the silicone to make it fully polymerized.
How it works
The concept for implantation of this lens is that the surgeon would perform cataract surgery using whatever technology is available, including, in the future, femtosecond laser. The foldable lens would be implanted through a standard-sized incision.
In the 1 to 3 weeks after surgery, the patient is given time to heal and must wear UV-filtering sunglasses anytime he or she is outdoors to reduce natural UV from polymerizing the silicone in the lens. The one challenge here is that we have to insist on patients being compliant.
The patient returns to the office 1 to 3 weeks later, and a refraction is performed. The results of the refraction are then used to perform an enhancement via a light delivery device, which employs a technology similar to that of an LCD projector. Essentially, the patient sits down behind a device that looks something like a YAG laser, except in this case the patient has a fixation target. According to Robert K. Maloney, MD, the medical monitor for Calhoun Vision, the patient sees no bright light, just a faint purple glow throughout this 2-minute procedure, during which the lens material becomes polymerized. This process actually corrects the residual refractive error.
Precision of correction
At this early stage, only postoperative sphere and cylinder are being adjusted. But with that alone, H. Burkhard Dick, MD, in Bochum, Germany, thus far with 120 eyes at 12 months, has shown that 97% of these patients are 20/25 or better and 86% are 20/20 or better compared with about one-third of patients who see 20/20 or better with conventional lenses. Clearly, we can achieve a high degree of satisfaction, even early on.
But what about higher-order aberrations? The next stage of development with this device will be to use wavefront sensors to determine to a high level of resolution what other aberrations beside sphere, cylinder and axis should be corrected. The lens material itself can be adjusted to a fine spatial resolution. In other words, you can get down to fine detail in customizing the shape of this lens. As the wavefront sensors improve, we will be able to achieve high levels of sophistication in how precisely we can engineer this lens to the patient’s ideal shaping.
One of the more exciting areas this technology addresses has to do with presbyopia correction. The biggest problem with multifocal lenses is that we do not have a good test before cataract surgery to determine who is a good candidate for them.
Some patients, about 10% in virtually all studies, are quite bothered by dysphotopsias. You could put a multifocal contact lens on a patient before cataract surgery and assess his or her level of tolerance because it is a reasonably good simulation of what a multifocal IOL would be like. The problem with doing that, of course, is that the patient has a cataract, so other aberrations limit the predictive value of a contact lens test.
With the Light Adjustable Lens, a surgeon can, in theory, test a patient in multifocal optics before committing to them. We can put in a spherical lens implant and then have an opportunity to modify it in a wide variety of ways, including putting a multifocal surface on it. Before making light adjustments, we can aim for –1 D, and then put a multifocal contact lens that corrects the –1 D and puts a multifocal surface in front of the patient’s eye. Now the patient has an opportunity to visibly understand what a multifocal modification of the optic would be like. The patient can try it for days and satisfy himself that the side effects of a multifocal will not be bothersome.
After this contact lens trial, if the patient so chooses, the surgeon can then use the light delivery device to modify the optic to correct any residual sphere and cylinder and to place a central multifocal zone on the lens. Now we will be able to find out whether this is the best option before we irreversibly put this surface on the lens.
If the patient does not tolerate the multifocal contact lens trial, the next option is to try contact lenses for monovision. Even if the patient has never previously experienced monovision, the surgeon would have the opportunity to try it and explore an almost infinite variety of options before finally making the patient commit. Once the patient is satisfied with a contact lens trial, the surgeon can make the alteration of the lens. The lens can be adjusted by 2 D in either the hyperopic or myopic direction, so one can go from –1 D to 0 D in the distance eye or to as high as –3 D in the nondominant eye.
This is truly customized surgery in its purest form. We can take a patient, even one who is not sure what he or she wants, and deliver precisely what is desired, and we can make that decision after surgery.
What’s to come
Although the Light Adjustable Lens is already available in Europe, there are still some hurdles to having this lens available in the U.S. There is a phase 3 U.S. Food and Drug Administration study set to begin in the coming months, and similar registration trials are going on in Mexico and Canada, as well. The cost of the commercial units, when they become available in the U.S., is yet to be determined.
As the technology moves forward, there is no good reason that this lens could not be coupled with other technologies, such as multifocal surfaces or even an accommodating lens design. Once we have that, we will have achieved a high level of sophistication in the lens implant technology we can deliver.
John A. Hovanesian, MD, FACS, can be reached at Harvard Eye Associates, 24401 Calle De La Louisa, Suite 300, Laguna Hills, CA 92653; 949-951-2020; fax: 949-380-7856; e-mail: email@example.com.