Latest AMD Advance Is in the Hands of Cataract Surgeons

Cataract surgeons do not normally find themselves treating late-stage macular degeneration. However, a new device in the approval pipeline, called the Implantable Miniature Telescope (Visioncare Ophthalmic Technologies, Inc., Saratoga, CA), invented by Isaac Lipshitz, MD, will give us the opportunity to positively affect a group of patients who currently have very few options. As part of a multidisciplinary team that includes retina and visual rehabilitation specialists, cataract surgeons will play a central role in this new implantation procedure.

CHARACTERISTICS

Although placed in the capsular bag, this visual prosthetic device for age-related macular degeneration (AMD) is like none we have seen before. The device utilizes multiple, wide-angle microlenses made of ultraprecision quartz that function as a fixed-focus telephoto system to project a magnified image onto the retina (Figure 1). The miniature telescope is secured in the capsular bag of the posterior chamber with PMMA haptics (Figure 2). It is designed to be implanted in one eye of patients with bilateral, untreatable AMD to improve the central vision. The fellow eye (without an implant) provides peripheral vision.

These patients, who have geographic atrophy, have either failed previous treatments for wet AMD or responded well to treatment but have resulting scotomata and usually severe visual impairment of 20/200 or worse. Previously, their only options have been magnifying glasses or an external telescope, neither of which provides very satisfactory vision. The telephoto function of the implant is designed to reduce the relative size of the scotomata while providing a wide field of view that allows for natural eye movements and a normal cosmetic appearance.

In fact, the implanted telescope gives patients a 20º to 24º field of vision, compared with an approximately 8º field with an external telescope (Figure 3). This wider field of view is accomplished by the device's wide-angle optics and intraocular placement. Postimplant vision should allow the scotoma to be less perceptible in a relatively large central field of view, so more detailed central visual information is available for such functional activities as recognizing people, cooking, and reading (Figures 4 and 5).

This is a marvelous device, but it has limitations. It is important to understand that the telescope is neither a cure for macular degeneration, nor can it fully restore a patient's lost vision. But, it can improve the quality of life and visual acuity of a desperate group of patients.

SIX-MONTH RESULTS
An unpublished, prospective, multicenter trial of the Implantable Miniature Telescope included 217 patients with 206 lenses successfully implanted. The mean age of the patients was 76 years. The mean preoperative distance visual acuity was 20/313; near acuity was 20/241 at 16 inches and 20/156 at 8 inches.

At the 6-month mark, 89% of patients had gained two or more lines of near or distance BCVA (Figure 6); most of these (79%) gained three or more lines. The vast majority of subjects doubled their BCVA for both mean near and distance in excess of three lines.

In addition, the National Eye Institute Visual Functioning Questionnaire showed a substantial increase of six to 16 points on relevant subscales. These patients began with a very low baseline questionnaire score of 44/100, which suggests severely impaired function compared with most other ocular pathologies.

Although an improvement of two or three lines of visual acuity from 20/400 vision may not sound like a lot, it represents a huge change for these patients. In AMD, it is rare to find a treatment that actually restores vision or improves quality of life; most approaches to this disease only maintain vision or slow AMD's progression at best. However, from the start, it is important to set appropriate expectations for the patient—and for the surgeon who may be accustomed to 20/20 cataract and LASIK outcomes. Success is based on improved visual function gained from reducing the scotoma and any resultant acuity change.

During the Implantable Miniature Telescope's clinical trial, capsular tears or suprachoroidal hemorrhages prevented implantation in 11 eyes, and two of the prostheses were explanted due to condensation between the anterior window and the first microlens. The condensation was due to microcracks from mechanical trauma during handling of the device. Postoperative anterior segment complications included transient elevated IOP and corneal edema in the first postoperative month, both of which were easily managed. Mean endothelial cell loss was 22%, a bit higher than the goal of <17% set for the trial. However, that rate improved with experience; surgeons generally had greater cell loss in their first three cases. There have not been any incidents of corneal decompensation, and there were no retinal complications in the trial.

APPROPRIATE CANDIDATES

To be considered for the implantation of the visual prosthesis, patients should have stable, late-stage, bilateral macular degeneration, with no active or recent treatment of choroidal neovascularization.

If the patient has any degree of cataract, as most in this age population do, they may achieve some minimal benefit simply from having the cataract removed, although their central vision will still be impaired by the dysfunctional macula. Patients who respond well to magnification are better candidates, but beyond that my colleagues and I are not yet able to predict visual outcomes based on the size or location of the preoperative scotoma.
Attitude is an important factor in patient selection. Rehabilitative work is required postoperatively so that patients can utilize their new visual status in daily activities. Those who accept their responsibility in their visual rehabilitation, who are eager for improved vision, and who are perhaps more flexible and adaptable to new vision are likely to be better candidates than those who have unreasonable expectations or low motivation.

SURGICAL TECHNIQUE

Cataract surgeons are certainly the best qualified individuals to implant this device, but its implantation is much more challenging than cataract surgery. The length and diameter of the device demand a unique surgical approach.

The first step, removing the crystalline lens, is fairly routine. Surgeons may use their standard technique for cataract removal as long as they take care to make a very large capsulorhexis, about 6 to 7mm in diameter. The telescope's haptics are much stiffer than those of an IOL (conventional three-piece), so a larger capsulorhexis is necessary to facilitate in-the-bag implantation. I remove the cataract through a 3-mm clear corneal temporal incision, and then I create a new incision superiorly to insert the implant.

Because this device is quite large—the cylinder of the device is 3.6mm in diameter and 4.4mm long—the incision must be 10 to 12mm in length, which is much larger even than the wound for a planned extracapsular extraction. The incision must be large enough to accommodate the profile of the implant without its touching the endothelium to avoid traumatic endothelial cell loss, which is the greatest risk of this procedure. I recommend a two-planed incision with an initial groove, a slight tunnel forward, then entry into the anterior chamber to help seal the wound. I also use copious amounts of a dispersive viscoelastic to coat the lens, open the bag, and coat the endothelium during implantation.

The surgeon should place the device's inferior haptic in the capsular bag first. After he slides in the optic, he may place the trailing superior haptic in the bag. In the clinical trial, my colleagues and I were very pleased with how well and easily the device centered and fixated in the capsular bag.

Finally, adequate closure of this large wound requires six to eight sutures—again, a significant departure from cataract surgery. Fortunately, surgeons need not worry that the induced astigmatism one would expect from such a large incision with sutures will limit the patient's vision. We found that the telescope's magnification (either 2.2X or 3.0X) rendered any induced astigmatism visually insignificant.

POSTOPERATIVE MANAGEMENT

Postoperative medical management is important with this procedure. The large incision necessitates a perioperative steroid injection and a longer course of postoperative anti-inflammatory medications. Because the implant marginally protrudes through the pupil, cycloplegia is also required for the initial 3 to 4 postoperative weeks.

Postoperatively, the surgeon will be able to see the posterior pole of the retina quite well through the device, despite a minified view. However, a peripheral retinal examination would be impossible without dilation.

MULTIDISCIPLINARY MODEL OF CARE

If approved, this AMD visual prosthesis will require a coordinated and multidisciplinary model of care that is somewhat rare in ophthalmology. Anterior segment surgeons are accustomed to referring macular degeneration patients to a retina specialist. With this device, retina specialists with access to late-stage AMD patients will likely determine patients' candidacy initially and then refer them to a cataract surgeon for the actual procedure. Of course, the retina specialist will need to continue to monitor the patient for any progression of AMD postimplantation.

Once the device is implanted, the cataract surgeon will follow the patient for up to 1 year to ensure the stability of the visual result and the wound. There will also be a need for a third consultant on the team: a visual rehabilitation specialist. Patients who receive this device definitely need visual training to improve their visual function with the new implant, much as one would have to learn to walk again with a prosthetic leg. In the clinical trial, six visual rehabilitation visits were required during the first 3 months following surgery, a frequency I would expect in a clinical setting. The doctor primarily responsible for the patient—most likely the referring retina specialist or low-vision optometrist—would prescribe the visual rehabilitation and oversee the patient's long-term care.

WRAPPING UP

The results of the clinical trials for the Implantable Miniature Telescope thus far have been very encouraging. Visioncare Ophthalmic Technologies, Inc., is completing analysis of the 12-month efficacy and 24-month safety data from the clinical trial, with plans for FDA submission this fall. If all goes well with the approval process, the implantable telescope may become available for general use by mid-2006. I believe it will present a subgroup of AMD patients with a unique opportunity for improved visual acuity and quality of life. 

Stephen S. Lane, MD, is Clinical Professor, University of Minnesota and is in private practice in Stillwater, Minnesota. He serves as Medical Monitor for VisionCare Ophthalmic Technologies' clinical trials. Dr. Lane may be reached at (651) 275-3000; sslane@associatedeyecare.com.