Patient eligibility for telescope implant begins with pre-screening

Take-home message: Careful preoperative assessment is imperative for patients who may be candidates for the telescope implant. After implantation, patients are actively engaged in their rehabilitation with a low-vision specialist.

By Michelle Dalton, ELS; Reviewed by William H. Benson, MD

Richmond, VA-When considering patient eligibility for the telescope implant (Implantable Miniature Telescope, VisionCare Ophthalmic Technologies), the best candidates may be those patients with dry age-related macular degeneration 65 years and older who demonstrate visual impairment of 20/160 to 20/800, said William H. Benson, MD.

These patients, who typically have been followed for several decades, become eligible for the implant “once they can no longer maintain that fine discriminatory vision that allows them to read small letters and numbers,” said Dr. Benson, professor of ophthalmology and holder of the Ragnit and Walter J. Geeraets Chair, Department of Ophthalmology, Virginia Commonwealth University, Richmond.

Objectively, that limits the potential patient population to those with 20/160 to 20/800.

“My patients have typically been around 20/400,” he said. “What we have learned is the better the baseline vision, the better the vision after implantation.”

His patients have improved to 20/125, “so they’re no longer considered legally blind because they’ve improved their vision to 20/200.” (The telescope provides up to 22.5° of visual field, Dr. Benson said.)

How the technology works

The more “healthy” retina that is available outside the atrophic fovea, the better the potential for an improved functional visual outcome, Dr. Benson said.

The device will recruit normal retina fibers to expand the field of view and “allow patients to discriminate smaller objects,” he said.

With a diameter of only 3.2 mm, the telescope expands the field of view onto the back of the eye, “much wider than what you would get with eyeglasses or cataract surgery. With eyeglasses and cataract surgery, you're essentially using that central 4° to 6° to read letters and numbers for your best discriminatory vision,” Dr. Benson explained.

“With the [telescope], if patients are at the extreme edge of that cone of light that’s recruiting normal retinal photoreceptors to expand the field of view outside the scotoma area, they may be able to see larger headlines that couldn't be seen before,” he said.

The more advanced the patient macular degeneration, “the fewer healthy retina fibers remain that can fall within that cone of light in the back of the eye. If a patient is beyond that, they may not benefit from the implant,” Dr. Benson said.

If a patient has a disciform scar, they’ve lost the central 4° to 6°, but “the [device] can recruit normal retina beyond the central scotomas to maybe 20° or 30°.”

If reading is an important aspect of patients’ lives, those patients with vision of 20/160 “are probably the best candidates” compared with those 20/400 or worse, he said.

Dr. Benson will also consider implantation in patients with “resolved” neovascular AMD-patients without evidence of choroidal neovascularization (CNV), confirmed with fluorescein angiography and optical coherence tomography.

“If they’ve been stable for at least 1 year, they could be eligible in that eye,” Dr. Benson said. “I would still be cautious in these patients, however, because the neovascularization could return. If someone has had 2 years of five to seven injections per year of an anti-vascular endothelial growth factor, they have not achieved sufficient stability to qualify for the [implant].”

Early multicenter study results

Of 217 patients with the telescope implanted (the original study included a 24-month follow-up), 90% had improved by 2 lines, 67% by 3 lines. There was also a “significant” improvement in quality of life for patients with bilateral end-stage AMD.

Because of the “unique configuration” of the device, “proper wound construction, anterior chamber management, and device insertion after phaco are critical for successful surgery,” according to an early publication on the device.¹

Evaluations and follow-up

To determine eligibility for implantation, patients undergo a rigorous preoperative evaluation using a low-vision specialist, Dr. Benson said.

A prototype telescope held up to the eye determines what, if any, functional reading vision the patient might gain from the implant. Once the retina specialist identifies patients suitable for consideration, patients are evaluated by the low-vision team that works with patients postoperatively to maximize their vision, Dr. Benson said.

The preoperative examination will give physicians enough data to confirm eligibility with Medicare, which usually requires postoperative documentation that the patient improved by at least 5 letters on the ETDRS chart before reimbursement will be approved.

Most of Dr. Benson’s patients are 20/400 bilaterally, so he prefers the implant in the non-dominant eye so that the dominant eye can continue to help patients navigate immediate surroundings.

“That may limit the potential of the telescope, because now they've got to re-train their non-dominant eye for distance vision and reading, which they used their dominant eye for when they were younger,” he said. “I'm making it more difficult for them-by maintaining their dominant eye for ambulation, I am reducing downside risk that may come with ambulating around the house with their non-dominant eye.”

In general, most patients need about 3 months of postoperative training with a low-vision specialist, and in some cases patients may need as much as 6 months, Dr. Benson said.

The device is implanted through an extracapsular incision, and stitches are removed throughout the first 4 postoperative months.

“As the astigmatism is being managed, their vision is improving, and they do much better in their occupational therapy,” he said.

Six months postoperative is when patients tend to achieve their maximal visual improvement, he added.

“By that time, patients know what they can do and what limitations remain,” Dr. Benson said. “It just takes time to re-train your brain.”

Reference

1.     Colby KA, Chang DF, Stulting RD, Lane SS. Surgical placement of an optical prosthetic device for end-stage macular degeneration: The Implantable Miniature Telescope. Arch Ophthalmol. 2007;125:1118-1121.

William H. Benson, MD

E: whbenson@vcu.edu

Dr. Benson did not indicate a proprietary interest in the subject matter.