March 2013

 

RETINA

 

Device focus

Retinal implants offer hope to late-stage AMD, RP patients


by Michelle Dalton EyeWorld Contributing Writer

 

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The Argus II implant

The Argus II with retinitis pigmentosa

The Argus II implant in a patient with retinitis pigmentosa

An artist's rendering of the Argus II Source: Second Sight

The Retina Implant

Retina Implant

The Retina Implant (also shown at left) in a patient with retinitis pigmentosa

How Retina Implant work

An artist's rendering of the Retina Implant and how it works

Walter G. Wrobel, Ph.D.

Walter G. Wrobel, Ph.D., president and chief executive officer of Retina Implant, with an artist's rendering of the implant Source: Retina Implant

Retinal disorders that leave patients blind or with limited vision may not be as dire as they once were, thanks to prostheses

Patients with end-stage age-related macular degeneration (AMD) and cataract have few options for retaining what vision they have, but a multidisciplinary team approach among posterior segment surgeons, anterior segment surgeons, and low vision specialists may help overcome those obstacles. The Implantable Miniature Telescope (IMT, VisionCare Ophthalmic Technologies, Saratoga, Calif.) provides a magnification of 2.2 or 3.0 X, projecting the image over a wider field of the retina to provide some of the central vision destroyed by AMD. The device is implanted unilaterally, must be placed at the time of cataract removal, and must be implanted by an anterior segment specialist because of potential complications, said Kathryn A. Colby, M.D., Ph.D., Massachusetts Eye and Ear Infirmary, Boston. "For this device to work, the capsular bag needs to be completely intact for additional stabilization since the optic protrudes through the pupillary plane," she said. "It's not realistic to think you could explant an IOL and still have the bag completely intact and get this device in the eye."

It "may be possible" to remove the IOL and then suture the IMT to the sclera/sulcus, "but the concern is that the IMT is too heavy for that," said Baruch D. Kuppermann, M.D., Ph.D., director, vitreoretinal services, Gavin Herbert Eye Institute, University of California, Irvine. In the U.S., the device is restricted to implantation by a corneal specialist; during the studies, patients had "significant endothelial cell loss, and it was determined by the FDA that corneal specialists have specialized training to allow safe implantation of the device," Dr. Colby said. Dr. Kuppermann is not convinced a cataract surgeon shouldn't implant the device, but "it should certainly be implanted by an anterior segment surgeon rather than a retina surgeon (speaking as a retina surgeon myself)."

The IMT patient

Patients who fare best with the IMT have undergone "rigorous preoperative testing as the IMT is difficult for a patient to learn how to use and requires an agile mind and a positive attitude," Dr. Kuppermann said. The device will not restore the patient's youthful vision, Dr. Colby said, but will improve visual function, sometimes as much as a few lines. "People who focus more on what they are able to get back in terms of vision, rather than what they still don't have, are much better candidates," Dr. Colby said. "It's really not the measured vision that matters in these patients, it's how they can use the vision in activities of daily living." Aside from a patient's personality and outlook, there are some physical requirements besides being phakic, including an anterior chamber depth of a sufficient amount to accommodate the device, intact support structures of the capsular bag, and the determination that no further treatment for AMD will be successful, Dr. Colby said.

Co-managing the patient

Low vision specialists "are probably the most important part in the management of these patients," Dr. Colby said. "The patient needs to learn how to use the device and that's really where the low vision rehabilitation specialist comes in." To that end, the VisionCare treatment program, CentraSight, ensures candidates for the IMT undergo vision rehab screening and will work with the patient postop.

Some patients are thrilled with any amount of visual improvement, others consider the improved central vision as a compromise to increased loss of peripheral vision in the implanted eye, and for others still loss of any vision is unacceptable. "In the studies, the most successful groups were those that had the best low vision specialists, people who were enthusiastic," Dr. Kuppermann said. "Having the surgery, determining if a patient is a candidate, all that is barely half the battle. The real challenge is in teaching people how to use it."

In development for RP

There are currently two devices being developed for retinitis pigmentosa (RP), a genetic disorder that eventually results in blindness. The Argus II (Second Sight Medical Products, Sylmar, Calif.) takes an epiretinal approach, while the Retina Implant (Retina Implant, Reutlingen, Germany) takes a subretinal approach. With the Argus II, a 55-electrode chip is placed on top of the macular region, and requires the patient wear glasses that have a camera mounted on it. The device includes a wireless processor and a battery pack patients wear around their waist, said Brian Mech, Ph.D., vice president of business development. The Argus II received FDA approval in February.

With the Retina Implant, the 1,500 electrode, 3x3 mm2 microchip is placed underneath the retina where photoreceptor cells exist in normally sighted people, said Walter G. Wrobel, Ph.D., president and chief executive officer. A wireless power supply is implanted subdermally behind the ear. The device is completely embedded in silicone for biocompatibility (except for the stimulating chip), with one half of the device implanted beneath the retina, the other half sewn onto the eye and covered by conjunctiva, Dr. Wrobel said. "Patients are able to distinguish between a fork and a spoon within days of the device being implanted," he said. "For them, it's really a miracle."

Dr. Kuppermann said he tells "everyone who can benefit from the device" about the Argus II, but acknowledges it's very few people.

"It's really the worst of the worst of the RP patients," he said.

Unlike the IMT, "a cataract in these patients is not as much of a concern," Dr. Mech said. "We advocate removing the natural lens if present to eliminate the possibility of cataract formation (which is now higher because of the surgery)."

Dr. Mech said Second Sight is considering the device for geographic atrophy, but notes the potential cost may be a barrier. "The device is $150,000 and in RP, that's likely spread out over 30 years so it's justifiable. But with AMD, patients are 80 so maybe there's five or 10 years' benefit, and it may not be as justifiable," Dr. Mech said. Dr. Kuppermann said, "If I was one of these patients with end-stage RP, I would give the electronic implant serious consideration, understanding all the risks. The potential to gain vision is better than the alternative."

Editors' note: Dr. Colby has no financial interests related to this article. Dr. Kuppermann has financial interests with Second Sight. Dr. Mech and Dr. Wrobel are employees of Second Sight and Retina Implant, respectively.

Contact information

Colby: 617-573-5537, kacolby@meei.harvard.edu
Kuppermann: 949-824-6256, bdkupper@uci.edu
Mech: 818-833-5026
Wrobel: walter.wrobel@retina-implant.de

Retinal implants offer hope to late-stage AMD, RP patients Retinal implants offer hope to late-stage AMD, RP patients
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