LONDON — The Alpha IMS retinal prosthesis (Retina Implant AG, Germany) gives a modicum of useful vision to some patients with severe visual loss from retinitis pigmentosa, a new study shows.
"Electronic implants are the only possibility for patients blind from hereditary retinal diseases to regain some vision," said Eberhart Zrenner, MD, from the Institute for Ophthalmic Research of the Center for Ophthalmology at the University of Tuebingen, Germany.
The results of the multicenter European and Asian study were presented here at the 14th EURETINA Congress.
The subretinal implant is currently approved for marketing in Europe, but is not available in the United States. Currently, the only retinal prosthesis approved in the United States is an epiretinal implant, the Argus II (Second Sight, Sylmar, California).
The subretinal position of the device corresponds to the location of natural photoreceptors, which allows the use of the patient's remaining retinal network, Dr. Zrenner explained. In addition, it is easier to fix the chip than it is to place an epiretinal device, he pointed out.
Each of the 1500 contact points on the implant chip consists of a photodiode, electrode, and amplifier. The device is connected to wires that run beneath the skin to a subdermal receiver and antenna that allow external activation and tuning of the device for brightness and contrast.
The study consisted of 29 patients who received Alpha IMS implants. The patients were tested for basic light and motion perception with the device in both the on and off positions. They were also assessed with regard to activities of daily living, and they made self-reports concerning their vision.
Basic Light and Motion
With the implant on, 25 patients had light perception, 17 were able to localize the light source, 15 successfully passed the grating acuity test, 6 had motion perception, and 4 successfully completed the Landolt C-ring task.
In addition, 15 were able to discern grayscale differences, 5 identified the hand position on a clock face, and 4 were able to discriminate letters against a high-contrast background.
Asked what they could discriminate visually, 8 patients said they could make out some details of faces or people, 10 could identify interior and exterior features of houses and buildings, 5 could see the lights or motions of passing vehicles, 4 reported being able to see flowers or animals, and 1 reported being able to read lit street signs.
Six patients rated their daily visual experiences as very good, 7 said they were useful, and 8 had the ability to localize light sources but were not able to distinguish shapes or details, reported Dr. Zrenner.
The subretinal implant appears to have an acceptable safety profile, he said, but noted that 4 patients had no light perception at all, owing to an optic nerve problem, retinal swelling after device repositioning, a vascular complication, and a technical problem.
A retinal specialist who was not involved in the study told Medscape Medical News that retinal prostheses are currently the only practical option for restoring some vision to patients blinded by retinitis pigmentosa and similar conditions. But, he said, whether the subretinal device or epiretinal implant will turn out to be better remains to be seen.
"These implants are very interesting, whichever form you go for, for patients who have lost vision or are at very advanced stage, because they can restore something that is reasonable," said Marc de Smet, MD, from the MIOS Retina and Inflammation Center in Lausanne, Switzerland.
The key to the eventual success of such devices is likely to be the number of contact points in each device. The Alpha IMS device reportedly has 1500 contact points, "and it's around that number that you start to see some fairly decent images," Dr. de Smet explained.
"One of the other questions, of course, is how long does it work? I know that with this system, there have been some problems in the past with it working for a period of time and then stopping, so there are still some engineering issues that have to be dealt with. Still, it is a very promising technology for a group of patients who don't really have very much," he said.
This study was supported by Retina Implant. Dr. Zrenner disclosed being a founder of the company, but said he is not compensated for advisory work. Dr. de Smet reports no financial relationships relevant to the study.
14th EURETINA Congress. Presented September 11, 2014.
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Cite this: Subretinal Device Restores Measure of Sight - Medscape - Sep 15, 2014.
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