Retinal Microchip Restores Vision in Retinitis Pigmentosa

Troy Brown

May 09, 2012

May 9, 2012 — A subretinal microchip implant has entered new clinical trials in the United Kingdom and Hong Kong, and early results are encouraging, according to researchers from 2 studies. An earlier clinical trial conducted in Germany was reported in the November 2010 issue of the Proceedings of the Royal Society.

The first of 3 patients in the first study was implanted on February 13 at the University of Hong Kong Eye Institute. That study is being led by David Wong, MB ChB, chair professor in ophthalmology and director of the Eye Institute at the University of Hong Kong.

The subretinal microchip in situ. Source: Retina Implant AG.

The first 2 of 12 patients in the United Kingdom were implanted in mid-April of this year. Tim Jackson, MBChB, PhD, a consultant retinal surgeon at King's College Hospital and senior clinical lecturer at King's College in London, is leading the research in London, and Robert MacLaren, MD, PhD, professor of ophthalmology at the University of Oxford and a consultant retinal surgeon at the Oxford Eye Hospital, is leading the study in Oxford.

The technology is important because until now, vision loss from retinitis pigmentosa, a genetic disorder that frequently leads to blindness, has been considered permanent. More than 200,000 people in the United States and Europe have retinitis pigmentosa at this time.

Retinitis pigmentosa is a progressive genetic disorder that causes an imbalance of proteins to be produced by photoreceptor cells. This in turn limits the retina's ability to produce eyesight, and the cells die gradually, eventually leading to blindness.

Antioxidants such as vitamin A palmitate may slow the disease, but they cannot restore lost vision, so their use would be limited to early in the disease.

Researchers believe that the microchip technology will work because inner retinal nerve cells continue to function even after vision has been lost. For this reason, 2 different approaches have been explored for restoring vision. The first involves epiretinal implantation of electrode arrays. These arrays interface with retinal ganglion cells forming the retinal output pathway. This approach requires external image and processing because it bypasses retinal image analysis.

The clinical trials in the United Kingdom and Hong Kong involve the second technology, the implantation of a 3 × 3-mm, 1500-electrode microchip below the retina, in the macular region. This type of microchip senses the light of an image and translates it, point by point, into small currents proportional to the light. Each electrode contains a photodiode amplifier electrode set within a single pixel that stimulates nearby neurons, closely resembling normal visual signals.

"It's undoubtedly very exciting. If you think of these patients who've really not got very many alternatives, and the patients we're treating have got the worst end of the spectrum in terms of their disease, so they have no vision at all. Any gain of any vision at all in this context is really quite exciting," said Dr. Jackson in a telephone interview with Medscape Medical News.

"The other thing that I find very interesting is that it's a treatment that's built around technology, and we all appreciate how quickly technology can advance, so there's the prospect that as the technology gets better, so too will the potential outcomes," Dr. Jackson said.

"One thing that I particularly like about this technology is that it's a very elegant design, in that they're not reliant on an external camera — it uses the focusing and optical powers of the eye, [and] it uses the natural eye movement as well. Although the surgery is technically quite difficult (it's a long operation), in the long term, this could be a winning strategy," Dr. Jackson noted.

The operation takes about 9 hours and requires maxillofacial surgeons; ear, nose, and throat surgeons; and ophthalmic surgeons.

Dr. Jackson is very pleased with his patient's progress. "The chip was nicely placed where we wanted it to be, and there weren't any real problems at all. As soon as we turned the chip on inside his eye, he could see the light that comes from it. Already, he's able to look at a table with objects on it — a plate, or a knife, or something like that — and recognize it," Dr. Jackson said. The patient also could sometimes, but not always, tell the time on the image of a clock when it was placed on a table in front of him.

The patient has been in touch with another patient from the earlier German trial who now has "quite fantastic vision, and can even read large letters." That patient's vision was about the same as the current patient's vision when she was at this stage in her recovery, Dr. Jackson said.

"The vision that these people have is not like the vision that they had when they were younger. It's a different quality of vision, and they've got to learn how to interpret that vision...it's a bit like learning a new language. He doesn't see what he saw before, but he does have image," Dr. Jackson said.

Dr. Jackson added that larger trials will be necessary to further determine how this technology will work. "It's early days. I wouldn't want this to be portrayed as a finished product or something that is ready to be rolled out nationwide," Dr. Jackson said. "It's a lot more than a proof of principle, it's showing that already, an artificial vision is possible."

K. Bailey Freund, MD, clinical correspondent with the American Academy of Ophthalmology, told Medscape Medical News in a telephone interview that he is cautiously optimistic about this technology. Dr. Freund is a retina specialist at Vitreous Retina Macula Consultants and a clinical associate professor of ophthalmology at New York University School of Medicine in New York City.

"We'll have to see how these patients do in the long term and what kind of visual function they achieve," said Dr. Freund.

"We'll want to see the results presented in a peer-reviewed publication or at meetings so we can critically assess what sort of visual response we're really getting," Dr. Freund said.

He cautions that what is being referred to as useful vision is much different than what people might assume. "We're talking about very crude vision with this device," he said.

Nevertheless, Dr. Freund is excited about the technology, and he expects that it will evolve over time.

The researchers and Dr. Freund have disclosed no relevant financial relationships.

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