Electronic implant allows the blind to see

Groups in Germany and the US have been testing electronic implants aimed at restoring vision to people with retinal dystrophy. The condition is hereditary or age-related, and causes degeneration of the photoreceptors – light-sensitive cells in the retina – leading to blindness. It affects 15 million people worldwide.

Eberthart Zrenner and colleagues at the University of Tübingen in Germany have developed a microchip carrying 1500 photosensitive diodes that slides into the retina where the photoreceptors would normally be. The diodes respond to light, and when connected to an outside power source through a wire into the eye, can stimulate the nearby nerves that normally pass signals to the brain, mimicking healthy photoreceptors.

The team reports that their first three volunteers could all locate bright objects. One could recognise normal objects and read large words.

Nerves in the eye normally adapt to visual input and stop transmitting signals after a short time. 

Tiny movements of the eye overcome this by constantly projecting the image back and forth between neighbouring nerve cells so that each has time to recover and resume transmitting signals. Because the implant is inside the eye, this mechanism worked normally in the trials. Another device being tested sends images from a head-mounted camera to ocular nerves, but as the image forms outside the eye the tiny movements cannot maintain it and patients must rapidly shake their head instead.

As a safety precaution, the implants in this first pilot study were removed after several weeks, says Walter Wrobel, head of Retina-Implant, a company based in Reutlingen, Germany, formed by the researchers to eventually market the implant. "Based on the results of this study, we have designed a new system, which is being implanted permanently, or as long as patients like it."

In the new system, the power source connects to the retinal implant via a electromagnetic coupling through intact skin, not via a wire through an incision in the skin as the earlier system did. "That means they can shower easily, leave the hospital and go around town on their own," says Zrenner. "They can go out for a meal, and really see things, like a nice glass of beer."

 

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2010.1747

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