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Stimulating Sight

Retinal implant could restore some vision to blind people
December 21, 2009

Inspired by the success of cochlear implants that can restore hearing to some deaf people, researchers at MIT are working on a retinal prosthesis that could one day help blind people regain a useful level of vision.

EYE SEE YOU In this model of the retinal implant, the coil surrounding the iris receives visual data from a camera mounted on glasses. A chip attached to the eyeball processes the data and sends it to electrodes implanted below the retina.

The eye implant is designed for people who suffer from retinitis pigmentosa or age-related macular degeneration, two of the leading causes of blindness. It would take over the function of lost retinal cells by electrically stimulating the nerve cells that normally carry visual input from the retina to the brain.

The device would not restore normal vision, but it could help blind people more easily navigate a room or walk down a sidewalk. “Anything that could help them see a little better and let them identify objects and move around a room would be an enormous help,” says Shawn Kelly ‘96, MEng ‘98, PhD ‘04, a researcher in MIT’s Research Laboratory for Electronics and a member of the Boston Retinal Implant Project, which has been working on the implant for more than 20 years.

Led by John Wyatt ‘68, an MIT professor of electrical engineering, the team recently reported a new prototype that they hope to start testing in blind patients within the next three years.

Patients would wear a pair of glasses outfitted with a camera that sends images to a microchip surgically attached to the eyeball. The microchip, in turn, would activate electrodes to stimulate nerve cells in the areas of the retina corresponding to the features of the visual scene. Those nerves would then carry signals to the brain, bypassing the damaged layers of retina.

One of the researchers’ biggest challenges is designing a surgical procedure and implant that won’t damage the eye. In the latest prototype, the electrodes are implanted behind the retina, reducing the risk of tearing it. The surgery required to place the electrodes in this location is also less invasive–one of the key differences between the MIT implant and retinal prostheses being developed by other research groups.

The new MIT prototype also encases the chip in a hermetically sealed titanium case; previous versions were encased in silicone, which would eventually allow water to seep in and damage the circuitry. The goal is to produce an implant that will last for at least 10 years.

So far, the prototypes have been successfully implanted for up to 10 months in Yucatan miniature pigs, which have roughly the same size eyeballs as humans. Further safety refinements must be made before human clinical trials can get under way.

Wyatt and Kelly say they hope that once human trials begin and blind patients can offer feedback on what they’re seeing, the researchers will learn much more about how to configure the chip to produce useful vision. Patients have said that what they would like most is the ability to recognize faces. “If they can recognize faces of people in a room,” says Kelly, “that brings them into the social environment as opposed to sitting there waiting for someone to talk to them.”

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