For many blind or partially sighted people, implants that stimulate healthy nerve cells still connected to their retinas could help restore some normal vision. Researchers have been working on such implants since the 1980s with limited success. A major hurdle has been making an implant that can stay in the eye for years without declining in performance or causing inflammation.

Researchers with the Boston Retinal Implant Project, a 1988 spinoff from MIT, Harvard Medical School, and the Massachusetts Eye and Ear Infirmary, have developed hardware, they say, overcomes such issues.

In retinal diseases, such as acute macular degeneration and retinitis pigmentosa, light-sensing cells of the retina might no longer work, even though the neurons that carry signals from these cells to the brain are still healthy. The Boston project uses an array of electrodes to stimulate these cells and reproduce a simplified visual image in the subject's brain. A camera mounted on a pair of eyeglasses captures an image which is rapidly processed by a microcontroller to produce a simplified picture. This is wirelessly beamed to the implant, which activates 15 electrodes inside the eye. The implant also receives power wirelessly from the microcontroller.

In current form, the implant can reproduce only a 15-pixel image, but the group is working on a version with about 100 pixels, and hopes to eventually get to 1,000.

The latest implant has been successfully tested in pigs, whose eyes are comparable in size to human eyes. The electrode array has previously been tested for short periods in patients who reported seeing clouds, red spots, and other images when the electrodes were activated one by one. The device previously was housed in a flexible plastic case wrapped around the outside of the eye. But the plastic absorbed water over time. Electronics inside the new device are housed in a waterproof titanium case similar to those used for heart pacemakers. The new retinal implant case has a large number of feed-through holes for the wires that connect to the electrode array, the wireless power component and the data coil. The new case makes for easier, safer surgery because it sits on the side of the eye, away from the entry point for the electrode array.

Other retinal implants sit inside the eye, which can cause biocompatibility issues. Shawn Kelly, a visiting scientist at MIT, said a goal is to develop implants that last for years so patients can learn to process the images produced by the device.

Another arm of the Boston research group is working on algorithms for converting camera signals into images the brain more easily interprets. An initial goal is to let people see enough to walk unaided around a room. Hence, the system's software focuses on edge detection. The group is also working on algorithms that help people recognize faces. In the accompanying photo, the new retinal implant sits mostly outside the eye. The coil around the iris receives wireless power and image data from a microcontroller that can be carried on a belt. The coil transmits data to electronics inside a waterproof titanium case (below). The electronics controls an electrode array (not visible) connected to nerves in the back of the retina.