Retinal implants may soon restore lost vision

Researchers are working on ways to implant tiny electrodes in the eye and help restore vision to the blind. Images: Retinal implants

For those who've lost their sight to retinal disease, there may be light at the end of the tunnel.

Researchers are making headway on high-tech fixes that would use implants to restore vision to the 25 million around the world who live in darkness because of retinal disease. Some of those implants could move from testing to the marketplace within just a few years.

The efforts are under way at a combination of universities, government agencies and private companies in the U.S., Belgium, Japan and Australia, among other countries.

At the end of this month, the efforts will be measured against each other when thousands of vision researchers gather at ARVO 2006, the annual meeting of the Association for Research in Vision and Ophthalmology, in Fort Lauderdale, Fla.

"There is a phenomenal race going on," said Gerald Chader, chief scientific officer at the Doheny Eye Institute at the University of Southern California. "Some of the more rudimentary implants are going to get out on the market fairly soon, and they are going to be really useful."

One of the U.S. efforts is the Boston Retinal Implant Project, which is affiliated with the Massachusetts Institute of Technology. The group is designing a wireless retinal prosthesis, intended to trick the brain into seeing by pinging it with electrical signals.

"Ears and eyes communicate what they sense from the external world to the brain using neural signals--electrical pulses that travel through the nerves," said Luke Theogarajan, an engineer working on the project. "The brain takes the electrical information, does some computations and says, 'Oh yes, this is your grandmother' or 'I heard this song on the radio yesterday.'"

The signals are fired when the photoreceptors--rods and cones--in the retina are hit by light from outside. Diseases such as retinitis pigmentosa and age-related macular degeneration cause the photoreceptors to die, which means that light is never translated into electricity.

Retinal nerve cells leading to the brain, however, remain intact.

"If you can make these cells fire in a specific fashion, the brain will process the information coming through the optic nerve as vision. You can mimic it by exciting remaining, healthy layers of neurons with current pulses," Theogarajan said.

The MIT fix is an artificial retina consisting of a small plate of electrodes, 1.2 millimeters wide, that's implanted in the eye. The person with the implants wears a pair of glasses linked to a video camera. A processor translates the visual information into radio signals, which are sent to a chip attached to the white of the eye. This chip communicates wirelessly with the retinal electrodes inside, and commands them to fire current pulses. Everything is powered by a battery pack at the belt of the carrier.

Researchers in Belgium and the Netherlands are also working on a technique involving video cameras.

"The idea is to give back some of the freedom and independence that the blind have lost, like being able to cross the street and eventually maybe read a newspaper with large print," Theogarajan said, emphasizing that these are complex tasks. "Our first goal is to make daily life easier, to detect edges and motion."

So far, the Boston Retinal Implant Project has only implanted the electrodes into animals, but other projects have gone further.

"The idea is to give back some of the freedom and independence that the blind have lost, like being able to cross the street and eventually maybe read a newspaper with large print."
--Luke Theogarajan, engineer, Boston Retinal Implant Project

A research project led by the Doheny Eye Institute has put similar implants in human volunteers, allowing them to detect lights being on or off, locate objects and describe how they move, and recognize simple shapes like a capital L.

The implanted chip has 16 electrodes, but more will be added to enable advanced seeing, Chader said. "We have done simulations. We know the level that will restore mobility, face recognition or reading the fine print in the New York Times."

Such abilities will take 1,000 electrodes and 10 more years, Chader said. Still, he's already bombarded with requests from volunteers who want to try the current, more primitive chip, although it requires six hours in surgery.

The chip in the eye connects via a wire underneath the skin to a processor implanted behind the ear. "A lot of plumbing, a lot of wiring is necessary at this point," Chader said. He, too, is aiming for a wireless system eventually.

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