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Retinal implants could restore partial vision

In lab tests on rat retinas, a photovoltaic chip helps display images through special goggles

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4:09pm, May 13, 2012
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Specialized goggles that send information to solar cell–like chips implanted in the eyes may one day help some blind people see. The new implants, which have been tested in rat retinas in a dish, would require less invasive surgery than similar devices now being tested and offer a higher-resolution view of the world.

The new system, reported online May 13 in Nature Photonics, still needs work before being tested in people. But one day it may return partial sight to people suffering from conditions such as retinitis pigmentosa, an inherited disease that can lead to night blindness and tunnel vision, or macular degeneration, in which sharp central vision is lost but peripheral vision remains.

In those conditions, vision suffers when light-detecting cells at the back of the inner eye are damaged, even though the nerve cells that send visual information to the brain may remain intact.

No current treatments can restore vision for such retinal damage, says Lotfi Merabet, an eye specialist at Massachusetts Eye and Ear in Boston. The new work “is certainly very promising,” he says.

Developing the implants took many years and many scientists, says study coauthor James Loudin, an electrical engineer at Stanford University. “The sheer number of new technologies that had to be developed — it’s amazing,” he says.

For starters, there are the goggles. A miniature video camera sits on the nosepiece, watching the world. Information from the camera streams to a portable computer about the size of a smartphone. This computer processes the video images, which are projected into the eyes by near-infrared lasers on the insides of the goggle lenses. The laser hits slender photovoltaic chips implanted beneath the retinas, which convert the light into electrical current, stimulating nerve cells that send information to the brain.

Other labs have also designed retinal prostheses; one has been approved for use in Europe, and another is in clinical trials. But these systems transmit information and power via coils and wiring that have to be surgically implanted along with the retinal chip. Most of the hardware for the new prosthetics is in the goggles, so only the thin solar cell–like chip needs to be implanted. And because the new chip has three photodiodes per pixel rather than one, the image resolution should be better than that of other devices.

The team was concerned that the laser light, which is far brighter than the light that working eyes see on a sunny day, would generate potentially damaging heat, says Loudin. But tests show that the heat is one-hundredth of the established ocular safety limit.

With that issue resolved, the researchers are now testing the system on living rats.

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