Retinal Implant Restores Limited Sight to Blind

Both the original and current versions of the retinal implants, each manufactured by study co-sponsor Second Sight Medical Products, are designed to communicate with an external camera and computer.

The implant patient is outfitted with a pair of glasses rigged with a video camera. The camera records incoming visuals and transmits the sights by wire to a customized computer for processing. The data is, in turn, sent wirelessly directly to the implant, whose electrodes decode the message into an electrical impulse that can be directed to the brain for visual interpretation.

The second-generation study will focus on patients over the age of 50 who once had healthy vision before contracting either RP or MD.

The researchers expressed enthusiasm about the new device's prospects, noting that this suped-up version will bring also faster implant and recovery times, because it is just one-quarter the size of the original model.

However, Dr. John Loewenstein, an associate chief of ophthalmology with the Massachusetts Eye and Ear Infirmary in Boston, cautioned that even these cutting-edge technologies cannot promise anything like complete eyesight.

"This is by no means a slam-dunk, in the sense that it will provide true vision in the way we usually think about it," said Loewenstein, who is also an associate professor at Harvard Medical School and involved in similar work.

"I don't want to denigrate the work, and this is a beginning," he said. "But the retina's electrical transmission process is very sophisticated, and we simply don't yet understand the language well enough to simulate it."

Loewenstein added that he has seen no evidence to suggest that electrode technology is yet poised to replicate the retina's complexity.

"When we put those electrodes in and stimulate the retina, people can see spots of light," he explained. "But we have not yet succeeded in translating those spots of light into true images. The analogy is to a scoreboard with individual light bulbs lined up to make up a '1' or a '2' or an 'A' or a 'B'. A person with normal vision can interpret all the bulbs as a whole to construe a letter or number. And we have all hoped, naively, that we could mimic this ability with a prosthesis. But, so far, it just hasn't worked out that way."

Jim Weiland , a member of Humayun's research team and an associate professor of ophthalmology, agreed there are many obstacles on the path toward full sight restoration. But he remains optimistic.

"Yes, it's true that how we stimulate the retina to convey useful information is still an open question," Weiland acknowledged. "So, this device is not something that's going to replace the natural vision that you and I have. But I do expect that there will be some benefit that a completely blind person may derive from this device, in terms of providing some ability to make out imagery and navigate about."

"Of course, this benefit has to be proven in a trial," added Weiland. "We think we're on the right road. But we still have a lot of work to do."

More information

For more on retinitis pigmentosa, head to the Foundation Fighting Blindness.

SOURCES: Mark Humayun, M.D., Ph.D., professor, ophthalmology, University of Southern California's Keck School of Medicine, Los Angeles; Jim Weiland, Ph.D., assistant professor, ophthalmology, USC's Keck School of Medicine, Los Angeles; John Loewenstein, M.D., associate chief, ophthalmology, Massachusetts Eye and Ear Infirmary, and associate professor, Harvard Medical School, Boston; Feb. 15, 2007, presentation, American Association for the Advancement of Science annual meeting, San Francisco