FRIDAY, Feb. 16, 2007 (HealthDay News) -- U.S. researchers say a new high-tech implant is restoring at least some sight to people blinded by eye disease.
The device -- known as the Argus II Retinal Prosthesis System -- is an updated and more powerful version of an electronic retinal implant that has been the subject of ongoing clinical trials since 2002.
Speaking in San Francisco on Thursday at the annual meeting of the American Association for the Advancement of Science, the device's developers announced that the U.S. Food and Drug Administration had recently granted approval for a new clinical trial of the technology.
The prototype artificial retina used an array of 16 electrodes surgically inserted into a diseased eye to function as light-sensitive surrogates for damaged retinal photoreceptor cells.
Implants of this original configuration were able to give six blind patients the limited ability to distinguish light, perceive motion, and identify general shapes and objects.
The second generation retinal prosthesis will be fitted with 60 electrodes -- an increase that the researchers say will offer the blind the opportunity to acquire higher-resolution sight.
"Our work to date with our retinal prosthesis has exceeded all expectations we had, and we are very excited and look forward to the results from our 60-channel implant," said lead researcher Dr. Mark Humayun, an ophthalmology professor at the Doheny Eye Institute of the University of Southern California's Keck School of Medicine in Los Angeles.
He said that clinical trials of the newest generation of retinal prosthesis will begin later this year.
The technology is being targeted at both young and elderly patients blinded by either retinitis pigmentosa or macular degeneration. Approximately 25 million people, six million in the United States alone, have lost most or all of their vision to such diseases, a figure Humayun said researchers expect will double by 2020.
The term "retinitis pigmentosa" (RP) refers to a number of hereditary eye diseases characterized by the slow deterioration of retinal receptor cells, known as rods and cones. Such cells are key in capturing and translating light into an electrical pulse, which the brain then interprets as an image.
Usually striking early in life, the condition most commonly results in the uncorrectable loss of peripheral vision and color perception.
By contrast, macular degeneration (MD) involves damage to the center of the retina and the loss of central vision, rendering the patient unable to focus clearly on objects straight ahead. Over time, reading, driving, and face recognition are all severely impaired by this incurable disease, which has no known cause and is most common among the elderly. By some estimates, more than 10 million Americans are currently afflicted with the illness.
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.
