Insert an artificial retina // or replace a malfunctioning gene // or infuse a cocktail of stem cells // then open your eyes to advances in the field of vision.
Restoring Vision: Hope in Sight
Jamie Chung for Proto
How many electrodes can fit on the back of an eye? For the scientists who have spent the past 20 years competing to create a sight-restoring artificial retina, the question is hardly metaphysical. Taking inspiration from the cochlear implant, a device that stimulates the auditory nerve to produce sound the deaf can make sense of, the inventors of visual prostheses think they can prompt healthy cells in the retina to send visual information to the brain. One design uses a tiny camera mounted in eyeglasses to capture images, which are then sent to a video processor worn at the waist that converts them to light and dark pixels—like those that create images on electronic scoreboards. The signals are transmitted to electrodes implanted in the retina and thence along the optic nerve to the brain.
The 50 or so people who have received artificial retinal implants say they can now differentiate walls from windows, detect whether a computer monitor is on, point to the location of a person standing silently in a room and sort dark socks from white ones. Such achievements would represent a major advance in accomplishing what long has seemed beyond hope: restoring sight to the sightless. But some of these cases involve people who had some vision before the implant, making it difficult to know if the devices improved their vision, says neurologist and ophthalmologist Joseph Rizzo, director of neuro-ophthalmology at the Massachusetts Eye and Ear Infirmary and director of the Center for Innovative Visual Rehabilitation at the VA Boston Health Care System.
“It is utterly clear that people who have been blind for decades can see something when you stimulate the retina,” says Rizzo, who in the late 1980s was the first scientist to receive funding for work on an artificial retina. “But there is no evidence that the vision we’re able to create at this point provides enough detail to really make a difference in someone’s life.”
And so, more electrodes. The first generation of artificial retinas, created in the past decade, had as few as 16, while the most advanced current devices have 64. Each electrical contact stimulates cells in the eye—so additional electrodes mean more stimulation and, perhaps, better vision. Typically, the electrodes are embedded in a substrate that is many times thinner than a human hair. This tiny electronic component can be tacked to the front of the retina or slid behind it. Now Rizzo and others are developing prototypes that pack as many as 200 electrodes onto the device. “With 200, people may be able to find the sidewalk and see cars, so they can safely navigate in an unfamiliar environment without a cane or a guide dog,” says Rizzo, who predicts the device will be ready for clinical trials as early as 2011. “Being able to do those things would be a stunningly large accomplishment.”
But if 200 electrodes are good, 1,000 could be much better, suggests Mark S. Humayun, a biomedical engineer and ophthalmologist who serves as associate director of research at the Doheny Retina Institute at the University of Southern California. Humayun expects to produce a 1,000-electrode artificial retina within five years and thinks such a device will enable formerly blind people to read and recognize faces. With each additional electrode, however, comes one more microscopic hole through the chip—a potential source of failure if it provides an opening for the corrosive saltwater of the eye. Electrodes also generate heat, which can burn the eye, and having a denser array increases “cross talk” among the electrodes that may interfere with signals to the optic nerve and brain.
Even surmounting those obstacles will take this technology only so far. Being able to stimulate retinal cells in a way the brain can fully comprehend is the ultimate goal, and although Rizzo thinks scientists will someday find their way across, that could take another two decades. Fortunately, people already losing sight probably won’t have to wait that long for vision repair advances. Gene therapy—once considered a potentially all-powerful therapeutic tool but then widely viewed as generally ineffective and possibly dangerous—has shown great promise in treating one rare eye disease and could be applied more broadly as more genetic targets are identified. New drugs, including one now used effectively against age-related macular degeneration—which affects an estimated 10 million people in the United States—may provide another way to attack vision loss. And work on reprogramming stem cells, though still at an early stage, might eventually provide yet another avenue for re-creating retinal cells and restoring sight. This steady drumbeat of breakthroughs during the past five years has led scientists to hope that treating and even curing devastating eye diseases involving the retina may now be within reach.