However, researchers still don’t know if they can control light levels, or even their color. Volunteers in the Hopkins studies, says Humayun, saw “yellow, green, and blue, but we haven’t figured out what we’re doing to generate those colors.” Nor do they know whether they can stimulate vision long-term, nor what the ideal current is, nor what amount of spatial resolution they can realistically hope for. To answer these questions, more sophisticated arrays need to be tested in people.
While Wyatt won’t forecast when he and Rizzo will be ready to do that, NCSU’s Liu says his group already has the three key elements-camera, external video processor, and an implant with 100 electrodes. Integration is the next step, says Liu, and he predicts that “within a year or two we will definitely have a completed device.”
Although the epiretinal approach appears to be the most advanced, it is not the only retinal repair system. Alan Chow, a Wheaton, Ill., ophthalmologist (and an alum of Wilmer Eye Institute) is working on a “subretinal” implant that he says will require no external camera, power source or transistors.
The subretinal implant, Chow explains, is a collection of microphotodiodes-think of the conventional solar cells that convert sunlight to electricity, except tinier-that will be implanted behind the retina. Chow’s idea is that as ambient light passes through the retina and strikes the microphotodiodes, they will generate enough electricity to activate healthy nerve cells. He figures that by electrifying cells upstream of the ganglion layer, his implant will take advantage of whatever signal processing capacity remains in the retina.
Chow’s prototype of what he calls the “Artificial Silicon Retina” is 3 millimeters in diameter, 25 micrometers thick, and contains more than 7,000 microphotodiodes. The results of tests in rabbits, says Chow, have been encouraging. “We were excited to find that the eye tolerated the chip very well, and it was able to stimulate the remaining cells to produce signals that seem to indicate that vision was being produced,” says Chow. But, he acknowledges, “while we know that some form of vision is being produced… we won’t know what is seen until we put this into a human.” He estimates that human tests could occur within two years.
Chow, who comes from a family of high-tech entrepreneurs, has raised $2.5 million from venture capitalists to fund his startup company, Optobionics Inc., which is developing his device. This success in the venture capital market may indicate that artificial eyes are ready to make the leap from academic research to corporate R&D project. So far, the Johns Hopkins/NCSU and Harvard/MIT teams have been surviving on research grants, but Humayun says “all the groups” are now looking for corporate allies to help with development. In Germany, a startup company named Intelligent Implants is working on a visual prosthesis based on technology from the University of Bonn, one of two retinal implant groups that the German government has funded with $10 million over five years.
Commercial interest is one indication of the excitement that recent progress has generated. Yet researchers in the field are trying hard to balance that excitement with a deep reluctance to raise false hopes among the blind. Today, all the researchers interviewed by TR say, there is no way to restore to a blind person anything that even remotely approximates normal sight. But the NIH’s Hambrecht observes that the scientific and technological fundamentals have now come into place to change that. Noting that it took cochlear implants about a decade to move from the “crude electrode” stage to commercial availability, Hambrecht puts vision prostheses on the market as early as “10 years from now.” Wyatt and Rizzo take a more conservative stance, arguing that “We don’t know if it will ever work, and if it does work, we don’t know when. Other people may tell you differently, but they don’t know either.”
Yet it is impossible to ignore the advances made so far-just ask Harold Churchey. Thinking back to the first experiments at Duke in 1992, he remembers vividly how “from the time they put that probe in my eye, I knew they were on the right track. That’s the first I’d seen anything in that eye for hard to tell how long.” For Churchey, seeing was believing-as it may ultimately be for many others.