Adults suffering from retinitis pigmentosa, a condition that causes progressive damage to the retina, could be close to regaining their vision. That's thanks in part to the work of IEEE Member Mark S. Humayun. As the leader of the U.S. Department of Energy (DOE) Artificial Retina Project, Humayun has spent the past two decades developing what might be called a bionic eye. He expects promising results soon from a clinical trial that has been under way for almost three years.
Humayun, a professor of biomedical engineering and cell and neurobiology, is associate director of research at the Doheny Retina Institute at the University of Southern California, in Los Angeles. He is also director of USC’s Biomimetic MicroElectronic Systems Engineering Research Center.
Humayun and other researchers there have developed an eye system called Argus II, manufactured by Second Sight Medical Products, a retinal implant developer in Sylmar, Calif. With Argus II, a nonfunctioning retina in a human eye is outfitted with an array of electrodes that receive an image from a camera mounted on a pair of eyeglasses.
PATTERNS OF LIGHT
The system includes a tiny charge-coupled device camera and a microcomputer chip mounted in the eyeglasses, a receiver implanted behind the ear, and an electrode array implanted on the retina. A wireless battery pack on the person’s belt powers the system. The camera captures an image and sends it to the microprocessor, which converts it to an electronic signal that is transmitted wirelessly to the receiver. The receiver sends the signals wirelessly to the electrode array, stimulating it to emit electric pulses. Those pulses travel along the optic nerve to the brain, which perceives patterns of light and dark spots corresponding to the electrodes stimulated. Patients learn to interpret the visual patterns produced.
“Basically, the Argus II system wirelessly connects a camera to the patient’s retina and jump-starts the blind eye,” Humayun explains. The implant relies on 60 electrodes—the most of any long-term medical implant in the world, he says.
It is the first and only retinal implant that has received U.S. Food and Drug Administration (FDA) approval for testing. Results of a clinical trial of 32 patients, begun in 2007, are expected in the third quarter of this year, and Humayun says he is excited by the preliminary findings.
“Clinical trials typically require long-term follow-up before the devices can be approved for the general public,” he notes, “but because the trials are going so well, we anticipate FDA approval in the next year or so.”
In trials, patients who are totally blind have been given rudimentary sight. For example, they can tell the difference between dark and light socks, see a full moon or a fireworks display, and locate a door and walk to it. Humayun says his 60-electrode system could be ready to be implanted in blind people in a year or two, and could last several years before needing replacement.
It’s a breakthrough he has dreamed of for years, he says. He was inspired to work on restoring vision by his grandmother, who lost her vision when he was 28. “I’ve dedicated 25 years—all of my academic life—to the goal of restoring sight through an artificial microelectronic retina,” he says.
PACKING THEM IN
Humayun and his team faced countless challenges over the years in developing the system. The first one they built, Argus I, had 16 electrodes and much lower resolution. Humayun was the surgeon who implanted the first patient with that model in 2002. Packing in all those extra electrodes into the next model was no simple task, he says.
“Going from 16 to 60 electrodes is like creating a totally different system,” he says. “Unlike cameras, in which it’s relatively easy to go from 1 to 8 megapixels, for retinal devices it’s more like going from building a car to building an airplane. The higher density of electrodes puts enormous engineering challenges on the power supply, the electrode material, and their waterproof packaging.” The electronics must be waterproof because of moisture in the eye.
Humayun and his team have been working with researchers from the DOE’s national laboratories, the National Science Foundation, and Second Sight.
They’re not stopping at 60 electrodes. “We know a denser electrode array can yield a higher-resolution image,” Humayun says. “We’ve been working on a device that fits 1000 electrodes in the same space on the retina as Argus II. Such resolution could make it possible for the blind to read and recognize faces.”
But technical obstacles aren’t the only roadblocks the researchers face. “There are challenges with the surgery to implant the electronics in the eye and with teaching the patients how to use the device,” Humayun says. “But we’ve made a lot of progress in these areas.
“The day our first patient saw light has been the single most exciting day of my career," he continues." "As the technology improves it will make me even happier that such a device can improve the lives of people who were told they would never see again.”