19 December 2008—Researchers from three major California universities are working on an artificial retina that could give limited sight to people with degenerative diseases of the retina, such as macular degeneration. Such a prosthesis is a more realistic future treatment than stem-cell therapy, gene therapy, or eye transplants, its developers say. The Californian researchers have been treating people using a 60-pixel retina in a clinical trial for two years. But they are now gunning for a system with a resolution of 1000 pixels, they reported Tuesday at the IEEE International Electron Devices Meeting (IEDM), in San Francisco. And in contrast with systems in trials today, the researchers hope to develop a system that would be completely sealed into the eye, without any external components.
James Weiland, an associate professor of ophthalmology at the University of Southern California’s Biomimetic MicroElectronic Systems (BMES) Engineering Research Center, reported on an experimental system that includes a 1000-pixel test chip. He expects to have the high-res retina at a point where they can begin clinical trials in about five years.
In the artificial retina, a camera mounted on glasses outside the eye sends the visual signals to two RF coils inside the front half of the eye. An electronics module inside the eye’s vitreous humor—the gelatinous saline sac that fills the space between the lens of the eye and the retina at the back of the eye—translates the RF signals into voltages for use in the high-res retina chip. Lying against the retina is a grid of 1000 electrodes on a flexible substrate; these electrodes apply voltage signals to the retina, which interprets them as photons. The rest of the visual process takes place as usual, and the system mimics relatively normal vision.
The group, which includes researchers from the BMES center, the California Institute of Technology, in Pasadena, and the University of California, Santa Cruz, which developed earlier prototypes in collaboration with Second Sight Medical Products. The first was the Argus 16, with 16 electrodes; the next, Argus II, has 60. Both have been in clinical trials. The Argus II implant enabled blind clinical-test subjects to follow a straight line for about 6 meters without deviating from the path. But the key to a medical device’s ability to grant true independence is whether it allows the person to identify faces or read. Artificial-eye researchers estimate that such tasks will require between 600 and 1000 electrodes.
Ideally, that artificial retina would be contained entirely within a person’s eyeball. In order to create a fully self-contained high-resolution system, the team must consider many different pieces: a parylene coating to protect the prosthesis from the corrosive effects of being inside the body for 60 years or more, a flexible substrate that can conform to the idiosyncracies of different individuals’ retinal curves, and, most important, wireless power.
Instead of batteries, the device uses inductive coils that pick up energy transmitted from outside the body. The researchers are also relying on insights from MEMS fabrication: the implant coils, interconnects, and 1000 electrodes are formed during a single parylene micromachining process.
”This is a really breathtaking system,” says MIT electrical engineering professor Jesus del Alamo, who organized the panel at IEDM where Weiland discussed the group’s research. ”They have every piece of the system in place—they have even designed their own software.”
But there is more work to be done. ”You need to get everything into the eye,” says Jamal Deen, a professor of electrical and computer engineering at McMaster University, in Ontario, ”including the camera.”
So far, the camera, image-processing hardware, power amplifier, and data modulator are external, but Weiland hopes to implant even the camera part of the system by fixing it to the lens of the eye. His collaborators at USC are working on miniaturizing the camera system so that it can be placed onto the lens in a routine surgical procedure similar to cataract surgery. ”If we can make a camera the size of the lens, we can implant it there,” he says. ”But again, the challenge is making a self-contained camera without a larger control circuit.”
He cautions that it will take several years to put the whole system together and start clinical trials. But those trials will lean heavily on what is learned from trials of the implant being tested today. So potential patients should not wait for the new chip. ”The 1000-channel device is likely more than five years away from even starting clinical testing,” says Weiland. ”In the meantime, our 60-channel device has been in clinical trials for over two years, and sometimes we run into difficulty recruiting for the trial because some prospective participants are aware of the research efforts on higher-channel-count devices.”