Electronic Design

MEMS-Based Imaging System Will Restore Sight To The Blind

Researchers at five national labs, two universities, and a private company have joined forces in an effort to enable the blind to see. They hope to use MEMS technology to combat disorders like age-related macular degeneration and retinitis pigmentosa, which affect hundreds of thousands of people in the U.S. each year.

These disorders blind their victims by damaging the light-gathering cells in the eye. The researchers hope to implant MEMS chips with thousands of electrodes directly on the retina, essentially replacing the damaged cells. The implant would receive signals broadcast by a tiny camera and RF transmitter on the patient's glasses and stimulate the nerve endings in the retina accordingly to produce the effect of sight (see the figure).

"Compared to the elegance of the original biological design, what we're doing is extremely crude," says project leader Kurt Wessendorf of Sandia National Laboratories. Rods and cones—the light-gathering cells in the retina—and their nerve connections are in the micron range. At this point, the researchers lack the technology for one-to-one replacement of electrodes to cells. But they are getting closer.

"We'll use a crude, shotgun approach that fires groups of nerves," explains Sandia manager Mike Daily. "In the long run, of course, we'd like to stimulate each individual nerve." The project is aiming for 10-by-10 electrode arrays by the end of the year, with 33-by-33 arrays expected by 2004. With these sizes, patients will see the equivalent of 1000 points of light.

"The aim is to bring a blind person to the point where he or she can read, move around objects in the house, and do basic chores," Wessendorf says. "They won't be able to drive cars, at least in the near future, because instead of millions of pixels, they'll see approximately a thousand. The images will come slowly and appear yellow, but people who are blind will see."

The MEMS package is key. It must ensure high-reliability operation in a saline environment for decades, Daily notes. The chip is made of LIGA (a German acronym for lithography, electroplating, and molding) and surface-micromachined silicon parts. Argonne National Laboratory is investigating the viability of diamond-based electrode arrays and biocompatible coatings. Lawrence Livermore National Laboratory is experimenting with rubberized electrode arrays.

The retina must be protected as well, as it can't handle much pressure. Sandia's researchers are counting on spring-loaded electrodes that ensure good contact with minimal force. Also, protein fouling can disturb interfaces intended to transmit electrical impulses. Biocompatibility, or whether or not the body will accept alien matter, is another issue.

Over the next five years, the researchers will begin with goggles and move toward corneal implants. If all goes well, five patients could be prepared for the procedure before the project is completed. The project began at Johns Hopkins University under Mark Humayun, who then founded the Intraocular Retinal Prosthesis Group at Doheny Retina Institute at the University of Southern California. It is now funded by a $9 million, three-year grant from the Department of Energy's Office of Biological Research.

Oak Ridge National Laboratory is managing the multilab effort and testing the components that the other labs develop. Los Alamos National Laboratory is modeling and simulating the neural paths of and from the retina to the brain. Second Sight of Santa Clara, Calif., will commercially produce the finished system. For more information, go to www.sandia.gov.

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