MEMS Chip Could See for the Blind

Enabling the blind to see — a task once thought the province of miracles — is the goal of a technical team that includes Sandia National Laboratories (Albuquerque, N.M.), four other national labs, a private company, and two universities.

The lead lab, Oak Ridge National Laboratory (Oak Ridge, Tenn.), will manage the multi-laboratory effort as well as test the various components developed by the other labs. Argonne National Laboratory (Argonne, Ill.) will investigate the viability of diamond-based electrode arrays and biocompatible coatings; Lawrence Livermore National Laboratory (Livermore, Calif.) will experiment with rubberized electrode arrays; and Los Alamos National Laboratory (Los Alamos, N.M.) will model and simulate neural paths of and from the retina to the brain. Personnel from the University of Southern California (Los Angeles) will implant the devices and test their medical effectiveness. Second Sight (Santa Clarita, Calif.), will commercially produce the finished system. North Carolina State University (Raleigh, N.C.) leads the development of the in situ medical electronics.

A prototype of the MEMS-based array that eventually may be inserted onto the retina of a blind patient. (Source: Sandia)

"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 household chores," said Sandia project leader Kurt Wessendorf. "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 a little slowly and appear yellow. But people who are blind will see."

The plan is to use a tiny camera and radio-frequency transmitter lodged in the frame of a patient's glasses to transmit information and power to modules placed within the eyeball. The modules will be linked to retinal nerves that will send electrical impulses to the brain for processing.

"We felt that blindness is a devastating problem and that the modern conjunction of materials science with micro- and nanotechnologies in our multidisciplinary national labs offers possibilities for advances where before people had hit brick walls," said Dean Cole, a biomedical engineer who directs the project at BER. The Sandia approach is to attach a MEMS chip on the retina — that is, within the vitreous humor of the eyeball — made of LIGA and surface micromachined silicon parts. (LIGA, a German acronym for lithography, electroplating and molding, makes small parts of metal, plastic, or ceramics.) The idea is to directly stimulate some of the nerve endings within the retina to produce images good enough to read large print and distinguish between objects in a room.

"Compared to the elegance of the original biological design, what we're doing is extremely crude," Wessendorf said. "We are trying to build retinal implants in the form of electrode arrays that sit on the retina and stimulate the nerves that the eye's rods and cones formerly served."

The size of cones and rods, as well as nerve connections, are in the micron range — a difficult but doable realm for scientists used to working with micromachines.

"We'll use a crude, shotgun approach that fires groups of nerves. In the long run, of course, we'd like to stimulate each individual nerve," said Sandia manager Mike Daily.

Goals of the project increase from 10 × 10 electrode arrays for fiscal year 2002 to 33 × 33 arrays for fiscal year 2004.

"Integrating microdevices into the human eye is incredibly challenging because of the need for high-reliability operation over decades in a saline environment," Daily said. "BioMEMS interfaces and biocompatibility issues drive much of the effort, particularly in the packaging of the microsystem." Packaging refers to sealing and securing a microdevice in place and linking it electronically and physically with its environment.

Counterintuitively, the rods and cones of the retina lie beneath nerves, not above them, which makes it slightly easier to connect directly to the nerves.

“The tissue housing the nerves is relatively clear. We’re investigating which electronic waveforms will best stimulate these nerves,” Wessendorf said. One problem, he explained, is that “if we excite a nerve with electrons, we don’t know exactly how that compares to the electrochemical response of light on a healthy retina.”

There are other issues, he added. For one, the retina can’t handle much pressure. Thus Sandia favors spring-loaded electrodes that ensure good electrode contact with minimal force. Also, protein fouling can mess up delicate interfaces intended to transmit electrical impulses. Other problems include biocompatibility and long-term reliability.

The project, underway since October 2001, is expected to identify the most promising implantation technologies. Over a five-year period, the project will begin with goggles and move in the direction of corneal implants, Cole said. If all goes well, plans are to prepare five patients for the procedure before the project’s end. After that, “the FDA will say they want 100 patients for long-term studies, and DOE will get out and leave the project in the hands of industry,” he added.

Sandia is receiving $400,000 each year for its part in the research, which is being led by Wessendorf and co-inventors Murat Okandan, David Stein and Michael Rightley.