During a videotaped procedure in 1994, surgeons put an electrode array into the eye of a blind patient, and while delivering small, controlled electrical pulses, asked what he could see.
"Well," replied the volunteer patient, "it was a black dot with a yellow ring around it."
Last spring, NSF-funded electrical engineering professor Wentai Liu and doctoral student Elliot McGucken created a microchip that will be used by the surgeons. Limited laboratory experiments have shown that this implant can expand artificial sight from the single dot in space to an array of pixels, like that of a television set. So far, the artificial retinal component chip (ARCC) has an array of 5 by 5 pixels--just enough to identify individual letters.
However, Liu, of North Carolina State University, and McGucken, of University of North Carolina at Chapel Hill, say that in the next five years the chip will grow to a 20 by 20 array, and may eventually hold a 250 by 250 array--enough to read a newspaper.
"There are very many complex engineering problems in this project," says Liu. "We had to consider biocompatibility of the device and how to provide a reliable power supply. We also had to design an electrical circuit that conforms to the biological specifications." Liu explains that he and McGucken work closely with doctors Mark Humayun and Eugene de Juan of Johns Hopkins University.
"The project is really a team effort," comments Humayun. "It's a marriage between biology and engineering."
The ARCC is designed to assist people who suffer from diseases that partially destroy the retinal photo sensors but leave the optic nerve and ganglion intact.
The retina, a membrane at the back of the eye, holds the eye's photo sensors--rods and cones--in place. The membrane also contains ganglion cells that interpret the messages from cones and rods and send them on to the brain via the optic nerve. In diseases such as retinitis pigmentation, the cones and rods are destroyed, but parts of the membrane and its ganglion cells survive.
The ARCC will use these remnants. Placed at the front of the damaged retina, the chip sends out electrical impulses to stimulate existing ganglion cells. The engineering team has suggested powering the chip through an external laser attached to a pair of glasses.
As for biocompatibility, researchers at Stanford University developed a new synthetic cell membrane that will adhere to both living cells and silicon chips. Liu told The Wall Street Journal, "It's an elegant solution that could prove useful to our work."
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