The original artificial retina had 16 electrodes; the current generation has 60. This is similar to the progress in digital cameras. In less than a decade the cameras went from 500,000 pixels to over 12 million pixels. The same future is being worked on for artificial retinas. The next generation will have hundreds of electrodes. The plan is for thousands.
Bionic eyes may soon follow bionic ears. Jo Ann Lewis lost her sight years ago to retinitis pigmentosa, a degenerative disease that destroys light-detecting cells in the eyes called rods and cones. Lately, however, she has partially regained her vision as a result of research by Mark Humayun, an ophthalmologist at the University of Southern California and a company called Second Sight.
As is common with this disease, part of an inner layer of her retina had survived. This layer, filled with bipolar and ganglion cells, normally gathers signals from outer rods and cones and passes them to fibers that fuse into the optic nerve. No one knew what language the inner retina spoke or how to feed it images it could understand. But in 1992, Humayun began laying, for a short time, a tiny electrode array on the retinas of RP patients undergoing surgery for other reasons.
“We asked them to follow a dot, and they could,” he says. “They could see rows, and they could see columns.” After another decade of testing, Humayun and his colleagues developed a system they dubbed Argus. (Greek mythology. A giant. Hundreds of eyes.) Patients got a pair of dark glasses with a tiny video camera mounted on them, along with a radio transmitter. Video signals were beamed to a computer worn on a belt, translated to electrical impulse patterns understood by ganglion cells, and then beamed to a receiver resting behind the ear. From there a wire took them inside the eye, to a square array of 16 electrodes gently attached to the retinal surface. The impulses triggered the electrodes. The electrodes triggered the cells. Then the brain did the rest, enabling these first patients to see edges and some coarse shapes.
In the fall of 2006 Humayun, Second Sight, and an international team increased the electrodes in the array to 60. Like a camera with more pixels, the new array produced a sharper image. Lewis, from Rockwall, Texas, was among the first to get one. “Now I’m able to see silhouettes of trees again,” she says. “That’s one of the last things I remember seeing naturally. Today I can see limbs sticking out this way and that.”
Pushing the neural prosthetic concept further, researchers are beginning to use it on the brain itself. Scientists behind a project called BrainGate are attempting to wire the motor cortex of completely immobilized patients directly into a computer so that patients can move remote objects with their minds. So far, test subjects have been able to move a cursor around a computer screen. Researchers are even planning to develop an artificial hippocampus, the part of the brain that stores memories, with the intent of implanting it in people with memory loss.
Not everything will work perfectly. One of the four initial BrainGate patients decided to have the plug removed because it interfered with other medical devices. And Jo Ann Lewis says her vision isn’t good enough for her to safely cross a street.