electric visuals

Eyesight to the Blind

by Pearl Tesler

Age, genetics, or sheer bad luck can land you among the 285 million people worldwide who are visually impaired. Among older adults in the Western world, the leading cause of blindness is degeneration of the photoreceptors in the eye—as in macular degeneration and retinitis pigmentosa.

Forming the top layer of the retina, photoreceptors are the screen on which the movie of your life plays. This thin, precious layer of cells detects light and converts it into electrical impulses that the visual system can understand. When the photoreceptors die, vision dies with them.

So far, stem cell therapy—so promising in theory—has failed to deliver any cures. Yet hope is taking clearer and clearer shape, in the form of tiny photovoltaic tiles that could do for vision what cochlear implants have done for hearing.

Speaking last week at the AAAS Annual Meeting in San Jose, Daniel Palanker of Stanford University explained the new prosthetic vision technology, successfully tested on rats.

First, tiny arrays of infrared-sensitive tiles—each just a millimeter across but bearing thousands of electrodes—are injected into the retina. Then, a pair of special glasses beams an infrared view of the world into your eye. Much as solar panels do, the tiles “see” the infrared light, converting it into electrical impulses that travel via existing neural pathways into the brain. Voila: Vision restored.

Unlike other prosthetic retinas, no power source is needed inside the eye—the infrared light from the glasses supplies all the energy. Why infrared? To work well, this light must be fiercely bright, 1,000 times normal. Blasting even an impaired eye with visible light this intense would be, well, blinding. Infrared light, however, is invisible to normal human photoreceptors.

The “installation” of the tiles is relatively non-invasive, in part because the tiles only need to be placed in a small region of the retina called the fovea, where photoreceptors are densely packed. “We live in a world of illusions,” says Palanker, “many of them created by the brain.” By constant jittering and shifting, our eyes keep the fovea darting this way and that, creating the illusion of a full-field view.

Human trials are scheduled to begin soon. Ultimately, by shrinking the size of the pixels on the tiles, Palanker expects the system could achieve visual acuities up to 20/100—not quite perfect, but a far sight better than blind.