Artificial vision is the use of special technology to give some vision to people without natural sight. Devices for artificial vision are largely experimental. However, scientists are working to develop functional models that will give some vision to certain people who would otherwise be blind.
Some artificial vision devices target the retina, the tissue lining the inside of the back of the eye. Light-sensitive cells in the retina—called rods and cones—_absorb light rays and change them into electrical signals. The signals are sent to the brain, which interprets them as visual images. Several diseases can damage the retina, causing _retinal degeneration that eventually leads to blindness. In some cases, disease causes the cones and rods to die but leaves undamaged other cells in the retina as well as the _optic nerve—_the retina’s connection to the brain. Patients in this condition may benefit from artificial vision systems implanted directly into the eye to restore sight.
One form of artificial vision, called a retinal prosthesis, uses small electrodes to stimulate certain cells in the retina. A surgeon places the electrodes in the back of the eye, in front of or behind the retina. In many designs an external camera, usually mounted in a pair of eyeglasses, captures visual imagery and relays it to a small computer. The computer sends radio or infrared signals to the implanted electrodes, which convert them to electrical signals. The stimulated retina cells send these signals to the brain, where they are interpreted as vision. Other designs do not require an external camera, and instead try to use the retinal implant as a more direct replacement for damaged rods and cones.
The image created by a retinal prosthesis appears as a pattern of lighted dots that are large and fuzzy. The retinal prosthesis cannot create a detailed picture, but it may help a blind person, for example, to find his or her way around obstacles and to locate objects at close range.
In patients with damaged optic nerves, signals cannot get from the eye to the portion of the brain responsible for vision. In these patients, physicians can implant electrodes directly in the brain to receive signals. In combination with an external camera and a computer, the electrodes stimulate brain cells to produce a crude image.
