FOCUS on...Visual Prostheses (Part 1)

"FOCUS on..." will be a periodic DeviceLine feature in which a specific part of the body or disease will be highlighted. Basic anatomy and physiology or pathology will be covered, followed by current research and companies that are developing devices."

We've come a long ways in helping visually-impaired people to see. Maybe not as far as Star Trek's Geordi LaForge, who even in early part of his career had far superior vision than most of his crewmates even with his VISOR, but technological advancements have given blind people opportunities for greater independence. In the near future, Braille could very well become less common as prostheses are being developed to allow people to see the real world around them.

Overview of Vision: Vision is accomplished by a coordination of motor and sensory systems in the eye. Ocular muscles move your eye to the desired target. Light reflected off this target enters the eye. The amount of light that enters is adjusted by the pupil, which changes in shape to allow more or less light to enter. The cornea refracts the light, while the lens also refracts the light and focuses the light more precisely through the eye. The image is then projected in an inverted fashion onto the retina, which contain specialized cells called photoreceptors. These photoreceptors are responsible for changing light into electrical signals that are sent to the brain.

Diseases of the Eye: Patients who use visual prostheses are usually diagnosed with age-related macular degeneration (AMD) or retinitis pigmentosa (RP). Both are related to damage to the retina.

AMD is the leading cause of blindness in western countries and is typically caused by abnormal deposits called drusen between the retina and the blood vessels in the back of the eye. The result is a slow, increasing loss of one's center of vision. Those with AMD never go totally blind, however, their perception is greatly impaired, as shown in the photo on the right. There is currently no cure, and laser treatment is the only current option available.

RP is a genetic eye condition that is the leading cause of inherited blindness. RP results in slow degradation of the photoreceptors in the retina, and can lead to total blindness. Those who suffer from RP typically begin to lose their peripheral vision, giving them tunnel vision that gets smaller and smaller over time (shown on left). There's currently no cure for RP.

While both AMD and RP currently don't have any cures, there are treatments being developed in the form of implantable prosthetic devices.

Tomorrow in Part 2, we'll look into some of the devices being developed for treatment of AMD and RP and the companies behind them, as well as engineering challenges for future devices.