Electronic implants that would help in restoring vision to people with retinal dystrophy-a hereditary or age-related condition that leads to blindness-may soon become a reality, thanks to US and German scientists.
The condition causes degeneration of the photoreceptors - light-sensitive cells in the retina-and leads to blindness.
Eberthart Zrenner and colleagues at the University of Tubingen in Germany have developed a microchip carrying 1500 photosensitive diodes that slides into the retina where the photoreceptors would normally be, reports New Scientist.
The diodes respond to light, and when connected to an outside power source through a wire into the eye, can stimulate the nearby nerves that normally pass signals to the brain, mimicking healthy photoreceptors.
The team reported that their first three volunteers could all locate bright objects. One could recognise normal objects and read large words. Nerves in the eye normally adapt to visual input and stop transmitting signals after a short time.
Tiny movements of the eye overcome this by constantly projecting the image back and forth between neighbouring nerve cells so that each has time to recover and resume transmitting signals.
Another device being tested sends images from a head-mounted camera to ocular nerves, but as the image forms outside the eye the tiny movements cannot maintain it and patients must rapidly shake their head instead.
In this first pilot study, the team removed the devices after a few weeks as a safety precaution. But they have designed a new system, which can be implanted permanently when approved.