Israeli and American researchers from Stanford University are developing solar-powered retinae designed to cure blindness caused by retinal disease, by stimulating nerve cells in the eye.

The research is aimed at curing retinitis pigmentosa, an inherited, degenerative disease of the retina, the sensory membrane that lines the eye. Approximately one person in 4,000 suffers from the disease, which leads to total blindness, sometimes before the age of 60.

The research is support by a grant from the U.S. National Institutes of Health and the U.S. Air Force. The team is headed by Daniel Palanker, an Israeli scientist from Stanford's ophthalmology department.

According to researchers, the device, a super-thin silicon plate measuring one square milimeter and 30 microns thick, is implanted below the retina using a relatively simple surgical procedure. That plate includes hundreds of photovoltaic cells that convert sunlight into electricity.

An external camera is then affixed to a pair of glasses that capture the image and, much like Google Glass optical head-mounted display, project the image into the eye and increase the levels of light.

The plate receives the picture and converts it to signals which stimulate the retinal nerve. From that point on, the device acts much like a human eye, with the nerve cells sending the information to the brain.

Researchers have successfully tested the device on rats and published their findings in "Nature Communications" in June.

"Rats with prosthetic retinal implants display visual responses to light," the study states. "The rats elicit responses in the part of the brain responsible for visual processing, when the prostheses are stimulated by light."

Yossi Mandel, one of the lead researchers at Stanford, told Haaretz during a visit to Israel that the operation to implant the retinal prosthesis is relatively easy compared to the products currently available, and that one plate implanted below the retina allows rats to see as sharply as someone with naturally good vision.

Researchers predict that the use of several plates will allow blind people to see well enough to identify objects; to see facial features, albeit crudely; and to read large letters.

"Theoretically, applying the technology in humans will make it possible to insert on the floor of the eyeball several plates, allowing hundreds of cells to increase the field of vision to up to 30 percent of a regular eye."

The study determined that bionic vision using retinal prostheses is actually faster than normal vision. Rats with the implants registered brain signals within 15/1,000ths of a second, as compared to 45/1,000ths of a second among healthy rats.

"It's a significant difference," says Mandel. "Normal vision requires converting light into a signal to the nervous system, taking time to process biochemical processes in the body. The retinal prosthesis allows skipping the processing stage."

The researchers plan to expand the study to humans and are currently developing plates suitable for the human eye. "Because the implant surgery on the rats was easy, and its eye is five times smaller than that of humans, we predict the accompanying surgery will be relatively easy," Manel says.

Existing treatments to prevent blindness among retinitis pigmentosa patients, including those involving vitamins and stem cells, have so far failed to produce significant results.

Second Sight's Argus II Retinal Prosthesis System got the green light from the U.S. Food and Drug Administration in February after 15 years of research, becoming the first device approved by the FDA for restoring some functional vision to people suffering from blindness. The product is available in the United States and Europe for $100,000 to 100,000 euros.

The artificial retina, according to the company, "includes a miniature video camera housed in the patient's glasses, which captures a scene" and sends it to "a small patient-worn computer" to "bypass the damaged photoreceptors and stimulate the retina's remaining cells." Because the internal component transmitting the signal to the brain operates on energy absorbed by the external device, the Argus II is large and requires relatively complicated surgery. It provides a resolution of 60 pixels.

Retina Implant AG, a German start-up, is developing a retinal prosthesis that includes a wireless sub-retinal device that works without glasses. Instead, it provides electricity using a threaded wire on the inside of the skull which exits from a point in the scalp.

Other companies are developing similar products, including Israeli startup Nano Retina and Bionic Vision Australia.

The main cause of blindness among Israelis is a disease affecting the retina known as AMD (age-related macular degeneration). However, this disease, which affects more than 10 percent of people over the age of 60, is not a target for an artificial retinal implant because it mostly affects the edges and not the center of the retina, allowing limited vision similar to artificial retinae under development.