New experiments on light-powered bionic eye

Even at the initial stage, a new prosthesis could restore sight to millions of people with retinal disease A pair of special eyeglasses and microchips like solar panels fitted directly in the retina. This is the technology that in just a few years' time could restore sight to people with such serious retinal diseases as age-related macular degeneration or retinal pigmentosa. The complex device was devised by a group of researchers from the department of ophthalmology at Stanford University School of Medicine, which just recently published in the journal Nature Photonics the outcome of the first experiments conducted on biological tissue. The results are so promising that the team has already begun experimenting on laboratory rats.   EYEGLASSES AND SOLAR PANELS – The integrated system devised by the American researchers attempts to compensate for the progressive degeneration of the retinal cells that capture light before the latter is sent to the brain in the form of electric impulses. Diseases like age-related senile macular degeneration or retinal pigmentosa damage the receptors but leave the nerve endings almost intact. The aim of the new prosthesis is to find sources other than visible light to stimulate these neurons. This is why the team has prepared a pair of special eyeglasses. They are fitted with a micro-camera and a system that projects the captured images onto a liquid crystal display located behind the lenses. But the display has a special feature: the projected images are not captured by normal visible light, but by pulsed light with a near infrared wavelength. And this is just the outside of the prosthesis. The other essential component is a microscopic chip about 3mm in diameter that is surgically implanted on the retina. «It works in exactly the same way as a solar panel on a roof», explained project coordinator Daniel Palanker. «It converts light into electric current. But instead of sending it to a refrigerator, it goes to the retina». The researchers hope that from there the stimulus will pass through the network of nerve endings in the deepest retinal layer to reach the brain and restore the ability to see.   SIGNAL RECEIVED – This is the complex system of devices that the researchers have used in experiments on healthy and damaged retinal tissue. With healthy tissue, they observed that the mini solar panel was able to receive images transmitted by the visible light spectrum as well as the near infrared spectrum and stimulated the nerve cells that capture these signals. With damaged tissue, it worked only with the information transmitted by the near infrared spectrum. «This means that our vision system is restored», commented Palanker, albeit with cautious optimism. Although this and other devices can help to restore sight, it is still not known what the quality will be. For example, the researcher explained, it is not possible to see color with currently available technologies. In healthy people, the system for capturing colors is managed inside the retina by various cell populations that specialize in receiving individual primary colors. A complex system that current devices are still unable to reproduce. In other words, the result could be very different from normal vision. However, it is progress that will be important for millions of people. This is why the team is forging ahead. The new prosthesis is already being tested on laboratory rats that will be observed for six months, and the researchers say that the first results suggest that the system works. But it will take many years before the prosthesis can be tested on people. Only then will it be understood whether the system's ability to transform reality into electric signals received by the brain will effectively restore sight.   Source: Corriere della Sera