Scientists at the Institute for Ophthalmic Research at the University of Tübingen have succeeded in restoring vision to blind patients using tiny retinal implants embedded in the eye. They ran an experimental trial with a group of the blind volunteers, who had all lost their vision through hereditary retinal dystrophy but could still detect light. Nine patients have been fitted with an Alpha IMS device, the latest retinal prosthesis that can restore sight to blind people.
The scientists have surgically implanted a light-sensitive, externally powered microchip near the macular region. As a result three previously blind persons could locate bright objects on a dark table, two of which could make out grating patterns. One of these patients could correctly describe and name objects on a table, geometric patterns, different kinds of fruit and discern shades of grey with only 15 per cent contrast. Moreover, the regained visual functions enabled him to localize and approach persons in a room freely and to read large letters as complete words after several years of blindness.
The image above is showing the implanted chip with wires running to it from the retina, with a dial behind the ear that can be used to adjust brightness. It is powered wirelessly via a battery in the pocket.
Such devices work only in patients who have lost their vision through diseases such as retinitis pigmentosa that destroy the light-detecting cells in the eye but leave the vision-processing neurons intact. The devices send signals directly to the brain.
The Alpha IMS joins the Argus II – the only other visual prosthesis to have so far undergone clinical trials. The Argus II was approved by the US Food and Drug Administration and has also been adapted to allow blind people to read Braille by sight rather than touch.
But the two devices work very differently. The Argus II converts video from a camera on a pair of glasses into electronic signals “displayed” on a grid of 60 electrodes implanted over a person’s retina.
The Alpha IMS, on the other hand, detects light entering the eye instead of using an external camera, which means that a patient can look around by moving their eyes rather than always having to move their head.
It uses a grid of 1500 electrodes implanted underneath, rather than over, the retina: this offers higher resolution. It also makes use of the natural processing power of the neurons in the middle layer of the retina that process motion and contrast.