A BIONIC eye that can restore sight to the blind has been successfully tested on human patients, scientists announced yesterday.

The revolutionary implant, which has been fitted to three blind people in the United States, has enabled them to detect light and motion, to count objects and even to distinguish between different shapes.

The breakthrough, by the University of Southern California and the technology company Second Sight, offers new hope to millions of people around the world who have lost their vision to degenerative eye diseases.

It will particularly benefit patients with macular degeneration, which is the most common cause of blindness, affecting up to 15 per cent of over-75s, and those with retinitis pigmentosa, an incurable condition that afflicts one in 3,500 people.

The device was first implanted into a blind patient in February last year. Two more patients were given implants in July last year and March this year. The first positive results were revealed at the Association for Research in Vision and Ophthalmology’s annual conference in Fort Lauderdale, Florida.

Mark Humayun, Professor of Ophthalmology at the university’s Keck School of Medicine, who is leading the research, said: “We have found that the devices are electrically conducting, and can be used by the patients to detect light or even to distinguish between objects such as a cup and a plate.”

Successful trials had previously been conducted on dogs, but the university’s team is the first to implant a working version into the eye of a blind person.

The system works using a 4mm by 5mm chip made of silicon and platinum that is attached to a patient’s retina. The chip stands in for rod and cone light receptors that have been damaged by disease. It contains 16 electrodes, arranged in a four-by-four square, which stimulate the receptor cells that are still undamaged, in response to light. This coaxes the retinal cells to produce electrical impulses, conveying an image to the brain along the optic nerve.

At present, the retinal prosthesis does not process light falling directly on to the retina through the lens. Instead, the blind person wears a pair of glasses that hold a special video camera. The camera “sees” an object, then transmits the images to a radio receiver implanted behind the patient’s ear. The receiver then relays this signal on to the retinal chip, where the pattern of the original image is recreated by lighting up the appropriate electrodes.

Though there are only 16 electrodes in the chip, each can stimulate dozens of rod and cone cells. The result is an image which, although nowhere near as sharp as normal vision, allows the patient to see light, movement and even the outline of objects.

The research team aims to enlarge the implant, using up to 1,000 electrodes to produce sharper images and a wider field of vision. In the longer term, scientists also aim to replace the video camera element of the device with a corneal implant.

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