The 1000-Electrode Array Retina Implant Gets Closer

“Retinal prostheses represent the best near-term hope for individuals with incurable blinding diseases of the outer retina,” said Dr Mark Humayun, a surgeon at the Doheny Eye Institute at the University of Southern California, Los Angeles, USA, who has implanted artificial retinas in patients.

A second-generation eye implant is currently being tested on 17 blind people in the US and Europe and more patients are being enrolled. Called, Argus Two and produced by Second Sight Medical Products, the implant has an array of 60 electrodes and provides a much sharper image to its users than its predecessor, says Brian Mech, the company’s Vice President. Patients report improvements in orientation and mobility: they were able to find a door from approximately 6 metres away and to follow a line on the floor for a similar distance.

The company produced the devices for the US Energy Department’s Artificial Retina Project, whose goal is to create sensitive devices that can be implanted in the eye and allow previously blind people to recognise faces and read large print. Researchers in the Energy Department’s National Laboratories are now creating a third-generation artificial retina. Much smaller than its predecessors, the device will contain 200 or more electrodes on a thin, flexible film that curves to fit the shape of the retina. Human tests are scheduled to begin in 2011.

“We’re aiming for a 1000-electrode array,” said Ray Orbach, the Department’s Undersecretary for Science. This device would “let a blind patient recognise objects and read large-scale newsprint,” Orbach told a scientific conference in December 2008.

Retinitis pigmentosa, which ruins peripheral vision, and macular degeneration, which causes a blurred or blind spot in central vision, affect millions of people, especially the elderly. Both diseases irreparably damage the retina. Tests of a relatively crude artificial retina began on six patients in 2002. This first-generation eye implant, Argus One, consisted of a tiny camera mounted on a pair of dark glasses and a hip-mounted microprocessor. The bionic gadget relayed images to a silicon chip containing an array of 16 electrodes that was surgically attached to the front of the retina. The electrodes created a 4 by 4 pattern of light and dark spots in the visual processing centre at the back of the brain.

With the aid of these devices, people who had been totally blind were able to read letters 30-cm high, tell a plate from a cup, find doors and windows and navigate around large objects. At first, patients saw only scattered bits of light. With this scant information and weeks or months of retraining they learned to make out straight lines, distinguish light areas from dark ones and detect motion. Argus One, although succeeded by the smaller, more sophisticated Argus Two, is still in use.

Artificial retinas remain experimental and will not be available for commercial use for years. The devices will cost at least $30 000, Mech said, and many technical problems remain. However, scientists are optimistic about the future of artificial retinas.

Source: www.physorg.com

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