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Hitting the Nerve
Latest eye implant offers hope to people with damaged retinas
From the New Scientist
THE first complete artificial "eye" that taps directly into the optic nerve is due to be implanted into a blind woman within the next four months. The device could one day restore some vision to many blind people, including those whose retinas have been damaged or destroyed.
Developed at the Catholic University of Louvain in Belgium, the artificial eye provokes visual sensations in the brain by directly stimulating different parts of the optic nerve. Other experimental implants stimulate the ganglia cells on the retina or the visual cortex of the brain itself. But Claude Veraart of the Louvain team says these techniques require large numbers of electrodes to create recognisable imagery, making them extremely complicated to build.
Instead, the Belgian device has a coil that wraps around the optic nerve, with only four points of electrical contact. By shifting the phase and varying the strength of the signals, the coil can stimulate different parts of the optic nerve, rather like the way the electron guns in TVs are aimed at different parts of the screen. The video signals come from an external camera and are transmitted to the implant via a radio antenna and microchip beneath the skin just behind the ear (see Diagram).
Veraart and his colleagues have spent the past two years experimenting with a volunteer who has the electrode implanted, with wires leading out of her body to the signal processor. By asking her to point in response to various stimuli, Veraart and his colleague Charles Trullemans were able to map camera pixels onto the corresponding parts of her visual field. This was possible, says Veraart, because the subject was once sighted and knows what it means to "look at" something.
The researchers hope the device will at least allow blind people to avoid obstacles, though more tests are necessary before the device is implanted. Most critical is the time it takes to realise that an object is looming large. "If it takes her 30 seconds to recognise an obstacle it will be of little use," says Veraart. If she reacts quickly, the team plan to implant at least three more patients, starting in August.
Rebecca Griffith, health promotion officer for the Royal National Institute for the Blind, in London, welcomes the advance but is wary of raising people's hopes prematurely. "It's four months to the testing phase, not four months to public availability," she says.
From New Scientist magazine, 29 April 2000.
Date last modified 6/4/2000