THE first complete artificial 鈥渆ye鈥� 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
(快猫短视频, 7 November 1998, p 23, and
22 January 2000, p 6). 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).
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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 鈥渓ook at鈥�
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. 鈥淚f it
takes her 30 seconds to recognise an obstacle it will be of little use,鈥� 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鈥檚
hopes prematurely. 鈥淚t鈥檚 four months to the testing phase, not four months to
public availability,鈥� she says.