Spinach protein implant could restore sight
14:36   01  October  01
Ian Sample
A team of scientists hopes to improve the sight of blind
people by implanting proteins
from spinach leaves into their eyes. When light falls on
the proteins, it creates
an electrical voltage, which could stimulate healthy
regions of the retina and produce
meaningful images, they say.
"The idea is to insert these proteins into cells in the
retina," says Elias Greenbaum
of Oak Ridge National Laboratory in Tennessee, US. "If we
can do that, we know light
can make them produce voltages high enough to stimulate
the optic nerve."
Greenbaum, who is working on the project with Mark Humayun
of the University of Southern
California's Doheny Eye Institute, Los Angeles, says the
spinach proteins - known
as photo-reaction centres - perform a similar task to
photoreceptor cells in the
retina. These cells, which lie at the base of the retina,
send electrical pulses
to the optic nerve when illuminated. These impulses are
then interpreted as images
by the brain. Humayun has already shown that artificially
stimulating retinal cells
with electrical voltages can produce very elementary
vision. "He found that if you
lay an electrode array over retinal tissue and stimulate
it, you can produce basic
images that the person can recognise," says Greenbaum.
Fatty spheres
The two now hope to use the photo-reaction centres to
replace damaged or diseased
photoreceptor cells in blind or partially-sighted people.
"In two of the major diseases that cause blindness, you
lose the photoreceptor cells,"
says Greenbaum. To do it, they plan to embed the photo-
reaction centres into tiny
fatty spheres called liposomes and inject these into the
membranes of retinal cells.
When light falls on them, Greenbaum hopes they will
produce voltages strong enough
to trigger electrical impulses down the optic nerve. "What
we need to do is find
out whether these voltages can trigger neural events and
allow the brain to interpret
the images," says Greenbaum.
Greenbaum and Humayun are currently experimenting with
implanting the proteins into
retinal cells in the laboratory and stress it will be some
time before they try the
technique in animals or humans.
14:36   01  October  01

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