A retinal implant based on a microchip could help treat blindness
MICROCHIPS form the basis of several
devices, such as Min (magnetic resonance imaging) scanners and pacemakers, which have revolutionised medical
diagnosis and treatment. Now, microchips may also provide relief to many
people suffering from blindness.
Researchers working on the Project
for a Retinal Implant, a joint effort
of the Massachusetts Institute of
Technology (MIT) and the Harvard
Medical School, have completed experiments that provide hope that a retinal
implant may soon be a reality (Science, Vol 268, No 5211).
The scientists have finished a series
of experiments in which prototype retinal implant components were used in
rabbits. These devices were used to
deliver tiny currents to the ganglion
cells (nerve bodies in the retina that feed
the optic nerve which transmits the
information to the visual cortex in the
brain) and a measurable response
was detected in the visual cortex of the rabbits.
The components tested will eventually form a part of an artificial eye
replacement kit that will include a
miniature camera mounted on eyeglasses, a laser beam to transmit the information and a microchip to convert light into electric pulses.
The camera will record the information in the visual field and digitise it for the laser to beam it to the retinal implant.
The retinal implant will be a
microchip with an electrode array to
convert the laser pulses into electrical
signals which then stimulate the ganalion cells to transmit the information
In the brain.
Though this is the ultimate goal,
ray of hope for the blind
there are still many hurdles to be crossed
before it can be realised.
First, there is still some controversy
on how many healthy ganglion cells are
there in the retinas of blind
human beings. After all,
because it is the ganglion
cells which are ultimately
ation transmitting the information, there should be
enough healthy ones to do
the job.
Experiments conducted at the Johns Hopkins
University Hospital, Baltimore, have indicated that
there may be as many as 70
per cent healthy ganglion
cells in patients with outer retinal degeneration.
cone Even if the ganglion sule cells are healthy, the
implant has to be such that
the retina is not harmed
physically. This tissue, says
John Wyatt, an MIT CeC
trical engineer, has the
mechanical properties of
about one ylayer of sticky wet
Klccnex." And that doesn't make things
easy, as the implant's electrode array,
made of polymicle plastif 50 microns (a
micron is a millionth of a metre) thick,
has razor-sharp edges, Before insertion,
therefore, the array is coated in silicone
and bent to match the retina's own
curve, so that it rests on the surface
without tearing it.
Finally, there is the most daunting
problem of the chip communicating the
information with the visual cortex in a
form that can be recognised by the
brain.
The ganglion cells in the retina
arc highly specialised and diverse types
of these cells respond to different
aspects of the stimuli like colour, intensity and movement. To determine
exactly how to stimulate the ganglion
Cells to Cause them to lire in an interpretable way is one of the major
unsolved problems.
Some 1.2 million people world-
wide suffer from eye ailments that
lead to blindness because the visual
receptors in the retina are lost. Though
the day when all these problems are
solved successfully is still far off (some
sceptics claim at least half a century
away), continuing research provides a
ray of hope.
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