Using space technology, scientists have developed
extraordinary ceramic photocells that could repair malfunctioning
by Steve Price and Dr Tony
Rods and Cones. Millions of them are in
the back of every healthy human eye. They are biological solar cells
in the retina that convert light to electrical impulses - impulses
that travel along the optic nerve to the brain where images are formed.
Without them, we're blind.
Indeed, many people are blind - or
going blind - because of malfunctioning rods and cones. Retinitis
pigmentosa and macular degeneration are examples of two such disorders.
Retinitis pigmentosa tends to be hereditary and may strike at an
early age, while macular degeneration mostly affects the elderly.
Together, these diseases afflict millions of people; both occur
gradually and can result in total blindness.
"If we could only replace those damaged
rods and cones with artificial ones," says Dr. Alex Ignatiev, a
professor at the University of Houston, "then a person who is retinally-blind
might be able to regain some of their sight."
Years ago such thoughts were merely
wishful. But no longer. Scientists at the Space Vacuum Epitaxy Centre
(SVEC) in Houston are experimenting with thin, photosensitive ceramic films that respond to light
much as rods and cones do. Arrays of such films, they believe, could
be implanted in human eyes to restore lost vision.
Image courtesy A. Ignatiev.
schematic diagram of the retina - a light-sensitive layer
that covers 65% of the interior surface of the eye. SVEC scientists
hope to replace damaged rods and cones in the retina with
ceramic microdetector arrays.
"There are some diseases
where the sensors in the eye, the rods and cones, have deteriorated
but all the wiring is still in place," says Ignatiev, who directs
the SVEC. In such cases, thin-film ceramic sensors could serve as
substitutes for bad rods and cones. The result would be a "bionic
The Space Vacuum Epitaxy Centre is
a NASA sponsored Commercial Space Centre (CSC) at the University
of Houston. NASA's Space Product Development (SPD) program, located
at the Marshall Space Flight Centre, encourages the commercialisation
of space by industry through 17 such projects. At the SVEC, researchers
apply knowledge gained from experiments done in space to develop
better lasers, photocells, and thin films - technologies with both
commercial and human promise.
Scientists at Johns Hopkins University,
MIT, and elsewhere have tried to build artificial rods and cones
before, notes Ignatiev. Most of those earlier efforts involved silicon-based
photodetectors. But silicon is toxic to the human body and reacts
unfavourably with fluids in the eye - problems that SVEC's ceramic
detectors do not share.
"We are conducting preliminary tests
on the ceramic detectors for biocompatibility, and they appear to
be totally stable" he says. "In other words, the detector does not
deteriorate and [neither does] the eye."
In 1996, during
shuttle mission STS-80, astronauts use Columbia's robotic
arm to deploy the Space Vacuum Epitaxy Centre's Wake Shield
"These detectors are thin films, grown
atom-by-atom and layer-by-layer on a background substrate - a technique
called epitaxy," continues Ignatiev. "Well-ordered, 'epitaxally-grown'
films have [the best] optical properties."
Crafting such films is a skill SVEC
scientists learned from experiments conducted using the Wake Shield
Facility (WSF) - a 12-foot diameter disk-shaped
platform launched from the space shuttle. The WSF was designed
by SVEC engineers to study epitaxial film growth in the ultra-vacuum
of space. "We grew thin oxide films using
atomic oxygen in low-Earth orbit as a natural
oxidising agent," says Ignatiev. "Those experiments helped us develop
the oxide (ceramic) detectors we're using now for the Bionic Eye
The ceramic detectors are much like
ultra-thin films found in modern computer chips, "so we can use
our semiconductor expertise and make them in arrays - like chips
in a computer factory," he added. The arrays are stacked in a hexagonal
structure mimicking the arrangement of rods and cones they are designed
The natural layout of the detectors
solves another problem that plagued earlier silicon research: blockage
of nutrient flow to the eye.
"All of the nutrients feeding the eye
flow from the back to the front," says Ignatiev. "If you implant
a large, impervious structure [like the silicon detectors] in the
eye, nutrients can't flow" and the eye will atrophy. The ceramic
detectors are individual, five-micron-size units (the exact size
of cones) that allow nutrients to flow around them.
Artificial retinas constructed at SVEC
consist of 100,000 tiny ceramic detectors, each 1/20 the size of
a human hair. The assemblage is so small that surgeons can't safely
handle it. So, the arrays are attached to a polymer film one millimetre
by one millimetre in size. A couple of weeks after insertion into
an eyeball, the polymer film will simply dissolve leaving only the
The first human trials of such detectors
will begin in 2002. Dr. Charles Garcia of the University of Texas
Medical School in Houston will be the surgeon in charge.
"An incision is made in the white portion
of the eye and the retina is elevated by injecting fluid underneath,"
explains Garcia, comparing the space to a blister forming on the skin
after a burn. "Within that little blister, we place the artificial
ceramic thin film microdetectors, each about 30 microns in
size, are attached to a polymer carrier, which helps surgeons
handle them. The background image shows human cones 5-10 microns
in size in a hexagonal array.
Scientists aren't yet certain how the
brain will interpret unfamiliar voltages from the artificial rods
and cones. They believe the brain will eventually adapt, although
a slow learning process might be necessary - something akin to the
way an infant learns shapes and colours for the first time.
"It's a long way from the lab to the
clinic," notes Garcia. "Will they work? For how long? And at what
level of resolution? We won't know until we implant the receptors
in patients. The technology is in its infancy."
Ignatiev has received over 200 requests
from patients who learned of the studies from earlier press reports.
"I'm extremely excited about this," he says. He cautions that much
more research is needed, but "it's very promising."