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 Americans; both occur gradually and can result in total blindness.
Above: "Eye chart with eyes." Copyright Philip Kaake. All rights reserved.
"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."
"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 eye."
The Space Vacuum Epitaxy Center is a NASA-sponsored Commercial Space Center (CSC) at the University of Houston. NASA's Space Product Development (SPD) program, located at the Marshall Space Flight Center, encourages the commercialization of space by industry through 17 such CSCs. 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.
Below: A 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. Image courtesy A. Ignatiev.
"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."
"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 oxidizing agent," says Ignatiev. "Those experiments helped us develop the oxide (ceramic) detectors we're using now for the Bionic Eye project."
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 to replace.
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 millimeter by one millimeter in size. A couple of weeks after insertion into an eyeball, the polymer film will simply dissolve leaving only the array behind.
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.
Left: These first-generation 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. Image courtesy A. Ignatiev.
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 colors 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."
Space Product Development -- The goal of NASA's Space Product Development (SPD) program is to help American businesses explore the potential--and reap the rewards--of doing business in space. Doing this helps bring the benefits of space down to Earth where it can, and does, enrich the everyday lives of the American public. "Industry investment in space is high," says Mark Nall, manager of NASA's SPD program at Marshall Space Flight Center. "We assist companies developing experiments and help them explore how space research can contribute to the growth of their businesses."
The Space Vacuum Epitaxy Center -- a NASA-sponsored Commercial Space Center (CSC) at the University of Houston
Webvision: An excellent guide to the human eye. Sections of interest include Gross Anatomy of the Eye and Facts and Figures concerning the Human Retina
Rods and Cones in the Human Eye -- Basic information from Hyperphysics Concepts
Astronomy and the Human Eye -- a tour of the inner eye from an astronomer's point of view.
The Bionic Eye -- a short technical description from the Space Vacuum Epitaxy Center
A Guide to Retinitus Pigmentosa -- from the British Retinitis igmentosa Society.
Macular Degeneration -- learn more about this disease from the National Institutes of Health
Anatomy of the Human Eye -- from the MEDLINE Plus medical encyclopedia
National Eye Institute
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