How does a "bionic eye" allow blind people to see?
Introduction to the Bionic Eye
This is what the world looks like to someone with macular degeneration.
Joe McNally/Getty Images
In the past 20 years, biotechnology has become the fastest-growing area of scientific research, with new devices going into clinical trials at a breakneck pace. A bionic arm allows amputees to control movements of the prosthesis with their thoughts. A training system called BrainPort is letting people with visual and balance disorders bypass their damaged sensory organs and instead send information to their brain through the tongue. Now, a company called Second Sight has received FDA approval to begin U.S. trials of a retinal implant system that gives blind people a limited degree of vision.
The Argus II Retinal Prosthesis System can provide sight -- the detection of light -- to people who have gone blind from degenerative eye diseases like macular degeneration and retinitis pigmentosa. Ten percent of people over the age of 55 suffer from various stages of macular degeneration. Retinitis pigmentosa is an inherited disease that affects about 1.5 million people around the globe. Both diseases damage the eyes' photoreceptors, the cells at the back of the retina that perceive light patterns and pass them on to the brain in the form of nerve impulses, where the impulse patterns are then interpreted as images. The Argus II system takes the place of these photoreceptors.
The second incarnation of Second Sight's retinal prosthesis consists of five main parts:
A digital camera that's built into a pair of glasses. It captures images in real time and sends images to a microchip.
A video-processing microchip that's built into a handheld unit. It processes images into electrical pulses representing patterns of light and dark and sends the pulses to a radio transmitter in the glasses.
A radio transmitter that wirelessly transmits pulses to a receiver implanted above the ear or under the eye
A radio receiver that sends pulses to the retinal implant by a hair-thin implanted wire
A retinal implant with an array of 60 electrodes on a chip measuring 1 mm by 1 mm
The entire system runs on a battery pack that's housed with the video processing unit. When the camera captures an image -- of, say, a tree -- the image is in the form of light and dark pixels. It sends this image to the video processor, which converts the tree-shaped pattern of pixels into a series of electrical pulses that represent "light" and "dark." The processor sends these pulses to a radio transmitter on the glasses, which then transmits the pulses in radio form to a receiver implanted underneath the subject's skin. The receiver is directly connected via a wire to the electrode array implanted at the back of the eye, and it sends the pulses down the wire.
When the pulses reach the retinal implant, they excite the electrode array. The array acts as the artificial equivalent of the retina's photoreceptors. The electrodes are stimulated in accordance with the encoded pattern of light and dark that represents the tree, as the retina's photoreceptors would be if they were working (except that the pattern wouldn't be digitally encoded). The electrical signals generated by the stimulated electrodes then travel as neural signals to the visual center of the brain by way of the normal pathways used by healthy eyes -- the optic nerves. In macular degeneration and retinitis pigmentosa, the optical neural pathways aren't damaged. The brain, in turn, interprets these signals as a tree and tells the subject, "You're seeing a tree."
It takes some training for subjects to actually see a tree. At first, they see mostly light and dark spots. But after a while, they learn to interpret what the brain is showing them, and they eventually perceive that pattern of light and dark as a tree.
The first version of the system had 16 electrodes on the implant and is still in clinical trials at the University of California in Los Angeles. Doctors implanted the retinal chip in six subjects, all of whom regained some degree of sight. They are now able to perceive shapes (such as the shaded outline of a tree) and detect movement to varying degrees. The newest version of the system should offer greater image resolution because it has far more electrodes. If the upcoming clinical trials, in which doctors will implant the second-generation device into 75 subjects, are successful, the retinal prosthesis could be commercially available by 2010. The estimated cost is $30,000.
Researchers are already planning a third version that has a thousand electrodes on the retinal implant, which they believe could allow for facial-recognition capabilities.
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