July 16, 2003.
By Lakshmi Sandhana,
Gaze deeply into his eyes and a silicon chip calmly stares back at you.
More than just the stuff that $6 million men are made of, several types of "bionic eyes" are beginning to make their presence felt in the area where they are most needed -- restoring sight to the blind.
Earlier this year, three people were successfully implanted with a permanent "retinal prosthesis" by researchers at the Keck School of Medicine of the University of Southern California. Each patient wore spectacles with miniature video cameras that transmitted signals to a 4-mm-by-5-mm retinal implant via a wireless receiver embedded behind the ear.
The device works by transmitting visual signals captured by the video camera to the retinal implant, which contains an array of 16 electrodes. The signal is then recreated by stimulating the remaining healthy retinal cells with the electrodes, which pass on the information to the brain through the optic nerve.
Dr. Mark Humayun, professor of ophthalmology at the Keck School, said the first target population would be those who had had sight once and then lost it due to certain types of blindness such as retinitis pigmentosa or age-related macular degeneration.
"If successful in these patients, then the device will be evaluated for use in other types of blindnesses, such as those blind from birth," Humayun said.
Test results so far have revealed that some patients were capable of detecting when a light was turned on or off, describing the motion of an object and counting discrete objects. The capability to recognize faces or read large print is thought to be possible only with 1,000 or more electrodes, however.
Australian researcher Nigel Lovell, from the University of New South Wales, is working on an implant with 100 electrodes, which he hopes will give patients the ability to differentiate between night and day, detect obstacles and provide some rudimentary reading skills. "100 channels is near the practical limit," said Lovell. "There are ways around these limits, but it's not the most important question at present."
While these approaches focus on the camera being outside the body, Dr. Alan Chow of Optobionics hopes to develop a silicon retina that has the sensing equipment onboard -- 4,000 to 5,000 microscopic solar cells that function in place of the eye's natural sensors.
Putting in the all the electronics, though, may prove to be a problem, since the eye is a corrosive environment where electronics don't do too well. "Certain materials have been shown to be biocompatible and thus will exist in the body without major tissue reactions," said Lovell in an e-mail. "Chow's devices have not been shown (at least to my knowledge) to be biocompatible."
A pea-size Implantable Miniature Telescope, or IMT, embedded in only one eye is the basis of the work done by California-based VisionCare Ophthalmic Technologies. Replacing the eye's lens, the telescope projects images over the undamaged area of the retina and provides central, "straight-ahead" vision while the other eye handles peripheral vision.
The technology aids those who haven't totally lost sight from blinding diseases. For those whose peripheral vision remains intact, the IMT could prove to be a great blessing.
"Central vision is the most important for functional and detailed everyday tasks," said Chet Kumar, VisionCare's director of business and market development. "You need your central vision to read a recipe, recognize people and to view the computer or TV screen."
So far, the majority of patients implanted with the device have generally improved two to three lines of vision on the eye chart. Currently in the last phase of clinical trials, the company is enrolling 200 patients for a two-year study, by the end of which they hope to have enough data to earn Food and Drug Administration market approval.
"Our goal is to help these individuals regain some degree of functional vision," said Kumar. "Though not a cure, we hope that they will be able to go about their daily activities and hobbies more independently."
Bypassing the need to have intact retinas entirely, the Dobelle Institute's brain implant approach uses an external camera and directly interfaces with the brain through electrodes attached to the visual cortex. While this technique offers treatment for a wider variety of vision problems, considerable difficulties exist in mapping the stimulation sites in the brain.
Though the bionic eye is still at least five years away by most estimates, experts are nevertheless hopeful. "While good progress is being made on both the retinal and the cortical (brain) chip implants, it is not clear if either of these approaches will finally work," said Dr. Gerald Chader, the chief scientific officer of the Foundation Fighting Blindness.
"While much of the work is still preliminary, we are very hopeful that one day these implants could restore ambulatory vision to patients," he added.
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