December 18, 2003.
By: Ivanhoe Broadcast News.
According to the Foundation Fighting Blindness, more than 6 million Americas of every age and race suffer vision loss from retinal degenerative disease.
An additional 15 million Americans have pre-symptomatic signs of macular degeneration that may lead to vision loss.
Retinitis pigmentosa is the collective name given to a group of diseases that cause deterioration in the retina. In the majority of RP patients, the rod shaped cells of the retina are affected. These rod-shaped cells are responsible for both peripheral vision and night vision.
Over time, these cells gradually stop working, causing "night blindness" and "tunnel vision" in those who suffer from RP. The exact reasons as to what causes RP are unknown.
Like other diseases, RP strikes people of all ages, although children are most commonly diagnosed. The onset of RP is usually noticed in late childhood to adolescence with night blindness often being the first symptom to appear. This is closely followed by the gradual loss of the peripheral field of vision. Day by day, people slowly lose a little more of their vision.
While some people with RP will be totally blind by age 20, others are able to maintain partial sight into later years. These people make up a group called the "sighted blind."
Researchers from the University of Southern California are involved in what they call a groundbreaking, FDA-approved feasibility trial of an intraocular retinal prosthesis. The prosthesis appears to restore some degree of sight to the blind. The microelectronic retinal prosthesis used in the first phase of the trial is intended to stand in for the damaged retinal cells in people suffering from diseases such as retinitis pigmentosa and macular degeneration.
The prosthesis is a sliver of silicone and platinum that is often incorrectly referred to as an "eye chip."
It's attached to and sits atop the retina. The implant measures 4 millimeters by 5 millimeters and is studded with 16 electrodes in a 4-by-4 array. It works by electrically stimulating the remaining healthy retinal cells via the array of electrodes. The retinal cells, in turn, pass on the visual information to the brain through the optic nerve.
Three patients have received the implants thus far. Initial tests in the three implanted patients have shown that they can perceive light on each of the 16 electrodes. Over time, the patients were "graduated" to images received by an external video camera. These images are sent to the intraocular electrode array attached to the retina via a receiver that is implanted behind the patients' ear during the implant surgery.
The signal is then recreated by stimulating the appropriate electrodes in the prosthesis. They are capable of detecting when a light is turned on or off, describing the motion of an object, and even counting discrete objects.
The next phase of research will include 60 electrodes and future trials will likely get to 1,000. With more electrodes, researchers say patients should be able to see much more definition.
For more information:
Retina Implant Hotline.
Doheny Eye Institute.
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