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Retinal Implants: Helping the Blind to See 
 
by Mark R. Whittington September 27, 2005

Hitherto, macular degeneration or retinitis pigmentosa has been followed a slow but steady decline in vision, sometimes followed by blindness. Research and development of retinal implants, microchips implanted in the eye's retina, will eventually cure this malady.

Currently, six million Americans are either blind or have greatly reduced vision because of diseases such as macular degeneration and retinitis pigmentosa. While they can be treated, there is currently no way to cure or to reverse either of these conditions. But a cutting edge technology is now under development that one day will be to the eye what cochlear implants are to the ear. It takes the form of a tiny, computer chip implanted in the retina of the eye.

Common Causes of Blindness

Macular Degeneration is the leading cause of severe vision loss in people over age 60, and can be slowed down with appropriate treatment. Macular Degeneration occurs when the small central portion of the retina, known as the macula, is damaged. The condition can cause distortion of the central vision, as well as blurriness and blind spots. Macular Degeneration can result, in some cases, in complete loss of central vision.

Current treatments for Macular Degeneration include vitamins, including C, E, beta carotene, zinc and copper, and laser therapies that kill off abnormal blood vessels in the eye that occur during MD. There are also a variety of low vision devices that can help a person make use of the vision he or she has left.

Retinitis Pigmentosa is one name for a large group of inherited visual disorders that causes progressive degeneration of the retina of the eyes. Peripheral vision gradually decreases and eventually is lost. Night vision is also affected. Central vision is usually preserved until late in these conditions.

Wearing sun glasses which block UV rays will, in some cases, delay the progress of RP. Some clinical trials have indicated the vitamin A can also delay the progress of the disease.

Usher Syndrome is a rare inherited disorder related to Retinitis Pigmentosa. Along with loss of vision that characterizes RP, Usher also results in loss of hearing.

Retinal Implants

The principle behind retinal implants, or as they are called implantable intraocular retinal prosthesis, relies upon the way the human retina works. The retina consists of tiny cells called rods and cones which receive light from the lens and transmits the images via electrical and chemical signals down the optic nerve to the brain. It is in the brain that the signals are translated to what we actually “see.”

The cells in the outer layer of the retina are called photoreceptor cells. People with eye diseases such as Macular Degeneration and Retinitis Pigmentosa have had their photoreceptor cells damaged. However the deeper layer of cells in the retina which act as neural pathways and are responsible for transmitting signals from the photoreceptor cells to the brain are left undamaged. The implantable intraocular retinal prosthesis takes over for the photoreceptor cells, stimulating the retina cells in the deeper layer and thus restoring vision.

Research into these types of retina implants is taking place in the United States, Great Britain, Germany, and other countries. Typical of these experimental implants are the ones being worked on at the Doheny Eye Institute at the University of Southern California. In its current form the retinal implant is a 4 mm x 5 mm device studded with 16 electrodes in a 4 x 4 array. It is implanted in the retina where the photoreceptor rods and cones are, and it transmits electrical impulses to the intact neural paths in the deper layer of the patient’s retina, which in turn transmit the signals to the brain, allowing for sight. The patient wears a pair of special eye glasses with a digital camera that transmits the images it captures to the implant.

Six patients with advanced Retinitis Pigmentosa have been given this implant and can now see on a limited basis. Patients have been able to experience light and, in later tests, make out some shapes, like a foot high letter at a distance of a few feet. They can also tell the difference between certain objects, such a plate or knife. The patients cannot tell detail, however. That improvement has to await more sophisticated implants now under development. Even so, the first implant was done about three and a half years ago and still functions very well.

Other implants being studied can be implanted on the optic nerve and even in the brain cortex itself. Each type of implant has its own advantages and disadvantages.

Research is also ongoing at University Eye Hospital in Cologne, the University of Bonn, MIT, North Carolina State University, and Glasgow University's Department of Physics among other places. Human trials have shown similar results as has been achieved at the Doheny Eye Institute.

On the Horizon

The FDA is now examining a second generation retina implant device for approval for human trials. It will be one fifth of the size of the current device, has sixty electrodes, and will take ninety minutes to implant as opposed to six hours it takes to implant the first generation device. The second generation implant is envisioned as being the first commercially available retinal implant.

Further on the horizon, researchers at the Doheny Eye Institute envision a third generation implant that will permit the patient to be able to read and recognize faces, in effect restoring functional eyesight to the blind. This device will have to be made of more sophisticated materials than the silicon/platinum now used in the first generation device. It will have 1000 electrodes. New implantation techniques will have to be developed to accurately align the electrodes of the device with the retina cells that need to be stimulated. The digital camera will be actually in the implant, relieving the patient of having to wear special eye glasses.

It is impossible to predict exactly one the third generation retina implant will be available for general use. More research and development remains before they are even available for human trials. And government bureaucracies like the Food and Drug Administration have their own schedule in approving new medical devices. Even so, researchers are confident that sooner or later, many people who are blind will be able to see again thanks to retinal implants.


 

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