Artificial retina implant

SAN FRANCISCO, Feb 16 (Reuters) A tiny electrical implant that attaches to the retina may someday restore partial sight to millions of patients blinded by age-related macular degeneration, US researchers said.

The device, in the early stages of human clinical testing, is part of a new class of so-called ''smart'' prostheses that link with the brain and nervous system to restore function lost to disease or injury, the researchers told reporters yesterday at the annual meeting of the American Association for the Advancement of Science in San Francisco.

Similar electrical stimulation devices known as cochlear implants have been used to treat deafness, and scientists are developing others to restore bladder control and movement to patients with spinal cord injury.

The artificial retina is designed to take the place of photoreceptor cells in the brain that are charged with capturing and processing light.

''We anticipate this technology will help blind patients who have lost their sight through macular degeneration,'' said Dr Mark Humayun, a professor of ophthalmology at the University of Southern California.

Macular degeneration is the leading cause of blindness in older adults in the United States and the developed world, affecting approximately 25 million to 30 million people.

Humayun and his colleagues have teamed up with with privately held Second Sight Medical Products to develop the implant, which just won clearance from US regulators to test a second-generation device in a US clinical trial.

An early version of the device implanted in six patients fared far better than its makers expected, allowing people who had been blinded for years to distinguish between simple objects, such as a cup, a plate and a knife.

The device consists of a tiny camera mounted on a pair of glasses that transmits information to the implant, which is attached to the outside of the eyeball with a cable running to the retina in the back of the eye. Patients wear a pager-sized transmitter on their belt, which handles the processing and powers the device.

Humayun, who helped implant the first six patients, said the best he had hoped for in that early trial was for patients to distinguish between light, dark and see some areas of gray.

''It really speaks to the brain's ability to fill in a lot of information,'' he said.

The earlier implant consisted of 16 electrodes or pixels.

The newer version has about 60 electrodes and is about a quarter the original half-inch size.

In patients with diseases of the retina such as macular degeneration or retinitis pigmentosa, photoreceptor cells progressively degenerate, causing vision loss.

The artificial retina is designed to work by creating a new route for images to reach the brain.

The trial will enroll 50 to 75 patients in five US centers, who will be followed for one to two years.

If it proves successful in a series of clinical trials, Humayun said the artificial retina could be on the U.S. market within two years.