2 Techniques Offer Hope for Restoring Partial Eyesight

Fetal cell transplants and electronic sensors may eventually help restore partial vision in people whose light-sensitive retinal cells have been destroyed by diseases such as diabetic retinopathy, researchers said in Los Angeles on Sunday.

In such diseases, which affect at least 1.8 million Americans, nerve pathways from the eye to the brain are functional. Only the eye’s ability to detect light is impaired.

Fetal cell transplants, which have been tested in rats, and electronic sensors, which have been tried in four people, each provide a way to convert light into an electrical signal that the brain can then interpret.

The electronic sensors work the same way as the cochlear implants routinely used to restore hearing in people with deafness caused by damage to the cells that detect sound.

Both approaches are still in an early stage of development and will require years of additional research. But they provide the best hope for restoring useful vision in such cases, experts said at a symposium organized by Research to Prevent Blindness.

“This is an extraordinarily simple solution,” said Dr. Manuel del Cerro, a neurobiologist at the University of Rochester in New York.

Del Cerro has been studying the transplantation of rat fetal retinal tissues onto the damaged retinas of blind adult rats for more than 10 years. He had shown that the transplanted cells survive and make connections to the underlying glial cells, the first link in carrying an electrical response to the brain for interpretation. But he had not been able to show until now that the brain received a useful signal.

The research reported Sunday showed for the first time that the transplantation produces a behavioral effect, indicating that the brain is, indeed, receiving an intelligible signal.

Del Cerro used the “startle” response of rats to show this effect.

Rats in the dark are startled by a loud noise; the degree to which they are startled--causing them to jump--can be measured with great accuracy. In sighted rats, the startle response is significantly reduced if a light is flashed a fraction of a second before the noise, in much the same way that seeing lightning reduces the surprise of a thunderbolt. No such effect is observed in blind rats.

Del Cerro found that rats that had received retinal cell transplants showed a significant reduction in their startle response when the light was used, although the reduction was only about 20% that of normal rats. Most important, he said, “the reaction to light was produced in the same time frame as that of a normal rat,” indicating that the correct visual pathways were being used.

“We believe that these results give strong support to the idea that retinal transplantation may one day provide a means of restoring function to visually impaired eyes,” he said.

Adopting a more direct approach, Dr. Eugene De Juan Jr., an ophthalmologist at Johns Hopkins University in Baltimore, used electrodes to apply a minute electrical impulse to the retina of blind people. “This research could not be performed in animals because we needed an objective response to the stimulation,” he said.

When an electrical pulse was applied to the electrode, the four patients reported seeing a flash of light, typically round and yellow. As De Juan moved the electrode while applying pulses, the patients were able to perceive differences in position and the direction of movement. “They always identified the correct location,” he said. When two electrodes were used, the subjects could determine their relative orientation.

De Juan is now constructing a grid of electrodes that could provide more sophisticated information. For example, a 5-by-7 array of electrodes, similar to the pattern of dots in a dot-matrix printer, would allow patients to see individual letters, providing a form of reading that would allow much quicker comprehension than is possible with Braille, he said.

De Juan noted that other researchers had obtained similar results by using electrodes to stimulate the brain, largely bypassing the visual pathway. “Our approach is much less invasive and much simpler,” he said.

De Juan envisions the development of miniature silicon chips that would have a network of miniaturized electrodes on one side, each connected to an individual photoreceptor on the other side. Transplanted into the eye, the chips would provide vision with a resolution that increases with the number of electrodes. As better miniaturization techniques are developed, he said, the quality of vision would improve.