New Chemical Restores Light Sensitivity to Mice

Degeneration of photoreceptors in the human eye causes blindness and is irreversible. However, a newly developed compound allows other cells in the eye to act like photoreceptors, helping to reverse the symptoms, if not the causes, of blinding diseases.

There are three layers of nerve cells that make up the retina. The outer layer contains photoreceptors, the rod and cone cells, which allow us to see and are the target of degenerative blinding diseases such as retinitis pigmentosa and age-related macular degeneration. As the rod and cone cells begin to die, the two inner layers of the retina remain intact but useless, since they are not sensitive to light, according to a press release announcing the results.

In a paper published in the journal Neuron, Richard Kramer of the University of California, Berkeley and his team have developed chemicals that make the ganglion cells, the innermost cells of the retina, sensitive to light in blind mice. Earlier studies have developed similar "photoswitch" chemicals but they were only effective at high light levels. Kramer's chemical, called DENAQ, is effective in ordinary daylight. One application of the chemical is effective for several days.

Experiment trials shows that DENAQ is only effective if rods and cones have already died. This is actually good news, because DENAQ's ineffectiveness on healthy retina tissue may reduce side effects for partially blind patients.

Kramer said he hopes his results will lead to application in human populations.

"Further testing on larger mammals is needed to assess the short- and long-term safety of DENAQ and related chemicals," said Kramer. "It will take several more years, but if safety can be established, these compounds might ultimately be useful for restoring light sensitivity to blind humans. How close they can come to re-establishing normal vision remains to be seen."