If it’s beyond repair, you find something else to do its job. This could soon apply to rods and cones, the light-sensitive cells in our eyes that can wither with age, causing blindness. A drug has been found that coaxes neighbours of ailing cells to do their work for them.
In 2012, Richard Kramer at the University of California, Berkeley, discovered that injecting a certain chemical into the eyes of blind mice made normally light-insensitive ganglion cells respond to light. These cells ferry optical signals from the rods and cones to the brain, so the mice regained some ability to see light.
But it only worked with ultraviolet light. Now, Kramer’s team has found a different drug that does the same with visible light. Just 6 hours after they were injected, blind mice could learn to respond to light in the same way as sighted mice – although Kramer says he doesn’t know whether they regained vision or just light sensitivity.
When the researchers studied the drug’s impact on retinal cells in more detail, they realised it had had no effect on healthy cells. “That’s what’s particularly remarkable and hopeful about this,” says Kramer. “It’s possible that if you put this drug in a partially damaged eye it would restore vision to the damaged regions and leave the healthy areas unaffected – although we haven’t done the experiments to test that.”
Last year, Robin Ali of University College London transplanted light-sensing cells made from embryonic stem cells into the eyes of blind mice. He says Kramer’s study is interesting, and may eventually be relevant for some people with age-related macular degeneration, the condition that results from withered rods and cones. However, he points out that it is not yet clear whether the drug restores any useful vision.
“The light responses that are generated could be very noisy and not useful – or even disturbing,” he says. “Or perhaps the brain could learn to interpret the new information. But this needs to be demonstrated.”
Journal reference: Neuron, DOI: 10.1016/j.neuron.2014.01.003
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