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Johns Hopkins UniversityArts and Sciences Magazine


Blind Mice Can “See”

Conventional wisdom has long held that a person's eyesight is dependent upon the millions of rods and cones that detect light, shape, movement, and color and make up the human retina.

But a study published recently in the journal Neuron challenges that thinking and provides new hope to people who have severe vision impairments or who are blind. A team led by Samer Hattar, assistant professor of biology in Arts and Sciences, found that mice that lacked rod and cone function could still see—and not just light, but also patterns and images—thanks to special photosensitive cells in the rodents' retinas.

Until now, it was presumed that those cells, called intrinsically photosensitive retinal ganglion cells (ipRGCs), didn't play a role in image formation, but instead served other functions, such as dictating when the animals went to sleep or woke up.

"Our study shows that even mice that were blind could form low-acuity yet measurable images, using ipRGCs," says Hattar, who studies mammals' sleep-wake cycles, also called circadian rhythms. "The exciting thing is that, in theory at least, this means a blind person could be trained to use his or her ipRGCs to perform simple tasks that require low visual acuity."

To conduct the study, the team used a special system to genetically label cells and then "trace" them to the rodents' brains before subjecting the mice to a number of vision tests. In one, mice followed the movements of a rotating drum, a test that assessed the animals' ability to track moving objects. In another, the rodents were placed within a Y-shaped maze and challenged to escape by selecting the lever that would let them out. That lever was associated with a certain visual pattern. The mice that were blind—lacking rods, cones, and ipRGCs—couldn't find the lever. But those with only ipRGCs could.

Hattar's team worked on this study in collaboration with groups led by David Berson of Brown University and Glen Prusky of Weill Cornell Medical College. It was supported by grants from the National Institutes of Health, the David and Lucile Packard Foundation, and the Alfred P. Sloan Foundation.