Could Complete Darkness Cure Lazy Eye?

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Being in the dark may have an upside: It could potentially cure lazy eye, a condition in which one eye has much weaker vision than the other, scientists say.

Researchers demonstrated the effect in kittens, but if the results could be replicated in humans, these findings would have implications for the millions of people who suffer from lazy eye, say the researchers who detailed their study today (Feb. 14) in the journal Current Biology.

Common condition

Up to 4 percent of the population suffers from amblyopia, or lazy eye, which has several causes. For instance, a cataract can block light coming into one eye, and as a result, the brain stops properly processing information from that eye, leading to a lazy eye, said study co-author Kevin Duffy, of the University of Toronto.

While children who have a lazy eye can wear a patch to cover the stronger one, forcing the other eye to do more work, it's difficult to make 4- or 5-year-olds keep their patch on all the time, and untreated adults can have serious difficulties seeing for life, Duffy said. [Top 10 Stigmatized Health Disorders]

Dark room

Duffy and his colleagues noticed several years ago that kittens with one impaired eye had smaller cells connecting to that eye in the brain, but that putting the animals in the dark seemed to change that trait. Did the darkness actually cure the kittens' "lazy eyes"?

To find out, the researchers studied several kittens, keeping one eye shut in each animal for a week and then letting the felines roam for several weeks with both eyes open, effectively creating a lazy eye.

Researchers then put the kittens, along with their littermates and moms, into a completely dark room.

"When I say dark, I mean really dark," Duffy told LiveScience. "There are zero photons of light. It's not like going and closing your windows or drapes."

After 10 days, the kittens emerged from the darkness. Over the course of several weeks, researchers found that the animals were completely cured of their amblyopia.

In another experiment, Duffy's team showed that putting the kittens into the dark room immediately after pursing one eye shut (for a week) prevented lazy eye altogether.

Based on other experiments, the researchers believe the darkness made the kitten visual system revert to an earlier stage of development, so that it could reset itself.

But before this method could be used in people, scientists would have to figure out how long children would have to remain in the dark, how dark it would need to be and how early in a child's development the treatment would need to occur, he said.

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