Retinal cells thought to be the same are not, biologist says

The old adage "looks can be deceiving" certainly rings true when it comes to people. And it is also accurate when describing special light-sensing cells in the eye, according to a Johns Hopkins University biologist.

In a study recently published in Nature, a team led by Samer Hattar of the Krieger School of Arts and Sciences' Biology Department and Tudor Badea of the National Eye Institute found that these cells that were thought to be identical and responsible for setting both the body's circadian rhythm and the pupil's reaction to light and darkness are actually two different cells, each responsible for one of those tasks.

"In biology, as in life, you can't always trust what you see. You have to delve deep to find out what's really going on," Hattar said. "This study has shown that two structurally similar neurons are actually quite different and distinct, communicate with different regions of the brain and influence different visual functions."

The findings are significant, Hattar said, because doctors sometimes use pupillary light reflex (the pupil's response to light and darkness) as a way of diagnosing patients who may have sleep problems, and those clinicians now must recognize that the cells controlling pupillary response and the sleep-wake cycle are different...

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