Your eyes tell you what?s happening, track moving objects and regulate your sleep cycle in response to light and darkness, but not all in the same way.
Findings by Johns Hopkins University biologist Samer Hattar suggest our eyes use modified nerve cells to detect changes in ambient light, as opposed to the rod- and cone-shaped cells that provide our view of the world.
Our sense of time depends on that light-detecting ability, Hattar said: “It?s like having a hand watch and it?s inaccurate. You have to wind it and set it every day.”
His findings, to be published Thursday in Nature, suggest that patients with trouble sleeping or seasonal depression ? disorders linked to lack of exposure to daylight ? could benefit from easier, more available tests to determine whether they can detect light properly in the eye.
In totally blind people, the circadian clock that regulates the sleep cycle runs free, researchers say.
But those who have some light-detecting ability have been able to regulate their own clocks even if they can?t see, Hattar said. His finding proves the reverse using animal studies.
“It seems that even if individuals have normal sight, they might be having a malfunction that is contributing to their inability to detect light, which can adversely affect their biological clocks,” Hattar said.
His team genetically engineered mice so they would lack a set of retinal ganglion cells that interpret signals from the rod and cone cells. The mice could still see normally but had trouble differentiating day and night cycles.
Further study is needed to verify the same mechanisms hold true for people, Hattar said, but the specialized ganglion cells have already been identified.
Hattar said his work reaffirms the understanding that daily exposure to natural light enhances memory, mood and learning.
“Our tips are simple: Get out in the sun for at least a little while each day,” Hattar said. “There?s a reason why we seek the sun and the beach and we feel better when we can sit in the sun and bask.”
