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Updated: October 15, 2009 16:25 IST

What helps us see in bright or low light?

IANS
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Strained Eyes: Adaptivity of eyes to darkness and bright light help us better understand the leading cause of blindness. Photo: N. Sridharan
THE HINDU Strained Eyes: Adaptivity of eyes to darkness and bright light help us better understand the leading cause of blindness. Photo: N. Sridharan

How do our eyes adjust during a blackout, seemingly without loss of time?

Vision scientists at Washington University School of Medicine-St. Louis (WUSM-SL) have identified an intricate process that allows the human eye to adapt to darkness very quickly, as well as function in bright light.

The discovery could contribute to better understanding of human diseases that affect the retina, including age-related macular degeneration, the leading cause of blindness in Americans over 50. That’s because the disease and the pathway the researchers have identified both involve cells called cone cells.

“Age-related macular degeneration may be modulated, perhaps, through this pathway we’ve identified in the retina,” says WUSM-SL’s principal investigator Mr. Vladimir J. Kefalov. “Deficiencies in this pathway affect cone cells, and so does macular degeneration, so it’s possible that if we could enhance activity in this pathway, we could prevent or reverse some of that damage to cone cells,” said Mr.Kefalov.

The retina’s main light-sensing cells are called rods and cones. Both use similar mechanisms to convert light into vision, but they function differently. Rods are highly sensitive and work well in dim light, but they can quickly become saturated with light and stop responding. They don’t sense colour either, which is why we rarely see colours in dim light. Cones, on the other hand, allow us to see colours and can adapt quickly to stark changes in light intensity.

The researchers began with studies of salamanders because their cone cells are abundant and easy to identify. Cones rely on light-sensing molecules that bind together to make up visual pigments. The pigments get destroyed when they absorb light and must be rebuilt, or recycled, for the cone cells to continue sensing light. He says this discovery means it may one day be possible to manipulate this pathway in the retina to improve vision when the other pathway has been interrupted by injury or disease, such as age-related macular degeneration. These findings were published in the journal Biology.

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