FYI Daily

The Surprising Reason Aging Eyes Need Bright Sunlight

Last updated: Feb 21, 2012

blue eye - close-up view

Nearly everyone knows that aging eyes need brighter light to read or even see. Now it turns out that bright indoor light, or better yet, bright sunlight, helps the body regulate all kinds of internal mechanisms influencing overall health. Older adults' eyes have a role in things as seemingly-unrelated to them as memory and depression, reports Laurie Tarkan in The New York Times.

Here's why: As we get older, the eye's lens gradually yellows and the pupil narrows. So less sunlight reaches key cells in the retina that regulate the circadian rhythm system, the body's exquisite internal clock.

Circadian rhythms, Tarkan explains, are the cyclical hormonal and physiological processes that start up in the morning and wind down at night. They regulate the release of hormones like melatonin and cortisol. Disturbed circadian rhythms are thought to have a role in conditions ranging from memory loss and slowed reaction time to insomnia and depression. Sundown syndrome in people with Alzheimer's is thought, for example, to be connected to disrupted circadian rhythms. People with low melatonin are known to have a higher incidence of illnesses, including cancer, diabetes, and heart disease.

A team at Brown University discovered that the inner retina contains photoreceptor cells that communicate directly with the brain, and these are especially receptive to blue light on the light spectrum. But blue light is filtered by the aging eye -- by age 45 adults receive only half the light needed to fully stimulate the circadian rhythm system, by 55 you're down to getting only 37 percent of the blue light, and by age 75, you get only 17 percent.

Older adults are at even greater risk when they lead a sedentary, indoor life.

What can caregivers do? Researchers recommend purposeful exposure to outdoor bright sunlight to counter these effects. Skylights and bright indoor lighting help, they say. But artificial lights are 1,000 to 10,000 times dimmer than sunlight and deliver the wrong part of the spectrum, notes Patrician Turner, an ophthalmologist in Leawood, Kansas, who specializes in the aging eye.

Also, if you or a loved one had cataract surgery, fine out what type of lens was used. Replacing clouded lenses with clear intraocular lenses has been shown to reduce insomnia and improve reaction time. But it's important that the replacement lenses don't block blue light, as one third of them do -- an innovation that was intended to protect against macular degeneration (an unproven connection) that may have unintended consequences for the rest of the body's health, researchers say.

Image by Flickr user Look Into My Eyes, used under a Creative Commons Attribution license.