A new study shows that even short periods spent outdoors can expose our eyes to harmful shortwave radiation from the sun.

It has been known for many years that ultraviolet-B radiation can lead to cataracts - a cloudiness in the lenses in the eyes.

But now researchers from the Johns Hopkins Wilmer Eye Institute say the risks are much greater than previously thought.

"We've found there is no safe dose of UV-B exposure when it comes to risk of cataract, which means people of all ages, races and both sexes should protect their eyes from sunlight year-round," says Dr Sheila West, professor of ophthalmology at Johns Hopkins.

Glasses and hats

Dr West is the senior author of the study published in the Journal of the American Medical Association.

More than 2,500 adults from Maryland were examined to determine their exposure to UV-B radiation. The researchers photographed the lenses of all the people and questioned them about their use of glasses, sunglasses and hats during work and at leisure.

The team also used a special device mounted on the eyeglasses of over 250 participants to measure the amount of UV-B light reaching their eyes.

Then, using a "correction factor" model developed by NASA (National Aeronautics and Space Administration), the researchers estimated exposure to UV-B the participants got when they travelled to areas outside of Maryland.

Childhood exposure

Although conducted on adults, Dr West says the research has important implications for children because they have many years of exposure ahead of them, and the effect of sunlight exposure appears to be lifelong.

"Kids get sunburned just like adults," she says. "So there's no reason to think they are more resistant than adults to lens damage from UV-B rays."

A cataract develops when proteins in the lens change their structure due to UV-B light exposure and block light coming into the eye. Cortical cataracts affect the front of the lens.

The research follows up previous work on local crab fisherman who had more cortical cataracts compared to people with less sunlight exposure.

Work indoors

The current findings show that even the general public, including those who work mainly indoors, may be at increased risk for cortical cataract if they fail to wear protective shades in the open.

"Every time you go out into the sun, your eyes can take a hit from UV-B rays," says Dr West.

"The good news is it's never too late to start protecting your eyes, because the lens change is probably from an accumulated dose over the years. That's why everyone needs to get into the habit of protecting their eyes."