Shades of summer.

Here it comes, the season of sun--and sunglasses. You'll probably see your share of slammin' shades as the days turn warmer. But there's more to the glass than flash. Sunglasses can also protect your eyes from the sun's harmful rays.

"Can" is one thing, "do" is another. Are all sunglasses created equal? Follow along as SW gets the facts from vision specialist Richard Young.

RAY-DIATION

The minute you step outside on a bright sunny day, you squint. "That's nature's way of protecting your eyes from sunlight damage," says Young. Sunglasses are human nature's way of looking cool while doing the same thing.

All sunglasses screen out some bright rays of visible light, Young explains. But the rays you can see are not the ones that cause the most serious forms of eye damage. If you want to keep your eyes healthy, "well-thy," and wide-open, you have to block out the sun's invisible ultraviolet (UV) rays (see diagram, p. 10).

These are the same high-energy rays that can zip through your skin to cause skin cancer (see SW 5/1/92, p. 22). And just as we've learned to protect our skin from the sun, says Young, we need to start protecting our eyes.

Better to do it while we're young, he says. That's when we spend most of our time outside, exposed to the sun's rays. It's also when our eyes are most vulnerable to sun damage.

Up until about age 20, Young explains, our corneas and lenses let UV rays go right through (see diagram, p. 10). As the rays zip by, they can damage molecules in these structures (and on the retina), leaving tiny scars behind. Over the years, the damage accumulates. By the time you hit seventy, say, your lenses might be completely clouded over--a condition called cataracts. With cataracts, no light passes through; you are blind.

If you doubt that UV rays can cause blindness, check out some animal data from South America, says Young. Severe depletion of Earth's UV-absorbing ozone layer there is allowing more and more UV rays to get through. Scientists are finding that sheep and cows that spend their time grazing under the harmful rays are going blind.

"The time has come for prevention," says Young. And while putting sunglasses on a cow may sound like a silly idea, you can certainly pick up a pair for yourself. Young recommends the kind that block 100 percent of the UV rays, and says you should wear them whenever you're in the sun.

LABEL FABLES

"It's very simple to make sunglasses impermeable to UV light," Young says. The manufacturers just have to dip the lenses in a hot dye bath for a couple of minutes. The chemicals that make up the dye then absorb the harmful UV wavelengths as light passes through the lenses.

"But you can't just look at a pair of sunglasses and tell whether they're going to block the UV or not," Young says. Instead, you have to read the labels (or do an experiment--see p. 18).

Not all sunglasses have labels; no law says they must. But many manufacturers use a set of voluntary standards established by the sunglasses industry and the U.S. Food and Drug Administration. By these standards, "cosmetic" lenses may let through as much as 30 percent of UVB rays. Those are the UV rays with the most energy, the rays most likely to be harmful, warns Young.

So-called "general purpose" sunglasses--which are supposed to be good enough for most people's sun exposure--block some 95 percent of UVB rays. That means 5 percent of the UVB gets through (along with some 40 percent of the less energetic UVA rays).

"That's not enough protection as far as I'm concerned," says Young. If you really want to save your sight, he says, look for the label that says "UV-400." It means the glasses absorb all the potentially damaging wavelengths of UV light.

These glasses are available for as little as $10-15. And they come in all kinds of styles, so you can get the "look" and complete protection, Young says.