Shades of protection.

It's a perfect summer day at the beach, and you've remembered the beach towel, the snacks, the hat, and the 15+ SPF sunscreen. You're all set for sun and fun -- except you forgot your sunglasses. No problem -- you'll stop at the store on the way and grab the coolest shades you can find.

Not so fast. If your sunglasses don't block ultraviolet (UV) rays, you could damage your eyes.

Those Penetrating Rays

The sun emits radiation of various wavelengths--cosmic rays, X-rays, ultraviolet rays, visible light, and infrared rays. The ozone layer absorbs the shorter wavelenghts, such as cosmic rays and X-rays. Longer wavelengths, such as the light you see, go through the ozone layer and reach the earth's surface. As the ozone layer thins, the ultraviolet rays, which are the middle wavelengths, are no longer absorbed, and more of them reach the surface of the earth.

Two kinds of UV rays cause problems:

1. UVA rays penetrate deeply into the body.

2. UVB rays, which are shorter than UVA rays, have more energy and cause burns.

What does this have to do with eyes? When ultraviolet rays enter your eyes, they may damage conjunctiva, the cornea (the clear window of the eye), the lens, or the retina. The effects may be immediate, producing a "sunburn" of the eyes. Over the years, the damage can accumulate, which may affect the lens and result in cloudy vision. This condition is called cataracts.

Damage can occur in summer and winter. At high altitudes in the snow, the cornea and conjunctiva can actually burn, resulting in show blindness. Although the problem usually goes away in 24 hours, it's very painful while it lasts.

Teens are more vulnerable to UV damage than adults. Until age 20, your eye lens is more transparent and allows UV rays to pass right through. Teens spend more time outdoors soaking up the sun than do adults. And the more years you expose your eyes to UV rays, the more damage will be done. So wearing sunglasses that give you proper UV protection should be high on your "must do" list.

Choosing Your Shades

The first priority in choosing sunglasses is to find a pair that blocks most of the UV radiation. Don't think you can't afford them--in this case, expensive doesn't necessarily mean better. The process of making glasses impermeable to UV rays is a simple one: Plastic lenses are dipped in a dye bath of chemicals that absorb the UV rays, or chemicals are incorporated directly into the glass mixture when the lens is made. Therefore, a properly treated $6 pair of sunglasses can protect your eyes as well as a $100 pair.

The Food and Drug Administration (FDA) has no official guidelines for what percent of UV rays a pair of sunglasses should block. However, manufacturers of sunglasses and the FDA have established voluntary standards to help consumers make choices. They've divided sunglasses into three categories:

* Cosmetic sunglasses are slightly tinted and block 70 percent of the UVB rays and 20 percent of the UVA rays. These are a good choice for short periods outdoors.

* General purpose sunglasses block 95 percent of the UVB rays and 60 percent of the UVA rays. These glasses are good for most outdoor activities.

* Special purpose sunglasses block 99 percent to 100 percent of the UVB light and 60 percent of the UVA light. Choose these if you're going to be in intense sunlight, such as at the beach or on a ski slope.

Watch Out for False Claims and Promises

Some sunglasses claim to be "blueblockers," blocking out the blue light (the band of light on the edge of the ultraviolet rays). There is debate as to whether this "protection" is really helpful. Filtering out blue light distorts your color perception; so blueblockers are not recommended for driving, for example, where there is a chance of misinterpreting traffic lights. If in doubt, check with your eye care professional.

Make sure the label on the glasses tells you the percent of rays that are blocked. Since there are no official standards, sunglasses can allow a significant amount of the UV rays to reach your eyes and still be advertised as having "maximum protection."

UV blocking chemicals and coatings are colorless, so darkness of lenses does not determine the degree of safety. Since dark lenses let your pupils dilate, those without UV protection may let more of the UV rays pass through your eyes. Wearing sunglasses that have no UV protection may actually be more harmful than squinting.

To make sure your sunglasses block a sufficient amount of visible light, put a glasses on and look in a mirror. You shouldn't be able to see your eyes behind the lenses.

What About Size and Colors?

Bigger is better. Larger lenses keep rays out from more angles. For intense sunlight, wrap-around glasses are the best since they prevent rays from coming in the side.

Red, orange, blue, and yellow lenses may look funky, but they also make it harder for you to see traffic signals. Gray or smoky lenses give the truest colors. Green makes everything brighter (great for New York or Seattle), while brown gives colors more contrast (great for the desert).

You can choose specialty sunglasses for specific situations:

* Gradient lenses are tinted darker at the top and are good for driving because you can see the dashboard more easily.

* Double gradient lenses are darker at both the top and bottom and are good for tennis players.

* Polarized lenses eliminate the glare reflected off water and are good for water activities.

* Photochromic glasses darken when you go outside, but they may not darken sufficiently when worn for driving.

Choose a pair you really like so you'll be sure to wear them. And don't put them away at the end of the summer--you'll need them as much on the ski slopes as you do at the beach.