Do old or cheap sunglasses increase the risk of eye damage from ultraviolet rays?

Dear Cecil: Having recently moved to Florida from Michigan, I’ve become increasingly concerned about the effects of ultraviolet rays on my eyes. You see, I have had the same sunglasses for ten years or so, which is no problem if the UV protection is inherent in the glass. But it might be time for new glasses if the UV protection was just a coating. Ten years of wiping might have removed it. Since the glasses are dark, my pupils must be enlarged and more vulnerable. Is the UV protection on or in my glasses? Is it different for new sunglasses? Has the quality of protection changed over the years? And lastly, when cheap plastic sunglasses say they offer UV protection, can they be trusted? Tell me, Cecil, how do I best protect my eyes in the Sunshine State? Steve, via AOL

Cecil replies:

Sorry, babe. You’re in Florida now, home of Disney World, pink flamingos, and Miami Beach. You’ll be lucky if you don’t go blind.

As for your sunglasses, you should definitely get new ones. This has nothing to do with UV but rather with the fact that your glasses, perhaps the most fashion-driven item in the average person’s wardrobe, are ten years old. Just a guess: do you work in the math department? No matter. Assuming you don’t want to spend two grand for gold frames a la Stevie Wonder, you can get shades that effectively block UV for maybe ten to forty bucks. (We’ve heard widely varying opinions, by the way, on whether protective coatings wear off, whether coatings ten years ago were any good, etc. All the more reason to buy new.)

You’re right to worry about UV. Due (probably) to the thinning ozone layer, UV-related health problems are skyrocketing. Look at Australia. The country has three strikes against it: it’s in the southern hemisphere, where the ozone layer is thinner; it gets a lot of strong sun because it’s close to the equator; and its high-risk Caucasian population is outdoors a lot. As a result Australia has the highest rate of skin cancer in the world. OK, we’re talking about eye problems now, not skin cancer, but they’re all related. Chances are we’ll be seeing increasing rates of cataracts, retinal and corneal damage, and other eye problems in years to come.

Choosing the right sunglasses is critical. Some experts think poor-quality shades actually will make matters worse — they don’t block UV but do cause your pupils to dilate, allowing more damaging rays to enter. It’s possible the danger is exaggerated, though. As other researchers point out, daytime light levels are so high that your pupils constrict even with sunglasses.

Even good sunglasses don’t mean your problems are over. Sunglasses can block UV from entering through the central part of your field of vision, but plenty of damaging rays can sneak in around the edges. Wraparound shades or glasses having side shields offer more but not total protection. One study found that, on average, sunglasses let in 3 percent of UV light when they’re snug against the bridge of the nose but 29 percent when they’re six millimeters distant. Pushing up your glasses might look geeky, but it sure beats cataract surgery.

Given the spotty protection offered by sunglasses, some experts say that if you’re going outdoors for any length of time your first line of defense should be a wide-brimmed hat. A baseball cap is OK too, provided you wear the bill in front. Better yet, wear both hat and shades. One study of 900 Chesapeake Bay shellfish harvesters found that those who wore sunglasses and brimmed hats got cataracts only a third as often as those who didn’t.

Tests of sunglasses have found wide variations in their effectiveness against UV, regardless of cost, tint color, or lens material. Ignore the sales hype and look for the following voluntary industry labels. “Cosmetic” sunglasses block 70 percent of the sun’s most damaging rays, “general purpose” shades block 95 percent, and “special purpose” glasses block 99 percent. “UV-400,” another label you often see, supposedly means the sunglasses block 100 percent of UV. A lot of experts recommend glasses in the latter two categories, the special purpose in this case being that they may keep you from going blind.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.