From the ABC 7 Weather team

What is ultraviolet light, and how does it damage your eyes?

September 13, 2011 - 05:00 AM
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It's sunglasses season, but do you need them? Two eye doctors from Washington, D.C., explain the risks you take by walking around exposed.

The UV Index forecast for Tuesday, Sept. 13. Map created on Monday by the EPA's SunWise Program. Orange over the D.C. region = a UV Index rating of 6, even darker orange =7, red = 8, and so on.

Most people probably understand the reasoning behind slathering on sunblock when heading out into the summer heat. With more than 1 million new skin cancer cases reported in the U.S. last year, it’s kind of easy to see it as smart prevention.

But what about sunglasses? Are we actually protecting anything by donning these ocular accessories – you know, anything beside our self-image as the coolest cat in the kitty pound?

With the 80-degrees days in D.C. dwindling fast, I sought out two local eye experts to unravel the story behind sunglasses. Meet Mary Catherine Fischer, the first Army ophthalmologist to perform LASIK, and Thomas Clinch, co-chief refractive surgeon at the Eye Doctors of Washington. Here are what the doctors have to say about the need for shades in the D.C. region, the types of gnarly eye diseases UV radiation can promote and the importance of knowing where your sunglasses came from.

Know thine enemy

Sunglasses are basically stylish shields against two types of ultraviolet light, UVA and UVB. The sun is constantly blasting out this light – it accounts for about 5 percent of the star’s energy – but the percentage of radiation that penetrates the earth’s atmosphere is greatly skewed toward UVA. About 95 percent of the ultraviolet radiation entering human eyes is UVA, which is good, because UVA waves are mostly thought of as responsible for skin tanning and wrinkling (although some recent studies have tied them to cancer growth, as well).

The shorter UVB rays, on the other hand, can cause sunburn and promote cancer by damaging skin-cell DNA. (A third type of UV radiation, UVC, is mostly absorbed by the atmosphere; humans recreate it on earth for de-germing purposes.) Here’s a decent breakdown of the types of UV rays out there:

types of ultraviolent light radiation

Do eyes really need sunglasses?

When you consider it from an evolutionary standpoint, the face is a radiation-deflecting marvel. The eyelids cut off most sunlight except that which comes from the level of the horizon, and the brow and eyelashes disperse a lot more. Squinting blocks still more light, and makes you look cool like Clint Eastwood. But the anatomy of the head is still not 100 percent effective in warding off the threat from above.

“The eyelid skin is some of the thinnest skin in the body and is extraordinarily sensitive to damage from sun,” says Clinch. “It’s not an uncommon place for skin cancers to present.”

That is one of the greatest assets of sunglasses: They’re not protecting your eyes so much as they’re protecting your near-eye skin. With a hat and sunglasses, your eyes are exposed to as much as 30 percent less UV radiation than what’s naturally in the air.

Take me to the gross stuff!

The typical amount of UV radiation in Washington, D.C., does not pose a tremendous threat to eye health. “I'm a sunglasses wearer,” says Clinch, “but we don't live in a latitude low enough that you need to wear them, to my understanding.” Still, perhaps you’ll want to after considering the flinch-worthy facial medical issues that UV radiation has been linked to. These include:

Pterygia: A pterygium is a “growth of fibrous and vascular tissue on the surface” of the eye, says Fischer. It is not uncommon to see these growths start on the white part of the eye and continue onto the cornea. They are non-cancerous but “certainly vision-threatening,” she says. They present as “chronic red eye that never really goes away. A lot of people use those get-the-red-out drops, but they don't help that much.”

Researchers have noted a relationship between pterygia and extended exposure to UV rays. Wind-blown dust might also be a causal factor, and there again, sunglasses are your friend.

Sufferers of smaller pterygia can get away with letting them be, but more advanced cases require surgery to cut them out. And surgery around the eye is never a great thing, says Fischer, because there is so little skin there to play around with. “It’s not like taking basal-cell [cancers] out of the arm or leg or back. You have to worry about the situation whenever you expose eyeballs to risk,” she says.

You want to see what a pterygium looks like? Eyeball this photo at your own risk.

Cataracts: This clouding of the eye accounts for about half of the age-related blindness cases worldwide. And while the complicated nature of the disease suggests it is caused by multiple factors, the harmful role of UV cannot be discounted.

A landmark study done in the late ‘80s among Chesapeake Bay watermen found a link between long-term exposure to UVB radiation and the development of cataracts. Researchers found that the watermen who worked outdoors a lot were up to three times more likely to develop cataracts. They were also seen as susceptible to something called Climatic Droplet Keratopathy. That disease is marked by “a spheroidal degeneration of the superficial corneal stroma” in which “yellow, oily-appearing subepithelial droplets” appear inside the membrane of the eye. Awesome!

Skin cancer: The same study of Chesapeake watermen found that persistent exposure to UVB rays was “positively associated” with the development of squamous cell carcinoma, a condition you definitely don’t want to Google-Image search. There’s also some research suggesting that UVB can affect the early stages of basal-cell carcinoma, which is the most common form of cancer appearing on the eyelids.

Clinch says that he sees skin cancer in his eye patients “on a monthly basis,” including basal-cell afflictions involving “scaly, ulcerative growths" around the eye. (Again, Google this at your own risk.) Untreated tumors can spread into the orbit of the eye, then penetrate the sinus cavities and even the brain. Eyelash loss, FYI, can mean the tumors are malignant.

What do sunglasses have to do with all this cancer talk? Probably not much here in the D.C. area if you don’t haul crabs for a living – but still, the slightest risk might motivate some folks to reach for the specs.

What kind of sunglasses are best?

When choosing shades, it’s best not to seek out the bargain barrel, says Clinch.

“There is not a government regulation on how much UV protection has to be in sunglasses,” he says. “They all tend to tell you they have a high UV protection, but in reality you get these knockoffs made in China for $5 dollars. I think with sunglasses don't be frugal. I tell people to use a name brand; it's one of the things I'm very strong about.”

Fischer agrees with that assessment. “Anything not made in the U.S. I would question. If something made in the U.S. says, ‘UVA and UVB protection,' you’re probably pretty well off.”

If you're in doubt, seek out an eye-care facility with a machine that can test the UV-absorption capacity of your glasses. And a side note to culture vultures? Those terrible, trendy, oversized sunglasses beloved by tipsy socialites the world over are actually pretty good UV blockers.

“The wraparound kind are much better, and fortunately the new sunglasses of the ‘bugeye’ kind are much more fashionable,” says Fischer. So think twice the next time you make fun of Kim Kardashian for looking like a housefly hit with a mutagen beam.

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