Lenses without a UV-ray-blocking filter are even worse than no sunglasses
By Wendy Haaf
A popular feature in Good Times magazine is Your Health Questions, where we answer questions submitted by our readers about health, nutrition, and well-being:
Which features should I look for in a good pair of sunglasses?
The most important feature in a pair of sunglasses is protection against ultraviolet (UV) light, exposure to which “has been linked to eye diseases such as cataracts, melanomas in the eye or the skin around the eye, pterygium—which is a growth of skin over the surface of the eye—and photokeratitis, which causes the dry, stinging, burning eyes that you get after exposure to a lot of bright light,” says Kirsten North, a policy and research consultant for the Canadian Association of Optometrists.
That means you should look for lenses with a filter that blocks 100 per cent of UVA and UVB rays—specifically, sunglasses labelled “UV 400.” (This measurement refers to 400 nanometres and below—the wavelengths in the ultraviolet region of the light spectrum.) “Generally, that’s noted on a tag attached to the glasses,” North says, but since there’s no guarantee such a claim is accurate, “buying from a reputable retailer is probably your best bet.” Cost isn’t a reliable indicator, either: you can get $20 pairs that are 100 per cent UV-ray-blocking, while some pricey fashion shades provide no protection.
In fact, dark lenses without a UV-ray-blocking filter are worse for your eyes than no sunglasses at all, notes John Haney, a registered optician and the optical services manager at the optometry clinic within the School of Optometry and Vision Science at the University of Waterloo (ON). Dark lenses cause your pupils to open wider to let in more light, which, if no filter is present, increases UV-light exposure. If you’re not sure whether your favourite sunglasses are doing the job, your eye-care professional can easily check.
You also can’t gauge the degree of protection by colour, since the UV-ray filter is in fact clear. In most cases, that makes the choice of lens colour a matter of preference. However, “If you don’t want colours affected,” say, because you’re a birdwatcher, “you’d go with grey, which only reduces the amount of light transmission,” Haney explains. In fact, certain colours are suited to certain activities; for instance, blue lenses will make a white golf ball stand out against green grass. Brown lenses, which block blue light, are “more comfortable to the eye,” Haney explains. If this is high on your priority list, he suggests opting for brown lenses that shut out 70 to 80 per cent
of visible light. (Your optician can offer specific advice suited to your personal situation.)
As for frames, North recommends choosing ones large enough to cover the thin skin surrounding your eyes. Ideally, they should be adjustable, Haney adds, since “you want the nose pads of the bridge to fit properly, and you want to be able to adjust the width so the arms aren’t too tight or too loose.” Proper fit equals comfort, which means you’re more likely to wear the glasses consistently.
What about the clip-on and flip-up varieties that attach to prescription glasses? While better than nothing, “they’re not as good as a dedicated pair of prescription sunglasses,” North says, “because you’re now looking through two lenses, so you have four surfaces for reflections, smudges, and glare.” Photochromic lenses, which darken on exposure to UV light, also have a drawback: they won’t activate in the car, North explains, since windshields are ultraviolet-filtering.
One thing regular sunglasses don’t do well is prevent light that bounces up from horizontal surfaces—such as snow, water, and sidewalks—from entering the eye. Lenses with polarized filters, though, which work something like an invisible venetian blind, are designed to do exactly that. “They cut reflected light and, therefore, glare,” Haney says. “You pay more for them, generally, but they’re a far superior lens.” Prices for a pair of good shades with polarized lenses start at around the $60 to $100 range.
Of course, once you’ve got the basics covered, you can have fun with the style. After all, as North points out, wearing sunglasses has a happy side benefit: “You look good!”