When it comes to your eye care, it's what you can't see that can hurt you. Most of the time when we purchase sunglasses, we make a decision based upon fashion and how well they stop glare, but what we really need to know is how well they fare against ultraviolet (UV) radiation.
UV light has a shorter wavelength than visible light, you'll remember from your high school Physics, and that shorter length enables it to penetrate objects. There are three types of UV light: UVA, UVB, and UVC. The last can't penetrate our atmosphere, but UVA and UVB can get through just fine. UVA could damage your retina, but most of it is absorbed by other parts of the eye before it can make its way through. This leaves UVB, and that's problem enough.
One study led by researchers at Case Western Reserve Universityindicates that UVB light can damage lens proteins in a distinct way that is typically seen in cataract and in cells damaged by oxidative stress. UVB ray exposure is also closely linked with photokeratitis, a kind of sunburn of the cornea. Other studies have tied UVB rays to pterygium, a white or creamy fleshy growth on the surface of the eye, and a form of eye cancer called squamous cell carcinoma of the conjunctiva.
Never mind that you don't ever look directly into the sun, your eyes can be exposed to UV radiation “on the rebound” from grass, soil and water, which throw back less than 10 percent of the radiation. Snow will hit you for an 80 percent bounceback, while even sea foam is good for a 25 percent reflection.
Multiply everything by a factor of 10 if the exposure occurs around noontime. But because so many of us are in the habit of wearing brimmed hats, the stats show that the most dangerous time for UV exposure to your eyes is in the morning and mid-afternoon.
It's all up to your sunglasses then, so make sure they are effective against UV radiation. Specifically you will want sunglasses that limit transmission to no more than 1 percent UVB and 1 percent UVA rays.
And save those cute small round steampunk shades for your cosplay at Comic Con You want lenses large enough to completely cover your eyes and prevent as much light as possible from entering through the edges of the glasses. Wrap-around sunglasses are best, with lenses as dark as you can bear and still not walk into walls.