Darker sunglasses that don’t protect against ultraviolet light allow more of these higher-energy waves into pupils that are overly dilated because of low-light conditions, leading to greater probability of injury, experts say.

“Dark shades cause more harm because you lose that protective reaction: you don’t squint, your pupils don’t constrict,” Edward Kondrot, an ophthalmologist in Dade City, Fla., told MedPage Today. “And you get excessive amounts of sunlight into the eyes.”

The key, he says, is to choose a pair of sunglasses that is guaranteed to block UVA and UVB rays.

On the electromagnetic spectrum, ultraviolet light occurs in the range of 100 to 400 nanometers. Most of the UV light that reaches the earth’s surface is UVA, from 315 to 400. Light in this range can alter chemical bonds in skin molecules, as seen in sunburn.

Like the skin, the eye also absorbs UV. Shorter and more dangerous wavelengths are caught by the cornea, with longer wavelengths potentially reaching the lens and retina, experts say. That’s why ophthalmologists insist that UVA and UVB protection in sunglasses is more important than the intensity of their tint.

— Posted by Alexander Reed Kelly.

MedPage Today:

“You should look for labels that say UV absorption 99% or 100%,” Majid Moshirfar, MD, of the Moran Eye Center at the University of Utah, told MedPage Today. “You may also see a label that says UV absorption up to 400 nm. That also means the absorption is up to 100% of UV.”

Moshirfar added that polarized lenses don’t do anything to stop UV light from hitting the eye; they just help to cut down on glare. Still, that can come in handy in glare-heavy situations, like driving or fishing.

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