What you should know before buying sunglasses

5/30/2017, 9:21 a.m.
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— As far as a "hard requirement," UV protection is it, he said. Tint doesn't matter, polarization doesn't matter, and although bigger is always better, "UV protection is the essential piece."

The inessentials, though, may also play a role in eye health.

Beyond UV rays

Thau says there are two parts to sunglass protection: One is non-visible radiation, and the second has to do with visible light -- how much brightness they block.

"When you're in the bright sun, like the beach, you do want something 75% or darker to block you from visible light," Thau said. Too much exposure to visible light "does bleach your receptors, and some studies have indicated it can impair your night vision and your color vision perception."

Yet blocking visible light has a downside if your sunglasses are not up to UV snuff, suggests Dr. James H. Diaz, an environmental medicine specialist and anesthesiologist.

"The darker the sunglass lenses, the more the pupils will dilate and allow more UV light to enter the eye," Diaz wrote in an email. This is true of blue light, which ranges in length from 400 to 440 nanometers.

"The longer the retinas are exposed to unfiltered blue light, the greater the risk of macular degeneration," Diaz said. However, the National Eye Institute does not list protection against blue light as necessary when purchasing sunglasses. In fact, research has shown blue light exposure is good for us, as it helps regulate our circadian rhythms and so affects both mood and cognition.

"Orange and yellow lenses provide the best protection from blue light, and blue and purple lenses provide the least protection," Diaz said.

Thau noted color is not crucial in protecting eye health. "Most popular colors are gray, green and brown. They are the least distorting for color perception, with gray being the most neutral," she said.

People who have color vision deficiencies generally find that they see much better with brown lenses, while "green seems to give more contrast," said Thau.

Whether you opt to filter out blue light or not, a good pair of UV-blocking sunglasses can protect both your short-term and long-term health.

Protect your thin skin

"Skin around the eyelid is the thinnest in the body, so it is susceptible to skin cancers," Thau said. This thin skin is most likely to develop basal cell and squamous cell cancers, so the recommendation is to wear the largest pair of sunglasses possible to protect the eyelids and surrounding skin.

Meanwhile, Pettey warns that cancers of the eye itself, including squamous cell carcinomas and malignant melanomas, also can result from sun exposure.

"The same damage that occurs to our skin occurs to the eye," he said: specifically "eye burn," a form of short-term damage similar to a sunburn.

Thau says sun exposure can also cause photokeratitis, an inflammation of the cornea, with temporary symptoms of blurry vision, light sensitivity and a burning or gritty sensation. Too much sunlight may also lead to a thickening and/or yellowing of the conjunctiva, the membrane covering the eye. Though unsightly and annoying -- your eyes will feel too dry when this happens -- this doesn't cause blindness, says Thau.