Buying sunglasses is one of life’s small pleasures. But as you’re searching for shades that will make you feel fabulous, keep in mind, those lenses also need to protect your eyes from the sun’s nasty rays. 

On that point, choosing a pair may not be as simple as it seems. To help, here are three key questions to ask yourself—plus three features to look for.

Question #1: Are They Too Dark?

Some people, in an attempt to get maximum eye protection, buy the darkest shades they can find. But, fact is, dark lenses may actually make your eyes more vulnerable to the damaging effects of UV radiation. 

“When eyes are in low-light conditions, pupils inherently enlarge to bring in as much light as they can. It’s a safety mechanism,” says Arizona ophthalmologist Anika S. Goodwin, M.D. “Really dark sunglasses create a situation of low light, so the pupils dilate.” 

This is true even if the dark lenses offer 100% UV protection, says Dr. Goodwin. 

She recommends moderately dark lenses, where others are still able to see your eyes, or mirror-coated lenses if you’re going to be around highly reflective surfaces like water, sand, or snow. Both styles are also good if you’re going to be under bright lights, like at a sports stadium or an amusement park.

Highly reflective, mirrored lenses cut back the amount of light that enters the eye, so they offer increased protection against intense visible light and improve vision in truly bright conditions.

Moderately dark lenses are also a good choice if you have light eyes. “Someone with blue eyes has a thinner iris than someone with brown eyes, and the darker brown your eyes are, the thicker your iris,” explains Dr. Goodwin. 

“Just like a shade or a curtain,” she continues, “the thicker the curtain, the less light that comes through. The thinner the curtain, the more light that comes through.”

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Question #2: Are They Too Small?

Small frames don’t provide enough protection, leaving room for too much UV radiation to reach your eye in the gaps of the frame. When the pupil is dilated because of too-dark lenses, the problem is even worse. 

“Small, dark sunglasses allow room for those UV rays to bounce off the back of the glasses or come around the glasses and enter the enlarged pupil,” Dr. Goodwin says. 

For maximum protection, more coverage is always better. A wraparound style offers the best coverage, because it doesn’t allow UV rays to slip in. If the sporty style isn’t the look you’re going for, consider bigger, bolder frames to protect the eyes. 

If you have your heart set on a smaller frame, Dr. Goodwin suggests asking the optician to have an anti-reflective (or anti-glare) coating applied to both sides of the lenses. Treating the inside “prevents those UV rays that may come around your glasses from bouncing off the lenses into your eye,” she says. 

Question #3: Are They Made of the Right Stuff?

To get the smartest protection when choosing sunglasses, Dr. Goodwin suggests finding a pair with a sticker or tag that states 100% UVA and UVB protection. 

Sometimes the label will say UV 400, and that is just as good. It means it blocks any wavelengths of 400 and less. “All ultraviolet light falls into that spectrum and will be blocked,” she says.

Looking for that sticker really does matter. Short-term consequences of UV exposure—in extreme cases—can include corneal sunburn, also called photokeratitis or snow blindness. This leaves victims with painful, inflamed, watery eyes for several days, and may cause temporary vision loss. 

In the long term, exposure to UV radiation increases the risk of cataracts and age-related macular degeneration. (A cataract is the clouding of the eye’s lens. Macular degeneration represents irreversible damage to the macula, the part of the eye that’s responsible for your central vision.) Both conditions gradually interfere with vision and are leading causes of vision impairment. 

Other risks include cancer of the eye, or cancer of fragile skin tissue surrounding the eye. Pterygium, also known as surfer’s eye, is another potential problem. This is an inflammation and thickening of the conjunctiva, the thin membrane covering the white of the eye, and may eventually compromise the cornea and block vision.

Find Your Perfect Pair: 3 Considerations

When trying to find the right pair of sunglasses, consider the following: 

1. The lens color. Lenses that are a shade of darker neutrals like gray, green, and brown are good everyday choices for outdoor activities and driving. 
   
   Light shades in yellow, amber, and pink work well in lower-light conditions, making them smart choices for snow sports, especially in cloudy conditions where they enhance both contrast and depth perception.
    
2. Lenses that change. Photochromic lenses, such as the popular Transitions brand, adjust automatically to changing light intensity, so you can go indoors to outdoors without having to switch glasses. 
    
3. Polarized lenses. These lenses contain a special filter that blocks intense reflected light, reducing glare. Whether your lenses are polarized or not won’t impact UV protection. But that glare reduction can contribute to greater visual comfort.
   
   They’re particularly popular for water activities, because they let you see under the surface. The downside is that they make it tough to view the digital screen of your phone or camera.