Longer days and harmful ultraviolet (UV) sunlight make summer a particularly threatening time for unprotected eyes, says ophthalmologist Ashley Behrens, chief of the Division of Comprehensive Ophthalmology at the Wilmer Eye Institute.

Besides posing a skin cancer risk to eyelids, these harmful rays can cause ocular disorders. According to the National Eye Institute, extended UV exposure causes about 20% of cataracts.

The best way to protect your eyes is to wear sunglasses outside as much as possible, says Behrens, and not only during the summer. He recently discussed the need for sunglasses and how to make sense of the options.

Q. Just how damaging can summer sun be without sunglasses?

A. Continuous exposure to sunlight can hasten the development of cataracts and other ocular surface diseases. It’s not quite as damaging as it is to skin. Eyelid protection is also very important for people who work outside, such as construction workers. Even while walking or playing sports outside, wearing sunglasses — and a brimmed hat — is important to prevent basal cell or squamous cell carcinomas on eyelids as well as skin. Too much UV exposure also causes pterygium (pronounced ter-i-jiy-um), an irritating growth on the white part of the eye, and photokeratitis (sunburned eyes).

Q. What are some common misconceptions about sunglasses?

A. You don’t need to buy expensive ones. As long as they have a sticker stating that they provide 95% to 100% UV protection, you should be safe. Also, sunglasses should be worn outdoors all year round, even though the sun’s rays are not quite as intense during other (not summer) seasons. Sunlight reflecting on snow or other surfaces can also affect the eyes.

Q. What about the lens colors? Does it matter in terms of protection?

A. It’s best to stick to brown, green and gray. Yellow doesn’t provide as much sunlight protection but gives you more contrast, especially when driving.

Q. What else should people look for in sunglasses?

A. It’s important to find out if lenses are “polarized.” That means they reduce glare/reflective rays, like on water while you’re on a boat. But be aware that polarized lenses filter light differently. So, with certain devices, like on a GPS in your car or some smartphones, you might see a dark or completely black image when you’re wearing polarized sunglasses.

Q. What do you think about transitional lenses, which turn darker while in the sun?

A. I’m wearing them right now. I like them but get annoyed in my car when they don’t get darker. Unfortunately, you can’t get around that. That’s because all cars now have UV-protected windshields. (The lenses) can’t react to a light source that isn’t getting through.

Q. Are people with lighter colored eyes more affected by sunlight?

A. Yes, people with lighter color irises, like blue or green, have more light sensitivity.

Q. Are sunglasses necessary on cloudy days?

A. Yes. Keep in mind that UV rays reach the Earth, even when clouds block the sun. These rays also reflect on many surfaces, including concrete, snow and sand. Wraparound sunglasses are the best choice for people who are outside a lot.

Q. How important is it for children to wear sunglasses?

A. The sooner they start wearing them, the better. My son was 3 when I discovered he had pterygium. I made sure he started wearing sunglasses.

Q. What might surprise people about their best sunglass options?

A. Clip-on sunglasses can be just as effective to protect your eyes.

Q. Anything else we should know about sunglasses?

A. Don’t believe people who say you need to wear them when you work indoors on a computer screen. Computer monitors may cause eye fatigue and dryness during extended viewing, but the monitors’ blue light is not going to damage your eyes.

Learn more:

hopkinsmedicine.org/news/articles/how-to-protect-your-eyes-from-uv-damage