July is UV Safety Awareness Month and Johns Hopkins Medicine wants you to know that not only should you be wearing a hat whenever you’re outdoors but also protective sunglasses. At the school’s Wilmer Eye Institute, ophthalmologist Irene Kuo, M.D. discusses how UV light can harm your eyes and what you can do to protect them.*

What is UV light? Can it affect vision?

Invisible to most humans, ultraviolet (UV) light is the basis of black lights and the cause of suntans and sunburns. Indeed, get too much UV radiation and you risk damaging your tissues. 

UV light is part of the electromagnetic spectrum emitted by the sun. UV has the energy to break chemical bonds, which can be beneficial for processing chemicals but harmful to living tissues—especially our skin and eyes.

Both UVA and UVB wavelengths can have harmful short- and long-term effects on vision. While short-term UV exposure can lead to photokeratitis (essentially a sunburn of the eye), repeated exposure over time can cause worse and longer-lasting eye damage.

UV damage and protecting your eyes

“UV light is damaging to almost ALL ocular structures including the eyelid,” says Kuo. With chronic UV exposure, severe eye conditions that can ultimately lead to vision loss can result, including:

• Corneal damage
• Cataracts
• Macular degeneration

Kuo says the skin of our eyelid is the thinnest of the body, and is vulnerable to UV damage, including cancer. Squamous cell carcinoma, for example, can happen not only on the skin but the conjunctiva (membrane covering the white part of the eye, or sclera), and can move into the cornea and inner eye. Removal of the entire eyeball is sometimes needed.

The cornea can also become cancerous or develop noncancerous growths, since nearly all UV radiation is absorbed by the eye’s front surface. Corneal damage can happen from UV light being reflected off water or snow, for example, as when boating or skiing.

UV exposure can lead to cataracts, or cloudy patches on the eye lens, which requires surgery to replace the lens if the damage affects daily life. UV damage and oxidative stress can also lead to age-related macular degeneration, a leading cause of blindness.

To protect your eyes from UV damage, Kuo advises:

• Protecting your skin and eyes whenever UV risk is highest
• Trying to avoid outdoor activities between 10 a.m. and 4 p.m., when the sun is strongest
• Never looking or staring at the sun, even during an eclipse, which can damage the retina and permanently reduce sight quality
• Wearing a wide-brimmed hat, and sunglasses with maximum UV protection

More than style: Choosing good sunglasses

Not all sunglasses are created equal. The American Academy of Ophthalmology (AAO) offers these practical tips to help you select the perfect shades.

• Only consider sunglasses that have a tag or sticker indicating 100% UV protection or “UV absorption up to 400 nm [nanometers].”
• Choose sunglasses with the largest lenses, preferably with an oversized or wraparound design to protect from UV entering the sides.
• Look for “100% UV protection” on the label; a darker lens won’t necessarily confer more protection. 
• A colored lens provides better contrast, and polarized lenses reduce glare from reflective surfaces like snow or water, but neither of these lenses will protect against UV by themselves.  
• Inexpensive drugstore sunglasses labeled as 100%-protective against UV are a better choice than designer sunglasses with no UV protection.

If you’re wondering how protective your current sunglasses are, AAO advises getting them tested at an optical store with a UV light meter.

*Kuo, I. C. (2019, July 24). How to Protect Your Eyes from UV Damage. Johns Hopkins Medicine. https://www.hopkinsmedicine.org/news/articles/how-to-protect-your-eyes-from-uv-damage