How to choose protective sunglasses
People purchase sunglasses for a variety of reasons, including looking good, visual comfort, protection or any combination of these reasons.
If your primary concern is looks, then ultraviolet radiation (UV) entering the eye is likely not a significant consideration. If you’re seeking an improvement in visual comfort, your main objective is to determine a tint that meets your color and intensity preference.
Keep in mind that, since sunglasses block light and therefore offer better visual comfort, this will result in a larger pupil size when the lenses are on. If the sunglasses don’t block UV, then more of that harmful radiation will enter the eye. For the health conscious individual, ensuring that the sunglasses absorb UV is critical. Fortunately, in all three cases, most sunglasses sold in the United States will protect you from harmful UV radiation.
It’s important to understand that the UV portion of the spectrum is broken up into three classifications based on wavelength: C, B and A. The shortest wavelength and most dangerous, UV-C, is absorbed by the atmosphere and doesn’t reach Earth’s surface. The other two, UV-B and UV-A, are everyday hazards.
With UV-B, the eye (specifically the cornea – front of the eye) blocks this energy from reaching the lens and retina (back of the eye). As the wavelength increases through the UV-A range, a progressively greater amount of UV reaches the ocular structures. The ocular structures of younger individuals allow more UV-A to reach the retina than in older individuals. This is due to the progressive changes that occur to the lens in the eye as we age. Although long-term exposure to UV hasn’t been clearly linked to retinal problems, it has a clear association with cataracts. Because of this, it’s very important for children and young adults to wear UV protection.
When purchasing sunglasses, you should look for labeling that states something along the lines of “Blocks 100% UV-A and UV-B” or UV400. The latter indicates that all wavelengths 400nm or shorter are blocked. If you want to be 100% sure that the lenses you purchase block UV-A and UV-B, you’ll need to find an eye doctor or optician who has a photometer to test your lenses. The good news is that inexpensive lenses, even the $5 pairs, offer the same UV protection as the ones costing hundreds of dollars.
Other things to keep in mind with UV are the effects of elevation, snow, polarization and occupations. In regard to elevation, for every 1,000 meters increase, there’s a 10-12% increase in UV exposure. Snow highly reflects UV and substantially increases UV exposure. For mountain climbers and skiers, it’s even more critical that proper UV protection is worn. It’s important to know that polarization on its own doesn’t block UV. Polarization is a really nice feature, but without a component of the lens absorbing UV it offers no protective benefit. Certain occupations may expose individuals to higher than normal levels of UV (water treatment plant for example) or prolonged UV exposure (outdoor workers). It’s critical that these individuals use appropriate UV-protecting eyewear.
Aaron B. Zimmerman is a clinical professor at The Ohio State University College of Optometry.