Sunglasses are labeled according to guidelines for UV radiation protection established by the American National Standards Institute (ANSI). There are three categories:
- Cosmetic. Lightly tinted lenses, good for daily wear. Block 70% of UVB rays (linked to sunburn and skin cancer), 20% of UVA (responsible for skin tanning and aging), and 60% of visible light.
- General purpose. Medium to dark lenses, fine for most outdoor recreation. Block 95% of UVB, 60% of UVA, and 60% to 90% of visible light. Most sunglasses fall into this category.
- Special purpose. Extremely dark lenses with UV blockers, recommended for places with very bright conditions such as beaches and ski slopes. Block 99% of UVB, 60% of UVA, and 97% of visible light.
Just because a lens appears darker doesn't mean its ability to block out UV radiation is any greater than a lighter lens. Look for the ANSI label; even inexpensive sunglasses can be effective.
There is some evidence that blue light from the sun may contribute to the development of age-related macular degeneration. Lenses with a red, amber, or orange tint may provide better protection against this light. You may find less distortion, however, with gray or green lenses.
If you aren't sure what kind of sunglasses to buy or think you may be at high risk for eye disease, consult an eye care professional.
More Answers from Laura Fine, MD