Monday, July 14, 2014
Sunglasses- more than a fashion statement
By : Adam Gordon, O.D., M.P.H. Clinical Associate Professor UAB School of Optometry
Most people know that sunscreen protects the skin from the damaging effects of sun exposure, such as premature aging and wrinkling, carcinomas, and potentially life-threatening malignant melanoma. However, most Americans are not aware of the damaging effects of excessive sun exposure on the eyes, nor are they aware that sunglasses serve as “sunscreen for the eyes.”
Just as sunscreen offers broad-spectrum protection to the skin, sunglasses should also block virtually all ultraviolet B (UVB) and ultraviolet A (UVA) radiation from entering the eyes. UVB is primarily absorbed by the external ocular surface and cornea, while the longer UVA rays can penetrate deeper, even reaching the crystalline lens and retina. Excessive sun exposure is associated with external ocular lesions such as pingueculae and pterygia, as well as basal and squamous cell carcinomas on the eyelids and periocular skin. Since the skin comprising the eyelids and surrounding area is relatively thin, it is very susceptible to sun damage such as loss of elasticity, wrinkling, and discoloration.
The cornea and crystalline lens of the eye are transparent, avascular, and immunologically unique. The deleterious effects of UV exposure on these structures are thought to be cumulative over decades. In childhood and adolescence, the crystalline lens is extremely transparent, allowing some UV radiation to reach the retina. Research suggests that up to 50% of our lifetime UV exposure occurs by age 18, suggesting that sunglasses are especially important during active childhood years.
Numerous large-scale epidemiological studies show a significant association between sun exposure and cataract formation. People with outdoor occupations or avocations may develop cataracts earlier in life that progress more rapidly compared to indoor workers. The regular use of sunglasses when outdoors may serve to decrease the risk of cataract formation in later life. The link between sun exposure and age-related macular degeneration is more tenuous than with cataract formation, but sunglasses may be an easy preventive measure to protect the retina from UV radiation.
Recent research in animal models suggests that short-wavelength blue light, also known as “high-energy visible” (HEV) light may be damaging to retinal cells and metabolic processes. The animals used in these studies developed retinal degeneration that may be similar to macular degeneration in humans. More research is needed before a definitive link to human retinal disease can be made, but there may be value in using sunglasses that block HEV rays in addition to UV radiation.
Here are some general tips about purchasing sunglasses:
• Sunglasses should have a label stating they block 100% of UVA and UVB rays (broad spectrum protection)
• The lenses should ideally be made of polycarbonate- a lightweight, impact-resistant plastic that provides excellent UV protection
• The lenses should fit as close to the eyes as possible, with a curved shape that wraps around the face to block light from the sides
• The lenses should be dark enough so that the wearer does not see, or barely sees, his or her eyes when looking in a mirror
• The most common sunglass lens colors are gray, green, and brown. Gray lenses have the least effect on color perception.
• The color of a lens and it’s darkness are not indicative of its ability to block UV rays
• Polarized sunglasses provide an additional glare-blocking benefit from water, sand, concrete, car bumpers and hoods, snow, and ice
• Good sunglasses providing 100% UV protection do not have to be expensive
A good web reference for consumers and health professionals is: http://www.allaboutvision.com/sunglasses/spf.htm#news2