So much has been made of sunscreen and the need to protect our skin from dangerous ultraviolet rays, it seems eye health has gotten lost in the message. As July is UV Safety Month, it is a perfect time to rectify this balance and discuss how ultraviolet rays affect vision.
There are three types of ultraviolet radiation (UV rays) emitted by the sun, but only two types cause damage. Absorbed by the ozone layer, UV-C does not pose a threat to human health. On the other hand, UV-A and UV-B rays present both short- and long-term negative effects on the eyes and vision. Long-term exposure to UV rays may contribute to the development of age-related macular degeneration and cataracts. According to the World Health Organization (WHO), 18 million people worldwide are blind as a result of cataracts and of these, as many as five percent may be due to UV radiation.
What are the effects of exposure to these rays?
If your eyes are exposed to excessive amounts of UV radiation over a short period of time, you are likely to experience an effect called photokeratitis, sometimes referred to as "sunburn of the eye." Photokeratitis symptoms include redness, a gritty feeling in the eyes, extreme sensitivity to light, and excessive tearing. Like a sunburn, this is usually temporary.
Long-term exposure to UV radiation, however, is a more serious matter. Scientific research has provided evidence that exposure to small amounts of UV radiation over a period of many years increases the chance of developing a cataract and may cause damage to the retina. The retina is the light-sensitive layer of tissue at the back of the inner eye that acts like film in a camera — images come through the eye's lens and are focused on the retina. The retina then converts these images to electric signals and sends them via the optic nerve to the brain.
Chronic exposure to shorter wavelength visible light — 'blue light' is that light with wavelengths in the 500nm to 381nm range and is often referred to as 'near UV' — may also be harmful to the retina. According to a review of eye research conducted by the Chinese University in Hong Kong, although cataracts have been associated with UV exposure, the researchers found insufficient evidence to determine whether age-related macular degeneration (AMD) is related to UV exposure. "It is now suggested that AMD is probably related to visible radiation especially blue light, rather than UV exposure," wrote the researchers.
Blue light is emitted by fluorescent lights, energy efficient lights, computer monitors, and many other electronic devices. Previous studies have linked exposure to 'night lights' to cancer (breast and prostate), diabetes, heart disease, and obesity, yet increasingly, scientists are finding a relationship between overexposure to blue light and retinal damage, including AMD. "Recent studies suggest that the blue end of the light spectrum may also contribute to retinal damage and possibly lead to AMD," states the American Macular Degeneration Foundation unequivocally. "The retina can be harmed by high-energy visible radiation of blue/violet light that penetrates the macular pigment found in the eye."
Naturally, protection is key.
When outside, sunglasses and a wide-brimmed hat are simple yet effective defenses against harmful UV rays. For those who spend a lot of time outdoors, wrap around frames provide the best protection from the harmful solar radiation. The lenses in sunglasses should be made from polycarbonate or Trivex material, and these are the minimum requirements to provide protection:
- They block out 99 to 100 percent of both UV-A and UV-B radiation;
- They screen out 75 to 90 percent of visible light;
- They are free of distortion and imperfection.
The ability to block UV light and protect your eyesight is not dependent on the darkness of the lens or the expense of the sunglasses. UV protection can come from adding chemicals to the lens material during manufacturing or from a chemical coating applied to the lens surface. Expensive sunglasses do not necessarily translate to greater protection as the high price is most often about style and frame quality and not necessarily protective UV ray-blocking ability.
Melanin lenses or 'computer glasses' are especially effective in absorbing glare and harmful rays, according to the American Macular Degeneration Foundation, and they are widely available in both prescription and non-prescription strength.
To strengthen the eyes through diet is another worthy approach to protecting eye health. In a study conducted at the University of Wisconsin, researchers found that diets rich in lutein and zeaxanthin are moderately associated with decreased prevalence of nuclear cataract in older women. Participants in the study included 1,802 women aged 50 to 79 years in Iowa, Wisconsin, and Oregon. Those women with high dietary levels of lutein and zeaxanthin had a 23 percent lower prevalence of nuclear cataract compared with those with low levels, while those in the highest quintile category of serum levels of lutein and zeaxanthin as compared with those in the lowest quintile category were 32 percent less likely to have nuclear cataract.
Of the 600 carotenoids found in nature, only two are deposited in high quantities in the retina (macula) of the eye: lutein and zeaxanthin. Lutein and zeaxanthin filter harmful high-energy blue wavelengths of light and act as antioxidants in the eye, helping protect and maintain healthy cells. Carotenoids are largely responsible for the red, yellow, and orange color of fruits and vegetables, and are found in many dark green vegetables; eating kale, spinach, collard greens, peppers, corn, and tangerines, among other foods, will boost your intake of lutein and zeaxanthin.
Finally, a recent study in Sweden investigated the use of topically applied caffeine with regard to protection against in vivo ultraviolet radiation cataracts. Three experiments were carried out on rats that were pretreated with either a single application of placebo or caffeine eye drops and then exposed to UV-B radiation. The researchers found significantly less UV-B radiation cataract in the caffeine group than in the placebo group. "Topically applied caffeine protects against ultraviolet radiation cataract, reducing lens sensitivity 1.23 times," wrote the authors.
Sources: Yam JC, Kwok AK. Ultraviolet light and ocular diseases. International Ophthalmology. 2013.
Kronschläger M, Löfgren S, Yu Z, Talebizadeh N, Varma SD, Söderberg P. Caffeine eye drops protect against UV-B cataract. Experimental Eye Research. 2013.
Roberts JE. Ultraviolet radiation as a risk factor for cataract and macular degeneration. Eye & Contact Lenses. 2011.
Moeller SM, Voland R, Tinker L, et al. Associations between age-related nuclear cataract and lutein and zeaxanthin in the diet and serum in the Carotenoids in the Age-Related Eye Disease Study, an Ancillary Study of the Women's Health Initiative. Archives of Ophthalmology. 2008.