The sun emits three types of ultraviolet (UV) radiation: UVA, UVB and UVC. These rays are neither seen nor felt by humans. UVC rays are completely absorbed by the Earth’s atmosphere; UVB rays are partially absorbed. The rest, including all UVA rays, pass through the atmosphere ultimately reaching the Earth’s surface.
UVA rays, which account for the majority of UV exposure, pierce the outer and middle layer of the skin and can damage the retina of the eye. UVB rays damage the skin’s outer layer and are the culprit for sunburns, pterygium (an abnormal growth on the surface of the eye) and photokeratitis (sunburn of the eye). UVB rays have also been shown to accelerate cataract development and age-related macular degeneration, and to cause squamous cell carcinoma of the eye (a form of cancer).
UVA and UVB rays can reflect off surfaces such as water, sand, snow and even buildings. Reflected UV increases exposure levels and can double UV risk to the eyes in certain conditions, such as with snow.
While the eyelid is designed to limit the amount of UV radiation that enters the eye, the thin, delicate tissue is not entirely effective at protecting the cornea, which is the clear surface of the eye. Over time, cumulative UV exposure can yellow both the lens and the cornea, making it more difficult to see contrast.
Short-Term UV-Related Eye Damage
Brief but intense doses of UV radiation can cause short-term ocular problems ranging from discomfort or pain to temporary blindness. Issues often appear after long days spent outdoors without UV-protective eyewear. Symptoms, which can appear up to 24 hours after exposure, include redness, swollen eyes, blurred vision and sensitivity to light. If the sun is strong enough, reflective rays can actually burn the cornea – a condition called photokeratitis.
Individuals with photokeratitis experience extremely swollen eyelids, uncontrollable watering of the eyes and a feeling of grit lodged inside their eyelids. Most cases of photokeratitis last just one day, but pain can persist for several days. For some people, corneal burns can cause temporary blindness. These conditions are temporary and do not result in permanent damage.
Long-Term UV-Related Eye Damage
Over time, accumulated UV damage can result in the development of pterygia and pinguecula. Pterygia-2Pterygium is a thin, noncancerous growth of tissue that surfaces on the conjunctiva (the thin, transparent membrane that covers the white part of the eye) and cornea. In addition to being unsightly, these growths are painful and irritating. Surgery may be required in cases where pterygia grow large enough to interfere with vision; however, growths may reappear after surgical removal. Similarly, a pinguecula is a yellow protein deposit on the conjunctiva. Unlike pterygia, pinguecula do not grow on the cornea and therefore don’t interfere with sight. Surgical removal is rare but available on a case-by-case basis.
Long-term exposure to the sun is also a risk factor for cataracts, a clouding of the eye’s lens. Over time, even low levels of UVB exposure can cause changes in the lens, including pigment changes, which contribute to cataract development. The World Health Organization estimates that up to 20 percent of all cataract cases may be attributable to UV radiation, and are therefore avoidable.
Given UVB’s correlation with cataract development, a depleting ozone layer could result in heightened exposure and increased incidence of cataracts. Just a 10 percent decrease in the ozone layer can lead to an increase of 1.6 million to 1.75 million cataract cases.
Age-related macular degeneration (AMD) is characterized by the deterioration of the eye’s macula. This condition limits central visual acuity, making it hard to perceive detail. AMD is the leading cause of blindness in the western world; there is currently no cure.
Studies suggest that prolonged exposure to UVA radiation can lead to AMD; however, the relationship between UV rays and AMD is not well understood. Emerging research reveals that exposure to high-energy visible (HEV) light can induce oxidative stress on the retina, resulting in AMD.
UV radiation can also cause different forms of cancer – both in the eye and the delicate skin surrounding the eye. Melanoma is the most frequent malignant cancer of the eye and often requires surgical removal. Basal cell carcinoma, a nonmelanoma type of cancer, is a small, fleshy bump or nodule that can form on the eyelid. In addition to being the most common form of skin cancer, basal cell carcinoma accounts for 90 percent of all eyelid cancers.