Don't Be Blinded by the Light
By A.Paul Chous, MA, OD, FAAO
With the approach of summer, more and more of us will be spending time in the ‘great outdoors’ enjoying the sunshine and longer days. Most of us, hopefully, will take some precautions to guard against sunlight damage, like wearing sunscreen, covering up exposed skin, and limiting the amount of time we spend in the sun. Most people are aware that invisible, ultraviolet (or UV) light is a major cause of skin damage and skin cancer. Unfortunately, fewer people appreciate the harmful effects of UV rays on our eyes, and far fewer take the basic measures to prevent those effects.
Light rays contain energy that travels in waves, and the amount of that energy depends on the wavelength of light (analogous to the distance between waves in water). The shorter the wavelength, the more energy light has, and the greater are its harmful effects on living tissues. UV light has a shorter wavelength and, hence, more energy than visible light. Similarly, blue light has a shorter wavelength and contains more energy than red light.
Not all UV rays are equal, however. UV-C has the shortest wavelength and is most damaging; fortunately, it is entirely blocked by the Earth’s atmosphere. UV-B is less harmful, but is the main cause of skin cancer, including basal cell carcinoma, squamous cell carcinoma and malignant melanoma. Energy from UV-B is absorbed by tissues on the eyes’ surface, the cornea (the clear windshield covering the colored part of the eye), the conjunctiva (the mucous membrane covering the white of the eye), and the delicate skin of the eyelids (a reason why eyelid cancers are very common). UV-A is the least damaging type of ultraviolet light, but may cause cumulative damage to skin and eye structures, including the retina. In addition, short wavelength blue light has also been implicated in cumulative oxidative damage to the retina.
Eye complications caused by or associated with UV light exposure include: photokeratitis (an extremely painful but temporary corneal ‘sun burn’ resulting from UV-B rays reflected off of sand, water or snow); pinguecula/pterygium formation (yellow calluses on the conjunctiva or cornea that may affect vision); eyelid skin cancers; tumors of the conjunctiva; cataract formation and accelerated cataract growth (progressive clouding of the eye’s internal lens affecting vision); early onset of macular degeneration of the retina caused by oxidative (free radical) damage that can lead to severe visual impairment (see my last column on macular degeneration), malignant melanoma of the iris (colored part of the eye) and choroid (the blood vessel layer of the eye, sandwiched between the retina and the white of the eye.)
It is worth noting that diabetic retinopathy results, at least in part, from oxidative (free radical) damage to the retina caused by elevated blood sugar levels, and that UV radiation similarly causes oxidative damage. Although no scientific studies have been conducted to assess the role that UV damage plays in diabetic retinopathy, per se, it makes sense for patients with diabetes to protect our eyes from harmful UV (and blue) light exposure to prevent getting a ‘double whammy’ from free radical molecules caused by both hyperglycemia and short wavelength light rays.
The best defense against the eye complications caused by short wavelength light includes wearing UV blocking lenses (any sunglass that blocks 99% of UV-A and UV-B, or any prescription eyewear made of UV-blocking polycarbonate plastic or coated with a UV-400 filter). Wearing sun protection that wraps around the eyes will provide additional UV protection. Although wearing sunglasses lets our pupils dilate a bit, thereby letting in more total light, UV blocking lenses filter out the most harmful rays providing far superior protection. Never buy blue tinted sunglasses as these selectively allow blue light to pass through the eye to the retina. Remember that UV rays penetrate clouds, so it’s important to wear UV blocking lenses whenever we’re outside during daylight hours. In addition, wearing a wide brimmed hat that keeps light from directly striking the eyes and face is an effective secondary strategy. Finally, see your eye doctor regularly to check for any signs of UV related eye damage and the latest advances in UV protection.
For more information on diabetic eye disease, consult Dr. Chous’ book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.
Read more about Dr. Chous here.
Visit Dr. Chous' website here.
NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.
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