Ophthalmic sun smarts for runners.
The article "Sun Smarts for Runners" by Meier and Adams (AMAA Journal 2007;20(1): 9-10) provided interesting and useful information about protecting the skin from harmful effects of ultraviolet radiation (UVR). Being sun smart about protecting the eyes is equally important. Several eye disorders are associated with sun exposure. They include pterygia (abnormal fibrovascular tissue arising from the conjunctiva and extending onto the cornea, sometimes partially blocking vision and requiring surgery for removal), photokeratitis (temporary but painful inflammation of the cornea, also known as "snow blindness" and "welders' flash"), cataracts, and age-related macular degeneration (AMD) (1). AMD is the primary cause of irreversible vision loss in Caucasians 50 years and older in the United States (1).
The eye has innate protective mechanisms against deleterious effects of UV-B (295-320 nm), UV-A (320-400 nm), and visible light (400-700 nm), but this protection is limited. Eyes of the young and of adults are protected by an efficient antioxidant system that reduces the amount of free radicals formed from the interaction of oxygen, photons, and receptor molecules. Protection also is provided by pigments that absorb ambient radiation and harmlessly dissipate its energy. However, after middle age, the production of antioxidants and antioxidant enzymes diminishes, and the protective pigments are modified. The lens pigment 3-hydroxykynurenin is converted to phototoxic xanthurenic acid, and both uveal and retinal melanin is converted from an antioxidant to a pro-oxidant. Concomitantly, fluorescent chromophores (lipofuscin) accumulate in sufficient amounts to produce reactive oxygen species (2).
The lens of the eye provides additional UVR protection to the retina, including the macula, which AMD afflicts. Except in early life, the lens absorbs most incident UV energy: wavelengths up to 400 nm early-on and up to 450 nm later in life (3). Hence, pseudophakia with an older, poorly UV-absorbing intraocular lens or aphakia can facilitate UVR-induced retinopathy. Because the cone system of the retina undergoes slower replacement of light-sensitive membranes, it is more likely to be damaged than the rod system (3).
Thus the protective mechanisms of the eye against UVR damage are especially limited in very young and post-middle-age individuals and in pseudophakes with poorly UV-absorbing intraocular lenses or aphakes. How can a runner-or anyone-supplement these mechanisms to maximally protect the eye against harmful effects of the sun? The American Academy of Ophthalmology (AAO) recommends wearing 99 percent or above UV-absorbent sunglasses and a brimmed hat anytime an individual is outdoors. Labels stating, "UV absorption up to 400 nm," provide 100 percent UV absorption. The color and darkness of a lens indicate nothing about its UV-light-blocking capability. Also, mirror finishes reduce the visible light entering the eye, and polarized lenses cut reflected glare, but neither significantly affects UV transmission (1).
Furthermore, although claims to the contrary are made, there is no evidence that infrared light is associated with eye disease, and it is controversial whether blue light harms the eye (1).
Of note, obliquely incident UVR can enter the eye temporally and reach the equatorial (germinative) area of the lens (4). Thus large-framed, wraparound sunglasses or UV-absorbent contact lenses (not all contacts) are more protective against UVR than sunglasses with ordinary frames.
Adherence to the AAO recommendations is especially important during the summer, when the level of UV radiation is at least three times that during the winter. Moreover, year-round adherence is particularly important for individuals with certain eye diseases, such as AMD or retinal dystrophy, which may increase the risk for UVR damage. Adherence also is paramount when taking medications or dietary supplements that cause photosensitivity, or for a short period after receiving photodynamic therapy for AMD. Photosensitizing drugs include psoralens (used to treat psoriasis), tetracycline, doxycycline, allopurinol, and phenothiazine (1).
Furthermore, contrary to common belief, research recently presented at the 111th Annual Meeting of the Japanese Ophthalmological Society indicates that during spring, summer, and autumn, exposure of the eye to UVR during early morning and late afternoon is approximately double that during mid-morning/early afternoon (5).
In summary, whenever anyone is outside in daylight, use of a brimmed hat and either wraparound, 99 percent and above UV-absorbent sunglasses or UV-absorbent contact lenses are important measures to protect the eye from UVR damage. Adherence to these measures is especially important for individuals with pseudophakia if the intraocular lens is poorly UV-absorbent, aphakia, or certain retinal diseases, and for individuals taking photosensitizing traditional or alternative medications or recently treated with photodynamic therapy for AMD.
1. American Academy of Ophthalmology website: www.aao.org.
2. Roberts JE. Ocular phototoxicity. J Photochem Photohiol 2001;64(2-3): 136-43.
3. Hunyor AS. Solar Retinopathy: its significance for the ageing eye and the younger pseudophakic patient. Aust N ZJ Ophthalmol 1987;15(4): 371-5.
4. Sliney DH. How light reaches the eye and its components. Int J Toxicol 2002;21(6): 501-9.
5. Study shows more uv exposure early morning, late afternoon. Ophthalmology Times. June 15, 2007: 53.
Alice T. Gasch, MS, RD, MD
Ophthalmologist, Washington, DC
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|Author:||Gasch, Alice T.|
|Article Type:||Letter to the editor|
|Date:||Sep 22, 2007|
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