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Ultraviolet Radiation
Protection Against Exposure
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In a previous article [Federal Air Surgeon's Medical Bulletin, Winter 1994], we discussed what ultraviolet (UV) radiation is and how it has been associated with numerous ocular disorders, particularly cataracts. We also learned that pilots may be at greater risk for exposure than non-pilots. In this article, we will focus our attention on how to best protect the pilot from UV radiation. Ulraviolet Radiation reaches the eye not only from the sky above, but also by reflection from the ground, especially water, snow, sand, and other bright surfaces. Protection from sunlight can be obtained by using a brimmed hat or cap and UV absorbing eyewear. A hat or cap can reduce UV radiation by about 50%. Ultraviolet absorbing eyewear provides the greater measure of UV protection, particularly if it has a wraparound design to limit the entry of peripheral rays. For outdoor use in bright sun, sunglasses that absorb 99-100% of the full UV spectrum up to 400 nanometers are recommended. There is presently no uniform labeling of sunglasses that provides adequate information to the consumer. If labels are available, they should be examined carefully to ensure that the lenses purchased absorb at least 99-100% of both UV-B (280 to 315 nanometers) and UV-A (315 to 400 nanometers). |
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The standard for UV transmittance in sunglasses is being debated. The Non-Prescription Sunglasses and Fashion Eyewear requirements, adopted by the American National Standards Institute (ANSI) Z80.3 Committee, identify three categories of sunglasses: Cosmetic use, General purpose (for use in any outdoor activity), and Special purpose (for use in very bright environments). The UV requirements for these categories are: Cosmetic use -blocks at least 70% UV-B and 20% UV-A; General purpose - blocks at least 95% UV-B and 60% UV-A; and Special purpose - blocks at least 99% UV-B and 60% UV-A. While ANSI allows 5% transmittance of UV-B for general purpose lenses, a recent announcement from the US Food and Drug Administration (FDA), reports it plans to allow only 1% transmission of UV-B and <5% of UV-A.
The American Optometric Association's (AOA) Commission on Ophthalmic Standards recently revised the testing protocol for its Seal of Acceptance program for non-prescription sunglasses and fashion eyewear. The new specifications require that sunglasses transmit no more than 1% UV-A and UV-B to receive the AOA Seal of acceptance. These new requirements are in concurrence with the joint position statement on ultraviolet radiation hazards in sunlight recently adopted by the AOA, Prevent Blindness America, and the American Academy of Ophthalmology.
For contact lens wearers, UV-absorbing contact lenses have been shown to provide excellent UV protection as compared to untreated lenses. For aphakic patients, UV-absorbing intraocular lenses are available and may be preferable for the pilot population. If these are not viable alternatives, recommending an appropriate UV-absorbing spectacle lens would be justified.
In summary, general recommendations for individuals at risk for high exposure to UV, include:
Wear a cap or wide-brimmed hat in the bright sunlight;
Wear approved UV-absorbing sunglasses outdoors;
For those with specialty ophthalmic devices (contact lenses, intraocular lens implants), UV-absorbing material should be incorporated into such devices and/or combined with appropriate UV-absorbing spectacle lenses.
REFERENCES
Ocular Ultraviolet Radiation Hazards in Sunlight. National Society to Prevent Blindness. American Optometric Association. The American Academy of Ophthalmology. November 10, 1993.
Testing Protocol for Non-Prescription Sunglasses and Fashion Eyewear. American Optometric Association. Commission on Ophthalmic Standards, October 1993.
Harris MG, Dang M, Garrod S, Wong W. Ultraviolet Transmittance of Contact Lenses. Optometry and Vision Science. 1994; 71(1):1-5. Sliney D and Wolbarsht M. Safety with Lasers and Other Optical Sources: A Comprehensive Handbook. New York: Plenum Press, 1980.
Pitts DG and Kleinstein RN. Environmental Vision: Interactions of the Eye, Vision, and the Environment. Boston: Butterworth-Heinemann, 1993.
By Van Nakagawara, OD
Dr. Nakagawara is the coordinator of the Civil Aeromedical Institute's
Vision Research Team, Aeromedical Research Division.
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