THE OCULAR DOSE OF ULTRAVIOLET RADIATION FROM SUNLIGHT EXPOSURE

Abstract— The ocular toxicity of ultraviolet radiation has been demonstrated in acute photokeratitis and is suspected of contributing to cataractogenesis and senile macular degeneration. While previous studies have emphasized photochemical and epidemiologic aspects of ocular UV-B irradiation, little is known about the extent of such exposure in human subjects. To determine levels of ocular UV-B exposure from sunlight, four mannikin headforms were fitted with UV-B sensitive film (polysulphone) and exposed on an unobstructed rooftop (Baltimore, Md.: latitude = 39.5 degrees) to four hours of sunlight (11 am-3 pm local time) over a three month period (June-August). Simultaneous measurements of ocular and ambient exposure revealed a ratio of 19.5 ± 2.9% that was independent of ambient level (P < 0.05). Measurements performed during earlier hours (8 am-11 am) revealed a similar ratio. Mannikin headforms fitted with brimmed baseball caps showed a22–95% reduction in ocular exposure, depending on the angle of the hat brim to the forehead. Three sets of spectacles substantially reduced ocular UV-B exposure,62–94% dependent on the absorption properties of the spectacle lenses. These anthropomorphic measurements indicate that a substantial percentage of ambient UV-B light is incident upon the cornea and that personal factors, such as wearing a hat or spectacles, can markedly affect UV-B exposure.