Solar UV exposure at eye is different from environmental UV: diurnal monitoring at different rotation angles using a...

Solar ultraviolet radiation (UVR) promotes pterygium and cataract development in the human eye. When outdoors, people are subject to varying ocular UVR exposure intensity depending on time of day and orientation to the sun. To assess this variability, a manikin eye was exposed to solar UVR at 12 rotation angles relative to the sun with a solar elevation angle (SEA) ranging from 24.6° to 88.2°. At rotation angles of 0°, 30°, and 330°, the diurnal variation of ocular UVR exposure intensity showed a bimodal distribution that peaked at a SEA of about 40°, which was 3 to 4 hr both before and after noon. This timing differed from peak environmental UVR exposure intensity. At the other rotation angles, diurnal variations in ocular UV exposure exhibited unimodal curves, with maximum intensity around noon, the same as for environmental UVR. Thus, the idea that UVR exposure is most intense at midday is true for skin surfaces positioned somewhat horizontally but not for the eyes in a 60° arc with a centerline toward the sun (i.e., ranging 30° clockwise or counter-clockwise from the centerline). Maintaining certain orientations relative to the sun's position (for example, being clockwise or counter-clockwise by 30° from the sun) should effectively reduce ocular UVR exposure, especially at times when the SEA is 40°.