Purpose: To assess the validity of the solar ultraviolet index (UVI) as a determiner of eye risk under different conditions of facial profiles and orientation, and reflected light.
Methods: Ocular UV radiation (UVR) exposure was measured as a function of the time of the day (solar altitude) using a two-dummy-type mannequin dosimetry system with embedded UVR (260-310 nm) sensors, in September and November in Kanazawa, Japan, on a motorized sun-tracking mount with one dummy face directed toward the sun and the other away from the sun.
Results: A bimodal distribution of UV-B exposure was found in September for the face directed toward the sun, which differed dramatically from the pattern of ambient UVR exposure and measurements taken on the top of the head and those for the eye taken later in the year. Although the overall level was lower, a higher solar altitude is associated with higher UVR exposure in the condition facing away from the sun.
Conclusions: The UVI is based on ambient solar radiation on an unobstructed horizontal plane similar to our measures taken on the top of the head, which differed so much from our measures of ocular exposure that UVI as a determiner of eye risk is deemed invalid. The use of the UVI as an indicator for the need for eye protection can be seriously misleading. Doctors should caution patients with regard to this problem, and eye protection may be warranted throughout the year.
From the Department of Ophthalmology (H.S., Y.S., N.F., N.H., K.S.), Kanazawa Medical University; Division of Vision Research for Environmental Health (H.S., Y.S., K.S.), Medical Research Institute, Kanazawa Medical University, Uchinada, Japan; Medical Affairs (C.S.), Vistakon, Johnson & Johnson Vision Care, Inc., Jacksonville, FL; Consulting Medical Physicist (D.H.S.), Fallston, MD; and Department of Rehabilitation (K.S.), Faculty of Medical Science and Welfare, Tohoku Bunka Gakuen University, Sendai, Japan.
The authors have no funding or conflicts of interest to disclose.
Address correspondence and reprint requests to Hiroshi Sasaki, M.D., Ph.D., Department of Ophthalmology, Kanazawa Medical University, 1-1 Daigaku, Uchinada-machi, Kahoku-gun, Ishikawa 920-0293, Japan; e-mail: firstname.lastname@example.org
Accepted April 14, 2011.