PURPOSE. To compare the characteristics of early cortical cataract localization in three groups in cataract epidemiologic surveys performed in Reykjavík, Melbourne, and Singapore. METHODS. Individuals who had right eyes with an area of cortical opacity less than 20% of the pupil when dilated 7 mm or more were selected as subjects. This included 197 subjects from the Reykjavík Eye Study, 231 from the Vitamin E, Cataract, and Age-Related Maculopathy (VECAT) study in Melbourne, and 92 from the

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... apore-Japan Cooperative Cataract Study, all showing early-stage cataract in pupils dilated to 7 mm or more. Scheimpflug and retroilluminated photographs were used to locate opacities. Localization of cortical cataract was determined by dividing the retroillumination image into seven concentric circles with diameters of 1 through 7 mm, and eight sections of 45°radial octants. The positive rate of opacification was then calculated for each quadrant. RESULTS. The highest positive rate of opacification was observed in the lower nasal quadrant in all groups. The relative risk of the prevalence of cortical opacity in the lower nasal oblique hemisphere to the upper temporal oblique hemisphere was the highest in the Singaporean subjects followed by those of Melbourne and then of Reykjavík. CONCLUSIONS. The prevalence of cortical cataract was higher in the lower nasal quadrant than in the other quadrants for all subjects of diverse race in three climatically different locations. This higher prevalence was most pronounced in subjects living at low latitude. These results support the view that solar UV exposure is a possible risk factor for development of human cortical cataract. (Invest Ophthalmol Vis Sci. 2003;44: 4210 -4214)