The relationship between cataract prevalence, altitude, and sunlight hours was investigated in a large national probability sample survey of 105 sites in the Himalayan kingdom of Nepal, December 1980 through April 1981. Cataract of senile or unknown etiology was diagnosed by ophthalmologists in 873 of 30,565 full-time life-long residents of survey sites. Simultaneously, the altitude of sites was measured using a standard mountain altimeter. Seasonally adjusted average daily duration of sunlight exposure for each site was calculated by a method which took into account latitude and obstructions along the skyline. Age- and sex-standardized cataract prevalence was 2.7 times higher in sites at an altitude of 185 meters or less than in sites over 1000 meters. Cataract prevalence was negatively correlated with altitude (r = -0.533, p less than 0.0001). However, a positive correlation between cataract prevalence and sunlight was observed (r = 0.563, p less than 0.0001). Sites with an average of 12 hours of sunlight exposure had 3.8 times as much cataract as sites with an average of only seven hours of exposure. Sunlight was blocked from reaching certain high altitude sites by tall neighboring mountains.

Explants from the retinal pigment epithelium and the underlying choroid and sclera were dissected from human eyes and transferred to culture wells. The mechanical trauma caused by the dissection and removal of the explants, and the changes in biological milieu caused by transfer of the tissue to an in vitro system causes injury, necrosis and detachment of cells from Bruch's membrane. In the retinal pigment epithelium, cells adjacent to damaged, spherical and detaching cells and smaller cell free zones from rosettes. At the periphery of big defects, the cells spread out to cover the denuded areas of Bruch's membrane. The present work has shown that cell injury in the human retinal pigment epithelium is followed by reactive cellular changes in vitro. The result of these reactive changes are increased variation in cellular form and magnitude and in pigment concentration per unit area.

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Fresh and undamaged cornea had unchanged endothelial cell density for four weeks in culture, while eyes removed at autopsy suffered a cell loss. Acceptable cell density was found in eyes removed within eight hours, and this was confirmed by the results of 55 penetrating grafts using cultured autopsy material. Storage in culture for more than one week seemed to influence the results unfavourably. Immune reactions were not seen.

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