Pterygium is said to be a common disease in many countries located between approximately 37 degrees north and south latitude.1,2 For example, in northern New Zealand, operations for pterygium outnumber those for cataract, whereas in England, at 50 to 60 degrees of latitude, pterygium is reported to account for less than 1% of all eye operations.3 In order to explain this apparent variation in geographic distribution, environmental differences in mean annual temperature, humidity, dust, and ultraviolet radiation have been proposed.1,3-8 Impressed by the common occurrence of pterygium in the American Southwest, McReynolds concluded that the responsible factors were "heat, a dry atmosphere, high winds, exposure to sunlight, and an abundance of dust."5 Anderson noted the increasing percentage of eye operations performed for pterygium toward the northern, western, and central parts of Australia and compared this pattern to the progressive decrease in humidity in the corresponding areas.
DARRELL RW, BACHRACH CA. Pterygium Among VeteransAn Epidemiologic Study Showing a Correlation Between Frequency of Pterygium and Degree of Exposure of Ultraviolet in Sunlight. Arch Ophthalmol. 1963;70(2):158-169. doi:10.1001/archopht.1963.00960050160004