Purpose: No detailed analysis of risk factors in the development of pterygia has been previously performed. In this report, the authors identify and quantify these risk factors.
Methods: In a case-control study, 278 patients treated in a Brisbane hospital for primary pterygium between 1973 and 1978 were compared with a similar number of people without pterygium who were matched for age, race, and sex, using information from a standard questionnaire completed during a personal interview.
Results: Risk of pterygium was increased among patients who, in their third decade of life, worked outdoors in an environment with high surface reflectance of ultraviolet light compared with those who worked indoors. The elevation of risk was raised several hundred-fold among those subjects who worked mainly on sand compared with those who worked indoors when results were adjusted for associated risk factors. When risk was measured among subjects who worked in an environment that was mainly concrete, risk was increased almost 20-fold. Those subjects who spent their first 5 years of life at latitudes less than 30 degrees had almost 40 times the risk of pterygium than those living at latitudes greater than 40 degrees; spending the majority of times outdoors in these earliest years was associated with a 20-fold increase in risk of developing pterygium. There was a strong protective element in the wearing of regular glasses, sunglasses, or a hat.
Conclusions: There is a strong suggestion of a causal relationship between ultraviolet light exposure and the development of pterygia during the early years of life and the cumulative exposure over the next 2 to 3 decades in occupations in which there is a high component of reflected ultraviolet light.