A survey of pterygia prevalence was done in 1,252 male sawmill workers and controls in British Columbia, Canada, northern India, Thailand, and Taiwan. The age-adjusted prevalence rate of pterygia in the sawmill workers was 25.3% compared to 7.1% in the control groups, a statistically highly significant finding indicating that the sawmill environment is associated with a high prevalence of pterygia. In addition, the likelihood of a pterygium developing in a sawmill worker's eye was found to increase with longer duration of employment in the mill. Both Punjabi Indian sawmill workers in British Columbia and in New Delhi had a higher prevalence of pterygia than Punjabi farmers in India. Since sawmill workers work indoors it is, therefore, unlikely that ultraviolet radiation alone is the cause of pterygia formation.
Detels R, Dhir SP. Pterygium: A Geographical Study. Arch Ophthalmol. 1967;78(4):485-491. doi:10.1001/archopht.1967.00980030487014