HIF1A and pterygium: In the epithelium of primary pterygium, 28 of 55 specimens (51%) stained positive for HIF1α, and 73 of 84 specimens (87%) for HIF2α. In the epithelium of recurrent pterygium, 3 of 6 specimens (50%) stained positive for HIF1α, and 19 of 28 specimens (68%) for HIF2α. In healthy conjunctiva, 20 of 20 specimens (100%) stained positive for both HIF1α and HIF2α. For a conservative approach, all specimens of each group were included in the following calculations of the mean immunoreactivity of HIF1α and HIF2α.