EPAS1 and pterygium: The observed difference of epithelial HIF1α and HIF2α immunoreactivity in primary pterygium vs healthy conjunctival tissue was statistically significant (p < 0.001 and p = 0.003, respectively) (Figs. 3, 4), as was the difference of epithelial HIF2α immunoreactivity in recurrent pterygium vs that in healthy conjunctiva (p < 0.001) (Fig. 4).