The aim of the present study was to evaluate the levels of GSH, GSSG, NO, 3-nitrotyrosine (3NT), catalase (CAT), and endothelial nitric oxide synthase (eNOS) in tissues samples of pterygium representing four conditions: untreated primary pterygium, recurrent pterygium, and primary pterygium treated with NAC, either systemic or topic. Here, CAT is linked to pterygium.