Pterygium is-
Pathologically pterygium is a degenerative and hyperplastic condition of conjunctiva. The subconjunctival tissue undergoes elastotic degeneration and proliferates as vascularised granulation tissue under the epithelium, which ultimately encroaches the cornea. The corneal epithelium, Bowman's layer and superficial stroma are destroyed. ref: A K KHURANA OPHTALMOLOGY,E4, Page-80
A vascular anomaly
A connective tissue degeneration
An inflammatory condition
Associated with Vit. A deficiency
Conjunctiva