It is a vertical skin fold to the root of the nose that covers the inner eye corner. Usually it is a congenital malformation and is present in Down syndrome. It can exist in healthy children, when it disappears by the age of five.
It is a degenerative hyperplasic change of the bulbar conjunctiva caused by ultraviolet radiation and mechanical stimuli (work in the dust).
If the pterygium is much vascularized and tends to grow, it needs to be surgically removed. If it grows out of the optical zone of the cornea, it will interfere with vision, and a scar on the cornea after removal of so extensive pterygium often reduces visual acuity. Recurrences after pterygium removal are not uncommon. Sometimes they require a plastic by the mouth epithelia. Each patient with pterygium is recommended to wear sunglasses with UV filters.