A pterygium is a reddish, triangular-shaped tissue that grows onto the cornea. It tends to grow slowly throughout a person's life. Although mostly harmless, a pterygium can rarely grow so large that it begins to cover the pupil of the eye.

Pterygia are more common in hot tropical climates and usually occurs in the 20-40 age group. The exact cause is unknown. However, ultraviolet (UV) light from the sun is the most likely contributing factor. In areas where sunlight is strong, the use of protective sunglasses and head gear with brims are suggested.

Because a pterygium is visible, many people want it removed for cosmetic reasons. Surgery to remove a pterygium is recommended especially when it threatens to block vision. When properly done, the risk of it growing back after the pterygium is surgically removed is low. A patch of translucent skin called the conjunctiva is used to patch over the site.