A Pterygium is a triangular-shaped growth of vascularized tissue on the conjunctiva, or clear membrane that covers the white part of the eye. Much of the time the growth extends onto the cornea, or clear window on the front of the eye. A Pterygium can grow large enough to interfere with vision. Pterygia can also become inflamed and swollen, leading to foreign body sensation and discomfort. Some Pterygia can affect the shape of the cornea, leading to significant astigmatism. Pterygia can be surgically removed if they threaten vision or remain chronically inflamed. Pterygia are thought to be related to UV exposure, and symptoms can be worsened by exposure to a dry, dusty environment.