A pterygium (pronounced ter-idge-ee-um, plural: pterygia) is a triangular-shaped lump of tissue with blood vessels that grow from the conjunctiva (the thin membrane that covers the white of the eye) on to the cornea (the clear central part of the eye). Pterygia frequently occur in both eyes, usually on the side of the eye closer to the nose. A pterygium is not cancer. People sometimes confuse pterygia with cataracts. A cataract is a clouding of the lens inside the eye and cannot be seen easily with the naked eye.