Pterygium (ter-yg'-i-um). (Gr. pteryx = wing.)

A thickening or growth of the conjunctiva,having the appearance of a fly's wing, usuallyon the nasal side of the eye, extending outtoward the cornea. It can be removed by operation, and should be as soon as it reaches thecornea, otherwise it will grow over it and impairvision.

Source: Ophthalmic Dictionary including pronunciation, derivation and definition of the words used in Optometry and Ophthalmology by James J. Lewis, Oph. D. Professor of Optometry in the Northern Illinois College of Ophthalmology and Otology, Chicago.