Pterygium is:

A pterygium is a proliferation of fibrovascular tissue on the surface of the eye, which extends onto the cornea. The etiology of pterygium is incompletely understood. However, chronic UV exposure is accepted as a causative agent. Treatment options: Pterygia are usually treated only when they interfere with vision. The standard therapy is surgical removal. Pterygia affect astigmatism and are associated with increased rates of macular degeneration; however, it is unclear whether treatment reduces this risk. Eyes with a pterygium or previous pterygium surgery (but not pinguecula) have a higher risk of incident late age-related maculopathy (ARM) (OR 3.3, 95% CI 1.1-10.3) and early ARM (OR 1.8, 95% CI 1.1-2.9). Ref: Chumley H. (2009). Chapter 11. Pterygium. In R.P. Usatine, M.A. Smith, H. Chumley, E. Mayeaux, Jr., J. Tysinger (Eds), The Color Atlas of Family Medicine.