A patient has a yellow mass on the corner of his eye and has been diagnosed with a pterygium. What is a pterygium?

A pterygium is characterized as a piece of degenerative tissue that grows from the conjunctiva, which is the clear tissue covering the white part of the eyeball, over the sclera, and onto the cornea. It typically appears as a yellowish, triangular-shaped mass, often associated with exposure to sunlight, dust, or wind, leading to its common occurrence in individuals who spend significant time outdoors. The growth can lead to changes in vision if it encroaches on the pupil or causes irritation.

In contrast to options that describe other ocular conditions, a pterygium is distinct because it specifically pertains to conjunctival tissue and its unusual growth onto the cornea, rather than being related to cataracts, tumors of the iris, or retinal issues. Each of those alternate options refers to different pathologies with different anatomical implications, making them inapplicable in the context of a pterygium.