What is the appearance of pterygium on the cornea?

The appearance of pterygium typically involves a distinct nasal or temporal corneal thickening, which is a key characteristic of this condition. Pterygium is a growth of pink, benign tissue on the conjunctiva that can extend onto the cornea, usually starting at the scleral area. The growth commonly occurs on the nasal side of the eye but can also appear temporally, thus explaining the option of nasal or temporal corneal thickening.

This feature is significant because it helps in differentiating pterygium from other ocular conditions, as the other options describe different or unrelated manifestations. Unilateral lesions on the eyelid are more in line with conditions like chalazion or other eyelid issues, and redness and swelling around the eye may accompany various ocular inflammatory conditions but are not specific to pterygium. Meanwhile, the presence of vesicular lesions suggests a viral infection, something entirely different from the growth characteristics seen with pterygium. Therefore, the identification of corneal thickening, specifically in the nasal or temporal regions, accurately represents the hallmark appearance of a pterygium on the cornea.