## Core Concept
Pterygium is a growth of the conjunctiva or mucous membrane that covers the white part of your eye over the cornea, which is the clear layer on the front of your eye. This condition can cause vision problems if it grows onto the cornea. The cause of blindness in pterygium is related to its location and effect on the cornea.

## Why the Correct Answer is Right
The correct answer is related to the complications arising from pterygium, specifically when it encroaches upon the visual axis or causes significant astigmatism. Pterygium can lead to **astigmatism**, a condition where the cornea becomes irregularly shaped, preventing light from focusing properly on the retina. If severe and untreated, this can lead to blindness. The mechanism involves the fibrovascular proliferation and scarring that alter the cornea's curvature.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because while pterygium involves the growth of conjunctival tissue, the direct cause of blindness is not merely its presence but its effect on the cornea and vision.
- **Option B:** This option is incorrect as there is no widely recognized cause of blindness in pterygium directly linked to this choice.
- **Option D:** This option is incorrect because, although infection could potentially complicate pterygium surgery or an advanced stage of the disease, it is not the most direct cause of blindness associated with pterygium.

## Clinical Pearl / High-Yield Fact
A key point to remember is that pterygium can cause blindness through **induced astigmatism** as it progresses onto the cornea. Early recognition and intervention can prevent this complication. A classic clinical correlation is that pterygium is more common in individuals with prolonged exposure to UV radiation.

## Correct Answer: C. Astigmatism.