**Core Concept**
Pterygium is a common ocular condition characterized by a progressive growth of fibrovascular tissue on the conjunctiva, often involving the cornea. The visual impairment associated with pterygium is a result of corneal involvement and subsequent changes in corneal shape and function.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of pterygium, specifically its impact on the cornea. Pterygium can cause visual impairment by inducing corneal astigmatism and irregular corneal surface due to the fibrovascular tissue growth. This can lead to irregular refraction and vision problems. The fibrovascular tissue can also invade the corneal stroma, causing corneal thinning and scarring.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the primary cause of visual impairment in pterygium.
**Option B:** This option is incorrect because while inflammation can be associated with pterygium, it is not the primary cause of visual impairment.
**Option C:** This option is incorrect because it is a treatment option for pterygium, not a cause of visual impairment.

**Clinical Pearl / High-Yield Fact**
It's essential to note that pterygium can be associated with UV exposure, dry eye, and other environmental factors. Early detection and treatment can help prevent progression and minimize visual impairment.

**Correct Answer:** A. Corneal astigmatism and irregular corneal surface.