**Core Concept**
Pterygium is a common ocular surface disorder characterized by the growth of a fibrovascular tissue on the conjunctiva, often extending onto the cornea. The corneal involvement in pterygium is primarily due to the encroachment of the conjunctival tissue, leading to a loss of corneal transparency and vision.

**Why the Correct Answer is Right**
The Bowman's layer of the cornea is involved most often in pterygium. This is because the conjunctival tissue of the pterygium invades the Bowman's layer, causing scarring and opacity of the cornea. The Bowman's layer is a dense, acellular layer of the cornea that provides structural support and is rich in collagen fibers. The invasion of the conjunctival tissue into the Bowman's layer disrupts the normal corneal architecture and leads to the clinical manifestations of pterygium.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the epithelium is not directly involved in the pathogenesis of pterygium. While the epithelium may be affected by the underlying corneal scarring, it is not the primary layer involved in pterygium.
* **Option B:** This option is incorrect because the stroma is the thickest layer of the cornea and is not typically involved in the initial stages of pterygium. The conjunctival tissue of the pterygium invades the Bowman's layer before affecting the stroma.

**Clinical Pearl / High-Yield Fact**
Pterygium is more common in individuals with prolonged exposure to UV radiation, such as outdoor workers or individuals living near the equator. This emphasizes the importance of sun protection measures in preventing the development of pterygium.

**Correct Answer:** C.