**Core Concept**
The cornea is the transparent outer layer of the eye, composed of several layers of cells and tissues. It plays a crucial role in refracting light and maintaining the eye's shape. The cornea's composition and structure are essential for its function.

**Why the Correct Answer is Right**
The correct answer is keratin. Keratin is a type of protein that provides structural support to the cornea. It is present in the epithelial and stromal layers of the cornea, making up a significant portion of its dry weight. The keratin proteins in the cornea help maintain its transparency and provide mechanical strength. The corneal stroma, which is the thickest layer of the cornea, contains a high concentration of keratin filaments that provide structural support.

**Why Each Wrong Option is Incorrect**
* **Option A:** There is no mention of collagen in the cornea. While collagen is an essential protein in other parts of the eye, such as the sclera, it is not specifically present in the cornea.
* **Option B:** Glycoproteins are present in the cornea, but they are not the primary component. Glycoproteins play a role in the cornea's adhesion and structural functions, but keratin is the main protein responsible for its structure and transparency.
* **Option D:** There is no mention of elastin in the cornea. Elastin is a protein found in other parts of the body, such as the skin and lung tissue, but it is not a significant component of the cornea.

**Clinical Pearl / High-Yield Fact**
Keratin in the cornea is essential for maintaining its transparency and mechanical strength. Damage to the corneal keratin can lead to corneal ulcers and vision loss.

**Correct Answer: C. Keratin is present in the cornea.**