**Core Concept**
The cornea, a transparent avascular layer of the eye, is composed of several layers with distinct cellular and molecular characteristics. The distribution of keratins, specifically intermediate filaments, in the cornea is crucial for maintaining its structural integrity and transparency.

**Why the Correct Answer is Right**
Keratins are a family of proteins that provide mechanical strength and rigidity to cells. In the cornea, keratins are expressed by epithelial cells and keratocytes, the main cell types in the corneal stroma. Type I and type II keratins are co-expressed in a specific ratio, with type I keratins (K12, K13, and K14) and type II keratins (K3, K4, and K5) forming heterodimers. This unique combination of keratins is essential for the mechanical properties of the cornea, particularly its resistance to stretching and shear forces.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately reflect the distribution of keratins in the cornea.
**Option B:** This option is incorrect because it suggests a uniform distribution of keratins throughout the cornea, whereas keratins are specifically expressed by epithelial cells and keratocytes.
**Option C:** This option is incorrect as it implies a different type of protein is responsible for the structural integrity of the cornea.

**Clinical Pearl / High-Yield Fact**
A key clinical correlation is that mutations in keratin genes can lead to corneal fragility and increased susceptibility to corneal ulcers, highlighting the importance of keratins in maintaining corneal integrity.

**Correct Answer: D. Type I and type II keratins are co-expressed in a specific ratio in the cornea.**