**Core Concept**
Vernal conjunctivitis is a seasonal, chronic inflammatory condition of the conjunctiva, characterized by the presence of cobblestone papillae on the upper tarsal conjunctiva. The pathophysiology involves an allergic response to environmental allergens, leading to the release of histamine and other chemical mediators.

**Why the Correct Answer is Right**
The cobblestone appearance is due to the presence of eosinophils and mast cells within the conjunctival stroma. These cells release granules that contain histamine, eosinophilic cationic protein, and other mediators, leading to the characteristic papillary reaction. The eosinophils also release major basic protein, which contributes to the formation of the cobblestone papillae.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the contents of cobblestone papillae in vernal conjunctivitis are not primarily composed of neutrophils.
* **Option B:** This option is incorrect because the presence of plasma cells is not a characteristic feature of cobblestone papillae in vernal conjunctivitis.
* **Option D:** This option is incorrect because the contents of cobblestone papillae are not primarily composed of lymphocytes.

**Clinical Pearl / High-Yield Fact**
It's essential to distinguish vernal conjunctivitis from other forms of conjunctivitis, such as giant papillary conjunctivitis, which can have similar clinical presentations. Vernal conjunctivitis is often associated with a history of allergies and seasonal exacerbation.

**Correct Answer: C. Eosinophils and mast cells.**