**Core Concept**
Vernal keratoconjunctivitis (VKC) is a chronic, bilateral, and seasonal allergic eye disease characterized by intense inflammation and scarring of the cornea and conjunctiva. It predominantly affects children and young adults, particularly in warm and dry climates.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of VKC, which involves an allergic response to environmental allergens such as pollen, dust, and grass. The immune system's overreaction leads to the release of histamine and other chemical mediators, causing blood vessels to dilate, and resulting in increased permeability, edema, and inflammation of the conjunctiva and cornea. The repeated exposure to allergens and the subsequent chronic inflammation can lead to the formation of **giant papillae** on the upper tarsal conjunctiva, which is a hallmark of VKC.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because VKC is not typically associated with a direct bacterial infection. While secondary bacterial infections can occur due to the compromised integrity of the ocular surface, it is not a primary complication of VKC.
**Option B:** This option is incorrect because VKC is not primarily characterized by a decrease in tear production. In fact, VKC often presents with an increase in tear production due to the allergic response and subsequent inflammation.
**Option C:** This option is incorrect because VKC is not typically associated with a direct viral infection. While viral infections can exacerbate VKC, it is not a primary complication of the disease.

**Clinical Pearl / High-Yield Fact**
VKC can be differentiated from other forms of conjunctivitis by the presence of **giant papillae** on the upper tarsal conjunctiva. This clinical finding is often accompanied by a history of seasonal exacerbations and a strong allergic predisposition.

**Correct Answer:** D.