**Core Concept:** Vitamin A is an essential micronutrient that plays a crucial role in maintaining proper vision, immune system function, and cell differentiation. It is involved in maintaining the integrity of the cornea, conjunctiva, and respiratory, gastrointestinal, and urogenital tracts. Vitamin A deficiency (VAD) results in impaired cellular differentiation, leading to various ocular, immunological, and mucocutaneous manifestations.

**Why the Correct Answer is Right:** The earliest feature of vitamin A deficiency is **night blindness**. This occurs due to the dysfunction of rod cells in the retina, which are essential for vision in low-light conditions. As VAD progresses, it can lead to keratomalacia, xerophthalmia, and eventually, blindness.

**Why Each Wrong Option is Incorrect:**

A. Night blindness is not the earliest feature of VAD; this occurs later in the course of deficiency.
B. Epitheliopathy (inflammation of the cornea) is a later feature of VAD, not the earliest.
C. Conjunctivitis (inflammation of the conjunctiva) is a later feature of VAD, not the earliest.
D. Scurvy (due to Vitamin C deficiency) and beriberi (due to thiamine deficiency) are not related to Vitamin A deficiency.

**Clinical Pearl:** Vitamin A deficiency is preventable in most cases, as it is mostly due to inadequate consumption of vitamin A-rich foods like carrots, sweet potatoes, liver, fish, and dairy products. Early identification and supplementation can prevent severe complications like blindness.

**Correct Answer:** **D.** Epitheliopathy (inflammation of the conjunctiva) is the earliest feature of Vitamin A deficiency.