First clinical sign of Vitamin-A deficiency is
**Core Concept**
Vitamin A deficiency is a condition where the body lacks sufficient amounts of vitamin A, leading to impaired vision, immune function, and skin health. The first clinical sign of vitamin A deficiency is often related to the retina and visual system.
**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of vitamin A deficiency, which affects the rod cells in the retina. Rod cells are responsible for peripheral and night vision, and their dysfunction leads to impaired night vision. This is because vitamin A is essential for the synthesis of rhodopsin, the pigment in rod cells that allows them to detect light. Without sufficient vitamin A, rhodopsin cannot be produced, leading to impaired night vision.
**Why Each Wrong Option is Incorrect**
**Option A:** Night blindness is not the first clinical sign of vitamin A deficiency, although it is a common symptom.
**Option B:** Cataracts are not directly related to vitamin A deficiency.
**Option C:** Xerophthalmia, a severe form of vitamin A deficiency, is not the first clinical sign.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that night blindness is often the first symptom of vitamin A deficiency, and it can be detected with a simple visual examination.
**Correct Answer: D. Night blindness.**