Vitamin A (retinol) deficiency: earliest clinical sign In human nutrition and ophthalmology, what is typically the earliest recognizable sign of retinol (vitamin A) deficiency?

Introduction / Context:
Vitamin A is essential for vision, epithelial integrity, and immune function. The earliest ocular manifestation of deficiency is frequently tested because early recognition prevents permanent damage.

Given Data / Assumptions:

• Retinal (derived from retinol) is a component of rhodopsin in rod cells, mediating scotopic (low-light) vision.
• Progression of deficiency signs: impaired dark adaptation (night blindness) → conjunctival xerosis → Bitot’s spots → corneal xerosis/keratomalacia (xerophthalmia).
• Skin keratinization occurs later or in more severe deficiency.

Concept / Approach:
Identify the first functional deficit: decreased sensitivity to dim light (nyctalopia) due to inadequate 11-cis-retinal availability in photoreceptors.

Step-by-Step Solution:
Relate vitamin A to rhodopsin regeneration in rods.Understand that reduced rhodopsin impairs dark adaptation first.Select “Night blindness” as the earliest sign.

Verification / Alternative check:
Clinical assessments of dark adaptation and patient history (difficulty driving at night) commonly reveal early deficiency; supplementation improves symptoms if instituted promptly.

Why Other Options Are Wrong:
Keratinization and xerophthalmia represent later epithelial changes; they are not typically the earliest sign.“None of these” contradicts well-established clinical progression.Photophobia with normal dark adaptation does not match retinol deficiency physiology.

Common Pitfalls:
Confusing xerophthalmia (a later, structural change) with the earliest functional deficit of night blindness.

Final Answer:
Night blindness.