Night blindness is a vision problem in which a person has difficulty seeing in dim light or at night. Deficiency of which specific vitamin is classically associated with the development of night blindness?

Introduction / Context:
Vitamins play essential roles in maintaining normal body functions, including vision, blood clotting, and immunity. Night blindness is a classic clinical sign linked with a particular vitamin deficiency. Understanding which vitamin is responsible helps in both exam questions and basic health awareness. This question focuses on the specific vitamin whose lack impairs the ability to see in low light conditions.

Given Data / Assumptions:

• Night blindness involves difficulty seeing in dim light or at night.
• The cause being asked is a deficiency of a specific vitamin.
• Options include Vitamin A, Vitamin B complex, Vitamin C, Vitamin K, and Vitamin D.
• We assume typical nutritional deficiency patterns as taught in school biology.
• We are not dealing with other causes such as inherited retinal diseases in this basic question.

Concept / Approach:
Vitamin A, also known as retinol, is crucial for the normal functioning of the retina, especially the rod cells responsible for vision in low light. In the retina, Vitamin A is involved in forming visual pigments such as rhodopsin. When Vitamin A is deficient, rhodopsin cannot regenerate properly, and rod cells fail to respond adequately to dim light. This leads to night blindness, where a person may see reasonably well in bright light but struggles to see when the light level drops. Prolonged deficiency can also cause dryness of the conjunctiva and cornea, leading to more serious eye damage. Other vitamins have different main functions and are not primarily associated with night blindness.

Step-by-Step Solution:
Step 1: Recall that Vitamin A is linked directly with the health of the retina and the visual cycle. Step 2: Understand that rod cells, which mediate low light vision, depend on a visual pigment derived from Vitamin A. Step 3: Recognise that when Vitamin A intake is low, rhodopsin regeneration is impaired, reducing sensitivity in dim light. Step 4: Note that individuals with Vitamin A deficiency often complain of difficulty seeing when driving at night or moving from bright to dim environments. Step 5: Compare this with the roles of other vitamins: Vitamin B complex is mainly involved in metabolism and nerve function, Vitamin C in collagen formation and immunity, Vitamin K in blood clotting, and Vitamin D in calcium absorption and bone health. Step 6: Since none of these other vitamins is specifically linked with night blindness in basic textbooks, they can be ruled out. Step 7: Conclude that Vitamin A deficiency is the classical cause of night blindness.

Verification / Alternative check:
Clinical nutrition references and ophthalmology texts list Vitamin A deficiency as a leading cause of preventable visual impairment in some regions, with night blindness as an early symptom. Public health programs that provide Vitamin A supplementation often report a reduction in night blindness among children. Other vitamin deficiencies produce different symptoms such as bleeding gums (Vitamin C), rickets (Vitamin D), or prolonged bleeding (Vitamin K), confirming that Vitamin A is the correct answer for night blindness.

Why Other Options Are Wrong:
Vitamin B complex: Deficiencies can cause anaemia, neuropathy, and other issues, but they are not primarily associated with night blindness. Vitamin C (ascorbic acid): Important for collagen synthesis and immune function; deficiency leads to scurvy, not night blindness. Vitamin K: Required for normal blood clotting; deficiency causes bleeding tendencies. Vitamin D: Essential for calcium absorption and bone health; deficiency leads to rickets in children and osteomalacia in adults.

Common Pitfalls:
Candidates sometimes confuse Vitamin A with other fat soluble vitamins because they are all stored in the body. Another mistake is to associate Vitamin A only with general vision and not specifically with night vision. To avoid errors, link Vitamin A with the retina and the visual pigment rhodopsin, and remember that difficulty in seeing in dim light is the hallmark of its deficiency. Making such mental connections between specific vitamins and characteristic deficiency symptoms can greatly improve accuracy in vitamin related questions.

Final Answer:
Night blindness is classically caused by a deficiency of Vitamin A (retinol).