Night blindness is most directly caused by a deficiency of which vitamin?

• A. Vitamin B2
• B. Vitamin A
• C. Vitamin D
• D. Vitamin E

Answer: (B)

Night vision depends on rod photoreceptors that use the pigment rhodopsin, whose light-sensing component is retinal derived from vitamin A. In darkness, rods must continuously regenerate rhodopsin to stay highly sensitive. If vitamin A is deficient, the supply of retinal is limited, slowing rhodopsin regeneration and impairing dark adaptation, which presents as night blindness. This reliance on vitamin A for the visual cycle makes its deficiency the classic cause of nyctalopia. The other vitamins don’t participate directly in regenerating the rod pigment in this way, so they don’t produce night blindness as a primary symptom.