Special senses: dark adaptation: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Special senses: dark adaptation

Sample item

A malnourished child in a rural area has Bitot spots and cannot see in dim light. What is the physiological basis of the night vision loss?

ALoss of cone pigments required for photopic visionBOveractive phosphodiesterase in cone cellsCFailure of bipolar cell glutamate release in the maculaDImpaired regeneration of rhodopsin from deficiency of 11-cis retinal

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Impaired regeneration of rhodopsin from deficiency of 11-cis retinal

Rhodopsin consists of opsin and 11-cis retinal, which is derived from vitamin A. In vitamin A deficiency, rod pigment cannot be regenerated after bleaching, so dark adaptation is slow and scotopic vision fails, causing night blindness. Bitot spots are conjunctival xerosis features of the same deficiency.

Option by option

A. Loss of cone pigments required for photopic vision
Cones mediate daylight and colour vision; night blindness reflects rod failure.
B. Overactive phosphodiesterase in cone cells
Phosphodiesterase overactivity is not the cause of night blindness from nutritional deficiency.
C. Failure of bipolar cell glutamate release in the macula
A macular bipolar cell defect would affect central vision in bright light, not rods at night.
D. Impaired regeneration of rhodopsin from deficiency of 11-cis retinal (correct)
Correct. Retinal deficiency limits rhodopsin regeneration in rods.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is D, Impaired regeneration of rhodopsin from deficiency of 11-cis retinal. Rhodopsin consists of opsin and 11-cis retinal, which is derived from vitamin A.

Why is "Loss of cone pigments required for photopic vision" not the answer?

Cones mediate daylight and colour vision; night blindness reflects rod failure.

Why is "Overactive phosphodiesterase in cone cells" not the answer?

Phosphodiesterase overactivity is not the cause of night blindness from nutritional deficiency.

Why is "Failure of bipolar cell glutamate release in the macula" not the answer?

A macular bipolar cell defect would affect central vision in bright light, not rods at night.

What concept does this question test?

It tests Special senses: dark adaptation in Physiology. In vitamin A deficiency, rod pigment cannot be regenerated after bleaching, so dark adaptation is slow and scotopic vision fails, causing night blindness. Bitot spots are conjunctival xerosis features of the same deficiency.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Special senses: dark adaptation?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.