Special senses: relative afferent pupillary defect: 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: relative afferent pupillary defect

Sample item

A woman with left optic neuritis has a normal-looking pupil size. On the swinging flashlight test, what happens when the light moves from the right eye to the left eye?

ABoth pupils dilate, since the left afferent signal is weaker than the rightBBoth pupils constrict more briskly than beforeCThe left pupil constricts and the right pupil dilatesDThe left pupil stays fixed while the right constricts

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

The answer and the reasoning

A. Both pupils dilate, since the left afferent signal is weaker than the right

The pupillary light reflex has a consensual bilateral efferent output driven by the combined afferent input. A damaged left optic nerve sends a weaker signal, so when light swings from the healthy right eye to the left eye, the net input falls and both pupils dilate, a relative afferent pupillary defect. Efferent lesions give anisocoria instead.

Option by option

A. Both pupils dilate, since the left afferent signal is weaker than the right (correct)
Correct. Reduced afferent input from the diseased eye makes both pupils dilate.
B. Both pupils constrict more briskly than before
A brisker constriction would happen only if the left afferent pathway were stronger.
C. The left pupil constricts and the right pupil dilates
Opposite responses in the two eyes would suggest an efferent defect of the oculomotor nerve.
D. The left pupil stays fixed while the right constricts
A fixed pupil with a normal contralateral response is not the pattern of afferent defect.

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 A, Both pupils dilate, since the left afferent signal is weaker than the right. The pupillary light reflex has a consensual bilateral efferent output driven by the combined afferent input.

Why is "Both pupils constrict more briskly than before" not the answer?

A brisker constriction would happen only if the left afferent pathway were stronger.

Why is "The left pupil constricts and the right pupil dilates" not the answer?

Opposite responses in the two eyes would suggest an efferent defect of the oculomotor nerve.

Why is "The left pupil stays fixed while the right constricts" not the answer?

A fixed pupil with a normal contralateral response is not the pattern of afferent defect.

What concept does this question test?

It tests Special senses: relative afferent pupillary defect in Physiology. A damaged left optic nerve sends a weaker signal, so when light swings from the healthy right eye to the left eye, the net input falls and both pupils dilate, a relative afferent pupillary defect. Efferent lesions give anisocoria instead.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: relative afferent pupillary defect?

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.