Neuroanatomy: pupillary light reflex in cortical blindness: practice question

A Anatomy 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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Anatomy · Neuroanatomy: pupillary light reflex in cortical blindness

Sample item

After bilateral posterior cerebral artery infarcts a man walks into furniture, yet insists his vision is normal. Both pupils constrict briskly to light. Which feature of the light reflex pathway explains this?

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

The answer and the reasoning

D. Afferent fibres leave the optic tract for the pretectal nuclei, bypassing the cortex

Retinal axons for the light reflex bypass the lateral geniculate body and end in the pretectal nuclei, which project bilaterally to the Edinger-Westphal nuclei. Bilateral occipital damage therefore causes cortical blindness with preserved pupillary reflexes, and the patient may deny the deficit (Anton syndrome).

Option by option

  • A. Afferent fibres travel in the optic radiation to the occipital pole then descend

    The optic radiation carries visual information to the cortex and is not used by the reflex.

  • B. Afferent fibres pass through the frontal eye field before reaching the midbrain

    The frontal eye field controls voluntary gaze and has no role in the light reflex.

  • C. Afferent fibres relay in the lateral geniculate body before reaching the midbrain

    The lateral geniculate body serves conscious vision and is not part of the reflex arc.

  • D. Afferent fibres leave the optic tract for the pretectal nuclei, bypassing the cortex (correct)

    Correct. The reflex arc runs retina, optic tract, pretectum, Edinger-Westphal nucleus, so the cortex is not needed.

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.

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Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is D, Afferent fibres leave the optic tract for the pretectal nuclei, bypassing the cortex. Retinal axons for the light reflex bypass the lateral geniculate body and end in the pretectal nuclei, which project bilaterally to the Edinger-Westphal nuclei.

Why is "Afferent fibres travel in the optic radiation to the occipital pole t…" not the answer?

The optic radiation carries visual information to the cortex and is not used by the reflex.

Why is "Afferent fibres pass through the frontal eye field before reaching th…" not the answer?

The frontal eye field controls voluntary gaze and has no role in the light reflex.

Why is "Afferent fibres relay in the lateral geniculate body before reaching…" not the answer?

The lateral geniculate body serves conscious vision and is not part of the reflex arc.

What concept does this question test?

It tests Neuroanatomy: pupillary light reflex in cortical blindness in Anatomy. Bilateral occipital damage therefore causes cortical blindness with preserved pupillary reflexes, and the patient may deny the deficit (Anton syndrome).

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 Neuroanatomy: pupillary light reflex in cortical blindness?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy 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.