Neurophysiology and special senses: light-near dissociation: 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 · Neurophysiology and special senses: light-near dissociation

Sample item

A patient with tertiary neurosyphilis has small irregular pupils that do not constrict to light but do constrict when focusing on a near object. Where is the lesion most likely located?

APrimary visual cortexBPretectal region, sparing the pathway for the near responseCCervical sympathetic chainDOculomotor nerve, paralysing the sphincter pupillae

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

The answer and the reasoning

B. Pretectal region, sparing the pathway for the near response

The light reflex passes through the pretectal nuclei to the Edinger-Westphal nucleus, whereas the near response reaches it by a separate cortical route. A pretectal lesion therefore abolishes the light reflex but spares the near response, the light-near dissociation of the Argyll Robertson pupil.

Option by option

A. Primary visual cortex
A visual cortex lesion causes cortical blindness with preserved pupillary light reflexes.
B. Pretectal region, sparing the pathway for the near response (correct)
Correct. Pretectal damage removes the light reflex but not the near response.
C. Cervical sympathetic chain
Sympathetic chain damage causes miosis but light and near reactions remain intact.
D. Oculomotor nerve, paralysing the sphincter pupillae
An oculomotor nerve lesion would paralyse constriction to both light and near, with a dilated pupil.

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 B, Pretectal region, sparing the pathway for the near response. The light reflex passes through the pretectal nuclei to the Edinger-Westphal nucleus, whereas the near response reaches it by a separate cortical route.

Why is "Primary visual cortex" not the answer?

A visual cortex lesion causes cortical blindness with preserved pupillary light reflexes.

Why is "Cervical sympathetic chain" not the answer?

Sympathetic chain damage causes miosis but light and near reactions remain intact.

Why is "Oculomotor nerve, paralysing the sphincter pupillae" not the answer?

An oculomotor nerve lesion would paralyse constriction to both light and near, with a dilated pupil.

What concept does this question test?

It tests Neurophysiology and special senses: light-near dissociation in Physiology. A pretectal lesion therefore abolishes the light reflex but spares the near response, the light-near dissociation of the Argyll Robertson pupil.

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 Neurophysiology and special senses: light-near dissociation?

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.