Neuro: anisocoria in dark or light: practice question

A Ophthalmology 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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Ophthalmology · Neuro: anisocoria in dark or light

Sample item

A patient has anisocoria that is greater in dim light than in bright light. What is the most likely cause?

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

The answer and the reasoning

B. Horner syndrome (the smaller pupil is abnormal)

If anisocoria increases in the dark, the smaller pupil fails to dilate, so it is the abnormal one, as in Horner syndrome. If anisocoria is greater in light, the larger pupil fails to constrict, as in third nerve palsy, Adie pupil or pharmacological dilation. Physiological anisocoria is equal in both lights.

Option by option

  • A. Third nerve palsy (the larger pupil is abnormal)

    Parasympathetic defects show more anisocoria in bright light.

  • B. Horner syndrome (the smaller pupil is abnormal) (correct)

    Correct. Greater anisocoria in the dark suggests a sympathetic defect.

  • C. Pharmacological mydriasis

    Pharmacological mydriasis is also worse in light.

  • D. Adie pupil

    Adie pupil is larger and shows more anisocoria in light.

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 Ophthalmology question

What is the answer to this Ophthalmology question?

The best answer is B, Horner syndrome (the smaller pupil is abnormal). If anisocoria increases in the dark, the smaller pupil fails to dilate, so it is the abnormal one, as in Horner syndrome.

Why is "Third nerve palsy (the larger pupil is abnormal)" not the answer?

Parasympathetic defects show more anisocoria in bright light.

Why is "Pharmacological mydriasis" not the answer?

Pharmacological mydriasis is also worse in light.

Why is "Adie pupil" not the answer?

Adie pupil is larger and shows more anisocoria in light.

What concept does this question test?

It tests Neuro: anisocoria in dark or light in Ophthalmology. If anisocoria is greater in light, the larger pupil fails to constrict, as in third nerve palsy, Adie pupil or pharmacological dilation. Physiological anisocoria is equal in both lights.

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 Neuro: anisocoria in dark or light?

Group the red eye by what to examine and what the pupil does. Then use the flashcards and the other Ophthalmology 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.