Pupil: third nerve palsy: 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 · Pupil: third nerve palsy

Sample item

A patient has sudden headache, ptosis, a dilated fixed pupil and a down-and-out eye. What is the most important cause to exclude?

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

The answer and the reasoning

D. Posterior communicating artery aneurysm

Pupil involvement indicates compression of the superficial parasympathetic fibres, and a PCom aneurysm is the emergency. Diabetic third nerve palsy typically spares the pupil.

Option by option

  • A. Myasthenia gravis

    Myasthenia does not cause pupillary changes.

  • B. Horner syndrome

    Horner has miosis.

  • C. Diabetic microvascular neuropathy

    Diabetic palsy usually spares the pupil.

  • D. Posterior communicating artery aneurysm (correct)

    Correct. A pupil-involving palsy needs urgent vascular imaging.

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 D, Posterior communicating artery aneurysm. Pupil involvement indicates compression of the superficial parasympathetic fibres, and a PCom aneurysm is the emergency.

Why is "Myasthenia gravis" not the answer?

Myasthenia does not cause pupillary changes.

Why is "Horner syndrome" not the answer?

Horner has miosis.

Why is "Diabetic microvascular neuropathy" not the answer?

Diabetic palsy usually spares the pupil.

What concept does this question test?

It tests Pupil: third nerve palsy in Ophthalmology. Diabetic third nerve palsy typically spares the 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 Pupil: third nerve palsy?

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.