Neuro-ophthalmology: 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-ophthalmology

Sample item

A man develops vertical double vision after a head injury. The diplopia is worst on looking down and inwards, as when reading or climbing stairs, and he tilts his head to the side opposite the affected eye. Which cranial nerve is involved, and what is the usual cause of its vulnerability?

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

The answer and the reasoning

C. Trochlear nerve, owing to its long slender intracranial course and exit from the dorsal midbrain

A fourth nerve palsy paralyses the superior oblique, which depresses the adducted eye, so diplopia is worst on downgaze and the patient tilts the head away from the affected eye to compensate. The trochlear nerve is the thinnest and has the longest intracranial course, and it exits dorsally, making it prone to closed head trauma.

Option by option

  • A. Oculomotor nerve, owing to compression by a posterior communicating artery aneurysm

    A third nerve palsy causes ptosis and a down-and-out eye, often with a dilated pupil.

  • B. Trigeminal nerve, owing to a fracture of the foramen rotundum

    The trigeminal nerve is sensory to the face and does not move the eye.

  • C. Trochlear nerve, owing to its long slender intracranial course and exit from the dorsal midbrain (correct)

    Correct. Superior oblique weakness explains the pattern of diplopia and head tilt.

  • D. Abducens nerve, owing to its long course over the petrous apex

    An abducens palsy causes horizontal diplopia, worse on looking toward the paralysed side.

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 C, Trochlear nerve, owing to its long slender intracranial course and exit from the dorsal midbrain. A fourth nerve palsy paralyses the superior oblique, which depresses the adducted eye, so diplopia is worst on downgaze and the patient tilts the head away from the affected eye to compensate.

Why is "Oculomotor nerve, owing to compression by a posterior communicating a…" not the answer?

A third nerve palsy causes ptosis and a down-and-out eye, often with a dilated pupil.

Why is "Trigeminal nerve, owing to a fracture of the foramen rotundum" not the answer?

The trigeminal nerve is sensory to the face and does not move the eye.

Why is "Abducens nerve, owing to its long course over the petrous apex" not the answer?

An abducens palsy causes horizontal diplopia, worse on looking toward the paralysed side.

What concept does this question test?

It tests Neuro-ophthalmology in Ophthalmology. The trochlear nerve is the thinnest and has the longest intracranial course, and it exits dorsally, making it prone to closed head trauma.

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-ophthalmology?

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.