Pupil: 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

Sample item

A 30-year-old has pain on eye movement and reduced vision in the right eye. On the swinging flashlight test, when the light moves from the left eye to the right eye, both pupils dilate. What does this indicate?

ALeft relative afferent pupillary defectBRight efferent defect from oculomotor nerve palsyCRight relative afferent pupillary defect from optic nerve diseaseDRight Horner syndrome

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

The answer and the reasoning

C. Right relative afferent pupillary defect from optic nerve disease

The right optic nerve transmits a weaker signal, so illuminating it produces less constriction than illuminating the healthy eye and both pupils paradoxically dilate. Optic neuritis commonly causes this finding with pain on eye movement. The pupils are equal in size because the efferent pathways are intact.

Option by option

A. Left relative afferent pupillary defect
A left defect would produce dilation when the light swings onto the left eye instead.
B. Right efferent defect from oculomotor nerve palsy
An efferent oculomotor defect gives an enlarged, poorly reacting pupil with ptosis and eye movement abnormality, not an afferent defect pattern.
C. Right relative afferent pupillary defect from optic nerve disease (correct)
Correct. Paradoxical dilation on illuminating the right eye shows a right afferent defect.
D. Right Horner syndrome
Horner syndrome causes a small pupil with ptosis and a normal light reflex.

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 Ophthalmology question

What is the answer to this Ophthalmology question?

The best answer is C, Right relative afferent pupillary defect from optic nerve disease. The right optic nerve transmits a weaker signal, so illuminating it produces less constriction than illuminating the healthy eye and both pupils paradoxically dilate.

Why is "Left relative afferent pupillary defect" not the answer?

A left defect would produce dilation when the light swings onto the left eye instead.

Why is "Right efferent defect from oculomotor nerve palsy" not the answer?

An efferent oculomotor defect gives an enlarged, poorly reacting pupil with ptosis and eye movement abnormality, not an afferent defect pattern.

Why is "Right Horner syndrome" not the answer?

Horner syndrome causes a small pupil with ptosis and a normal light reflex.

What concept does this question test?

It tests Pupil in Ophthalmology. Optic neuritis commonly causes this finding with pain on eye movement. The pupils are equal in size because the efferent pathways are intact.

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?

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.