Neuro-ophthalmology and pupils: congenital Horner syndrome: 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 and pupils: congenital Horner syndrome

Sample item

An infant has mild right ptosis and a smaller right pupil since birth. The right iris is lighter in colour than the left. What explains the iris colour?

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

The answer and the reasoning

B. Sympathetic supply is needed for normal iris stromal pigmentation

Sympathetic innervation during early life is needed for normal melanocyte pigmentation of the iris stroma. A congenital or early-acquired Horner syndrome therefore leaves the affected iris lighter, which is heterochromia iridis. Acquired Horner syndrome in an adult does not change the iris colour.

Option by option

  • A. Absence of the iris dilator muscle

    The dilator muscle is present, but its nerve supply is lost.

  • B. Sympathetic supply is needed for normal iris stromal pigmentation (correct)

    Correct. Early loss of sympathetic supply leaves the iris stroma hypopigmented.

  • C. A local pigment epithelial defect of the retina

    A retinal pigment defect does not change the iris colour.

  • D. Parasympathetic lesion causing iris atrophy

    A parasympathetic lesion causes a dilated pupil rather than a small one with pigment change.

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, Sympathetic supply is needed for normal iris stromal pigmentation. Sympathetic innervation during early life is needed for normal melanocyte pigmentation of the iris stroma.

Why is "Absence of the iris dilator muscle" not the answer?

The dilator muscle is present, but its nerve supply is lost.

Why is "A local pigment epithelial defect of the retina" not the answer?

A retinal pigment defect does not change the iris colour.

Why is "Parasympathetic lesion causing iris atrophy" not the answer?

A parasympathetic lesion causes a dilated pupil rather than a small one with pigment change.

What concept does this question test?

It tests Neuro-ophthalmology and pupils: congenital Horner syndrome in Ophthalmology. A congenital or early-acquired Horner syndrome therefore leaves the affected iris lighter, which is heterochromia iridis. Acquired Horner syndrome in an adult does not change the iris colour.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 and pupils: congenital Horner syndrome?

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.