Glaucoma: pupillary block mechanism: 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 · Glaucoma: pupillary block mechanism

Sample item

In primary angle closure, why does the iris bow forward?

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

The answer and the reasoning

D. Higher pressure in the posterior chamber due to resistance at the pupil

Contact between iris and lens at the pupil margin impedes aqueous flow, raising posterior chamber pressure and pushing the peripheral iris forward against the trabecular meshwork (iris bombe). The mechanism is relative pupillary block, greatest in mid-dilation. This is why iridotomy is curative.

Option by option

  • A. Anterior displacement of the lens by zonular laxity only

    Zonular laxity is not the main mechanism.

  • B. Atrophy of the iris dilator

    Dilator atrophy would give a small pupil.

  • C. Contraction of the ciliary muscle

    Ciliary contraction would deepen the angle.

  • D. Higher pressure in the posterior chamber due to resistance at the pupil (correct)

    Correct. Relative pupillary block raises posterior chamber pressure.

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, Higher pressure in the posterior chamber due to resistance at the pupil. Contact between iris and lens at the pupil margin impedes aqueous flow, raising posterior chamber pressure and pushing the peripheral iris forward against the trabecular meshwork (iris bombe).

Why is "Anterior displacement of the lens by zonular laxity only" not the answer?

Zonular laxity is not the main mechanism.

Why is "Atrophy of the iris dilator" not the answer?

Dilator atrophy would give a small pupil.

Why is "Contraction of the ciliary muscle" not the answer?

Ciliary contraction would deepen the angle.

What concept does this question test?

It tests Glaucoma: pupillary block mechanism in Ophthalmology. The mechanism is relative pupillary block, greatest in mid-dilation. This is why iridotomy is curative.

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 Glaucoma: pupillary block mechanism?

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.