What drug can be used that will provide only mydriasis and no cycloplegia, for a fundus examination in a young adult patient?

Question

Image below highlights jugular foramen. Which of the following structures do not pass through the marked structure “A”?

Answer 1

The question is testing whether you know which mydriatic drug spares accommodation, since it asks for pupil dilation without loss of near focus.

Atropine ointment: An antimuscarinic with a very long action, sometimes over a week. It gives both strong mydriasis and strong cycloplegia, so it is wrong here.
Phenylephrine: A sympathomimetic that acts only on the dilator pupillae through alpha-1 receptors. It widens the pupil but does not touch the ciliary muscle, so near focus stays normal. This fits the question.
Homatropine: Another antimuscarinic, shorter acting than atropine but still causes cycloplegia along with mydriasis.
Tropicamide: A short acting antimuscarinic commonly used for fundus exams, but it too causes some cycloplegia, so it does not give mydriasis alone.

Only phenylephrine dilates the pupil while leaving accommodation working, since its target is the dilator muscle and not the ciliary muscle.

Let's summarize:

Antimuscarinics such as atropine, homatropine, and tropicamide cause both mydriasis and cycloplegia.
Phenylephrine, a sympathomimetic, causes mydriasis alone.

The correct answer is phenylephrine.

Answer 2

The question is testing whether you know which mydriatic drug spares accommodation, since it asks for pupil dilation without loss of near focus.

Atropine ointment: An antimuscarinic with a very long action, sometimes over a week. It gives both strong mydriasis and strong cycloplegia, so it is wrong here.
Phenylephrine: A sympathomimetic that acts only on the dilator pupillae through alpha-1 receptors. It widens the pupil but does not touch the ciliary muscle, so near focus stays normal. This fits the question.
Homatropine: Another antimuscarinic, shorter acting than atropine but still causes cycloplegia along with mydriasis.
Tropicamide: A short acting antimuscarinic commonly used for fundus exams, but it too causes some cycloplegia, so it does not give mydriasis alone.

Only phenylephrine dilates the pupil while leaving accommodation working, since its target is the dilator muscle and not the ciliary muscle.

Let's summarize:

Antimuscarinics such as atropine, homatropine, and tropicamide cause both mydriasis and cycloplegia.
Phenylephrine, a sympathomimetic, causes mydriasis alone.

The correct answer is phenylephrine.

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