A patient presents with ptosis, pupillary dilation, and an eye that is "down and out." Which cranial nerve is most likely affected?

A Trochlear nerve (CN IV)

B Abducens nerve (CN VI)

C Oculomotor nerve (CN III)

D Facial nerve (CN VII)

✓ Correct Answer: Option C

Damage to the oculomotor nerve (CN III) impairs innervation to most extraocular muscles, causing the eye to be "down and out," and also affects parasympathetic fibers to the pupil, causing dilation and ptosis.

💡 Why is C) the correct answer?

The correct answer to the question "A patient presents with ptosis, pupillary dilation, and an eye that is "down and out." Which cranial nerve is most likely affected?" is Option C: Oculomotor nerve (CN III).

The other options — A) Trochlear nerve (CN IV), B) Abducens nerve (CN VI), D) Facial nerve (CN VII) — are incorrect for this USMLE Exam Prep question. As explained above: Damage to the oculomotor nerve (CN III) impairs innervation to most extraocular muscles, causing the eye to be "down and out," and also affects parasympathetic fibers to the pupil, causing dilation a…

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This 3-level USMLE Exam Prep question from the Step 1 – Basic Sciences topic is part of BrainForge Quiz's free exam preparation library. Each question includes the correct answer and a detailed explanation to help you understand the underlying concept, not just memorize the answer.

How to use this page: Read the question above, consider all four options (A through D), then check the highlighted correct answer and explanation. For active timed practice, start a free USMLE Exam Prep practice test or use flashcards for spaced repetition review.

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A patient presents with ptosis, pupillary dilation, and an eye that is "down and out." Which cranial nerve is most likely affected?

✓ Correct Answer: Option C

📚 About This USMLE Exam Prep Practice Question

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