Which of the following is NOT a feature of oculomotor nerve palsy?
**Core Concept**
The oculomotor nerve (cranial nerve III) controls several extraocular muscles, including the levator palpebrae superioris, which is responsible for eyelid elevation, and the sphincter pupillae, which constricts the pupil. Oculomotor nerve palsy results from damage to this nerve, leading to impaired motor function.
**Why the Correct Answer is Right**
Oculomotor nerve palsy typically presents with ptosis (drooping eyelid), due to the impaired function of the levator palpebrae superioris muscle. Patients may also experience diplopia (double vision) because of the impaired coordination of eye movements. Additionally, pupillary dilatation can occur due to the unopposed action of the dilator pupillae muscle, which is innervated by the sympathetic nervous system. The correct answer is a feature that is NOT typically associated with oculomotor nerve palsy.
**Why Each Wrong Option is Incorrect**
**Option A:** Ptosis is indeed a feature of oculomotor nerve palsy, so this option is incorrect.
**Option B:** Diplopia is also a common symptom of oculomotor nerve palsy, making this option incorrect.
**Option D:** Pupillary dilatation can occur in oculomotor nerve palsy, so this option is also incorrect.
**Clinical Pearl / High-Yield Fact**
A classic clinical pearl to remember is the "3 Ps" of oculomotor nerve palsy: ptosis, pupillary dilatation, and pain (often retro-orbital). This triad can help differentiate oculomotor nerve palsy from other causes of diplopia.
**Correct Answer:** C.