Which of the following is not a feature of occulomotor nerve palsy: September 2010
## **Core Concept**
The oculomotor nerve (cranial nerve III) is responsible for controlling several extraocular muscles, including the medial rectus, superior rectus, inferior rectus, and inferior oblique muscles. It also carries parasympathetic fibers that control pupillary constriction and accommodation. Oculomotor nerve palsy leads to weakness or paralysis of these muscles, resulting in characteristic clinical features.
## **Why the Correct Answer is Right**
Ptosis (drooping of the eyelid) is a feature of oculomotor nerve palsy due to the involvement of the levator palpebrae superioris muscle, which is innervated by the oculomotor nerve. Diplopia (double vision) occurs because of the imbalance in extraocular muscle function. The pupil may be dilated due to the loss of parasympathetic input. However, the **intact sensation of the cornea** is not a direct feature of oculomotor nerve palsy but rather a function related to the ophthalmic branch of the trigeminal nerve (V1), not the oculomotor nerve.
## **Why Each Wrong Option is Incorrect**
- **Option A: Ptosis** - This is a feature of oculomotor nerve palsy, as the nerve supplies the levator palpebrae superioris muscle.
- **Option B: Diplopia** - This is also a feature due to the imbalance of extraocular muscles.
- **Option C: Dilated pupil** - This can occur in oculomotor nerve palsy due to the interruption of parasympathetic fibers.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that in a case of oculomotor nerve palsy, if the pupil is spared (not dilated), it suggests a microvascular cause (like diabetes) rather than an aneurysmal compression, which typically affects the pupil.
## **Correct Answer:** D. intact sensation of cornea.