Damage to which cranial nerve results in ptosis, impaired extraocular movements, and a dilated pupil due to impaired parasympathetic function?

Damage to which cranial nerve results in ptosis, impaired extraocular movements, and a dilated pupil due to impaired parasympathetic function?

• A. Oculomotor nerve (CN III)
• B. Trochlear nerve (CN IV)
• C. Abducens nerve (CN VI)
• D. Trigeminal nerve (CN V)

Answer: (A)

Damage to the oculomotor nerve causes a CN III palsy, which presents with ptosis, limited eye movements, and a dilated pupil due to loss of parasympathetic input. This nerve supplies most of the extraocular muscles (so its injury leaves the eye with impaired movements and the eye often sits "down and out") and also carries parasympathetic fibers to the pupil via the ciliary ganglion to constrict the pupil. Without this parasympathetic influence, the pupil remains dilated. The other nerves either don’t control both eyelid elevation and pupil constriction or don’t carry those parasympathetic fibers, so they don’t produce this combination of findings.

Damage to the oculomotor nerve causes a CN III palsy, which presents with ptosis, limited eye movements, and a dilated pupil due to loss of parasympathetic input. This nerve supplies most of the extraocular muscles (so its injury leaves the eye with impaired movements and the eye often sits "down and out") and also carries parasympathetic fibers to the pupil via the ciliary ganglion to constrict the pupil. Without this parasympathetic influence, the pupil remains dilated. The other nerves either don’t control both eyelid elevation and pupil constriction or don’t carry those parasympathetic fibers, so they don’t produce this combination of findings.