Damage to CN III results in which ocular findings?

Damage to CN III results in which ocular findings?

• A. Innervates levator palpebrae superioris and sphincter pupillae; causes ptosis and dilated pupil
• B. Innervates lateral rectus
• C. Innervates inferior oblique
• D. Innervates superior oblique

Answer: (A)

Damage to the oculomotor nerve disrupts both eyelid elevation and pupil constriction, because this nerve carries motor fibers to the levator palpebrae superioris and parasympathetic fibers to the sphincter pupillae. Loss of levator palpebrae superioris results in ptosis, while loss of sphincter pupillae causes the pupil to remain dilated. Although CN III also innervates several extraocular muscles (leading to misalignment or “down and out” eye), the combination of ptosis and a dilated pupil directly reflects CN III damage. The other options point to muscles supplied by other nerves or describe only part of CN III’s innervation, so they don’t capture the characteristic findings.

Damage to the oculomotor nerve disrupts both eyelid elevation and pupil constriction, because this nerve carries motor fibers to the levator palpebrae superioris and parasympathetic fibers to the sphincter pupillae. Loss of levator palpebrae superioris results in ptosis, while loss of sphincter pupillae causes the pupil to remain dilated. Although CN III also innervates several extraocular muscles (leading to misalignment or “down and out” eye), the combination of ptosis and a dilated pupil directly reflects CN III damage. The other options point to muscles supplied by other nerves or describe only part of CN III’s innervation, so they don’t capture the characteristic findings.