Which sign is most characteristic of a palsy of the oculomotor nerve?

Which sign is most characteristic of a palsy of the oculomotor nerve?

• A. Ptosis
• B. Inability to close eyelid
• C. Medial Strabismus
• D. Constricted pupil

Answer: (A)

Ptosis is the most characteristic sign because the oculomotor nerve supplies the levator palpebrae superioris, the muscle that lifts the upper eyelid. When the nerve is impaired, this muscle cannot function, causing the eyelid to droop consistently. The eye may also drift outward and downward due to loss of most extraocular muscles, and the pupil may become dilated if the parasympathetic fibers are involved. Inability to close the eyelid points to facial nerve involvement, and medial deviation is not the typical direction seen in CN III palsy (the eye tends to move outward). A constricted pupil is not typical; pupil dilation is more common with CN III involvement affecting parasympathetic fibers. So ptosis stands out as the hallmark feature.

Ptosis is the most characteristic sign because the oculomotor nerve supplies the levator palpebrae superioris, the muscle that lifts the upper eyelid. When the nerve is impaired, this muscle cannot function, causing the eyelid to droop consistently. The eye may also drift outward and downward due to loss of most extraocular muscles, and the pupil may become dilated if the parasympathetic fibers are involved. Inability to close the eyelid points to facial nerve involvement, and medial deviation is not the typical direction seen in CN III palsy (the eye tends to move outward). A constricted pupil is not typical; pupil dilation is more common with CN III involvement affecting parasympathetic fibers. So ptosis stands out as the hallmark feature.