A 50-year-old heavy smoker presents with mild right ptosis, miosis and anhidrosis on the same side. Imaging shows an apical lung mass. The mild degree of ptosis is explained by denervation of which muscle?

• A Levator palpebrae superioris
• B Inferior tarsal muscle
• C Orbicularis oculi
• D Superior tarsal (Mueller) muscle ✓

Explanation

Sympathetic fibers from the superior cervical ganglion reach the eye along the ophthalmic artery and supply the smooth superior tarsal (Mueller) muscle, which adds roughly 2 mm of lid elevation. Loss of this tone in Horner syndrome produces only mild ptosis. Complete ptosis occurs in third nerve palsy when the striated levator palpebrae superioris is paralysed. Orbicularis oculi closes the lid and is supplied by the facial nerve.

Reference: Snell's Clinical Anatomy, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.