A 62-year-old woman presents with progressive bilateral ptosis that is worse at the end of the day. The upper lid creases are high, the levator function is normal (13 mm bilaterally), and there is mild superior sulcus hollowing. She reports a history of prolonged contact lens wear and cataract surgery two years ago. The MOST likely mechanism is:

• A Myogenic failure of the levator muscle
• B Dehiscence or disinsertion of the levator aponeurosis ✓
• C Loss of sympathetic innervation to Mueller's muscle
• D Mechanical loading by redundant upper lid skin

Explanation

Aponeurotic (involutional) ptosis features a normal levator function with a high or absent lid crease and superior sulcus defect, because the aponeurosis dehisces from the tarsal plate so the levator still moves but does not transmit force to the lid. Contact lens wear and intraocular surgery are recognised risk factors for aponeurotic disinsertion. Myogenic ptosis shows poor levator function, which this patient does not have.

Reference: Parsons' Diseases of the Eye, 22nd ed.

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Written and medically reviewed by the StethoPrep medical team.