Question: Can you identify this condition?

A 30-year-old woman presents with a 4-month history of a slightly droopy left upper eyelid. She has no other ocular complaints. On examination, visual acuity is 6/6 in each eye. There is a 1- to 2-mm ptosis of the left upper eyelid. Motility is otherwise normal. Pupil examination reveals anisocoria, with the left pupil smaller, especially in dark surroundings. Results of the rest of the examination, including fundoscopy, are normal, and the patient is otherwise healthy.

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