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What is Ptosis may occur due to damage to: and explain in detail?
Ptosis is the drooping eyelid, may be seen in some clinical cases.
Oculomotor ptosis due to paralysis of the levator palpebrae (e.g., transtentorial herniation). 
Oculosympathetic ptosis due to paralysis of the superior tarsal (Muller) muscle as seen in Horner syndrome. This is a very slight ptosis, or pseudoptosis (e.g., Pancoast tumor).