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drooping of the upper eyelid. It may be unilateral or bilateral, total or partial, or congenital or acquired. Congenital ptosis is caused by incomplete development or absence of the muscle that lifts the upper lid. The condition is treated by surgery.
Acquired ptosis is generally unilateral; it results from such diseases as neuritis of the oculomotor nerve and encephalitis, which lead to paresis or paralysis of the oculomotor nerve that innervates the muscle lifting the upper lid. The condition is treated by eliminating the underlying disease, by physiotherapy, and occasionally by surgery.