Cardinal features of common underlying causes of ptosis

Cause	Levator function	Eyelid crease margin	Laterality	Other clinical features
Congenital abnormality of the levator muscle^*	Reduced	Crease often absent	Often unilateral	Many patients also have amblyopia, strabismus.
Aponeurotic ptosis	Normal	Often increased	Uni- or bilateral	Isolated finding of ptosis.
Third cranial nerve palsy	Reduced	Normal	Usually unilateral	Impaired extraocular movement in ipsilateral eye. If ipsilateral pupil dilated, urgent evaluation for aneurysm is required.
Horner syndrome	Normal	Normal	Usually unilateral	Ipsilateral miotic pupil.
Myasthenia	Reduced	Normal	Uni- or bilateral	Variable and fatigable. Diplopia and extraocular movement abnormalities often present.
Muscle disease	Reduced	Normal	Usually bilateral	Orbicularis oculi, other extraocular or bulbar muscles may be affected.

* Other, less common causes of congenital ptosis are discussed in the UpToDate text.

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