What causes drooping eyelids?

Ptosis (drooping eyelid) may be caused by various factors. It can be congenital, associated with underdevelopment of the oculomotor nucleus or absence of the superior eyelid muscle. Acquired causes include oculomotor nerve palsy, sympathetic nerve palsy, myogenic ptosis (such as in myasthenia gravis), and mechanical ptosis (due to lesions within the eyelid itself). Additionally, excessive fatigue, aging, trauma, ocular infections, diabetes, and other factors may also lead to ptosis.