Ptosis is defined as drooping of the eyelid[^1].
Etiology
Ptosis is a symptom that can have various different causes:
Congenital ptosis
Congenital ptosis is frequently caused by malformation or incomplete development of the muscle responsible for elevating the upper eyelid, the Musculus levator palpebrae superioris. It is hereditary and usually unilateral. A hemangioma of the upper eyelid also frequently causes congenital ptosis. The clinical features of mandibulopalpebral synkinesis (Marcus-Gunn syndrome) and Möbius syndrome are likewise associated with congenital ptosis.
Levator muscle injury
Injury to the Musculus levator palpebrae superioris or its delicate terminal tendon may result from trauma or age-related dysplasia and leads to drooping of the upper eyelid.
Paralytic ptosis
Damage to the nerve responsible for the levator, the Oculomotor nerve, also leads to ptosis. Since this Cranial nerve also provides motor innervation to four of the six extraocular muscles, paralytic strabismus is usually also present.
Sympathetic ptosis
Ptosis caused by damage to the sympathetic nervous system of the head is usually mild to moderate, as the levator remains functional. It results from loss of function of the Musculus tarsalis. This consists of smooth muscle embedded in the eyelid that vertically contracts the eyelid. Damage to the sympathetic nervous system also causes other ocular deficits, the so-called Horner syndrome.
Ptosis in muscle disorders
In disorders affecting the musculature as a whole (e.g., myasthenia gravis), the levator may also be affected.
