Congenital - due to weakness of the levator muscle. May be unilateral or bilateral. Ptosis is present in the primary position of gaze, with reduced movement of the lid in upgaze and impaired closure on downgaze. If the visual axis is covered, a compensatory head posture may be evident; if it cannot be cleared, sensory amblyopia will develop.
- 50% have concomitant weakness of superior rectus muscle
- 5% demonstrate Marcus Gunn syndrome
- 5% demonstrate blepharophimosis - ptosis, telecanthus, epicanthal folds, cicatricial ectropion of lower lid
Acquired:
- neurogenic:
- III nerve palsy - often, the ptosis is complete and the pupil dilated. Aberrant regeneration is common causing bizarre ocular movement
- Horner's syndrome - causes paralysis of Muller's muscle; ptosis is usually mild
- myasthenia gravis - ptosis, usually unilateral, and diplopia may be early signs of this condition. Lid fatigue is demonstrable
- chronic progressive external ophthalmoplegia e.g. oculopharyngeal dystrophy
- tabes dorsalis
- myogenic:
- senile - associated with degenerative changes in the levator and its aponeurosis. It is the most common cause of ptosis
- myotonic dystrophy - also, cataracts, pupillary abnormalities
- mechanical - mass effect of a tumour, tethering effect of scar formation, vascular abnormality e.g. haemangioma, following enucleation
- trauma, botulism