Isolated congenital ptosis is incomplete retraction of the upper palpebrae since birth, usually bilateral, and not associated with external ophthalmoplegia, facial weakness or other neurological deficits, neuromuscular disease (myasthenia; congenital myopathies), systemic metabolic disease (mitochondrial cytopathy; organic acidurias) or structural lesions of the eyelid (plexiform neurofibroma; haemangioma; Meibomian or epithelial cysts; abscess). It may occur as a Mendelian trait, especially if the parents are consanguinous, or a genetic defect may not be evident from family history. Treatment is surgical resection of palpebral tissue from the conjunctival side of the eyelid.

We performed pathological examination of such resections in 28 infants and children, including immunocytochemical markers for smooth and striated slow and fast muscle myosin. Results showed structural lesions in 3; agenesis or hypoplasia of the striated levator palpebrae muscle with preservation of the smooth Müller muscle in 23, selective agenesis of Müller muscle in 1 case, and no evident lesions in 1 patient. Mild subconjunctival and perivascular lymphocytic infiltrates were almost universal, but probably secondary inflammation from chronic rubbing of the eyes and not pathogenetic. Many examples of congenital absence of specific striated muscles throughout the body are known and congenital ptosis is another. Isolated absence of smooth muscles is rarer. The upper eyelid is one of only a few sites in the body where smooth and striated muscle must work together for function, the absence of one not fully compensated by the other.