[Anatomical modification of the levator muscle of the eyelid in congenital ptosis].

Congenital ptosis of the upper lid is classified as a developmental anomaly of the levator muscle. We report the histochemical findings in 38 specimens of levator muscle removed in patients with congenital ptosis and operated on by a resection of the levator muscle. Results demonstrated a close relationship between the presence or the absence of muscular fibres in the specimen and the degree of ptosis and the levator function. We suggest that congenital ptosis may result from a failure of differentiation and/or fusion of the anterior portion of the superior orbital mesoderm complex.