Etiology and pathogenesis of aponeurotic blepharoptosis.

How and why aponeurotic blepharoptosis develops was investigated in terms of the relationship between the levator aponeurosis and Mueller's muscle functioning as the muscle spindle of the levator muscle. A total of 200 consecutive patients with moderate to severe acquired blepharoptosis completed questionnaires regarding their history of physical irritations to the eyelids, and intraoperative conditions of the levator aponeurosis and Mueller's muscle were evaluated. Several kinds of physical irritations to the eyelids were reported, such as habitual rubbing of the eyelids, contact lens usage, cataract surgery, and continuous rubbing of the eyelids while crying all night. The two main findings for aponeurosis were that it was disinserted from the tarsus, resulting in a large amount of play between the aponeurosis and the tarsus, and that the aponeurosis and Mueller's muscle were attenuated and elongated. The authors believe that rubbing may have caused disinsertion as well as attenuation and elongation of the aponeurosis, which result in transmission failures between the levator muscle and the tarsus as well as between the levator muscle and the mechanoreceptor of Mueller's muscle, leading to clinical blepharoptosis.