Evaluation of levator muscle integrity in ptosis with levator force measurement.

Purpose: To determine the efficacy of the force the levator muscle can generate as a diagnostic tool for ascertaining the cause of ptosis.

Methods: A total of 187 patients with ptosis were evaluated clinically, their levator force was measured, and each ptotic eyelid subsequently had surgical correction. At each step, patients received a diagnosis of congenital or acquired (history- dependent) aponeurotic, myogenic, neurogenic, or mechanical ptosis. To measure the levator force, a clamp placed on the upper eyelid lashes was attached to a force transducer. The maximum force generated on upgaze was recorded as the levator force. Data from healthy subjects were used to determine whether each levator muscle of the ptotic eyelids produced normal or less than normal force. The correct diagnosis was considered to be the diagnosis based on the findings at the time of surgery. The diagnosis of each patient with ptosis determined by eyelid excursion, eyelid excursion plus examination, levator force, and the levator force plus examination results were compared with the correct diagnosis.

Results: Eyelid excursion predicted the correct diagnosis 78.2% of the time. When eyelid excursion was combined with the examination results, the diagnosis was correct 84.0% of the time. Levator force predicted the correct diagnosis 95.2% of the time. When levator force was combined with the examination, the diagnosis was correct 97.9% of the time.

Conclusion: Diagnosis of the cause of ptosis based on levator force measurement is significantly more accurate than when the diagnosis is based on eyelid excursion, even when information obtained on examination also is considered. Levator force measurement should be an integral part of ptosis evaluation.