Resection of the superior tarsal muscle (STM) is effective in correcting congenital or acquired blepharoptosis in patients who have satisfactory elevation of the eyelid with a preoperative phenylephrine eye drops test. Advantages of this procedure are that only the STM is resected, the conjunctiva and basic lacrimal secretors are preserved, tarsal stability is maintained, no special instruments are required, and the preoperative phenylephrine eye drops test reliably predicts the postoperative result.