Levator resection may be performed if there is fair to good levator function. This is determined by measuring upper eyelid margin excursion when looking from downward to upward with manual fixation of the upper brow. Classic teaching requires >4 mm of levator function for levator resection; however, typically, levator function of at least 6-7 mm correlates to better results with less under correction. Levator function of 4 mm or less usually requires a frontalis suspension procedure. Minimal ptosis (2 mm or less) with normal levator function and good response to phenylephrine may be corrected with a mullerectomy.

Deciding the amount of levator muscle to resect is the most important preoperative consideration in repairing congenital ptosis. The amount of ptosis, levator function, and intraoperative lid position will help determine the final amount of levator resection. Beard¹ described resection amount based on levator function and severity of ptosis (Table 39.1), whereas Berke² emphasized intraoperative lid position after resection based on preoperative levator function (Table 39.2). Carraway³ promoted a standard 4-mm resection for every 1 mm of ptosis. Using a combination of these guidelines and considering individual patient needs and characteristics is usually the most helpful approach. In general, the better the levator function, the more postoperative rise is expected. However, the appearance of the muscle including dystrophy, thickness, fibrosis, or fatty infiltration should also be considered when determining the amount of resection. It is important to communicate with caregivers that the procedure may result in over or undercorrection, asymmetry of height and/or contour, and possible need for revision in the future.