A Histological Analysis of the Müllerectomy: Redefining Its Mechanism in Ptosis Repair

Background: The goals of this study were to determine whether the surgical target amount of Müller's muscle removed is consistent with the histological amount obtained, to assess the clinical outcome of ptosis repair based on these amounts, and to evaluate the role of the levator aponeurosis in the procedure. Methods: The Müllerectomy procedure was performed on eight eyelids of four cadavers and eight eyelids of seven patients (six unilateral, one bilateral). Histologically, the dimensions of the Müller and levator muscles were measured in the specimens removed. If present, the elastic fiber network of the levator aponeurosis was noted. Ptosis measurements were analyzed according to the target amount of resection and histologic amount obtained. Results: The median percentage of Müller's muscle histologically measured compared with the target tissue resection obtained was 23.25 percent (0 to 37.5 percent, n = 8) in cadavers, compared with 31.13 percent (2.8 to 58.8 percent) in patient specimens. Levator aponeurosis was identified in all cadaver specimens (n = 8) and all patient specimens (n = 8). Elastin stain identified the elastic fiber network of the levator aponeurosis. There was no statistically significant difference between amount of resection and presence of the Müller or levator muscle in cadaver (p > 0.05) or patient specimens (p > 0.05). Conclusions: There is a consistent presence of levator aponeurosis that may play a role in ptosis repair via aponeurosis advancement and resection using a modified internal Müllerectomy approach. Using the authors' surgical technique, there is no correlation of the histologically measured amount of Müller's muscle to the postoperative marginal reflex distance-1 change in the operative eyelid. The levator aponeurosis may play a greater role in ptosis repair using an internal Müllerectomy approach than previously thought.