A Detailed Anatomic Study Based on the Mechanical Conduction Mechanism of Upper Eyelid to Facilitate Blepharoplasty and Repair of Complications.

[OBJECTIVE] Through clinical intraoperative observation, gross anatomy and histologic observation, the authors will preliminarily clarify the detailed structures of various tissues related to the upper eyelid opening and closing movement and their position and adjacent relationships, and explore the mechanical transmission characteristics during the physiological upper eyelid opening and closing process, so as to provide theoretical support for creating vivid and natural double eyelids and repair complications.

[METHODS] First, by performing blepharoplasty on 15 patients, the characteristics of each layer of upper eyelid and its adjacent relationship, as well as the movement and mechanical relationship of each structure during eye opening and closing, were carefully observed. Second, by dissecting the upper eyelids of 6 cadaveric specimens, the hierarchical structure and position adjacency of each layer of upper eyelid tissue structure were observed and clarified. Third, by sectioning 5 cadaveric upper eyelid specimens, hematoxylin-eosin, Masson's trichrome staining, and anti-smooth muscle actin immunohistochemical staining were used to observe the histological structure and relationship of each layer of the upper eyelid.

[RESULTS] Clinical observation results showed that the upper eyelid can be divided into structural layer such as skin, subcutaneous fat, orbicularis oculi muscle, orbital septum, orbital fat, levator palpebrae superioris and levator aponeurosis, Müller's muscle, and conjunctiva. On the superficial side of the tarsus, the structures mainly include the skin, subcutaneous fat (thin and clinically indistinct in some individuals), preseptal orbicularis oculi muscle, pretarsal fascial tissue, and tarsal plate. During eye opening, the levator palpebrae superioris contracts, transmitting force through levator aponeurosis to the tarsal plate and pretarsal tissues, causing the entire upper eyelid to move posteriorly and superiorly. Simultaneously, the orbital fat moves posteriorly and superiorly along with the levator aponeurosis. The gross anatomic observation of the upper eyelid showed that the skin of the upper eyelid gradually thickens from the eyelid margin toward the eyebrow, being thinnest anterior to the tarsal plate. In most specimens, the subcutaneous fat anterior to the tarsal plate is thin, and the orbicularis oculi muscle is circular. Below the orbicularis oculi muscle, the retro-orbicularis oculi fat-layer is dense, with significant interindividual variability. Histological observation showed that the levator palpebrae superioris divided into the anterior layer (levator aponeurosis) and the posterior layer (Müller's muscle). The levator aponeurosis can be further divided into anterior and posterior layers. The anterior layer is continuous with the orbital septum, whereas the posterior layer disperses and inserts into the tarsal plate, pretarsal tissues, and orbicularis oculi muscle, with some fibers penetrating the orbicularis oculi muscle to terminate in the subcutaneous layer.

[CONCLUSIONS] The levator palpebrae superioris-Müller's muscle complex serves as the primary dynamic structure for upper eyelid movement. It transmits force through the levator aponeurosis to the tarsal plate and skin, interacting with the detailed anatomic structures of the upper eyelid to complete the process of eye opening and closing. Through comprehensive analysis such as clinical observation, gross anatomy, and histological observation, the authors have clarified that the detailed anatomic structure of the upper eyelid and its mechanical balance are the prerequisite for successful upper eyelid plasty and provide a new theoretical basis for repairing various complications after blepharoplasty.