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ANATOMY

The eyelid is composed of three distinct anatomic layers, similar to those found in the nose: the external skin, a middle supportive layer, and an internal lining (Fig. 54-1). One should view the eyelids as trilamellar structures, which are supported in space across the orbital rim by medial and lateral anchors, namely, the medial and lateral canthal tendons. The three lamellae include an outside layer of skin that is especially thin over the tarsus and preseptal areas with minimal to no subcutaneous fat. The middle, or supportive, layer includes the orbicularis muscles with the pretarsal portion lying in front of the tarsal plate and the preorbital portion lying anterior to the orbital septum. The tarsal plate is a rigid cartilaginous-like structure that measures 4 to 6 mm on the lower eyelid and 8 to 10 mm on the upper eyelid. This structural layer is pierced by glands that drain posterior to the eyelashes, or ciliary line, and number approximately 10 on the lower lid and 20 on the upper lid. These Meibomian glands and ducts are responsible for oil secretion, and when they become inspissated they may be responsible for hordeola or styes (acute inflammation), chalazia (chronic noncaseating granulomas), and other inflammatory processes. These are also the sites for inflammation in the postcosmetic blepharoplasty, including meibomianitis and blepharitis. The tarsal plate is particularly important for vertical support of the eyelid, which is fundamental to maintaining the lower eyelid position 1 to 2 mm above the corneoscleral junction or limbus. The internal lining of the eyelid is mucosa, which reflects off the globe and onto the posterior surface of the eyelids, including the posterior surfaces of the medial and lateral canthal tendons. The conjunctival surface, rich in secretory glands, is a virtually frictionless surface for the lids and globe to move against one another.

Figure 54-1

Oblique cross-section of the right orbit and adnexa beginning anteriorly with the skin and ending posteriorly with the conjuctiva covering the anterior sclera. The orbicularis muscle is contiguous with the frontalis, occipitalis, and superficial musculoaponeurotic (SMAS) layer. The orbital septum is confluent with the periosteum of the skull and orbit, as well as the periorbita. The orbital septum is also fused to the levator palpebrae and therefore serves as a complete boundary between the anterior and deep orbit. One cannot access the preaponeurotic fat without violating the superior septum. Analogously, the inferior orbital septum is intimately linked to the periosteum and the capsulopalpebral fascial system. The main retractors of the upper and lower lids are the levator and capsulopalpebral fascia, respectively. The levator is suspended from the superior orbit by Whitnall’s ligament. This structure allows the muscle to change vector forces from anterior to posterior and superior to inferior, thus serving as a pulley. The preaponeurotic and precapsulopalpebral fat is loosely but definitely linked to the respective retractors; hence, dehiscence of the levator fascia from the tarsal plate will lead to a superior ...

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