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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.
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