In sagital section, the upper eyelid consists of at least five distinct layers: the skin, the orbicularis oculi muscle, the orbital septum above or levator palpebrae superioris aponeurosis below, Muller's muscle/tarsus complex, and the conjunctiva (Fig. 5-1). The skin, orbicularis oculi muscle, and conjunctiva of the upper eyelid are similar to those of the lower eyelid (see previous text). The upper eyelid differs from the lower eyelid, however, by the presence of the levator palpebral superioris aponeurosis and Muller's muscle.
Orbital Septum/Levator Aponeurosis Complex. Deep to the orbicularis oculi muscle lies the orbital septum/levator aponeurosis complex. Unlike the situation in the lower eyelid, where the orbital septum inserts into the tarsal plate, in the upper eyelid the orbital septum extends inferiorly and blends with the levator aponeurosis approximately 10 to 15 mm above the upper eyelid margin. The levator muscle usually becomes aponeurotic at the equator of the globe in the superior orbit. The aponeurosis courses anteriorly to insert onto the anterior surface of the lower two thirds of the tarsal plate. Extensions of the levator aponeurosis also extend anteriorly into the skin of the lower portion of the upper eyelid. The aponeurotic portion of the levator behind the orbital septum is much wider than the muscle from which it is derived, and its medial and lateral extensions are known as horns or cornua. The lateral horn is prominent and deeply indents the anterior portion of the lacrimal gland to divide it into thin palpebral and thick orbital portions; its lateral extension attaches to the orbital wall at the orbital (Whitnall's) tubercle. The weaker medial horn of the levator aponeurosis blends with the orbital septum and the medial check ligament.
Muller's Muscle/Tarsus Complex. Deep to the levator aponeurosis is Muller's muscle superiorly and the tarsus along the lid margin. Muller's muscle is a nonstriated, sympathetically innervated elevator of the upper eyelid. It takes its origin from the inner surface of the levator aponeurosis and inserts onto the superior surface of the upper tarsal plate. The tarsal plate of the upper eyelid is a thin, pliable fibrocartilaginous structure that gives form and support the upper eyelid. Embedded within the tarsal plate are large sebaceous glands, the tarsal or Meibomian glands. The edge of the tarsus adjacent to the free border of the lid parallels this, while the deeper (superior) border is curved so that the tarsus is somewhat semilunar in shape. It is also, of course, curved to conform the outer surface of the eyeball. The superior tarsus is considerably larger than the inferior one, the greatest height of the superior being about 10 mm and that of the inferior about 4 to 5 mm (see Figs. 2-5 and 2-6). The tarsal glands sandwiched between the layer of fibrocartilage in the upper eyelid exit on the lid margin near the lash follicles. The lashes are supported by their roots, attached to fibrous tissue on the tarsal plate, not in the orbicularis oculi muscle anterior to the tarsal plate. Laterally, the tarsal plate becomes a fibrous band that adjoins the structural counterpart from the lower lid, forming the lateral canthal tendon. Medially, the tarsal plate also becomes fibrous and shelters the superior lacrimal canaliculus behind as it becomes the medial canthal tendon.
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