The upper eyelid retractors are the levator palpebrae superioris muscle with its aponeurosis and the superior tarsal muscle (Müller muscle). In the lower eyelid, the retractors are the capsulopalpebral fascia and the inferior tarsal muscle.
Upper eyelid retractors
The levator muscle originates in the apex of the orbit, arising from the periorbita of the lesser wing of the sphenoid, just above the annulus of Zinn. The muscular portion of the levator is approximately 40 mm long; the aponeurosis is 14–20 mm in length (Fig 9-17). The superior transverse ligament (Whitnall ligament) is a sleeve of elastic fibers around the levator muscle. It is located near or above the area where the levator muscle transitions into the levator aponeurosis (Figs 9-18, 9-19).
The Whitnall ligament functions primarily as a suspensory support for the upper eyelid and the superior orbital tissues. The ligament also acts as a fulcrum for the levator, transferring its vector force from an anterior-posterior to a superior-inferior direction. Its analogue in the lower eyelid is the Lockwood ligament. Medially, the Whitnall ligament attaches to connective tissue around the trochlea and superior oblique tendon. Laterally, it forms septa through the lacrimal gland stroma, then arches upward to attach inside the lateral orbital wall several millimeters above the lateral orbital tubercle via attachments to the lacrimal gland fascia, with a small group of fibers extending inferiorly to insert onto the lateral retinaculum. The Whitnall ligament should not be confused with the horns of the levator aponeurosis, which lie more inferior and more toward the canthi (see Fig 9-18). The lateral horn inserts onto the lateral orbital tubercle; the medial horn inserts onto the posterior lacrimal crest. The lateral horn of the levator aponeurosis is robust and divides the lacrimal gland into the orbital and palpebral lobes, attaching firmly to the orbital tubercle. The medial horn of the aponeurosis is more delicate and forms loose connective attachments to the posterior aspect of the medial canthal tendon and to the posterior lacrimal crest.
As the levator aponeurosis continues toward the tarsus, it divides into an anterior portion and a posterior portion a variable distance above the superior tarsal border. The anterior portion is composed of fine strands of aponeurosis that insert into the septa between the pretarsal orbicularis muscle bundles and skin. These fine attachments are responsible for the close apposition of the pretarsal skin and orbicularis muscle to the underlying tarsus. The upper eyelid crease is formed by the most superior of these attachments and by contraction of the underlying levator complex (see Fig 9-10). The upper eyelid fold is created by the overhanging skin, fat, and orbicularis muscle superior to the crease.
The posterior portion of the levator aponeurosis inserts firmly onto the anterior surface of the inferior half of the tarsus. It is most firmly attached approximately 3 mm above the eyelid margin and is only loosely attached to the superior 2–3 mm of tarsus. Disinsertion, dehiscence, or rarefaction of the aponeurosis following ocular surgery or due to intraocular inflammation, eyelid trauma, or senescence may give rise to ptosis. The levator muscle is innervated by the superior division of CN III, which also supplies the superior rectus muscle. A superior division palsy, resulting in ptosis and decreased upgaze, implies an intraorbital disruption of CN III.
The Müller muscle originates from the undersurface of the levator palpebrae superioris muscle approximately at the level of the Whitnall ligament, 12–14 mm above the upper tarsal border (Fig 9-20). The levator muscle divides into an anterior branch, which becomes the aponeurosis, and a posterior branch, which becomes the Müller muscle. This sympathetically innervated smooth muscle extends inferiorly to insert along the superior tarsal border. The muscle provides approximately 2–3 mm of elevation of the upper eyelid; if it is interrupted (as in Horner syndrome), mild ptosis results. The Müller muscle is firmly attached to the conjunctiva posteriorly, especially just above the superior tarsal border. The peripheral arterial arcade is found between the levator aponeurosis and the Müller muscle, just above the superior tarsal border (see Fig 9-20). This vascular arcade serves as a useful surgical landmark to identify the Müller muscle.
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Ng SK, Chan W, Marcet MM, Kakizaki H, Selva D. Levator palpebrae superioris: an anatomical update. Orbit. 2013;32(1):76–84.
Lower eyelid retractors
The capsulopalpebral fascia in the lower eyelid is analogous to the levator aponeurosis in the upper eyelid (Fig 9-21). The fascia originates as the capsulopalpebral head from attachments to the terminal muscle fibers of the inferior rectus muscle. The capsulopalpebral head divides as it encircles the inferior oblique muscle and fuses with the sheath of the inferior oblique muscle. Anterior to the inferior oblique muscle, the 2 portions of the capsulopalpebral head join to form the Lockwood suspensory ligament. The capsulopalpebral fascia extends anteriorly from this point, sending strands to the inferior conjunctival fornix, to the inferior tarsal border after fusing with the orbital septum, and to the skin to create the eyelid crease.
The inferior tarsal muscle in the lower eyelid is analogous to the Müller muscle, although it is less well developed structurally. It runs posterior to the capsulopalpebral fascia, with smooth muscle fibers most abundant in the area of the inferior fornix.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.