Orbicularis oculi muscle anatomy. (A) Frontalis, (B) corrugator superciliaris, (C) procerus, (D) orbital orbicularis, (E) preseptal orbicularis, (F) pretarsal orbicularis.
Upper lid retractors
The levator palpebra superioris (LPS) arises at the orbital apex from the undersurface of the lesser wing of the sphenoid bone. The levator muscle and superior rectus muscle share a developmental origin and are connected by fibrous attachments. The LPS proceeds anteriorly for 40 mm and ends in an aponeurosis approximately 10 mm behind the orbital septum. The levator complex changes direction from a horizontal to a more vertical direction at the superior transverse ligament (Whitnall ligament).
The superior transverse ligament lies near the junction of the muscular and aponeurotic levator and represents an orbital fascial condensation spanning the anterosuperior orbit between the trochlea and the lacrimal gland fascia. Variations in thickness and adherence to the levator complex are evident. Thin fascial attachments lie between the superior transverse ligament and superior orbital rim.
The levator aponeurosis spreads laterally and medially to form lateral and medial horns. The medial horn attaches to the posterior lacrimal crest. The lateral horn divides the lacrimal gland into orbital and palpebral lobes before attaching to the lateral retinaculum at the lateral orbital tubercle. The aponeurosis fuses with the orbital septum prior to reaching the level of the superior tarsal plate border. At the inferior edge of this fusion, some aponeurotic fibers descend to insert into the lower third of the anterior surface of the tarsal plate. An anterior extension from this fusion inserts into the pretarsal orbicularis oculi muscle and overlying skin, forming the upper lid skin crease.
Kakizaki proposed that the levator aponeurosis consists of 2 layers, anterior and posterior, which also contain smooth muscle in their proximal parts.
[4]The anterior layer ends in the junctional region with the orbital septum and pulls the preaponeurotic pad of fat in conjunction with the orbital septum and the submuscular fibroadipose tissue. The posterior layer is attached to the anterior inferior one-third of the tarsal plate. It thus regulates the tension of the eyelid and the ordered movement of the lid.
Müller muscle is smooth muscle innervated by the sympathetic nervous system. Fibers originate from the undersurface of the levator in the region of the aponeurotic muscle junction, travel inferiorly between the levator aponeurosis and conjunctiva, and insert into the superior margin of the tarsus. With age, fatty infiltration may occur, giving the muscle a yellowish color.
Contrary to previous understanding, the Müller muscle may also be involved in thyroid eye disease, by fibrosis and mast cell infiltration. The Müller muscle may function as a large, serial muscle spindle. The stretching of the Müller muscle by the initial eye opening action of the levator may initiate a reflex via the mesencephalic trigeminal nucleus, which subsequently is routed through the ipsilateral or bilateral levator muscle, evoking involuntary tonic contraction to maintain an adequate visual field.
The peripheral vascular arcade of the upper eyelid lies adherent to the lower border of the anterior surface of the Müller muscle, just above the upper border of the tarsus, and is apparent during blepharoptosis surgery as a plane of dissection is created between the levator aponeurosis and the Müller muscle. The action is to widen the palpebral fissure with increased sympathetic tone. About 2 mm of ptosis is observed in
Horner syndrome. Sympathetically innervated smooth muscle fibers are also noted in the lower eyelid and constitute the inferior tarsal muscle.
Lower lid retractors
The lower eyelid retractor is a fascial extension from the terminal muscle fibers and tendon of the inferior rectus muscle, originating as the capsulopalpebral head. As it passes anteriorly from its origin, it splits to envelop the inferior oblique muscle and reunites as the inferior transverse ligament (Lockwood ligament). From there, the fascial tissue passes anterosuperiorly as the capsulopalpebral fascia. The bulk of the capsulopalpebral fascia inserts on the inferior border of the inferior tarsus. Fibers also pass forward, to unite with the Tenon capsule, and to the inferior fornix conjunctiva, through orbital fat to the orbital septum, and forward to the subcutaneous tissues forming the lower eyelid crease. The orbital septum fuses with the capsulopalpebral fascia approximately 5 mm below the inferior tarsal border.
The inferior tarsal muscle (Müller muscle) lies just posterior to the fascia and is intimate with its structure. The sympathetically innervated smooth muscle fibers are first noted near the origin of the capsulopalpebral head. The capsulopalpebral head splits into 2 portions to pass around the inferior oblique muscle sheath; the portion beneath the muscle is thin and devoid of smooth muscle, while the portion above is a much thicker fascial layer and contains the smooth muscle fibers. As they continue to pass forward, the smooth muscle fibers do not insert directly onto the inferior tarsal border but into the fascia several millimeters below the tarsal border.
In the Asian lower lid, the line of fusion of the orbital septum to the capsulopalpebral fascia is often higher, or indistinct, with anterior and superior orbital fat projection, and overriding of the preseptal orbicularis oculi over the pretarsal orbicularis.
