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Eyelid Anatomy http://tajmeel.ta.ohost.de Dr. Mohamed El Rouby .د يبورلا دمحأ دمحم Lecturer of Plastic Surgery ليمجتلا ةحارج سردم +20101556023 or +20126531265 or elroubyegypt@gmail.com Last Updated: April 11, 2006 Synonyms and related keywords: periocular anatomy, periorbital anatomy, lid anatomy, eyelid anatomy INTRODUCTION Section 2 of 11 The eyelids act to protect the anterior surface of the globe from local injury. Additionally, they aid in regulation of light reaching the eye, in tear film maintenance by distributing the protective and optically important tear film over the cornea during blinking, and in tear flow by their pumping action on the conjunctival sac and lacrimal sac. For excellent patient education resources, visit eMedicine's Eye and Vision Center. Also, see eMedicine's patient education article Anatomy of the Eye. SURFACE ANATOMY Section 3 of 11 The upper eyelid extends superiorly to the eyebrow, which separates it from the forehead. (Upper eyelid anatomy can be seen in Picture 1.) The lower lid extends below the inferior orbital rim to join the cheek, forming folds where there is a juxtaposition of the loose connective tissue of the eyelid with the denser tissue of the cheek. (Lower eyelid anatomy can be seen in Picture 2.) The upper eyelid skin crease (superior palpebral sulcus) is approximately 8-11 mm superior to the eyelid margin and is formed by the attachment of the superficial insertion of levator aponeurotic fibers (8-9 mm in men and 9-11 mm in women). The inferior eyelid fold (inferior palpebral sulcus), which is seen more frequently in children, runs from 3 mm inferior to the medial lower lid margin to 5 mm inferior to the lateral lid margin. The nasojugal fold runs inferiorly and laterally from the inner canthal region along the depression of separation of the orbicularis oculi and the levator labii superioris, forming the tear trough. The malar fold runs inferiorly and medially from the outer canthus toward the inferior aspect of the nasojugal fold. The open eye presents the palpebral fissure, a fusiform space between the lid margins that is 28-30 mm in length and about 9 mm in maximal height. The natural curvature of the upper lid is a function of the static shape of the tarsus combined with adaptation of the lid to the curvature of the globe. In the normal adult fissure, the highest point of the upper lid is just nasal to the center of the pupil, while the lowest point of the lower lid is just temporal to the center of the pupil. In youths, the upper lid margin rests at the upper limbus, while in adults, it rests 1.5 mm below the limbus. The lower eyelid margin rests at the level of the lower limbus. The lateral canthal angle is 2 mm higher than the medial canthal angle in Europeans; it is 3 mm higher in Asians. The distance from the medial canthus (see Picture 3) to the midline of the nose is approximately 15 mm. The palpebral fissure presents the lateral canthus (an angle of 30-40° approximately 5 mm from the lateral orbital rim); the medial canthus (forming the medial angle of the fissure, with the upper border passing inferomedially and the lower border horizontally); and the lacrimal papillae, which rest on the free lid margin, with the punctum lacrimale serving as an opening to the canaliculus. OVERVIEW OF STRUCTURE Section 4 of 11 Structures that must be considered in a description of lid anatomy are skin and subcutaneous tissue, orbicularis oculi muscle (see Picture 4), submuscular areolar tissue, the fibrous layer consisting of the tarsi and the orbital septum, lid retractors of the upper and lower eyelids, retroseptal fat pads, and conjunctiva. The anatomy of the lid is best approached initially by reviewing a sagittal cross section of the eyelid. The exact number of tissue layers and the relationship between the many layers are modified significantly by the level of the lid examined. The orbital septum represents the anatomic boundary between the lid tissue and the orbital tissue, but an assessment of eyelid function and preparation for lid surgery requires knowledge of these postseptal structures. The upper and lower lids may be considered analogous structures, with differences mainly in the lid retractor arrangement. In eyelid reconstruction, it is more practical to consider the repair of the anterior and posterior lamellae, with the anterior lamella being the skin and orbicularis, and the posterior lamella being the tarsus and conjunctiva. SKIN, SUBCUTANEOUS TISSUE, AND ORBICULARIS OCULI MUSCLE Section 5 of 11 Skin and subcutaneous tissue The skin of the eyelids is the thinnest of the body (<1 mm). The nasal portion of the eyelid skin has finer hairs and more sebaceous glands than the temporal aspect, making this skin smoother and oilier. The transition from this thin eyelid skin to the thicker skin of the eyebrow (approximately 10 mm below the lower eyebrow hairs) and the cheek skin (below the nasojugal and malar folds) is clinically evident. These boundaries should be considered in reconstructive eyelid surgery. The subcutaneous tissue consists of loose connective tissue. Fat is very sparse in preseptal and preorbital skin and is absent from pretarsal skin. Subcutaneous tissue is absent over the medial and lateral palpebral ligaments, where the skin adheres to the underlying fibrous tissue. Dermatochalasis, blepharochalasis, and epicanthic folds all are conditions that primarily involve the skin and subcutaneous tissue of the eyelids. Orbicularis oculi muscle The orbicularis oculi muscle is one of the superficial muscles of facial expression. Invested by the superficial musculoaponeurotic system (SMAS), muscle contracture is translated into movement of the overlying tissues by the fibrous septa extending from the SMAS into the dermis. The muscle may be arbitrarily divided into the orbital and palpebral parts, with the latter being divided further into the preseptal and pretarsal portions. The palpebral portion is used in blinking and voluntary winking, while the orbital portion is used in forced closure. Facial nerve innervation is from the temporal branches and from zygomatic branches of the facial nerve. The nerves are orientated horizontally and innervate the muscle from the undersurface. The orbital portion extends in a wide circular fashion around the orbit, interdigitating with other muscles of facial expression. It has a curved origin from the medial orbital margin, being attached to the superomedial orbital margin, maxillary process of the frontal bone, medial palpebral ligament, frontal process of the maxilla, and inferomedial orbital margin. Fibers from this medial origin sweep around the orbital margin in a horseshoe fashion. The muscle fibers extend superiorly to intermix with the frontalis muscle and corrugator supercilii muscle, laterally to cover the anterior temporalis fascia, and inferiorly to cover the origins of the lip elevators. The preseptal orbicularis muscles overlie the orbital septum and take origin medially from a superficial and deep head associated with the medial palpebral ligament (q.v.). The fibers from the upper and lower lid join laterally to form the lateral palpebral raphe, which is attached to the overlying skin. The pretarsal portion lies anterior to the tarsus, with a superficial and deep head of origin intimately associated with the medial palpebral ligament. Fibers run horizontally and laterally to run deep to the lateral palpebral raphe to insert in the lateral orbital tubercle through the intermediary of the lateral canthal tendon (LCT). Submuscular areolar tissue Submuscular areolar tissue consists of variable loose connective tissue below the orbicularis oculi muscle. The lid may be split into anterior and posterior portions through this potential plane, which is reached by division at the gray line of the lid margin. In the upper lid, this plane is traversed by fibers of the levator aponeurosis, some of which pass through the orbicularis to attach to the skin to form the lid crease. In the lower eyelid, this plane is traversed by fibers of the orbitomalar ligament. Superior continuance in this submuscular plane arrives at the retro-orbicularis oculi fat (ROOF), which is best developed in the eyebrow region. Additionally, the suborbicularis oculi fat (SOOF) is found in the lower lid in a continuance of this plane. TARSI AND ORBITAL SEPTUM Section 6 of 11 Tarsal plates The tarsal plates are composed of dense fibrous tissue and are responsible for the structural integrity of the lids. Each tarsus is approximately 29 mm long and 1 mm thick. The crescentic superior tarsus is 10 mm in vertical height centrally, narrowing medially and laterally. The lower border of the superior tarsus forms the posterior lid margin. The rectangular inferior tarsus is 3.5-5 mm high at the eyelid center. The posterior surfaces of the tarsi adhere to conjunctivae. Each tarsus encloses about 25 sebaceous meibomian glands that span the vertical height of the tarsus. Their ducts open at the lid margin posterior to the grey line and just anterior to the mucocutaneous junction. The medial and lateral ends of the tarsi are attached to the orbital rims by the medial and lateral palpebral ligaments. Medial palpebral ligament The medial palpebral ligament (medial canthal tendon [MCT]) is a fibrous band stabilizing the medial tarsi and is intricately related with the orbicularis oculi muscle and the lacrimal system. The superficial head of the pretarsal orbicularis muscle lies anterior to the canaliculi and forms the anterior limb of the MCT. This head is primarily horizontal but also has a superior supporting extension inserting onto the frontal bone. The deep head of the pretarsal orbicularis muscle (also constituting the Horner muscle) inserts into the posterior lacrimal crest and onto the fascia of the lacrimal sac. The upper and lower lid preseptal orbicularis have a superficial head that inserts into and augments the MCT and deep heads that insert into the lacrimal sac fascia. Thus, the lacrimal sac, encased in fascia, is related anteriorly, laterally, and posteriorly to constituents of the MCT and medially to the bony fossa of the lacrimal sac. Lateral palpebral ligament The lateral palpebral ligament (lateral canthal tendon [LCT]) is formed by dense fibrous tissue arising from the tarsi and passes laterally deep to the septum orbitale to insert into the lateral orbital tubercle 1.5 mm posterior to the lateral orbital rim. The tendon is approximately 10.5 mm in length and 6.5 mm in width, and the midpoint of the LCT inserts 10 mm inferior to the frontozygomatic suture. A small pocket of fat (Eisler pocket) lies between the septum and the LCT. Superiorly, the LCT is contiguous with the lateral horn of the levator aponeurosis, while the inferior edge is well-defined and arcs inferiorly to its insertion. About 2 mm of lateral movement of the lateral canthal angle occurs during abduction, presumably caused by posterior fibrous attachments to the lateral cheek ligament of the lateral rectus muscle. Orbital septum The orbital septum is a connective tissue structure that attaches peripherally at the periosteum of the orbital margin (the arcus marginalis); it centrally fuses with the lid retractor structures near the lid margins, thus acting as a diaphragm reported to retain orbital contents. While usually depicted diagrammatically as a discrete layer immediately posterior to the orbicularis oculi muscle, the orbital septum is a multilaminated structure that is part of the anterior orbital connective tissue framework. The septum has a laxity consistent with the mobility of the eyelids. Laterally, the septum is attached to the orbital margin, 1.5 mm in front of the lateral orbital tubercle attachment of the lateral palpebral ligament. The Eisler fat pocket separates the lateral palpebral ligament from the orbital septum. From there, the septum continues along the superior orbital rim at the arcus marginalis. Superomedially, the septum bridges the supraorbital groove, passes inferomedially anterior to the trochlea, and then follows the posterior lacrimal crest. As it runs down the posterior lacrimal crest, it lies anterior to the medial check ligament and posterior to the Horner muscle (and hence behind the lacrimal sac). The line of attachment crosses the lacrimal sac fascia to reach the anterior lacrimal crest at the level of the lacrimal tubercle. From there, it passes inferiorly down the anterior lacrimal crest and laterally along the inferior orbital rim. A few millimeters lateral to the zygomaticomaxillary suture, the attachment leaves the rim and lies several millimeters from it on the facial aspect of the zygomatic bone, thus forming the fat-filled premarginal recess of Eisler. The line of attachment then continues to again reach the lateral orbital rim just below the level of the Whitnall ligament. RETRACTORS OF THE EYELID AND POSTSEPTAL FAT PADS Section 7 of 11 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. 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. The peripheral vascular arcade of the upper eyelid lies adherent to the lower border of the anterior surface of 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 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 also are 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. These 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. Fat pads Upper eyelid pre-aponeurotic fat is found immediately posterior to the orbital septum and anterior to the levator aponeurosis. A central fat pad and a medial fat pad are described in the upper lid, while the lacrimal gland occupies the lateral compartment. The medial fat pad usually is pale yellow or white and lies anterior to the levator aponeurosis extending superomedial to the medial horn of the levator. The central fat pad is yellow and broad. A portion of the lateral end of this pad surrounds the medial aspect of the lacrimal gland. The lacrimal gland has a pinkish lobulated firm structure in contrast to the yellow soft intraorbital fat. The lacrimal gland's anterior border normally is just behind the orbital margin, but involutional changes may lead to prolapse anteroinferiorly, which is prominent on external lid examination. Three retroseptal fat pads are associated with the lower eyelid. The medial and central fat pads are separated by the inferior oblique. However, an isthmus of fat generally lies anterior to the muscle belly. The inferior oblique muscle takes a bony origin from a shallow depression on the anteromedial orbital floor, directly posterior to the orbital margin and lateral to the nasolacrimal canal. The inferior oblique muscle courses posterolaterally, passing inferior to the inferior rectus muscle, penetrating the Tenon capsule, and inserting onto the globe near the macula. Its course makes it susceptible to injury during surgical dissection of the surrounding fat pads. The medial and lateral fat pads are separated by the arcuate expansion, a fascial band extending from the capsulopalpebral fascia to the inferolateral orbital rim. Notably, the inferolateral orbital septum inserts 2 mm outside the orbital rim, creating the recess of Eisner, allowing the lateral fat pad to just spill over the orbital rim. CONJUNCTIVA Section 8 of 11 The conjunctiva is a smooth translucent mucous membrane. Palpebral conjunctiva lines the posterior surface of the lids as tarsal conjunctiva (from the mucocutaneous junction of the lid margin to the tarsal plate border) and continues as orbital palpebral conjunctiva into the fornix. The tarsal conjunctiva is adherent to the tarsus, while a submucosal lamina propria underlies the orbital palpebral conjunctiva and allows dissection from the vascular Müller muscle. At the depths of the fornices, conjunctiva reflects anteriorly onto the globe as bulbar conjunctiva. NERVES, VESSELS, AND LYMPHATICS Section 9 of 11 Nerves Sensory innervation of the eyeli