MALENA M. AMATO , BLYTHE MONHEIT and JOHN W. SHORE
Table Of Contents
|Knowledge of the relationship between structure and function in the human
eyelid is essential to understand its anatomic complexity (Fig. 1). The primary function of the eyelid is to protect the eye and to preserve
vision. Glands within the eyelids produce the complex tear film that
provides nutrition, lubrication, and protection for the ocular surface.1 The eyelids also contribute to the lacrimal pump and their blinking action
helps eliminate tears from the lacrimal lake. The eyelids play an
essential role in protecting the ocular surface by means of eye protective
mechanisms. These are normal physiologic responses that maintain
the precorneal tear film and ensure ocular surface defense. Important
eye protective mechanisms provided by the eyelids that act to protect
the ocular surface from drying and exposure include tear production, eyelid
closure, blink frequency and adequacy, and stabilization of the
precorneal tear film by reduction of evaporative tear loss.|
The eyelids are divided into anterior and posterior layers, termed lamellae (Fig. 2). The anterior lamella includes skin and orbicularis oculi muscle. A thin, multilayered septum separates the anterior preseptal tissues from the postseptal orbital structures. The posterior lamella includes the tarsus and its attachments and the conjunctiva. The upper and lower eyelid retractor muscles have attachments onto the tarsus. Knowledge of the concept of an anterior and posterior lamella is essential to understanding eyelid reconstruction, because creation of both elements is required.
This chapter briefly reviews embryology, growth, and development of the eyelids to provide a better understanding of eyelid anatomy. The anatomy and function of the layers of the eyelid are discussed including skin and eyelid margin, orbicularis muscle, septum, orbital fat, retractor muscles, tarsus, and conjunctiva. Other important components of the adnexal structures will also be discussed; the surrounding lacrimal drainage system; and the vascular, lymphatic, and nervous supply to the orbit and eyelids.
|The eyelids are derived from an “inductive interaction” between
mesodermal and ectodermal tissues. Development of the five brachial
or pharyngeal arches occurs in the first few weeks of gestation. At
about 5 weeks, a sheet of immature mesoderm originates from the first
brachial arch, called the mandibular arch. Mesenchymal proliferation
occurs cephalad to the first brachial arch to form the facial processes: the
frontonasal, medial nasal, lateral nasal, and mandibular2 (Fig. 3). The upper eyelids are formed from the frontonasal process, which is
an extension of orbital or paraxial mesoderm.3 At about 6 weeks of gestation, mesoderm from the dorsal portion of the
first brachial arch forms the maxillary process. The mesoderm of the
maxillary process lies in apposition to the paraxial mesoderm of the eye
and nasal process and extends superiorly to form the lower eyelid. The
appearance of the eyelid fold marks the beginning of eyelid development
during the sixth or seventh week of gestation. Incomplete eyelid
fold development is thought to be the cause for a number of congenital
eyelid anomalies, including ablepharon, cryptophthalmos, and microblepharon.4|
The embryonic eyelids undergo a process of fusion, development, and dysjunction, or separation, during development (Fig. 4). Fusion of the eyelids occurs at about the eighth gestational week and is complete at about 10 weeks. During eyelid fusion, differentiation of the eyelid structures occurs. The cilia and meibomian and sweat glands are derived from an inward migration of ectodermal cells. Simultaneous condensation of mesenchymal tissue surrounds the meibomian glands to form the tarsus.5 Failure of fusion of the eyelids results in colobomas of the eyelid margin. At 10 weeks, the levator palpebrae superioris (LPS) begins to develop and separates from the superior rectus muscle by the fourth month. Poor development of these retractor muscles in the upper eyelid is thought to be the cause of congenital ptosis. Dysjunction, or separation, of the eyelids does not occur until the end of the fifth month and is discussed in more detail later.
The nasolacrimal duct derives from ectodermal tissue in the nasolacrimal groove between the lateral nasal and maxillary processes.6 This tissue is known as the nasolacrimal ectodermal cord. Mesenchymal tissues from the maxillary process cover the ectodermal tissue medially, before it canalizes. The central cells of the cord degenerate until there is a superior membrane composed of canalicular and conjunctival epithelium, as well as an inferior membrane of nasolacrimal and nasal epithelium. These superior and inferior ends are usually patent at the time of birth. The lacrimal gland arises from an outpouching of the conjunctiva as a modified salivary gland.
Mesodermal tissue from the second brachial arch spreads to cover the entire head and neck by way of myoblast induction. This superficial embryonic muscle plane becomes the superficial skeletal muscle of the eyelids. The orbicularis oculi, corrugator supercilii, and procerus muscles arise from the infraorbital lamina, immediately below the orbital rim, whereas the frontalis muscle develops from the temporal lamina. Aponeurotic fibers of the galea envelop the developing frontalis muscle and split into deep and superficial layers. The thinner superficial galea continues as the anterior muscle sheath of the frontalis and orbicularis, whereas the deep galea encompasses the sub-brow fat and continues into the eyelid as the posterior orbicularis fascia.7
Eyelid dysjunction occurs at approximately 21 to 26 weeks of gestation and results from keratinization of the eyelid margins, contraction of the inferior eyelid retractors, and secretion of sebum by the meibomian glands.8 Although separation of the eyelids is usually complete by the sixth month of gestation, it may persist until shortly before birth. Failure of eyelid separation may result in conditions such as ankyloblepharon, blepharophimosis, epicanthus, and euryblepharon. Nests of melanocytes presenting on the eyelid margins at the time of separation may form kissing nevi that can be seen after birth.
The eyelid skin is composed of a thin dermis and contains little subcutaneous fat.9 It is very elastic and is one of the thinnest of the body. It is loosely adherent to the underlying orbicularis oculi muscle. The skin of the upper eyelid is thinner than that of the lower eyelids. In later years, the skin becomes redundant. The excess skin provides an excellent source for skin grafting for eyelid reconstruction. There is a marked transition from the thin eyelid skin to the thicker skin of the eyebrow and cheek. The redundancy and elasticity of the eyelid skin and other eyelid structures allows for primary closure of fairly large defects (up to 30% of the eyelid in older adult patients). Upper eyelid skin laxity increases with age. This is called dermatochalasis. Dermatochalasis may progress and cause hooding, which results in mechanical ptosis that constricts the superior visual fields, or cause a mechanical upper eyelid entropion. Prominence of the lower eyelids may result from prolapse of the orbital fat, malar bags, or hypertrophic or overriding orbicularis oculi muscle. Excising excessive amounts of skin from either the upper or lower eyelids can create lagophthalmos or frank ectropion.
Transverse eyelid creases are present in both upper and lower eyelids, measuring 8 to 10 mm above the upper eyelid margin and 4 to 5 mm below the lower eyelid margin.3 The upper eyelid crease, more specifically called the superior palpebral crease, represents the cutaneous insertion of fibers of the levator aponeurosis into the preseptal orbicularis oculi, which is usually the site of the eyelid fold. The upper eyelid fold refers to the roll of skin overlying the eyelid crease. Absence of an eyelid crease implies lack of LPS function, such as seen in congenital blepharoptosis. Dehiscence of the levator aponeurosis from its insertion on the tarsus, as seen in involutional ptosis, may also result in an elevated eyelid crease. Insertions of the levator aponeurosis into the preseptal orbicularis oculi and dermis are either weak or absent in the Asian eyelid. The anatomy of the Asian eyelids is discussed later in the chapter. The region between the upper eyelid crease and the superior orbital margin is referred to as the superior orbital sulcus. Loss of orbital volume following enucleation or atrophy of orbital fat as seen with aging may result in a concavity of the superior sulcus skin and muscle.
The lower eyelid has three creases (Fig. 5). The inferior palpebral crease is a true crease marking the inferior edge of the tarsus and the insertions of the lower eyelid retractor muscles. The other two creases are less well defined and are the nasojugal crease inferomedially and the malar crease inferior to the lateral canthus, which marks the junction of the orbicularis muscle and the malar fat pad. These topographic landmarks demarcate the inferior border of the lower eyelid.
The upper and lower eyelid margins are composed of several identifiable structures (Fig. 6). The lash line is the most anterior line found along the eyelid margin, which is the site of origin of the cilia. Approximately 100 to 150 cilia are found in the upper eyelid, and approximately 50 to 75 cilia are in the lower eyelid. The eyelashes arise from hair follicles on the anterior surface of the tarsus and project outward, anterior to the eyelid margin. Both meibomian glands and eyelashes differentiate during the second month of gestation from a common pilosebaceous unit. Congenital distichiasis can result from poor differentiation, because an extra row of lashes arises from the meibomian orifices. A lash follicle may also develop from a meibomian gland following trauma in certain disease states, or with chronic irritation, leading to acquired distichiasis.10 Each hair follicle contains approximately two sebaceous glands called glands of Zeis. Sweat glands, or glands of Moll, also lie near the cilia and empty into the adjacent follicles. Glands of Moll and Zeis secrete lipid that contributes to the superficial layer of the tear film and slows evaporation.9 Posterior to the lash line and anterior to the tarsus on the eyelid margin is the gray line. The gray line is also referred to as the muscle of Riolan and represents the pretarsal orbicularis muscle on the eyelid margin.11 An incision posterior to the gray line along the eyelid margin demarcates the anterior lamella from the posterior lamella of the eyelid. The meibomian glands and tarsus comprise the layer of the eyelid margin located immediately posterior to the gray line and is part of the posterior lamella. The meibomian glands are arranged vertically within the tarsus with their orifices at the marginal surface. A mucocutaneous junction is located posterior to the meibomian gland orifices on the eyelid margin. The lacrimal puncta are also visible on all four eyelids near the medial canthal angle. The puncta represent the opening from the eyelid margin into the ampulla and canaliculi, which is the beginning of the lacrimal drainage apparatus. The lacrimal drainage system is described later in the chapter.
THE ORBICULARIS OCULI MUSCLE
The orbicularis oculi muscle is a thin sheet of concentrically arranged muscle fibers covering the eyelids and periorbital region. It is the main protractor of the eyelids and its primary function is narrowing of the palpebral fissures and closure of the eyelids. It also plays a role in the lacrimal pump system. The orbicularis oculi muscle is innervated by the facial nerve, and although it is a skeletal muscle, it is under voluntary, as well as reflex, control.12 The orbicularis oculi muscle is classically divided into three anatomic parts13 (Fig. 7). The pretarsal orbicularis overlies the tarsus, the preseptal orbicularis overlies the orbital septum, and the orbital portion lies beneath the skin that surrounds the remaining orbital aperture (Fig. 8). The pretarsal and the preseptal orbicularis together are referred to as the palpebral orbicularis. Voluntary squeezing of the orbital orbicularis closes the palpebral fissure and protects the globe and orbit from injury. Involuntary movements, such as blinking and the functioning of the lacrimal pump, result mainly from contraction of the palpebral portion of the orbicularis oculi muscle.10
The orbital portion of the orbicularis oculi muscle is the outermost and the largest segment. It is responsible for forcible eyelid closure (squeezing) and voluntary eyelid closure (winking). The orbital portion of the orbicularis muscle originates from the periosteum of the frontal and maxillary bones at the insertion of the medial canthal tendon (MCT). It is a continuous muscle that encircles the orbit before reinserting at the medial canthus inferiorly where it is attached to the periosteum of the posterior lacrimal crest, the lacrimal fascia, and the MCT.12 Superiorly, the orbital portion extends to the eyebrow and interdigitates with the frontalis and the corrugator superioris muscles. Medially, attachments extend from the supraorbital notch to the side of the nasal bone. Inferiorly, the orbital portion arises from the anterior limb of the MCT and the surrounding periosteum and extends to the infraorbital foramen where it continues along the infraorbital margin. Laterally, the orbital orbicularis portion courses over the zygoma and cheek and over the temporal fascia.
The preseptal portion of the orbicularis oculi muscle overlies the orbital septum and functions in voluntary eyelid closure (winking) and involuntary eyelid closure (blinking). The action of the superior preseptal orbicularis muscle can also force the eyelid margin below the level of its canthal attachments as seen in looking down.14 The preseptal portion has a superficial origin from the anterior limb of the MCT and a deep origin, called the Jones muscle, which arises from the posterior lacrimal crest and the fascia surrounding the lacrimal crest.8 The orbital segment interdigitates with the preseptal orbicularis muscle and courses laterally across the upper and lower eyelids. The two segments fuse to form the lateral horizontal raphe, which overlies the lateral canthal tendon (LCT) and the lateral orbital rim.
The pretarsal portion of the orbicularis muscle is primarily responsible for horizontal movement of the eyelid, which is important in the function of the lacrimal pump. It also assists in eyelid closure mainly during involuntary blinking. The lower one third of the pretarsal muscle in the upper eyelid is adherent to the underlying tarsus, whereas the upper two thirds of the muscle is adherent to the superficial insertion of levator aponeurosis at the superior tarsal border.14 There are two medial insertions of the pretarsal portion of the orbicularis muscle. The superficial head condenses to form the anterior limb of the MCT and inserts into the anterior lacrimal crest. The deep head, called the tensor tarsi muscle of Horner, shares the same site of origin as the preseptal muscle. It inserts on fascia covering the lacrimal sac fossa and on the periosteum of the posterior lacrimal crest. Here, it is identified as the posterior limb of the MCT15 (Fig. 9). Contraction of the Horner's muscle draws the eyelids (especially the lower) medially and posteriorly. The resulting lateral pull on the lacrimal diaphragm creates a negative pressure in the lacrimal sac and draws the tears from the canaliculi into the sac. The deep and superficial heads of the pretarsal orbicularis oculi muscle encircle both lacrimal canaliculi and along with the Jones muscle facilitate tear drainage. Contraction shortens the ampullae of the canaliculi system and facilitates the movement of tears into the sac. The lacrimal drainage system is described in further detail later in the chapter. Laterally, the upper and lower pretarsal muscles fuse to form the LCT and insert 3 to 4 mm deep to the lateral palpebral raphe onto the lateral orbital tubercle. The deep medial and lateral attachments of the pretarsal orbicularis oculi muscle are important in maintaining eyelid to globe apposition.
The orbital septum is a thin, fibrous, multilayered sheath that arises from the anterior periorbita (periosteal lining of the orbit) at the arcus marginalis (Fig. 10). The orbital septum separates the eyelids from the orbit and serves as an important anatomic barrier to infection, hemorrhage, and edema. Inflammatory or infectious processes anterior to the septum are considered preseptal, whereas similar findings posterior to the orbital septum are considered orbital. In older individuals, the septum can become tenuous. Orbital or preaponeurotic fat is an important anatomic landmark and herniation of orbital fat through the septum from trauma or surgery indicates a disruption of the orbital septum.
From the arcus marginalis, the septum spans the anterior orbit in a plane deep to the orbicularis oculi muscle and ultimately fuses with the eyelid retractors or tarsus (Fig. 11). In the upper eyelid, the orbital septum adjoins the posterior epimysium of the orbicularis before it fuses with the levator aponeurosis approximately 2 to 3 mm above the superior tarsal border and about 10 mm above the lash line.16 In the lower eyelid, the septum arises from the inferior orbital rim as a condensation of the periorbita and periosteum. It continues anteriorly until it joins with the lower eyelid retractors as a single unit at a point 4 to 5 mm below the inferior tarsus or it inserts on the lower border of the tarsus. The septum travels medially with the pretarsal orbicularis muscle and attaches to the posterior lacrimal crest with a few fibers extending to the anterior lacrimal crest. Laterally, the septum attaches to the deep insertion of the pretarsal segment of the orbicularis muscle and inserts onto the lateral orbital tubercle.17
In the Asian eyelids, the eyelid creases vary in position in relation to the eyelid margin and may be lower than the occidental eyelid, or they may be absent altogether. In the upper eyelid, the orbital septum may fuse with the aponeurosis as is inserts into the tarsus. This insertion can occur as high as the superior border of the tarsus or as low as the lash line accounting for the lower or absent upper eyelid crease.3 There are also differences in the Asian lower eyelids. Epiblepharon is a common finding in the Asian lower eyelid and is seen as an additional fold of skin running horizontally below the lower eyelid margin. It is often associated with a loss of the eyelid crease or with a crease that rests very close to the eyelid margin of the lower eyelid. The absence of an eyelid crease may be due to lack of deep anchoring of the superficial skin to the preseptal portion of the orbicularis oculi muscle.18 An overriding orbicularis muscle is also associated with epiblepharon. The weight of the skin fold and the orbicularis muscle may rotate the lower eyelid margin inward, creating an entropion.
Fat within the orbit and eyelids serves as a protective cushion for the globe and facilitates movement of the globe. There are three general locations of fat that are described: eyelid, sub-brow, and orbital. In the upper eyelid, there are two fat pads, medial and central (preaponeurotic) (Fig. 12). The central preaponeurotic fat is divided by the trochlea of the superior oblique tendon and fascial strands of the medial retinaculum. These divisions are arbitrary and the fascial planes can be variable, because eyelid fat is interconnected and contiguous with deeper orbital fat. The preaponeurotic fat pad is an important surgical landmark, because it lies just posterior to the orbital septum and anterior to the levator aponeurosis (Fig. 13). The central preaponeurotic fat pad tends to be yellow as compared with the whiter more fibrous medial fat pad. The medial fat pad is derived from orbital fat deep to the levator muscle. It is more vascular because of the location of the palpebral arterial arcade that serpiginously courses through the medial fat pad.19,20 The lacrimal gland occupies the temporal space lateral to the central preaponeurotic fat pad. The lacrimal gland is a firm, pink, vascular, lobulated structure that produces the aqueous component of the precorneal tear film. (The anatomy and function of the lacrimal gland is described later in the chapter.) Care must be taken to avoid excision of the lacrimal gland while liposculpturing during blepharoplasty. Fine connective tissue septa extend anteriorly from the capsule of preaponeurotic fat to the orbital septum and posteriorly to the levator aponeurosis.17 The postaponeurotic or pretarsal space, located between the levator aponeurosis anteriorly and the tarsus posteriorly, may contain a small amount of peripheral orbital fat. The fibrous septa compartmentalizing superficial and deep orbital fat and extensions of the fascial sheaths of the orbital muscles and eyelid structures are of great importance to the movement of the upper eyelid.
Sub-brow fat can form a redundant upper eyelid skin fold and undergoes gravitational descent during aging (Fig. 14). In females, the eyebrow is generally arched and above the level of the supraorbital rim. The male eyebrow is flatter and at the level of the supraorbital rim. The eyebrow fat pad is more prominent in the male, producing a fuller appearance in the lateral brow area. The position of the eyebrow can affect the height and excursion of the upper eyelid and must be considered in a patient being evaluated for blepharoptosis or for blepharoplasty. The retro-orbicularis oculus fat (ROOF) is defined as the layer of fibrofatty tissue deep to the orbicularis oculus muscle, superficial to the orbital septum and orbital rim, and extending medially from the superior orbital nerve and laterally over the lateral upper orbit.21 Resection of the ROOF in conjunction with aesthetic blepharoplasty can soften and flatten heaviness and bulkiness in the lateral upper orbital and brow region. A direct or indirect browplasty or browpexy may be an alternative treatment for patients with brow ptosis.22 One must discern patients with eyebrow ptosis from those with eyelid ptosis caused by levator muscle or Muller's muscle dysfunction.
Some surgeons consider the lower eyelid to have three fat pads.9,23 A medial fat pad is subdivided by the origin of the inferior oblique muscle. Temporally, a small fat pad lies inferior to the lateral canthus and is separated from the main fat pad by a fibrous extension of connective tissue from the orbital septum and periorbita that joins with the capsulopalpebral fascia (CPF) and Lockwood's ligament.24 Because the eyelid fat pads are in direct communication with the deep extraconal fat of the orbit, caution must be exercised when handling orbital fat in the anterior orbit. Traction on the fat pad may injure deep orbital vessels causing orbital hemorrhage and permanent loss of vision.19,25
The midfacial fat compartments include the suborbicularis oculi fat (SOOF) and malar fat pads. These fat compartments are bound to the orbicularis muscle by the superficial muscular aponeurotic system (SMAS) of the cheek. The SOOF is composed of the deep subcutaneous fat and connective tissue, which is located beneath the orbicularis muscle in the lower eyelid and extends into the midface. In the aging lower eyelid, eyelid tone decreases with associated skin and muscle laxity. Horizontal laxity of the lower eyelid increases, and pseudoherniation of orbital fat may result in contour irregularities. The SOOF can become apparent with the gravitational descent seen in the midface with aging and contributes to the aesthetic deformity of the lower lids. Malar bags may also develop from descent of the malar fat pad. A SOOF lift is a technique used for midfacial rejuvenation that includes subperiosteal dissection of the SMAS to elevate the SOOF and redraping the orbicularis muscle to reposition the midface.26 Recent emphasis has been placed on a SOOF lift for midfacial rejuvenation surgery in conjunction with a lower eyelid blepharoplasty and lateral canthoplasty.27 The SOOF lift has also been used for functional repair of lower eyelid deformities seen in patients with significant involutional or cicatricial ectropion.
Asian eyelids characteristically have a fuller appearance than the eyelids of Caucasian individuals. Upper eyelid fullness in the Asian person is typically caused by extension of preaponeurotic fat and brow fat into the upper eyelid. A recent study by Carter and colleagues28 used high-resolution magnetic resonance images to compare Asian and Caucasian lower eyelids. The study revealed two major differences in the lower eyelid anatomy: (1) there is more anterior projection of orbital fat with respect to the orbital rim in the Asian eyelid as compared with whites and (2) there is a more superior projection of orbital fat that extends to the inferior border of the tarsus with poorly defined eyelid creases in Asians.
The eyelid retractor muscles include the LPS muscle and the superior tarsal muscle, called Muller's muscle, in the upper eyelid and the CPF and the inferior tarsal muscle (ITM) in the lower eyelid (Fig. 15). The LPS is a skeletal muscle, whereas the ITM and Muller's muscle are both composed of smooth muscle. The action of the LPS is to elevate the upper eyelids. The oculomotor nerve (third cranial nerve) provides the motor innervation of the LPS. The superior division of the oculomotor nerve enters the orbit through the supraorbital fissure and the annulus of Zinn. It passes around the medial border of the superior rectus muscle to pierce the undersurface of the LPS at its posterior 1/3 anterior 2/3 junction, which is 12 to 13 mm from the orbital apex. Muller's muscle and the ITM are sympathetically innervated and also act to open the upper and lower eyelids.
In the upper eyelid, the LPS muscle begins to develop at about 10 weeks of fetal life.14 The LPS muscle arises from the lesser wing of the sphenoid bone at the orbital apex above the annulus of Zinn and superolateral to the optic foramen. The mesenchymal origin of both the levator and the superior rectus muscles is immediately below at the annulus of Zinn. The first 40 mm of the LPS is the muscular portion, and the remaining anteriorly projecting 14 to 20 mm becomes the levator aponeurosis.10 The levator muscle crosses over the superior transverse ligament of Whitnall (STL), which is a condensation of horizontally oriented connective tissue resting within the anterior aspect of the fibrous sheath surrounding the body of the levator muscle.29 Whitnall's ligament marks the junction where the LPS changes from a skeletal muscle to a fibrous sheath, the levator aponeurosis.
STL, composed of collagen and elastic fibers, is seen as a white line traversing horizontally across the eyelid, approximately 10 mm above the superior border of the tarsus (Fig. 16). The STL medially attaches to the trochlear fascia and superior oblique tendon and sends wisps of connective tissue to the medial retinaculum. It attaches laterally to the fascia surrounding the orbital portion of the lacrimal gland and at the frontozygomatic suture. The STL acts to suspend the levator complex and also serves as a fulcrum, adding a mechanical advantage to levator muscle action on the upper eyelid.3 Just posterior to Whitnall's ligament a dense intermuscular fascia interconnects the undersurface of the levator aponeurosis and the superior surface of the superior rectus muscle. A superior conjunctival fornix suspensory ligament arises from the anterior surface of this intermuscular membrane.30,31 The superior rectus muscle and the levator muscle are also joined by fibrous attachments along their medial borders.
The horns of the levator aponeurosis are broad fibrous condensations in the lateral and medial edges and should be distinguished from the STL. The lateral and medial horns of the levator aponeurosis and its osseous insertions are located inferior to the STL. The lateral horn has more strength and is more tendinous than the less dense medial horn. Laterally, it courses through the lacrimal gland, dividing the gland into the palpebral and orbital lobes. The lateral horn continues inferiorly to join the lateral retinaculum and together they form a strong insertion into the lateral orbital tubercle. The medial horn of the levator aponeurosis passes over the superior oblique tendon where it has weak attachments from the STL. The medial horn continues medially to join the medial retinaculum to reach the MCT and posterior lacrimal crest. The weaker attachments medially are thought to allow a greater mobility of the medial upper eyelid.32 The lateral and medial posterior attachments are important in eyelid to globe apposition.
The levator aponeurosis continues anteriorly until it joins with fibers of the orbital septum about 2 to 3 mm above the tarsal border. The orbital septum fuses with the aponeurosis at or just above the eyelid crease. At this point, additional fibers interdigitate with the orbicularis oculi muscle. The eyelid crease may vary but is typically located near the superior edge of the tarsal border at about 8 to 10 mm above the eyelid margin.29 The actual eyelid crease is formed from the attachment of the levator aponeurosis to the preseptal orbicularis muscle and subcutaneous tissue. The levator aponeurosis sends connective tissue attachments to insert on the lower one third of the anterior surface of the tarsus with its strongest attachments 3 mm above the eyelid margin.33,34,35 These tarsal attachments are crucial for upper eyelid function.
Attenuation of the levator muscle and dehiscence of its attachments may demonstrate aging changes of the upper eyelid. This can result in elevation of the eyelid crease as seen in involutional blepharoptosis.3 Congenital and acquired ptosis is a drooping of the upper eyelid usually caused by poor elevating power of the upper eyelid. Congenital ptosis is typically characterized by lagophthalmos and an absence of an eyelid crease resulting from fibrofatty degeneration and poor function of the LPS. There are several classifications of ptosis. (See Volume 5, Chapter 78.)
Muller's muscle, also known as the superior tarsal muscle, is the other retractor muscle of the upper eyelid (Fig. 17). It is a smooth, sympathetically innervated muscle that acts in concert with the levator muscle to elevate the upper lid. Sympathetic innervation is derived from nerve fibers, which travel along the peripheral arterial arcade and other small arteries.29 Muller's muscle is highly vascularized and is often a source of bleeding in surgery. It originates from the underside of the levator muscle approximately 20 to 22 mm above the superior tarsal border at the origin of the aponeurosis.24 High in the eyelid, Muller's muscle is loosely attached to the aponeurosis anteriorly and to the conjunctiva posteriorly. It is more adherent posteriorly to the conjunctiva as is nears the upper boarder of the tarsus. The superior tarsal muscle inserts into the upper border of the tarsal plate. Clinically, increased sympathetic stimulation as seen in fright or Grave's ophthalmopathy can retract the upper lid 2 to 3 mm above the normal resting position. Diminished tone as seen in fatigue, paralysis, or Horner's syndrome may cause the lid to drop as much as 2 mm. Topical administration of a short-term sympathomimetic agent (i.e., phenylephrine) can be used to determine preoperatively the effect of tarsal muscle surgery on ptosis.36,37 A positive result following topical administration of phenylephrine is elevation the upper eyelid 2 to 3 mm, which suggests that Muller's muscle resection may be beneficial. (See Volume 5, Chapter 78.)
The retractor muscles of the lower eyelids include the inferior tarsal muscle and the CPF. The CPF arises from the inferior rectus muscle sheath just posterior to the inferior oblique muscle (Fig. 18). The CPF is analogous to the levator aponeurosis of the upper eyelid, and they are also embryologically related.3 The CPF has no distinct innervation, but its action mirrors the action of the inferior rectus muscle, which is innervated by sympathetic postganglionic fibers running with the inferior branch of the oculomotor nerve. The ITM lies posterior to the CPF and arises from the CPF extending from the sheath of the inferior rectus muscle. The ITM is adherent to the overlying CPF and to the underlying conjunctiva38 (Fig. 19). The ITM is analogous to the Muller's muscle of the upper eyelid as a retractor muscle for the eyelids, and it is also sympathetically innervated. In Horner's syndrome, the atonic sympathetic ITM may allow the lower lid to elevate as much as 1 mm. The fascial sheaths of the CPF and the ITM divide and surround the inferior oblique muscle and reunite before inserting into the anterior aspect of the inferior tarsus.
Anterior to the inferior oblique muscle, the two portions of the capsulopalpebral head join to form Lockwood's suspensory ligament. Lockwood's ligament acts as a suspensory hammock for the globe.9 It is composed of intramuscular septa and check ligaments, thickened Tenon's capsule, and fibers from the inferior rectus sheath and lower eyelid retractors. Its attachments are to the medial orbital wall posterior to the posterior lacrimal crest, to the medial retinaculum, and at the lateral orbital tubercle through the lateral retinaculum. Anterior projections from Lockwood's ligament send strands into the conjunctival fornix, forming the suspensory ligament of the fornix. The fibers of the CPF and the ITM fuse with the orbital septum 4 to 5 mm below the inferior tarsus and insert as a single layer onto the inferior border of the inferior tarsus.35,39 The lower eyelid opens passively by traction from the inferior rectus muscle through the CPF.9
Excursion from full depression of the upper eyelid to full elevation is about 15 to 20 mm, which is primarily the action of the LPS. Muller's muscle is responsible for approximately 2 mm of upper eyelid elevation. The muscles of the forehead and brow also play a role in assessing the elevating power of the eyelid. The primary muscle of the forehead is the frontalis muscle innervated by the seventh cranial nerve. It is a muscle of facial expression, whose primary action is elevation of the forehead and brow. Other muscles of the forehead play a role in eyebrow function. The corrugator muscle draws the head of the eyebrows to the nose. It is responsible for vertical furrows on the bridge of the nose.10 Depression of the head of the eyebrow is a result of contraction of the procerus muscle, which can result in horizontal furrows in the skin of the glabellar region of the forehead overlying the bridge of the nose. In examination of patients for ptosis, it is important to distinguish recruitment of the forehead muscles to elevate the eyelids and the eyebrows from the use of eyelid retractor muscles. The forehead should be in a completely relaxed position toaccurately measure the severity of blepharoptosis. (See Volume 5, Chapter 78.)
The tarsal plate is part of the posterior lamellae of the eyelid and provides the structural framework of the eyelid. It is composed of condensed fibrous and elastic tissue but contains no cartilage (Fig. 20). It extends along the entire length of the upper and lower eyelids measuring approximately 25 mm horizontally and 1 mm in width. It extends horizontally in a convex curve tapering medially and laterally. The superior tarsal plate is approximately 9 to 10 mm in vertical height at its highest point just medial to the pupil.14 The inferior tarsal plate of the lower eyelid measures 4 to 5 mm in central vertical height and tapers medially and laterally in a convex curve.40 Both upper and lower tarsal plates are anchored to the orbital bones by their connections to the medial and LCTs. On the anterior superior tarsal surface are the attachments of the septum and retractor muscles. The upper tarsus contains approximately 30 meibomian glands, and the lower tarsus contains approximately 20. The oil-secreting glands are aligned vertically, and their orifices are seen at the eyelid margin just posterior to the gray line and anterior to the mucocutaneous junction. The posterior surface of both tarsal plates is covered by conjunctiva. Only 4 to 5 mm of tarsus is needed for upper eyelid stability, when the tarsus is used in eyelid reconstruction. Aging changes in the tarsus and surrounding eyelid structures, including atrophy of the tarsus, laxity of its medial and lateral attachments, and decreased orbicularis tone, contribute to the loss of horizontal structural stability in the eyelid.41 In addition, weakness of elastin fibers in the tarsus has been found in patients with floppy eyelid syndrome. These patients demonstrate significant horizontal eyelid laxity.
The conjunctiva is composed of nonkeratinizing stratified squamous epithelium and forms the posterior layer of the eyelids. It is a transparent mucous membrane lining the eye socket from the eyelid margin to the corneal scleral limbus. The bulbar conjunctiva loosely attaches to the globe, whereas the palpebral conjunctiva adheres tightly to the eyelids. The conjunctiva contains mucous-secreting goblet cells and aqueous-producing glands of Krause and Wolfring. The glands of Krause and Wolfring are accessory lacrimal glands and are histologically identical to the structure of the main lacrimal gland. These glands are mainly localized in the subconjunctival tissue in the upper eyelid between the superior tarsal border and the fornix. Few glands are found in the lower eyelid at the inferior fornix. Mucin-secreting goblet cells are scattered throughout the conjunctiva and are concentrated in the crypts of Henle just above the tarsal border. Mucin is an essential component of the basic secretion of the tear film. Medially, the conjunctiva forms the semilunar fold, a vestige of the nictitating membrane of some animals. A small, fleshy body of transitional tissue, called the caruncle, lies at the medial commissure and contains multiple sebaceous glands and hair follicles.9
LATERAL CANTHAL TENDON
The LCT, often called the lateral canthal ligament, is a broad band of dense fibrous connective tissue, which serves as the upper and lower crus of the lateral border of the upper and lower tarsus3 (Fig. 21). The true anatomic origin of the LCT remains controversial. The LCT fuses at the lateral border of the tarsal plates to join with the lateral retinaculum, a sheath of connective tissue, which is a condensation of several structures that insert onto the lateral orbital tubercle of Whitnall. The lateral retinaculum consists of fibers from the LCT, the lateral horn of the levator aponeurosis, the inferior suspensory ligament of Lockwood, the STL (of Whitnall), the check ligament of the lateral rectus muscle (before its insertion 1.5 mm posterior to the lateral orbital rim onto the lateral orbital tubercle of Whitnall), and deep fibers of the pretarsal orbicularis muscle. The lateral orbital tubercle of Whitnall is located 2 to 4 mm posterior to the lateral orbital rim at the level of the lateral commissure. In a space between the anteriorly placed orbital septum and the lateral retinaculum is sometimes found a small fat pad, called Eisler's pocket.36 The insertion of the LCT is approximately 3 mm superior to the MCT insertion. This gives a slightly upward slope of the eyelids from medial to lateral. The connection of the check ligament of the lateral rectus muscle with LCT plays another important role in mobility of the lateral canthal angle on far lateral gaze. Gioia and colleagues42 were the first to describe that on far lateral gaze, the lateral canthal angle is displaced 2 mm laterally, which in part increases the peripheral visual field.
The LCT functions to fixate the lateral canthal angle and upper and lower tarsus to the lateral orbital tubercle. This enables the eyelids to be properly opposed to the globe laterally. LCT dehiscence or laxity is a common involutional change that appears as a rounding of the lateral canthal angle or as lower eyelid laxity. Severing the inferior crus of the LCT as performed in a lateral canthotomy or cantholysis provides an access to the orbit in decompression or reconstruction. A lateral canthoplasty is a commonly used procedure to reestablish lower eyelid stability and support of the globe. The periosteum overlying the lateral orbital tubercle is an excellent surgical anchor for lateral canthal angle fixation in surgery.
MEDIAL CANTHAL TENDON
The MCT or ligament provides eyelid support and aids in the proper functioning of the lacrimal pump.43 The MCT has two components: the anterior limb and a posterior limb (Fig. 22). The anterior limb is a broad fibrous structure attaching the eyelids to the frontal process of the maxillary bone and to the anterior lacrimal crest. It is the origin of the superficial head of the pretarsal and preseptal orbicularis muscles. The posterior limb of the medial canthal ligament inserts on the posterior lacrimal crest and the lacrimal fossa. The posterior limb and deep heads of the pretarsal and preseptal orbicularis muscles draw the medial portion of the eyelids posteriorly for good apposition of the eyelids to the globe.16
The lacrimal system has a dual function: a secretory component contributing to the formation of tears and an excretory component that provides a conduit though which tears drain from the eye into the nose9 (Fig. 23). Three types of glands comprise the basic secretors that produce the tear film (Fig. 24). The first group consists of conjunctival tarsal and limbal mucin-secreting goblet cells, which produce the inner mucoprotein layer of the tear film. The second group consists of the main lacrimal gland and accessory lacrimal exocrine glands of Kraus and Wolfring in the subconjunctival tissues. These glands produce the middle aqueous layer of the tear film. The third group is the oil-producing meibomian glands in the tarsus and the palpebral glands of Zeiss and Moll. These produce the superficial lipid layer, which is essential in slowing evaporation and stabilizing the tear film.44
The main lacrimal gland is an almond shaped structure located in the superior temporal bony orbit. The main lacrimal gland secretion contributes to the aqueous layer of the tear film. It contains the reflex secretors, and the tears it produces are mainly triggered by peripheral sensory or emotional stimuli. The lacrimal gland is surrounded by fibrous tissue that is superiorly attached to the periosteum of the frontal bone and inferiorly to the orbital portion of the zygomatic bone. The lateral horn of the levator aponeurosis divides the lacrimal gland into a larger superior orbital lobe and a smaller inferior palpebral lobe. The orbital lobe comprises 70% of the gland measuring approximately 20 mm × 5 mm × 12 mm.3 The palpebral lobe represents approximately 30% of the gland and lies in the subaponeurotic space. It extends anteriorly beyond the orbital rim and is the visible portion through the conjunctiva (Fig. 25). The lacrimal gland has approximately 12 secretory ducts, 2 to 5 originate in the orbital lobe, and 6 to 8 are from the palpebral lobe.45 The ductules from the orbital portion pass through the palpebral lobe before exiting into the superotemporal portion of the conjunctival fornix.
The accessory lacrimal exocrine glands of Wolfring and Krause structurally are similar to but much smaller than the main lacrimal gland. They mainly are located in the superior conjunctival fornix and above the tarsus, and fewer lie in the inferior conjunctival fornix. These are called the basal secretors because they lack direct secretory motor fibers. Other basal secretors include sebaceous glands (meibomian and Zeis) and mucous glands (goblet cells). The accessory lacrimal glands provide the tears for daily corneal hydration and secrete the aqueous layer of the tear film.
Drainage of tears begins with the lacrimal puncta located medially on upper and lower eyelid margins. The punctal orifice is directed posteriorly towards the lacrimal lake where it accepts the tears. Lacrimal papillae are seen as a fibrous ring on the eyelid margin surface surrounding the lacrimal puncta. The puncta is the opening to the lacrimal drainage system and empties into the ampulla. The ampulla is oriented 1 to 2 mm vertically and is surrounded by a portion of the pretarsal orbicularis muscle and opens into the canaliculus. The canaliculus is a horizontal structure, which is directed between the plica semilunaris and the caruncle. The canaliculi are surrounded by thick pretarsal orbicularis oculi muscle fibers. The upper canaliculus in the upper eyelid is approximately 8 mm long, and the lower canaliculus is approximately 10 mm long in the lower eyelid.
The blinking action of the muscles of the eyelid helps direct tears medially toward the puncta46 (Fig. 26). Capillary attraction allows tears to enter the punctum into the ampulla and canaliculus. On eyelid closure, the ampulla collapses, while the canaliculus shortens. The action of the lacrimal pump is then to draw tears through the canaliculi into the lacrimal sac, which is approximately 10 mm long. Gravity forces fluid through the elastic nasolacrimal duct, measuring approximately 12 mm, into an opening or ostium at the inferior meatus of the nose and into the nasopharynx.
Valve-like folds of epithelium line the nasolacrimal duct preventing the retrograde flow of tears and air. The valve of Rosenmüller is located at the junction of the common canaliculus as it enters the nasolacrimal sac. This fold prevents reflux of tears back into the sac from the canaliculi. An incompetent valve may allow reflux of purulent material from the sac into the eye in nasal lacrimal duct obstruction. The valve of Hasner is located on the distal end of the duct. This is often imperforate at birth in neonates and is a major cause of epiphora in infants. It usually undergoes perforation within 6 months after birth spontaneously or after manual massage of the sac.
A network of vessels derived from two major sources, the internal and the external carotid arteries, richly vascularizes the eyelids (Fig. 27). The internal carotid artery supplies the deep or intraorbital vascular system including the ophthalmic artery, whose terminal branches primarily supply the upper eyelid. The external carotid artery supplies the superficial arterial system namely facial and angular arteries, which principally supply the lower eyelid. Collateralization between the internal and external systems contributes to the rapid wound healing and the low incidence of infection following eyelid surgery. As the vessels approach the eyelids, branches of the ophthalmic artery from the internal carotid artery and branches of the lacrimal arteries off of the maxillary branch of the external carotid artery form the marginal and peripheral vascular arcades of the eyelids.
At the orbital apex, the ophthalmic artery, a branch of the internal carotid artery, enters the orbit through the optic canal lateral to the optic nerve (Fig. 28). As the ophthalmic artery passes over the optic nerve and continues supermedially within the orbit, four terminal branches pierce the orbital septum to supply the upper eyelid. The four branches include the lacrimal artery, the supraorbital artery, the supratrochlear (frontal) artery, and the dorsal nasal artery.47,48 The lacrimal artery runs temporally along the upper border of the lateral rectus muscle along with the lacrimal nerve and terminates as the lateral palpebral artery. This is the blood supply to the lacrimal gland, the conjunctiva and the lateral aspect of the upper eyelids. The supraorbital artery branches off the ophthalmic artery as it courses over the optic nerve and travels forward between the levator muscle and the periorbita of the roof. It accompanies the supraorbital nerve through the supraorbital foramen to supply the upper eyelid, scalp, forehead, levator muscle, periorbita, and diploë of the frontal bone.3 The supratrochlear (frontal) artery accompanies the supratrochlear nerve to supply the skin of the superior medial aspect of the orbit, the forehead, and scalp. The ophthalmic artery pierces the orbital septum dorsonasally to become the dorsal nasal artery. This supplies the skin of the bridge of the nose and the lacrimal sac, terminating as the medial palpebral artery. The medial palpebral artery and the lateral palpebral artery anastomose to form the vascular arcades of the upper eyelids. The marginal palpebral arcade lies on the anterior tarsal surface 2 to 3 mm from the eyelid margin. The peripheral palpebral arcade courses above and parallel to the superior border of the tarsus, between the levator aponeurosis and Muller's muscle in the upper eyelid. Medially, the arcades run a tortuous course throughout the medial fat pad. The medial fat pad is often a site of bleeding during blepharoplasty.20 The deep peripheral palpebral arcade anastomoses with the anterior ciliary arteries near the corneal scleral limbus and supplies the superior conjunctival fornix.3
In the lower eyelid, a marginal arcade arises from the medial and lateral palpebral branches running horizontally approximately 3 mm inferior to the lower eyelid margin and anterior to the lower eyelid tarsus.35 The lower eyelid does not have a peripheral arcade like the upper eyelid. Lateral anastomoses from the zygomatico-orbital branch of the superficial temporal artery also feed into these branches.
SUPERFICIAL BLOOD SUPPLY
From the external carotid artery, three branches of the facial vascular system ultimately supply the eyelid: the facial artery, the superficial temporal artery, and the infraorbital artery (Fig. 29). The facial artery crosses the mandible anterior to the masseter muscle, coursing diagonally to the nasolabial fold. Within the orbicularis muscle it travels as the angular artery 6 to 8 mm medial to the medial canthus and 5 mm anterior to the lacrimal sac. The angular artery perforates the orbital septum above the medial canthal ligament to anastomose with the dorsal nasal branch of the ophthalmic artery. The superficial temporal artery is a terminal branch of the external carotid artery. It arises from within the parotid gland and ascends superiorly in the preauricular region to cross the zygomatic process of the temporal bone, approximately 1 cm anterior to the tragus. The superficial temporal artery gives off three branches to supply the eyelids: the frontal branch, zygomatico-orbital branch, and the transverse facial branch.20 The frontal branch courses upward across the temple to the frontalis muscle and the orbicularis oculi muscle anastomosing with the lacrimal and supraorbital arteries. The zygomatico-orbital branch travels along the upper border of the zygoma and supplies the upper eyelid and anterior orbit. The transverse facial branch courses below the zygoma to supply the malar region and the lower lateral eyelid and anastomoses with the lacrimal and infraorbital arteries. The infraorbital artery is a branch of the internal maxillary artery and enters the orbit from the pterygopalatine fossa, passing through the posterior end of the infraorbital fissure through the infraorbital canal. It exits the orbit through the infraorbital foramen to supply the lower eyelid.
The venous drainage system of the eyelids is through the tributaries of the ophthalmic vein and superficially through the angular and superficial temporal veins12 (Fig. 30). The junction of the superficial frontal vein and the supraorbital vein from the orbit forms the angular vein. The angular vein has a dual drainage: posteriorly into the deep venous system by the superior ophthalmic vein and superficially and inferiorly into the anterior facial vein. The angular vein then empties into the common facial vein, which empties into the internal jugular vein. Superiorly and laterally, venous blood from the forehead, eyebrow, and eyelid drain from the supraorbital vein into the superficial temporal vein to drain into the external jugular vein.24 Anteriorly, the angular vein anastomoses with the orbital venous system.
The deep venous system draining the forehead, eyebrow, and upper eyelid is via the supraorbital vein coursing into the frontal vein and into the superior ophthalmic vein. The union of the angular and supraorbital veins forms the superior ophthalmic vein at the supranasal aspect of the orbit. The superior ophthalmic vein is formed at the supranasal orbit by union of the supraorbital and angular veins. It is in close proximity to the ophthalmic artery as it travels posterolaterally in the orbit. The superior ophthalmic vein penetrates the muscle cone and receives drainage from the superior vortex veins of the globe. The superior ophthalmic vein also receives drainage from the ethmoidal, lacrimal, central retinal, and ciliary veins. It is joined at the orbital apex by the inferior ophthalmic vein. It leaves the orbit through the superior orbital fissure and enters the cavernous sinus. The inferior ophthalmic vein is part of a venous plexus at the anterior orbital floor that is a tributary for the lower eyelid, lacrimal sac, inferior rectus muscle, inferior oblique, and two inferior vortex veins. At the orbital apex, one branch of the inferior orbital vein feeds into the superior ophthalmic vein and enters the cavernous sinus and another branch drains through the inferior orbital fissure to the pterygoid plexus.
The lymphatic system of the eyelids is divided into a superficial and a deep system. The superficial system drains skin and orbicularis, whereas the deep system drains the tarsi and the conjunctiva.49 The upper eyelid, lateral ½ of the lower eyelid, and the lateral canthus empty into the preauricular and deep parotid nodes. The skin and orbicularis oculi muscles drain into the deep cervical nodes near the internal jugular vein. The medial portion of the upper and lower eyelids, the medial canthus, and the conjunctiva drain into the submandibular nodes. Lymphadenopathy may correlate to inflammation or infection of the affected anatomic eyelid structure.
Three of the 12 cranial nerves essentially supply the eyelids: the oculomotor nerve (CN-3), the trigeminal (CN-5), and the facial nerve (CN-7). The eyelids also receive sympathetic innervation.
CN-3: The oculomotor nerve provides motor innervation to several extraocular muscles and the upper eyelids. The oculomotor nerve originates from the midbrain and passes into the interpeduncular fossa to enter the middle cranial fossa piercing the dura and enters the lateral wall of the cavernous sinus. As it travels along the lateral wall of the cavernous sinus, it divides into the superior and inferior divisions before entering the orbit through the superior orbital fissure into the annulus of Zinn.3,7 The superior division courses 1 mm anterior to the annulus of Zinn and innervates the superior rectus muscle. The nerve courses medially where it innervates the LPS. The inferior division courses beneath the optic nerve branching to innervate the medial rectus, inferior rectus, and inferior oblique muscles. Parasympathetic fibers run with the oculomotor nerve and synapse in the ciliary ganglion.
CN-5: The trigeminal nerve divides into the ophthalmic, maxillary, and mandibular branches and is the major sensory nerve of the eyelids and face (Fig. 31). It arises from the pons from the sensory, motor, and mesencephalic roots. These roots meet at the gasserian ganglion at the petrous bone. The first two branches continue in a path to provide sensory supply to the eyelids, coursing through the middle cranial fossa and piercing the dura to enter the lateral wall of the cavernous sinus. The first ophthalmic division enters the orbit through the supraorbital foramen where it subdivides into the lacrimal, frontal, and nasociliary nerves.
The lacrimal nerve enters the orbit above the annulus of Zinn and gives sensory innervation to the lacrimal gland, the lateral aspect of the eyelid, and the forehead. A superior branch sends sensory fibers to the lacrimal gland and skin as the lateral palpebral nerve. An inferior branch of the lacrimal nerve innervates the lacrimal gland and anastomoses with the fibers from the zygomaticotemporal branch of the maxillary division of V2, which carries parasympathetic secretory fibers to the lacrimal gland from CN-7. The frontal nerve enters the orbit outside the annulus of Zinn and courses anteriorly to branch into the supraorbital and supratrochlear nerves (Fig. 32). The supraorbital nerve leaves the orbit through the supraorbital foramen or supraorbital notch and innervates the skin of the upper eyelid, forehead, and scalp. The supratrochlear nerve passes above the trochlea and pierces the septum at the superonasal aspect of the orbit giving sensory innervation to the medial commissure, the skin of the root of the nose, the middle forehead, and the lacrimal drainage structures. It also sends a branch to an infratrochlear twig of the nasociliary nerve.50
The nasociliary nerve enters the orbit laterally within the annulus of Zinn, courses over the optic nerve along the medial orbit and gives off several branches. Branches of the nasociliary nerve include: (1) long sensory root of the ciliary ganglion; (2) long ciliary nerves to supply the iris, ciliary body, and cornea; (3) infratrochlear nerve supplying the medial canthus, conjunctiva, lacrimal sac, canaliculus, and caruncle; and (4) posterior ethmoidal nerve supplying the ethmoidal air cells and sphenoid sinus.49 Patients with herpes zoster ophthalmicus who have skin lesions along a V1 dermatome and a lesion on the tip of the nose with associated kerato-uveitis (Hutchison's sign) typically have nasociliary nerve (branch of V1) involvement (Fig. 33).
The maxillary nerve branch or V2 division proceeds from the gasserian ganglion to enter the inferior cavernous sinus. It leaves the middle cranial fossa from the foramen rotundum and crosses the pterygopalatine fossa. It then enters the orbit through the inferior orbital fissure where it becomes the infraorbital nerve branch. The infraorbital nerve passes through the infraorbital canal and exits through the infraorbital foramen 4 to 8 mm below the infraorbital rim (Fig. 34). It supplies the skin and conjunctiva of the lower eyelid, the medial and lateral canthi, the ala of the nose, and the superior lip.3,7 This nerve is often involved in orbital floor fractures, resulting in paraesthesia of the cheek, lip, teeth, and gums. The maxillary nerve branches into the zygomatic nerve before it enters into the infraorbital canal. The zygomatic nerve divides into the zygomaticotemporal nerve, which communicates with the lacrimal nerve and the zygomaticofacial nerve, giving sensation to the cheek. The third branch of CN-5 or mandibular division is the motor supply for the muscles of mastication, with additional sensory fibers giving sensation to the jaw and lower lip.
CN-7: The facial nerve supplies most of the muscles of facial expression and motor function of the eyelids. It has both motor and parasympathetic secretomotor elements. The facial nerve arises from the brain stem ventrally at the pons-medullary junction near the cerebellum. The nerve enters the temporal bone at the internal auditory meatus along with the sensory intermedius nerve and the acoustic nerve (CN-8). As the fibers reach the geniculate ganglion, they branch into motor fibers or parasympathetic secretomotor fibers. The motor fibers exit the facial canal of the temporal bone through the stylomastoid foramen and pass anteriorly through the parotid gland. The nerve divides into five branches within the gland: temporal, zygomatic, buccal, mandibular, and cervical. These branches serve as the muscles of facial expression. The temporal, zygomatic, and buccal divisions supply the orbicularis oculi, the procerus, and corrugator muscles.9
PARASYMPATHETIC NERVE SUPPLY
The facial nerve also contains a parasympathetic secretomotor component. The parasympathetic secretomotor fibers pass through the geniculate ganglion as preganglionic parasympathetic sensory fibers and course into the middle cranial fossa as the great superficial petrosal nerve. These fibers join with the great deep petrosal sympathetic nerve to form the vidian nerve. Fibers then synapse at the pterygopalatine or sphenopalatine ganglion. Postganglionic parasympathetic fibers travel along with the zygomaticotemporal and lacrimal branches of CN-5 to supply parasympathetic secretory function to the lacrimal gland. Parasympathetic fibers that control pupillary constriction and accommodation of the eye run with the oculomotor nerve in the middle cranial fossa, cavernous sinus, and superior orbital fissure to enter the orbit. They branch off the nerve to the inferior oblique muscle and synapse in the ciliary ganglion to supply the constrictor pupillae and ciliary muscles of the eye.
SYMPATHETIC NERVE SUPPLY
Sympathetic nerves to the orbit provide vasoconstriction, smooth muscle function, pupillary dilation, hidrosis, eyelid retraction, and pilomotor and sweat gland function of the skin and face. The sympathetic pathway begins in the hypothalamus and descends the brain stem as uncrossed fibers through the pons and mesencephalon. The fibers come together in the lateral medulla oblongata traveling as first-order neurons to terminate in the intermediolateral cell column at the level of the eighth cervical to second thoracic vertebrae of the spinal cord. The fibers exit the spinal cord and enter the cervical sympathetic chain at the superior portion of the stellate ganglion as second-order neurons. They ascend the chain and synapse in the superior cervical ganglion. Postganglionic, or third-order neuron fibers travel with the internal carotid artery to form a sympathetic nerve plexus surrounding the intracavernous carotid artery, then branch at the orbital apex. The branches supplying the pupil are thought to enter the orbit through the superior orbital fissure traveling along the ophthalmic branch of CN-5.10 Nerve fibers course along the nasociliary nerve, pass through the ciliary body, pass through the long ciliary nerves, and terminate in the dilator muscles of the iris. Sympathetic innervation to the superior and inferior tarsal muscles of the eyelids remains controversial.51,52 The branches of the ophthalmic artery and nerves in the orbit are thought to carry sympathetic fibers.7 In the eyelids, it is thought that sympathetic fibers travel along the peripheral arcades to supply the superior and inferior tarsal muscles. Interruption of the sympathetic nerve fibers anywhere along the sympathetic chain may result in Horner's syndrome with ptosis, anhidrosis, miosis, vascular dilation, and heterochromia. (See Chapter 78.)
A thorough understanding of embryology, anatomy, and function of the structures of the eyelid is integral in the management of eyelid disorders. The eyelids can be subject to a variety of conditions including congenital, infectious, inflammatory, neoplastic, traumatic, degenerative, and involutional. Knowledge of anatomy will enable the surgeon to make informed decisions in surgical planning and to optimize the outcome in eyelid reconstruction, both functionally and aesthetically.
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20. Tucker S, Linberg J. Vascular anatomy of the eyelid. In Hawes M (ed). Twenty-Fourth Annual Scientific Symposium. Chicago: American Society of Ophthalmic Plastic and Reconstructive Surgery, 1993:35
30. Lockwood CB. The anatomy of the muscles, ligaments, and fascia of the orbit, including an account of the capsule of Tenon, the check ligaments of the recti, and of the suspensory ligament of the eye. J Anat Physiol 1986;20:1
31. Shovlin J, Lemke B, Dortzbach R. The anatomy of the suspensory apparatus of the conjunctival fornix. In Flemming JC (ed). 25th Annual Scientific Symposium. San Francisco: American Society of Ophthalmic Plastic and Reconstructive Surgery, 1994:96
33. Cook C, Ozanics V, Jacobiec F. Prenatal development of the eye and its adnexa. In Tasman W, Jaeger E (ed). Foundations of Clinical Ophthalmology. Vol 1, 2nd ed. Philadelphia: Lippincott-Raven, 1997:1
38. Goldber R, Lufkin R, Farahani K et al. Physiology of the lower eyelid retractors: Tight linkage of the anterior capsulopalpebral fascia demonstrated using dynamic ultrafine surface coil MRI. Ophthtal Plast Recontr Surg 1994;2:87