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EMBRYOLOGY

EARLY DEVELOPMENT OF THE EMBRYO

A general understanding of thedevelopment of the embryo facilitates anunderstanding of the development of theeyelids. The fertilized ovum is the originalcell, which undergoes several divisions toform a solid clump of cells called a morula .The morula then enlarges and forms acentral cavity, to become known as

a blastula or blastodermic vesicle ( Fig. 1 ).The outer wall of the blastula forms theplacenta. The blastodermic vesicle embedsitself in the uterine mucosa, enlarges, andforms two cavities each with a singlelayer of cuboidal epithelium. The uppercavity is the amnion, the lower is thearchenteron or yolk sac . The embryodevelops from the embryonic plate at thearea of contact between the two. At thisstage, the embryonic plate consists of twolayers: an outer ordorsal ectoderm (epithelial lining of theamnion) and an inner orventral entoderm (epithelial lining of theyolk sac). A central depression (theprimitive streak) followed by a groovedevelops on the ectodermal surface of theembryonic plate. A middle layer(intraembryonic mesoderm ) appears, thusdividing the embryonic plate into three
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germinal layers from which all tissues of the body develop. The neural groovecloses to form the neural canal (24th day).The surface ectoderm within the neuralcanal is known as the neuroectoderm. 1 3

Fig. 1. Early celldivision: ( A)fertilized ovum, ( B)morula ( C) blastula.

At the anterior end of the embryonic plate,three headfolds form: the forebrain, themidbrain, and the hindbrain. At the front of the forebrain, a small depression is notedon each side of the midline. Thisdepression is the anlage of the eye and iscalled the optic pit . Toward the end of thethird week of gestation, the optic pit

deepens until it contacts the surfaceectoderm and becomes the primary optic vesicle . At this stage, the eyes are at theside of the head at an angle of 180 ( Fig.2 ). The embryo consists of a head with thethree divisions of the brain, a segmentedbody with spinal canal, and a tailfold. Thatportion of the mesoderm closest to the

spinal canal is known as paraxial mesoderm . The primary optic vesicle thenundergoes invagination to formthe secondary optic vesicle or the optic cup . This starts at 2.5 weeks' gestation
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and is complete by 1 month . 3 5

Fig. 2. Fetal optic axis.At 3 to 4 weeks'gestation, the primaryoptic vesicles are at180.

SEGMENTATION

Humans are segmented beings.

Segmentation begins simultaneously withclosure of the neural groove (24th day).Segmentation extends posteriorly andanteriorly to the head region, wheresegmentation is lost. Instead,five branchial or pharyngeal arches form.At 5 weeks' gestation, a sheet of immaturemesoderm originates from the first

branchial arch ( mandibular arch ). Thefirst branchial arch consists of a smalldorsal portion known as the maxillary

process , which extends forward beneaththe eye to develop into the lower eyelid.Cephalad to the first branchial arch,mesenchymal proliferation creates otherfolds that form other facial processes: the

frontonasal, medial nasal, lateral nasal,and mandibular processes ( Fig. 3 ). 1 8
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Fig. 3. The facial processes.

EYELID FORMATION

The maxillary process lies in apposition tothe paraxial mesoderm of the eye and thenasal process. Between them is a groove

of thickened ectoderm, which becomesburied as the maxillary process overgrowsthe nasal process. This occurs at 5 weeks'gestation and is the first indication of thenasolacrimal duct. The maxillary processextends superiorly to form the lower eyelidat 6 weeks' gestation. In doing so, theinner end folds in a layer of ectodermal

tissue that is continuous with thenasolacrimal duct at its lower end. Beforethe lower lids are apparent, the upper lidsare formed by an extension of orbital orparaxial mesoderm known as thefrontonasal process. Thus, the upper lidarises from the frontonasal process slightlybefore the lower lid arises from themaxillary process. The inner end of theupper lid also folds in a portion of ectodermal plate, which forms the uppercanaliculus. This unites with the lowercanaliculus at the upper end of the
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nasolacrimal duct . 6 8

LID FUSION

At 1.5 months' gestation, the lateralcanthus is formed by the union of theupper and lower eyelid folds. The two lidscome together and temporarily fuse fromwithin outward at 8 weeks' gestation ( Fig.4A ). Closure is complete at 10 weeks'gestation. Desmosomal adhesions betweenthe lid margins isolate the eye from theamniotic fluid. 1 All lid structures areformed during this period of adhesion ( Fig.4B ). Riolan's muscle can be identified bythe end of the third month. Hair bulbs of eyelashes appear first in the upper lids,then in the lower lids in an anteroposteriordirection. 2 Development is slightly moreadvanced in the upper lid, compared withthe lower. At the beginning of the fourthmonth, the meibomian glands begin toappear. The posterior half of the lid showsa greater condensation of basal lamina andcollagen fibers, indicating the tarsal

plate region. The meibomian glands growinto the tarsal plates first in the upperthen in the lower lids. The apocrine Moll'sglands also appear around the cilia folliclesduring the fourth month, followed shortlyby the sebaceous glands of Zeis . 3 , 6
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Fig. 4. Eyeliddevelopment. ( A)Eyelid fusion (8 to

10 weeks'gestation); ( B)development of margin structures (3 to 4months' gestation); eyelid dysjunction (5to 6 months' gestation).

At 2.5 months' gestation, the levator palpebrae superioris develops. It separates

from the superior rectus muscle at thefourth month of gestation. Clinically, failureof separation of these muscles would resultin congenital ptosis.

LID DYSJUNCTION

At the end of the fifth month (weeks 21 to26 gestation), the epithelial adhesionsbetween the lids begin to break down(see Fig. 4C ). This process is usuallycompleted by the sixth month but maypersist until shortly before birth. Holocrineproduction of lipids from the meibomianglands, keratinization of the lid margin,and pull of the developing eyelid retractorsare responsible for the dysjunction. 7 ,8

ABNORMALITIES OF EYELIDDEVELOPMENT

When normal progression of liddevelopment is interrupted, a spectrum of
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congenital anomalies occurs. 8 , 9

Cryptophthalmia (ablepharon) absence of the eyelid is due to failure of the eyelidfolds to embryologically develop. Thecornea undergoes metaplasia and iscovered with skin, which passescontinuously from the forehead to thecheek. Most are sporadic but a recessiveinheritance pattern has beensuggested. 10 Cryptophthalmia occursbilaterally twice as often as unilaterally andis slightly more common in males. It canbe associated with ear and nosemalformations, cleft lip and palate,hypertelorism, laryngeal atresia, lacrimalduct defects, renal anomalies, syndactyly,and meningoencephalocele. 11

Microblepharia is an incomplete liddevelopment wherein the eyeball is notcovered, resulting in congenitallagophthalmos.

Coloboma of the eyelid is a defect in the lidmargin, with absence of lashes and glands.The most common site is in the upper lidat the junction of the inner third and theouter two thirds. In the lower eyelid, it ismore frequently seen at the junction of theouter third and the inner two thirds. Theseabnormalities may be due to the formationand pressure of amniotic bands or from
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failure of the eyelids to fuse duringembryonic life. This may be associatedwith cleft palate, mandibulofacialdysotosis, limbal dermoids, lipodermoids,iris colobomas, or brow colobomas . 9

Epicanthus is a fold of skin that extendsfrom the side of the nose to the upper lidand partially hides the inner canthus. Thiscondition is normally present in theembryo and early infancy. Frequently, it isassociated with ptosis, although it mayoccur independently. Epicanthus is usuallybilateral but may be asymmetric orunilateral. There are four known types,depending on the origin of the upper endof the fold. In epicanthus superciliaris , thefold arises in the region of the eyebrowand extends over the lacrimalsac. Epicanthus palpebralis ( Fig. 5 ) has anepicanthal fold arising from the uppertarsal area, extending toward the lowermargin of the orbit. The fold is equallydistributed in the upper and lower lids.In epicanthus tarsalis ( Fig. 6 ), theepicanthal fold arises from the tarsal foldand ends close to the inner canthus. Thus,

the fold is more prominent in the upper lid.It is a normal variation of the Asian eyelid.In epicanthus inversus , ( Fig. 7 ) the foldarises in the lower lid and extends upward,partially covering the inner canthus,usually terminating in the upper lid.
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Fig. 5. Epicanthuspalpebralis (alsoknown as simple

epicanthus). Theamount of tissue aboveis the same amount as

below the canthal angle.

Fig. 6. Epicanthustarsalis. The epicanthalfold is more prominantin the upper eyelid.

Fig.7. Blepharophimosissyndrome. Thecommon triad of ptosis, horizontalshortening of the

palpebral fissures, and epicanthusinversus (fold more prominent in lowerlid) is seen.

Congenital ptosis is most commonly seenbecause of the absence or fibrotic natureof the levator palpebrae superioris. It maybe unilateral or bilateral and associatedwith weakness of the superior rectusmuscle from which the levator is derived.In the jaw winking pheno mena, ptosisappears when the patient chews. This isdue to an abnormal association of the
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nerve to the levator muscle and the nerveto the external pterygoid muscle.

Many abnormalities exist of eyelid margindifferentiation. Distichiasis is a condition inwhich aberrant lashes develop at or nearthe orifices of the meibomianglands. Ankyloblepharon is an abnormalfusion of the lid margins from incompleteseparation of the lid folds. The fusion maybe complete but is more common at theinner canthus. A variant is

ankyloblepharon filiform adnatum, inwhich the lid margins are connected bymultiple fine bands. Blepharophimosis is ahorizontal narrowing of the palpebralaperture. The triad of blepharophimosissyndrome includes ptosis, horizontalshortening of the palpebral fissures, andepicanthus inversus ( Fig. 7 ). Telecanthus,lower eyelid entropion or ectropion,hypoplasia of the superior orbital rims, apoorly developed nasal bridge, andhypertelorism can also be seen with thiscondition.

Epiblepharon is an additional fold of skinrunning horizontally below the lower eyelidmargin. It often is associated with loss of the eyelid crease and may be partly due toa lack of deep anchoring of the superficialskin to the orbicularis oculi muscle. Theweight of the skin fold may rotate the
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lower lid margin inward, creating anentropion. With growth of the face andnasal bridge, epiblepharon usuallydiminishes. It is seen more commonly inAsian eyelids.

Euryblepharon is a rounding or almond-shaped deformity of the lower lid at thelateral canthal angle. It may be associatedwith an inferiorly displaced lateral canthaltendon.

Congenital entropion is characterized by aninward turning of the eyelid margin due tohypertrophy of the orbicularis muscle,defects in lower lid retractor, or tarsalabnormalities. 12

Congenital ectropion is characterized byeversion of the eyelid margin. It is rarely

seen in the upper lid. In the lower lid, it isusually seen with Down's syndrome orblepharophimosis syndrome.

Back to Top

SURFACE TOPOGRAPHY

Except for prepuce and that of the labiaminor, the skin of the eyelids is thethinnest in the body. It is pliable andcontains relatively little adipose tissue. It issubject to unusual amounts of stress andrelaxation with each blink. Such movement
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predisposes the paraorbital skin to severalnatural and dynamic topographiclandmarks ( Fig. 8 ) . 13 15 The upper liddisplays a prominent horizontal crease,the superior palpebral crease . It marks theupper border of the tarsus, is locatedabout 10 mm above the lid margin in whitewomen and 7 to 8 mm above the lidmargin in men. It is accented when the lidis raised. It denotes the dividing pointbetween loosely adherent preseptal skin

and that from more adherent pretarsalskin. In the Asian eyelid, the superiorpalpebral crease is absent or is displacedinferiorally.

Fig. 8. Surface topography.

The lower lid displays three creases.The inferior palpebral crease is lessnoticeable than the superior palpebralcrease and marks the lower border of thelower tarsus. It courses from about 5 mmbelow the lower lid margin medially toabout 7 mm laterally. The nasojugal crease is located below the medial aspectof the inferior palpebral crease andextends infralaterally at 45. The malar crease originates lateral to and below the
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lateral canthus. It courses inferomediallyuntil it meets the nasojugal fold 15 mmbelow the center of the lower eyelidmargin.

The palpebral fissure is the openingbetween the eyelid margins. The verticalpalpebral fissure is normally 9 to 10 mm,whereas the horizontal fissure measures28 to 30 mm. The upper eyelid rests at theupper limbus in the child and about 1 to 2mm below the upper limbus in the adult.The upper and lower lids rest over theanterior surface of the globe, allowingabout 20% of its surface to be exposed inthe normal palpebral fissure. The lowereyelid is generally found at the level of thelower limbus. The upper eyelid is slightlycurved, with the highest point nasal to thepupil. The lowest point of the lower eyelidis slightly temporal to the pupil. The pointwhere the upper eyelid and the lowereyelid meet medially is known asthe medial commissure . The point wherethe upper and lower eyelid meet laterally isknown as the lateral commissure .The medial canthus and the lateral

canthus are the angles formed at themedial commissure and at the lateralcommissure, respectively. The lateralcanthal angle is normally more acute thanthe slightly rounded medial canthal angle.The lateral commissure rests on the globe,


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whereas the medial commissure isanteriorly displaced by the caruncle andplica semilunaris.

The superior orbital sulcus is that areabetween the upper eyelid crease and thesuperior orbital margin. With age or afterenucleation, a concavity ( Fig. 9 ) of thesuperior sulcus can be seen because of lack of supporting tissue. Convexity ( Fig.10 ) of the superior sulcus is seen withherniation of orbital fat.

Fig. 9. Concavity of superior orbital sulcusafter enucleation of theright eye.

Fig. 10. Convexity of superior sulcus fromherniated orbital fat.

Langer lines ( Fig. 11 ) are present in theupper and lower lids and in the canthal

areas. These natural static skin lines areformed by collagenous, reticular, andelastic fibers in the reticular layer of thedermis. Gravitational lines ( Fig. 12 ) areformed with age by progressive thinning of relaxed skin. In contrast, dynamic
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lines ( Fig. 13 ) result from repetitiousrelaxation and contraction of paraorbitalmuscles. Horizontal forehead furrows showthe lateral extent of the frontalis muscleused to correct chronic physiologic ptosis.The action of the procerus and corrugatorsuperciliaris muscles create the frownlines between th e eyebrows.

Fig.11. Langer

lines ( A)as theyappear in adiagram

and ( B) clinically. These static skin linesare formed by collagenous, reticular, andelastic fibers in the reticular dermis.

Fig. 12. Gravitational

lines formed byprogressive thinning of relaxed skin.

Fig. 13. Dynamic lines.Overaction of theprocerus and

corrugator superciliarismuscle create thesefrowns line in this

patient with ocular phemigoid.

The skin of the eyelids is thin. The
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transition to the thicker skin of theeyebrow above and to the skin of themalar region below is abrupt. In thepreorbital and preseptal skin,subcutaneous fat is sparse. Fat is absent inthe pretarsal skin. Pretarsal skin is firmlyadherent to the underlying tarsus becauseof attachments of the levatoraponeurosis. 16 Clinically, edema collectsunder the loose preorbital and preseptalskin, leaving an identifiable border at the

pretarsal skin where there are densersubcutaneous fibroadipose attachments.

Back to Top

BASIC EYELID ANATOMY

PROTRACTORS

The orbicularis oculi muscle is a thin sheetof concentrically arranged muscle fiberscovering the eyelids and periorbital region( Fig. 14 ). It is oval, with the long axis beinghorizontal, corresponding to the palpebralopening. Contraction of the orbicularis oculimuscle results in the protraction or closureof the eyelid. The orbicularis is firmly

attached to the underlying lateral palpebralraphe, the medial canthal region, theinsertions of the upper and lower eyelidretractors, the supraorbital ridge, the naso-orbital valley and the malar crease.Jones 14 , 17 divided the orbicularis oculi
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muscle into three regions: orbital,preseptal, and pretarsal.

Fig. 14. Orbicularis oculimuscle, cadaver

dissection. ( A) Orbital portion; ( B)preseptal portion; ( C) pretarsal portion.

The broad orbital orbicularis portion extendssuperiorly to the eyebrow, where itinterdigitates with the frontalis and thecorrugator superciliaris muscles. Medially, itextends from the supraorbital notch in acurvilinear fashion over the side of thenose, inferiorly to the infraorbital foramen.
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It continues along the infraorbital margin.Laterally, it extends to the temporalismuscle. These thick course fibers play animportant role in voluntary lid closure(winking) and forced eyelid closure.

The preseptal orbicularis overlies the orbitalseptum. In between is a fibroadipose layer,which is continuous superiorly with theeyebrow fat pad. If this postorbicularis layercontains a significant amount of fat, theptosis surgeon may misinterpret it as beingpreaponeurotic fat. Laterally, the preseptalorbicularis muscle inserts directly ontoWhitnall's lateral orbital tubercle 3 to 4 mmdeep to the lateral palpebral raphe. Becauseof the fibrous component of this lateralattachment, Jones misleadingly termed thisthe lateral canthal tendon rather than thelateral canthal ligament . 14 ,17 Medially, theinsertions of the preseptal orbicularis arecomplicated by the lacrimal sac, its fascia,and the lacrimal crests. The medial origin of the preseptal orbicularis is thought to arisefrom two heads the deep and thesuperficial heads. The deep head or Jonesmuscle 17 ,18 is adherent to the lacrimal sac

and lacrimal fascia, whereas the anterior orsuperficial head arises from the anterior rimof the medial canthal ligament ( Fig. 15 ).Functionally, the preseptal fibers contributeto voluntary lid closure (winking) and
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involuntary lid closure (blinking).

Fig. 15. Medialattachments of theorbicularis oculi muscle.

The pretarsal orbicularis is firmly adherentto the underlying tarsus and to thesuperficial insertion of the levator

aponeurosis at the superior tarsal border.The medial origin of the pretarsal orbicularisis thought to arise from two heads thedeep and the superficial heads. The deephead , Horner's tensor tarsi muscle , 19 ,20 arises from 4 mm behind theposterior lacrimal crest and from thelacrimal fascia to insert medially on the tarsi

of the upper and lower eyelids. Itscontraction pulls the eyelid medially andposteriorly, allowing the eyelids to followand cover the convex globe. In addition, itslateral contraction on the lacrimaldiaphragm creates a negative pressure inthe lacrimal sac that draws tears from thecanaliculi. The superficial head of thepretarsal orbicularis inserts on the anteriorlacrimal crest and anterior limb of themedial canthal ligament. Superficial fibers also surround the canaliculi.Contraction shortens the canaliculi, forcing
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lacrimal fluid into the lacrimal sac.Functionally, involuntary lid closure(blinking) is primarily the responsibility of the smaller pretarsal orbicularis fibers.

Medially, both Horner's and Jones musclesare essential for proper functioning of thelacrimal pump. The deep fibers medially andposteriorly are responsible for propereyelid-to-globe apposition. Laterally, theorbital and preseptal fibers fuse over thezygoma to form the lateral palpebral raphe.The deep fibers of the pretarsal orbicularis

join the inferior and superior crux of thelateral canthal ligament, which inserts 3 to4 mm posterior to the lateral orbital rim onWhitnall's tubercle. 21 It is these latterposteriorly oriented attachments that areresponsible for proper eyelid-to-globeapposition and not the more superficialfibers.

ORBITAL SEPTUM

Upper Eyelid

Historically, the orbital septum has beenconsidered as a discreet, well-defined

structure arising from the arcus marginalis .The arcus marginalis is a discrete line seenat the supraorbital rim, representing thecondensation of the periosteum of theforehead with the periorbita of the orbit.Alternatively, the orbital septum may be
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region. 26

Lower Eyelid

In the lower eyelid, the orbital septum ( Fig.18 ) arises from the inferior orbital rim as acondensation of the periosteum and theperiorbita. It continues anteriorly andsuperiorly to a point 4 to 5 mm below theinferior tarsus, where it joins with the lowereyelid retractors and as a single structureinserts on the lower border of the inferiortarsus. 23 , 27 Medially, the orbital septum splitsand is carried posteriorly by the pretarsalorbicularis muscle (Horner's muscle) andattaches to the posterior lacrimal crest.Laterally, the orbital septum also splits andis carried deep by the insertion of theorbicularis.

Fig. 18. Cross-section of thelower eyelid.

The orbital septa of the upper and lower

eyelids form an anatomic barrier betweenthe preseptal and orbital structures.Infectious processes anterior to the septaare considered to be more benign thanthose posterior to the septa. Functionally,the suborbicularis oculi fibroadipose layer
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extend anteriorly from the capsule of thepreaponeurotic fat to the orbital septumand posteriorly to the levatoraponeurosis. 23 Clinically, these connectionsare easily broken by blunt dissection,exposing an encapsulated preanoneuroticfat pad. Connective tissue septa also existswithin the preaponeurotic fat, dividing itinto lobules. Although the preaponeuroticfat pad is contiguous with deeper orbital fat,these connections are more rudimentary

than the medial and lower eyelid fat pads.The preaponeurotic fat pad is less vascularthan the other fat pads. Conversely, themedial fat pad is more vascular because of the location of the palpebral arterial arcade,which serpiginously courses through thispad. 29 ,30 The medial fat pad is separatedfrom the preaponeurotic fat pad by delicate

fibrous septal attachments to the trochlea.

Fig. 19. Fat pads of the upperand lower eyelids.

Fig. 20. Cadaverdissection, eyelid fatpads.
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Lateral to the preaponeurotic fat pad liesthe lacrimal gland, which is typically pinkerin appearance, firmer in texture, anddistinctly more vascular than thepreaponeurotic fat pad . 31 During removal of orbital fat, the eyelid surgeon is careful toavoid injury to the laterally located lacrimalgland.

Lower Eyelid

In the lower eyelid, there exists a smallertemporal fat pad and a larger medial fatpad (see Figs. 19 and 20 ). The temporal fatpad lies inferior to the lateral canthus. It isseparated from the larger medial fat pad bya fibrous extension from the periorbita andorbital septum infralaterally, joining withthe capsulopalpebral fascia and Lockwood's

ligament.28 ,32

The medial pad extends from the fascialband to the medial canthal area. It is asingle pad anteriorly but posteriorly isdivided by the origin of the inferior obliquemuscle ( Fig. 21 ). With this subdivision of the larger medial fat pad of the lower lid,

some surgeons consider the lower lid tohave three fat pads . 15 ,32
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Fig. 21. Fat pads of thelower lid. This cadaverdissection demonstrates

the posterior division of the large medial fat padby the inferior oblique

muscle ( pointer ).

The lower eyelid fat pads are in directcommunication with the deeper extraconalfat of the orbit. Clinically, this is important

during lower eyelid surgery becauseexcessive traction may be transmitteddeeper into the orbit, resulting inintraoperative or postoperative orbitalhemorrhage. 29 ,33 During transconjunctivallower eyelid blepharoplasty, the lateraleyelid fat pad tends to be more fibrotic andprolapses less easily. Care is also taken to

avoid the inferior oblique muscle, whichoriginates just lateral to the ostium of thenasolacrimal canal.

RETRACTORS

Each eyelid contains two retractors, whichopen the palpebral fissures. In the upperlid, they are the levator palpebraesuperioris muscle and the sympatheticallyinnervated muscle of Mller. In the lowerlid, they are the capsulopalpebral fascia andthe sympathetically innervated inferiortarsal muscle.
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Upper Eyelid

In the upper lid, the major retractor isthe levator palpebrae superioris . It arisesfrom the same superior mesenchyme as thesuperior rectus muscle. At the orbital apex,the levator originates from the lesser wingof the sphenoid bone, superolateral to theoptic foramen. Immediately beloworiginates the superior rectus muscle arisingfrom the annulus of Zinn. 14 ,34 As thetriangular levator muscle courses anteriorlyin the orbit from its origin, it is composed of striated muscle. The average length of themuscular portion of the levator is 36mm . 28 ,34

At the level of the globe, the levator musclefans out and thins as the whitish graysuperior transverse ligament of Whitnallor Whitnall's ligament . It represents atransition zone where the horizontal levatormuscle becomes more fibrous, forming themore vertical levator aponeurosis. Theaponeurosis measures 18 mm in width.Whitnall's ligament is located 14 to 20 mmabove the superior border of the tarsus. Themedial attachment of Whitnall's ligament isto the fascia of the trochlea, whereas thelateral attachment of Whitnall's ligament isat the frontozygomatic suture ( Fig. 22 ).
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Fig. 22. Whitnall'sligament. Its medialattachment is to the fascia

of the trochlea. The majorlateral attachment is to thefrontozygomatic suture,

with minor attachments to the lateralorbital tubercle.

Anteriorly, the aponeurosis expandshorizontally to insert onto the medial and

lateral retinacula as the horns of thelevator. The medial horn of the levatorattaches to the medial canthal ligament. Itsattachment is looser and more ill-definedthan the lateral attachment. 24 ,35 The lateralhorn of the levators splits the lacrimal glandinto the larger orbital lobe and the smallerpalpebral lobe ( Fig. 23 ). It then attaches to

the lateral orbital tubercle by the lateralcanthal tendon and may provide suspensorysupport for the gland . 24 ,25 The levatorpalpebral aponeurosis continues anteriorlyto a point 2 to 5 mm above the superiortarsal border, where it joins with fibers of the multilayered orbital septum (see Fig.17 ). The thin fibrous connections between

these two structures is somewhat roundedand convex. Below this point, at the level of the superior tarsal border, the fusedlamellae of the orbital septum and thelevator aponeurosis send connective tissue
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attachments to secondarily insert onto theoverlying orbicularis oculi muscle andsubcutaneous tissue . 23 These attachmentsresult in a sharp upper eyelid crease.Variations in these attachments result invariations in the location of the upper eyelidcrease. The levator aponeurosis then sendsconnective tissue attachments, which insertprimarily on the anterior inferior third of thesuperior tarsus, with the strongestattachments 3 mm from the lid

margin.25 ,34

It is these tarsal attachmentsthat are more important for proper uppereyelid function. 24

Fig. 23. The lateral hornof levator aponeurosis.With the lateral walland roof of the orbit

removed, the levatoraponeurosis ( widearrow ) is seen dividing the lacrimal glandinto the larger orbital lobe ( thin arrow ) andsmaller palpebral lobe ( pointer ).

The levator muscle and the superior rectusmuscle are joined along their medial

borders by fibrous attachments thatbecome stronger anteriorly. A denseintermuscular fascia connects theundersurface of the levator aponeurosiswith the superior surface of the superiorrectus muscle just posterior to the level of
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Whitnall's ligament. From the anteriorsurface of this intermuscular membrane,the superior conjunctival fornix suspensoryligament (see Fig. 17 ) arises . 36 ,37 Anterior tothis point, Mller's muscle takes its originfrom the underside of the levator muscle 22mm above the superior tarsal border. 28 Themotor innervation of the levator muscle isthe superior division of the oculomotornerve (cranial nerve III). After entering theorbit through the supraorbital fissure and

through the annulus of Zinn, the superiordivision of the oculomotor nerve thenpasses around the medial border of thesuperior rectus muscle or directly throughthe superior rectus muscle to enter theundersurface of the levator muscle at itsposterior third and anterior two thirds

junction.

The other retractor of the upper eyelidis Mller's muscle , also known as thesuperior tarsal muscle (see Fig. 17 ; Fig.24 ). Mller's muscle is a smooth musclearising from the underside of the levatormuscle, just below the level of Whitnall'sligament, 22 mm above the superior tarsal

border. It inserts on the superior tarsalborder. Superiorly, Mller's muscle isloosely adherent to the conjunctiva butbecomes more adherent near the tarsus.Sympathetic nerve fibers innervating themuscle are thought to enter by the
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peripheral arterial arcade and other smallarteries . 24 ,28 Clinically, increasedsympathetic stimulation (as seen in Graves'disease) is thought to be a factor in thyroideyelid retraction ( Fig. 25 ).

Fig. 24. Mller's muscle.A 10-mm strip of Mller's muscle ispreserved in thiscadaver to demonstrate

its origin from theunderside of the reflected levator muscle( thick arrow ) and its insertion onto thesuperior edge of the tarsus. The tarsus isseen with the vertically orientedmeibomian glands ( thin arrow ).

Fig. 25. Thyroid lidretraction. Sympathetic

stimulation of Mller'smuscle and the inferiortarsal muscle is a factorin this patient with

Graves' disease.

Lower Eyelid

Posterior to the globe, a fibrous extensionarises from the inferior rectus muscle.These extensions are collectively termedthe capsulopalpebral head of the inferiorrectus muscle. The capsulopalpebral headsplits to surround the inferior oblique
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muscle. The external portion is termedthe capsulopalpebral fascia , whereas theinner counterpart that contains smoothmuscle is termed the inferior tarsal muscle .The two layers fuse anterior to the inferioroblique muscle to form a dense fibrousstructure termed Lockwood's suspensory ligament of the globe. 27 ,36 This ligamentsuspends the globe position within the orbit,even if all bone inferior to its attachmentsat the medial and lateral orbital walls are

removed. The outer fibers of thecapsulopalpebral fascia fuse with the innerfibers of the inferior orbital septum 4 to 5mm below the inferior tarsus and togetheradvance as a single layer to insert on theinferior border of the inferior tarsus(see Fig. 18 ). 27 ,38 Although morerudimentary in their development, the

capsulopalpebral fascia and the inferiortarsal muscle are analogous to the levatoraponeurosis and the superior tarsal muscleof the upper eyelid.

The capsulopalpebral fascia has no inherentinnervation but its action mirrors the theaction of the inferior rectus muscle, which is

innervated by the inferior division of theoculomotor nerve. Depression of the lowereyelid in downgaze is less than themovement of the globe in downgaze.Magnetic resonance imaging studies 39 haveshown that this discrepancy is due to
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stretching of the capsulopalpebral headposterior to the inferior oblique muscle,whereas the length of the anterior portionof the capsulopalpebral fascia (betweenLockwood's ligament and the tarsus) remainconstant.

In the lower eyelid, the more rudimentaryinferior tarsal muscle arises from the innersurface of the capsulopalpebral head as itsplits to surround the inferior obliquemuscle. The inferior tarsal muscle consistsof numerous discontinuous smooth musclebundles and becomes totally fibrous as theinferior tarsus is approached . 27 The inferiortarsal muscle is adherent to both theoverlying capsulopalpebral fascia and to theunderlying conjunctiva. The adherence of the capsulopalpebral fascia to the inferiortarsal muscle is stronger than theadherence of the inferior tarsal muscle tothe conjunctiva. Thus, the capsulopalpebralfascia and the inferior tarsal muscle areoften grouped together and termed thelower lid retractors, which during lowereyelid surgery are treated as one anatomicunit.

The inferior tarsal muscle is sympatheticallyinnervated. Clinically, in Horners' syndrome,the atonic muscle may allow the lowereyelid to elevate as much as 1 mm.Conversely, in thyroid eye disease, the
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lower eyelid may retract from increasedsympathetic tone.

TARSAL PLATES

The tarsal plates are thickened fibrousconnective tissue that provide structuralsupport to the eyelids. Medially andlaterally, the tarsal plates are connected tothe bony orbital margins by ligamentousfibrous tissue ( Fig. 26 ) . 40

Fig. 26. The upper and lowertarsal plates.

Upper Eyelid

The superior tarsal plate is 10 mm invertical height and 25 to 30 mm inhorizontal dimension. The border nearestthe eyelid margin is flat, whereas theantimarginal border is curved with itslargest vertical dimension centrally. Fromtheir central portion, each tarsal platetapers toward the canthal ligaments. Withineach superior tarsus lies 30 to 40 verticallyoriented sebaceous secreting glands, themeibomian glands, which produce the outerlipid portion of the tear film. The orifices of the meibomian glands are located at the
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eyelid margin just anterior to themucocutaneous junction.

Lower Eyelid

The inferior tarsal plate is 3 to 5 mm invertical height and measures 25 to 30 mmhorizontally. 41 The lower tarsus also tapersmedially and laterally. Within each lowertarsus, there are 20 to 30 verticallyoriented meibomian glands whose orificesare located anterior to the mucocutaneous

junction of the lower eyelid.

The tarsi span the anterior orbital openingwhile articulating with the globe. With eyesclosed, the lower eyelid covers a smallerarea of the globe surface than does itsupper eyelid counterpart. The posteriorsurface of both the tarsal plates is covered

by conjunctiva.

CONJUNCTIVA

Embryologically, the conjunctiva representsthe differentiated inner portion of the skinfold that forms the eyelid. It is composed of nonkeratinized stratified squamous

epithelium with goblet cells. The goblet cellsproduce mucous for the inner layer of thetear film. The conjunctiva has twocomponents: the bulbar conjunctiva, whichlines the globe extending to the corneallimbus, and the palpebral conjunctiva,
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which lines the eyelid. These twoconjunctival components meet at theconjunctival fornices. The superiorconjunctival fornix is stabilized bythe suspensory ligament of the superior fornix , which arises from the conjoining of the levator and the superior rectusmuscles. 37 The inferior conjunctival fornix isstabilized by the inferior suspensory ligament , which arises from the inferiorrectus extensions that sheath the inferior

oblique muscle. The superior fornix islocated 13 mm from the open eyelid marginand 25 mm from the closed eyelid margin.The inferior fornix, however, is located 9 to10 mm from the open or closed lower eyelidmargin because the lower eyelid does notelevate significantly with eyelid closure.

The bulbar conjunctiva is loosely attachedto the globe, except at the limbus where itis tightly bound at the episclera.Similarly, the palpebral conjunctiva isloosely adherent, except at the tarsus andat the superior tarsal muscle where it istightly adherent. In the lower eyelid, theconjunctiva is adherent to the lower tarsus

but can be elevated from the lower eyelidretractors without difficulty. Theconjunctival fornices are also stabilized byattachments medially and laterally to thecanthal tendon. 14 ,42
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In addition to goblet cells, the conjunctivaalso contains the accessory lacrimalglands. 43 The glands of Wolfring are locatedalong the antimarginal border of the tarsalplate, whereas Krause's glands are found inthe conjunctival fornices. These glands areknown as the basic tear secretors becausethey provide the middle aqueous layer of the tear film at a constant basal rate. Themain lacrimal gland, however, is a reflexsecretor, providing additional aqueous fluid

for the middle layer of the tear film on areflex basis (ocular irritation or emotion).The orifices of the lacrimal gland ducts arelocated 4 to 5 mm superior and lateral tothe upper edge of the upper tarsus.

Medially, the conjunctiva formsthe semilunar fold , a vestige of thenictitating membrane of some animals.The caruncle is a small collection of transitional tissue at the medial commissurethat has multiple sebaceous glands.

Back to Top

SPECIAL CONSIDERATIONS

SUSPENSORY SYSTEM OF THE EYELIDS Five anatomic structures provide supportand mechanical function to the eyelid andeyeball: Whitnall's ligament, Lockwood'sligament, the lateral canthal ligament, the
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medial canthal ligament, and the eyelidmargin.

Whitnall's Ligament

The superior transverse ligament of Whitnall provides the dual function of acting as the main suspensory ligament of the upper eyelid and as a check ligamentfor the levator aponeurosis and levatormuscle . 24 ,44 ,45 It also gives superiorconjunctival fornix suspension. 34 , 37 Thesuspensory role and fulcrum effect of Whitnall's ligament is assisted by thecurvature of the globe, which also providesa fulcrum and support for thelevator. 34 Whitnall's ligament is suspendedfrom the periorbita of the orbital roof,extending medially fromthe trochlea across the horizontaldimension of the orbit tothe frontozygomatic suture , 10 mmsuperior to the lateral orbital tubercle (Whitnall's orbital tubercle).Laterally, it sends weaker attachments toWhitnall's tubercle but the most significantlateral attachment site of Whitnall'sligament is at the frontozygomatic suture(see Fig. 22 ). Whitnall's ligament is found15 to 20 mm superior to the superiorborder of the tarsus as a white, shiny,glistening structure where the levator
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muscle becomes an aponeurosis.

Clinically, this is an important structureencountered frequently during eyelidsurgery.

Lockwood's Ligament

Lockwood's ligament in the lower eyelid ismore rudimentary than Whitnall's ligamentin the upper eyelid but it acts as asuspensory hammock for the globe . 36 It

also serves as an anchor for the inferiorconjunctival fornix. Lockwood's ligament isa condensation of the capsulopalpebralfascia anterior to the inferior obliquemuscle . 27 It is composed of thickenedTenon's capsule, intramuscular septa,check ligaments, fibers from the inferiorrectus sheath, and lower lid retractors.

Medially, it attaches to the medial canthalligament and laterally to the lateral canthalligament.

Lateral Canthal Ligament

Often called the lateral canthal tendon, thelateral canthal ligament is comprised of a

superior crux from the superior tarsus andan inferior crux from the inferior tarsus.The superior and inferior crux of the lateralcanthal tendons fuse at the lateral borderof the tarsal plates to join the lateralretinaculum, a condensation of several
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anatomic structures that inserts onto thelateral orbital tubercle of Whitnall. Thistubercle is located 2 to 4 mm posterior tothe lateral orbital rim, 10 to 12 mm inferiorto the frontozygomatic suture, and at thelevel of the lateral commissure. 40 Thelateral retinaculum consists of fibers fromthe lateral horn of the levator aponeurosis,Lockwood's ligament, check ligaments of the lateral rectus muscle, fibers of thesuspensory ligaments of the lacrimal

gland, and some deep fibers of thepretarsal orbicularis oculi muscle. In thespace between the lateral retinaculum andthe more anteriorally placed orbital septumis sometimes found a small fat pad, Eisler's

pocket . 22

The lateral canthal ligament is a clinicallyimportant anatomic structure. The inferiorand superior crux of the lateral canthalligament must be released from the tarsalplates during a lateral canthotomy orcantholysis to decompress the orbit and tolower intraorbital pressure.

Medial Canthal Ligament

The medial canthal ligament, often calledthe medial canthal tendon, providessupport to the eyelids and aids in thefunction of the lacrimal pump . 18 The medialcanthal ligament has two components an
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anterior limb and a posterior limb.The anterior limb ( Fig. 27 ) is a broadfibrous structure that attaches the eyelidsto the frontal process of the maxillary boneand to the anterior lacrimal crest. It givesorigin to the superficial head of thepretarsal orbicularis oculi muscle.The posterior limb of the medial canthalligament inserts on the posterior lacrimalcrest and the lacrimal fascia. It is weakerthan the anterior limb but with the deep

heads of the pretarsal and preseptalorbicularis muscle draws the medialportion of the eyelids posteriorly to followthe vector forces necessary for goodmedial apposition of the eyelids to theglobe. 31

Fig. 27. Anterior limb

of medial canthalligament. In thiscadaver dissection, theanterior limb of themedial canthal

ligament ( arrow ) is seen originating fromthe frontal process of the maxillary bone( pointer ). Forceps reflect the medial

aspect of the eyelid.

Eyelid Margin

The eyelid margins are divided by thelacrimal puncta into a medial lacrimal
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portion and a lateral palpebral portion. Atthe lid margin near the medial edge of thetarsus, the lacrimal papilla is seen as thefibrous ring surrounding the lacrimalpunctum. The medial lacrimal portion isrounded and without lashes. It carries thehorizontal portion of the canaliculi 1 to 2mm from the marginal surface. The upperpunctum is located at the junction of themedial 1/6 and the lateral 5/6 of eacheyelid. The lower punctum is located

slightly more laterally than the upperpunctum. The longer lower canaliculus (10mm) is directed into the lacrimal lakelateral to the plica semilunaris, whereasthe shorter superior canaliculus (8 mm) isdirected between the plica semilunaris andthe caruncle. The canaliculi are surroundedby thick pretarsal orbicularis oculi muscle

fibers. Posterior and horizontal contractionslightly inverts the medial eyelid margin.

The lateral portion of the lid margin has amore distinct or sharp border, which actslike a squeegee or windshield wiper toassist in moving the tear film toward thepunctum.

At the level of the tarsus, both the upperand lower eyelids consist of four anatomicstructures: the skin, the orbicularis oculimuscle, the tarsus, and the conjunctiva. Atthe eyelid margin, the eyelids are


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arbitrarily divided into an anterior lamella,consisting of the skin and orbicularis oculimuscle, and a posterior lamella, consistingof the tarsus and conjunctiva. Thisdistinction is only approximate becausefibrous elements from the tarsus extendanteriorly, hair follicles may extendposteriorly to imbed in the tarsus, and fineinterdigitations of the eyelid retractors maybe found. The skin of the anterior lamellacontains 100 to 120 cilia in the upper

eyelid and 50 to 75 in the lower eyelid.Each ciliary follicle also contains about twosebaceous glands (glands of Zeis). Nearthe cilia lie the sweat glands of the eyelid(Moll's glands), which empty into theadjacent follicles. A strip of pretarsalorbicularis oculi muscle, isolated from theremainder of the orbicularis muscle by the

eyelash follicles, is known as the ciliarybundle of Riolan or Riolan's muscle . Thisstrip of muscle deep within the eyelid skincreates an optical (Tyndall) effect knownas the gray line ( Fig.28 ). 46 The mucocutaneous junction at theeyelid margin is found posterior to the grayline. In the posterior lamella, the orifices of

the meibomian glands are seen exiting thetarsus. Division of the eyelid margin intoan anterior and posterior lamella haspractical implications when consideringeyelid malpositions and eyelid
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reconstruction.

Fig. 28. Lid margin.

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VASCULAR AND LYMPHATIC SUPPLY

TO THE EYELIDS ARTERIAL SYSTEM

The eyelids receive a rich and anastomoticsupply of blood from the internal carotidsystem (the deep or intraorbital system)and the external carotid system (thesuperficial or facial system).

Deep Arterial System

At the orbital apex, the ophthalmic artery a branch of the internal carotidartery lies lateral to the optic nerve. Asthe ophthalmic artery passes over the opticnerve and supramedially within the orbit,

four terminal branches pierce the orbitalseptum to supply the upper eyelid ( Fig.29 ). The four named branches are thelacrimal artery, the supraorbital artery, thesupratrochlear (frontal) artery, and the
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dorsal nasal artery.

Fig. 29. Deep arterialcirculation of theeyelid.

The lacrimal artery is the most temporalbranch and runs forward along the upperborder of the lateral rectus muscle with the

lacrimal nerve to supply blood to thelacrimal gland, the conjunctiva, and thelateral aspect of the upper eyelids . 47 Thelacrimal artery terminates as the lateral

palpebral artery .

The supraorbital artery arises from theophthalmic artery as it courses over the

optic nerve. The supraorbital artery travelsforward in the orbit between the levatormuscle and the periorbita of the orbitalroof. It accompanies the supraorbital nervethrough the supraorbital foramen to supplyblood to the upper eyelid, scalp, forehead,levator muscle, periorbita, and diploe of the frontal bone.

The supratrochlear (frontal)artery accompanies the supratrochlearnerve to supply arterial blood to the skin of the superior medial aspect of the orbit, the
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forehead, and the scalp.

The ophthalmic artery continues dorsallyand nasally within the orbit to terminate asthe fourth branch, which pierces the orbitalseptum and is known as the dorsal nasal artery . It supplies the skin of the bridge of the nose and the lacrimal sac. Itterminates as the medial palpebral artery .

The medial palpebral artery and the lateralpalpebral artery richly anastomose to formtwo well-defined arterial arcades in eachupper eyelid the marginal palpebralarcade and the peripheral palpebralarcade. The marginal palpebral arcade lieson the anterior tarsal surface 2 to 3 mmfrom the eyelid margin. The peripheral

palpebral arcade parallels superior to thesuperior border of the tarsus, posterior tothe levator aponeurosis, and anterior toMller's muscle ( Fig. 30 ). Medially vasculararcades have a serpiginous course throughthe medial fat pads of the upper eyelid,which may result in bleeding if incisedduring eyelid surgery. 30 The deepperipheral palpebral arcade supplies thesuperior conjunctival fornix andanastomoses with the anterior ciliaryarteries near the corneal scleral limbus.
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Fig. 30. Peripheralarcade of the upper lid.With the levator

reflected in theforceps, the peripheralarterial arcade ( thin

arrow ) is seen superior to the tarsus( thick arrow ).

In the lower eyelid, a well-developedmarginal arcade is found anterior to the

tarsus, 2 to 3 mm from the eyelid margin.The peripheral arcade is less welldeveloped. 14 ,48 These arcades arise in thelower lid, as in the upper lid, from themedial palpebral branches and from thelateral palpebral branches. They alsoreceive lateral anastomoses from thezygomatico-orbital branch of the superficial

temporal artery.Superficial Arterial System

The facial system ( Fig. 31 ) is derived fromthe external carotid artery and gives off three branches that eventually supply theeyelid the facial artery, the superficialtemporal artery, and the infraorbitalartery.
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Fig. 31. Superficial arterial supply.

The facial artery crosses over the mandibleanterior to the masseter muscle andcourses diagonally to the nasolabial fold. Itcourses between the levator labii superiorismuscle and levator alae nasi muscle tobecome the angular artery . The angularartery lies within the orbicularis oculimuscle 6 to 8 mm medial to the medialcanthus and 5 mm anterior to the lacrimalsac. The angular artery perforates theorbital septum above the medial canthalligament to anastomose with the dorsalnasal branch of the ophthalmic artery.

The superficial temporal artery is aterminal branch of the external carotid,which courses posterior to the angle of the

jaw and in front of the ear. It lies beneaththe skin but superficial to the fascia of thetemporalis muscle. 28 The superficial temporal artery gives off three branches tosupply the eyelids the frontal branch ,which courses upward across the temple tosupply the frontalis muscle of the foreheadand the orbicularis oculi muscleanastomosing with the lacrimal and
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supraorbital arteries; the zygomatico-orbital branch , which courses along theupper border of the zygoma supplying theupper eyelid and anterior orbit; andthe transverse facial branch , which runsbelow the zygoma to supply the malarregion and the lateral aspect of the lowereyelid to anastomoses with the lacrimaland infraorbital arteries.

The infraorbital artery enters the orbitthrough the pterygopalatine fossa andpasses through the posterior end of theinfraorbital fissure, through the infraorbitalcanal, and exits the orbit through theinfraorbital foramen to give a richcontribution of arterial blood to the lowereyelid. The infraorbital artery is a branch of the internal maxillary artery.

VENOUS SYSTEM

Like the arterial system, the venoussystem has both a superficial and a deepdistribution. The superficial systemconsists of the angular vein, the anteriorfacial vein, and the superficial temporalvein. Branches of the deep venous systeminvolving the eyelids consist of the superiorophthalmic vein and the inferiorophthalmic vein.

Superficial Venous System


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The angular vein is formed by the junctionof the superficial frontal vein from theforehead and the deep supraorbital veinfrom the orbit. The angular vein is locatedabout 8 mm medial to the inner canthusand lies lateral to its artery deep in theskin ( Fig. 32 ). Venous blood from theangular vein has a dual drainage:posteriorly into the deep venous system bythe superior ophthalmic vein orsuperficially and inferiorly into the anterior

facial vein . The anterior facial vein crossesthe mandible and joins the posterior facialvein to form the common facial vein, whichthen drains into the internal jugular vein.Superiorly and laterally, venous blood fromthe forehead, eyebrow, and eyelid drainfrom the supraorbital vein intothe superficial temporal vein , then pass in

front of the ear to drain into the external jugular vein. 14 ,28 , 49

Fig. 32. Superficial venoussystem.

Deep Venous System

The supraorbital vein drains the forehead,eyebrow, and upper eyelid and runs
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horizontally deep to the orbicularis oculimuscle to course medially into the frontal vein and then into the superior ophthalmic vein . The superior ophthalmic vein isformed at the supranasal aspect of theorbit by the union of the angular andsupraorbital veins. It travelsposteriolaterally into the orbit, penetratesthe muscle cone in the mid-orbit, andreceives venous drainage from the superiorvortex veins of the globe. It then leaves

the orbit near the annulus of Zinn by thesuperior orbital fissure to enter thecavernous sinus. When present,the inferior ophthalmic vein begins as aplexus near the anterior aspect of theorbital floor. It receives venous blood fromthe lower eyelid, lacrimal sac, inferiorrectus muscle, inferior oblique, and the

two inferior vortex veins. It coursesposteriorly to divide into two branches: asmaller branch to the pterygoid plexus bythe inferior orbital fissure and a largerbranch into the superior ophthalmic vein toenter the cavernous sinus. Occasionally, alarger branch may drain directly into thecavernous sinus.

Other branches of the deep orbital systeminclude the central retinal vein, theanterior ciliary veins, and the cavernoussinuses.


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LYMPHATIC SYSTEM TO THE EYELIDS

The lymphatic system of the eyelids hastwo divisions: a superficial system and adeep system . 14 ,49 The superficial systemdrains the skin and orbicularis oculimuscle, whereas the deep system drainsthe tarsi and the conjunctiva. Most of theupper eyelid,lateral third of the lowereyelid, and lateral canthus drain intothe preauricular and deep parotid nodes ( Fig. 33 ). They eventually emptyinto the deep cervical nodes near theinternal jugular vein. The medial portion of the upper eyelids, the medial canthus andthe medial two thirds of the lower lid andconjunctiva drain into the submandibular nodes by channels following the angularand facial veins. Lymph drainageeventually empties into the internal jugularvein.

Fig. 33. Facial lymphatic system.

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NERVE SUPPLY

a n a t o m i a p a l p e b r a l

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