Anatomy of orbit otolaryngologist's perspective

Abstract

A careful study of anatomy of orbit is very important to an ENT surgeon because of its proximity to the
para nasal sinuses. A comprehensive knowlege of orbital and peri orbital anatomy is necessary to
understand the various disorders of this region and in its surgical mangement. Current day
otolaryngologists venture into other unchartered territories like orbit, lacrimal sac etc. Anatomical
knowledge of this area will help otolaryngologists to avoid complications during surgical procedures
involving this area. This article attempts to explore this topic from otolaryngologist’s perspective.

Full text

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
1/16
Anatomy of Orbit
Otolaryngologist's perspective
February 9, 2013 · Rhinology
AcarefulstudyofanatomyoforbitisveryimportanttoanENTsurgeonbecauseofitsproximitytothe
paranasalsinuses.Acomprehensiveknowlegeoforbitalandperiorbitalanatomyisnecessaryto
understandthevariousdisordersofthisregionandinitssurgicalmangement.Currentday
otolaryngologistsventureintootheruncharteredterritorieslikeorbit,lacrimalsacetc.Anatomical
knowledgeofthisareawillhelpotolaryngologiststoavoidcomplicationsduringsurgicalprocedures
involvingthisarea.Thisarticleattemptstoexplorethistopicfromotolaryngologist’sperspective.
Introduction:
Orbitsupportstheeyeandensuresthatthisorganfunctionsinanoptimalmanner.Italsoprotects
thisvitalstructure.Theshapeoftheorbitresemblesafoursidedpyramidtobeginwithbutasone
goesposterioritbecomesthreesidedtowardstheapex.Thevolumeoftheorbitalcavityinanadultis
roughlyabout30cc.Therimoforbitinanadultmeasuresabout40mmhorizontallyand35mm
vertically.Themedialwallsoforbitareroughlyparallelandareabout25mmapartinanadult.The
lateralwallsoforbitanglesabout90degreesfromeachother.Thisisactuallyafixedcavitywithno
scopeforenlargement,henceasmallincreaseinocularpressurecanleadtodisastrous
consequences.
Osteology:
Sevenbonesjointogethertoformtheorbit .Theseinclude:
1.Frontalbone
2.Lacrimalbone
3.Zygoma
4.Maxilla
5.Ethmoid
6.Sphenoid
7.Palate
Theorbitalrimismoreorlessspiralwithitstwoendsoverlappingmediallyoneithersideoflacrimal
fossa.Theinferiororbitalrimisformedbythemaxillarybonemediallyandzygomaticbonelaterally.
Thezygomaticboneformsthelateralorbitalrim,whilethefrontalboneformsthesuperiororbitalrim.
Abstract
Anatomy of orbit
1
Author
ProfessorBalasubramanianThiagarajanBalasubramanianThiagarajan

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
2/16
Thesuperiorrimiscommonlyindentedbyasmallnotchknownasthesupraorbitalnotch.Thisnotch
isinvariablypresentatthejunctionofmedialandlateral1/3.Thesupraortbitalnerveandarterypass
throughthisnotchtoreachtheforehead.
Bonesconstitutingorbit
Themedialportionoftheorbitalrimisformedbythefrontalprocessofmaxillaandthemaxillary
portionofthefrontalbones.Adepressionknownasthelacrimalfossaisformedintheinferomedial
orbitalrim.Thisfossaisformedbythemaxillaryandlacrimalbones.Thislacrimalfossaisbounded
bytwoprojectionsofbonesi.e.theanteriorlacrimalcrestofmaxillaryboneandtheposteriorlacrimal
crestoflacrimalbone.Thisfossahousesthenasolacrimalsac.Thisfossaopensintothe
nasolacrimalcanalthroughwhichthenasolacrimalducttraverses.
Thenasolacrimalductis3–4mmindiameter,coursesinaninferolateralandslightlyposterior
directiontowardstheinferiorturbinateunderwhichitopensintotheinferiormeatus.Thisductis
roughly12mmlong.Allthewallsofthelacrimalductexceptitsmedialwallisformedbythemaxillary
bone.Themedialwallisformedbythelatealnasalwallinferiorlyandthedescendingprocessof
lacrimalbonesuperiorly.
Inthefrontalprocessofmaxillajustanteriortothelacrimalfossaafinegrooveknownasthesutura
longitudinalisimperfectaofWeber.Thissuturerunsparalleltotheanteriorlacrimalcrest.Small
branchesofinfraorbitalarterypassthroughthisgroovetosupplythenasalmucosa.Thepresenceof
thesevesselsshouldbeanticipatedinanylacrimalsacsurgerytoavoidunneccessarytroublesome
bleeding.
Medialwalloforbit:
Largestbonycomponentofmedialwallisthequadrangularshapedorbitalplateofethmoidbone.
Thisbonycomponentseparatesorbitfromthenasalcavity.Thisplateofbonearticulatessuperiorly
withthemedialedgeoforbitalplateoffrontalbone.Thesearticulatingbonystructureshavetwo
notches(anteriorandposteriorethmoidalnotches).Thesenotchesintheseboneswhencombined
formstheanteriorandposteriorethmoidalcanals.Thesecanalstransmittheethmoidalbranchesof
nasociliarynerve(branchofophthalmicdivisionoftrigeminalnerve)andbranchesofopthalmic
artery.Thesebranchesfromopthalmicartery(anteriorandposteriorethmoidalarteries)supplynasal

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
3/16
mucosaandduramateroffrontalbonearea.Thecranialopeningoftheseethmoidalcanalsare
relatedtotheanteriorandposteriorlimitsofcribriformplate.Theroofofthenasalcavityispartially
formedbythecribriformplateofethmoid.Thesecranialopeningsofethmoidalcanalsdivideanterior
skullbaseintofrontal,cribriform,andplanumareas.Ethmoidalcanalsdivideorbitintobulbar,
retrobulbarandapicalportions.Thisintricateknowledgeoforbitalanatomyhelpsduringadvanced
endoscopicskullbasesurgicalprocedures .
Themedialwalloftheorbitisformedfromanteriortoposteriorby:
1.frontalprocessofmaxilla
2.lacrimalbone
3.ethmoidbone
4.lesserwingofsphenoidbone
Thethinnestportionofthemedialwallisthelaminapapyraceawhichseparatestheethmoidal
sinusesfromtheorbit.Itisoneofthecomponentsofethmoidbone.Infectionsfromethmoidalsinus
caneasilybreachthispaperthinboneandaffecttheorbitalcontents.Themedialwalloftheorbitis
thickerposteriorwherethesphenoidboneispresentandanteriorlywheretheposteriorlacrimalcrest
ispresent.
Thefrontoethmoidalsuturelinemarkstheapproximatelevelofethmoidalsinusroof,henceany
dissestionabovethislinemayexposethecranialcavity.Theanteriorandposteriorethmoidal
foraminathroughwhichbranchesofophthalmicartery(anteriorandposteriorethmoidalarteries)and
branchesofnasociliarynervepassesarepresentinthissuture.Theanteriorethmoidalforamenis
locatedatadistanceof24mmfromtheanteriorlacrimalcrest,whiletheposteriorethmoidalforamen
islocatedatadistanceof36mmfromtheanteriorlacrimalcrest.
Averticalsuturethatrunsbetweentheanteriorandposteriorlacrimalcrestsistheanastomoticarea
betweenthemaxillaryandthelacrimalbone.Ifthissutureislocatedmoreanteriorlyitindicatesa
predominanceoflacrimalbone,whileamoreposteriorlyplacedsuturelineindicatesapredominance
ofmaxillaryboneintheanastomoticrelationship.Thelacrimalboneattheleveloflacrimalfossais
prettythin(106micrometer).Thisbonecanbeeasilypenetratedduringdacryocystorhinostomy
surgery.Ifthemaxillarycomponentispredominantitbecomesdifficulttoperformtheosteotomyin
thisareatoaccessthesacbecausethemaxillaryboneisprettythick.Hencelacrimalbone
predominancemakesiteasytoexposethesacduringdacryocystorhinostomy .
Appliedanatomyofmedialwalloforbit:
Thiswallisalignedparalleltotheanteroposterioraxisandisveryfragilebecauseofitsproximityto
anteriorethmoidalaircells.Disruptionofthiswallduetotraumacauseshypertelorism(Traumatic
Hypertelorism).Lateraldisplacementoffrontalprocessofmaxillawillcausetraumatictelecanthus
becausethemedialpalpebralligamentisattachedhere.Bothhypertelorismandtelecanthuscanbe
causedduetotrauma.
Contributionofethmoidbone:
Ethmoidboneformsthemedialboundaryoforbit.Itisseparatedfromobitalcontentsbyapaperthin
bone(Laminapapyracea).Thisbonecanbebreachedduetodiseasesinvolvingethmoidsorduring
nasalsurgeriesallowinginfectionstoreachtheorbitalcavity.Inferiorlyethmoidbonearticulateswith
theorbitalplateofmaxilla.Posteriorlytheethmoidbonearticulateswiththebodyofsphenoid
2
3

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
4/16
completingthemedialbonywalloforbitalcavity.
Sphenoidbone:
Sphenoidbonecontributestotheformationofbonyorbitbyitsgreaterandlesserwings.Thelesser
wingsofsphenoidarticulateswithorbitalplateoffrontalbonetoformtheroofoforbit.Thegreater
wingsofsphenoidarticulateslaterallywiththeorbitalplateofzygomaformingthelateralwallofbony
orbit.
Lateralwalloforbit:
Understandingthiswalloftheorbitisvitalfromthesurgeon’spointofview.Twocomponentsare
involvedintheformationofthiswall.Thegreaterwingofsphenoidfacestheorbitonitsexocranial
sideanditsendocranialsurfaceformstheanteriorlimitofmiddlecranialfossa.Thezygomaticbone
onthecontrarydoesnothavecerebralsurface/endocranialsurface.Itvirtuallyfacestheorbitwhile
itsoppositesurfacefromstheanteriorlimitofinfratemporalfossa.Thisanatomicalrelationship
provideslateralaccesstotheorbitwithoutresortingtocraniotomy.Inthelateralorbitalapproach,the
contentsoftheorbitcanbereachedjustbydisplacingthetemporalboneandperformingzygomatic
osteotomy.
Therecurrentmeningealbranchofmiddlemeningealarterymaybeseencoursingthrougha
forameninthesuturelinebetweenthefrontalandsphenoidbones.Thisarteryformsaanastomosis
betweentheexternalandinternalcarotidarterialsystems.Roughly4–5mmbehindthelateral
orbitalrimand1cminferiortothefrontozygomaticsutureisthelateraltubercleofWhitnall.The
followingstructuresgetsattachedtothistubercle:
1.Lateralcanthaltendon
2.Lateralrectuscheckligament
3.Suspensoryligamentoflowereyelid(Lockwoodsligament).
4.Orbitalseptum
5.Lacrimalglandfascia.
Lateralcanthaltendon:
Thepretarsalmusclesjoinlaterallytoformthelateralcanthaltendon.Thistendoninsertsintothe
periosteumofWhitnall’stubercleabout5mmbehindtheinfraorbitalrim.
Lateralrectuscheckligament:
Thisisafibrousmembranearisingfromthelateralrectusmuscleandgetsattachedtothezygomatic
tubercle,posterioraspectoflateralpalpebralligamentandthelateralconjunctivalfornix.
Beingmostproneforinjurythiswalloftheorbithappenstobethethickest.Itisverystrongatthe
orbitalmargin.Behindthisthickportionoflateralwallcomesthesomewhatthinnerportion,behind
thisthinportionthewallagainbecomesthick.Posteriormostportionofthislateralwallisthin(about1
mm)nearlytranslucent.
Thiswallisfurtherweakendbythepresenceofsuperiororbitalfissurebetweenlateralandsuperior
wallsoforbit.Thepresenceofinferiororbitalfissurebetweenlateralandinferiorwallsoforbitcreates
anotherareaofweakness.

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
5/16
Diagramshowinglateralwalloforbit:GW(Greaterwingofsphenoid)
Superiororbitalfissure:
Thisisalsoknownassphenoidalfissurebecauseitliesbetweenlesserandgreaterwingsof
sphenoid.Thisspaceisclosedlaterallybythefrontalbone.Thisfissureliesbetweenthelateralwall
androofoforbit.Atitsmedialenditisslightlywider.Atthispointitliesbelowtheopticforamen.This
fissuregraduallyreducesinsizeasitreachesitslateralextremity.Superiororbitalfissurehence
shouldbeconsideredtohaveanarrowlateralandawidemedialpart.Thisfissureisabout22mm
longandisthelargestcommunicationbetweentheorbitandthemiddlecranialfossa.Itstipis
situatedabout3040mmfromthefrontozygomaticsutureline.Itsmedialendisseparatedfromoptic
foramenbytheposteriorrootoflesserwingofsphenoid.Thisportionofsphenoidbonehasasmall
tubercleknownasinfraoptictubercle.TheannulusofZinnfromwhichalltheintraocularmuscles
originatespansthesuperiororbitalfissurebetweenitsmedialwideandlateralnarrowportions.
AnnulusofZinnsurroundstheopticnerveatitsentranceintotheorbit.
ThefollowingstructurespassthroughtheannulusofZinn:
1.Superiordivisionof3rdnerve
2.Nasociliarynerve
3.Sympatheticrootofcervicalganglion
4.Inferiordivisionof3rdnerve
5.6thnerve
6.Opthalmicvein(superioropthalmic)
Thisistheroughorderofstructurespassingthroughtheannulusfromabovedownwards.
Inferioropthalmicveinpassesbelowtheannulus.

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
6/16
Lockwood’sligament:
Thisligamentactsasahammocksupportingtheglobeinferiorly.Thisisactuallyadense
condensationofconnectivetissueengulfinginferiorrectusandinferiorobliquemusclesproviding
supporttotheundersurfaceoftheglobe.Thisligamentisattachedtofacialstructuresconnectedto
thelowerlid.DamagetoLockwood’sligamentcancauselowereyelidptosiswhichisseeninpatients

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
7/16
undergoingtotalmaxillectomy.
FigureshowingLockwood’sligamentactingasaHammockholdingtheglobe
Orbitalseptum:
Thisisalsoknownaspalpebralligament.Thismembranoussheetactsastheanteriorboundaryof
theorbit .Itextendsfromtheorbitalrimstotheeyelids.Withagethisseptummayweakencausing
prolapseoforbitalfatforwards.Blepharoplastyisusuallyperformedtocorrectthisanamoly.Orbital
septumhelpsindifferentiatingorbitalcellulitis(behindtheseptum)andperiorbitalcellulitis(infrontof
theseptum) .Thisstructureisusuallypenetratedbyvesselsandnervesthatpassfromtheorbitto
faceandscalp.
Thefrontalprocessofzygomaticboneandthezygomaticprocessoffrontalbonearethickandthey
protecttheglobefromlateraltrauma.Justbehindthisfacialbuttressareatheposteriorzygomatic
boneandtheorbitalplateofgreaterwingofsphenoidarethinnerthusmakingthezygomatico
sphenoidsutureaconvenientlandmarkforlateralorbitotomy.Thezygomaticofacialandzygomatico
temporalnervesandvesselspassthroughthelateralwalloftheorbittoreachthecheekand
temporalregions.Posteriorlythelateralwallthickensandmeetsthetemporalbonewhichformsthe
lateralwallofthecranialcavity.Whenlateralorbitotomyisbeingdoneonly12–13mmseparatethe
posterioraspectoflateralorbitotomytothatofthemiddlecranialfossa.Thisdistancecouldstillbe
shorterinfemales.
Foramenandfissuresoforbit:
Thefollowingarethevariousforaminaandfissuresoforbit:
1.Superiororbitalfissure(sphenoidalfissure)
2.Inferiororbitalfissure(sphenomaxillaryfissure)
3.Anteriorandposteriorethmoidalcanals
4.Opticcanal/foramen
Orbitshowingvariouscomponents
4
5

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
8/16
Inferiororbitalfissure:
Alsoknownassphenomaxillaryfissure.
Thissamecombinationofzygomaticboneandgreaterwingofsphenoidformstheposteriorborderof
infraorbitalfissure.Theanteriorborderisformedbyorbitalplateofmaxillaandtheposteromedial
partisformedbyorbitalprocessofpalatinebone.
Theinferiororbitalfissureliesbetweenthelateralorbitalwallandtheflooroftheorbit.Itisabout20
mmlong.Thisisalsoknownassphenomaxillaryfissure.Itisboundedanteriorlybythemaxillaand
theorbitalprocessofpalatinebone,posteriorlybythelowermarginoforbitalsurfaceofgreaterwing
ofsphenoid.Thisfissureisnarroweratitscenterwhencomparedtoitsextremities.Theactualwidth
ofthisfissureisdependentonthedevelopmentofmaxillarysinus.Thisfissureissomewhatwiderin
infantsandchildren.Thisfissureliesneartheopeningsofforamenrotundumandthesphenopalatine
foramen.
Thefollowingstructurespassthroughthisfissure:
1.Maxillarydivisionoftrigeminalnerve
2.Zygomaticnerve
3.Branchesfromthesphenopalatineganglion
4.Branchesofinferiorophthalmicveinleadingontopterygoidplexus.
Themaxillarydivisionoftrigeminalnerveandtheterminalbranchofinternalmaxillaryarteryenterthe
infraorbitalgrooveandcanaltobecometheinfraorbitalnerveandartery.Thesestructuresexit
throughtheinfraorbitalforamentosupplythelowereyelid,cheek,upperlipandupperanterior
gingiva.Theorbitcommunicateswithpterygopalatinefossathroughthemedialmostportionofthis
fissureandthroughthisintothenasalcavity.Laterallyinfraorbitalfissureisincontactwithtemporal
andinfratemporalfossa.Thislateralaspectofthefissureisfilledwithsmoothmuscleandfattissue
makingitasuitableplaceforbonecuts.
InlivingpersonsthisfissureisclosedbyperiorbitaltissueandMuller’smuscle.
Flooroftheorbit:
Thisareaisactuallyinterestingbecauseitcanbeinvolvedinpureblowoutfractureswithout
involvmentofzygoma.Itismoreorlesstriangularinshapewithroundedcorners.Itisnarrow

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
9/16
posteriorly.Thisisactuallynothorizontal,butslopesupwardsandmediallyatanangleof45°.Itends
astheanteriormarginofinferiororbitalfissure.Inthisareathisboneabruptlycurvesdownwards
towardstheinfratemporalfossaformingtheposteriorwallofmaxilla.
Componentsoftheflooroftheorbit:
1.Orbitalplateofmaxilla(largestcomponent)
2.Orbitalplateofzygomaticbone(anterolateralpart)
3.Orbitalprocessofpalatinebone(formsasmallportionbehindthemaxilla)
Theflooroftheorbitistraversedbyinferiororbitalfissure.Thisfissureinfactweakensthefloor.Most
ofblowoutfracturesoccurmedialtothisfissure.Fracturelinecancauseentrapmentofinfraorbital
nerveleadingontoanesthesiaofcheekareaofthatside.Infraorbitalcanalformedfromthisfissure
sinksanteriorlyandopensintotheinfraorbitalforamen.
Theroofoftheorbitslopesdownmedially.Infactthisslopecontinuesuptofrontoethmoidalsuture
toformtheroofoftheethmoidsinus.Thisisotherwiseknownasfoveaethmoidalis.
Theanatomicalrelationshipbetweentheanteriorethmoidalaircellsandthelacrimalfossashouldbe
borneinmindtoavoidconfusionbetweentheethmoidandnasalcavitiesduring
dacryocystorhinostomysurgery.
Ethmoidalforamen:
Theseforaminaliebetweentheroofandmedialwalloforbit.Theseforaminainvariablyliewithinthe
frontoethmoidalsuturelineorinthefrontalbone.Theseopeningsformcanalsknownasanteriorand
posteriorethmoidalcanals.Thesecanalsareformedbyfrontalbonetoagreatextentwithminor
contributionsfromethmoids.
Anteriorethmoidalcanal:
Thiscanalisdirectedbackwardsandlaterally.Thisforamenislocatedabout24mmfromtheanterior
lacrimalcrest.Theposteriorborderofthiscanalisnotwelldefinedandiscontinuouswithagroove
ontheorbitalplateofethmoid.Thiscanalopensintotheanteriorcranialfossaatthesideofcribriform
platetransmittinganteriorethmoidalnerveandartery.
Figureshowinganteriorethmoidalartery

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
10/16
Posteriorethmoidalcanal:
Thiscanallieposteriortoanteriorethmoidalcanal.Thisforamenislocated36mmfromtheanterior
lacrimalcrest.Ittransmitsposteriorethmoidalnerveandposteriorethmoidalartery.
Opticforamen:
Alsoknownasopticcanal.Itbeginsfromthemiddlecranialfossaandextendsuptotheapexofthe
orbit.Thisforamenisformedbytworootsofthelesserwingofsphenoid.Thisforamenisdirected
laterally,forwardsanddownwards.Thiscanalisfunnelshaped,themouthofthefunnelisitsanterior
opening.Thisforamenisovalinshapewiththeverticaldiameterbeingthegreatest.Itsintracranial
openingisflattendabovedownwards,whereasitsmiddleportioniscircularinnature.Itslateral
borderiswelldefinedandisformedbytheanteriorborderoftheposteriorrootoflesserwingof
sphenoid.Itsmedialborderislesswelldefined.Opticcanalisseparatedfromthemedialendof
superiororbitalfissurebyabarofbone.Thisbarofbonehasatuberclefortheattachmentof
annulustendinous.
Diagramshowingviewofskullafterremovalof
lateralwall
Opticnervecanaltransmits:
1.Opticnerve
2.Coveringsofopticnerveincludingduramater,arachnoidmaterandpiamater.
3.Opthalmicarteryliesbelowandlateraltothenerveembeddedintheduralsheath
Orbitalindex:
Thewidthoftheorbitislargerthanthatofitsheight.
Orbitalindexvariesamongvarioushumanraces.Goingbyorbitalindex3typesoforbitshavebeen
identified.
Orbitalindex=heightoftheorbit
_______________X100
Widthoftheorbit
Megaseme:Thisisaratherlargeorbitalindex.Heretheorbitalindexcalculatedusingtheformula
aboveismorethan89.Thisorbitistheclassicfeatureofyellowraces.

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
11/16
Mesoseme:Thisisintermediateorbitalindex.Heretheindexrangesbetween8389.Thisis
commonlyseeninEuropeanwhites.
Microseme:Thisisthesmallestorbitalindex.Thevaluehereislessthan83.Thisorbitistypically
seeninblackraces .Orbitalopeningisrectangular.
Orbitalmargin:
Thisismadeupofthreebones.
Frontal
Zygomatic
Maxilla
Superiororbtialmargin:
Thisisentirelyformedbyfrontalbone.Thisportionoffrontalboneisalsoknownasorbitalarch.This
marginissharpinlateral2/3androundedinmedialthird.Atthejunctionofthesetwoportionsabout
25mmfrommidlineissituatedthesupraorbitalnotch.Thisnotchtransmitssupraorbitalvesselsand
nerves.Thisnotchisconvertedintoaforamenduetoossificationoftheligamentwhichliesinferiorto
thisnotch.Thisnotchcaneasilybepalpatedintheliving.
Arnold’snotch:
Thisisrarelyseenmedialtosupraorbitalnotch.ThisnotchisalsoknownastheArnold’snotch.This
notchtransmitsthemedialbranchesofsupraorbitalvesselsandnerves.
Lateralorbtialmargin:
Thismarginisthemostexposedoneandisthestrongestoftheorbitalmargins.Itisformedbythe
zygomaticprocessoffrontalboneandzygomaticbone.Thelateralorbitalrimisrecessedto
accomodatelacrimalgland.Thisrecessmaybeinvolvedinsegmentalfratureinthisregion.The
narrowestandweakespartofthisrimisthefrontozygomaticsutureline.Separationofthissutureline
isacommonfeatureoftraumainthisregion.
Inferiororbtialmargin:
Thismarginisraisedsligthlyabovetheflooroftheorbit.Thismarginisformedbyzygomaticbone
andmaxillainequalproportions.Theinfraorbitalmarginisclearlydefinedatitslateralmarginandis
easilypalpable.Innerportionoftherimisroundedandisnoteasilypalpable.
Medialmargin:
Thismarginisformedbyanteriorlacrimalcrestpresentonthefrontalprocessofmaxillaandthe
posteriorlacrimalcrestonthelacrimalbone.Themedialmarginishencenotacontinuousridge.
Agechangesinorbit:
Anatomicalchangesinvolvingorbitdependsonthedevelopmentoffacialskeletonandthe
neighbouringparanasalsinuses.
Atbirththeorbitalmarginsaresharpandcompletelyossified.Thishelpsinprotectingtheeyesduring
thestressfuleventofparturition.Atabouttheageof7theorbitalmarginsbutforthesuperiormargin
becomefairlyroundedandlesssharp.Atthisagethesuperomedialandinferolateralanglesarewell
6

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
12/16
markedthanotherangles.Thiscausestheorbittobetriangular.
Infant’sorbitlookmorelaterallythanadults.
Orbitalfissuresarelargeinachildwhencomparedwiththatofadults.Thisisbecauseofthenarrow
orbtialsurfaceofgreaterwingofsphenoid.
Theorbitalindexishigherinachildwhencomparedtoadults.Theverticaldiameteristhesameas
thatofhorizontaldiameter.Asgrowthprogressesthetransversediameterincreasesmorethanthe
vertical..
Theinterorbitaldistanceisrathersmallinchildren.Thismimikssquint.
Theroofoftheorbitismuchlargerthantheflooratbirth.
Ininfantsopticcanalisnotacanal.Itisjustaforamen.Astheinfantgrowsthisforamenelongatesto
becometheopticcanal.
Theperiorbitaisthickerandstrongeratbirththaninadults.
Oldagechangesoccuringintheorbitareactuallyduetoboneabsorption.Theroofoftheorbitin
elderlypersonmayactuallycontainholeswhichcausesperiorbitatocomeintodirectcontactwith
dura.Partsoflacrimalbonetoocanbeabsorbedduetoageingprocess.
Softtissuesoforbit:
Orbitalseptumistheanteriorsofttissueboundaryoftheorbit.Itactsasaphysicalbarrieragainst
pathogens.Thisisathinmultilayeredfibroustissuederivedfromthemesodermallayerofeyelid.This
septumiscoveredanteriorlybythepreseptalorbicularisoculimuscle.
Periorbita:istheperiostealliningoforbitalwalls.Theperiorbitaisattachedtothesuturelines,
fissuresandforaminaoftheorbit.Posteriorlytheperiorbitaiscontinuouswiththeopticnervesheath.
Orbitalfat:Adiposetissuepresentintheorbithasacushioningeffectonthecontentsoforbit.
Theextraocularmusclesoforbitarisefromtheannulusofzinnandareresponsibleforthe
movementoftheglobe.Thesemusclesare:
lateralandmedialrectus
Superiorandinferiorrectus
Superiorandinferioroblique
Thefourrectimusclesarisefromtheannulusofzinn.Theannulusofzinnactuallyhastwotendons.
Thelowertendonofannulusofzinnisattachedtothemedialendofsuperiororbitalfissureenclosing
theopticforamen.Thistendongivesorigintopartsofmedialandlateralrecti.Italsogives
attachmentofentireinferiorrectusmuscle.Theuppertendonoftheannulusofzinnalsoknownas
tendonofLockwoodarisesfromthebodyofsphenoid.Thistendongivesorigintopartofmedialand
lateralrectiandallofthesuperiorrectusmuscle.Theattachmentsofsuperiorandmedialrecti
musclesareclosetotheduralsheathofopticnerve.Thisfactexplainsthepaincausedduring
extremesofeyemovementsinretrobulbarneuritis.
Medialrectus:
Thisisthelargestoftheocularmuscles.Itisalsostrongerthanthelateralrectus.Fromitsoriginfrom

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
13/16
theannulusofZinnitinsertsintotheglobemedially5.5mmfromthelimbus.Itsbloodsupplyis
derivedfromtheinferiormuscularbranchofopthalmicarteryandanteriorciliaryarteries.Itderivesits
motorinnervationfromthethirdcranialnerveonitslateralsurfaceatthejunctionofmiddleand
posteriorthirds.Itisapureadductor.
Inferiorrectus:
Thisistheshortestofallrectimuscles.Fromitsoriginintheannulusofzinnclosetoopticforamenit
insertsintotheglobeinferiorly6.5mmfromthelimbus.Itisalsoattachedtothelowereyelidviaits
facialexpansion.Itderivesitsbloodsupplyfromtheinferiormuscularbranchofophthalmicartery,
infraorbitalarteryandanteriorciliaryvessels.Itderivesitsmotorinnervationfromtheinferiordivision
ofthirdnerveonitsupperaspectatthejunctionofitsmiddleandposteriorthirds.Itmovestheeye
downwardsandmedially/rotatesitlaterally(extorsion).Itcanalsodepressthelowereyelidbyits
facialslingwhichinsertsintoit.Itsprincipalactionisdepressionofoutturnedeye.Infactitistheonly
depressoroftheabductedeye.
Lateralrectus:
Fromitsoriginfromtheannulusofzinnitisinsertedlaterallyintotheglobeabout6.9mmfromthe
limbus.Itreceivesbloodsupplyfromlacrimalartery.Itistheonlyocularmusclewithsinglesourceof
bloodsupply.Itisinnervatedbythe6thcranialnerveinitsmedialaspect.Itisapureabductor
makingtheeyetolookdirectlylaterally.
Superiorrectusmuscle:
Arisingfromthesuperiorportionofannulusofzinnitisinsertedintothebulbsuperiorlyabout7.7
mmfromthelimbus.Itreceivesitsbloodsupplyfromthesuperiormuscularbranchofophthalmic
arteryandanteriorciliaryarteries.Itisinnervatedbysuperiordivisionofoculomotornerve.Thisnerve
enterstheundersurfaceofthemuscleatthejunctionofmiddleandposteriorthirds.Ithelpsin
upwardsandmedialrotationoftheeyeandisalsocapableofintortingtheeyeball.
Superiorobliquemuscle:
Thisisthelongestandthinnestofocularmuscles.Itarisesmedialtotheopticforamenandgets
insertedintothetrochleaontheorbitalrim(ontheanterosuperiorportionofthemedialwalloforbit).
Itstendongetsinsertedontothetemporalaspectoftheeyebehindtheequator.Thesuperior
muscularbranchofopthalmicarteryandciliaryarteriessupplythismuscle.Itmovestheeye
downwardsandlaterally.Itistheonlymusclethatcandepresstheeyeinadductedposition.Itis
suppliedbythe4thnerve.
Inferioroblique:
Thisistheonlyextrinsicmuscletotakeoriginfromthefrontoftheorbit.Thismusclearisesfromthe
orbitalfloorinadepressionneartheorbitalrim.Someofitsfibresmayalsoarisefromthefascia
coveringlacrimalsac.Itisinsertedintotheposteriorinferiortemporalquadrantatthelevelofmacula.
Itderivesitsbloodsupplyfromtheinferiorbranchofophthalmicarteryandinfraorbitalartery.Itis
innervatedbytheinferiordivisionofoculomotornerve.Thisnerveentersthemusclefromitsupper
surface.Thismusclehelpstheeyetolookupwardsandlaterallyandinextorsionoforbit.Thisisthe
onlymusclethatelevatestheeyeintheadductedposition.
Levatorpalpebraesuperioris:
Thisstriatedmuscleelevatestheeyelid.Thismusclearisesfromtheundersurfaceoflesserwingof

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
14/16
sphenoidjustaboveandinfrontofopticforamen,andusuallyitisblendedwiththeoriginofsuperior
rectusmuscle.Fromthisattachmentthisribbonlikemusclepassesforwardsbelowtheroofontopof
thesuperiorrectusmuscle.Itgetsinsertedintotheskinoftheuppereyelid,anduppertarsalplate.It
receivesitsnervesupplyfromthesuperiordivisonof3rdcranialnerve.Thismusclebyitselevating
actionraisestheuppereyelid,thusuncoversthecorneaandportionsofsclera.Theactionofthis
muscleisantogonizedbyorbicularisoculimuscleinneravatedbyfacialnerve.
Muller’smuscle:
Thissmoothmuscleactsasaneyelidelevator.Itarisesfromtheinferioraspectoflevatorpalpebrae.
Thismuscleisinsertedintotheupperedgeoftarsalplate.Itisinnervatedbysympatheticfibers.The
actionofthismuscleaccountsforthepresenceofupperlidelevationinpatientswith3rdcranialnerve
palsy.
Thelacrimalsystem:
Themainlacrimalglandislocatedinthesuperotemporalportionoforbit.Itliesintheshallowlacrimal
fossaofthefrontalbone.Theglandiscomposedofnumeroussecretoryunitsknownasaciniwhich
progressivelydrainintosmallandlargerducts.Theglandmeasures20mmby12mm.Afibrous
bandincompletelydevidesthelacrimalglandintotwolobesi.e.posteriorlargerorbitallobeanda
smalleranteriorpalpebrallobe.2–6ductsfromtheorbitallobepassthroughthepalpebrallobe
joiningwiththeductsfromthepalpebrallobetoform6–12tubulestoemptyintothesuperiolateral
conjunctiva.Hencedamagetothepalpebrallobemayblockdrainagefromtheentiregland.About20
–40accessorylacrimalglandsofKrausearelocatedinthesuperiorconjuctivalfornix,abouthalfthis
numberislocatedoverthelowerfornix.
Thelacrimalglandisinnervatedbybranchesfrom5thand7thcranialnerves,sympatheticsupplyto
lacrimalglandisviathenervesfromthesuperiorcervicalganglion.Theparasympatheticfibersare
suppliedviathe6thnerve.Sensorysupplyisviathebranchesoftrigeminalnerve.
Diagramillustratingrolesplayedbyvariousmuscles
inocularmovement
Thelacrimalexcretorysystembeginsata0.3mmatthemedialendofeacheyelidsknownasthe
punctum.Thesepunctaaredirectedposteriorly.Thepunctalopeningwidensintoampulla,whichis
perpendiculartotheeyelidmargin.Theampullamakesasharpturntodrainintothecanaliculi.The
canaliculimeasures0.5–1mmindiameterandcoursesparalleltothelidmargins.Thesuperior
canaliculusis8mmlongandtheinferiorcanaliculusis10mmlong.Inmajorityofindividualsthe
superiorandinferiorcanaliculimergeintoacommoncanaliculibeforedrainingintonasolacrimalsac.
Theopeningofcommoncanaliculiintothenasolacrimalsacisknownasthecommoninternal

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
15/16
punctum.Thereisavalveatthejunctionofcommoncanaliculusandlacrimalsacatthecommon
internalpunctumlevel.ThisisknownastheRosenmullervalve.Anothervalveknownasthevalveof
Hasnerisfoundatthelowerendofthenasolacrimalductatthelevelofinferiormeatusofnose.
IfthisHasner’svalveisimperforateinnewborninfantsitcausescongenitalnasolacrimalobstruction.
Thelacrimalsacresidesinthelacrimalfossa.Itmeasuresabout12–15mmvertically,and4–8mm
anteroposteriorly.
Diagramshowinglacrimalapparatus
Locationoflacrimalsac:
Agoodintranasallandmarkforthelocationoflacrimalsacistheanteriorportionofmiddleturbinate,
thesacliesjustlateraltoit.Thelacrimalfossaisboundedbytheanteriorlacrimalcrest,which
consistsofthefrontalprocessofthemaxillarybone.Theposteriorlacrimalcrestismadeupofthe
lacrimalboneitself.
Figureshowingintranasallandmarkoflacrimalsac
1. DoxanasMT,AndersonRL.ClinicalOrbitalAnatomy.Baltimore:Williams&Wilkins;1984.
2. C.Martins,A.Yasuda,A.Campero,A.J.Ulm,N.Tanriover,andA.L.RhotonJr.,“Microsurgical
anatomyoftheduralarteries,”OperativeNeurosurgery,vol.56,no.2,pp.1–41,2005.
3. http://drtbalu.co.in/orbit.html
4. MahmoodF.Mafee;GaldinoE.Valvassori;MinervaBecker(10November2004).Imagingofthe
headandneck.Thieme.pp.200–.ISBN9781588900098.Retrieved16June2010.
5. Cellulitis,Orbital:eMedicineOphthalmology".Retrieved20100616.
References

2/8/13
Anatomy of Orbit – ENT SCHOLAR
entscholar.com/?articles=anatomy-of-orbit
16/16
6. NovitM.Facial,upperfacial,andorbitalindexinBatak,Klaten,andFloresstudentsofJember
UniversityDentJ.(Maj.Ked.Gigi).2006;39(3):116119