Orbital and Ocular AnatomyOrbital and Ocular Anatomy

Abdulrahman Al-Muammar, MD, FRCSC King Saud University

Periorbital SinusesPeriorbital Sinuses

The eyes lie within two bony The eyes lie within two bony orbits, located on either side of orbits, located on either side of the root of the nose. the root of the nose. They border the nasal cavity They border the nasal cavity anteriorly and the ethmoidal air anteriorly and the ethmoidal air cells and the sphenoid sinus cells and the sphenoid sinus posteriorly. posteriorly. The lateral walls border the The lateral walls border the middle cranial, temporal, and middle cranial, temporal, and pterygopalatine fossae. pterygopalatine fossae. Superior to the orbit are the Superior to the orbit are the anterior cranial fossa and the anterior cranial fossa and the frontal and supraorbital sinus. frontal and supraorbital sinus. The maxillary sinus and the The maxillary sinus and the palatine air cells are located palatine air cells are located inferiorly.inferiorly.

Orbital VolumeOrbital Volume

The volume of each adult orbit The volume of each adult orbit is slightly less than 30 cc is slightly less than 30 cc The orbital entrance averages The orbital entrance averages about 35 mm in height and 45 about 35 mm in height and 45 mm in width. The maximum mm in width. The maximum width is about 1 cm (behind the width is about 1 cm (behind the anterior orbital margin)anterior orbital margin)In adults, the depth of the orbit In adults, the depth of the orbit varies from 40 to 45 mm from varies from 40 to 45 mm from the orbital entrance to the orbital the orbital entrance to the orbital apexapexBoth race and sex affect each of Both race and sex affect each of these measurements.these measurements.

Bony OrbitBony Orbit

Seven bones make Seven bones make up the bony orbit:up the bony orbit:

FrontalFrontal

ZygomaticZygomatic

MaxillaryMaxillary

EthmoidalEthmoidal

SphenoidSphenoid

LacrimalLacrimal

PalatinePalatine

Orbital RoofOrbital Roof

The orbital roof The orbital roof formed from both formed from both the orbital plate of the orbital plate of the frontal bone and the frontal bone and the lesser wing of the lesser wing of the sphenoid bone.the sphenoid bone.

Lacrimal glandLacrimal gland

Fovea trochlearisFovea trochlearis

Medial Orbital WallMedial Orbital Wall

Then medial wall of the Then medial wall of the orbit is formed from four orbit is formed from four bones:bones:

Frontal process of the Frontal process of the maxillarymaxillaryLacrimalLacrimalOrbital plate of the Orbital plate of the ethmoidalethmoidalLesser wing of the Lesser wing of the sphenoidsphenoid

Lacrimal fossaLacrimal fossaLamina papyraceaLamina papyracea

Orbital FloorOrbital Floor

The floor of the orbit The floor of the orbit is formed from three is formed from three bones:bones:

MaxillaryMaxillaryPalatinePalatineOrbital plate of the Orbital plate of the zygomaticzygomatic

Infraorbital grooveInfraorbital grooveInferior oblique Inferior oblique musclemuscle

Lateral Orbital WallLateral Orbital Wall

Formed from two Formed from two bones:bones:

ZygomaticZygomaticGreater wing of the Greater wing of the sphenoidsphenoid

Thickest and Thickest and strongeststrongestLateral orbital Lateral orbital tubercle (Whitnall’s tubercle (Whitnall’s tubercle)tubercle)

Orbital ForaminaOrbital Foramina

The optic foramenThe optic foramenThe supraorbital foramen, or The supraorbital foramen, or notchnotchThe anterior ethmoidal The anterior ethmoidal foramenforamenThe posterior ethmoidal The posterior ethmoidal foramenforamenThe zygomatic foramenThe zygomatic foramenNasolacrimal ductNasolacrimal ductInfraorbital canalInfraorbital canalSuperior orbital fissureSuperior orbital fissureInferior orbital fissureInferior orbital fissure

Extraocular MusclesExtraocular Muscles

The four recti and The four recti and two oblique musclestwo oblique muscles

All are supplied by All are supplied by oculomotor nerve III oculomotor nerve III except superior except superior oblique (Trochlear oblique (Trochlear N) and lateral rectus N) and lateral rectus (Abducens)(Abducens)

Optic nerveOptic nerve

The optic nerve The optic nerve consists of more consists of more than 1 million axons than 1 million axons that originate in the that originate in the ganglion cell layer of ganglion cell layer of the retina and the retina and extend toward the extend toward the occipital cortexoccipital cortex

Optic NerveOptic Nerve

The optic nerve may be divided The optic nerve may be divided into the following topographic into the following topographic areas:areas:

Intraocular portion of the optic Intraocular portion of the optic nerve: optic disc, or nerve nerve: optic disc, or nerve head; prelaminar; and laminar head; prelaminar; and laminar portionsportions

Intraorbital portion (located Intraorbital portion (located within the muscle cone)within the muscle cone)

Intracanalicular portion (located Intracanalicular portion (located within the optic canal)within the optic canal)

Intracranial portion (ending in Intracranial portion (ending in the optic chiasm)the optic chiasm)

Optic ChiasmOptic Chiasm

The chiasm measures The chiasm measures approximately 12 mm wide, approximately 12 mm wide, 8 mm long in the 8 mm long in the anteroposterior direction, anteroposterior direction, and 4 mm thick. The exact and 4 mm thick. The exact location of the chiasm with location of the chiasm with respect to the sella is respect to the sella is variable. Most of the time it variable. Most of the time it is directly superior is directly superior Within the chiasm, the fibers Within the chiasm, the fibers coming from the nasal retina coming from the nasal retina (approximately 53% of total (approximately 53% of total fibers) cross to the opposite fibers) cross to the opposite side to join the side to join the corresponding contralateral corresponding contralateral fibers fibers

Optic TractOptic Tract

Each optic tract Each optic tract contains ipsilateral contains ipsilateral temporal and temporal and contralateral nasal contralateral nasal fibers from the optic fibers from the optic nerves . Fibers (both nerves . Fibers (both crossed and uncrossed) crossed and uncrossed) from the upper retinal from the upper retinal projections travel projections travel medially in the optic medially in the optic tract; lower projections tract; lower projections move laterally. move laterally.

Lateral geniculate bodyLateral geniculate body

The lateral geniculate body, The lateral geniculate body, or nucleus, is the synaptic or nucleus, is the synaptic zone for the higher visual zone for the higher visual projectionsprojectionsIt has six alternating layers It has six alternating layers of gray and white matter. of gray and white matter. Layers 1, 4, and 6 of the Layers 1, 4, and 6 of the lateral geniculate body lateral geniculate body contain axons from the contain axons from the contralateral optic nerve. contralateral optic nerve. Layers 2, 3, and 5 arise from Layers 2, 3, and 5 arise from the ipsilateral optic nervethe ipsilateral optic nerve

Optic radiationsOptic radiations

The optic radiations connect The optic radiations connect the lateral geniculate body the lateral geniculate body with the cortex of the with the cortex of the occipital lobeoccipital lobeThe fibers of the optic The fibers of the optic radiations leave the lateral radiations leave the lateral geniculate body and run geniculate body and run around the temporal horn of around the temporal horn of the lateral ventricle, the lateral ventricle, approaching the anterior tip approaching the anterior tip of the temporal lobe (the so-of the temporal lobe (the so-called loop of Meyer)called loop of Meyer)

Visual cortexVisual cortex

The visual cortex, the thinnest The visual cortex, the thinnest area of the human cerebral area of the human cerebral cortexcortexMacular function is extremely Macular function is extremely well represented in the visual well represented in the visual cortex and occupies the most cortex and occupies the most posterior position at the tip of posterior position at the tip of the occipital lobe the occipital lobe The posterior cerebral artery, a The posterior cerebral artery, a branch of the basilar artery, branch of the basilar artery, supplies the visual cortex almost supplies the visual cortex almost exclusively. The blood supply to exclusively. The blood supply to the occipital lobe does show the occipital lobe does show anatomical variation, however, anatomical variation, however, with the middle cerebral artery with the middle cerebral artery making a contribution in some making a contribution in some persons.persons.

Cranial Nerve III (Oculomotor)Cranial Nerve III (Oculomotor)

It supplies all the extraocular muscles It supplies all the extraocular muscles except the superior oblique and the except the superior oblique and the lateral rectus lateral rectus

It also carries cholinergic innervation to It also carries cholinergic innervation to the pupillary sphincter and the ciliary the pupillary sphincter and the ciliary musclemuscle

Cranial Nerve IIICranial Nerve III

The CN III nucleus consists of several The CN III nucleus consists of several distinct, large motor cell subnuclei, each distinct, large motor cell subnuclei, each of which subserves the extraocular of which subserves the extraocular muscle it innervates muscle it innervates

The Edinger-Westphal nucleus provides The Edinger-Westphal nucleus provides the parasympathetic preganglionic the parasympathetic preganglionic efferent innervation to the ciliary muscle efferent innervation to the ciliary muscle and pupillary sphincterand pupillary sphincter

Cranial Nerve IIICranial Nerve III

CN III usually divides into CN III usually divides into superior and inferior superior and inferior divisions after passing divisions after passing through the annulus of Zinn through the annulus of Zinn in the orbitin the orbitThe superior division of CN The superior division of CN III innervates the superior III innervates the superior rectus and levator palpebrae rectus and levator palpebrae muscles. The larger inferior muscles. The larger inferior division splits into three division splits into three branches to supply the branches to supply the medial and inferior rectus medial and inferior rectus muscles and the inferior muscles and the inferior oblique.oblique.

Cranial Nerve IIICranial Nerve III

The parasympathetic The parasympathetic fibers wind around the fibers wind around the periphery of the nerveperiphery of the nerveEnter the inferior Enter the inferior division, and course division, and course through the branch that through the branch that supplies the inferior supplies the inferior oblique muscle. They oblique muscle. They join the ciliary ganglionjoin the ciliary ganglionThey synapse with the They synapse with the postganglionic fibers, postganglionic fibers, which emerge as many which emerge as many short ciliary nervesshort ciliary nerves

Cranial Nerve IV (Trochlear)Cranial Nerve IV (Trochlear)

Cranial nerve IV has the Cranial nerve IV has the longest intracranial courselongest intracranial courseThe CN IV the only cranial The CN IV the only cranial nerve that is completely nerve that is completely decussated and the only decussated and the only motor nerve to exit dorsally motor nerve to exit dorsally from the nervous system. from the nervous system. CN IV enters the orbit CN IV enters the orbit through the superior orbital through the superior orbital fissure outside the annulus fissure outside the annulus of Zinn and runs superiorly of Zinn and runs superiorly to innervate the superior to innervate the superior oblique muscleoblique muscle

Cranial Nerve V (Trigeminal)Cranial Nerve V (Trigeminal)

The largest cranial nerveThe largest cranial nerve

Possesses both sensory and motor divisions Possesses both sensory and motor divisions The sensory portion subserves the greater The sensory portion subserves the greater part of the scalp, forehead, face, eyelids, eye, part of the scalp, forehead, face, eyelids, eye, lacrimal gland, extraocular muscles, ear, dura lacrimal gland, extraocular muscles, ear, dura mater, and tonguemater, and tongue

The motor portion innervates the muscles of The motor portion innervates the muscles of mastication through branches of the mastication through branches of the mandibular divisionmandibular division

Divisions of Cranial Nerve VDivisions of Cranial Nerve V

Ophthalmic Ophthalmic FrontalFrontal

LacrimalLacrimal

NasociliaryNasociliary

MaxillaryMaxillary

MandibularMandibular

Cranial Nerve VI (Abducens)Cranial Nerve VI (Abducens)

The nucleus of cranial nerve VI is situated in The nucleus of cranial nerve VI is situated in the floor of the fourth ventricle, beneath the the floor of the fourth ventricle, beneath the facial colliculus, in the caudal ponsfacial colliculus, in the caudal pons

CN VI runs below and lateral to the carotid CN VI runs below and lateral to the carotid artery and may transiently carry sympathetic artery and may transiently carry sympathetic fibers from the carotid plexusfibers from the carotid plexus

It passes through the superior orbital fissure It passes through the superior orbital fissure within the annulus of Zinn and innervates the within the annulus of Zinn and innervates the lateral rectus muscle on its ocular surfacelateral rectus muscle on its ocular surface

Arterial systemArterial system

Internal carotid artery

Ophthalmic artery

Central retinal AShort post ciliary ALong post ciliary AAnterior ciliary A

Lacrimal ASuperior muscular AInferior muscular APosterior ethmoidal AAnterior ethmoidal ASupraorbital ASupratrochlear A

Venous systemVenous system

Central retinal VSuperior vortex VSuperior episcleral plexus

Inferior vortex VInferior episcleral plexus

Pterygoid plexus

Superior ophthalmic V

Cavernous sinus

Jugular v

The EyeThe Eye

The adult human The adult human eye averages 24 eye averages 24 mm in diametermm in diameter

The eye reaches The eye reaches maximum size maximum size before puberty. The before puberty. The transverse vertical transverse vertical diameter is less diameter is less variable.variable.

CorneaCornea

The cornea occupies the The cornea occupies the center of the anterior pole of center of the anterior pole of the globe. In the adult, it the globe. In the adult, it measures about 12 mm in measures about 12 mm in the horizontal meridian and the horizontal meridian and about 11 mm in the verticalabout 11 mm in the verticalThe cornea is transparent The cornea is transparent and form a positive lens of and form a positive lens of about 40 D and constitute about 40 D and constitute the main refractive element the main refractive element of the eyeof the eye

CorneaCornea

EpitheliumEpithelium

Bowman’s layerBowman’s layer

StromaStroma

Descemet’s Descemet’s membranemembrane

EndotheliumEndothelium

ScleraSclera

Sclera is opaque Sclera is opaque and whiteand whiteThe sclera covers The sclera covers the posterior four the posterior four fifths of the surface fifths of the surface of the globe, with an of the globe, with an anterior opening for anterior opening for the cornea and a the cornea and a posterior opening for posterior opening for the optic nervethe optic nerve

LimbusLimbus

Transition zone Transition zone between the between the peripheral cornea peripheral cornea and the anterior and the anterior sclerasclera

ConjunctivaConjunctiva

Mucous membrane with Mucous membrane with non keratinized non keratinized squamous epithelium squamous epithelium and goblet cellsand goblet cellsThin, richy vascularized Thin, richy vascularized substantia propriasubstantia propriaCan be divided into Can be divided into three geographic zones:three geographic zones:

PalpebralPalpebralFornicealFornicealBulbarBulbar

Anterior chamberAnterior chamber

The anterior chamber is The anterior chamber is bordered anteriorly by bordered anteriorly by the cornea and the cornea and posteriorly by the iris posteriorly by the iris diaphragm and the pupildiaphragm and the pupilThe depth of the The depth of the anterior chamber variesanterior chamber variesThe anterior chamber is The anterior chamber is filled with aqueous filled with aqueous humor, which is humor, which is produced by the ciliary produced by the ciliary epitheliumepithelium

Anterior chamberAnterior chamber

The fluid passes through the pupil The fluid passes through the pupil aperture and drains chiefly by the aperture and drains chiefly by the conventional pathway through the conventional pathway through the trabecular meshworktrabecular meshworkThe anterior chamber angle, which The anterior chamber angle, which lies at the junction of the cornea and lies at the junction of the cornea and the iris, consists of the following the iris, consists of the following structures :structures :

Schwalbe's lineSchwalbe's line

Schlemm's canal and the trabecular Schlemm's canal and the trabecular meshworkmeshwork

Scleral spurScleral spur

Anterior border of the ciliary body Anterior border of the ciliary body

LensLens

The lens is a biconvex The lens is a biconvex structure located directly structure located directly behind the posterior behind the posterior chamber and pupil chamber and pupil It is the lesser of the two It is the lesser of the two refractive elements in the refractive elements in the dioptric systemdioptric system The equatorial diameter in The equatorial diameter in adult is about 9-10 mmadult is about 9-10 mm The anteroposterior width of The anteroposterior width of the lens is about 6 mm the lens is about 6 mm The lens has certain unusual The lens has certain unusual features. It lacks innervation features. It lacks innervation and is avascular. and is avascular.

Uveal TractUveal Tract

The uveal tract is the The uveal tract is the main vascular main vascular compartment of the compartment of the eye. It consists of three eye. It consists of three parts:parts:

IrisIris

Ciliary body (located in Ciliary body (located in the anterior uvea)the anterior uvea)

Choroid (located in the Choroid (located in the posterior uvea)posterior uvea)

IrisIris

Ciliary BodyCiliary Body

The ciliary body, which The ciliary body, which is triangular in cross is triangular in cross section. The apex of the section. The apex of the ciliary body is directed ciliary body is directed posteriorly toward the posteriorly toward the ora serrata. Its base ora serrata. Its base gives rise to the iris. gives rise to the iris. The only attachment of The only attachment of the ciliary body to the the ciliary body to the sclera is at its base, via sclera is at its base, via its longitudinal muscle its longitudinal muscle fibers, where they insert fibers, where they insert into the scleral spur.into the scleral spur.

Ciliary bodyCiliary body

The ciliary body has The ciliary body has three principal three principal functions:functions:

aqueous humor aqueous humor formation and lens formation and lens accommodationaccommodationIt also plays a role in It also plays a role in the trabecular and the trabecular and uveoscleral outflow uveoscleral outflow of aqueous humorof aqueous humorAccommodationAccommodation

ChoroidChoroid

The choroid, the posterior The choroid, the posterior portion of the uveal tract, portion of the uveal tract, nourishes the outer portion of nourishes the outer portion of the retina. It averages 0.25 mm the retina. It averages 0.25 mm in thickness and consists of in thickness and consists of three layers of vessels:three layers of vessels:

The choriocapillaris, the The choriocapillaris, the innermost layerinnermost layer

A middle layer of small vesselsA middle layer of small vessels

An outer layer of large vesselsAn outer layer of large vessels

RetinaRetina

The fundus is the part of the The fundus is the part of the eye that is visible on eye that is visible on ophthalmoscopy, including ophthalmoscopy, including the retina and its vessels the retina and its vessels and the optic nerve head (or and the optic nerve head (or optic disc)optic disc)The macula, 5–6 mm in The macula, 5–6 mm in diameter, lies between the diameter, lies between the temporal vascular arcades. temporal vascular arcades. At the macula's center lies At the macula's center lies the fovea, rich in cones and the fovea, rich in cones and responsible for color vision responsible for color vision and the highest visual acuityand the highest visual acuity

VitreousVitreous

The vitreous cavity occupies four The vitreous cavity occupies four fifths of the volume of the globefifths of the volume of the globeThe transparent vitreous humor is The transparent vitreous humor is important to the metabolism of the important to the metabolism of the intraocular tissues because it intraocular tissues because it provides a route for metabolites provides a route for metabolites used by the lens, ciliary body, and used by the lens, ciliary body, and retina retina Its volume is close to 4.0 ml Its volume is close to 4.0 ml Although it has a gel-like structure, Although it has a gel-like structure, the vitreous is 99% waterthe vitreous is 99% waterIts viscosity is approximately twice Its viscosity is approximately twice that of water, mainly because of the that of water, mainly because of the presence of the presence of the mucopolysaccharide hyaluronic acidmucopolysaccharide hyaluronic acid

Ocular EmbryologyOcular Embryology

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