Orbital Cavity Anatomy PDF

Orbital cavity (contents & boundaries) By Dr. Maher Finjan  Bony Orbit Bony orbit has the shape of 4-sided pyramid, narrow behind and wide infront, the base of which is the orbital opening on the face where is its apex lies at the medial end of superior orbital fissure. Contains: Eye...

Orbital cavity (contents & boundaries) By Dr. Maher Finjan  Bony Orbit Bony orbit has the shape of 4-sided pyramid, narrow behind and wide infront, the base of which is the orbital opening on the face where is its apex lies at the medial end of superior orbital fissure. Contains: Eyeball, Extra-ocular muscles, Nerves and vessels, Lacrimal gland, and Fascia and fat  Margins of Bony Orbit The orbital opening is quadrangular in shape and has upper, lower, medial, and lateral margins. Orbital margins Is formed by: 1-frontal bone 2-maxillary bone 3-zygomatic bone.  Walls of bony orbit Medial wall: the medial wall of two orbits are approximately parallel to each other, each medial wall is formed from front to back by: 1-frontal process of maxilla. 2-lacrimal bone. 3-orbital plate of ethmoid. Features of medial wall: 1-anteriorly: lacrimal fossa for lacrimal sac. 2-lacrimal groove leads downwards to nasolacrimal canal which communicates with inferior meatus of nose. 3-at the junction of medial wall and roof of orbit lies anterior and posterior ethmoidal foramina (transmit anterior and posterior ethmoidal vessels and nerves), these foramina lead into canals connect orbit with anterior cranial fossa Lateral wall: the lateral wall of each orbits lie at right angles to each other. It forms two bones: 1-mainly formed by greater wing of sphenoid, which separate the orbit from middle cranial fossa. 2-it is completed infront by frontal process of zygomatic bone which separates the orbit from temporal fossa. Features of lateral wall: 1-behind the lateral wall separated from roof by superior orbital fissure which connect orbit with middle cranial fossa. 2- also behind the lateral wall separated from floor by inferior orbital fissure which connects orbit with pterygopalatine fossa infront and infratemporal fossa behind. Roof of orbit: it is formed by: 1-orbital plate of frontal bone. 2-completed posteriorly by lesser wing of sphenoid. Roof separates orbit from anterior cranial fossa and then from frontal lobe of brain, and anteromedial from frontal sinus. Features: 1-Anterolaterally: there is lacrimal fossa in which lacrimal gland. 2- anteromedially: there is trochlear fossa for trochlea of superior oblique muscle. 3- posteriorly: there is optic foramen which lies between two roots of lesser wing of sphenoid. Floor of orbit: lies above maxillary sinus and is formed mainly by orbital surface of maxillary bone, its completed infront by orbital surface of zygomatic bone and limited posterolaterally by inferior orbital fissure. Features: infraorbital groove then converted into infraorbital canal that ends as foramen below inferior orbital margin.  The structures passing through Fissures, canals, and foramina of orbit 1. Superior orbital fissure: Communicates with middle cranial fossa. is bounded by: greater and lesser wings of sphenoid. Transmits: oculomotor, trochlear, abducent, and ophthalmic nerve (three branches) and ophthalmic veins. 2. Inferior orbital fissure: Communicates with infratemporal and pterygopalatine fossae. Is bounded by : greater wing of sphenoid (above) and maxillary and palatine bones (below). Transmits: maxillary (or infraorbital) nerve and its zygomatic branch & infraorbital vessels. 3. Optic canal Connects orbit with middle cranial fossa. Is formed by two roots of lesser wing of sphenoid is situated in posterior part of roof of orbit. Transmits optic nerve and ophthalmic artery. 4. Infraorbital groove and infraorbital foramen Transmit infraorbital nerve and vessels. 5. Supraorbital notch or foramen Transmits supraorbital nerve and vessels. 6. Anterior and posterior ethmoidal foramina Transmit anterior and posterior ethmoidal nerves and vessels, respectively, and connect the orbit with anterior cranial fossa. 7. Nasolacrimal canal Is formed by 1. maxilla, 2. lacrimal bone, and 3. inferior nasal concha. Transmits nasolacrimal duct from lacrimal sac to inferior nasal meatus. Eyelids Protective fibromuscular structures. Palpebral fissure separates between the two eyelids. Consist of thin skin and subcutaneous tissue overlying muscle layer. Orbicularis occuli closes the eye and supplied by facial nerve: a) Palpebral part. b) Orbital part. c) Lacrimal part. Palpebral ligaments (medial & lateral). Orbital septum An extension of periosteum into both the upper and lower eyelids from the margin of the orbit into Tarsal plate and levator palpebrae superioris. Tarsal glands (in tarsal plate called Meibomian gland), sebaceous glands and sweat glands (in skin of eyelid). Infection of tarsal gland called chalazion. Blood Vessels of eyelid: 1-The supratrochlear, supra-orbital, lacrimal, and dorsal nasal arteries from the ophthalmic artery (branch of internal carotid). 2-The angular artery from the facial artery. 3-The transverse facial artery from the superficial temporal artery. 4-braches from infraorbital artery (branch of maxillary artery)  Innervation of eyelid both sensory and motor. Sensory: 1-Supra-orbital, supratrochlear, infratrochlear, and lacrimal branches of the ophthalmic nerve. 2-Infra-orbital branch of the maxillary nerve. Motor: 1-Facial nerve: palpebral part of Orbicularis Occuli. 2-Occulomotor nerve: levator palpebebrea Superioris. 3-Sympathetic fibers: tarsal muscles (Muller’s muscle). (paralysis of Muller's muscle cause Horner’s syndrome)  Nerves of orbital cavity A. Ophthalmic nerve: is the smallest and most superior of the three divisions of the trigeminal nerve. It passes forwards through lower part of lateral wall of cavernous sinus (below trochlear and above maxillary nerves), its purely sensory nerve, Just before reaching superior orbital fissure it divides into three branches, all of which enter the orbit through the fissure: 1. Lacrimal nerve: Enters orbit through superior orbital fissure outside the common tendinous ring, it runs forwards along upper border of lateral rectus. Then Enters lacrimal gland, giving rise to branches to lacrimal gland, conjunctiva, and skin of upper eyelid. Its terminal part is joined by zygomaticotemporal nerve that carries postganglionic parasympathetic (from pterygopalatine ganglion) and sympathetic fibers (from internal carotid plexus). 2. Frontal nerve: its main branch of ophthalmic nerve enters orbit through superior orbital fissure outside the common tendinous ring (below lacrimal nerve). Runs superior to levator palpebrae superioris. Divides near the margin of orbit into: 1-supraorbital nerve, which passes through supraorbital notch or foramen and supplies scalp, forehead, frontal sinus, and upper eyelid, & 2-supratrochlear nerve, which passes through trochlea and supplies scalp, forehead, and upper eyelid.  3. Nasociliary nerve: enters the orbit through lower part of superior orbital fissure (within common tendinous ring) between the two heads of lateral rectus and between the superior and inferior divisions of oculomotor nerve. It passes forward and medially above optic nerve from lateral to medial side parallel behind ophthalmic artery to reach medial wall of orbit. it then passes between medial rectus and superior oblique muscles. Ends by dividing into infratrochlear and anterior ethmoidal nerves. Is sensory nerve for eye and mediates afferent limb of corneal reflex. Nasocilliary Gives rise to following: a- The small communicating branch of the ciliary ganglion is a small branch of the nasocilliary nerve which supplies sensory fibers through the ciliary ganglion. These fibers do not synapse in the ganglion but pass directly into the short ciliary nerves to supply sensation to the sclera, cornea, iris and ciliary body. b-Short ciliary nerves: which carry postganglionic parasympathetic and sympathetic fibers (pass through the ciliary ganglion without forming synapses) to ciliary body and iris and afferent fibers from iris and cornea. c-Long ciliary nerves: 2-3 in number passes medially to optic nerve. it transmit postganglionic sympathetic fibers to dilator pupillae and sensory innervation to the eyeball, including the cornea. d-posterior ethmoidal nerve: which passes through posterior ethmoidal foramen in the medial wall of the orbit to sphenoidal and posterior ethmoidal sinuses. e-anterior ethmoidal nerve: which passes through anterior ethmoidal foramen to appear on cribriform plate the descend through a slit at the side of crista galli to enter the nasal cavity supply anterior ethmoidal air cells. It then divides into: internal nasal branches, which supply septum & lateral walls of nasal cavity, and passes between lower border of nasal bones as external nasal branches, which supply skin of tip of nose. f-infratrochlear nerve: is a continuation of nasocilliary nerve leaves the orbit below the trochlea of superior oblique. it innervates eyelids, conjunctiva, skin of nose, and lacrimal sac. B. Optic nerve: it enters orbit through optic foramen, runs forwards and laterally to pierce sclera medial to posterior pole of eyeball. The nerve longer than the distance between optic foramen and posterior pole of eye this makes movements of eye easy. Joins optic nerve from corresponding eye to form optic chiasma. Consists of axons of ganglion cells of retina, Carries fibers for vision from retina to brain and mediates afferent limb of pupillary light reflex. It is surrounded by the cranial meninges, including the subarachnoid space, which extend as far forward as the eyeball. The optic nerve is not true peripheral nerve, it is actually a tract of central nervous system, and like the C.N.S. it has meninges, and its fibers don’t have neurolemma, so if its cut it does not regenerate. The nerve is traversed by central artery of retina which runs in the nerve till the optic disc, where it divides into branches to supply the retina. C. Oculomotor nerve It leaves the anterior surface of the brainstem between the midbrain and the pons. It passes forward between superior cerebellar & posterior cerebral arteries, then It passes forward in the lateral wall of the cavernous sinus. Then enters orbit through lower part of superior orbital fissure. Just before entering the orbit the oculomotor nerve Divides into: 1-superior division, which innervates: superior rectus and levator palpebrae superioris muscles. 2-inferior division, which innervates medial rectus, inferior rectus, a inferior oblique muscles. Inferior division carries preganglionic parasympathetic fibers (with cell bodies located in Edinger-Westphal nucleus) to ciliary ganglion (supply sphincter pupillae and ciliary muscle). D. Trochlear nerve The trochlear nerve arises from the posterior surface of the midbrain, and passes around the midbrain to enter the edge of the tentorium cerebelli, passes between superior cerebellar and posterior cerebral arteries, then Passes through lateral wall of cavernous sinus below oculomotor nerve during its course. Enters orbit by passing through upper part of superior orbital fissure. In the orbit the trochlear nerve ascends and turns medially, crossing above the levator palpebrae superioris muscle to enter the upper border of the superior oblique muscle. (notes: all muscles of orbit receive their nerve supply on their ocular surface i.e. towards the eyeball except superior oblique which is supplied from its upper surface). E. Abducens nerve: exit between pons and medulla then ascend on clivus of skull to enter the cavernous sinus and passes inside it lateral to the internal carotid artery then Enters orbit through lower part of superior orbital fissure, between the two head of lateral rectus muscle that supply it. F. Ciliary ganglion Is a parasympathetic ganglion situated behind eyeball, between optic nerve and lateral rectus muscle. 1-Parasympathetic root : through oculomotor nerve, synapse through ganglion and supply ciliary muscle and sphincter pupillae. 2-Sensory root: afferent fibers from iris and cornea, through short ciliary nerves without rely in ganglion. 3-Sympathetic root: from superior cervical ganglion through plexus around internal carotid artery. It reaches the eyeball and supplies dilator pupillae muscle.  Common tendinous ring: Is a fibrous ring that surrounds optic canal and medial part of superior orbital fissure. Is site of origin of four rectus muscles of eye, transmits following structures: enter orbit through superior orbital fissure and common tendinous ring: 1-Oculomotor, 2-nasocilliary, and 3-abducens nerves, enter orbit through optic canal and tendinous ring: 1-Optic nerve, 2-ophthalmic artery, and 3-central artery and vein of retina. enter orbit through superior orbital fissure but outside tendinous ring: 1-Superior ophthalmic vein 2-Trochlear. 3-frontal, and 4-lacrimal nerves  The above mentioned nerves pass through superior orbital fissure in the following order from above downward: 1-live lacrimal 2-free frontal 3-to trochlear 4-see superior division of oculomotor 5-no nasocilliary 6-isult inferior division of oculomotor 7-at all abducent  Blood Vessels of orbital cavity A. Ophthalmic artery Is a branch of internal carotid artery arising from it when the internal carotid artery leaves the roof of cavernous sinus. It passes forwards to enter orbit through optic foramen in a groove below optic nerve. In the orbit the artery makes a spiral turn round the lateral side of optic nerve then crosses above it to reach the medial wall of orbit parallel to nasocilliary nerve. Near anterior part of orbit at the medial angle of eye it ends by dividing into supratrochlear and dorsal nasal arteries. Gives rise to ocular and orbital vessels. Branches of ophthalmic artery: 1. Central artery of retina: Is most important branch of ophthalmic artery. Travels in optic nerve; it divides into superior branches & inferior branches to optic disk, and each of those further divides into temporal and nasal branches. Is an end artery that does not anastomose with other arteries, its occlusion results in blindness. 2. Long posterior ciliary arteries Pierce sclera and supply ciliary body and iris. 3. Short posterior ciliary arteries Pierce sclera and supply choroid. 4. Lacrimal artery: largest branch Passes along superior border of lateral rectus and supplies lacrimal gland, conjunctiva, and eyelids. Gives rise to two lateral palpebral arteries, which contribute to arcades in upper and lower eyelids. 5. Medial palpebral arteries Contribute to arcades in upper and lower eyelids. 6. Muscular branches Supply orbital muscles and give off anterior ciliary arteries, which supply iris. 7. Supraorbital artery Passes through supraorbital notch (or foramen) and supplies forehead and scalp. 8. Posterior ethmoidal artery Passes through posterior ethmoidal canal, then through the cribriform plate of ethmoid to supply meninges and posterior ethmoidal air cells. 9. Anterior ethmoidal artery Passes through anterior ethmoidal foramen to anterior and middle ethmoidal air cells, frontal sinus, nasal cavity, and external nose. 10. Supratrochlear artery Passes to supraorbital margin and supplies forehead and scalp. 11. Dorsal nasal artery Supplies side of nose and lacrimal sac. B. OPHTHALMIC VEINS 1. Superior ophthalmic vein Is formed by union of supraorbital, supratrochlear, and angular veins. Receives branches corresponding to most of those of ophthalmic artery, receives inferior ophthalmic vein before draining into cavernous sinus. 2. Inferior ophthalmic vein Begins by union of small veins in floor of orbit, Communicates with pterygoid venous plexus & infraorbital vein. terminates directly or indirectly in cavernous sinus.  Muscles of the orbit The orbit contains 10 muscles: 1-seven extraocular striated voluntary muscles: 4 recti (superior, inferior, medial, and lateral recti), 2 obliques (superior and inferior), one levator palpebrae superioris. Levator palpebrae superioris acts on upper eyelid while recti and oblique muscles act on eye ball. 2-three intraocular smooth involuntary: 1-sphincter pupillae and ciliary both supply by parasympathetic nerve. 2-dilator pupillae supply by sympathetic nerve. Positions of 4 recti: 1-lateral rectus: on lateral wall of orbit. 2-medial rectus: on medial wall of orbit below superior oblique. 3-superior rectus: on median plane above eye ball separated from roof of orbit by levator palpebrae superioris. 4- inferior rectus: on median plane below eye ball separated from floor of orbit by inferior oblique.  Levator palpebrae superioris: it arises from the roof of orbit immediately infront of optic foramen and forwards on the upper surface of superior rectus. It is inserted into 3 sites: a-skin of upper lid. b-anterior surface of the tarsus. c-upper fornix. The deep part of levator palpebrae is formed of smooth muscle fibers called Muller's muscle which inserted into upper border of tarsus. Muller's muscle is supplied by sympathetic fibers, and in Horner's syndrome in which the sympathetic supply to head and neck is interrupted lead to ptosis i.e. dropping of upper lid take place due to paralysis of Muller's muscle.  The four recti muscles they arise from tendinous ring which is attached to the upper, lower and medial margins of optic foramen and crosses the medial end of superior orbital fissure. The superior, inferior, and medial recti muscles arise from upper, lower, and medial parts of tendinous rings respectively. While lateral rectus arises by two heads: the lower head adjoins the inferior rectus while upper head arises from part of tendinous ring which crosses superior orbital fissure. The recti pass forwards through orbit and become wider and diverge from each other as if to form a sort of muscular capsule for optic nerve and posterior part of eyeball. The insertion of recti pierce the fascial sheath of eyeball and become inserted at variable distance from corneoscleral junction (medial rectus= 5.5mm, inferior rectus=6.0mm, lateral rectus=7.0mm, superior rectus=7.7mm) Superior oblique muscle Arises from roof of orbit immediately above and medial to optic foramen, just above the medial rectus and passes forwards above medial recuts in the angle between medial wall and roof of orbit. when reaches anterior part of orbit, it ends in a slender tendon which passes through a fibrocartilagenous pulley called trochlea (attached to anteromedial part of roof). The tendon then change direction by passing backwards and laterally above eyeball to become inserted into the sclera half way between cornea infront and the exit of optic nerve behind. Inferior oblique muscle Arises from anteromedial part of floor of orbit lateral to opening of nasolacrimal canal and passes backwards and laterally in the anterior part of floor of orbit below inferior rectus, it then passes upwards and slightly backwards to be inserted on the lateral side of sclera under cover of lateral rectus. The insertion of superior and inferior oblique muscles not far from each other. Nerve supply of ocular muscles SO4, LR6, Remainder3; which means that superior oblique muscle is innervated by trochlear nerve, lateral rectus muscle is innervated by abducens nerve, remainder of these muscles (means extra and intraocular muscles) are innervated by oculomotor nerve. Actions of ocular muscles: 1-action of lateral and medial recti is simple because they move the eye ball in one axis: lateral rectus abducts the eye, and the medial rectus adducts the eye. 2-the action of other 4 muscles more complex as each of these muscles moves the eye ball in three axes as follows: a-superior rectus: elevates, adducts and rotates medially. b-inferior rectus: depresses, adducts and rotates medially. c-superior oblique: depresses, abducts and rotates laterally. d-inferior oblique: elevates, abducts and rotates laterally. 3-pure downwards rotation of the eye ball (Intorsion: Is a medial inward rotation of upper pole 12 o'clock position of cornea) can be produced only when inferior rectus and superior oblique work together. 4-to look straight upwards (Extorsion Is a lateral outward rotation of upper pole of cornea) the superior rectus and inferior oblique must work together.  Inf. oblique Sup. rectus Sup. rectus Inf. oblique Lat. Lat. rectus rectus Med. Med. rectus rectus Sup. oblique Inf. rectus Inf. rectus Sup. oblique RIGHT EYE LEFT EYE  Fascial sheath of eyeball (fascia bulbi or Tenon's capsule) This is a fascial sheath which invests the posterior 5/6 of eye ball. Infront, it blends with sclera near the corneoscleral junction while behind it becomes continuous with the sheath of optic nerve. At each side the fascial sheath is connected to the bony wall in such a way as to form a check ligament. The lateral and medial check ligaments prevent excessive action of lateral and medial rectus muscles. The anterior part of fascial sheath is thickened inferiorly to form suspensory ligament; whose extremities are attached to the bony walls of orbit near the check ligaments. the check and suspensory ligaments prevent any unnecessary movements of the eyeball.  Lacrimal Apparatus A. Lacrimal gland: Lies in upper lateral region of orbit (the gland lies in the lacrimal fossa in the anterolateral part of the roof of greater wing of sphenoid separates the orbit from middle cranial fossa) on lateral rectus and levator palpebrae superioris muscles. Is drained by 12 lacrimal ducts, which open into superior conjunctival fornix. B. Lacrimal canaliculi: Are two curved canals that begin as a lacrimal punctum (or pore) in the medial end of the margins of the upper and lower eyelid and open into lacrimal sac. C. Lacrimal sac: Is upper dilated end of nasolacrimal duct, opens into inferior meatus of nasal cavity. Which lies in the lacrimal groove in the anterior part of the medial wall of the orbit D. Tears: Are produced by lacrimal gland. Pass through excretory ductules into superior conjunctival fornix. Are spread evenly from lateral to medial over eyeball by blinking movements and accumulate in area of lacrimal lake. Enter lacrimal canaliculi through their lacrimal puncta (which is on summit of lacrimal papilla) before draining into lacrimal sac, the drain to nasolacrimal duct, and finally inferior nasal meatus. E. Innervation of lacrimal gland: 1-Sensory: lacrimal branch of ophthalmic nerve. 2-Secretomotor (parasympathetic): through facial nerve then through greater petrosal nerve the through the nerve of pterygoid canal. 3-Sympathetic: through superior cervical ganglion through plexus around internal carotid artery then through deep petrosal nerve then fuse with greater petrosal nerve as a nerve of pterygoid canal, then this nerve pass through pterygopalatine ganglion, then through zygomatic branch of maxillary nerve, then through zygomaticotemporal nerve that give communicating branch to lacrimal nerve which supply lacrimal gland  Eyeball A. External white fibrous coat: Consists of sclera and cornea. 1. Sclera: Is a tough white fibrous tunic enveloping posterior five sixths of eye. 1. Cornea: Is a transparent structure forming anterior one sixth of external coat. Is responsible for refraction of light entering eye. B. Middle vascular pigmented coat: Consists of choroid, ciliary body and iris. 1-Choroid: Consists of an outer pigmented (dark brown) layer and an inner highly vascular layer, which invests posterior five sixths of eyeball. Nourishes retina and darkens eye. 2- Ciliary body: Is a thickened portion of vascular coat between choroid and iris and consists of A-ciliary ring, b-ciliary processes, and c-ciliary muscle. ciliary processes are radiating pigmented ridges that encircle margin of lens. ciliary muscle consists of meridional and circular fibers of smooth muscle innervated by parasympathetic fibers. It contracts to pull ciliary ring and ciliary processes, relaxing suspensory ligament of lens and allowing it to increase its convexity. 3. Iris :Is a thin, contractile, circular, pigmented diaphragm with a central aperture, pupil. Contains circular muscle fibers (sphincter pupillae), which are innervated by parasympathetic fibers, and radial fibers (dilator pupillae), which are innervated by sympathetic fibers. C. Internal nervous coat: Consists of retina, which has an outer pigmented layer and an inner nervous layer. Has a posterior part that is photosensitive; its anterior part, which is not photosensitive, constitutes inner lining of ciliary body and posterior part of iris. 1. Optic disk (blind spot): Consists of optic nerve fibers formed by axons of ganglion cells. These cells are connected to rods and cones by bipolar neurons. Is located nasal (or medial) to fovea centralis and posterior pole of eye, has no receptors, and is insensitive to light. Has a depression in its center termed physiologic cup. 2. Macula (yellow spot or macula lutea): Is a yellowish area near center of retina on temporal side of optic disk for most distinct vision. Contains fovea centralis. 3. Fovea centralis: Is a central depression (fovea) in macula. Is avascular and is nourished by choriocapillary lamina of choroid. Has cones only (no rods), each of which is connected with only one ganglion cell, and functions in detailed vision. 4. Rods: Are approximately 120 million in number and are most numerous about 0.5 cm from fovea centralis. Contain rhodopsin, a visual purple pigment. Are specialized for vision in dim light. 5. Cones: Are 7 million in number and are most numerous in fovea region. Are associated with ‫مهمة هذه املناطق تكون شفافة وتخلي الفوكس ع‬ visual acuity and color vision. ‫الرتنا‬ Position ,lateral and medial wall D. Refractive media: Consist of cornea, aqueous humor, lens, and vitreous body. 1. Cornea 2. Aqueous humor: Is formed by ciliary processes and provides nutrients for avascular cornea and lens. Passes through pupil from posterior chamber (between iris & lens) into anterior chamber (between cornea and iris) and is drained into scleral venous plexus through canal of Schlemm at iridocorneal angle. Its impaired drainage causes an increased intraocular pressure, leading to atrophy of retina and blindness. 3. Lens: Is a transparent avascular biconvex structure enclosed in an elastic capsule. Is held in position by radially arranged zonular fibers (suspensory ligament of lens), which are attached medially to lens capsule and laterally to ciliary processes. Flattens to focus on distant objects by pulling zonular fibers and becomes a globular shape to accommodate eye for near objects by contracting ciliary muscle and thus relaxing zonular fibers. 4. Vitreous body: Is a transparent gel called vitreous humor, which fills eyeball posterior to lens (vitreous chamber between lens & retina). Holds retina in place and provides support for lens.