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Orbit anatomy

Dr. Prajakta Matey.(resident at BJGMC)

Introduction Orbit is the anatomical space bounded:*Superiorly-Anterior cranial fossa*Medially Nasal cavity & Ethmoidal air cells*Inferiorly Maxillary sinus*Laterally-Middle cranial fossa

Made up of 7 bones :-Ethmoid-Frontal-Lacrimal-Maxillary-Palatine-Spenoid-Zygomatic

Embryology

Derived from above mesenchyme that encircles the optic vessicle below & laterally maxillary processes medially - fronto nasal process behind orbitosphenoid.

Developes by Enchondral ossification (part derived from base of skull) Membrenous ossification (rest all)

By 6 -7 th month laying down of bone starting with maxillary process

During this time optic vesicles which are 170 apart are rotated anteriorly.

At birth hemisphericalGrowth corresponds to eyeball till puberty

Congenital anamolies Craniosynostosis premature closure of skull suturesCrouzon syndrome - short AP diameter of skull - mid facial hypoplasia - prominent lower jaw - shallow orbit - hypertelorism - V exotropia

Apert syndrome -Oxycephaly-Syndactyly -Beaked nose-low set ears-Developmental delay-Shallow orbit-Proptosis-hypertelorism

Pfeiffer syndrome

Dermoid cyst -MC orbital cystic lession-Origin pouches of ectoderm trapped in bony sutures MC site frontozygomatic suture.

Cephalocoele -Reflects orbital entrapment of neuroectoderm -MC site- Frontal & Ethmoid - pathology-herniaton of brain parenchyma into orbit.

Fibrous dysplasia-Benign developmental fibro-oscious lesion -Origin-arrest in maturation at woven bone stage- Pathology bone is replaced by fibrous tissue.

Gross anatomyDimensionsDepth 42 mm along medial wall 50 mm along lateral wallIntraorbital width distance between medial margins of both orbits 25 mmExtraorbital width distance between lateral margins of both orbits 100 mmOrbital index = (height / width) 100 >89 megasenes (orientals) 83 89 mesosenes (caucasian) < 83 microsenes (nigros) Volume 30ml -volume of orbit : volume of eyeball = 4.5:1

Angulations Between lateral wall & sagital plain 45 - Between visual axis & orbital axis 23 - Medial wall of both orbits are parallel to each other - Lateral wall of both orbits bears an angle of 90

Contents of orbit:Eyeball : 1/5 of orbit

Muscles : 4 Recti , 2 Oblique , LPS , Mullers muscle

Nerves :II , III ,IV , VI , V1 (Lacrimal , frontal , nasociliary) V2 (Infraorbital & zygomatic)

Vessels :Ophthalmic artery & its br infraorbital vessels br of middle meningial artery sup & inf ophthalmic vein

Orbital fat & reticular tissue& orbital Fascia

Lacrimal Gland & Sac

Walls of orbit :i)Medial wall: a)Frontal process of maxillaQuadranular b)Lacrimal boneMade up of c)Orbital plate of ethmoid bone d)Body of sphinoid

In anterior part lacrimal fossa bounded by (d) (c) (b) (b)Anterior Posterior lacrimal lacrimal (a) crest crest (maxilla) (lacrimal bone)

Attachments behind post lacrimal crest are* Horners muscle* Septum orbitale* Check lig of MR

Relations a)Anterior ethmoid sinus Medially b)Middle meatus c)Middle ethmoid sinus d)Posterior ethmoid sinus

Orbital surface related to SO & MR ,in between two lies Ant & post ethmoidal nerveIntratrochlear nerveTerminal br of ophthalmic artery

Clinical application:-Thinnest wall-Ethmoiditis is commonest cause of orbital cellulitis due to erosion of this wall especially in children.-It is commonly erroded by chronic inflammatory lesion, cysts and neoplasms originsting in adjuscent air sinuses.-Injury to this wall causes troublesome haemorrhages d/t injury to ethmoidal vessles.-Easily fractured during injuries or orbitotomy operations.-Medial wall is easily visualised in PA view of radiograph of skull

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ii)Inferior wall-Triangular -Shortest a) Medially - maxillary bone -Made up of b) Laterally - zygomatic bone c)Posteriorly -Palatine bone

-Inferior orbital fissure separates posterior part of floor from lateral wall.-Fissure groove canal Infraorbital foramena (Infraorbital nerve & vessels)

-Relations: Below maxillary & palatine air sinuses Above Inferior oblique & rectus muscle & nerve to IO.

-Clinical application: * Commonly involved in blow out # & easily invaded by tumours of maxillary antrum. * Orbital floor can be appraoched by inferior orbitotomy i.e antral approach. * Blow out # - Infraorbital nerves & vessels are involved - clinically diplopia, restricted movements in up gaze, parasthesis & enophthalmos.

iii)Lateral wall :-Triangular- Made up of Anteriorly (a) Zygomatic bone Posteriorly (b)Greater wing of sphenoid

(b) (a)

-Spina recti lateralis Bony projection on posterior part of wall gives attachment to some fibres of LR

-Lateral orbital tubercle of whitnall - Bony projection on anterior part of wall gives attachment to check lig of LR

-Separated from roof by sup orbital fissure& from floor by inferior orbital fissure.

-Relations:Laterally in anterior part temporal fossa In posterior part middle cranial fossaMedially - LR , Lacrimal nerve & vessels , zygomatic nerve & their communication.

-Clinical application :

*Lateral wall protects only post of eyeball , anterior is not covered with bone .

*So , palpation of retroorbital tumours easier from lateral side than nasal side.

*This wall is almost devoid of foramina , so its anterior ortion can be easily broached without serious haemorrhages.

*Because of its advantageous anatomical position lateral orbital surgical approach is popullar .

* Zygomatico-sphenoid suture is most important landmark on creating a flap in Kronleins operation . Once this flap has been turned , there is direct access to superolateral , inferolateral & retrobulbar quadrants of orbit.

iv)Superior wall /Roof :-Triangular-Made up of Anteriorly (a)Frontal bone Posteriorly (b)Laser wing of sphinoid

(a) (b)

-Separates orbit from frontal sinus & anterior cranial fossa.-Fossa for lacrimal gland present in anterolateral part of roof-Trochlear Fossa present in medial part , - attachment for pulley of SO

-Relations : Above Frontal lobe & meninges Below Periorbita , frontal nerve , trochlear nerve, LPS , SR , SO & Lacrimal gland-Ant & post Ethmoidal canals: present at junction of roof & medial wall

-Clinical significance:

* A sharp object injury through upper lid penetrates the roof & may damage frontal lobe.

* Orbital roof anamolies or fractures can lead to pulsatile exophthalmos.

* Since roof is neither perforated by major nerves nor vessels , it can be easily nibbed away in transfrontal orbitotomy.

Base of orbit:- anterior open end of orbit. - bounded by orbital margins i.e. ring of compact bone which gives attachment to orbital septum.- Divided into 4 margins (frontal)

i) Superior orbital margin:- Formed by frontal bone.- Lateral 2/3 is sharp & medial 1/3 is rounded.- At this junction lies supraorbital notch transmiting supraorbital nerves & vessels.- About 10 mm medial to supraorbital notch is supratrochlear groove transmitting supratrochlear nerve & artery.

ii)Lateral orbital margin:-Strongest -Formed by zygomatic process of frontal bone & zygomatic bone.-It does not reach as anteriorly as medial margins.

iii)Inferior orbital margin:-Formed by laterally zygomatic bone medially maxilla- Medially it continues with anterior lacrimal crest.- 4-5cm below orbital margin in line with supraorbital notch lies infraorbital foramena transmitting infraorbital nerve & vessels

iv)Medial orbital margin:- Formed by below anterior lacrimal crest (maxilla) above frontal bone

frontal bone

(maxilla)

Appertures at the base of orbit:

- Base of orbit is closed partly by globe , extraocular muscles & their fascial expansions.

- These fascial expansions & sup and inferior oblique muscles bound 5 orifices between them & orbital margins .

-These are the communications between orbital cavity & deep portion of eyelid.

- Through them blood & pus passes out of orbit . Further spread in lid is prevented by orbital septum.

i) superior apperture:-comma shaped-lies between roof & upper surface of LPS -Fat from superomedial lobe may herniate through this apperture.

ii) Superomedial apperture:-Vertically oval-Lies between reflected tendon of superior oblique & medial check ligament-It transmits Infratrochlear nerve , dorsal nasal artery angular vein.

-Heniation of fat through this space is common cause of lobulated prominence in old people.iii) Inferomedial apperture:-Vertically oval-lies between medial check ligament & inferior oblique and Lacrimal sac.iv) Inferior apperture:-Triangular -Bounded by inferior oblique , arcuate expansion of inf oblique & floor of orbit.

v) InferoLateral apperture:-Vertically oval -Lies between arcuate expansion of inf oblique ,Inf oblique muscle & Lateral check ligament.

Apex of orbit:-Posterior end of orbit.-Has 2 orifices

i)Optic canal:- Connects orbit to middle cranial fossa.-Transmits Optic nerve & surrounding meninges Ophthalmic artery.-Normal adult dimensions are attended by 4-5 yrs.-Length 6-11mm-Orbital end is vertically oval Centre is circular Cranial end is horizontally oval- Optic nerve glioma & meningioma causes unilateral enlargement of optic canal.

ii)Superior orbital fissure:-Comma shaped-Bounded by greater & lesser wing of sphinoid.-Fissure is divided into upper middle & lower part by common tendinous ring .

Structures Passing

Upper Middle Lower -Superior ophthal. V. -Nasociliary Nerve (V1) -Inferior ophthalmic -Lacrimal nerve (V1) - Oculomotor Nerve Vein- Frontal nerve (V1) - Abducent Nerve -Sympathetic Plexus- Trochlear nerve-Reccurent br of ophthalmic artery.

Periorbita:-Periosteum lining orbital bones.

-Loosely adherant except at orbital margins, sup & inf orbital fissures , optic canal, lacrimal fossa & at sutures.

-In optic canal dural sheath is adherant to periorbita.

-Arcus marginale: -thickened periorbita at orbital margins -gives attachment to orbital septum.

-Lacrimal fascia: - periorbita at post lacrimal crest splits into 2 layers reunits at anterior lacrimal crest to enclose Lacrimal sac.

-Tendinous ring of zinn:- Thickened periorbita at orbital apex which gives attachment to 4 recti muscles.

Orbital fascia:-Thin connective tissue membrane lining various intraorbital structures.-Described under following structuresi)Fascia bulbi :-Envelopes globe from from limbus to optic disc.-Outer surface lies in contact with orbital fat posteriorly & subconjunctival tissue anteriorly with which it merges at limbus.-Tenons capsule is seperated from sclera by Episcleral space / tenons space .-Lower part of fascia bulbi is thickened forming asling on which the globe rest k/a suspensory ligament of lockhood. which extends from posterior lacrimal crest to lateral orbital wall.

-stuctures piercing tenons capsule: Optic nerve - posteriorlyCiliary nerve & vessels -posteriorlyVenae vorticosae just behind equatorExtraocular muscles - anteriorly ; where it becomes conteneous with fascial sheaths of muscles.ii)Fascial sheaths of extraocular muscles:-At a point where fascia bulbi is pierced by muscles , it sends tubular reflections which clothes the muscle & continues as perimysium.

iii)Fascial expansions of extraocular muscles:Lateral & medial check ligament:- Expansions of lateral & medial rectus are strong & are attached to tubercles on Zygomatic & Lacrimal bone respectively.Expansion of Superior Rectus is attached to LPS ensures synergestic action of two muscles. Hence when SR makes eye to look up , the upper lid is also raised. In maximal levetor resection for ptosis surgery , hypotropia can be induced if these connections are not severed.Expansion of Inferior rectus is attached to capsulopalpabral fascia. Expansion from Superior oblique passes to trochlea. Expansion from Inferior oblique passes to lateral part of roof & floor.

Superior transverse ligament of whitnall:-Condensation of superior sheath of LPS & reflected tendon of superior oblique.-Extends from trochlear pulley to lacrimal gland fossa.- True check ligament of LPS.

Suspensory ligament of fornices..(Sup & inf)-Superior suspensory Lig During ptosis surgery if this lig is cut fornix conjuntiva can prolapse,

Orbital septa.-passes from periorbita to fascia bulbi.-These provides specific channels for ophthalmic veins.

iv) Intermuscular septa / membrane:-It is a Sheath of all 4 recti muscles are joined to each other by facial membrane.It has divided orbital cavity & orbital fat into central & peripheral part.

Surgical spaces in orbit:- Orbit is divided into 4 surgical spaces- Importance of these spaces is that most of the orbital tumours tends to remain with in a space in which they are formed (unless they are large or malignant or represents an infiltrative process such as pseudotumour )

1.Subperiosteal space.2. Peripheral orbital space.3.Central orbital space.4. Subtenons space

1. Subperiosteal space:-Lies between orbital bone & periorbita.-Tumours arising from bone separates periorbita from bone .-Here periorbita acts as a effective barrier against spread of tumour to eye.-Tumours in this space are: Dermoid cyst Epidermoid cyst Mucocoele Subperiosteal abscess Myeloma Osteomatous tumour Hematoma Fibrous dysplasia.

2.Peripheral orbital space:- Lies between - periorbita at periphery - extraocular muscles & their intermuscular septa internally - orbital septum anteriorlly.-Posteriorly it merges with central space.

- Contents Periorbital fat SO , IO , LPS Lacrimal , frontal , trochlear, ant & post ethmoidal nerve. superior & inferior ophthalmic vein Lacrimal gland & Lateral of lacrimal sac.

-Tumours in this space are: Malignant lymphoma Capillary haemangioma of childhood Intrinsic neoplasm of lacrimal gland Pseudotumours

-Tumours in this space are usually approached by anterior orbitotomy & sometimes by lateral orbitotomy.-Tumours in this space produce eccentric proptosis.

3. Central orbital space:- k/a muscle cone / retro-orbital space / posterior space.- Bounded by - anteriorly tenons capsule -posteriorly by 4 recti & intermuscular septa- In posterior part ,space becomes continuous with peripheral space.-Content : a) Nerves: -Optic nerve with meninges - Sup & inf division of oculomotor nerve. - Abducent nerve - Nasociliary nerve - Cilliary ganglion b) Artery - Ophthalmic artery c) Vein - Sup ophthalmic vein d) Central orbital fat.

- Tumours of this space: Cavernous haemangioma of adults Solitary neurofibroma Neurolemoma Nodular orbital meningiomas Optic nerve glioma

-Produces axial proptosis-Tumours are approached through lateral orbitotomy.

Axial proptosis

4. Subtenons space:- Space around eyeball between sclera & tenons capsule - Pus collection in this space is drained by incision on tenons capsule through conjunctiva.

Orbital fat & reticular tissue:-It is divided by intermuscular septa into

*Central part *Peripheral part - 4 lobules superomedial inferomedial superotemporal inferotemporal

-Both becomes continuous with each other postereriorly.

-Benign encapsulated tumours do not alter the normal articular structure of reticular tissue except these are under great pressure.

-Malignant & infiltrative lesions like pseudotumours & endocrine exophthalmos , this basic matrix may alter depending on nature & duration of lesion.

Thank you .....