DETAILED ANATOMY OF ORBIT WITH ITS SURROUNDINGS

ANATOMY OF ORBIT

1. Orbit anatomy

2. Int r oduction  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

3. C ontents of orbit:  Eyeball : 1/5 of orbit  Muscles : 4 Recti , 2 Oblique , LPS , Muller’s muscle  Nerves :II , III ,IV , VI , V 1 (Lacrimal , frontal , nasociliary) V 2 (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

4. Walls of orbit : i) Medial wall:  Quadranular Frontal process of maxilla Lacrimal bone Orbital plate of ethmoid  Made up of bone d)Body of sphinoid  In anterior part lacrimal fossa bounded by (d) (c) (b) (a) Anterior lacrimal crest ( m a x i l l a ) P osterior lacrimal crest (lacrimal bone)

5.  Attachments behind post lacrimal crest are Horners muscle Septum orbitale Check lig of MR  Relations Medially Anterior ethmoid sinus Middle meatus Middle ethmoid sinus d)Posterior ethmoid sinus

6. Orbital surface related to SO & MR ,in between two lies Ant & post ethmoidal nerve Intratrochlear nerve Terminal 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

7. ii)Inferior wall - T ri a ng u lar -Shortest -Made up of Medially - maxillary bone Laterally - zygomatic bone c)Posteriorly -Palatine bone

8. -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.

9. - 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.

10. iii) Lateral wall : - T ri a ng u lar - 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

11. - 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 fossa Medially - LR , Lacrimal nerve & vessels , zygomatic nerve & their communication.

12. -Clinical application : *Lateral wall protects only post ½ of eyeball , anterior ½ 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 Kronlein’s operation . Once this flap has been turned , there is direct access to superolateral , inferolateral & retrobulbar quadrants of orbit.

13. iv) Superior wall /Roof : - T ri a ng u lar -Made up of Anteriorly –(a)Frontal bone Posteriorly – (b)Laser wing of sphinoid (a) (b)

14. -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

15. - 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

16. -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.

17. 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.

18. 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

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

20. 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.

21. 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.

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

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

24. Apex of orbit: -Posterior end of orbit. -Has 2 orifices i)Optic canal: - Connects orbit to middle cranial fossa. -Transmits Opt i c nerve & surroun d ing meni n ges 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.

25. 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 .

26. Structures Passing Middle -Nasociliary Nerve (V 1 ) Lower -Inferior Oculomotor Nerve Abducent Nerve Vein -Sympathetic Upper -Superior ophthal. V. ophthalmic -Lacrimal nerve (V 1 ) Frontal nerve (V 1 ) Plexus Trochlear nerve -Reccurent br of

27. 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.

28. -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.

29. Orbital fascia: -Thin connective tissue membrane lining various intraorbital structures. -Described under following structures i)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. -Tenon’s capsule is seperated from sclera by Episcleral space / tenon’s 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.

30. -stuctures piercing tenons capsule: Optic nerve - posteriorly Ciliary nerve & vessels -posteriorly Venae vorticosae –just behind equator Extraocular 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.

31. 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.

32. 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.

33. 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.

34. Orbital fat & reticular tissue: -It is divided by intermuscular septa into * Central part *Peripheral part - 4 lobules  superomedial  inferomedial  superotemporal  inferotemporal

35. -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.