1. The orbit is bounded by seven bones and contains the eyeball, extraocular muscles, nerves, vessels and orbital fat. 2. It develops from mesenchyme that surrounds the optic vesicle and later forms from endochondral and membranous ossification. 3. The orbit has four walls - medial, inferior, lateral and superior - with characteristics and clinical applications such as approach routes.

1. Orbit anatomy

2. 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

3. Embryology
 Derived from above –mesenchyme that encircles the optic vessicle
below & laterally – maxillary processes
medially - fronto nasal process
behind – orbitosphenoid.
 Developes by  Endochondral ossification
(part derived from base of skull)
 Membrenous ossification
(rest all)
 By 6 -7 th month laying down of bone starting with maxillary process

4.  During this time optic vesicles which are 170 ͦ apart are
rotated anteriorly.
 At birth – hemispherical
 Growth corresponds to eyeball till puberty

5.  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˚

6.  Contents of orbit:
Eyeball : 1/5 of orbit
Muscles : 4 Recti , 2 Oblique , LPS , Muller’s 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

7.  Walls of orbit :
i)Medial wall:
Quadranular
a)Frontal process of maxilla
b)Lacrimal bone
c)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
(maxilla)
Posterior
lacrimal
crest
(lacrimal bone)

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

9. 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 PAview of radiograph of skull

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

11. -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.

12. -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.

13. 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

14. -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.

15. -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.

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

17. -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

18. -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

19. -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.

20.  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.

21. 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

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

23.  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.

24. 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.

25. -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.

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

27.  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.

28. 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 .

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

30. 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.

31. -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.

32.  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.

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

35. 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.

36.  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.

37. 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.

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

39. -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.