The document provides an overview of the anatomy of the orbit, including its development, shape, dimensions, walls, contents, and openings. Some key points: - The orbit is formed from mesenchyme surrounding the optic vesicle during gestation. Its walls are derived from neural crest cells. - It has a quadrangular pyramid shape, with depths of 42mm medially and 50mm laterally. The walls include frontal, ethmoid, lacrimal, palatine, maxilla and zygomatic bones. - Contents include the eyeball, extraocular muscles, vessels, nerves, lacrimal gland and orbital fat. There are three surgical spaces: subperiosteal,

1. ANATOMY OF ORBIT
Dr.Arino John
Junior Resident
Dept of Ophthalmology

2. PRESENTATION LAYOUT
Development of orbit
Shape and Dimensions
Walls of Orbit
Contents of orbit
Orbital apex
Openings of orbit.

3. DEVELOPMENT OF ORBIT
• Bony orbit is formed from the mesenchyme that encircles the
optic vesicle
• Orbital bones: 6th to 7th week of gestation (starts with maxilla
)
• During this time optic vesicle rotates 170 degree anteriorly.
•Orbital walls : derived from neural crest cells which expand to
form
1. Frontonasal process
2.Maxillary process.
• Capsule of forebrain forms the orbital roof.

4. SHAPE AND DIMENSIONS
Quadrangular truncated pyramids.
Depth – 42mm (medial wall) , 50mm (lateral wall)
Base – 40mm in width and 35mm in height
Intraobital width – 25mm
Extraorbital width – 100mm
Orbital index : ht/width *100
Megasenes : >89 (eg : Asians )
Mesosenes : 83-89 (eg : Caucasians)
Microsenes : <83 (eg : Blacks)
Vol of each orbit :30cc
Vol of orbit : eyeball = 4.5:1

5. Bones forming orbit are
 Frontal
 Ethmoid
 Lacrimal
 Palatine
 Maxilla
 Zygomatic
 Sphenoid

6. CONTENTS OF ORBIT
1.Eyeball
2. Muscles : 4 recti muscles,2 obliques ,Mullers muscles,LPS
3.Vessels :ophthalmic artery,sup and inf ophthalmic veins, and
lymphatics
4.Nerves : CN 2,3,4 nerves :branches of ophthalmic and maxillary
nerves and sympathetic nerves.
5.Lacrimal gland.
6.Orbital fat & orbital fascia.

7. ROOF FLOOR MEDIAL WALL
4
WALLS LATERAL WALL

8. WALLS OF ORBIT
Roof of orbit
•Triangular in shape
•Formed by orbital plate of frontal bone & lesser wing of sphenoid at the
apex of roof
•Relations : superiorly roof separates the orbit from the frontal lobe of brain.
anterolaterally is the lacrimal fossa containing the lacrimal gland
anteromedially is the trochlear fossa giving attachment to the
fibrous pulley for the tendon of SOM.
• Apex of roof formed by lesser wing sphenoid has the optic foramen.(optic
nerve and ophthalmic artery).
• Roof of orbit is separated from its lateral wall by superior orbital fissure
through which orbit communicates with middle cranial fossa.

9. CLINICAL SIGNIFICANCE
Thin and fragile
Easily fractured by direct violence
(penetrating orbital injuries)
Frontal lobe injury

10. - Laterally – greater wing of sphenoid
-Anteriorly – superior orbital margin
So fracture tend to pass towards medial side
At junction of the roof and medial wall ,the suture line lies in
proximity to cribifrom plate of ethmoid.
rupture of duramater
CSF escapes into orbit or nose.

11. CLINICAL IMPORTANCE
Transfrontal craniotomy : roof is nibbled away easily since it is not
perforated by any major nerves or blood vessels.
• Orbital roof anomaly.
•Deficient orbital roof will result in CSF pulsation pulsatile
exophthalmos.

12. FLOOR OF ORBIT
Shortest orbital wall
Roundly triangular
Anteromedially : orbital plate of the maxillary bone.
Anterolaterally : orbital process of the zygomatic bone.
Posteriorly : superior plate of the palatine bone.
The floor separates the orbit from the maxillary sinus.

13. • The infraorbital canal runs in posteroanterior direction and exits as
infraorbital foramen,located 5mm below the inferior orbital rim,at the
level of anterior portion of pyramidal maxillary process.
• Its contents are infraorbital nerve and vessels.
• LANDMARKS
•At the junction of the anterior part of the floor and medial wall is the
fossa for lacrimal sac.
• Between the floor and lateral wall is the inferior orbital fissure..
Infraorbital
groove
Infraorbital
canal
Infraorbital
foramen

14. CLINICAL SIGNIFICANCE
Blow out fractures :
most common fracture of the orbit
fractures of the orbital floor
infraorbital nerves and vessels are almost invariably
involved.
causes the entrapment of the inferior rectus muscle results
in tear drop sign on CT scan.
 Patient presents with
Diplopia
Restricted movements (upgaze)
Paresthesia
Enophthalmos

16. LATERAL WALL
It is the thickest and strongest of all walls of orbit.
Formed by greater wing of sphenoid(posteriorly)
Orbital surface of zygomatic bone (anteriorly)
Relations :
 Laterally is the temporal fossa through which passes the tendon of
temporalis muscles.
SOF occupies the posterior part
Foramen of zygomatic nerve is in zygomatic bone.
Whitnalls or zygomatic tubercle is a palpable elevation on zygomatic bone
just within the orbital margin.

17. LANDMARKS
 LATERAL ORBITAL TUBERCLE OF WHITNALL :
4-5mm behind the lateral orbital rim.
11mm inferior to the frontozygomatic suture line.
 Gives attachemnet to :
Check ligament of lateral rectus
Lockwoods ligament
Lateral canthal tendon
the aponeuorosis of levator palpebrae superioris
Orbital septum
Lacrimal fascia

18. CLINICAL SIGNIFICANCE
• In resection of maxilla,the whitnalls tubercle is spared,otherwise
Damage to Lockwood’s ligament
Inferior dystopia of eyeball
Diplopia

19. MEDIAL WALL
Also k/a nasal wall. Thinnest wall.
Formed by 1.frontal process of maxilla
2.lacrimal bone
3.orbital plate of ethmoid
4.anterior part of lateral surface of body of sphenoid.
Between the medial wall and roof are the anterior and posterior
ethmoidal formina.
The anterior medial wall contains the lacrimal canal,bounded
anteriorly by the anterior lacrimal crest and posteriorly by
posterior lacrimal crest.

20. 24-12-6” rule applies to this wall.
 Its refers to the distance between the anterior lacrimal crest
and the anterior ethmoidal foramen (24mm).
The distance between the anterior ethmoidal foramen and posterior
ethmoidal formen (12mm)
And from this foramen to the optic canal (6mm).
This rule is significant in surgical purposes mainly in orbital decompression

21. OPENINGS IN ORBITAL CAVITY
oSuperior orbital fissure
oInferior orbital fissure
oOptic canal
oNasolacrimal canal
oSupraorbital foramen
oInfraorbital foramen

22. SUPERIOR ORBITAL FISSURE
Also known as sphenoidal fissure
Comma shaped gap between the roof and lateral wall
22mm long
Largest communication between the orbit
and middle cranial fossa.

23. SUPERIOR ORBITAL FISSURE
It is divided into 3 parts by common tendinous ring
Structures transmitted through the fissure are :
A) Upper part and lateral part (medial to lateral) :
Trochlear nerve.
Frontal nerve.
Lacrimal nerve.
Superior ophthalmic vein.
B) Middle part (within the tendinous ring) :
2 divisions of oculomotor nerve (sup and inf)
Abducent nerve
Nasociliary nerve.
C)Lower and medial parts transmits inferior ophthalmic vein.

24. LANDMARK
Annulus of Zinn
- Spans both superior orbital fissure and optic canal.
- gives origin to four recti muscles .

25. CLINICAL SIGNIFICANCE
Inflammation of the SOF and apex may result in multitude of signs
including ophthalmoplegia and venous outflow obstruction
TOLOSA HUNT SYNDROME

26. Fracture at Superior orbital fissure
Involvement of cranial nerves
Diplopia,Opthalmoplegia,Exophthalmos,Ptosis
SUPERIOR ORBITAL SYNDROME

27. INFERIOR ORBITAL FISSURE
 Also known as sphenomaxillary fissure.
Lies between lateral wall and floor of orbit,giving access to the
pterygopalatine and inferotemporal fossae. It transmits following
1. infraorbital and zygomatic branches of the maxillary division of
the of Vth cranial nerve.
2. orbital branch of pterygopalatine ganglion
3. branch of inferior ophthalmic vein which communicates with the
pterygoid plexus.
 serves as the posterior limit of surgical subperiosteal dissection
along the orbital floor.

28. OPTIC CANAL
Connects the orbit to the middle cranial fossa.
Contents : optic nerve and ophthalmic artery.
Average length : 6-11mm (lateral wall is shortest and medial wall is
longest)
Its orbital end is vertically oval (6*5mm),
 centre is circular (5*5mm),
 cranial end horizontal (4.5mm*6mm)
Clinical significance
Tumours such as optic nerve glioma and meningioma can
lead to unilateral enlargement of optic canal.

29. PERIORBITA
Orbital periosteum .
Loosely adherent to the bones.
Sensory innervation by branches of V’th cranial nerve.
Fixed firmly at
-Orbital margines (arcus marginale)
-Suture lines
-Lacrimal fossa (lacrimal fascia)
-Optic canal,Superior and inferior orbital fissures.
At the apex of orbit,the periorbita is thickened to form common
tendinous ring of Zinn.

30. FASCIA BULBI
•Also known as Tenon’s capsule or bulbar sheath.
•Dense,elastic and vascular connective tissue that surrounds the globe
( except over the cornea).
•Begins anteriorly at the perilimbal sclera,extends around the globe to
the optic nerve ,and fuses with dural sheath and the sclera.
•Separated from sclera by periscleral lymph space,which is in
continuation with subdural and subarachnoid spaces.
•The lower part of fascia bulbi is thickened and takes part in formation
of a sling on which the globe rests.(suspensory ligament of
Lockwood).
•Pierced anteriorly by six extraocular muscles
• posteriorly by optic nerve,ciliary nerves and vessels.

31. SURGICAL SPACES IN ORBIT

33. SUBPERIOSTEAL SPACE
Space between orbital bones and the periorbita.
Limited anteriorly by strong adhesions of periorbita to
orbital rim.
Tumours arising from the bones separate periobita from
bones,forming and effective barrier against the spread of tumour
towards eye.

34. PERIPHERAL ORBITAL SPACE
Bounded
-peripherally by periorbita
-internally by the 4 recti with intermuscular septa.
-anteriorly by the septum orbitale.
-posteriory it merges with the central space.
Tumours present in this space eccentric proptosis.

35. CONTENTS
Peripheral orbital fat
Muscles
- Superior oblique
-Inferior oblique
-Levator palpebrae superioris
Nerves
-Lacrimal nerve
-frontal
-trochlear
-anterior ethmoidal
-posterior ethmoidal nerve
Veins
-superior and inferior ophthalmic veins
Lacrimal gland
Lacrimal sac

36. CENTRAL SPACE
Also called muscular cone or retrobulbar space.
Bounded anteriorly by Tenon’s capsule and sclera.
CONTENTS :
1.Optic nerve and its meninges
2.Superior and inferior divisions of oculomotor nerve
3.Abducent nerve
4.Nasociliary nerve
5.Ciliary ganglion
6.Ophthalmic artery
7.Superior ophthalmic vein
8.Orbital fat

37. CLINICAL SIGNIFICANCE
Tumours in central space axial proptosis.
Tumours are often removed by lateral orbitotomy.

38. SUBTENON’S SPACE
oSpace around eyeball between sclera and Tenon’s capsule.
oPus collected in this area are drained by incision of
Tenon’s capsule through the conjunctiva.

39. THANK YOU