Anatomy of orbit By- Dr. Kawshik Nag, Resident, Ophthalmology, Phase-A Chittagong Medical College.

1. Orbital Anatomy
By- Dr. Kawshik Nag,
Resident,
Ophthalmology, Phase-A
Chittagong Medical College.

2. Anatomy Of Orbit
 Quadrangular truncated
pyramidal in shape.
 Bounded by-
• Superiorly- Anterior cranial
fossa
• Medially- Nasal cavity and
ethmoidal air sinuses
• Inferiorly- Maxillary sinus
• Laterally- Middle cranial fossa
and Temporal fossa.

3. Dimensions
 Volume: 30cm3
 Rim: Horizontally- 4cm
Vertically- 3.5cm
 Intra orbital width: 2.5cm
 Extra orbital width: 10cm
 Depth: Medially- 4.2cm
Laterally- 5.0cm
 Ratio of vol. of orbit : vol. of
globe: 4.5:1

4. Bony Orbit
Seven bones make
up the bony orbit :
 Frontal bone
 Zygomatic Bone
 Maxillary bone
 Ethmoid bone
 Sphenoid bone
 Lacrimal bone
 Palatine bone

5. Walls Of The Orbit
 The bony orbit has four
walls:
 Medial wall
 Lateral wall
 Roof
 Floor

6. Medial Orbital Wall
The medial wall is
formed from front to
back by the:
 Frontal process of maxilla
 Lacrimal bone
 Orbital plate of the ethmoid
bone
 Body of the sphenoid bone.

7. Medial Orbital Wall
Clinical applications:
• It is the thinnest wall of the orbit, so it is frequently fragmented as a
result of indirect blow out fractures and during orbitotomy operations.
• Frequently eroded by chronic inflammatory lesions, neoplasms, cysts.
• Medial wall provide alternate access route to the orbit through sinus.
• Haemorrhage can occur due to trauma to ethmoidal vessels.
• Accidental lateral displacemet of medial wall causes traumatic
hypertelorism.

8. Lateral Orbital Wall
 Thickest and strongest.
 Formed by two bones:
• Zygomatic
• Greater wing of sphenoid.

9. Lateral Orbital Wall
Clinical applications:
• The anterior half of globe is not covered by bone on lateral side.
Hence, palpation of retrobulbar tumours is easier from the lateral
side.
• The zygomatico-sphenoid suture is an important landmark in creating
the flap in lateral orbitotomy.
• It is the strongest portion of the orbit and needs to be sawed open in
lateral orbitotomy.
• Since lateral wall is almost devoid of foramina, bleeding is less.

10. Roof Of Orbit
 Underlies frontal sinus and
anterior cranial fossa.
 Formed by-
• Orbital plate of frontal bone
• Lesser wing of sphenoid.
 Triangular.
 Faces downwards and slightly
forwards.

11. Roof Of Orbit
Clinical applications:
• Thin and periorbita peels away easily.
• Objects piercing upper eyelid penetrate roof and damage frontal
lobe.
• In old age roof may be absorbed so that periorbital and duramater
comes into contact.
• Any trauma of dura mater and CSF escapes into orbit or nose or
both.

12. Floor Of Orbit
 Shortest orbital wall.
 Formed by:
• Maxillary bone- medially
• Zygomatic bone- laterally
• Palatine bone- posteriorly.
 Triangular in shape.
 Bordered laterallly by inferior
orbital fissure and medially by
maxilloethmoidal sinus.
 Overlies maxillary sinus.

13. Floor Of Orbit
Clinical applications:
• Commonly involved in Blow
out fractures of the orbit.
Infra orbital vessels and
nerves almost always
involved.
• Diplopia is the main
symptoms of blow-out
fracture.
• Easily invaded by tumors of
the maxillary antrum.
Figure- Mechanism of blow-out fracture
from displacement of the globe itself into
the orbital walls. The globe is displaced
posteriorly, striking the orbital walls and
forcing them outward.

14. Base Of Orbit
 The anterior open part.
 Bounded by four orbital
margins-
• Superior orbital margin
• Inferior orbital margin
• Medial orbital margin
• Lateral orbital margin.
 It gives attachment to the
septum orbitale.

15. Apex Of Orbit
 Orbital apex is the posterior
end of the orbit.
 Four orbital walls converge.
 Two orifices:
• Optic Canal
• Superior orbital fissure

16. Optic Canal
 It connects the orbit to the
middle cranial fossa.
 It transmits:
• Optic Nerve
• Ophthalmic artery.

17. Superior Orbital Fissure
 Structure passing:
 Upper lateral part:
• Lacrimal and frontal nerves
• Trochlear nerve
• Superior ophthalmic vein
• Recurrent branch of
ophthalmic artery.
 Middle part:
• Superior and inferior divisions
of occulomotor nerve
• Nasociliary branch of
ophthalmic division of
trigeminal nerve.
• Abducent nerve.
 Lower medial part:
• Inferior ophthalmic vein.

18. Superior Orbital Fissure
Clinical applications:
• Radiographic enlargement of superior orbital fissure may
accompany pathologic processes,
 Aneurysm
 Meningioma
 Choroidoma
 Pituitary adenoma
 tumours of orbital apex.
• When idiopathic inflammation involves the superior orbital fissure,
the “Tolosa Hunt syndrome” which is painful ophthalmoplegia
results.

19. Periorbita
 Periorbita refers to periosteum
lining the orbitlal surface of the
bones of orbit.
 Loosely adherent to the bones.
 Fixed firmly at-
• Orbital margins
• Suture lines
• Various fissures and foramina
• Lacrimal fossa.
 Applied Anatomy-
• Surgery in the orbital roof in
the areas of fissures and
suture lines may be
complicated by cerebrospinal
fluid leakage.

20. Orbital Fascia
 It is a complex interwoven thin
connective tissue membrane
joining the various intraorbital
contents.
 Parts-
• Fascia bulbi,
• Muscular sheaths,
• Intermuscular septa,
• Membranous expansions of
the extraocular muscles,
• Ligament of Lockwood.

21. Extraocular Muscles
 Voluntary Muscles:
• Superior rectus
• Inferior rectus
• Medial rectus
• Lateral rectus
• Superior oblique
• Inferior oblique
• Levator palpebrae superioris.
 Involuntary Muscles:
• Superior tarsal or Muller’s
muscle,
• Inferior tarsal muscle.

22. Surgical Spaces In Orbit
 Orbit is divided into 4 surgical spaces-
• Subperiosteal space
• Peripheral orbital space/ Extraconal space
• Central orbital space/ Intraconal space
• Subtenon’s space

23. Surgical Spaces In Orbit
 Importance of these spaces-
• 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.

24. Subperiosteal Space
 Lies between orbital bone and
periorbita.
 tumours arising from bone
separates periorbita from
bone.
 Here periorbita acts as a
effective barrier against spread
of tumour to eye.

25. Subperiosteal Space
 tumours in this space are-
• Dermoids cyst
• Epidermoid cyst
• Mucocele
• Subperiosteal abscess
• Osteomatous tumour

26. Peripheral Orbital Space
 Known as extraconal space.
 Lies between periorbita at
periphery, extraocular muscles
and their intermuscular septa
internally and orbital septum
anteriorly.
 Posteriorly it merges with
central space.
 tumours in this space are
usually approached by anterior
orbitotomy and sometimes by
lateral orbitotomy.

27. Peripheral Orbital Space
 tumours in this space produce eccentric proptosis.
 tumours in this space are-
• Malignant Lymphoma
• Capillary haemangioma of childhood
• Intrinsic neoplasm of lacrimal gland
• Pseudotumours.

28. Central Orbital Space
 Known as muscle cone/ retro-
orbital space/posterior space/
intraconal space.
 Bounded by-
• Anteriorly tenon’s capsule
• Posteriorly by 4 recti and
intermuscular septa.
 In posterior part, space
become continuous with
peripheral space.

29. Central Orbital Space
 tumours of this space-
• Cavernous haemangioma of adults
• Solitary neurofibroma
• Neurolemoma
• Nodular orbital meningiomas
• Optic nerve glioma.
 Produce axial proptosis.
 tumours are approached through lateral orbitotomy.

30. Subtenon’s space
 Space around eyeball between
sclera and tenon’s capsule.
 Pus collection in this space is
drained by incision on tenon’s
capsule through conjunctiva.

31. Contents Of The Orbit
 Eyeball
 Fascia: Orbital and bulbar.
 Muscles: Extraocular.
 Vessels:
• Ophthalmic artery
• Superior and inferior ophthalmic
vein
• Lymphatics.
 Nerves: Optic,Oculomotor,
Trochlear, Abducent, Branches of
ophthalmic nerves and
sympathetic nerves.
 Ciliary ganglion
 Lacrimal gland and lacrimal sac
 Orbital fat.