The orbit is the bony cavity that houses the eye and its appendages. It has a quadrilateral pyramidal shape and is bounded superiorly by the frontal bone, medially by the ethmoid and lacrimal bones, inferiorly by the maxilla and floor, and laterally by the zygomatic bone. It contains the eye, extraocular muscles, blood vessels, and nerves. The thin walls provide multiple pathways between the orbit and surrounding areas like the paranasal sinuses and cranial fossae, allowing for spread of infection or tumors. Anatomical landmarks like the optic canal, superior orbital fissure, and infraorbital fissure transmit important neurovascular structures between the orbit and other areas

1. Orbital Structure
and It’s application
dr. Frenky R. de Jesus
National Eye Centre
Postgraduate diploma in Ophthalmology

2. Orbital structure & it’s application
Definition
The orbit is the cavity or socket of the skull in which
the eye and its appendages are situated.
DIMENSIONS
- Quadrilateral pyramid.
- Base - forwards, laterally, downwards
- Apex - optic foramen
Rim
• Horizontally: 40 mm
• Vertically: 35 mm.
• Interorbital width: 25 mm
• Extraorbital width: 100 mm
Depth
◦ Medially ≈ 42 mm ◦ Laterally ≈ 50 mm.
BOUNDED
Superiorly: Anterior cranial fossa
Medially: Nasal cavity and ethmoidal air cells
Inferiorly: Maxillary sinus
Laterally: Middle cranial fossa.

3. Orbital structure & it’s application
Bones of Orbit

4. Orbital structure & it’s application
ROOF
LATERAL
MEDIAL
FLOOR
WALL OF ORBIT

5. Orbital structure & it’s application
ROOF
• Underlies Frontal sinus and Anterior cranial fossa.
• Formed by:
๏ Frontal bone (Orbital plate)
๏ Lesser wing of Sphenoid
• Triangular
• Faces downwards, and slightly forwards
• Concave anteriorly, almost flat posteriorly
• The anterior concavity is greatest about 1.5 cm
from the orbital margin & corresponds to the
equator of the globe.
• Thin, transluscent and fragile (except the lesser
wing of the sphenoid).

6. Orbital structure & it’s application
ROOF (Landmarks)
FOSSA FOR THE LACRIMAL GLAND
LOCATION:
Behind the zygomatic process of the frontal bone
CONTENTS:
• Lacrimal gland.
• Some orbital fat (accessory fossa of Rochon- Duvigneaud)
TROCHLEAR FOSSA (FOVEA)
LOCATION:
4 mm from the orbital margin.
CONTENTS:
• Insertion of tendinous pulley of Superior Oblique.
• Sometimes surmounted by a spicule of bone (Spina
trochlearis)
• Extremely rarely trochlea completely ossified cracks easily
SURFACE ANATOMY:
Palpable just within the supero-medial angle.

7. Orbital structure & it’s application
ROOF (Landmarks)
SUPRAORBITAL NOTCH:
LOCATION:
15 mm lateral to the superomedial angle
TRANSMITS:
- Supraorbital nerve
- Supraorbital vessels
SURFACE ANATOMY:
• At the junction of lateral 2/3rd and medial 1/3rd
• About two finger breadth
OPTIC FORAMEN
LOCATION
• Lies medial to superior orbital fissure
• At the apex
• Present in the lesser wing of sphenoid
TRANSMITS
• Optic nerve with its meninges
• Ophthalmic artery

8. Orbital structure & it’s application
ROOF (Clinical Significance)
Thin & Fragile
Easily fractured by direct violence (penetrating orbital injuries)
Easily fractured by direct violence
(Penetrating orbital injury)
Frontal lobe injury

9. Orbital structure & it’s application
MEDIAL WALL
• Thinnest orbital wall.
• Formed by:
1. Frontal process of Maxilla
2. Lacrimal bone
3. Orbital plate of Ethmoid
4. Body of Sphenoid

10. Orbital structure & it’s application
MEDIAL WALL (Landmarks)
LACRIMAL FOSSA
Formed by:
• Frontal process of Maxila
• Lacrimal bone
Content
Lacrimal sac
Boundaries:
• Anterior lacrimal crest
• Posterior lacrimal crest
• Frontoethmoidal suture
• Anterior ethmoidal foramen
• Posterior ethmoidal foramen

11. Orbital structure & it’s application
MEDIAL WALL (Clinical Significance)
• Anteriorly located suture indicates predominance of lacrimal bone
• Posteriorly located suture indicates the predominance of maxillary bone
• If maxillary component is predominant, it becomes difficult to perform osteotomy to reach the sac during DCR, because
the maxillary bone is very thick.
• Medial wall extremely fragile (presence of ethmoidal air cells and nasal cavity)
• Accidental lateral displacement of medial wall- traumatic hypertelorism
• Medial wall provides alternate access route to the orbit through the sinus
Ethmoid
• Thinnest bone of the orbit
• Vascular connections with ethmoid sinus through foramina
• Inflammation in the ethmoid sinus spreads readily to the orbit
• Tumours of the nasal cavity can breach the lamina papyracea to involve the orbit
• Lacrimal bone can be easily penetrated during endoscopic DCR
• During surgery, hemorrhage is most troublesome due to injury to ethmoidal vessels.

12. Orbital structure & it’s application
FLOOR
• Shortest orbital wall.
• Roughly triangular.
• Bordered laterally by inferior orbital fissure and medially by
maxilloethmoidal suture
• Overlies maxillary sinus.
Formed by:
• Orbital plate of maxilla (major)
• Orbital surface of Zygomatic bone (anterolateral)
• Orbital plate of Palatine bone

13. Orbital structure & it’s application
FLOOR (Landmarks)

14. Orbital structure & it’s application
FLOOR (Clinical Significance)
BLOW OUT FRACTURE

15. Orbital structure & it’s application
LATERAL WALL
• Thickest orbital wall
• Separates orbit from
๏ Middle cranial fossa
๏ Temporal fossa
Formed by:
• Zygomatic bone
• Greater wing of sphenoid

16. Orbital structure & it’s application
LATERAL WALL (Landmarks)
LATERALORBITAL TUBERCLE OF WHITNALL:
- 4-5 mm behind the lateral orbital rim
- 11 mm inferior to the frontozygomatic suture line
Gives attachment to:
• Check ligament of lateral rectus
• Lockwood’s ligament
• Lateral canthal tendon
• The aponeurosis of the levator palpebrae superioris
• Orbital septum
• Lacrimal fascia

17. Orbital structure & it’s application
In resection of maxilla, the Whitnall’s tubercle is spared, otherwise
• Damage to Lockwood’s ligament
• Inferior dystopia of eye ball
• Diplopia
ZYGOMATIC GROOVE:
EXTENT
From the anterior end of the inferior orbital fissure to a foramen in the zygomatic bone
CONTENTS
- Zygomatic nerve
- Zygomatic vessels
• Lateral wall protects only the posterior half of the eyeball, hence palpation of retrobulbar tumours is easier.
• Frontal process of zygoma & zygomatic process of frontal bone protect the globe from lateral trauma- known as facial
buttress area.
• Just behind the facial buttress area, is the zygomaticosphenoid suture, which is the preferred site for lateral orbitotomy.
LATERAL WALL (Clinical Significance)

18. Orbital structure & it’s application
ORBITAL MARGINS
SUPERIOR ORBITAL MARGIN
• Formed by Frontal bone
• Concave downwards, convex forwards sharp in lateral
2/3rd, rounded in medial 1/3rd - at the junction-
supraorbital notch (sometimes foramen)*
*Site for nerve block.
Arnold’s notch/foramen
Present medial to supraorbital notch
Transmits
medial branches of supraorbital nerve & vessels
Supraciliary canal
Near the supraorbital notch
Transmits
• Nutrient artery
• A branch of supraorbital nerve to frontal air sinus
Surface anatomy
• Well marked prominence
• More prominent laterally than medially
• Eyebrow corresponds to the margin only in a part -
Head- under the margin
• Body- along the margin
• Tail- above the margin

19. Orbital structure & it’s application
LATERAL ORBITAL MARGIN
• Formed by zygomatic process of frontal and the
zygomatic bone.
• Strongest portion of margin.
Clinical significance
• Lateral orbital rim is recessed on its deep aspect 0.75
cm above the rim margin to accommodate the lacrimal
gland.
• Prone to fracture.
• Narrowest and weakest part- frontozygomatic suture.
• Prone for separation following blunt trauma.
ORBITAL MARGINS
INFERIOR ORBITAL MARGIN
• Formed by Zygomatic - Maxilla
• suture between the two is sometimes marked by a
tubercle- felt 4-5 mm above the infraorbital foramen
Surface anatomy
• Palpable as a sharp ridge, beyond which the finger can
pass into the orbit
Clinical significance
• At the junction of lateral 2/3rd & medial 1/3rd just within
the rim- small depression- origin of Inferior oblique
• Prone to fracture
• Disruption of Inferior oblique
• Diplopia
Penetrating injuries may severe lacrimal passages
MEDIAL ORBITAL MARGIN
Formed by Frontal process of maxilla (anterior lacrimal
crest) - Lacrimal bone (posterior lacrimal crest).

20. Orbital structure & it’s application
FISSURES AND FORAMINA
• Leads from the middle cranial fossa to the apex of the
orbit.
• Orbital opening- vertically oval.
• In the middle - circular (≈5mm)
• Intracranial - horizontally oval.
• Length; 8-12 mm
Boundaries
- Medially; Body of the sphenoid
- Laterally; Lesser wing of the sphenoid
Transmits
• Optic nerve & its meninges
• Ophthalmic artery
Optic Canal
Clinical significance: Optic nerve glioma or Meningioma may lead to unilateral enlargement of Optic canal

21. Orbital structure & it’s application
• Also known as Sphenoidal fissure
• Bounded by Lesser and greater wings of the sphenoid
• Lateral to the optic foramen at the orbital apex.
• 22 mm long.
• Largest communication between the orbit and the
middle cranial fossa.
• Its tip lies 30-40 mm from the frontozygomatic suture.
• Landmarks: annulus de zinn.
• Transmits the lacrimal, frontal, trochlear (CN IV),
oculomotor (CN III), nasociliary and abducens (CN VI)
nerves. It also carries the superior ophthalmic vein.
Superior orbital fissure
Clinical significance
• TOLOSA HUNT SYNDROME; Inflammation of the
superior orbital fissure and apex may result in a
multitude of signs including ophthalmoplegia and venous
outflow obstruction
• SUPERIOR ORBITAL SYNDROME (Rochon-Duvigneaud
syndrome)
๏Fracture at superior orbital fissure.
๏Involvement of cranial nerves
๏Diplopia, Ophthalmoplegia, Exophthalmos, Ptosis.
FISSURES AND FORAMINA

22. Orbital structure & it’s application
• Also known as sphenomaxillary fissure
• Between floor and the lateral wall
• Bounded by;
o Medially- Maxilla and orbital process of palatine
o Laterally- Greater wing of the sphenoid
o Anterior aspect- closed by Zygomatic bone
Transmits;
• Venous drainage from the inferior part of the
orbit to the pterygoid plexus
• Neural branches from the pterygopalatine ganglion
• The zygomatic nerve - the infraorbital nerve
Inferior orbital fissure
FISSURES AND FORAMINA

23. Orbital structure & it’s application
Others Pathways into the Orbit
• Transmits the optic nerve and
ophthalmic artery
• Transmits the lacrimal, frontal,
trochlear (CN IV), oculomotor
(CN III), nasociliary and
abducens (CN VI) nerves. It also
carries the superior ophthalmic
vein.
• Transmits the zygomatic branch of the
maxillary nerve, the inferior ophthalmic
vein, and sympathetic nerves
Nasolacrimal
canal • Which drains tears
from the eye to the
nasal cavity,
Supraorbital
foramen and
infraorbital canal
• They carry small
neurovascular
structures.

24. Orbital structure & it’s application
CONTENTS OF THE ORBIT
• Nerves
◦ Sensory- branches of V’th Nerve
◦ Motor- III’rd, IV’th & VI’th Nerve
◦ Autonomic- Nerves to the Lacrimal gland.
• Ciliary ganglion
• Eye ball
• Muscles
◦ 4 Recti
◦ 2 obliques
◦ Levator palpebrae superioris
◦ Muller’s muscle (Musculus orbitalis)
Vessels
•Arteries
๏Internal carotid system- branches of ophthalmic artery
๏External carotid system- a branch of internal maxillary artery
•Veins
๏Superior ophthalmic vein
๏Inferior ophthalmic vein
• Lymphatics
๏none
Lacrimal gland
Lacrimal sac
Orbital fat, reticular tissue & orbital fascia

25. Orbital structure & it’s application
Ciliary Ganglion
• Ciliary ganglion is a parasympathetic ganglion
• It measures 1-2 mm in diameter and contains 2.500
neurons.
• Lies between Optic nerve and Lateral Rectus
muscle
• The oculomotor nerve coming into the ganglion
contains preganglionic axons from the Edinger-
Westphal nucleus which form synapses with the
ciliary neurons.
• The posganglionic axons run in the short ciliary
nerves and innervate 2 muscles:
๏ The sphincter pupillae (miosis) and mydriasis.
๏ Ciliary muscle.

26. Orbital structure & it’s application
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