Scene 1

The eyeball is protected by a bony socket called the orbit on the two 
sides of the nose.  The seven bones that make up the orbit are FS 
MZPEL (frontal, sphenoid, Maxilla, Zygoma, Palatine, Ethmoid and 
Lacrimal). The four-sided orbital cavity is pyramidal in shape with an 
open base in front and an apex on the back. The four walls of the orbit 
converge posteriorly to reach the apex on their back formed by the 
optic foramen.

Base: Opens out into the face, bounded by the orbital margins.

Walls: roof, floor, and medial and lateral walls.

Apex: Posterior, located at the opening of the optic canal, the optic 
foramen.

Nasal
Lærimal
Frontal
Lesser sphenoid
wing
Greater sphenoid
Wing
Palatine
Maxilla
Zywmatc

Scene 2

Entry Points: the optic canal, superior orbital fissure, and the inferior 
orbital fissure.

Sinuses: air-filled cavities in the bones; frontal, ethmoidal, sphenoid, 
and maxillary

The skull has 22 bones divided into cranial and facial bones. We start 
our discussion here because the bones of the orbit are made of 7 
different bones from the cranium and the face. The bones of the skull 
protect the brain. There are 8 cranial bones and 14 facial bones.

Cranial Bones: Frontal, Parietal (2), Temporal (2), Occipital, Sphenoid 
and Ethmoid

The 14 facial bones are; Frontal bone, Maxilla, Mandible, Zygoma, 
Palatine bones, Lacrimal bones, nasal bones, vomer and inferior nasal 
conchae. Out of the skull bones, only mandible and auditory ossicles

FRONTAL BONE
Coronal suture
suture
PARIETAL

Paretal brarnna
Suture
Sutural
BONE
(a) Superior view

Scene 3

The orbits are two bony cavities on either side of the mid-sagittal 
plane below the anterior cranium that houses the eyeball. It houses 
other structures such as the extraocular muscles, nerves, lacrimal 
apparatus, fat and blood vessels. The bony orbit is shaped like a four-
sided pyramid comprising of an apex and four walls.

Three cranial bones form part of the orbit: the frontal, sphenoid, and 
the ethmoid bones. The rest are facial bones—maxillary, zygomatic, 
palatine, and lacrimal bones. The lacrimal bone is the smallest bone of 
the face and articulates with maxillary bone, ethmoid and frontal 
bones.

1. Frontal bone 
2. Sphenoid 
3. Maxilla 
4. Zygoma

Parietal bone
SSAK•noidal bone
Temporal bone
Ethnu•idal bone
Vomer
Frontal bone
Supra-orbital
Nasal bone
Lacrimal bone
Zygomatic bone
Inira.orbital
fora rnen
Maxilla

Scene 4

Out of the 7 orbital bones, 3 are single; ethmoid, frontal and sphenoid 
(EFS). The rest are paired, 1 in each orbit.

The base or front of the orbits is formed by 2 margins each. The 
supraorbital margin which is a thick ridge of the frontal bone and the 
inferior orbital margin. The inferior orbital margin is formed laterally by 
the zygomatic bone and medially by part of the maxilla. The cavity is 
often compared to the shape of a pear whose stalk is formed by the 
optic canal. Its medial walls are parallel to each other.

The bony orbit is bounded by 4 walls; roof, floor, lateral and medial 
walls.

The orbital roof is triangular and composed of;

1. Orbital plate of the frontal bone. (anterior) 
2. Lesser wing of the sphenoid bone. (posterior)

• Frontal bone forms the ridge of the superior orbital margin.

• Cartilaginous u-shape structure called trochlear attached to the

Scene 5

• Tendon of the superior oblique muscle passes through the

CLINICAL NOTES: Refer to Orbital Rim Fracture in the clinical notes.

The orbital floor is also triangular and made up of:

Supraorbital notch
ethmoidal canal
Frontal sinus
ethmoidal canal
Ethnwid
Triangular roof
Fossa br
lacrimal gland
Lesser wing
of sphenoid

orbital
margin
Orbital plate Of
frontal tX)ne
Fßsa for
lacrimal
Apex of triangle
Fraltal sinus
Maxillary prcxess
Of frontal
Optic forarnen
wing Of
Suprior orbital

Scene 6

3. Small orbital process of the palatine bone.

• Maxillary bone makes up most of the floor with largest part of the

• Floor is separated from the lateral wall by the inferior orbital

• The floor is the shortest of the walls.

CLINICAL NOTES: Refer to Blow Out Fracture in the clinical notes.

The medial wall is rectangular and formed by:

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Scene 7

 The ethmoid bone forms most of the medial wall.

• The orbital plate of the ethmoid is sometimes said to be “paper

• The medial wall is the thinnest of the orbital walls but the least

prone to fracture due to support of the honeycombed structure 
of the ethmoid bone

• The lacrimal sac lies in the lacrimal fossa

• The thickness of the fossa allows easy penetration of needle

• The anterior and posterior ethmoidal canals are located within the

2. Greater wing of the sphenoid posteriorly

3. The zygoma separates the orbit from the temporal fossa.

• One or more foramina may be present, serving as a conduit for

nerves and blood vessels between face and orbit.

Scene 8

 The lateral wall is directed posteriorly and allows for a wide field

of view but makes the eye prone to injury.

 The zygomaticosphenoidal suture is the thinnest portion of the

lateral wall and a good point of entry during lateral orbitotomy

 The lateral (marginal) orbital tubercle is a small bony prominence

located on the orbital surface of zygoma. It is the attachment for

o the aponeurosis of the levator palpebrae superioris

 Greater wing of the sphenoid separates the orbit from the middle

 The roof is separated from the lateral wall in back by the superior

orbital fissure and in front by the frontozygomatic and 
frontosphenoidal sutures.

 The inferior orbital fissure separates the posterior part of the floor

Frontal sinus
lacrinal
(PLC.)
Anterior
crest (AL.C.)
Lacrimal fcssa
Frontal præess
maxdla (F.PM.)
Ethmoid (E)
Of sphenoid (S)
Brarnen
bone (L)

Scene 9

CLINICAL NOTES: Refer to ZMC in the clinical notes section.

The infraorbital groove and canal constitute weak spots in the floor of 
the orbit. Another weak spot, as shown in is the thin bone ethmoid, 
which separates the eye from the medial wall. Ethmoiditis in children 
may give rise to orbital cellulitis, and severe contusion injuries can 
cause rupture of the medial wall and periorbital crepitus. The lacrimal 
fossa in the medial wall is also a weak spot. The fossa lies between the 
anterior and posterior lacrimal crests and lodges the lacrimal sac, 
which is continuous below with the nasolacrimal duct. The duct’s 
lower end opens into the inferior meatus of the nose for drainage of 
tears when severe emotional stress occurs.

Although dimensions of the orbit vary widely, the average

horizontal diameter of the orbital margin is 4 cm, the average vertical

diameter is 3.5 cm, and the average depth is 4.5 cm. The frontal bone

forms the superior orbital margin. The highest point of this arch is

Scene 10

supraorbital notch. and is the conduit for the supraorbital vessels and

The lateral orbital margin is the orbital region most exposed to 
possible injury and therefore is the strongest area of the orbital margin. 
It is formed by the zygomatic process of the frontal bone superiorly 
and by the frontal process of the zygomatic bone inferiorly.

It is the entry site of all the nerves & blood vessels to the eye and all 
the extraocular muscles except the inferior oblique. This lies near the 
medial end of the superior orbital fissure and contains the optic canal. 
The superior and inferior orbital fissures and the optic canal open into 
the orbit. They transmit important nerves and vessels.

Greater wing
of sphenoid
Zyprnatic
Whitnars lateral
orbital
IOG
Frontal
Zygomatic
Maxilla
Base of orbit quadrangular in front
At apex orbit
On back — OF - Optic foramen
Supraorbital notch
Træhlear
Infraoptic
Frontal
Of maxila
Lacrinal tutercle
Orbital plate
of maxilla

SOF - Supenor orbital
fissure
IOF - Interior orbital
fissure
In floor orbit — - Infraorbital grcxwe
IOC - Intraorbital canal
IOF - Infraorbital foramen

Scene 11

There are three main pathways by which structures enter or leave the 
orbit—the optic canal, superior and inferior orbital fissure.

The optic canal conveys the optic nerve and ophthalmic artery from 
the optic canal into the orbit. The canal is housed in the lesser wing of 
the sphenoid bone with a contribution from the inferomedial optic 
strut. It runs 8–10 mm in length and is 5–6 mm in diameter. The optic 
canal and foramen attain adult dimensions by 3 years and are 
symmetric in most persons. A canal/foramen that is larger in diameter 
by at least 1 mm than the contralateral side may be considered 
abnormal.

Scene 12

This is the gap between the lesser wing and the greater wing of the 
sphenoid. It is located between the roof and the lateral wall. It 
connects the middle cranial cavity with the orbit. A circular band of 
connective tissue, the common tendinous ring or ANNULUS OF ZINN 
is located anterior to the fissure and optic canal. The ring is the origin 
of the four rectus muscles.

Superior orbital fissure
o
Lacrimal nerve (CN Va)
Frontal nerve (CN Va)
Trcx;hlear nerve (CN IV)
o
Superior division Of the
oculomotor nerve (CN Ills)
Nascx:iliary nerve (CN Va)
Inferior division of the
LAT
oculomotor nerve (CN Illi)
Abducens nerve (CN VI)
Ganglionic branches (from pterygopalantine
ganglion to maxillary nerve)
SUP
Superior ophthalmic vein
Tendinous ring
(of Zinn)
o
o
o
o
Optic canal
Optic nerve (CN II)
Ophthalmic a
MED

Lacründ nerve
Frontal nerve
Superior ophthaknic vein
ner.e
Nzæiiary nerve
Abducens nerve
Inferbr oakrnotor nerve
nerve
Lateral recus musde
Levator musde
recus musde
Su— nusde
of
Opic nave
Medal recttß musde
art«y
rectus rmsde
ophtlamc

Scene 13

Structures that enter the orbit within the annulus:

1. Inferior division of the oculomotor nerve

4. Superior division of the oculomotor nerve

Vessels and Nerves enter the orbit outside the annulus.

It is bounded above by the greater wing of the sphenoid, below by the 
maxilla, the palatine and laterally by the zygoma. The fissure connects 
the orbit with the pterygopalatine and infratemporal fossa.

 Infraorbital and zygomatic branches of the maxillary nerve 
  Inferior ophthalmic vein.

Paranasal sinuses are cavities within the bones that form the skull and 
the orbit. They include;

1. Frontal sinus 
2. Ethmoidal sinus 
3. Sphenoid sinus 
4. Maxillary sinus

Scene 14

CLINICAL NOTES: Refer to Orbital Cellulitis in clinical notes section

Sphenoidal sinus
Ethmoidal sinus
Maxillary sinus
Frontal sinus

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