The Orbital Cavity

OPTOMETRY · SEMESTER 2

Ocular Anatomy and Physiology

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The Orbital Cavity

CHAPTER 2. THE ORBITAL CAVITY

THIS CHAPTER SHOULD BE READ WITH A SKULL MODEL IN FRONT

BY THE END OF THIS CHAPTER YOU WILL KNOW:

DEFINITION,SHAPE, MEASUREMENTS, RELATIONSHIPS

THE WALLS OF THE ORBIT

ORBITAL CONTENTS

THE FUNCTIONS OF THE ORBIT

OPENINGS OF THE ORBIT

CLINICAL CONSIDERATIONS

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1. DEFINITION, SHAPE , MEASUREMENTS, RELATIONSHIPS.
1.1. The shape of the orbit.
It is like a hollow pyramid or a pear with an open base facing forwards
ja and the a of the pee or the stem of the pear facing
The stalk of the pear represents the optic nerve and lies in an opening called
the optic foramen.
The medial walls are almost parallel.
The apex of the orbit is
Important nerves and vessels are crowded here,
1.2. Measurements of the orbit.
a. Height: 35mm
b. Width: 45mm
c. Depth: 40-45mm from the entrance to apex
d. Volume (adult): ~30cc
1.3. Relationships – the paranasal sinuses.
Adjacent to the orbital cavities lie the paranasal sinuses.
These are bony cavities filled with air, located as follows:
the frontal sinus (FS ), superiorly;
e the ethmoid sinus (ES ), medially;
e the maxillary sinus ( MS ), inferiorly;
e the sphenoid sinus posteriorly.
Fig. 2.1. The relationship of the orbits to the paranasal sinuses.
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2. THE WALLS OF THE ORBIT.
The walls of the orbit are:
The roof (superior wall)
The floor (inferior wall)
The medial wall
The lateral wall
The bones that make up the orbit are:
Maxillary
Zygomatic
Ethmoidal
Sphenoid (has a body and two wings – the greater and lesser
wings)
Frontal
Palatine
Lacrimal
The frontal, sphenoid, and ethmoid are each a single bone and take part in
the

formation of both orbits.

Frontal Superior Palatine

bone orbital rim bone
Optic
eral Ethmoid
bone
Lesser
sphenoid
wing: Medial
orbital
Lateral —~ | ve
orbital
rim
Greater
sphenoid

wing,

Zygomatic Inferior Maxillary Lacrimal

bone orbitalrim bone bone
Fig. 2.2. The bones of the orbit.
2.1. The Roof of the orbit.
The roof is triangular made up of two bones:
e the frontal bone;
e the lesser wing of the sphenoid bone.
There is on the anterolateral part of the roof, called fossa
. This is where the lacrimal gland lies.
At the junction of the medial third and lateral two-thirds is found a small
notch called the supraorbita/ notch or foramen. This notch can be palpated
easily. In 25% of orbits the supraorbital notch is enclosed to form a foramen.
At the superior medial corner is a less well- defined groove, the
supratrochlear notch, through which pass the nerve and vessels of the same
name.
This allows the passage of the supraorbital nerves and vessels and is an
important landmark while giving retro bulbar anesthesia.
roves 4mm from the orbital the pul located on the frontal ae
The frontal lobe of the brain and the frontal sinusis found lying above the
orbital roof.
2.2. The Floor of the orbit.
It is made up of three bones:
e the maxillary bone;
e the zygomatic bone,
e the palatine bone.
The maxillary bone makes up the largest part of the floor, and most of the
remainder is provided by the zygomatic bone. The orbital process of the
palatine bone is a small, flattened area at the top of the vertical arm and is
located at the most posterior edge of the orbital plate of the maxilla. The
floor does not reach all the way to the apex and is separated from the lateral
wall posteriorly by the inferior orbital fissure.
There is an oe at the posterior part of the floor called the inferior
Below the floor is found another para nasal sinus called the maxillary sinus.
This is an important structure clinically.
2.3. The Medial wall.
The medial wall is rectangular. From front to back, it is formed by the frontal
process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid,
and apart of the
body of the sphenoid.
A ridge on the frontal process of the maxilla that forms the anterior part of
the medial orbital margin also forms the anterior lacrimal crest, which
demarcates one border of the fossa for the lacrimal sac. The lacrimal bone, a
small bone approximately the size of a thumbnail,
It is made up of four bones:
e the maxillary;
e the /acrimal;
e the ethmoid
¢ part of the sphenoid body.
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The
ethmoid bones form the largest part of the wall.
These are very thin, paper-like bones that separate the orbital cavity from
yet another paranasal sinus called the etfimotdal sinus. Those paperlike
bones are called lamina papyracea thus the medial wall is the thinnest of the
orbital wall.
A groove that holds the lacrimal sac is found on the anterior part of the wall.
This, the /acrimal groove, continues inferiorly as a canal that opens in the
nose and is called the naso/acrimal canal.
2.4. The Lateral wall.
This is the thickest and strongest wall, and is made up of two bones: The
lateral wall is roughly triangular and is composed of the zygomatic bone in
front and of the greater wing of the sphenoid bone behind. The zygomatic
bone separates the orbit from the temporafossa
whereas the two lateral walls, if extended posteriorly, would form
approximately a
90- degree angle with each other
e the zygomatic,
e the greater wing of the sphenoid.
The lateral wall and roof are fused together anterior|
posteriorly by an opening called the Po
The /ateral or marginal orbital tubercle (Whitnall’s tubercle) is a small, bony
prominence located on the orbital surface of the zygomatic bone and is the
attachment site for the aponeurosis of the superior palpebral levator muscle,
the lateral palpebral ligament, and the lateral check ligament. The greater
wing of the sphenoid separates the orbit from the middle cranial fossa.
This fissure transmits a number of cranial nerves from the mid-brain as well
The lateral wall protects only the posterior half of the eyeball, hence the
vulnerability of the eye laterally to trauma.
3. ORBITAL CONTENTS.
The orbit contains the following structures:
the eyeball and the optic nerve;
the lacrimal gland;
the lacrimal sac;
orbital fat;
extraocular muscles;
connective tissue;
blood vessels ;
nerves;
the ciliary ganglion;
fasciae in a complex arrangement;
periostium.
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4. FUNCTIONS OF THE ORBIT.
The orbit provides all the following:
1.'Housing’ to the eyeball;
2.Strong protection for the eyeball;
3.Strong attachments for the muscles that move the eyeball;
4.Attachments to the connective tissues that suspend the eyeball;
5.Firm attachments for the eyelids and the surrounding associated
tissues;
6.Passage for the blood vessels and nerves to and from the eye and
associated structures;
7.Accommodation for the major part of the lacrimal system;
8.Cushioning to the eye through the orbital fat.
5. ORBITAL OPENINGS (FISSURES ,FORAMINA, CANALS, DUCTS).
There are several openings in the orbit that transmit nerves, vessels and
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other structures to and from the eye and the surrounding structures.
Some of these openings are listed below.
5.1. The Optic Foramen and the Optic Canal.
This is an peas in the postero- medial part of the orbit in the lesser wing
The sphenoid sinus is medial to the canal.
It transmits:
a. the optic nerve;
b. the ophthalmic artery;
c. sympathetic nerve fibers.
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5.2. The Superior Orbital Fissure.
This is a fairly large opening between the roof and the lateral wall of the
orbit, connecting the middle cranial fossa withthe orbital cavity.
Lies between the greater and the lesser wings of the sphenoid.
Bridging the superior orbital fissure and attached to it, is the common
tendinous ring of origin for the four recti muscles.
It transmits the following structures :
a. cranial nerve III (oculomotor ) ;
b. cranial nerve IV(trochlear );
c. cranial nerve VI ( abducens );
d. branches of cranial nerve V(trigemen );
e. the superior ophthalmic vein.
Fig. 2.3. Structures passing through the Superior Orbital Fissure.
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5.3. The Inferior Orbital Fissure.
This
Lies between the .
It transmits:
a. the maxillary nerve ( 2 branch of the trigemen);
b. the inferior ophthalmic vein;
c. other nerves and vessels to the surrounding structures.
6. CLINICAL CONSIDERATIONS.
Some or all of the following symptoms and signs may indicate orbital
disease (the list is not exhaustive):
Periorbital pain;
Pain while moving the eye;
Forward propulsion of the eyeglobe ( proptosis or exophthalmos );
Restriction of eye movements;
Double vision ( diplopia);
Pulsating eye;
Lid swelling;
Loss of vision.
There
Most common causes of a nation are
There is an intimate relationship between the orbit and paranasal
sinuses. Thus, pathophysiologic processes (tumours, inflammations
)common to these spaces, secondarily affect the orbit.
The
They are vulnerable in the case of a direct blow to the eye when the orbital
contents are suddenly compressed , leading to a blow- out fracture .
Clinical features of a blowout fracture, may include: diplopia, enophthalmos,
entrapment of orbital tissues, radiographic evidence of fluid level in the
maxillary sinus.