Ocular Anatomy: The Orbit (Lecture 2, pt 2)

Orbit

Bony cavity on either side of the midline of the skull below the cranium.

What does the orbit consist of?

• Orbital roof

• Orbital floor

• Medial orbital wall

• Lateral orbital wall

Each orbit contains:

• Globe

• Extraocular muscles

• Orbital nerves

• Blood vessels

• Connective tissue

• Adipose tissue

What is the orbit shaped like?

Like a four-sided pyramid.

Where is the base of the orbit?

Anterior orbital margin

Where is the apex of the orbit?

Posterior margin within skull

How are the medial walls of the orbital formed?

Run parallel to each other and the sagittal plane.

How do the lateral walls of the orbit form?

Forms a ~90-degreee angle with each other.

Height of the Orbit

~35mm

Width of the Orbit

~40mm

Length of the medial wall of orbit

~45mm

Length of lateral wall of orbit

~35mm

Volume of the orbit

~30mL

(eye takes up ~6.5mL)

What is the interorbital distance?

25-35mm

Functions of the orbital connective tissue

• Lines, covers and separates orbital structures.

• Anchors soft tissue structures to bone

• Compartmentalizes orbit

Orbital Compartments

• Intraconal

• Extraconal

Orbit: Intraconal compartment

Within the muscle cone.

What does the intraconal compartment contain?

• Optic nerve (and other nerves)

• Ophthalmic artery

• Central retinal artery and vein

• Adipose tissue

Orbit: Extraconal compartment

Outside the muscle cone.

What does the extraconal compartment contain?

• Lacrimal gland

• Adipose tissue

• Nerves

Periorbita

(Connective Tissue)

• Covers/lines bones and glands.

• Attachment of muscles, tendons and ligaments

What is another name for the periorbita?

Orbital fascia

Periorbita is loosely attached to underlying bone EXCEPT at?

• Orbital margins

• Sutures

• Edge of fissures/foramina

Orbital Septum

Is a thin sheet of fibrous connective tissue embedded within the eyelids.

What is another name for the orbital septum?

Palpebral fascia

Functions of the Orbital Septum

• Maintains orbital fat

• Separates orbital contents from eyelid structures

• Barrier preventing facial infections from spreading into orbit

What does the orbital septum encase?

The orbital margins (superiorly and inferiorly).

Superior Margin of the Orbital Septum

• Originates at the superior orbital rim

• Inserts into levator aponeurosis (~4mm above the superior tarsal plate)

Inferior Margin of the Orbital Septum

• Originates at inferior orbital rim

• Inserts into tarsal plate of inferior eyelid

Tenon’s Capsule

Is a dense sheet of connective tissue encasing the globe.

What is the function of Tenon’s Capsule?

Acts as a barrier to prevent orbital infections from reaching the globe.

Where is Tenon’s Capsule located?

Lies between the conjunctiva and episclera.

Tenon’s Capsule: Sub-Tenon’s Space

A potential space between episclera and Tenon’s capsule.

What is the function of Sub-Tenon’s space?

• Allows for smooth eye movements

• Site for injections of medications or anesthetics

Tenon’s Capsule: Anteriorly

Merges with conjunctiva and episclera at corneal limbus.

Tenon’s Capsule: Posteriorly

Merges with dural sheath of optic nerve.

Suspensory Ligament of Lockwood

Hammock-like sheet of dense connective tissue, located inferiorly to the globe.

What is the function of the suspensory ligament of lockwood?

Provides support to hold globe in position.

What is the suspensory ligament of lockwood attached to?

• Lacrimal bone on medial orbital wall

• Zygomatic bone on lateral orbital wall

What is the function of canthal tendons?

(Aka “palpebral ligaments”)

Keeps tarsal plates and eyelid margins against globe.

Medial Canthal Tendon

• Located anteriorly to the orbital septum.

• Attaches medial region of tarsal plates to medial orbital margin.

• Attaches to anterior lacrimal crest.

Lateral Canthal Tendon

• Located posteriorly to orbital septum

• Attaches lateral region of tarsal plates to lateral orbital margin

• Attaches to lateral orbital tubercle

What are Check Ligaments?

Extensions of fascia of the extraocular muscles.

What are the functions of check ligaments?

• Support movement of extraocular muscles

• Maintain globe positioning

Medical Check Ligament

• Originates at lateral rectus muscle sheath

• Inserts at lateral orbital tubercle at lateral orbital wall

• Stabilizes globe laterally

Lateral Check Ligament

• Originates at lateral rectus muscle sheath

• Inserts at lateral orbital tubercle at lateral orbital wall

• Stabilizes globe laterally

What is the Whitnal Ligament also called?

“Superior transverse ligament”

What is the Whitnall ligament?

Fibrous condensation of orbital fascia within superior orbit.

• Extends from the trochlea to lateral orbital wall.

What are the functions of the Whitnall Ligament?

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Upper eyelid support/suspension

Pulley for levator muscle

Where does orbital fat lie?

Fills unoccupied spaces.

What are the functions of orbital fat?

• Protection of globe (acts as cushion)

• Maintains positioning of globe and eyelids.

How many orbital bones are there?

7

(Combination of cranial and facial bones)

What are the 7 Orbital Bones?

1. Frontal

2. Maxillary

3. Zygomatic

4. Sphenoid

5. Ethmoid

6. Palatine

7. Lacrimal

What is the thickest wall of the orbit?

Lateral wall.

What is the weakest wall of the orbit?

Floor of orbit.

What is the thinnest wall of the orbit?

Medial wall.

What is the strongest wall of the orbit?

Lateral wall.

(it is also the most exposed wall)

What bones does the medial wall contain?

• Sphenoid bone

• Frontal processes of maxillary bone

• Orbital plate of ethmoid bone

• Lacrimal bone

What is the lacrimal fossa?

Depression within medial orbital wall that contains the nasolacrimal sac.

What is the anterior lacrimal crest?

A boundary formed by the maxillary bone.

What is the posterior lacrimal crest?

A boundary formed by the lacrimal bone.

What is the medial palpebra ligament?

(also called canthal tendon);

Keeps the tarsal plate and eyelid margin against the globe.

What does the medial palpebral ligament attach to?

The anterior and posterior lacrimal crest.

How many bones make up the lateral orbital wall?

Two.

What bones make up the lateral orbital wall?

• Zygomatic bone

• Greater wing of the sphenoid bone.