Chapter 3: The Orbit Study Guide updated August ‘08

Part 1: basic vocabulary

Canal: (pipe or channel) Optic canal contains Optic nerve, ophthalmic artery

Suture: (Latin – sutura meaning seam)

Foramen (plural foramina) Latin forare – a hole in the bone for nerves and blood vessels to pass through

Fossa – an anatomical pit or depression in bone for nerves or blood vessels to pass through

Tubercle [tube Latin: lump] a small prominence; used as an attachment site for muscle or ligament

Fissure - a natural cleft between body parts, narrow slit-like opening

Notch

Zygomatic – to join or bridge

Ethmoid – sieve, like a strainer

Trochlear – U-shaped pulley for the tendon of the superior oblique muscle

Sphenoid - wedge shaped or wing like

(Pterygoid – shaped like a wing)

Sinus – air pocket in bone, or common pooling area for drainage

(There are four sinuses: Frontal, Ethmoid, Sphenoid, and Maxillary)

Part 2: Eleven Bones that make up the orbit are:

Single: Frontal Paired: Maxillary

Ethmoid Zygomatic

Sphenoid Lacrimal

Palatine

Part 3:

Optic Canal (or Optic foramen) – the tunnel in the sphenoid bone through which the optic nerve

and the ophthalmic artery passes

Superior Orbital Fissure – the opening between the greater and lesser wings of the sphenoid

bone at the back of the orbit; most of nerves and major veins pass through except the optic and zygomatic nerves, and ophthalmic artery

Inferior Orbital Fissure – the opening in the orbit between the posterior part of the orbital floor

and the lateral wall

Ethmoid Foramina (anterior & posterior) – the openings in the medial wall of the orbit through

which the ethmoidal arteries and nerves pass

Infraorbital foramen – the opening in the maxillary bone below the orbital rim through which

the infraorbital artery and nerve pass

Infraorbital groove – the groove in the orbital floor that becomes the infraorbital canal leading to

the infraorbital foramen

Supraorbital Notch – the notch, sometimes a foramen, near the middle of the superior margin of

the orbital; it contains the supraorbital artery and nerve

Supraorbital Margin -

Zygomatic foramen – innervates the cheek

Pterygoid canal (of sphenoid bone)

Infraorbital canal

Nasolacrimal canal – the tunnel that leads from the lacrimal fossa to the nasal cavity

Greater and lesser wing of Sphenoid bone

Trochlear spine or trochlear fossa – the small depression in the frontal bone at the site of the

Trochlea

Palantine – smallest contribution to the orbital structure (the orbit floor)

Orbital plate of ethmoid bone is in which orbital wall? How about the frontal or maxillary bones?

What is a blowout fracture? Where does it occur?

A blowout fracture is caused by force trauma to the orbit. Due to the sheer strength of the orbital bones, the force of the trauma is transmitted to the orbital plate of the maxillary wall, where the thin layer of bone is “blown out.”

How about a comminution fracture?

It is the breakage of one or more of the bones forming the margin (frontal, zygomatic, or maxillary).

Part 4: Know and be able to identify bones of the orbit floor, ceiling, lateral and medial walls. What are the sutures that connect them? What are the fossas, fissures and foramina on these walls?

Orbit Ceiling

Frontal

Bits of sphenoid

Lacrimal Fossa, trochlear fossa

Orbit Floor

Maxillary

Zygomatic

Palantine

Inferior orbital groove, inferior orbital fissure, nasolacrimal canal

Lateral Wall

Zygomatic

Sphenoid (greater wing)

Lateral Orbital Tubercle (Whitnall’s tubercle)

Medial Wall

Maxillary (anteriorly)

Sphenoid (posteriorly)

Ethmoid &

lacrimal bones fill the gap between them

Nasolacrimal fossa

Lacrimal crests (anterior & posterior)

Nasolacrimal canal

Periosteum – a thin layer of connective tissue that adheres to the surfaces of bones

Periobita – the periosteum that lines the orbital bones

Tenon’s capsule – a sheet of connective tissue that lines all of the eye out to the limbus and

ensheathes the extraocular muscles, it fits like a glove.

Whitenall’s ligament – a sling of connective tissue attached to the orbital ceiling through which

the levator muscle passes; also called superior transverse ligament

Lockwood’s ligament – suspensory ligament

Medial and lateral check ligament

Septum orbitale (aka orbital septum and palpebral fascia) – the sheet of connective tissue that is

attached to the orbital margin and runs into the eyelids

Exophthalmos – a condition in which the eye protrudes farther forward from its normal position

in the orbit; also called proptosis

Enophthalmos - a condition in which the eye is placed farther back in the orbit than normal