Orbit Flashcards
List the key components found in the orbit
Bones and foramina Extrinsic eye muscles Nerves Blood vessels Lacrimal system
What are the orbits
The orbits are bilateral structures in the upper half of the face below the anterior cranial fossa and anterior to the middle cranial fossa that contain the eyeball, the optic nerve, the extra-ocular muscles, the lacrimal apparatus, adipose tissue, fascia, and the nerves and vessels that supply these structures.
How many bones contribute to the framework of each orbit and what are they
Seven bones contribute to the framework of each orbit (Fig. 8.73). They are the maxilla, zygomatic, frontal, ethmoid, lacrimal, sphenoid, and palatine bones.
Describe the shape of the bony orbit
Together they give the bony orbit the shape of a pyramid, with its wide base opening anteriorly onto the face and its apex extending in a posteromedial direction. Completing the pyramid configuration are medial, lateral, superior, and inferior walls.
What is the apex of the bony orbit
The optic foramen
What is the base of the orbital rim formed by
superiorly by the frontal bone,
▪
medially by the frontal process of the maxilla,
▪
inferiorly by the zygomatic process of the maxilla and the zygomatic bone, and
▪
laterally by the zygomatic bone, the frontal process of the zygomatic bone, and the zygomatic process of the frontal bone.
Summarise the bones that form the roof, floor and lateral walls of the orbit
Roof orbital plate of frontal bone Floor orbital plate of maxilla Lateral wall zygoma greater wing of sphenoid
Summarise the bones that form the medial part of the orbit
Frontal process of maxilla
Lacrimal bone
Orbital plate of ethmoid
Lesser wing of sphenoid
Describe the musculature of the eye as a confounder
Its anatomy confounds the clinical investigation
Describe the importance of the lacrimal system
Keeps the eye moist and therefore functional
How can we open up the contents of the orbit
Remove the orbital plate of the frontal bone.
Describe the roof of the orbit
The roof (superior wall) of the bony orbit is made up of the orbital part of the frontal bone with a small contribution from the sphenoid bone (Fig. 8.73). This thin plate of bone separates the contents of the orbit from the brain in the anterior cranial fossa. Posteriorly, the lesser wing of the sphenoid bone completes the roof.
Describe two unique features of the roof of the orbit
anteromedially, the possible intrusion of part of the frontal sinus and the trochlear fovea, for the attachment of a pulley through which the superior oblique muscle passes;
▪
anterolaterally, a depression (the lacrimal fossa) for the orbital part of the lacrimal gland.
Describe the medial walls of the bony orbit
The medial walls of the paired bony orbits are parallel to each other and each consists of four bones—the maxilla, lacrimal, ethmoid, and sphenoid bones (Fig. 8.73).
The largest contributor to the medial wall is the orbital plate of the ethmoid bone. This part of the ethmoid bone contains collections of ethmoidal cells, which are clearly visible in a dried skull.
Describe the anterior and posterior ethmoidal foramina
Also visible, at the junction between the roof and the medial wall, usually associated with the frontoethmoidal suture, are the anterior and posterior ethmoidal foramina. The anterior and posterior ethmoidal nerves and vessels leave the orbit through these openings.
Describe the lacrimal bone
Anterior to the ethmoid bone is the small lacrimal bone, and completing the anterior part of the medial wall is the frontal process of the maxilla. These two bones participate in the formation of the lacrimal groove, which contains the lacrimal sac and is bound by the posterior lacrimal crest (part of the lacrimal bone) and the anterior lacrimal crest (part of the maxilla).
Describe the floor of the orbit
The floor (inferior wall) of the bony orbit, which is also the roof of the maxillary sinus, consists primarily of the orbital surface of the maxilla (Fig. 8.73), with small contributions from the zygomatic and palatine bones. Posteriorly, the orbital process of the palatine bone makes a small contribution to the floor of the bony orbit near the junction of the maxilla, ethmoid, and sphenoid bones.
Describe the inferior orbital fissure in the floor of the orbit
Beginning posteriorly and continuing along the lateral boundary of the floor of the bony orbit is the inferior orbital fissure. Beyond the anterior end of the fissure the zygomatic bone completes the floor of the bony orbit
Describe the lateral wall of the orbit
The lateral wall of the bony orbit consists of contributions from two bones—anteriorly, the zygomatic bone and posteriorly, the greater wing of the sphenoid bone (Fig. 8.73). The superior orbital fissure is between the greater wing of the sphenoid and the lesser wing of the sphenoid that forms part of the roof
Summarise orbital fractures
Fractures of the orbit are not uncommon and may involve the orbital margins with extension into the maxilla, frontal, and zygomatic bones. These fractures are often part of complex facial fractures. Fractures within the orbit frequently occur within the floor and the medial wall; however, superior and lateral wall fractures also occur. Inferior orbital floor fractures are one of the commonest types of injuries. These fractures may drag the inferior rectus muscle and associated tissues into the fracture line. In these instances, patients may have upward gaze failure (upward gaze diplopia) in the affected eye. Medial wall fractures characteristically show air within the orbit in radiographs. This is due to fracture of the ethmoidal labyrinth, permitting direct continuity between the orbit and the ethmoidal paranasal sinuses. Occasionally, patients feel a full sensation within the orbit when blowing the nose.
