The Normal Orbit Flashcards
What four major anatomic are used to subdivide the orbit when constructing a differential diagnosis?
A. Globe
B. Optic nerve and sheath
C. Conal-intraconal area
D. Extraconal area
The main portion of the triangular orbital roof is comprised of what bone?
Frontal bone, with the frontal sinus within
Anteriorly the orbital roof is thin. In its more posterior aspect it becomes thick.
The anterolateral part of the orbital roof forms a shallow fossa for the lacrimal gland.
The orbital roof can be imaged completely only in the coronal plane.
The orbital floor is formed by what bone?
Formed by the orbital plate of the maxilla, the orbital process of the palatine bone, and the orbital surface of the zygomatic bone.
Like the orbital roof the orbital floor is studied completely only from the coronal perspective.
The anterior aspect of the medial orbital wall is formed by what bone?
Formed by the frontal process of the maxillary bone.
Together with the lacrimal bone the frontal process of the maxillary bone forms the lacrimal fossa. The lacrimal fossa contains the lacrimal sac.
What forms the midportion of the medial orbital wall?
The lamina papyracea (Latin for “paper plate”) of the ethmoidal air cells.
For obvious reasons this very thin bony wall is the site of medial blowout fractures.
A small portion of the sphenoid bone forms the posterior portion of the medial orbital wall.
The anterior portion of the lateral orbital wall is formed by what bone?
Orbital surface of the zygomatic bone
Where is the superior orbital fissure located?
It sits at the margin between the lateral wall and the orbital roof.
This bony fissure is surrounded by the sphenoid bone. The greater wing of the sphenoid bone forms its lateral boundary and the lesser wing its medial boundary.
The medial tip of the superior orbital fissure lies beneath the optic canal. It is separated by the _________, which is a bridge of bone formed by the lesser wing of the sphenoid bone.
Optic strut
The inferior orbital fissure is located where?
Found between the floor and the lateral wall of the orbit.
This bony fissure connects with the petrygopalatine fossa and the nasopharyngeal masticator space (i.e., infratemporal fossa) inferolaterally.
Inferior orbital fissure
What are the contents of the inferior orbital fissure?
A. Infraorbital and zygomatic nerves
B. Nerve branches from pterygopalantine ganglion
C. Venous connections between inferior ophthalmic vein and pterygoid plexus
What bone is optic canal seen?
The optic canal is completely formed by the lesser wing of the sphenoid bone.
The canal courses from its origin in the suprasellar cistern in an anterior, inferolateral direction. Its most intracranial portion has no bony roof.
What are the contents of the optic canal?
The canal contains the optic nerve and ophthalmic artery, both of which are contained in a dural sheath.
What is Zinn’s ligament, or the “ring of Zinn”?
What structures pass through it?
The four recto, superior orbital, and legato palpebral muscles originate from the common annulus tendineus communis (i.e., Zinn’s ligamentous ring).
The tendinous ring encloses the central portion of the superior orbital fissure and the optic foramen.
The optic nerve/sheath complex, ophthalmic artery, distal aspects of cranial nerves III and IV all pass through the annulus.
This area is the region between the muscle cone and bony orbit.
Extraconal area
