Interval 12: Orbit Flashcards
What can an eye exam tell us?
- Function of CN II-VII
- Peripheral and central visual defects
- Systemic diseases: autoimmune, lipid disorders, hypertension
- Brain tumors
- Glaucoma
- Autonomic functions and disorders (CN 3,7)
What is the shape of the eye orbit?
- cone-shaped
- pointed posteriorly and open anteriorly
What 7 bones make up with orbit?
- frontal
- ethmoid
- lacrimal
- maxillary
- zygomatic
- palatine
- sphenoid
Describe the arrangment of the optic foramen and superior orbital fissure
-optic foramen is always medial to the superior orbital fissure
Why is there a significant amount of fat in the orbit?
-protects orbital structures from injury and helps stabilize vision
Define exophthalmos and why it is common.
- protrusion of the orbital contents anteriorly
- bc it is a bony cavity, and increase in space or pressure will only be able to move anteriorly
In blowout fractures, there is commonly blunt force to the front of the face. What happens to the orbital fat in these instances?
- orbital floor is fractured and the eye is exploded inferiorly into the maxillary sinus
- they can not only displace to eyeball, with resulting double vision, but the infraorbital nerve may also be lesioned causing loss of sensation of the skin of the cheek and gum on that side
- entrapment of the inferior rectus may limit upward gaze
What is the largest opening of the orbit? Where are most nerves/vessels coming from that use these openings?
- anterior orbital opening
- middle cranial fossa
List the 6/7 muscles found in the orbit and their innervation
- Superior rectus: Oculomotor n (CNIII)
- Medial rectus: Oculomotor n (CNIII)
- Inferior rectus: Oculomotor n (CNIII)
- Inferior oblique: Oculomotor n (CNIII)
- Lateral rectus: Abducens n (CN VI)
- Superior oblique: Trochlear n (CN IV)
- Levator palpebrae: Oculomotor n (CNIII)** not true EOM
The 4 rectus muscles and the ________ muscle take their origin from where?
- superior oblique
- tendinous ring (annulus of Zinn) which surrounds optic canal
What is the only EOM to not have an origin from the annulus of Zinn? Where does it arise?
- inferior oblique
- arises from orbit floor
The 4 rectus muscles pull on the globe from front to back; how is the superior oblique muscle unique?
-it passes through a connective tissue sling called the trochlea then heads posteriorly to insert on the globe; so it pulls it form back to front
The center of the cornea or the center of the pupil is used as the anatomic ________ of the eye.
-anterior pole
What movements can occur with the eye?
- elevation
- depression
- abductions
- adduction
- internal and external rotation
T/F: The axis of the orbit and the axis of the globe are the same.
-False; globe looks straightforward, but orbit does not
