Orbit Flashcards
The orbit attains its widest diameter where?
1 cm behind the orbital rim
The orbital roof is what shape?
Triangular shape
Orbital Roof is formed by which bones?
Frontal bone and lesser wing of the sphenoid bone (posterior to the frontal bone)
The strongest portion of the orbital rim?
Laterally
(zygomatic bone + zygomatic process of the frontal bone)
Is the lateral rim a posteriorly or anteriorly directed concavity?
Posteriorly
What is the function of the orbital rim?
protection from trauma
The orbial rim is (thick or thin) and (rounded or flat) at its (posterior or anterior) aperture?
Thick
Rounded
Anterior
Where is the lacrimal fossa found?
In the antero-lateral angle of the orbital roof
Seven bones that make up the 4 walls of the orbit?
Sphenoid
Frontal
Ethmoid
Maxillary
Zygomatic
Palatine
Lacrimal
Which bones make up both orbits?
Ethmoid
Sphenoid
Frontal
What is the bony orbit designed to do?
Support and provide protection to the orbital soft tissues
What do the soft tissues of the orbit consist of?
The globe and its supporting adnexa
The bony orbit serves as the ______ of the globe
Socket
The bony orbit is described of being made up of a ______, _____ wall, _______ , and _____ wall
Roof
Lateral
Floor
Medial
Is the oribital floor thin or thick?
thin
What bone(s) does the orbital floor mainly consist of?
The orbital plate of the maxillary bone
What is the function of the orbital floor?
Support to the eye and adnexal tissues and separates them from the maxiallry sinus.
Which part of the orbit is the weakest?
The orbital floor
The floor does not extend to the _____ and is ____ to ____ mm long
apex
35 - 40
The eyeball is about ____ inch(es)
1 inch
Why is there an increase in the rate of fractures in the orbital floor?
Thin bone and lack of support
The orbital floor easily ______ to blunt trauma
deforms
The floor act like a ____ ____ and blows out into the _____ _____ providing protection to the eye and tissue
release valve
maxillary sinus
What symptom does the patient experience with a blow-out fracture of the orbital floor?
Loss of vision
Diplopia
Enophthalmos
Numb Cheek (damage to infraorbital nerve)
What bone(s) make up the lateral orbital wall? What shape do they make?
Zygomatic (malar) bone anteriorly
Greater wing of the sphenoid bone posteriorly
Triangular shape
Which portion of the orbit is smallest?
Medial Orbital Wall
Is the medial wall of the orbital thin or thick?
thin
Which bone(s) makes up the meidal orbit wall?
Lamina papyracea of the ethmoid bone
How is the ethmoid bone supported?
Uniformly supported by the honeycombed structure of the ethmoid sinus bony lamina
Which wall is fractured more often? Medial Wall or Floor of the Orbit?
At birth, the anteroposterior diameter of the globe is ______ mm
16 mm
When does the globe reach 90% of its adult size?
At 20 months of age
At adulthood the anteroposterior diameter of the globe is?
~24 mm
(can vary 20-30 mm)
What is the volume of the globe?
7 cm3
What is the volume of the orbit?
30 cm3
The anteroposterior diameter of the globe is?
~24 mm
What is the vertical diameter of the globe?
~23 mm
What is the horizontal diameter of the globe?
~23.5 mm
What is proptosis?
The forward displacement of any object (not specific to the eyeball)
What is exophthalmos?
The forward displacement of the globe
Where is the only place the orbit can acutely expand?
anteriorly
What is enophthalmos?
The retrodisplacement of the globe posterior into the orbit
What is the most common cause of exophthalmos?
Thyroid eye disease
What causes thyroid eye disease?
Caused by inflammatory reaction of an unknown cause
Glycosaminoglycans accumulate in the extraocular muscles and/or connective tissue and fat and lead to swealling
Other causes of exophthalmos?
Hemangiomas
Inflammatory pseudotumors
Benign and malignant tumors
Craniostenoses and the craniofacial dysostis
severe myopia and buphthalmos may simulate exophthalmos (elognated globe)
Enophthalmos may lead to ______exophthalmos of the contralateral eye
pseudo
How is protusion usually measured?
From the deepest part of the lateral orbital rim to the cornal apex
What is the most accurate exophthalmometer?
The Hertel exophthalmometer
Which artery provides the primary blood supply to the orbit?
opthalmic artery
orbital veins (do or do not) parallel orbital arteries, except _____ and ____ veins
Do Not
lacrimal and ethmodial veins
Do orbital veins possess valves?
No
