The Orbit Flashcards
How many bones make up the boney orbit’s 4 walls? What are they?
- Sphenoid, frontal, zygomatic, ethmoid, lacrimal, palatine, and maxillary.
Which part of the orbital rim is thick and rounded and is protected from trauma?
Anterior aperture.
The strongest portion of the orbital rim is?
Lateral wall. (The zygomatic bone + zygomatic process of the frontal bone).
What is the tradeoff of the lateral orbital rim?
Strongest portion that’s a posteriorly directed concavity which allows for strong visual field but makes eye prone to injury.
The triangular shape of the orbital roof is formed by what two bones?
Frontal bone and the lesser wing of sphenoid bone (posterior to frontal).
The lacrimal fossa (fossa for the lacrimal gland) is found where?
Antero-lateral angle
Which part of the orbital rim is the weakest and thin and mainly consists of the orbital plate of the maxillary bone?
Orbital floor.
What is the main purpose of the orbital floor?
Gives support to the eye and adnexal tissues and separates them from the maxillary sinus.
How long is the orbital floor?
35-40 mm long.
True or False: The orbital floor does not extend to the apex.
True.
What happens during a blow-out fracture? What are some problems patient’s experience with this fracture?
The orbital floor blows out into the maxillary sinus providing protection to the eye and tissue. Loss of vision, diplopia, enophthalmos (eyeball sucked inwards), numb cheek.
What two bones form the lateral orbital wall?
Zygomatic bone anteriorly and greater wing of sphenoid bone posteriorly.
Which part of the rim is the smallest and thin?
Medial orbital wall.
Why is the medial wall less likely to fracture then any other part of the rim?
Lamina Papyracea of the Ethmoid Bone (extremely thin but uniformly supported by the honeycombed structure of the ethmoid sinus body lamina) is what helped medial wall from fracturing.
Which wall is fractured most often?
Floor.
What protects the medial wall from being fractured?
Lamina papyracea (honeycombed structure).
At birth, what is the diameter of the globe from posterior to anterior?
16 mm.
The globe reaches 90% of its adult size when an infant is how old?
20 months.
At adulthood, the anteroposterior diameter of the globe is?
24 mm. (But varies with gender, ethnicity, and refractive error).
What is the volume of the globe?
7 cm^3.
What is the volume of the orbit?
30 cm^3.
What is the vertical diameter of the globe?
23 mm.
What is the horizontal diameter of the globe?
23.5 mm.
What is the anteroposterior diameter of the globe?
24 mm.
What is Enophthalmos?
Inward displacement of the globe.
What is Exophthalmos?
Forward displacement of the globe.
The only place the orbit can acutely expand is which direction?
Anteriorly.
The forward displacement of any object, not specific to the eye, is called what?
Proptosis.
Thyroid Eye Disease is the most common cause of what?
Exophthalmos.
What happens in the eye that causes Thyroid Eye disease?
GAG’s accumulate in the EOMs and/or connective tissue and fat and lead to swelling.
What are other causes of exophthalmos?
- Hemangiomas
- Inflammatory pseudotumors
- Benign and malignant tumors
- craniostenoses and the craniofacial dysostosis.
True or False: Enophthalmos may lead to pseudoexophthalmos of the contralateral eye.
True.
In exophthalmos eye, will patient most likely be hyperopic in that eye or myopic?
Myopic. Eye bulged out.
How is protrusion measured?
From the deepest part of the lateral rim to the corneal apex.
Orbital connective tissue consist of what?
Fibroblasts and endothelial cells, collagen type I, III, IV.
What is the purpose of collagen type I connective tissue?
Structural integrity.
What is the purpose of collagen type III connective tissue?
Adhesion between connective tissue and adipocytes.
What is the purpose of collagen type IV connective tissue?
Basement membranes of connective tissue vessels.
What artery provides the primary blood supply to the orbit?
Ophthalmic artery.
True or False: Orbital veins parallel orbital arteries.
Fails. Do not parallel.
Do orbital veins possess valves?
No.
