Orbit Flashcards
Name the functions of the bony orbit (2)
- Serves as a socket for the globe
2. Supports and provides protection for orbital soft tissues (globe + supporting adnexa)
What is found in the orbit that is necessary for normal function of visual system?
muscles, nerves, and blood vessels
What is the orbit composed of? Parts of orbit? (4)
floor, medial wall, lateral wall, roof
Name the bones that make up surrounding walls of orbit (7)?
lacrimal, sphenoid, frontal, maxillary, ethmoid, zygomatic, palatine
Where is the orbital rim thick and rounded?
anterior aperture (protects from trauma)
The strongest portion of the rim?
laterally; zygomatic bone/ zygomatic process of frontal bone
Describe the lateral rim?
it is a posteriorly directed concavity (increases lateral visual field but makes eye more prone to injury)
Describe the shape of the orbital roof and what it is formed by?
Triangular shape formed by frontal bone and lesser wing of sphenoid bone
Describe the orbital floor and what its made of?
thin and is made up of the orbital plate from maxillary bone; separates tissues and adnexa from maxillary sinus
How large is orbital floor?
35- 40 mm and does not extend to apex
What is the weakest part of orbit?
Orbital floor
How does the orbital floor protect the eye and tissues?
deforms to blunt trauma; blows out into maxillary sinus; pressure is increased
Patient with a blow-out fracture may experience?
diplopia, loss of vision, numb cheek (damage to infraorbital nerve; damaged facial nerve, enophthalmus
When sensation is reduced orbital floor involved with fracture and needs repair to prevent?
strabismus caused by lapse of tissues, enopthalmus, and thyroid eye disease
Describe the lateral wall and what bones make up the wall?
triangular in shape and zygomatic bone (anteriorly) and greater wing of sphenoid (posterior)
Describe the medial wall
very thin and is the smallest
Why is the medial wall less fractured than the orbital floor?
It is supported by the lamina papyracea of the ethmoid bone which is very thin but is supported by honeycomb structure of ethmoid sinus bony lamina
What is the Anteroposterior diameter of globe at birth?
16mm
When does globe reach 90% of adult size?
20 months of age
Anteroposterior Diameter of adult size globe?
24mm ; but varies 20-30mm
How long is eyeball?
About 1 inch; not a perfect sphere
What is exophthalmos?
Forward displacement of globe; only place orbit can expand is anteriorly
What is proptosis?
forward displacement of any object
What is endophthalmos?
retrodisplacement of globe, posterior to orbit
Most common cause of unilateral and bilateral exo in adults?
Thyroid eye disease; inflammatory reaction of unknown cause; Glycosaminoglycans accumulate in connective tissue/ fat/ EOM and cause swelling
What are other causes of exophthalmos?
hemangiomas (build up of blood vessels), tumors, inflammatory pseudo tumors, craniostenoses and the craniofacial dysostosis (fault in fusing bones; defect in ossification), pseudo ex caused by enophthalmos of contralateral eye
severe myopia can stimulate it
How is protrusion measured? What’s most accurate way?
From deepest part of lateral rim to corneal apex
Most accurate way is exophthalmeter
What does the orbital connective tissue consist of?
fibroblasts, endothelial cells, collagen I (structural integrity) , collagen III (adhesions between connective tissues and adipose) , collagen IV (basement membrane of connective tissue vessels)
I and IV= structural strength
Vascular supply of orbit?
opthalmic artery; 3% of people have medial meningeal artery
Orbital veins?
do not parallel arteries (except lacrimal and ethmoid); don’t posess valves
