Orbit

Question 1

what are the 4 areas of the orbit

Answer 1

roof, lateral wall, floor and medial wall

Question 2

what is the purpose of the orbit

Answer 2

to support and provide protection to the orbital soft tissues (globe and adnexa)

Question 3

how many bones make up the surrounding walls

Answer 3

7

Question 4

name the 7 bones that make up the 4 walls of the orbit

Answer 4

sphenoid, frontal, ethmoid, maxillary, zygomatic, palatine, and lacrimal bones

Question 5

which bones are common to both orbits

Answer 5

ethmoid, sphenoid, and frontal

Question 6

what is the purpose of the orbital rim

Answer 6

protection from trauma

Question 7

what is the strongest portion of the orbit

Answer 7

the lateral portion of the orbital rim (zygomatic bone and zygomatic process of frontal bone)

Question 8

why does the lateral rim have a concavity posteriorly directed

Answer 8

the increase the visual field, but the eye is prone to injury

Question 9

what shape is the orbital roof

Answer 9

a triangular shape

Question 10

what bones form the orbital roof

Answer 10

frontal bone and lesser wing of the sphenoid bone

Question 11

where is the lacrimal fossa found

Answer 11

in the antero-lateral angle of the orbital roof

Question 12

what is the thinnest portion of the orbit

Answer 12

the floor

Question 13

what makes up the orbital floor

Answer 13

orbital plate of the maxillary bone

Question 14

what is the purpose of the orbital floor

Answer 14

the support the eye and adnexal tissues, separate them from the maxillary sinus

Question 15

how long is the orbital floor

Answer 15

35-40mm (doesn’t extend to the apex)

Question 16

during a blow out fracture, where does the eye blow out to

Answer 16

the maxillary sinus

Question 17

why does the orbital floor break in a blow out fracture

Answer 17

it acts as a release valve to decrease orbital pressure and blows out to provide protection to the eye and adnexa

Question 18

what symptoms might a person have with a blow out fracture

Answer 18

loss of vision, diplopia, enophthalmos, or a numb cheek

Question 19

what nerve damage would cause the cheek to go numb in an orbital blow out fracture

Answer 19

damage to the infraorbital nerve (CN 7 facial)

Question 20

why might someone have diplopia following a blow out fracture

Answer 20

it may cause restrictive strabismus (recti muscles get trapped)

Question 21

what is enophthalmos

Answer 21

where the eye is sunken in and sometimes downward

Question 22

why might a doctor purposely break the orbital floor

Answer 22

if they have thyroid eye disease (graves disease) to allow for the exophthalmos eye to have more room

Question 23

what bones form the lateral wall and what shape do they make

Answer 23

zygomatic (anteriorly) and greater wing of sphenoid bone (posteriorly)- triangular shape

Question 24

which wall of the orbit is the smallest

Answer 24

the medial wall

Question 25

what bones make up the medial wall

Answer 25

Lamina Papyracea of the ethmoid bone, supported by the honeycomb structure of ethmoid sinus bony lamina

Question 26

what protects the medial wall from being fractured

Answer 26

because it is being supported by the honeycomb structure of the ethmoid sinus bony lamina

Question 27

what is the anterior-posterior diameter of the globe at birth

Answer 27

about 16mm

Question 28

when does the globe reach 90% of its adult size

Answer 28

at 20 months (or about 2 years old)

Question 29

what is the anterior-posterior diameter of an adult globe

Answer 29

about 24mm (varies from 20-30mm)

Question 30

what may cause the anterior-posterior diameter of the adult globe to vary

Answer 30

refractive error (most common), gender, ethnicity

Question 31

which ethnicity origin has the smallest anterior-posterior diameter of the globe

Answer 31

chinese origin

Question 32

what is the volume of the globe

Answer 32

7 cm^3

Question 33

what is the volume of the orbit

Answer 33

30cm^3

Question 34

why does the eye get displaced forward (exophthalmos)

Answer 34

the bony orbit is incapable of acute expansion, except anteriorly

Question 35

what are 2 causes of enophthalmos

Answer 35

blow out fracture and as we age the fat content decreases

Question 36

what is the most common cause of exophthalmos

Answer 36

thyroid eye disease

Question 37

what causes exophthalmos in thyroid eye disease

Answer 37

an inflammatory reaction of an unknown cause, glycosaminoglycans accumulate in the EOMs and/or connective tissue and fat, leads to swelling

Question 38

what is a hemangioma

Answer 38

an abnormal buildup of blood vessels (can cause exophthalmos)

Question 39

what is craniostenosis

Answer 39

fault in fusing bones in an infant skull (fusing too early), not enough room for eyeball and can cause exophthalmos

Question 40

what is craniofacial dysostosis

Answer 40

defect in normal ossification of the fetal cartilages (embryo)

Question 41

what is buphthalmos

Answer 41

"ox eye" a condition where the eye is stretched (in early years of development the IOP can increase and collagen isn't fully formed)

Question 42

how might severe myopia cause exophthalmos

Answer 42

the large refractive error will elongate the globe and stimulate exophthalmos

Question 43

what instrument is the most accurate in measuring exophthalmos

Answer 43

Hertel exophthalmometer

Question 44

where is the protrusion measured from with an exophthalmometer

Answer 44

from the deepest part of the lateral orbital rim to the corneal apex

Question 45

what does the orbital connective tissue consist of

Answer 45

fibroblasts, endothelial cells, collagen types 1, 3, 4

Question 46

what is collagen type 1

Answer 46

protein that provides structural integrity

Question 47

what is collagen type 3

Answer 47

a cellular adhesion molecule between the connective tissue and adipocytes

Question 48

what is collagen type 4

Answer 48

associated with the basement membranes of the vessels found in connective tissue

Question 49

what artery provides the primary blood supply to the orbit

Answer 49

the ophthalmic artery

Question 50

what is the blood supply to the orbit in about 3% of the population

Answer 50

the middle meningeal artery contributes equally with the opthalmic artery

Question 51

which veins do parallel the orbital arteries

Answer 51

the lacrimal and ethmoidal veins