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Ocular Physiology > Orbit > Flashcards

Orbit Flashcards

1
Q

what are the 4 areas of the orbit

A

roof, lateral wall, floor and medial wall

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2
Q

what is the purpose of the orbit

A

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

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3
Q

how many bones make up the surrounding walls

A

7

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4
Q

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

A

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

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5
Q

which bones are common to both orbits

A

ethmoid, sphenoid, and frontal

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6
Q

what is the purpose of the orbital rim

A

protection from trauma

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7
Q

what is the strongest portion of the orbit

A

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

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8
Q

why does the lateral rim have a concavity posteriorly directed

A

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

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9
Q

what shape is the orbital roof

A

a triangular shape

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10
Q

what bones form the orbital roof

A

frontal bone and lesser wing of the sphenoid bone

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11
Q

where is the lacrimal fossa found

A

in the antero-lateral angle of the orbital roof

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12
Q

what is the thinnest portion of the orbit

A

the floor

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13
Q

what makes up the orbital floor

A

orbital plate of the maxillary bone

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14
Q

what is the purpose of the orbital floor

A

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

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15
Q

how long is the orbital floor

A

35-40mm (doesn’t extend to the apex)

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16
Q

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

A

the maxillary sinus

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17
Q

why does the orbital floor break in a blow out fracture

A

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

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18
Q

what symptoms might a person have with a blow out fracture

A

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

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19
Q

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

A

damage to the infraorbital nerve (CN 7 facial)

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20
Q

why might someone have diplopia following a blow out fracture

A

it may cause restrictive strabismus (recti muscles get trapped)

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21
Q

what is enophthalmos

A

where the eye is sunken in and sometimes downward

22
Q

why might a doctor purposely break the orbital floor

A

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

23
Q

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

A

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

24
Q

which wall of the orbit is the smallest

A

the medial wall

25
Q

what bones make up the medial wall

A

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

26
Q

what protects the medial wall from being fractured

A

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

27
Q

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

A

about 16mm

28
Q

when does the globe reach 90% of its adult size

A

at 20 months (or about 2 years old)

29
Q

what is the anterior-posterior diameter of an adult globe

A

about 24mm (varies from 20-30mm)

30
Q

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

A

refractive error (most common), gender, ethnicity

31
Q

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

A

chinese origin

32
Q

what is the volume of the globe

A

7 cm^3

33
Q

what is the volume of the orbit

A

30cm^3

34
Q

why does the eye get displaced forward (exophthalmos)

A

the bony orbit is incapable of acute expansion, except anteriorly

35
Q

what are 2 causes of enophthalmos

A

blow out fracture and as we age the fat content decreases

36
Q

what is the most common cause of exophthalmos

A

thyroid eye disease

37
Q

what causes exophthalmos in thyroid eye disease

A

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

38
Q

what is a hemangioma

A

an abnormal buildup of blood vessels (can cause exophthalmos)

39
Q

what is craniostenosis

A

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

40
Q

what is craniofacial dysostosis

A

defect in normal ossification of the fetal cartilages (embryo)

41
Q

what is buphthalmos

A

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

42
Q

how might severe myopia cause exophthalmos

A

the large refractive error will elongate the globe and stimulate exophthalmos

43
Q

what instrument is the most accurate in measuring exophthalmos

A

Hertel exophthalmometer

44
Q

where is the protrusion measured from with an exophthalmometer

A

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

45
Q

what does the orbital connective tissue consist of

A

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

46
Q

what is collagen type 1

A

protein that provides structural integrity

47
Q

what is collagen type 3

A

a cellular adhesion molecule between the connective tissue and adipocytes

48
Q

what is collagen type 4

A

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

49
Q

what artery provides the primary blood supply to the orbit

A

the ophthalmic artery

50
Q

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

A

the middle meningeal artery contributes equally with the opthalmic artery

51
Q

which veins do parallel the orbital arteries

A

the lacrimal and ethmoidal veins

Ocular Physiology (6 decks)

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