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ANATOMY1: Osteology > Osteology of the orbit > Flashcards

Osteology of the orbit Flashcards

1
Q

What separates the two orbits from each other?

A

the nasal cavity and the ethmoidal and sphenoidal air sinuses

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2
Q

What are the 7 types of bones of which parts contribute to the walls of the orbit?

A
  1. Frontal
  2. Maxilla
  3. Sphenoid
  4. Zygomatic
  5. Palatine
  6. Ethmoid
  7. Lacrimal
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3
Q

What is the approximate shape of each orbit and what does it lead to?

A

quadrilateral pyramid, base is the orbital margin (yellow ring), apex narows at the optic canal

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4
Q

Where is the orbit widest?

A

1.5cm behind the orbital margin

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5
Q

How are the medial vs lateral walls of the orbit angled?

A

medial walls approx parallel to mid sagittal plane, whereas lateral walls angled approx 45 degrees to this plane

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6
Q

In which direction is the orbital aperture directed?

A

forwards, laterally and slightly downwards

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7
Q

In which direction do nerves and muscles passing from the apex into the orbit pass?

A

forward and laterally

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8
Q

What are the approximate dimensions of the orbit - height, width and depth?

A

40mm height, 40mm width, 40mm depth

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9
Q

What is the volume of the orbit and what proportion of this is occupied by the eye?

A

30ml total; one fifth occupied by eye (6ml)

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10
Q

What are the 2 key bones which form the roof of the orbit?

A
  1. Orbital plate of the frontal bone
  2. Small area of lesser wing of the sphenoid
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11
Q

What are the two key bones that form the lateral wall of the orbit?

A
  1. Orbital surface of zygomatic bone anteriorly
  2. Orbital surface of greater wing of sphenoid posteriorly
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12
Q

What are the 4 key bones which form the medial wall of the orbit?

A
  1. Frontal process of the maxilla
  2. Lacrimal bone
  3. Orbital plate of the ethmoid
  4. Body of the sphenoid bone
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13
Q

What are the 3 key bones which form the floor of the orbit?

A
  1. Orbital plate of the maxilla
  2. Orbital surface of the zygoma
  3. Orbital process of the palatine bone
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14
Q

What are 3 noteworthy features of the orbital roof?

A
  1. Fossa for the lacrimal gland
  2. Trochlear fossa (fovea)
  3. Anterior and posterior ethmoidal canals
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15
Q

Where in the orbital roof is the fossa for the lacrimal gland located?

A

in the anterolateral aspect of the roof, behind the zygomatic process of the frontal bone

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16
Q

Where in the orbital roof is the trochlear fossa (fovea)?

A

in the anteromedial aspect of the roof, 4mm from the margin

Is the site at which the trochlea (small pulley) is attached; tendon of the superior oblique passes through the trochlea

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17
Q

What is the trochlear fossa the site of?

A

the site at which the trochlea (ligamentous sling, acts as small pulley) is attached

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18
Q

What passes through the trochlea?

A

the tendon of the superior oblique

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19
Q

Where in the orbital roof are the anterior and posterior ethmoidal canals?

A

positioned at the junction of roof and medial wall above the frontoethmoidal suture

transmit the anterior and posterior ethmoidal nerves and vessels

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20
Q

What is the function of the anterior and posterior ethmoidal canals?

A

transmit the anterior and posterior ethmoidal nerves and vessels

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21
Q

What are the relations of the roof of the orbit (i.e. what lies above it)?

A

separates the orbit from the anterior cranial fossa and frontal lobes of the brain

anteriorly, the frontal sinus lies above the orbit

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22
Q

What is the thickness like of the orbital roof?

A

it is thin and translucent except at the lesser wing of the sphenoid

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23
Q

What are 2 key features of the medial orbital wall?

A
  1. lacrimal fossa for the lacrimal sac
  2. vertical sutures which separate the four bones that comprise this wall (ethmoid, lacrimal, maxilla, sphenoid)
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24
Q

What is the shape of the medial orbital wall?

A

oblong and thin (0.2-0.4mm)

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25
Q

Where within the medial orbital wall is the lacrimal fossa for the lacrimal sac?

A

bound by anterior and posterior lacrimal crests and is continuous below with the nasolacrimal canal

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26
Q

Explain the locations of the fossa for the lacrimal gland, and the lacrimal fossa for the lacrimal sac?

A

the fossa for the lacrimal gland is in the roof of the orbit (in the anterolateral aspect of the roof behind the zygomatic process of the frontal bone), whereas the lacrimal fossa for the lacrimal sac is in the medial wall (bound by anterior and posterior lacrimal crests and continuous below with the nasolacrimal canal)

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27
Q

How thin is the medial wall of the orbit?

A

it is the thinnest of the walls, largely transparent or semi-transparent

the ethmoidal air sinuses can easily be seen through the wall in a dried skull

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28
Q

What are the relations of the medial wall of the orbit i.e. what lies medial to it?

A

anterior to posterior: anterior, middle, posterior ethmoidal air cells and the sphenoidal sinus

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29
Q

What can infection rapidly spreading through the thin walls of air cells in the ethmoidal/sphenoid sinuses cause?

A

orbital cellulitis

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30
Q

Which is the thinnest of the walls of the orbit?

A

medial wall

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31
Q

In what direction does the floor of the orbit slope?

A

slightly downwards from medial to lateral wall

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32
Q

What are the 2 key features of the orbital floor?

A
  1. inferior orbital fissure
  2. infraorbital groove –> becomes infraorbital canal
33
Q

What is the course of the infraorbital groove/canal?

A

the infraorbital groove runs forward from the inferior orbital fissure

before reaching the orbital margin, the fissure becomes the infraorbital canal

opens as the infraorbital foramen 4mm below the orbital margin on the anterior surface of the maxilla

34
Q

What are the relations of the orbital floor?

A

separates the orbit from the maxillary sinus

35
Q

What is the thickness of the orbital floor?

A

only 0.5-1mm thickness

36
Q

Which orbital wall is most likely to be damaged following trauma such as in orbital blowout fractures?

A

the orbital floor

37
Q

What are 4 key features of the lateral orbital wall?

A
  1. Spina recti lateralis: small bony pine on the greater wing of the sphenoid
  2. Zygomatic foramen
  3. Lateral orbital tubercle
  4. Foramina for small veins that communicate with middle cranial fossa
38
Q

What is the spina recti lateralis?

A

small bony spine on greater wing of sphenoid near apex of orbit

gives origin to part of the lateral rectus muscle

39
Q

What is the zygomatic foramen?

A

foramen in lateral orbital wall that transmits the zygomatic nerve and vessels to the temporal fossa and cheek (zygomaticotemporal nerve and zygomaticofacial nerve)

40
Q

What is the lateral orbital tubercle?

A

tubercle within the lateral orbital wall

forms the atachment of the check ligament of the lateral rectus, suspensory ligament (Lockwood’s) of the eye, superior transverse ligament (Whitnall’s) and aponeurosis of levator palpebrae superioris

41
Q

What are the 4 things that attach to the lateral orbital tubercle?

A
  1. check ligament of lateral rectus (expansion of the sheaths of LR that attach to the zygomatic bone)
  2. suspensory ligament (Lockwood’s ligament)
  3. superior tranverse ligament (Whitnall’s ligament)
  4. Aponeurosis of levator palpebrae superioris
42
Q

What are the 2 nerves that are transmitted in the zygomatic foramen (within the lateral orbital wall)?

A

zygomaticotemporal nerve and zygomaticofacial nerve

43
Q

What are the 3 lateral relations of the lateral orbital wall (anterior to posterior)?

A
  1. skin
  2. temporal fossa
  3. middle cranial fossa
44
Q

What is the orbital margin?

A

thickened rim of bone that helps protect the orbital contents

45
Q

What are the 3 bones that comprise the orbital margin?

A

frontal bone

zygomatic bone

maxilla

46
Q

Of the lateral and medial margins of the orbital margin, which reaches further anteriorly?

47
Q

Why is the medial margin of the orbital margin sharper in the lower half?

A

due to anterior lacrimal crest; it is indistinct superiorly

48
Q

What is the superior orbital fissure?

A

communication between the orbital and cranial cavities that lies between the roof and lateral wall of the orbit, bounded by the lesser and greater wings of the sphenoid bone

49
Q

What bones bound the superior orbital fissure?

A

bounded by the lesser and greater wings of the sphenoid bone

50
Q

How does the width of the superior orbital fissure change along its length?

A

wider at its medial end and narrowest at its lateral end

51
Q

How long is the superior orbital fissure?

52
Q

What separates the orbital fissure from the optic foramen above?

A

the posterior root of the lesser wing of the sphenoid bone

53
Q

What soft tissue structure spans between the narrow and wide parts of the superior orbital fissure?

A

the part of the common tendinous ring that gives origin to the lateral rectus muscle

54
Q

What are 5 structures that pass above or outside the tendinous ring / annulus spanning the superior orbital fissure?

A
  1. lacrimal nerve
  2. frontal nerve
  3. trochlear nerve
  4. superior ophthalmic vein
  5. recurrent branch of the lacrimal artery
55
Q

Which bood vessel does the recurrent branch of the lacrimal artery anastamose with (and where may it more commonly travel rather than the superior orbital fissure)?

A

middle meningeal artery

in a small cranio-orbital foramen lateral to the superior orbital fissure

56
Q

What are 5 structures that pass within the common tendinous ring that gives origin to the lateral rectus (and thus within the apex of the muscle cone) that spans the superior orbital fissure?

A
  1. oculomotor nerve (superior and inferior divisions)
  2. abducent nerve
  3. nasociliary nerve
  4. sympathetic root of the ciliary ganglion
  5. inferior ophthalmic vein (variably)
57
Q

How many orbital cellulitis develop as a result of infection spread?

A

consequence of infection spreading from air sinuses to the orbit via the paper-thin medial wall (lamina papyracea)

58
Q

What is the anatomical location of the inferior orbital fissure?

A

lies between the lateral wall and floor of the orbit, below the superior orbital fissure

59
Q

What does the inferior orbital fissure form a communication between?

A

between the orbit and the infratemporal fossa and the pterygopalatine fossa

60
Q

What is the length of the inferior orbital fissure and where does it end?

A

runs forward and laterally for approximately 20mm, ends 20mm from the orbital margin

61
Q

Where is the inferior orbital fissure narrowest?

A

in the middle section

62
Q

What covers the inferior orbital fissure?

A

periorbita and a sheet of smooth muscle of unknown function, called the orbitalis or ‘muscle of Müller’

63
Q

What are 4 things transmitted within the inferior orbital fissure?

A
  1. infraorbital nerve
  2. zygomatic nerve
  3. branches from pterygopalatine ganglion
  4. branches from inferior orbital vein
64
Q

What may branches of the inferior ophthalmic vein, tranmitted within the inferior orbital fissure, communicate with?

A

pterygoid venous plexus below

65
Q

What is the optic canal?

A

bony channel in the sphenoid that passes anteriorly, inferiorly and laterally (36 degrees) from the middle cranial fossa to the apex of the orbit

66
Q

Which bones form the optic canal?

A

the two roots of the lesser wing of the sphenoid

67
Q

How far apart are the optic canals anterior and posteriorly?

A

anteriorly: 30mm
posteriorly: 25mm

68
Q

What is the shape of the optic canal and where is it narrowest?

A

funnel shaped, narrowest where its opening into the orbit is oval with sharp upper and lower borders and a prolonged roof (10-12mm in length)

69
Q

How long is the prolonged roof of the optic canal?

70
Q

What is the shape of the opening of the optic canal at the cranial aspect?

A

oval with a prolonged floor

71
Q

What are 2 important relations of the optic canal?

A
  1. sphenoidal and posterior ethmoidal air sinuses (medial)
  2. olfactory tracts (superior relations)
72
Q

What are 4 things transmitted within the optic canal?

A
  1. optic nerve, with its meningeal coverings
  2. ophthalmic artery
  3. sympathetic nerve fibres originating from superior cervical ganglion that form plexus around internal carotid artery (accompany ophthalmic artery)
73
Q

What is the relation of the ophthalmic artery to the optic nerve within the optic canal?

A

ophthalmic artery lies below and lateral to the nerve within the dural sheath for part of its course

74
Q

Why is it thought that the orbital floor is more commonly involved in orbital blow-out fractures (even though the medial wall is thinner)?

A

because the floor lacks the buttress-like supports of the ethmoidal air cells and the protection of the nose

75
Q

Where may orbital contents herniate into in the event of orbital blowout fracture affecting the orbital floor?

A

maxillary sinus

76
Q

What are the 4 types of paranasal sinuses?

A
  1. frontal
  2. ethmoidal
  3. sphenoidal
  4. maxillary
77
Q

What are the paranasal sinuses?

A

air-filled cavities within the skull that are in communication with the nasal cavity via a series of apertures

78
Q

What are 3 functions of the paranasal sinuses?

A
  1. warm and moisten air
  2. add resonance to voice
  3. lighten skull
79
Q

What is the way to remember the cranial nerves passing through the superior orbital fissure?

A

LFT SNIA: Loose foreskin trapping smegma never impressed anyone

L: lacrimal nerve (V1)

F: frontal nerve (V1)

T: trochlear nerve (IV)

S: superior division of oculomotor n (III)

N: nasociliary nerve (V1)

I: inferior division of oculomotor n (III)

A: abducent nerve (VI)

ANATOMY1: Osteology (4 decks)

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