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B3 CAI > Eyes: Orbit and Extraocular Muscles > Flashcards

Eyes: Orbit and Extraocular Muscles Flashcards

1
Q

what is the orbit?

A

a fibro-osseous compartment containing the eyeball, extraocular muscles and neurovasculature

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2
Q

how many bones of the skull contribute to the walls of the orbit?

A

7

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3
Q

what covers the orbit anteriorly?

A

the eyelid, as well as a sheath of connective tissue (orbital septum) that prevents the eyelid from displacing anteriorly

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4
Q

what does the orbital fat do?

A

helps support the eyeball but also permits free movement

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5
Q

what does the orbital septum do?

A

provides support to the anterior aspect of the orbit

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6
Q

where should the orbital fat sit?

A

within the confines of the orbit, but orbital wall fractures can permit orbital fat to move outside of the confines of the orbit

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7
Q

what can increases in orbital fat volume cause?

A

exophthalmos since the eyeball can only become displaced anteriorly

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8
Q

what sits in between the left and right orbit?

A

the nasal cavity and associated paranasal air sinuses

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9
Q

where do the neurovasculature structures enter/exit the orbit?

A

via its apical region

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10
Q

what forms the roof of the orbit and some of the medial wall?

A

the frontal bone

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11
Q

what parts of the sphenoid bone contribute to the orbital wall?

A

the greater and lesser wings

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12
Q

what contibutes to the medial wall of the orbital wall?

A

lacrimal, ethmoid and palatine bones

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13
Q

what contributes to the lateral wall of the orbit?

A

the zygoma

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14
Q

what contributes to the inferior wall of the orbit?

A

the maxilla and zygoma

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15
Q

what forms the margin of the orbit anteriorly?

A

the maxilla, zygoma and frontal bone

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16
Q

where is the supraorbital notch?

A

in the medial part of the superior margin of the orbit

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17
Q

where is the infraorbital foramen found?

A

just inferior to the inferior margin of the orbit

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18
Q

what does the supraorbital notch transmit?

A

the supraorbital nerve

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19
Q

what does the infraorbital foramen transmit?

A

the infraorbital nerve

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20
Q

what is the nasolacrimal canal?

A

a large opening in the lower medial aspect of the orbit, which is the passage for the nasolacrimal duct

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21
Q

what does the P on the below diagram refer to?

A

the palatine bone

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22
Q

what are the superior anatomical relations of the orbit?

A

anterior cranial fossa, frontal paranasal air sinus

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23
Q

what are the medial anatomical relations of the orbit?

A

ethmoid air cells (lamina propria separates)

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24
Q

what are the inferior anatomical relations of the orbit?

A

maxillary sinus, infraorbital nerve

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25
Q

what are the main ways that neurovascular structures travel between the orbit and cranial cavity?

A

superior orbital fissure (CN III, IV, Va, VI) and optic canal (CN II)

26
Q

where do the infraorbital nerves pass?

A

along/just below the inferior wall of the orbit

27
Q

where do the infraorbital veins drain?

A

posteriorly into the dural venous sinus (e.g. cavernous sinus), which is a potential route for infection spread

28
Q

what can blunt trauma to the eyeball or perimeter of the orbit cause?

A

an orbital blowout fracture

29
Q

when do orbital blowout fractures occur?

A

when the pressure within the orbit increases excessively

this increase in pressure needs to be decompressed - occurs via fracture of the walls of the orbit

30
Q

which walls of the orbit will usually fracture when intra-orbital pressure increases?

A

medial and/or inferior walls as these walls are relatively thin

31
Q

where will the orbital contents pass with a medial blowout fracture?

A

into the ethmoid sinus

32
Q

where will the orbital contents pass with an inferior blowout fracture?

A

the maxillary sinus and they may also damage the infraorbital nerve

33
Q

what 3 muscles act on the eyelid to open or close it?

what signs and symptoms may be observed when each of these muscles stops working?

A

levator palpebrae superioris, orbicularis oculi, superior tarsal

ptosis?

34
Q

describe the path of levator palpebrae superioris

A

originates in the posterior part of the orbit at the apex, passes anteriorly along the superior wall of the orbit above the eyelid and the muscles that move the eyeball, and anteriorly inserts into the tissues of the upper eyelid

35
Q

what will contraction of levator palpebrae superioris do?

A

open the upper eyelid

36
Q

what innervates levator palpebrae superioris?

A

CN III

37
Q

what is orbicularis oculi?

A

a muscle of facial expression, that is arranged in concentric rings and thus forms a sphincter around the eyelid, and closes the eye

38
Q

what innervates orbicularis oculi?

A

CN VII

39
Q

in which direction does the eyelid close?

A

from lateral to medial, which sweeps tear fluid across the eyelid to the medial region where the tear fluid is drained via the nasolacrimal duct into the nasal cavity

40
Q

describe the path of superior tarsal

A

originates in the levator palpebrae superioris and passes down to insert into the tarsal plate of the eyelid

41
Q

what innervates superior tarsal?

A

the sympathetic nervous system

42
Q

what does contraction of the superior tarsal muscle do?

A

helps to lift/open the eyelid

43
Q

what are the 6 extraocular muscles that move the eye?

A

4 rectus:

superior rectus, inferior rectus, medial rectus, lateral rectus*

2 oblique:

superior oblique, inferior oblique

*LR does not move the eye itself, it moves the eyelids.

44
Q

what are the 3 pairs of antagonist muscles that move the eye?

A

SR and IR, MR and LR, SO and IO

45
Q

describe the path of the superior oblique muscle of the eye

A

it originates at the apex of the orbit, travels along the superomedial wall and becomes tendinous, with this tendon passing through a trochlea and down to the eyeball

46
Q

describe the path of the inferior oblique muscle of the eye

A

it originates in the medial part of the floor of the orbit close to the orbital margin, and passes under the eyeball to insert into the posterolateral surface of its inferior half

47
Q

describe the path of the rectus muscles in the eyes

A

they begin at the apex of the orbit and take a straight path to the eyeball

48
Q

what type of muscle are the extraocular muscles?

A

skeletal muscles

49
Q

what nerves innervate the extraocular muscles?

A

CN III, IV, VI

50
Q

what is the golden rule of innervation of the extraocular muscles?

A

all skeletal muscles are innervated by CN III except the superior oblique muscle (innervated by CN IV) and the lateral rectus muscle (innervated by CN VI)

51
Q

how do the cranial nerves enter the orbit?

A

CN II, III, IV, Va and VI enter the orbit via its apex located posteriorly, through the superior orbital fissure or optic canal

52
Q

how do the superior and orbital fissures orientate us to tell us which eye we are looking at?

A

they create a boomerang shaped opening, with the apex pointing towards the nose

53
Q

where do the rectus muscles in the eye originate?

A

from a common tendinous ring located at the posterior part of the orbit

54
Q

which is the only extraocular muscle that does not originate from the posterior part of the orbit?

A

the inferior oblique muscle

55
Q

what eye movements do the inferior oblique bring about?

A

abduction and elevation

56
Q

what eye movements do the superior oblique bring about?

A

abduction and depression

57
Q

what eye movements do the superior rectus bring about?

A

adduction and elevation

58
Q

what eye movements do the inferior rectus bring about?

A

adduction and depression

59
Q

what eye movement does the lateral rectus bring about?

A

abduction, away from nose

60
Q

what eye movement does the medial rectus bring about?

A

adduction, towards nose

61
Q

What causes a retrobulbar haematoma?

A

The periosteal lining of the bones of the orbit binds to regional suture joints and foramen. In between these attachments it is relatively loosely attached - this provides a space for blood to accumulate following fracture.

62
Q

What visual symptoms are associated with an orbital blowout fracture?

A

Swelling around eye

Diplopia

Subcutaneous emphysema

B3 CAI (13 decks)

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