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Anatomy & Physiology 2 > Extraocular Muscles > Flashcards

Extraocular Muscles Flashcards

1
Q

When we head tilt to the left what does the LE & RE do to keep the image still?

A

The ipsilateral eye to the head tilt INTORTS so the LE intorts and RE extorts

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2
Q

What is the mnemonic for remembering what cranial nerves innervate the extraocular muscles?

A

LR6 SO4 AO3

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3
Q

Where does the inferior oblique attach to the sclera in relation to the IR?

A

Inferior to the IR

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4
Q

Where does the superior oblique attach to the sclera in relation to the SR?

A

Inferior to the SR

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5
Q

How the axis of the orbit and axis of the eyeball different?

A

There is a 23 degree difference in primary position (axis of orbit more lateral to the eye but directly down to the “cone”)

Resultant effect on the vertical axis

Axis of Eyeball = straight into the pupil

Axis of Orbit = straight down to the optic nevre

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6
Q

What are the longest to shortest Recti muscles?

A

Superior
Medial
Lateral
Inferior

(Some Men Love Ice)

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7
Q

What is the common tendinous ring?

A

Oval thickening of periosteum (around bone) at the apex of the orbital cavity and encloses the optic foramen and the medial end of the SOF

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8
Q

What is the spiral of tillaux?

A

Recti muscle insertions

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9
Q

What are the recti muscle insertions also known as?

A

Spiral of Tillaux

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10
Q

What is the clinical relevance of the limbus in terms of the recti muscles?

A

It’s often used as a landmark for distances and has the potential of being useful in corneal regeneration as containing stem cells

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11
Q

What is the limbus?

A

The area where the cornea meets the sclera

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12
Q

What are the recti distances of insertion to the limbus?

A

Medial Rectus = 5.5mm
Inferior Rectus = 6.5mm
Lateral Rectus = 6.9mm
Superior Rectus = 7.7mm

(sometimes a 0.1 difference on these)

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13
Q

What recti muscle inserts closest to the limbus?

A

The medial rectus

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14
Q

What’s the largest recti muscle?

A

Medial Rectus

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15
Q

What is the origin of the medial rectus?

A

Medial portion of the common tendinous ring/annulus of zinn

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16
Q

How does the medial rectus travel? and what ligament does it send off?

A

Anteriorly, close to the medial orbital wall and sends off medial check ligament

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17
Q

Where does the medial rectus insert?

A

Medial sclera, 5.5mm from the limbus

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18
Q

What innervates the medial rectus?

A

Inferior division of the CN III

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19
Q

What travels in the Superior and the Inferior CN III?

A

Superior = LPS & SR
Inferior = MR, IO, IR

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20
Q

What’s the function of the medial rectus?

A

Rotates the eye medially in adduction

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21
Q

What’s the origin of the lateral rectus?

A

Lateral portion of the common tendinous ring but has a small 2nd head with the origin from the greater wing of the sphenoid

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22
Q

How does the lateral rectus travel?

A

Anteriorly close to the lateral orbital wall, sending off lateral check ligament

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23
Q

How does the lateral rectus insert?

A

Lateral sclera, 6.9mm from the limbus

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24
Q

How is the lateral rectus innervated?

A

Abducens nerve

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25
Q

What is the function of the lateral rectus?

A

Rotates the eye laterally in abduction

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26
Q

Where does the superior rectus originate?

A

The tendinous ring, attached to dural sheath of optic nerve (ON)
Dura surrounds the optic nerve and has 2 origin points but still the common tendinous ring

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27
Q

How does the superior rectus travel?

A

Passes forwards and laterally.
Fascial sheath is connected to sheath of LPS by a band of connective tissue

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28
Q

How is the superior rectus inserted?

A

7.7mm posterior to the limbus.
The line of insertion is curved and oblique.

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29
Q

How is the superior rectus innervated?

A

Superior division of CN III
The nerve pierces the inferior surface and then continues to supply the LPS

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30
Q

What is the function of the superior rectus?

A

“Up & In”
Elevates
Intorts (rotates eye medially on anteroposterior axis)
Adducts

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31
Q

What is the origin of the inferior rectus?

A

Tendinous ring

32
Q

How does the inferior rectus travel?

A

Passes forwards, & slightly laterally along the floor of orbit superior to the infraorbital canal.

Fascial sheath is attached to the sheath of the IO and to suspensory ligament.

Attaches slightly oblique to the sclera

33
Q

How does the IR insert?

A

6.5mm from limbus

34
Q

How is the IR innervated?

A

Inferior division of CN III

35
Q

What are check ligaments on the LR and MR?

A

Like a hammock for the eye which is the suspensory ligament

36
Q

What is the function of the inferior rectus?

A

“Down & Out”

Depresses
Extorts (rotates eyeball laterally on its anteroposterior axis)
Adducts

37
Q

What is the origin of the superior oblique?

A

Body of the sphenoid bone above and medially to the optic canal

38
Q

What gives rise to the rounded tendon?

A

The belly of the superior oblique runs forward between the roof and medial orbital wall which gives rise to a rounded tendon

39
Q

How does the rounded tendon of the SO pass?

A

Through a fibrocartilageous (like a tough bit of bone) pulley (trochlea) that’s attached to the trochlear fossa and frontal bone. it then bends downward and backward behind the half-line of the equator and laterally under the SR

40
Q

How is the SO inserted?

A

Sclera posterior to the equator of the eyeball

41
Q

How is the SO innervated?

A

Trochlear nerve (CN IV)

42
Q

What is the functional and anatomical origin of the SO?

A

Functional Origin = Trochlea
Anatomical Origin = Back of Sphenoid Bone

43
Q

What’s the function of the SO?

A

“Down & Out”

Intorts (rotates cornea medially on anteroposterior axis)
Depresses (in adduction)
Abducts

44
Q

What EOM is the only one to take origin from the front of the orbit?

A

Inferior Oblique

45
Q

What’s the origin of the inferior oblique?

A

Anterior orbital floor - orbital surface of maxilla, just lateral to the nasolacrimal canal

46
Q

How does the IO travel?

A

Laterally, posteriorly and superiorly and is inferior to the inferior rectus. Fascial sheath is attached to that of the IR.

47
Q

How is the IO inserted?

A

Into sclera under cover of lateral rectus

48
Q

How is the IO innervated?

A

Inferior division of CN III

49
Q

What is the function of the IO?

A

“Up & Out”

Extorts (rotates the eye laterally on its anteroposterior axis)
Elevates (in adduction)
Abducts

50
Q

What’s the oculocardiac reflex caused by?

A

Eye-heart reflex. The connection between them is caused by CN V Ophthalmic branch via the ciliary ganglion & the Vagus nerve’s parasympathetic function.

51
Q

What is the Oculocardiac reflex?

A

Bradycardia precipitated by pressure on orbital contents or the extraocular muscles.
Decrease in pulse rate is associated with traction applied to EOM (e.g. strabismus surgery) and/or compression of the globe (e.g. orbital cellulitis). Profound in neonates and children.

52
Q

How do we assess the EOMs in clinical testing?

A

We isolate the muscle so different to the anatomical function.

53
Q

What is duction?

A

Monocular movement
(adduction, abduction, supraduction & infraduction)

54
Q

What is version?

A

Binocular, simultaneous, conjugate eye movements
(Dextroversion = right gaze, Laevoversion = left gaze)

55
Q

What is vergence?

A

Binocular, simultaneous, disjugate eye movements
(Convergence & divergence)

56
Q

What’s important to consider when thinking of muscle function?

A

Axis of Orbit & Axis of Eyeball

57
Q

What are agonist-antagonist pairs?

A

Pairs of muscle in the SAME eye that move the eye in OPPOSITE directions
E.g. right lateral rectus relaxes & right medial rectus contracts

The innervation are equal to both eyes to keep the eyes in primary position

58
Q

What pair type are the right inferior rectus and right inferior oblique?

A

Agonist-Antagonist
RIR depresses and RIO elevates

59
Q

What are Synergistic muscles?

A

Muscles of the SAME eye that move the eye in a particular direction of gaze
E.g. RSR and RIO both elevate
SR and IO both depress

60
Q

What are the synergist muscles to the left medial rectus?

A

The left medial rectus adducts

The left superior rectus and left inferior rectus both adduct

61
Q

What are Yoke muscles?

A

Pairs of muscles in EACH EYE that work together to allow simultaneous, conjugate gaze (eyes looking in the same direction)

E.g. Right lateral rectus & left medial rectus for right gaze

62
Q

What is Sherrington’s Law?

A

Law of reciprocal innervation

INCREASED innervation to an EOM is accompanied by a DECREASED innervation in its antagonist

E.g. when looking to the right the right lateral rectus receives increased innervation to allow for abduction. As per Sherrington’s law, the right medial rectus receives decreased innervation.

63
Q

When looking to the right, how does Sherrington’s Law work?

A

When looking to the right the right lateral rectus receives increased innervation to allow for abduction. As per Sherrington’s law, the right medial rectus receives decreased innervation.

64
Q

What is Hering’s Law of ocular motility?

A

During a CONJUGATE (up, down, left, right) eye movement, YOKE pairs receive EQUAL and SIMULTANEOUS innervation for fusion to occur

65
Q

How does Hering’s law apply during left gaze?

A

E.g. during left gaze, the left lateral rectus and right medial rectus receive equal, simultaneous innervation

66
Q

On the left eye, what are the six cardinal positions of gaze?

A

Inferior Oblique Superior Rectus

Medial Rectus Lateral Rectus

Superior Oblique Inferior Rectus

67
Q

How do we test the medial rectus?

A

Ask patient to look towards their nose

68
Q

How do we test the lateral rectus?

A

Ask the patient to look away from midline

69
Q

How do we test the superior rectus?

A

As elevation involves both the SR and IO we have to isolate the function of the SR. We therefore need the SR to be in a position where only it can elevate the eye.

It’s achieved by aligning the visual axis with the line of insertion of the muscle. For the SR this would be in ABDUCTION of the eye at 23 degrees. The SR cannot adduct or intort when 23 degrees abducted.

SR is tested in ABDUCTION and Elevation = Up & Out

70
Q

How is the inferior rectus tested?

A

IR tested DOWN & OUT (DEPRESSION & ABDUCTION)

Depression is aided by both the IR and the SO. Through abduction, only the IR can depress the eye as the SO only depresses in adduction.

71
Q

How is the Superior Oblique tested?

A

DOWN & IN (DEPRESSION & ADDUCTION)

By abducting the eye 51 degrees, the visual axis is aligned with the insertion of the SO
When in abduction it means the SO can only depress the eye and so is isolated in its function.
This means that the SO is best tested in DOWN & IN (DEPRESSION & ADDUCTION)

72
Q

How is the inferior oblique tested?

A

UP & IN (ELEVATION & ADDUCTION)

In adduction, the visual axis and line of muscle insertion of the IO are aligned

This means the IO is only able to elevate the eye so is tested Up & Out (Elevation & Adduction)

73
Q

What is the Parks-Bielschowsky 3-step test?

A

Used for diagnosis of cyclovertical muscle palsy which would be caused by either the obliques or by vertical recti

74
Q

What are the 3 steps in the Parks-Bielschowsky 3-step test?
(See powerpoint)

A

1) Which eye is hypertopic?
2) Does hypertropia increase in right or left gaze?
3) Does hypertropia increase in right or left head tilt?

75
Q

Where is the macular located in relation to the optic nerve/disc?

A

Temporally (macular temporal to optic disc)

76
Q

When we turn our head to the right what eye intorts and what eye extorts?

A

Turn head to the right = RE intorts, LE extorts

77
Q

When we turn our head to the left what eye intorts and what eye extorts?

A

Turn head to the left = LE intorts, RE extorts

Anatomy & Physiology 2 (12 decks)

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