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Head and Neck > Extraocular muscles > Flashcards

Extraocular muscles Flashcards

1
Q

Why do we have binocular vision (two eyes)?

A

Wider field of vision and depth perception (3D image)

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2
Q

What must happen to both eyes to ensure objects are seen clearly?

A

Visual axis of both eyes need to be aligned - light needs to hit same spot at the back of each eye

Eyes need to co-ordinate and move together - conjugate eye movement

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3
Q

What happens to each eyes image?

A

They are fused together

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4
Q

What happens if the visual axes are not aligned?

A

Image focuses on different area of each retina (shoud=ld both hit the same spot at each back of eye)

Brain is unable to fuse image = see two images = dipoplia

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5
Q

6 Extraocular muscles

A

Four recti
Two obliques

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6
Q

Four recti muscles (in each eye)

A

Superior rectus
Inferior rectus
Lateral rectus
Medial rectus

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7
Q

Two oblique muscles (in each eye)

A

Superior oblique
Inferior oblique

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8
Q

Where do all the extraocular muscles insert?

A

The sclera

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9
Q

Where do all the extraocular muscles originate from?

A

The apex of the orbit (except for inferior oblique which arises from anterior orbital floor)

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10
Q

Where do the 4 recti muscles specifically all arise from?

A

Common tendinous ring

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11
Q

What are most extraocular muscles innervated by? Exceptions:

A

Most - CN III - oculomotor

Lateral rectus - CN VI abducens

Superior oblique - CN IV - Trochlear

(LR6SO4)

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12
Q

Two axis within the eye

A

Visual axis - eyeball axis

Axis of orbit

(these don’t fully align)

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13
Q

What axis do the extraocular muscles run in? and what does this mean for them?

A

The axis of the orbit - some attach at an oblique angle, this means they can have different actions

(those attaching to superior and inferior globe surface)

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14
Q

Superior oblique unique structure

A

Passes through trochlear pully which swings muscle back to insert onto superior posterolateral edge

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15
Q

What muscles are involved in primary resting gaze?

A

ALL - equal and opposite pull of all muscles
Actions are balanced (each muscle has antagonist to it’s movement)

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16
Q

What must happen when changing position of gaze?

A

Muscles moving both eyes must be co-ordinated and move simultaneously

Visual axis must remain aligned (conjugate gaze) - otherwise dipoplia

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17
Q

Terms of directions of eye movements

A

Elevation
Depression
Adduction (towards nose)
Abduction (away from nose)
Internal rotation - intorsion
External rotation - extorsion

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18
Q

Which muscles have singular action on eye?

A

Medial rectus - Adduction
Lateral rectus - abduction

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19
Q

Medial and lateral rectus insertion on sclera

A

Medial - attaches to medial sclera (nose side)

Lateral - attaches to lateral sclera

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20
Q

Superior rectus insertion

A

Inserts obliquely into superior anterolateral sclera

(on top and slightly lateral)

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21
Q

Actions of superior rectus (if starting from primary resting gaze)

A

ELEVATION - main function
Slight adduction (medial pull)
Slight intort (internal rotation)

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22
Q

When is superior rectus a more powerful elevator?

A

When the eye is positioned laterally

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23
Q

Inferior rectus insertion

A

Obliquely into anteroinferior surface of globe

24
Q

Actions of inferior rectus

A

Depress - main action
Slightly adducts
Slightly extorts

(Adduct as rectum is central)

25
Q

When is inferior rectus a more powerful depressor?

A

When eye is positioned laterally

26
Q

Superuor oblique insertion

A

Passes through trochlea, inserts into superior posterior globe

**consider pull coming from trochlea area

27
Q

Action of superior oblique (resting gaze starting position)

A

Intort (main action)
Depress (main action)
Slight abduction

SOD AI

28
Q

When is superior oblique a more powerful depressor?

A

When eye is positioned medially

29
Q

Inferior oblique muscle insertion

A

Inferoposterior aspect of globe

(arises from anteromedial floor of orbit)

30
Q

Actions of inferior oblique

A

Extort (main action)
Elevate (main action)
Slightly abduct

31
Q

When is inferior oblique a more powerful elevator?

A

when eye is positioned medially

32
Q

Which extraocular muscles elevate the eyeball?

A

Superior rectus
Inferior oblique

33
Q

Which extraocular muscles depress the eyeball?

A

Inferior rectus
Superior oblique

34
Q

Which extraocular muscles are strong elevators and depressors when the eye is adducted?

A

Elevator - inferior oblique
Depressory - superior oblique

(remember these abduct so opposite, more tension will be on them when they are being pulled in opposite direction)

35
Q

Which extraocular muscles are more powerful elevators and depressors when abducted?

A

Superior rectus - elevate
Inferior rectus - depress

36
Q

What happens if muscle is weakened?

A

It’s influence is lost - antagonist dominates and takes over

37
Q

What is it called when muscle action is no longer antagonised/balanced out?

A

Deviation = strabismus (squint) due to actions of remaining muscles

38
Q

If eye is adducted what muscle is weakened, what muscle is taking over?

A

Lateral rectus weakened (no abduction, innervated by abducens nerve)

Medial rectus takes over (adduction)

39
Q

If eye is elevated and adducted, what muscle is weakened, which is taking over?

A

Superior oblique weakened (usually abducts and depresses, trochlear nerve innervation)

Superior rectus is taking over (elevates and adducts)

40
Q

What do the 2 superior and inferior rectus muscles all have in common?

A

Adduction

41
Q

What do the oblique muscles have in common?

A

Abduction

42
Q

How do we separate testing muscles that have same function? eg superior rectus and inferior oblique both elevate?

A

Change the gaze/starting position we test them in - ones are more dominant in adducted and abducted gaze

43
Q

Example of changing starting position when testing?

A

We form a H when testing eye movements, eg when at the edge of the H and one eye is adducted - oblique muscles will be more dominant
The other eye, which is abducted - rectus muscles will be more dominant

We can test elevation and depression at these two extremes of gaze to detect

44
Q

What is strabismus?

A

Ocular misalignment

45
Q

Is ocular misalignment common?

A

Common in children - congenital or develops in infancy, cause not always known

Adults - acquired die to pathology or disease involving different structures, more concerning

46
Q

Structures that can have pathology causing ocular misalignment

A

Neuromuscular junctions (myasthenia gravis)
Nerves supplying muscles - cranial (III, IV, VI)

47
Q

How can cranial nerves be affected by pathology?

A

Vasculopathic - micovascular ischaemia secondary to diabetes or HTN

Physical compression - tumour, aneurysm

Raised intracranial pressure

48
Q

CN III palsy presentation

A

Eye is down and out - innervates all extraocular muscles except lateral rectus and superior oblique, these are unopposed so depress and abduct eye

49
Q

Two acquired causes of CN III lesion

A

Vasculopathic - microvascular ischaemia (DM or HTN)
= pupil spared

Compressive - raised ICP, tumour, posterior communicating artery aneurysm=
= pupil involving (PS fibres on periphery of nerve)

50
Q

CN IV palsy - trochlear

A

Extorted, elevated and adducted

(superior oblique depresses, intorts and abducts and these are lost)

51
Q

How do pt’s try and compensate by losing extorsion in loss of trochlear innervated superior oblique?

A

Tilt head to try and compensate (eg if R trochlear is out and eye extorted, pt tilts head to left)

52
Q

When is dipoplia worse with CN IV trochlear lesion?

A

On downward gaze medially it is worse - eg walking down stairs, reading

Superior oblique is main depressior when adducted remember = worse when eye adducts

53
Q

What happens to eye in CN VI abducens lesion?

A

Affected eye is adducted - no apposition to adduction with lateral rectus abduction (innervated by CN VI)

54
Q

When is dipoplia worse for CN VI lesion?

A

In horizontal gaze

55
Q

Most likely cause of CN III, IV and VI lesions?

A

Vasculopathic
- they will be asymptomatic other than CN signs, usually self resolve in few months

56
Q

What history suggests other cause than vasculopathic?

A

Headache +/- vomitting - raised ICP from tumour/haemorrhage

Recent head trauma

Pupil involved in CN III lesions with eye pain and headache suggest compressive

Head and Neck (26 decks)

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