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Semester 3 - Head and neck > 13. Extra ocular eye muscles and movements > Flashcards

13. Extra ocular eye muscles and movements Flashcards

1
Q

why do we have binocular vision?

A

Binocular vision allows for wider field of vision and depth perception enabling ‘3D’ vision (stereoscopic vision)

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2
Q

What is needed so that binocular vision is effective?

A
  • Visual axis of both eyes need to be aligned
  • Eyes need to co-ordinate and move together- conjugate eye movement
  • Two images that reach cortex are ‘fused’, so perceived as one
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3
Q

Describe how two eyes work together to look at an object?

A

if both eyes looking at the same object, they need to work together so that light from the object hits the same spot on the back of each eye

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4
Q

Describe how the two eyes work together to look at a moving object

A

If an object is moving, both eyes need to move together so that the light from the object hits the same spot on the back of the both eyes

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5
Q

what does misalignment of visual axis result in?

A

Diplopia - double vision

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6
Q

Why does misalignment cause diplopia?

A

Misalignment of two visual axes image focuses on different area of each retina
– Brain unable to ‘fuse’- thus see two separate images

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7
Q

Describe diplopia

A

two images seen, can be displaced horizontal, vertically and/or diagonally

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8
Q

What makes up the extrinsic muscles of the eyes?

A
  • muscles of the eye lid

- extraocular muscles that move the eyeball

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9
Q

What are the intrinsic muscles of the eye?

A
  • sphincter pupillae
  • dilator pupillae
  • ciliary muscle
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10
Q

What makes up the intrinsic muscles of the eyes?

A
  • Muscles of the iris (dilator and constrictor of
    the pupil)
  • Ciliary muscle controls thickness of the lens
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11
Q

What are the muscles of the eyelid and what innervates them?

A
  • orbicularis oculi (palpebral part): facial nerve
  • levator palpebrae superioris: oculomotor nerve
  • superior tarsal smooth muscle: sympathetic innervation
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12
Q

What are the extraocular muscles of the eye and what is their innervation?

A

4 Recti:

  • superior rectus
  • inferior rectus
  • medial rectus
  • lateral rectus

2 obliques:

  • superior oblique
  • inferior oblique
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13
Q

What is the general function of the extra occular muscles

A

move the eyeball

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14
Q

where do the extra-ocular muscles insert?

A

sclera

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15
Q

where do the extra-ocular muscles originate?

A

Apex of orbit (exception of IO, arises floor of orbital cavity anteriorly)

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16
Q

Where exactly do the 4 recti extra-ocular muscles originate in the apex of the orbit?

A

from a common tendinous ring

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17
Q

What are the innervations of the extra- ocular muscles?

A 
Oculomotor:
- superior rectus, inferior rectus, medial rectus, inferior oblique
Trochlear:
- superior oblique
Abducens:
- lateral rectus
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18
Q

How can the innervation of extra-ocular muscles be remebered?

A

LR6SO4

lateral rectas = CN 6
superior oblique = CN 4
everything else = CN 3

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19
Q

What is the effect of the different extra-ocular muscles inserting at slightly diffferent positions of the sclera?

A

Each muscle will have a certain ‘pull’ and action on eye movement

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20
Q

What are the two axis of the eye?

A
  • Axis of the orbit

- Visual axis (axis of the eyeball)

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21
Q

In what axis do the extraocular muscles run?

A

In line with axis of orbit

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22
Q

Which and why do some muscles have more than one action on the eyeball?

A

Run in line with orbit axis so attach to eyeball at an oblique angle
- superior/inferior rectus/oblique
• Confers several ‘actions’ of movement on globe (not just simply ‘up’ and ‘down’) for some of the extra ocular muscles

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23
Q

Contractions of which muscles is responsible for the primary resting gaze?

A

• Equal and opposite pull of all extraocular muscles
• During resting gaze their actions are balanced
allowing for forward gaze
• Each muscle has antagonist of its movement

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24
Q

What is required to change position of gaze?

A

Exert greater pull through action of certain extraocular muscles, while antagonists relax

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25
Q

What is a conjugate gaze?

A

Visual axis remain aligned
- eyes move together

• Muscles moving both eyes must be highly coordinated and move simultaneously

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26
Q

What are the terms used for direction of eye movement?

A

Up: elevation, Down: depression
Lateral: abduction, Medial: adduction
External and internal rotation

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27
Q

What is the action of the medial and lateral rectus muscles (if starting from primary resting gaze)?

A

Lateral rectus: abduction of eyeball

Medial rectus: adduction of eyeball

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28
Q

What are the actions of superior rectus (if starting from primary resting gaze)?

A
  • elevation (main action)
  • slightly adducts
  • slightly intorts (internally rotates)
29
Q

Where do the superior an inferior rectus originate from?

A

from apex of the orbit

30
Q

Where does the superior rectus insert?

A

SR inserts into superior anterolateral surface of globe

31
Q

When is the superior rectus a more powerful elevator?

A

when eye is positioned laterally

32
Q

Where does the inferior rectus insert?

A

inserts obliquely into anteroinferior surface of globe

33
Q

What are the actions of inferior rectus muscles (if starting from primary resting gaze)?

A
  • depression (main action)
  • slightly adducts
  • slightly extorts (externally rotates)
34
Q

When is the inferior rectus a more powerful depressor?

A

when eye is positioned laterally

35
Q

Where does the superior oblique originate and insert?

A

Arises from apex of orbit, passes through trochlea, inserts into superior-posterior aspect of globe (posterior to equator)

36
Q

What are the actions of superior oblique muscle (if starting from primary resting gaze)?

A
  • intortion (main action)
  • depression
  • slight abduction
37
Q

What is the main action of the superior oblique muscle when eye is positioned medially?

A

more powerful depressor

38
Q

What is the origin and insertion of inferior oblqiue?

A

IO arises from anteromedial surface of floor of orbit;

inserts into infero-posterior aspect of globe (posterior to equator)

39
Q

What are the actions of inferior oblique muscle (if starting from primary resting gaze)?

A
  • extortion (main action)
  • elevation
  • slight abduction
40
Q

What is the main action of the inferior oblique muscle when eye is positioned medially?

A

more powerful elevator

41
Q

Which extra-ocular muscles have an action in elevating the eye ball?

A

superior rectus, inferior oblique

42
Q

Which extra-ocular muscles have an action in depressing the eye ball?

A

inferior rectus, superior oblique

43
Q

Which extra-ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the adducted position?

A

strongest elevator - inferior oblique

strongest depressor - superior oblique

44
Q

Which extra-ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the abducted position?

A

strongest elevator - superior rectus

strongest depressor - inferior rectus

45
Q

What the term for deviation of resting position of eyeball?

A

Strabismus (condition of having a squint)

46
Q

What is the effect of an extra-ocular muscle is weakened?

A

• If a muscle(s) weakened, its ‘influence’ (i.e. exerted by its anatomical action on the eyeball) is lost (or reduced)
• Other muscle actions no longer antagonised (“balanced” out)
– Resting position of eyeball may deviate = strabismus (squint) due to actions of remaining working muscles
• Difficulties with moving eye in certain directions of gaze

47
Q

What is the action of lateral rectus?

A

abduction

48
Q

what is the action of medial rectus?

A

adduction

49
Q

What is important when testing movements of the eye?

A

Need to Isolate an Action of Each Muscle to Test Them

50
Q

What shape is used to test the movements in each eye?

A

H (for each eye)

51
Q

How are the lateral/medial rectus muscles tested?

A

Abduction (LR) and adduction (MR) of the eye

52
Q

Why is elevation and depression of eye more complicated to test?

A

elevation and depression (in midline) involves two muscles each

53
Q

How is are the superior/inferior rectus muscles testing?

A

Start with the eye in the abducted position:

  • elevate to test superior rectus
  • depress to test inferior rectus

(as Recti muscles are main elevator (SR) and depressor (IR) of the eye when the eyeball is starting from the lateral position)

54
Q

How is are the superior/inferior oblique muscles testing?

A

Start with the eye in the adducted position:

  • elevate to test the inferior oblique
  • depress to test the superior oblique

(as Oblique muscles are main elevator (IO) and depressor (SO) of the eye when the eyeball is starting from the medial position)

55
Q

who are ocular misalignment common in and what causes it?

A

Common in children (congenital or develops in infancy)

– exact cause not always known

56
Q

if ocular misalignment is acquired in adults, what could be the cause?

A

• pathology or disease involving number of different structures…
– E.g. Neuromuscular junctions (e.g. myasthenia gravis)
– Nerves supplying the muscles (CN III, IV, VI)

57
Q

What are the possible causes of cranial nerve palsies?

A
  • Vasculopathic (microvascular ischaemia -secondary to diabetes, hypertension)
    – Physical compression e.g. from tumour or aneurysm (III)
    – raised intracranial pressure
58
Q

what do the CNIII innervate?

A
  • all extra -ocular muscles(except LR and SO)
  • muscle of eyelid(LPS)
  • sphincter pupillae muscle
59
Q

How will the eye be positioned in a CN III palsy?

A

Down and out - abducted and depressed

60
Q

What type of CNIII lesions typically affect the pupil?

A

Compressive lesions (parasympathetics in periphery of the nerve)

61
Q

What type of CNIII lesions typically spare the pupil?

A

Vasculopathic lesions (microvascular ischaemia -secondary to diabetes, hypertension)

62
Q

What type of commpressive lesions might affect cause a CNIII palsy?

A

raised ICP, tumour, posterior communicating artery aneurysm

63
Q

How will the eye be positioned in a CN IV palsy and why?

A

EXTORTED, slightly elevated and adducted

  • unopposed action of inferior oblique as loss of actions of superior oblique (only muscle innervated by CN IV)
64
Q

How might a person with CN IV palsy compensate?

A

Compensate for the slight extortion of eyeball by tilting the head slightly

65
Q

When is diplopia worse in CNIV palsy?

A 
Worsening diplopia (on downward vertical gaze) especially looking down and medially e.g. walking down stairs, reading
- Remember SO is main depressor of the eyeball when in adduction so this action affected when weak
66
Q

What is the presentation of CNVI palsy, when is it worse?

A
  • Unable to abduct the eye on affected side - eye thus adducted - unopposed pull of medial rectus
  • CNVI innervates lateral rectus
  • Report diplopia, made worse on horizontal gaze
67
Q

What other symptoms may be associated with CN lesions and what might these indicate?

A
  • Headache (+/-) vomiting could suggest raised ICP (secondary to tumour or haemorrhage)
  • Recent head injury
  • Presence of pupil involvement in CN III lesio
68
Q

what is the most likely cause for CN III, IV, VI lesions?

A

vasculopathic
– Patients will be otherwise asymptomatic (apart from signs/symptoms directly relating to CN lesion)
– Lesions usually self-resolve within few months

Semester 3 - Head and neck (17 decks)

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