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OV2018 binocular vision > extraocular muscles 1 > Flashcards

extraocular muscles 1 Flashcards

1
Q

what are 7 extra-ocular muscles ?

A
  • levator palpebrae superioris ( LPS ) controls the eyelid
the 6 other muscles 
. superior rectus SR
. inferior rectus  IR
. lateral rectus LR
. medial rectus MR
. inferior oblique IO 
. superior oblique SO
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2
Q

what are the two branches of the oculomotor nerve ?

A
  • superior division

- inferior division

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3
Q

what does the third (III) cranial nerve ( oculomotor ) superior division supply ?

A

supplies
. superior rectus
. levator palpebrae superioris

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4
Q

what does the third (III) cranial nerve ( oculomotor ) inferior division supply ?

A

. medial rectus
. inferior rectus
. inferior oblique

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5
Q

what is the superior oblique supplied by ?

A
  • so4

- the fourth (IV) cranial nerve ( trochlear )

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6
Q

what is the lateral rectus supplied by ?

A
  • the sixth (VI) cranial nerve ( abducens )- function to look out
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7
Q

where is the anatomical origin of the four recti ?

A
  • at the annulus of zinn
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8
Q

where is the mechanical origin of the four recti ?

A
  • about 10mm posterior to the globe
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9
Q

how is the muscle insertion ?

A
  • all muscles are inserted anterior to equator .

- as muscle contracts cornea rotates towards the body of the muscle itself

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10
Q

what happens when superior rectus muscle contracts ?

A

-as the mechanical pull is from behind and the insertion is from the front :
the cornea will rotate towards the body of the muscle and therefore elevate the eyes

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11
Q

what happens when lateral rectus contracts ?

A
  • because the insertion is infront and pull is from behind

- the cornea will bend towards the body of the muscle and will abduct

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12
Q

what happens when medial rectus contracts ?

A
  • the cornea will move towards body of muscle
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13
Q

what happens when inferior rectus contracts ?

A
  • the cornea will move towards body of muscle and eye will depress
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14
Q

what is the anatomical origin of superior oblique ?

A
  • annulus of zinn - behind the equator (asssertion behind)
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15
Q

what is the anatomical origin of inferior oblique ?

A
  • anterior infero-nasal corner - behind the equator
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16
Q

what is the mechanical origin of superior oblique ?

A
  • anterior supero-nasal corner of orbital rim
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17
Q

what is the mechanical origin of inferior oblique ?

A
  • anterior and inferior to globe

- coupled to IR tendon

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18
Q

what happens when superior oblique muscle contracts?

A
  • the cornea will move away from the body of muscle
  • superior oblique will depress the eye
  • this is because the insertion is behind the equator and the pull is from the front
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19
Q

what happens when inferior oblique muscle contracts ?

A
  • the cornea will move away from the body of muscle and inferior oblique muscle will elevate
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20
Q

what happens to the two obliques when muscle contracts ?

A
  • as muscle contracts
  • cornea rotates away from the body of the muscle
  • superior oblique: downwards
  • inferior oblique: upwards
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21
Q

what is the shape of the recti insertions ?

A
  • insertions form a concave arc
  • MR and LR - concentric with limbus
  • SR and IR
    . tilted slightly nasally
    . closest to limbus on nasal side
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22
Q

what is the shape of superior oblique insertions ?

A
  • forms convex arc

- insertions fan out

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23
Q

what is the position of normal insertions ?

A
  • MR closest to limbus
    . distance behind limbus 5.5mm
  • IR next
    . distance behind limbus 6.5mm
  • LR next
    . distance behind limbus 7.0mm
  • SR farthest from limbus
    . distance behind limbus 7.5mm
  • IO insertion lies under LR
    . posterior end overlies the position of the fovea
  • SO insertion lies under SR
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24
Q

what is the centre of rotation?

A
  • the eye performs rotary movements around a centre of rotation within the globe
  • in the primary position the centre of rotation is located about 13.5mm behind the apex of the cornea
25
Q

what is fick’s axes ?

A

1- Z axis ( runs vertically through the eye )

  • MR and LR
  • allows us to look horizontally to the right and left ( abduction and adduction ) z- horiZontal movements

2- X axis

  • SR, IR, IO, SO
  • runs horizontally through the eye
  • elevation and depression - allows eye to look up and down (depress) - X controls vertical eye movements

3- Y axis

  • runs through the middle of the eye straight through the cornea through the pupil
  • cyclo-rotation or torsion
  • IO, SO , SR ,IR
26
Q

what is duction movement ?

A
  • rotation of one single eye is termed duction

- movement : limited by length of muscle + tendon, edge of orbit and soft tissue of orbit

27
Q

what does Z axis control ?

A
  • Z axis controls horizontal eye movement ( allow you to look out ) known as abduction
  • also Z axis allows us to make inward movements towards the nose known as adduction- ad duction
28
Q

what does X axis control ?

A
  • controls vertical eye movements
  • allows us to look up and down
  • elevation ( both eyes ) or supraduction ( one eye)
  • depression ( both eyes) or infraduction ( one eye )
29
Q

what does Y axis control ?

A
  • allows us to make torsional type movements
  • extrosion ( both eyes turn outwards in anti-clock wise ) or excyloduction ( one eye )
  • intorsion ( eye move clock wise towards the nose ) or incyloduction ( two eyes )
30
Q

how are oblique movements ?possible

A
  • a combination of the horizontal and vertical movements, moves the globe into various oblique positions ( up and to the right, down and to the left etc )
31
Q

what is primary position ?

A
  • when the eyes are looking straight ahead with body and head erect
32
Q

what happens when a muscle axis of rotation coincides with one of fick’s axis of rotation ?

A
  • contraction of that muscle will produce a rotation purely around that particular muscle
  • this means that if a muscle axis of rotation coincides with the z axis then the type of movement the eye will produce will be horizontal
  • if it coincides with a X axis - then they type of movement the eye will produce will be purely vertical etc etc.
33
Q

how do we know what muscles axis of rotation is ?

A
  • comes down to the muscle plane that is muscle plane is horizontal , the muscle axis of rotation is always perpendicular ( will be vertical )
34
Q

what is the relationship between muscle axis and muscle plane ?

A
  • muscle axis of rotation is perpendicular to the muscle plane
35
Q

where is muscle plane ?

A
  • point where the muscle first touches the globe ( tangential point ) and the centre of rotation
36
Q

what happens in primary position ?

A
  • in primary position the horizontal rectus muscle axis of rotation completely coincides with the z-axis of rotation
  • as a result contraction of the muscle produces a pure rotation around the vertical axis
37
Q

what happens when eyes look in or out (side to side)?

A
  • the muscle axis of rotation is still coincident with z - axis
  • no matter where the eyes look , the lateral rectus and medial rectus will always produce completely horizontal type of eye movements
  • as the eyes abduct or adduct the horizontal rectus muscle axis of rotation still coincides with z-axis of rotation therefore still no vertical nor torsional component
38
Q

what type of horizontal eye movement will be produced when the lateral rectus and medial rectis contracts ?

A
  • when LR contracts - eyes look away from nose
    ( abduction )
  • when MR contracts - eye will look into towards the nose
    ( adduction)

(HORIZONTAL)

39
Q

what is the action of the superior rectus in primary position ?

A
  • in primary position the superior rectus muscles axis of rotation does not completely coincide with one of axes of the coordinate system ( fick’s axes )

. primary action : elevation

. secondary action : incycloduction

. tertiary action : adduction

40
Q

what happens when the superior rectus globe is abducted by 23 degrees ?

A
  • when eye is abducted by 23 degrees the muscle axis of rotation is the same but fick’s - axis will move because the cornea is going to look out away from the nose
  • X AXIS WILL ROTATE and coincide with ficks axis of rotation- turning this eye into a pure elevator
  • the superior rectus now becomes a pure elevator
41
Q

what happens when the the superior rectus globe is adducted by 67 degrees?

A
  • the muscle axis of rotation is the same
  • coincides with y-axis
  • y axis controls t ortion eye movements
  • the superior rectus now produces pure incyloduction
42
Q

how many actions do SR, IR , SO , IO have in primary position ?

A

. the SR, IR, SO and IO have 3 actions in primary position

. but when the eyes move sometimes these muscles only have one

43
Q

what happens when the eye is adducted ?

A
  • superior oblique produces depression

- inferior oblique produces elevation

44
Q

what happens when eye is abducted ?

A
  • superior rectus produces elevation

- inferior rectus produces depression

45
Q

what is the inferior rectus muscle axis of rotation ?

A
  • axis of rotation doesn’t coincide with fick’s axis
  • so in the primary position , inferior rectus has 3 actions
  • the IR axis of rotation forms an angle of about 23 degrees with the x axis and 67 degrees with the y axis
46
Q

what are the three actions of inferior rectus in the primary position ?

A
  • primary action: depression
  • secondary action: excycloduction
  • tertiary action : adduction
47
Q

what happens in the inferior rectus muscle when the eye looks away from nose by 23 degrees ?

A
  • when the globe is abducted 23 degrees
  • muscle axis of rotation coincides with the x axis
  • axis always controls vertical movements
  • the inferior rectus now becomes a pure depressor
48
Q

what happens to IR when you adduct the eye by 67 degrees ?

A
  • the muscles axis of rotation coincides with the y axis
  • the y axis control tortion
  • the inferior rectus now produces pure excyloduction
49
Q

what is the action of the SO in the primary postion ?

A
  • axis of rotation doesn’t coincide with any of fick’s axis

- the SO axis of rotation forms an angle of about 36 degrees with the y axis and 54 degrees with the x axis

50
Q

what are the 3 actions of S0 in primary position ?

A
  • primary action: incycloduction
  • secondary action : depression
  • tertiary action : abduction
51
Q

what happens when to SO when abduct eye by 36 degrees ?

A
  • the muscle axis of rotation coincides with y axis - y produces cyclo hence
  • the so now produces pure incyloduction
52
Q

what happens to SO when you look in towards the nose by 54 degrees ?

A
  • the muscle axis of rotation coincides with x axis which controls vertical movements
  • the SO now becomes a pure depressor
53
Q

what is the action of the inferior oblique in primary position ?

A
  • the IO axis of rotation forms an angle of about 39 degrees with the y axis and 51 degrees with the X axis
54
Q

what are the 3 primary actions of IO ?

A

primary action :
excyloduction

secondary action :
elevation

tertiary action:
abduction

55
Q

what action does the IO muscle have when we abduct the eye by 39 degrees aways from the nose ?

A
  • the muscle axis of rotation will coincide with the y axis

- the inferior oblique now produces pure excycloduction

56
Q

what action does the IO muscle have when we adduct the eye by 51 degrees towards the nose ?

A
  • the muscle axis of rotation will coincide with the x axis
  • the x axis controls vertical eye movement
  • the inferior oblique now becomes a pure elevator
57
Q

what deviation will patient have if they had a large SR weakness ?

A
  • the right eye will hyportropia
  • the eye will exotropic
  • the eye will become extorsion
58
Q

what deviation will patient have if they had a large right IO weakness ?

A
  • RE - introted
  • RE - hyoptropic
  • RE - esotropia

OV2018 binocular vision (15 decks)

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