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OV2018 binocular vision > extraocular muscle 4 > Flashcards

extraocular muscle 4 Flashcards

1
Q

what is the purpose of an ocular motility assessment ?

A
  1. test integrity of the smooth pursuit system

2. allows you to tell if a deviation is concomitant or incomitant

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2
Q

what is a concomitant deviation ?

A

. where the size of the deviation does not vary with direction of gaze or which ever eye is made to fix
. less likely to have an EOM weakness or other neurological problem

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3
Q

what is incomitant deviation ?

A

. where the size and or type of deviation does vary with direction of gaze and when fixing either eye
. more likely to have an EOM weakness or other neurological , myogenic or mechanical problem
. if recent onset refer urgently

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4
Q

what is the technique for testing ocular motility ?

A

1 . torch is held approximately 50 cm form the patient
2 . head kept stationary and remove spectacles
3 . ask the patient to maintain central fixation on the light while you move it slowly into the 8 directions of gaze
4 . ask patient to report ( any sensation of pain or any double vision )

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5
Q

why do you move the eyes into 8 positions of gaze?

A

1 . the further you take a muscle into their maximum action , the more subtle weakness you can detect
2 . if a muscle is weak , it becomes most evident in position of gaze where it has maximum action

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6
Q

what happens if RE fails to go into dextro elevation ?

A

. this suggests a RSR weakness as it is the only muscle maximally used in this direction

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7
Q

what happens LE fails to go into laevoversion ?

A

. this suggests a LLR weakness as it is the only muscle maximally used in this direction

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8
Q

how many muscles work in direct elevation ?

A

. SR

. IO

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9
Q

how many muscles work in direct depression?

A

. SO

. IR

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10
Q

what happens if RE fails to elevate?

A

. you would not be able to tell if SR or IO is weak

. this is because two muscles are maximally used

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11
Q

what is the reason that we take the eyes to direct elevation and direct depression ?

A

. to assess if either eye fully elevated and depressed

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12
Q

what is V exo pattern ?

A

. exophoria or tropia increases on elevation

. exo decreases on depression

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13
Q

what is V eso pattern ?

A

. eso decreases on elevation and increases on depression

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14
Q

what is A exo pattern ?

A

. exo decreases on elevation

. exo increases on depression

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15
Q

what is A eso pattern ?

A

. eso increases on elevation

. eso decreases on depression

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16
Q

what are the methods of assessing ocular motility ?

A
  1. via corneal reflections
  2. subjective responses via diplopia charts ( widest separation of images in a particular line of gaze equals palsied muscle )
  3. via alternating cover test ( largest deviation in the line of gaze of the palsied muscle )
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17
Q

how do you know that you have moved your pen torch far enough during an ocular motility examination?

A

. the further you go the more subtle an EOM weakness you can detect

. too far and one corneal reflection disappears

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18
Q

how do you know when there is no muscle weakness ?

deviation concomitant

A

. when the corneal reflection is the same in primary position as well as dextro version and other positions

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19
Q

how to detect an over action by corneal reflections in dextro version in RE?

A

. when an eye has been pulled too far into dextro version

. this suggests a right lateral rectus over-action

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20
Q

how to detect an under action by corneal reflection in dextro elevation of RE ?

A

. RE has not been pulled up far enough

. this suggest under action of superior rectus

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21
Q

how to know if there is an over action in dextro elevation of LE ?

A

. LE has been pulled up too far into elevation

. over action of inferior oblique

22
Q

what is the limitation of corneal reflections with ocular motility ?

A

. if you rely on corneal reflections you will miss many smaller deviations

. 1mm of displacement of corneal reflections = 20 Dioptres

. not good method for subtle muscle weakness

23
Q

how to assess ocular motility by subjective diplopia ?

A

. hold pen torch
. ask patient if light is single or double
. move pen torch in 8 positions of gaze
. ask the patient to describe the double in the 8 positions of gaze ( is it side by side , on top of each other and how far apart they are )
. use red/green goggles to differentiate the RE and LE images if patient has diplopia
. clearly label diplopia chart

24
Q

how to assess torsion ?

A

. by using a steak ret

25
Q

when recording diplopia what do distant image mean ?

A

. the distal image belongs to the under-acting eye

26
Q

how is concomitant deviation seen when plotting diplopia chart using a spot light ?

A

. the double vision remains the same in all positions of gaze
. equal horizontal separation of images in all positions of gaze
. no EOM weakness

27
Q

how is inconcomitant deviation see when plotting diplopia chart using a spot light ?

A

. the double vision is not the same in all positions of gaze
. eg. in dextro version the red light is distal
. this suggests a horizontal muscle weakness
. red light is distal , this suggests a right lateral rectus weakness

28
Q

how to detect a right superior oblique palsy when plotting diplopia chart using a streak of light ?

A

. diplopia changes in different positions therefore incomitant
. widest separation of images is on leavo depression
. the furthest images ( distal image ) on leavo depression is the red light
. the red light is seen by RE
. the muscle that is maximally used in the RE on laevo depression is the RSO

29
Q

what is the summary of rules on how to analyze a diplopia chart ?

A

1 . is the deviation concomitant or incomitant ?
2 . does the RE see the red or green light ?
3 . where is dextroversion and laevoversion ?
4 . where is the largest separation of images ?
5 . which is the distal image
6 . which muscle pulls the distal image in this position

30
Q

what are the limitations of diplopia chart ?

A

. may not be possible due to

  • suppression
  • young or old
  • may not understand language
  • inconsistent responses
  • functional
31
Q

how to carry alternating cover test with motility ?

A
  1. carry out an alternating cover test in primary position
  2. carry out an alternating cover test in 8 directions of gaze
  3. remember to move pen torch as far as possible
    4 . compare deviation in 8 different directions of gaze
    5 . if the deviation remains the same in all positions of gaze then is it concomitant and there is no EOM weakness
32
Q

how to detect an under action in cover test with motility ?

A

. when you cover one eye , the eye which is attempting fixation has to move more towards the light to see it then it was under-acting

33
Q

how to detect an over action in cover test with motility?

A

. when you force the eye to fixate ( by covering the other eye ) the eye attempting fixation has to move back in towards the light to see it then it was over-acting

34
Q

how to record motility diagrammatically?

A 
. movement graded on a 9 point scale 
. under-actions = negative
. over-action = position 
. 0 = normal 
. 1  75% = of normal movement 
. 2 50% = of normal movement 
. 3  25%= of normal movement 
. 4 no movement from midline 
. > 4 eye not reaching midline
35
Q

how to carry out ductions versus versions ?

A

. binocular eye movements tested first ( versions)

. repeat test monocularly by occluding one eye ( ductions) whenever limitation of movement expected

36
Q

what does ductions versus versions do ?

A

. discriminates between paretic and mechanical incomitancy
. if more movement of eye occurs during duction then paresis ( neurogenic ) is more likely
. if similar under-action occurs during version and duction then mechanical restriction more likely

37
Q

what other clinical signs or symptoms should be observed during an assessment of ocular motility ?

A 
. ptosis 
. lid retraction
. lid lag
. change in palpebral aperture or globe position 
. pupil changes
. nystagmus changes 
. pain 
. effect of fatigue
38
Q

how to use hess chart ?

A

. based on total dissociation
. foveal projection
. lees screen uses mirror dissociation ( patient uses a rod to locate each point on the screen)
. plot one eye’s movement in relation to the other
- RE fixates: patient indicates where LE is looking
- LE fixates: patient indicates where RE is looking

39
Q

what do Hess charts monitor ?

A

. monitor muscle weakness and binocular vision problem

40
Q

how to interpret hess charts?

A

. find the smallest field which is the affected eye
. under-action = inwards displacement of dots
. over-action = outward displacement of dots
. the central dot indicates the deviation in primary position
. the higher field belongs to the higher eye

41
Q

what happens if left superior oblique is under-acting?

A

. the right inferior rectus to drag eyes down into dextro depression by over-acting
. the left inferior oblique starts to over-act
. the superior rectus under-acts

42
Q

what does an unequal sized fields in hess chart mean?

A

. incomitant strabismus

43
Q

what does equal sized fields mean?

A

. concomitant strabismus ( e.g. exophoria )

. incomitant strabismus however has become concomitant with time

44
Q

how to fix primary deviation ?

A

. fix with non affected eye

45
Q

how to fix secondary deviation?

A

. fix with the affected eye

46
Q

how much is each square on hess chart worth?

A

. each square = 5 degrees

47
Q

what are the advantages of hess chart?

A

. A or V pattern can be seen
. uniform examination
. repeatable examination

48
Q

what are the disadvantages of hess chart?

A

. doesn’t go as far as ocular motility test

. should not be used in isolation of a full binocular vision examination

49
Q

how to differentiate between hess chart: longstanding versus recent onset in paralytic ( neurogenic ) strabismus?

A
  1. longstanding
    - muscle sequelae fully developed
    - primary deviation and secondary deviations approximately equal
    - the field in either eye will be approximately equal size
  2. recent onset
    - over-action of the contralateral synergist only. Other sequelae will not have developed
    - secondary deviation significantly larger than primary
    - the field of the affected eye will be significantly smaller
50
Q

how to differentiate between hess chart: paralytic ( neurogenic ) versus mechanical ?

A
  1. neurogenic
    - proportional spacing between inner and outer fields
    - the field is displaced in the direction of the problem
    - full muscle sequelae will develop with time
  2. mechanical
    - outer and inners fields close together ( squashed appearance )
    - the field may be displaced in opposite whole plains of gaze : horizontally ( adduction and abduction ) or vertically ( elevation and depression ). Except to the rule is Brown’s syndrome
    - full muscle sequelae will not develop ( only over-action of the contralateral synergist )
51
Q

what useful clinical information can be gained from a hess chart?

A

. the type of deviation in primary position
. which is the affected eye
. is it neurogenic or mechanical
. longstanding or recent onset neurogenic problem
. helps identify A or V pattern
. enables cyclotropia to be measured
. monitoring progression

OV2018 binocular vision (15 decks)

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