extraocular muscle 4 Flashcards
what is the purpose of an ocular motility assessment ?
- test integrity of the smooth pursuit system
2. allows you to tell if a deviation is concomitant or incomitant
what is a concomitant deviation ?
. 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
what is incomitant deviation ?
. 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
what is the technique for testing ocular motility ?
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 )
why do you move the eyes into 8 positions of gaze?
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
what happens if RE fails to go into dextro elevation ?
. this suggests a RSR weakness as it is the only muscle maximally used in this direction
what happens LE fails to go into laevoversion ?
. this suggests a LLR weakness as it is the only muscle maximally used in this direction
how many muscles work in direct elevation ?
. SR
. IO
how many muscles work in direct depression?
. SO
. IR
what happens if RE fails to elevate?
. you would not be able to tell if SR or IO is weak
. this is because two muscles are maximally used
what is the reason that we take the eyes to direct elevation and direct depression ?
. to assess if either eye fully elevated and depressed
what is V exo pattern ?
. exophoria or tropia increases on elevation
. exo decreases on depression
what is V eso pattern ?
. eso decreases on elevation and increases on depression
what is A exo pattern ?
. exo decreases on elevation
. exo increases on depression
what is A eso pattern ?
. eso increases on elevation
. eso decreases on depression
what are the methods of assessing ocular motility ?
- via corneal reflections
- subjective responses via diplopia charts ( widest separation of images in a particular line of gaze equals palsied muscle )
- via alternating cover test ( largest deviation in the line of gaze of the palsied muscle )
how do you know that you have moved your pen torch far enough during an ocular motility examination?
. the further you go the more subtle an EOM weakness you can detect
. too far and one corneal reflection disappears
how do you know when there is no muscle weakness ?
deviation concomitant
. when the corneal reflection is the same in primary position as well as dextro version and other positions
how to detect an over action by corneal reflections in dextro version in RE?
. when an eye has been pulled too far into dextro version
. this suggests a right lateral rectus over-action
how to detect an under action by corneal reflection in dextro elevation of RE ?
. RE has not been pulled up far enough
. this suggest under action of superior rectus
how to know if there is an over action in dextro elevation of LE ?
. LE has been pulled up too far into elevation
. over action of inferior oblique
what is the limitation of corneal reflections with ocular motility ?
. 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
how to assess ocular motility by subjective diplopia ?
. 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
how to assess torsion ?
. by using a steak ret
when recording diplopia what do distant image mean ?
. the distal image belongs to the under-acting eye
how is concomitant deviation seen when plotting diplopia chart using a spot light ?
. the double vision remains the same in all positions of gaze
. equal horizontal separation of images in all positions of gaze
. no EOM weakness
how is inconcomitant deviation see when plotting diplopia chart using a spot light ?
. 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
how to detect a right superior oblique palsy when plotting diplopia chart using a streak of light ?
. 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
what is the summary of rules on how to analyze a diplopia chart ?
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
what are the limitations of diplopia chart ?
. may not be possible due to
- suppression
- young or old
- may not understand language
- inconsistent responses
- functional
how to carry alternating cover test with motility ?
- carry out an alternating cover test in primary position
- carry out an alternating cover test in 8 directions of gaze
- 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
how to detect an under action in cover test with motility ?
. 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
how to detect an over action in cover test with motility?
. 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
how to record motility diagrammatically?
. 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
how to carry out ductions versus versions ?
. binocular eye movements tested first ( versions)
. repeat test monocularly by occluding one eye ( ductions) whenever limitation of movement expected
what does ductions versus versions do ?
. 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
what other clinical signs or symptoms should be observed during an assessment of ocular motility ?
. ptosis . lid retraction . lid lag . change in palpebral aperture or globe position . pupil changes . nystagmus changes . pain . effect of fatigue
how to use hess chart ?
. 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
what do Hess charts monitor ?
. monitor muscle weakness and binocular vision problem
how to interpret hess charts?
. 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
what happens if left superior oblique is under-acting?
. 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
what does an unequal sized fields in hess chart mean?
. incomitant strabismus
what does equal sized fields mean?
. concomitant strabismus ( e.g. exophoria )
. incomitant strabismus however has become concomitant with time
how to fix primary deviation ?
. fix with non affected eye
how to fix secondary deviation?
. fix with the affected eye
how much is each square on hess chart worth?
. each square = 5 degrees
what are the advantages of hess chart?
. A or V pattern can be seen
. uniform examination
. repeatable examination
what are the disadvantages of hess chart?
. doesn’t go as far as ocular motility test
. should not be used in isolation of a full binocular vision examination
how to differentiate between hess chart: longstanding versus recent onset in paralytic ( neurogenic ) strabismus?
- longstanding
- muscle sequelae fully developed
- primary deviation and secondary deviations approximately equal
- the field in either eye will be approximately equal size - 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
how to differentiate between hess chart: paralytic ( neurogenic ) versus mechanical ?
- 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 - 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 )
what useful clinical information can be gained from a hess chart?
. 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
