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Measurement of ocular deviations Flashcards

1
Q

list the reasons why we measure ocular deviations

A
  • diagnosis
  • find maximum deviation
  • consistency between examiners
  • monitor progression
  • to relate to fusion range
  • to calculate AC/A
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2
Q

why is diagnosis an important point of measuring ocular deviations

A

as some deviations are greater at distance than near or greater at near than distance & some deviations are equal at both distances

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3
Q

why is monitoring progression important when measuring ocular deviations

A

incase the deviation gets larger
eg a large eso at distance can be dangerous, and cannot respond to exercises & large exo at near can be normal and fixed by exercises

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4
Q

why is it important to calculate AC/A when measuring ocular deviations

A

if have higher than 1D or accommodation at 4 prism dioptres, we have eso at near & if we converge less than 1D = exo at near (for every 1D or accommodation, we converge by 4prism dioptres)

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5
Q

what distance should all measurements of ocular deviations be taken at

A
  • 6 meters
  • at 1/3 metre
  • at > 6 meters plus for distance exo
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6
Q

why is it important to state whether the px was wearing refractive correction when measuring their ocular deviation

A

to know the effect of the refractive error on the deviation

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7
Q

what is the objective technique of measuring ocular deviation, using total dissociation

A

prism cover test

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8
Q

what is the objective techniques of measuring ocular deviation, using corneal reflection

A
  • hirschberg
  • krimsky
  • prism reflection test
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9
Q

what are the subjective techniques or measuring ocular deviation

A
  • subjective prism cover test
  • maddox rod
  • maddox wing
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10
Q

what is a disadvantage of a measuring technique which tests the eyes in total dissociation

A

do not allow the practitioner to distinguish between a manifest and latent deviation
(but thats irrelevant as we would have already done a cover test to know if they have latent or manifest deviation)

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11
Q

what does the prism cover test (PCT) require from the patient

A

co-operation

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12
Q

what type of target is required for the prism cover test

A

accommodative (which requires precise fixation & controls accommodation)

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13
Q

why is it important to have a target which controls accommodation during the prism cover test

A

as accommodation can effect the size of the deviation

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14
Q

what type of target is used with the prism cover test if px has VAs better than 6/60

A

letter on the line above that which the weakest eye can see e.g. R 6/18, L 6/12 use 6/24 letter

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15
Q

what type of target is used with the prism cover test if px has VAs worse/less than 6/60

A

spot light

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16
Q

why is it important to use a target which is a letter on the snellen chart on the line above that which the weakest eye can see in the prism cover test

A

so each eye can separately resolve that letter, when the other eye is covered

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17
Q

which type of deviations is the prism cover test used to measure

A
  • latent
  • manifest
  • vertical
  • horizontal
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18
Q

which deviation is the prism cover test not able to measure and under which exception can it work

A

cyclo deviation - unless they have an iris freckle

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19
Q

which type of technique must be done first in the prism cover test and why

A

cover/uncover test to determine if the px has an eso or an exo deviation and the size

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20
Q

once the cover/uncover test is done to determine the deviation and the size of it, what is done next

A

place prism of estimated strength before:

  • deviated eye in manifest deviation
  • either eye is latent
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21
Q

in the prism cover test, which direction must the base of the prism be placed for a hyper deviated eye

A

base down

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22
Q

in the prism cover test, which direction must the base of the prism be placed for a eso deviated eye

A

base out

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23
Q

in the prism cover test, which direction must the base of the prism be placed for a exo deviated eye

A

base in

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24
Q

in the prism cover test, which direction must the apex of the prism be placed

A

in the direction that the eye is deviated

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25
Q

why is it important for the patients head to be erect during the prism cover test

A

for a cycle or vertical deviated eye, the px may find that my tilting their head, they can reduce the symptoms/angle of deviation

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26
Q

in the prism cover test, once the estimated prism is placed before the eye, what must be performed next and why

A

alternating cover test

to see the effect that the prism has on the angle of deviation/estimate the angle

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27
Q

in the prism cover test, once the alternating cover test is performed and the angle of deviation is estimated, what must you do with the prism

A
  • increase prism until no movement is seen
  • increase prism until opposite movement is seen
  • then reduce prism again until no movement is seen
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28
Q

in the prism cover test, how must you record the results

A

in prism dioptres, the point at which no movement was detected
eg distance: 10 prism dioptres exo, 6 prism dioptres L/R with rx
near: 6 prism dioptres eso, 2 prism dioptres L/R without rx
(prism dioptres should be the prism triangle sign instead)

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29
Q

during the prism cover test, why is it important to always make sure the eyes are dissociated when doing the alternating cover test and changing the prism on one of the eyes whilst keeping the other eye covered

A

to not allow them to fuse as any point as it results in underestimating the angle

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30
Q

what is the point in adding a prism to the deviated eye in the prism cover test

A

so that the object of regard falls on the fovea of both eyes, so when you occlude the other eye, no movement is seen

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31
Q

in XOP, when is reversal seen during the prism cover test

A

when either eye moves out, to take up fixation (eyes made eso)

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32
Q

what is the reason for carrying out a simultaneous PCT

A

to measure habitual angle

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33
Q

which types of cases in a simultaneous PCT carried out on

A
  • manifest deviations ONLY
  • microtropia (very small deviations, but abnormal retinal correspondence, so they fixate with an extra foveal point, and tend to have a little phoria)
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34
Q

what is the first thing to be performed during the simultaneous PCT

A

cover/uncover test to estimate angle of deviation and don’t allot for full dissociation

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35
Q

following the cover/uncover test in simultaneous PCT, what is carried out next

A

place prism of estimated strength before:

  • deviated eye in manifest deviation
  • use prisms to neutralise deviation
  • in the end take prism and cover away together so the eyes do NOT dissociate
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36
Q

what are the advantages of a prism cover test

A
  • quick and easy to perform (on horizontal, vertical deviations)
  • accurate measurements, down to 2 prism dioptres
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37
Q

what are the disadvantages of a prism cover test

A
  • depend upon ability to fixate accurately
  • can not be used to measure cyclo deviations
  • unreliable in the presence of poor visual acuity
  • difficult to measure combined horizontal and vertical deviations
38
Q

what are corneal reflections only used to measure

A

estimate angle in manifest deviations

39
Q

when looking at a corneal reflection, what are the looking at the deviation between

A

centre of the pupil and the corneal reflection

40
Q

what is angle kappa, in a corneal reflection

A

the angle formed between the pupillary axis and the visual axis

41
Q

which direction is a corneal reflection seen in most cases

A

nasal, (macula sits temporal on the eye)

42
Q

what is the angle kappa in a normal position (slightly nasal) of a corneal reflection

A

+ve angle kappa or 3 degrees, fovea lies temporally to posterior pole

43
Q

what is the angle kappa in a central corneal position of a corneal reflection

A

angle kappa = 0, fovea coincides with the posterior pole

44
Q

what is the angle kappa in a corneal reflection which lies temporally

A

-ve angle kappa, fovea lies nasally to posterior pole

most look like they have a manifest pseudo deviation

45
Q

in the hirschberg test, what does the patient fixate on and at what distance

A

pen at 33cm

46
Q

what is noted during the hirschberg test

A

corneal reflections noted in fixing eye and compared with other eye

47
Q

how are the measurements estimated from the hirschberg test

A

displacement estimated 1mm = 12 degrees = to 20-22 prism dioptre deviation approx
(22 for children as they have steeper corneas & 20 prism dioptres for adults)

48
Q

in the krimsky test, what does the patient fixate on and at what distance

A

light at 33cm

49
Q

in the krimsky test, what is noted when the patient is looking at a light at 33cm

A

the position of the corneal reflex in FIXING eye

50
Q

once the corneal reflex position of the fixing eye is noted, during the krimsky test, what is done with the prism

A

prism strength is increased until corneal reflexes in deviated eye is equal to position in fixing eye initially

51
Q

in the krimsky test, which eye is the prism put before and why

A

prism put before the fixing eye so it is easier to see the corneal reflection of the deviating eye clearly

52
Q

in the krimsky test, in which case will the prism be placed before the deviating eye

A

on young children called prism reflection test

but it is less accurate as its more difficult to view the corneal reflex

53
Q

what are the advantages of measuring deviations via corneal reflections

A
  • uncooperative patients eg infants, learning difficulties

- blind or eyes with very poor vision/amblyopic eye (as can only do on manifest deviations)

54
Q

what are the disadvantages of measuring deviations via corneal reflections

A
  • not suitable for latent deviations
  • will not detect microtropias (small angle manifest deviations)
  • accommodation not controlled = less accurate
55
Q

which subjective test is the only reliable subjective test for manifest deviations

A

synoptophore

56
Q

list the steps of how the subjective cover test is carried out

A
  • find prism strengths to neutralise movement of images as cover is moved from one eye to the other
    (reliance placed upon patients subjective responses)
  • target - letter on line above that which weakest eye can see
    (spot light if less than 6/60)
  • letter target controls accommodation
57
Q

what is the advantage of a subjective cover test

A

useful for small vertical deviations

58
Q

what are the disadvantages of a subjective cover test

A
  • good subjective observations required from patient (cannot use on children)
  • inaccurate in presence of abnormal retinal correspondence
59
Q

list the steps of how a subjective prism cover test is carried out

A
  • perform cover/uncover test to estimate angle of deviation
  • place prism of estimated strength before:
    strabismic eye in manifest deviation
    either eye if latent
  • patient notes movement of target
  • record prism power and direction that gave no movement
60
Q

in the subjective prism cover test, what direction does the target move if you need to increase base in prism

A

same direction as occluder

61
Q

if the target moves in the same direction of the occluder as the cover was removed in the subjective cover test, what deviation does that patient have

A

exo deviation

62
Q

in the subjective prism cover test, what direction does the target move if you need to increase base out prism

A

opposite direction as occluder

63
Q

what is the maddox rod

A

a series of high powered cylinders which blur a spot of light into a streak at 90 degrees to the directions of the grooves

64
Q

with the maddox rod, which eye views the spot

A

the eye which does not have the lens of high powered cylinders placed infront of it

65
Q

what colour is the lens of high powered cyls for the maddox rod

A

traditionally red (for distance), but sometimes clear or blue

66
Q

when can you use a green lens of high powered cyls for the maddox rod test

A

green at near, to control accommodation

67
Q

what does the displacement of the streak and spot indicate in the maddox rod

A

the degree of the angle of deviation

68
Q

what will an orthoptic patient see in the maddox rod test

A

spot and streak on top

69
Q

which type of deviation is maddox rod used for and not used for

A

latent

not for manifest

70
Q

before which eye is the maddox rod lens placed before

A

either eye if latent

71
Q

in which surroundings must the maddox rod test be carried out and why

A

darkened room as additional light sources produce additional streaks

72
Q

in the maddox rod test, which eye is the prism placed before

A

before the eye which does not have the lens of high powered cyls

73
Q

at which direction should the apex of the prism be faced in the maddox rod test

A

apex to face the direction we want the spot to move

  • increased until sport and image coincident
  • prism at this point is equal to the angle of deviation
74
Q

what is seen by the patient if they have a right eso deviation in the maddox rod test

A

high powered coyly placed before right eye,

streak of light seen temporally to spot

75
Q

when will you do a maddox double rod test

A

if px reports that the line is tilted or if torsion is suspected

76
Q

state how the maddox double rod test is carried out

A

two maddox rods are inserted into trial frame, different colours rods can be used

  • one before each eye, cylinder axis vertical produces horizontal streaks
  • patient or practitioner rotates rods so that they appear straight or parallel
  • amount of cyclodeviation is measured on trial frame in degrees e.g. is trial frame axis moved by 10 degrees to make horizontal line, cyclo deviation = 10 degrees
  • used for distance and near viewing in primary position
77
Q

in the maddox rod test, if the lens is before the right eye, when will there be an exo deviation

A

when px reports streak to be on the left of the spot

78
Q

in the maddox rod test, if the lens is before the right eye, when will there be a left hyper deviation

A

when px reports the streak to be above the spot

79
Q

in the maddox rod test, if the lens is before the right eye, if the patient reports the streak to be below the spot, what deviation to they have

A

right hyper deviation

80
Q

in the maddox rod test, if the lens is before the right eye, if the patient reports the streak to be to the right to the spot, what deviation do they have

A

eso deviation

81
Q

what are the advantages of the maddox rod

A
  • detects and measured torsion in cyclo deviations

- can be used to detect presence of abnormal retinal correspondence

82
Q

what are the disadvantages of the maddox rod

A
  • accommodation not controlled (as no accommodative target)
  • not accurate in the presence of abnormal retinal correspondence
  • not good for manifest deviations
  • slight head tilt may simulate vertical deviations
83
Q

what will a patient report with the maddox rod if their accommodation is not under control

A

the spot and streak will be aligned, then not aligned, then aligned etc

84
Q

what is the patient asked during the maddox wing test

A

what number the white arrow is pointing to and what number the red arrow is pointing to

85
Q

what may the patient report if an arrow falls between 9 and 11 in the maddox wing

A

10

86
Q

what do even numbers suggest with the maddox wing

A

exo deviation

87
Q

what numbers do patients report when they have an eso deviation with the maddox wing

A

odd numbers

88
Q

what will each eye see when they look through the two separate eye pieces of the mad wing

A

one eye will see arrow & other eye will see number scale, when eyes are dissociated i.e. they take up the fusion free position

89
Q

when is torsion indicated with the maddox wing

A

if the red horizontal arrow is not parallel with the white horizontal grading scale
patient should be asked to adjust it themselves until it is parallel

90
Q

what are the advantages of the maddox wing

A
  • easy to use

- measures latent and manifest deviations, horizontal, vertical and cyclo deviations

91
Q

what are the deviations of the maddox wing

A
  • near only
  • set distance of 33cm
  • septa bend easily not fully preventing peripheral fusion (doesn’t give complete dissociation)
  • accommodation effects results, instruct px to keep numbers clear
    increases exos
    reduces esos
  • PD fixed

Binocular vision (12 decks)

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