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binocular vision > lecture 6 - measurement of ocular deviation > Flashcards

lecture 6 - measurement of ocular deviation Flashcards

1
Q

why should you measure ocular deviation?

A
  • enables us to diagnose
  • ensures consistency between examiners
  • find max deviation therefore can decide when to manage/monitor
  • monitor progression
  • relate size to fusion range or other clinical features
  • to calculate AC/A ratio
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2
Q

how do you measure ocular deviations using the objective prism cover test

A
  • carry out normal cover test
  • place prism of estimated strength in front of deviated eye (either if phobia)
  • apex always in direction of deviation
  • carry out alternating cover test SLOWLY
  • look at eye behind the prism bar
  • increase prism strength until opposite movement then record results as the prism seen before reversal
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3
Q

how do you measure ocular deviations using the Hirschberg test

A

px fixates on pen torch at 33 cm
corneal reflections noted in foxing été and compared to other eye
displacement estimated

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4
Q

how do you measure ocular deviations using the krimsky test

A

Patient fixes on light at 33cm — —
Corneal reflection noted in both eyes —
Estimated prism placed in front of fixing eye —
Strength increased until the corneal reflexes in deviated eye equal to position in fixing eye initially —
Can be used with prism before deviating eye (prism reflection test)

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5
Q

how do you measure ocular deviations using the subjective prism cover test

A
  • Head straight- target same size as before — - Carry out Cover Test —
  • Place prism of estimated strength before deviated eye or either if phoria
  • Carry out alternating cover test
  • Ask the patient if they notice image moving from— side to side or Up to down —
  • Find prism strength to neutralise movement of images as cover is moved from one eye to the other —
  • Make deviation reverse then record prism before reversal —
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6
Q

how do you measure ocular deviations using the Maddox rod

A

high powered cyls make the spot of light turn into a streak perpendicular to the direction of the grooves

other eye views the spot light

placed before either eye in latent

conducted in darkened room

increase prism until spot and image coincident

prism is equal to angle of deviation

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7
Q

how do you measure ocular deviations using the Maddox wing?

A
  • held in reading position
  • allow px time to dissociate
  • px asked what number the white and red arrow point to
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8
Q

does prism cover test measure latent or manifest deviations?

A

both - it gives you the total deviation

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9
Q

disadvantages of prism cover test

A

only as reliable as the clinician

requires px co-operation

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10
Q

which accommodative target do you use for prism cover test?

A

line above weakest VA

spot light if less than 6/60

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11
Q

how does the prismatic correction in the PCT work? eg. using RSOT

A

fixation target stimulates fovea of LE and nasal retina of RE - which projects temporally resulting in uncrossed diplopia
place base out in front of RE to alleviate diplopia, as the base out prism will move the image towards the apex, bringing it back into the centre

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12
Q

advantages of PCT

A

accurate measurement

measures full angle

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13
Q

disadvantages of PCT

A

dependant on ability to fixate accurately
cannot measure cyclodeviations
unreliable with poor VA
cant be used in young children

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14
Q

when would you use simultaneous prism cover test?

A

when your px has a manifest strabismus with a latent component

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15
Q

what does SPCT measure?

A

manifest deviation only

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16
Q

how do you carry out SPCT?

A

Perform cover test to determine type & estimate angle of deviation —
Prism of estimated strength placed before deviated eye while occluder simultaneously covers fixing eye (cover/uncover cover test) —

Keep increasing strength until neutral movement achieved

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17
Q

how do you carry out SPCT?

A

Perform cover test to determine type & estimate angle of deviation —
Prism of estimated strength placed before deviated eye while occluder simultaneously covers fixing eye (cover/uncover cover test) —

Keep increasing strength until neutral movement achieved

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18
Q

if red reflex is brighter in one that then the other what does this indicate?

A

they could have cataract, corneal abrasion, foreign body or strabismus

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19
Q

what is the Bruckner test?

A

screening test that allows you to detect manifest deviation

20
Q

1mm displacement of corneal reflectionis approx how many degrees?

A

12

21
Q

1mm displacement of corneal reflection is how many prism dioptres?

A

20-22

22
Q

when do you use the krimsky test?

A

when you have manifest deviation and fairly poor vision in one eye

23
Q

when do you use the prism reflection test

A

when you have manifest deviation and fairly good vision in both eyes

24
Q

how do you do the prism reflection test?

A

base in opposite direction, put in front of manifest eye, increase bar strength until corneal reflection in the same in both eyes

25
Q

advantages of using corneal reflections?

A

prism reflection test is good for uncooperative px’s

krismky is good for blind or one eye with very poor vision

26
Q

disadvantages of using corneal reflections

A

cant measure latent deviations
will not detect microtropias
accommodation is not controlled

27
Q

why is subjective PCT useful?

A

Useful in small symptom producing vertical deviation

28
Q

if the image appears to move side to side WITH the occluder when carrying out subjective PCT…

A

exophoria

29
Q

if the image appears to move side to side WITHOUT the occluder when carrying out subjective PCT…

A

esophoria

30
Q

advantage of Maddox Rod

A

relatively easy to use

detects and measures torsion in cyclodeviation

31
Q

disadvantage of Maddox rod

A

accommodation not controlled
can’t have suppression or ARCC
slight head tilt may stimulate vertical deviation
nears fairly good VA in either eye

32
Q

disadvantage of Maddox rod

A

accommodation not controlled
can’t have suppression or ARCC
slight head tilt may stimulate vertical deviation
nears fairly good VA in either eye

33
Q

if Maddox Rod is places before the right eye where will the red bar be in relation to the spot light - esodeviation

A

to the right (uncrossed)

34
Q

if Maddox Rod is places before the right eye where will the red bar be in relation to the spot light - exodeviation

A

to the left (crossed)

35
Q

how to test cyclodeviations using the Maddox rod

A

px reports if tilted or torsion is syspected

  • 2 vertical Maddox rods are inserted into trial frame
  • if separation between lines use a vertical prism
  • px or practitioner rotates rods so that they appear straight and parallel
  • amount of cyclodeviation is measured on trial frame in degrees
  • used for distance and near viewing in primary position
36
Q

if a patient reports even numbers when using Maddox wing, what does this suggest?

A

they have an exodeviation

37
Q

if a px reports odd numbers when using Maddox wing, what does this suggest?

A

they have an esodeviation

38
Q

how is torsion indicated when using the Maddox wing?

A

if the red horizontal arrow is not parallel with the grading scale

in this case the px is asked to adjust arrow themselves until it is parallel

39
Q

advantages of Maddox wing

A

easiest
quickest
measures latent horizontal, vertical and cyclodeviations

40
Q

disadvantages of Maddox wing

A
  • near only
  • set distance of 33 cm
  • accommodation effects results PD fixed
  • can’t have suppression or ARC
  • unreliable in the presence of poor VA
  • not good with uncooperative px’s
  • septa bend easily not fully preventing peripheral fusion
41
Q

should these tests be carries out with correction?

A

All tests SHOULD be carried with and without correction if it influences their deviation

42
Q

when do spectacles not impact the deviation?

A

when you are presbyopic

43
Q

what target do you use for prism fusion range if:

R - 6/9
L - 6/5

A

6/60 - you always choose 6/60 when they can see it, if not it is the spotlight

44
Q

which tests can measure torsional components?

A

Maddox wing and rod

45
Q

how would you explain what a PCT measures to a px? (esophoria)

A

“your eyes are slightly turned in towards your nose, so i’m going to measure how much it is turned in by”

46
Q

how would you explain what a PCT measures to a px? (exophoria)

A

“your eyes are straight but when i cover one eye at a time, they have a tendency to move out a little bit so i’m going to measure how much it is”

binocular vision (10 decks)

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