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Binocular vision > accommodation & convergence > Flashcards

accommodation & convergence Flashcards

1
Q

list the things which assessment of near point measures

A
  • convergence
  • accommodation
  • relationship between accommodation and convergence
  • near pupil response
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2
Q

which ways can convergence be measured

A
  • near point (bringing target to px)

- fusional reserves

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3
Q

which ways can accommodation be measured

A
  • near point (bring target towards px until blurred)
  • facility (measure of how accurate accommodation is)
  • lag (ability to change accommodation quickly)
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4
Q

what are you measuring when measuring the facility of accommodation

A

how accurate your accommodation is, e.g. at 25cm you should accommodate by 4D etc

  • speed of change in accommodation
  • rapid refixation from near to distance viewing
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5
Q

which ways can you measure the relationship between accommodation and convergence

A
  • AC/A ratio

- +ve and -ve relative accommodation/convergence

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6
Q

what is +ve relative accommodation

A

increasing our accommodation whilst keeping our vergence fixed

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7
Q

what is -ve relative accommodation

A

relaxing our accommodation whilst keeping our accommodation fixed

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8
Q

what is used to measure the near point of convergence

A

RAF rule

  • dot provides a fixation point
  • single high contrast line helps recognition of diplopia
  • use cm scale for measurement to measure near point convergence (when lines just go into two)
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9
Q

what does the dot target on the RAF rule provide

A

a fixation point

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10
Q

what does the high contrast line provide on the RAF rule

A

helps recognition of diplopia

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11
Q

what is a subjective example of measuring near point convergence

A

patient reports diplopia

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12
Q

when can a subjective method of near point convergence i.e. patient reporting diplopia not reliable

A
  • on young children

- on adults - as we have physiological diplopia so we can learn to ignore when a target splits into two

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13
Q

what are the objective examples of measuring near point convergence

A
  • watch the patients eyes
  • when convergence breaks note:
    which eye diverges first
    at which distance from the face
    does the patient report diplopia
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14
Q

what must be noted when objectively measuring near point convergence by when convergence breaks

A
  • which eye diverges first
  • at which distance from the face
  • does the patient report diplopia
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15
Q

what is the reason for when convergence breaks, when objectively measuring near point convergence

A

they have reached the limit of their convergence

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16
Q

list the steps of how you would do the push up and back of the target of the RAF rule when measuring near point convergence

A 
- push target towards patient -
 record break point 
- bring target away from patient -
watch for fusion
record recovery point 
- repeat
- normal 6-10cm 
- record NPC 5cm (subjective)left eye convergence breaks
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17
Q

which patients should wear rx when measuring near point convergence

A

high hypermetropes
high myopes
presbyopes

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18
Q

what reasons may wearing rx when measuring near point convergence not a good idea

A
  • for myopes - base in prisms due to -ve lens will assist in convergence
  • lens edge and frame contours may obscure target
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19
Q

what is the assessment of accommodation measured with

A

RAF rule

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20
Q

list which aspects of accommodation is measured when measuring the assessment of accommodation

A
  • accommodative amplitude or range
  • accommodative facility
  • accommodative lag or lead
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21
Q

how is the accommodative amplitude measured as an assessment of accommodation

A
  • near point -
    bring target towards until it becomes blurred
  • minus lenses -
    keep adding minus lenses until they can no longer accommodate through them, and report its blurred = reached limit of accommodation
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22
Q

how is the accommodative facility measured as an assessment of accommodation

A

flipper lenses - ability to change accommodation rapidly by using +/- confirmation test lenses

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23
Q

how is the accommodative lag or lead measured as an assessment of accommodation

A
  • dynamic retinoscopy
    monocular estimation method
    nott method
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24
Q

list the steps of how you would measure near point

A
  • test monocularly and binocularly
  • ensure full distance rx is worn
    max +ve or least -ve
  • find nearest point of clear vision
    measure in cm and convert into dioptres
    use dioptric scale
  • target
    N5 or smallest visible print or target
  • technique
    push up target until patient reports target blur
    pull back until patient reports target is clear
    repeat push up and pull back
    if difference is less than 1D - record mean
    if difference is more than 1D - record range
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25
Q

when measuring near point how do you record your results if there is a difference of less than 1D between readings

A

record mean

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26
Q

when measuring near point how do you record your results if there is a difference of more than 1D between readings

A

record range

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27
Q

when measuring near point, is it done monocularly or binocularly

A

both

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28
Q

is rx worn when measuring near point

A

yes full distance rx

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29
Q

what is the target viewed on the RAF rule when measuring near point

A

N5 or smallest visible print or target

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30
Q

what is the technique when measuring near point with an RAF rule

A
  • push up target until patient reports target blur
  • pull back until patient reports target as clear
  • repeat push up/pull back
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31
Q

why is it important to select the smallest visible line of text on the RAF rule when measuring near point

A

printed text is more demanding target than single letter presentation

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32
Q

what must you do if the amplitude is less than 2D (50cm) on the RAF rule when measuring near point

A
  • include binocular near add e.g. +2.00DS
  • find near point and subtract add from final result
    e. g. if measure accommodation with +2.00DS add, if you find +6.00D of accommodation, they actually have +4D
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33
Q

which type of person may have an amplitude less than 2D (50cm) and why do you need to give them an add e.g. +2D when using the RAF rule to measure near point

A

presbyopes, so that their range is brought towards the middle of the RAF unit

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34
Q

when measuring accommodative amplitude or range via minus lenses, which rx should be used

A

full refractive correction (must do when measuring accommodation)

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35
Q

what target and at which distance must be used when measuring accommodative amplitude or range with minus lenses

A

near card at 40cm

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36
Q

list the steps of how you would measure accommodative amplitude or range with minus lenses

A
  • one eye occluded
  • negative lenses are placed infront of eye
  • increased in 0.25DS steps
  • encourage patient to make print clear
  • end point when letters cannot be cleared (reached limit of accommodation)
  • repeat for other eye and binocularly
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37
Q

when measuring accommodative amplitude or range with minus lenses, is it done monocularly or binocularly

A

both

monocularly first them do binocularly

38
Q

which ways are there to measure amplitude of accommodation subjectively

A
  • near point
    or
  • far point through minus lenses
39
Q

when is recording near point as a subjective measure of amplitude of accommodation slightly better and why

A

binocularly as convergence strives accommodation

40
Q

when is recoding far point through minus lenses as a subjective measure of amplitude of accommodation slightly better

A

monocularly

41
Q

what are the disadvantages of measuring amplitude of accommodation subjectively i.e. by recording near point and far point through minus lenses

A
  • an unreliable end point
  • large differences between stimulus and response accommodation
    depth of field increased by small pupils (accommodate more than they actually accommodate)
  • changing subjective criteria
  • cannot do on children
42
Q

define accommodative facility

A

change in accommodative effort with change in accommodative demand

43
Q

how are flippers/confirmation test used to measure accommodative facility

A
  • binocular + and - spheres
    ask to look through +ve lenses, when clear flip round to -ve lenses and ask them to make it clear, so they’re exerting and relaxing accommodation whilst keeping their vergence fixed
  • rapid change in accommodative demand
  • number of cycles per minute
    normal young adult or child with ±2.00 lens 9-11 cyc/min
44
Q

what is the normal range of cycles per minute with ±2.00DS lenses, when measuring the accommodative facility

A

9-11 cyc/minute

45
Q

what are the objective techniques of measuring accommodation

A
  • accommodative lag

- dynamic retinoscopy

46
Q

which two ways in accommodative lag measured, as an objective technique of measuring accommodation

A 
- stimulus accommodation
distance of fixation target in D sphere
if their accommodation is equal to the stimulus accommodation = neutral reflex 
- response accommodation
objective assessment of accommodation
47
Q

how can dynamic retinoscopy measure accommodation

A
  • nott method
    changing distance of retinoscope to neutralise
  • MEM (monocular estimate) method
    use lenses to neutralise
  • difference between accommodative demand and plane of neutralisation, in dioptres
48
Q

when using dynamic retinoscopy MEM to measure accommodation, where must the target be placed

A

same distance as ret, normally 1/3rd metre

px fixates of detailed target e.g. pictures for children

49
Q

when does neutralisation occur when using dynamic retinoscopy MEM to measure accommodation

A

when back focal plane of the eye is conjugate with back focal plane of retinoscope

50
Q

what movement shows lag in ret reflex, when using dynamic retinoscopy MEM to measure accommodation

A

with movement

51
Q

what does an against movement in ret reflex show, when using dynamic retinoscopy MEM to measure accommodation

A

accommodative lead

52
Q

how do you neutralise, when using dynamic retinoscopy MEM to measure accommodation

A

using appropriate spheres in one meridian only very briefly

53
Q

what does it mean when theres an accommodative lag/with movement in ret reflex, when using dynamic retinoscopy MEM to measure accommodation

A

accommodation is falling slightly behind the target, need to hold up +ve lens in front of eye until it becomes neutral.
can have an exo deviation larger than normal

54
Q

what does it mean when theres an accommodative lead/against movement in ret reflex, when using dynamic retinoscopy MEM to measure accommodation

A

accommodating too much & can have an eso deviation

55
Q

what distance must the target be when using dynamic retinoscopy Nott to measure accommodation

A

same distance as ret, normally 1/3rd metre

px fixates on detailed target

56
Q

when does neutralisation occur when using dynamic retinoscopy Nott to measure accommodation

A

when back focal plane of eye is conjugate with back focal plane of retinoscope

57
Q

what does a with movement in ret reflex show when using dynamic retinoscopy Nott to measure accommodation

A

accommodative lag

58
Q

what must you do to neutralise, when there is an accommodative lag/with movement in ret reflex, when using dynamic retinoscopy Nott to measure accommodation

A

move ret backwards until back focal plane of eye and ret are conjugate

59
Q

what must you do to neutralise, when theres an accommodative lead/against movement in ret reflex, when using dynamic retinoscopy Nott to measure accommodation

A

move ret forwards

60
Q

how do you measure neutralisation when using dynamic retinoscopy Nott to measure accommodation

A

lag is the dioptric difference in distance of ret and target
eg
- target at 33cm (3D = stimulus of accommodation)
- if ret reflex neutralised at 40cm (2.5D = response accommodation)
- lag = 0.5D
- normal lag is between 0-0.75 dioptres

61
Q

what is normal lag, when using dynamic retinoscopy Nott to measure accommodation

A

0-0.75D

62
Q

what does the AC/A ratio as a measure of relationship between accommodation and convergence stand for

A

amount of convergence per dioptre of accommodation
(amount you converge per unit of accommodation)
prism dioptre/DS

63
Q

when using +ve and -ve relative convergence as a measure of relationship between accommodation and convergence, what is kept constant and what changes

A
  • accommodation constant

- change in vergence demand

64
Q

when using +ve and -ve relative accommodation as a measure of relationship between accommodation and convergence, what is kept constant and what changes

A
  • vergence constant

- change in accommodative demand

65
Q

list the three different methods of measuring AC/A ratio

A
  • heterophoria method
  • gradient method
  • fixation disparity method
66
Q

what is the heterophoria method of AC/A ratio, finding the difference in

A

difference in angle of deviation (phoria or tropia) on near and distance fixation

67
Q

what measurement do you take when using the heterophoria method of AC/A ratio

A
  • pd (cm)
  • prism cover test at distance & near
  • angle of deviation on distance fixation
  • angle of deviation on near fixation
68
Q

what is the AC/A calculation for the heterophoria method

A

pd + ((angleN - angleD)/accommodative demand)

69
Q

in the heterophoria method of calculating the AC/A ratio, what sign does a eso and exo prism dioptres deviation have

A

eso +ve

exo -ve

70
Q

what does the heterophoria method of calculating the AC/A ration make no allowance for

A

proximal convergence

71
Q

give an example of the heterophoria method of measuring AC/A ratio

A
  • distance viewing: 2 prism dioptres XOP (-ve)
  • 1/3rd m viewing: 8 prism dioptres XOP
  • pd = 64mm (6.4cm)
  • pd + ((phoriaN - phoriaD)/accomm demand)
  • 6.4 = ((-8 - (-2)/3) = 6.4 - 2
  • = 4.4:1
72
Q

what is the normal AC/A range when using the heterophoria method

A

3:1 to 5:1

73
Q

what does the gradient method of measuring AC/A ratio measure

A

the change in angle or heterophoria when viewing through +ve or -ve spheres

74
Q

when measuring the change in angle or heterophoria when viewing through +ve or -ve spheres, in the gradient method of AC/A ratio, what is altered and what is kept the same

A
  • accommodative demand altered

- vergence demand kept the same

75
Q

when using the gradient method to measure AC/A ratio, list what type of fixation is required and which types of prism cover tests are required

A
  • near fixation
  • near PCT
    compare near PCT with +3.00DS binocularly or without +3.00DS
  • distance PCT
    compare PCT with -3.00DS binocularly or without -3.00DS
    to get angle of deviation
76
Q

what is the calculation of the AC/A ration with the gradient method

A

PCT with accomm - PCT without accomm/accomm demand

77
Q

give an example of the gradient method of measuring AC/A ratio

A

PCT at near (0.33m)
24^ base out
3^ base out with +3.00DS
(exo deviations = -ve value)

AC/A = 24^ - 3^/3 (as used +3DS lens) = 7:1

78
Q

what is considered a normal AC/A ratio

A

3-5:1

3-5 convergence to 1D of accommodation

79
Q

what does a high AC/A ratio indicate

A

excessive change in angle of deviation between near and distance fixation i.e. when we accommodate/converge excessively when we’re emmetropic

  • near eso called covergence excess (nv probs)
  • dist exo called divergence excess (dv probs)
80
Q

what does a low AC/A ratio indicate

A

insufficient change in angle between near and distance fixation when we’re emmetropic

  • near exo called convergence weakness
  • distance eso called divergence weakness
81
Q

what happens when you don’t have a good fusion range and give an example of someone who is orthoptic at near but has a high AC/A ration at distance

A

will have uncontrolled phorias which may become manifest
if orthoptic at near but have high AC/A ratio at distance, at DV will have poorly controlled exophoria and can become manifest i.e. exotropia

82
Q

what can +ve and -ve relative convergence measure

A

how much we can change convergence with keeping accommodation fixed (by looking at 40cm target)

83
Q

what is used to measure +ve and -ve relative convergence

A

prism bar or flipper prisms

84
Q

how do you measure +ve relative convergence

A
  • use base out prisms (to increase their convergence = positive relative convergence)
  • eso deviation of visual axis
  • measure to blur point (point where can no longer increase convergence & keep accommodation static/fixed = keeping one thing constant and changing the other)
85
Q

how do you measure -ve relative convergence

A
  • use base in prisms (so converge less but keep accommodation the same)
  • exo deviation of visual axis
  • measure to blur point or break point if breaks prior to blur
86
Q

what can +ve and -ve relative accommodation measure

A

how much we can change accommodation whilst keeping vergence fixed (by looking at a fixed target)

87
Q

which flipper lenses are used when measuring +ve relative accommodation

A

-ve

88
Q

what accommodation does +ve flipper lenses measure

A

-ve relative convergence

89
Q

what happens to the accommodation when placing +2.00DS flipper lenses infront of eyes whilst it focuses on a target to keep convergence fixed

A

accommodation relaxes

90
Q

what happens to the accommodation when placing -2.00DS flipper lenses infront of eyes whilst it focuses on a target to keep convergence fixed

A

accommodating twice as much

91
Q

how can dynamic ret high neutral objectively measure -ve relative accommodation

A

patient looks at the target and the plane of the ret & add +ve lenses until get neutralisation, then keep adding +ve lenses until get an against reflex and try to see the point where they can no longer keep their accommodation fixed

92
Q

list how to measure with the near pupil response of assessing near point/accommodation

A
  • patients face should be well illuminated
  • keep light on face constant during eye movement
    isolate near reflex from light responses
  • use of UV lamp assists visibility of pupil
  • observe pupil réponse
  • rapidly shifting fixation
    from a distance to a near target or vice versa
    use detailed target for near and distance
    looking for pupillary miosis when looking from distant target to near

Binocular vision (12 decks)

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