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Binocular vision > Stereopsis > Flashcards

Stereopsis Flashcards

1
Q

what is the best form of depth perception

A

stereopsis

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2
Q

what is depth perception

A

how far or how near something is away from you

& allows you to see the world in 3D

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3
Q

what are the two forms of depth perception

A
  • monocular (one eye) cues

- binocular (two eyes) cues

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4
Q

which type of people do not have stereopsis but can perceive some sort of depth perception which is not as good as a person with normal BSV

A
  • person with one eye

- person with a large strabismus

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5
Q

list and the things which represent monocular pictorial cues

A
  1. relative size
  2. occlusion (interposition)
  3. relative height
  4. shadows
  5. atmospheric perspective
  6. linear perspective
  7. familiar size
  8. texture gradient
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6
Q

explain relative size in relation to monocular pictorial cues

A

two objects equal in size, the one far away will take up less field of view

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7
Q

explain occlusion (interposition) in relation to monocular pictorial cues

A

one object is hidden by another object, and that hidden object is considered further away

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8
Q

explain relative height in relation to monocular pictorial cues

A

Two types which describe the object as being further away:

  • below horizon = objects further away have higher bases
  • above horizon = objects further away have lower bases
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9
Q

explain shadows in relation to monocular pictorial cues

A

shadows removes the contradictions of an object which occludes another yet has a higher base and is claimed to be further away, as the shadow shows that the object is in front and elevated

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10
Q

explain atmospheric perspective in relation to monocular pictorial cues

A

furtherest object is shown by light scatter and haziness in the atmosphere which makes it look further away

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11
Q

explain linear perspective in relation to monocular pictorial cues

A

with depth the distance between parallel line becomes smaller in 2D picture e.g. train tracks converge as they go further away

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12
Q

explain familiar size in relation to monocular pictorial cues

A

previous knowledge of the object’s size is used to determine the absolute depth of the object e.g the man is closer to the camera and the taj mahal is further away yet we know the taj mahal is larger than the person

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13
Q

explain texture gradient in relation to monocular pictorial cues

A

objects are closer as can see more fine detail and objects further away as they are less defined and more blurry

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14
Q

what is terror subterra (shepard)

A
  • due to the background, we perceive the upper object to be further away & therefore the larger one, but both objects (monsters) are actually the same size, but linear perspective and convergent lines makes the back monster bigger
    another example
  • the ames room, where all men are the same size, but the room has been constructed so that the left hand corner is twice as far away from the observer as the right hand corner
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15
Q

name the two types of monocular movement produced cues

A
  1. monocular parallax

2. kinetic depth effect

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16
Q

what is monocular parallax

A

when near objects pass retinal image plane faster than distance objects e.g. japan bullet train

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17
Q

what is kinetic depth

A

when a three dimension form of an object can be perceived when the object if moving e.g. the moon (which we know is spherical and not flat due to its kinetic effect)

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18
Q

how do we perceive depth and size

A

oculomotor cues

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19
Q

what are the two types of oculomotor cues which allows us to perceive depth and size

A
  • accommodation (monocular)

- convergence (binocular)

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20
Q

explain how accommodation allows us to perceive depth and size

A

kinesthetic sensations from the ciliary muscles are sent to the visual cortex where it is used for interpreting distance/depth

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21
Q

explain how convergence allows us to perceive depth and size

A

kinesthetic sensations from the extra ocular muscles also help in depth/distance perception e.g. the medial rectus sends signals to the brain when it contracts so we know when an object is close, so that we can converge

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22
Q

name a type of binocular disparity (cues)

A

stereopsis

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23
Q

what is stereopsis known for

A

the best form of depth perception

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24
Q

explain how stereopsis occurs

A
  • eyes located at different positions on the head which allows us to see two separate images and
  • binocular vision results in two slightly different (disparate) images are projected to the retinas
  • the disparities are processed in the visual cortex to yield depth perception (stereopsis)
  • the perception of depth and 3-dimensional structure is possible with information visible from one eye alone however not as vivid as stereopsis
  • binocular disparities are naturally present when viewing a real 3-dimensional scene with two eyes
  • when viewing a 2D scene, disparities need to be simulated artificially by presenting two different images separately to each eye
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25
Q

what does binocular vision result in

A

two slightly different (disparate) images are projected to the retinas

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26
Q

where are the disparities processed

A

in the visual cortex to yield depth perception (stereopsis)

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27
Q

how else is the perception of depth and 3-dimensional structure possible

A

with information visible from one eye alone however not as vivid as stereopsis

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28
Q

when are binocular disparities naturally present

A

when viewing a real 3 dimensional scene with two eyes

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29
Q

when viewing a 2D scene, how do disparities need to simulated

A

artificially by presenting two different images separately to each eye

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30
Q

list the advantages of binocular single vision

A
  • stereopsis
  • binocular summation
  • better space perception
  • eye hand co-ordination
  • better reading
  • seeing objects in camouflage
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31
Q

what job will be difficult to carry out without stereopsis

A

delta flight

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32
Q

what can cause bad stereopsis

A

monovision contact lenses

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33
Q

what is stereo acuity

A

the smallest depth difference we can detect

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34
Q

if the disparity is greater, what also is greater

A

the greater the dept effect

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35
Q

what is the stereo acuity of the best observer

A

as good as 20 sec of arc

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36
Q

what is the average stereo acuity

A

10 secs of arc

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37
Q

what factors effect stereo thresholds

A
  • practice effects
  • luminance (too light or too dark gives different results)
  • exposure duration (do it too quick)
  • retinal eccentricity
  • crowding effects
  • motion in depth
  • monocular blur is more detrimental to stereo acuity than binocular blur (e.g. must correct both eyes at best especially if -6.00, better to have correction in both eyes rather than just one eye)
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38
Q

when is stereopsis absent

A

initially when we’re born

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39
Q

when does stereopsis develop

A

between 3-4 months

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40
Q

when does stereopsis reach normal levels

A

at 6 months (visual evoked potentials)

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41
Q

at which age will someone reach normal adult level stereopsis

A

9 years old (achieve 40 secs of arc on titmus

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42
Q

how is research of stereopsis carried out

A

using real stereo-tests

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43
Q

what do majority of adults achieve on the TNO test

A

60 secs of arc

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44
Q

at what age does stereopsis start to decline

A

> 70 years old

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45
Q

where is stereopsis tested

A

clinically

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46
Q

what two types of data can be collected from stereopsis tests

A
  • qualitative

- quantitative

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47
Q

what does qualitative data show from a stereo test

A

evidence of stereopsis i.e. it just shows that the px has stereopsis, not how good it is, so a yes/no answer

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48
Q

what does quantitative data show from a stereo test

A
  • a measure of stereo acuity e.g. how many mins/secs of arc
  • graded response - calibrated for a specific viewing distance
  • assumes an average p.d.
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49
Q

what measures the total dissociation

A
  • stereoscope (not used)

- synoptophore

50
Q

explain how the synoptophore works

A
  • each eye has a different viewing tube where two images are presented, one to each eye
  • major amblyoscope
  • ask px is arrows are coming towards or away, if they are doing either, then they have stereopsis
  • is a qualitative test
51
Q

what does a px see when measuring partial dissociation

A

both eyes see the same picture but each eye sees different parts of the image

52
Q

which stereo tests use polarisation during the test

A
  • titmus (wirt)
  • randot
  • mallet unit
53
Q

which stereo test uses red/green filters

A

TNO

54
Q

which stereo test is optical

A

lang

55
Q

how is the titmus (wirt) measured

A

partial dissociation using polarised 3D glasses

56
Q

what does the titmus (wirt) measure

A

relative depth

57
Q

what results of relative depth does the titmus (wirt) measure

A 
- qualitative assessment 
fly = 3000 sec of arc 
- quantitative assessment 
animals = 500-100 sec of arc 
circles = 500-40 sec of arc
58
Q

if the px cannot see 3000 sec of arc during titmus (wirt) test, then what can they see

A

can’t see anything as this is the grossest test there is

59
Q

which part of the quantitative assessment of the titmus (wirt) is a normal value for adults

A

circles = 500-40 sec of arc which just touches the normal value

60
Q

what is the viewing distance for the titmus (wirt) test

A

16” or 40cm

61
Q

what happens when rotate the card by 90 degrees with the titmus (wirt)

A

no depth/3D effect

62
Q

what happens when rotate the card by 180 degrees with the titmus (wirt)

A

inversion of depth (goes in rather than coming out)

63
Q

what is the disadvantage of the titmus (wirt) test

A

monocular cue as the 2nd picture on row A, is blurry with both and one eye, so some children get the picture right because they’ve guessed it which is not a good clue of whether they have stereopsis = false positive answer

64
Q

what is the randot test measured with

A

partial dissociation using polarised 3D glasses

65
Q

how many monocular cues does the randot test have

A

part contour stimuli = left side has monocular cues
part random dot principle = right side does not have monocular cues, but has simple geometric shapes (making it better than the titmus)

66
Q

which type of assessment is the randot test

A

quantitative

67
Q

how many seconds of arc does the randot measure

A

500-20” of arc

68
Q

what is 20” of arc better than

A

adult standard

69
Q

what viewing distance is the randot carried out at

A

16” or 40cm

70
Q

what are the disadvantages of randot test

A
  • monocular cues

- some false positive responses

71
Q

what is the mallett unit measured with

A

polaroid dissociation

72
Q

how is the mallett unit test carried out

A
  • two rows of symbols
  • fuse the two rows to give a 3D image
  • if struggle to fuse together, use 3 base out prism
  • when fuse together, the objects should look like they’re in 3D
73
Q

how do the symbols vary in disparity in the mallett unit test

A

10’ (600”) at the top, to 30” or arc at the bottom row

74
Q

what is the viewing distance of the mallett unit test

A

36cm
calibration given
will change with viewing distance

75
Q

what is the TNO test measured with

A

partial dissociation

red/green glasses (red before the LE)

76
Q

what principle does the TNO use

A

random dot principle

77
Q

does the TNO have monocular cues

A

no monocular cues so is the safest test and can do on all patients

78
Q

how many screening plates does the TNO test have

A

three 1980 sec of arc

79
Q

how many quantitative plates does the TNO have

A

three

80
Q

how may presentations are there of each of the three plates of the TNO test

A

4 presentations of each plate

81
Q

how many presentations are there at each level of the TNO test

A

2 presentations at each level

82
Q

what sec of arc do the 2 presentations at each level range between with the TNO

A

480-15 sec of arc

83
Q

what is the significance of 15 seconds of arc which can be measured in the TNO

A

it is the lowest seconds of arc that can be measured

84
Q

what is the viewing distance of the TNO test

A

40cm

85
Q

what are the disadvantages of the TNO test

A

often the method of choice is subject to

  • age
  • understanding
  • wearing glasses
86
Q

how is the lang test measured with

A

panography dissociation

  • high powered cylinders
  • separate image in strips
87
Q

what principle does the lang use

A

random dot

88
Q

are glasses required for lang

A

no

89
Q

what pictures are present with lang 1

A

cat, car, star

90
Q

what distance is lang 1 carried out at

A

40cm

91
Q

what is the range of seconds of arc which the lang 1 measures for

A

1200” - 550” of arc

92
Q

what pictures are present with lang 2

A

elephant, car, star, moon

93
Q

what distance is the lang 2 carried out at

A

40cm

94
Q

what is the range of seconds of arc which the lang 2 measures for

A

600-200” of arc (so better for qualitative yes/no stereopsis test

95
Q

what are the advantages of the lang test

A
  • the value of having a control - star is a control, if can see star only, theres no stereopsis as can see the control with one eye
  • good screening test as a quantitive measure
96
Q

name a no dissociation test

A

free space tests

97
Q

what do free space tests measure

A

perception of real depth

98
Q

what simulation does the free space test NOT have

A

no 2D simulation

99
Q

give examples of free space tests

A

langs 2 pen

frisby

100
Q

explain how to do the langs 2 pen test

A
  • patient and examiner each hold a pen vertically
  • patient brings points of pens into contact
  • cover one of patients eyes
  • repeat test
101
Q

if accuracy of the langs 2 test is poorer when using only one eye, what does that indicate

A

presence of stereopsis under binocularly conditions

102
Q

what does an equal monocular and binocular response indicate from the langs 2 test

A

absence of stereopsis

103
Q

what type of assessment is the langs 2 pen test

A

qualitative test

104
Q

what grade of bsv does the langs 2 pens test

A

low grade bsv

gross (coarse) stereopsis

105
Q

explain how to do the frisby test

A
  • random array of shapes
  • 4 squares of shapes per sheet
  • one square contains a central circle which stands out in 3D
  • observe behaviour or ask px to point to where the circle is
  • turn around the sheet and ask again
106
Q

does the frisby require glasses

A

no

107
Q

as low as what age can there be responses of the frisby test

A

infants as young a 6 months

108
Q

how many thicknesses of sheets are there in the frisby test

A

3

  • 6mm
  • 3mm
  • 1mm
109
Q

what is the range of disparity of the frisby test in seconds of arc

A

875” - 20”

110
Q

what does the disparities depend on

A
  • sheet thickness

- viewing distance

111
Q

what is the viewing distance of the frisby test

A

30cm - 80cm

112
Q

what test would you use on a < 2 year old

A
  • lang
  • frisby
  • titmus or TNO
113
Q

what test would you use on a 5 year old

A

titmus or TNO

114
Q

what test would you use on a small angle strabismus with only very slightly reduced stereo acuity

A

TNO

to see how far they can go

115
Q

what test would you use on a patient about to decompensate

A

frisby

as when you have glasses you decompensate, and frisby requires n specs

116
Q

what test would you use when you require the most accurate test and they are 8 years old

A

TNO

117
Q

what test would you use on a child refusing to wear glasses

A

lang 2 pen test, but destine rate the stereo acuity

so frisby is better to rate stereo acuity as it goes down the furthest

118
Q

what test would you use on a home visit and you have no stereo tests

A

langs 2 pen

119
Q

what question would you ask to a 2 year old when carrying out a frisby test

A

in reference to the circle ‘can you see where the ball is’

120
Q

what question would you ask to an 8 year old when carrying out a TNO test

A

‘can you see the pizza slice or cake, and ask where the slice is missing by pointing to it’

Binocular vision (12 decks)

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