Stereopsis

Question 1

what is the best form of depth perception

Answer 1

stereopsis

Question 2

what is depth perception

Answer 2

how far or how near something is away from you

& allows you to see the world in 3D

Question 3

what are the two forms of depth perception

Answer 3

• monocular (one eye) cues

- binocular (two eyes) cues

Question 4

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

Answer 4

• person with one eye

- person with a large strabismus

Question 5

list and the things which represent monocular pictorial cues

Answer 5

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

Question 6

explain relative size in relation to monocular pictorial cues

Answer 6

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

Question 7

explain occlusion (interposition) in relation to monocular pictorial cues

Answer 7

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

Question 8

explain relative height in relation to monocular pictorial cues

Answer 8

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

Question 9

explain shadows in relation to monocular pictorial cues

Answer 9

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

Question 10

explain atmospheric perspective in relation to monocular pictorial cues

Answer 10

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

Question 11

explain linear perspective in relation to monocular pictorial cues

Answer 11

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

Question 12

explain familiar size in relation to monocular pictorial cues

Answer 12

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

Question 13

explain texture gradient in relation to monocular pictorial cues

Answer 13

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

Question 14

what is terror subterra (shepard)

Answer 14

• 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

Question 15

name the two types of monocular movement produced cues

Answer 15

1. monocular parallax

2. kinetic depth effect

Question 16

what is monocular parallax

Answer 16

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

Question 17

what is kinetic depth

Answer 17

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)

Question 18

how do we perceive depth and size

Answer 18

oculomotor cues

Question 19

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

Answer 19

• accommodation (monocular)

- convergence (binocular)

Question 20

explain how accommodation allows us to perceive depth and size

Answer 20

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

Question 21

explain how convergence allows us to perceive depth and size

Answer 21

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

Question 22

name a type of binocular disparity (cues)

Answer 22

stereopsis

Question 23

what is stereopsis known for

Answer 23

the best form of depth perception

Question 24

explain how stereopsis occurs

Answer 24

• 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

Question 25

what does binocular vision result in

Answer 25

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

Question 26

where are the disparities processed

Answer 26

in the visual cortex to yield depth perception (stereopsis)

Question 27

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

Answer 27

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

Question 28

when are binocular disparities naturally present

Answer 28

when viewing a real 3 dimensional scene with two eyes

Question 29

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

Answer 29

artificially by presenting two different images separately to each eye

Question 30

list the advantages of binocular single vision

Answer 30

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

Question 31

what job will be difficult to carry out without stereopsis

Answer 31

delta flight

Question 32

what can cause bad stereopsis

Answer 32

monovision contact lenses

Question 33

what is stereo acuity

Answer 33

the smallest depth difference we can detect

Question 34

if the disparity is greater, what also is greater

Answer 34

the greater the dept effect

Question 35

what is the stereo acuity of the best observer

Answer 35

as good as 20 sec of arc

Question 36

what is the average stereo acuity

Answer 36

10 secs of arc

Question 37

what factors effect stereo thresholds

Answer 37

- 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)

Question 38

when is stereopsis absent

Answer 38

initially when we're born

Question 39

when does stereopsis develop

Answer 39

between 3-4 months

Question 40

when does stereopsis reach normal levels

Answer 40

at 6 months (visual evoked potentials)

Question 41

at which age will someone reach normal adult level stereopsis

Answer 41

9 years old (achieve 40 secs of arc on titmus

Question 42

how is research of stereopsis carried out

Answer 42

using real stereo-tests

Question 43

what do majority of adults achieve on the TNO test

Answer 43

60 secs of arc

Question 44

at what age does stereopsis start to decline

Answer 44

>70 years old

Question 45

where is stereopsis tested

Answer 45

clinically

Question 46

what two types of data can be collected from stereopsis tests

Answer 46

- qualitative | - quantitative

Question 47

what does qualitative data show from a stereo test

Answer 47

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

Question 48

what does quantitative data show from a stereo test

Answer 48

- 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.

Question 49

what measures the total dissociation

Answer 49

- stereoscope (not used) | - synoptophore

Question 50

explain how the synoptophore works

Answer 50

- 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

Question 51

what does a px see when measuring partial dissociation

Answer 51

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

Question 52

which stereo tests use polarisation during the test

Answer 52

- titmus (wirt) - randot - mallet unit

Question 53

which stereo test uses red/green filters

Answer 53

TNO

Question 54

which stereo test is optical

Answer 54

lang

Question 55

how is the titmus (wirt) measured

Answer 55

partial dissociation using polarised 3D glasses

Question 56

what does the titmus (wirt) measure

Answer 56

relative depth

Question 57

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

Answer 57

``` - qualitative assessment fly = 3000 sec of arc - quantitative assessment animals = 500-100 sec of arc circles = 500-40 sec of arc ```

Question 58

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

Answer 58

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

Question 59

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

Answer 59

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

Question 60

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

Answer 60

16" or 40cm

Question 61

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

Answer 61

no depth/3D effect

Question 62

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

Answer 62

inversion of depth (goes in rather than coming out)

Question 63

what is the disadvantage of the titmus (wirt) test

Answer 63

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

Question 64

what is the randot test measured with

Answer 64

partial dissociation using polarised 3D glasses

Question 65

how many monocular cues does the randot test have

Answer 65

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)

Question 66

which type of assessment is the randot test

Answer 66

quantitative

Question 67

how many seconds of arc does the randot measure

Answer 67

500-20" of arc

Question 68

what is 20" of arc better than

Answer 68

adult standard

Question 69

what viewing distance is the randot carried out at

Answer 69

16" or 40cm

Question 70

what are the disadvantages of randot test

Answer 70

- monocular cues | - some false positive responses

Question 71

what is the mallett unit measured with

Answer 71

polaroid dissociation

Question 72

how is the mallett unit test carried out

Answer 72

- 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

Question 73

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

Answer 73

10' (600") at the top, to 30" or arc at the bottom row

Question 74

what is the viewing distance of the mallett unit test

Answer 74

36cm calibration given will change with viewing distance

Question 75

what is the TNO test measured with

Answer 75

partial dissociation | red/green glasses (red before the LE)

Question 76

what principle does the TNO use

Answer 76

random dot principle

Question 77

does the TNO have monocular cues

Answer 77

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

Question 78

how many screening plates does the TNO test have

Answer 78

three 1980 sec of arc

Question 79

how many quantitative plates does the TNO have

Answer 79

three

Question 80

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

Answer 80

4 presentations of each plate

Question 81

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

Answer 81

2 presentations at each level

Question 82

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

Answer 82

480-15 sec of arc

Question 83

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

Answer 83

it is the lowest seconds of arc that can be measured

Question 84

what is the viewing distance of the TNO test

Answer 84

40cm

Question 85

what are the disadvantages of the TNO test

Answer 85

often the method of choice is subject to - age - understanding - wearing glasses

Question 86

how is the lang test measured with

Answer 86

panography dissociation - high powered cylinders - separate image in strips

Question 87

what principle does the lang use

Answer 87

random dot

Question 88

are glasses required for lang

Answer 88

no

Question 89

what pictures are present with lang 1

Answer 89

cat, car, star

Question 90

what distance is lang 1 carried out at

Answer 90

40cm

Question 91

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

Answer 91

1200" - 550" of arc

Question 92

what pictures are present with lang 2

Answer 92

elephant, car, star, moon

Question 93

what distance is the lang 2 carried out at

Answer 93

40cm

Question 94

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

Answer 94

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

Question 95

what are the advantages of the lang test

Answer 95

- 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

Question 96

name a no dissociation test

Answer 96

free space tests

Question 97

what do free space tests measure

Answer 97

perception of real depth

Question 98

what simulation does the free space test NOT have

Answer 98

no 2D simulation

Question 99

give examples of free space tests

Answer 99

langs 2 pen | frisby

Question 100

explain how to do the langs 2 pen test

Answer 100

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

Question 101

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

Answer 101

presence of stereopsis under binocularly conditions

Question 102

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

Answer 102

absence of stereopsis

Question 103

what type of assessment is the langs 2 pen test

Answer 103

qualitative test

Question 104

what grade of bsv does the langs 2 pens test

Answer 104

low grade bsv | gross (coarse) stereopsis

Question 105

explain how to do the frisby test

Answer 105

- 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

Question 106

does the frisby require glasses

Answer 106

no

Question 107

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

Answer 107

infants as young a 6 months

Question 108

how many thicknesses of sheets are there in the frisby test

Answer 108

3 - 6mm - 3mm - 1mm

Question 109

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

Answer 109

875" - 20"

Question 110

what does the disparities depend on

Answer 110

- sheet thickness | - viewing distance

Question 111

what is the viewing distance of the frisby test

Answer 111

30cm - 80cm

Question 112

what test would you use on a < 2 year old

Answer 112

- lang - frisby - titmus or TNO

Question 113

what test would you use on a 5 year old

Answer 113

titmus or TNO

Question 114

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

Answer 114

TNO | to see how far they can go

Question 115

what test would you use on a patient about to decompensate

Answer 115

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

Question 116

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

Answer 116

TNO

Question 117

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

Answer 117

lang 2 pen test, but destine rate the stereo acuity | so frisby is better to rate stereo acuity as it goes down the furthest

Question 118

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

Answer 118

langs 2 pen

Question 119

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

Answer 119

in reference to the circle 'can you see where the ball is'

Question 120

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

Answer 120

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