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binocular vision > lecture 5 > Flashcards

lecture 5 Flashcards

1
Q

define depth perception

A

being able to judge where things are in 3D

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2
Q

how many forms of cues are there for depth perception

A

2:

- monocular and binocular

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3
Q

binocular cues give you…

A

stereopsis

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4
Q

list the monocular pictorial cues

A 
relative size
occlusion (interposition)
relative height 
shadows
atmospheric perspective
linear perspective
familiar size
texture gradient
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5
Q

list monocular movement produced cues

A

motion parallax

kinetic depth effect

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6
Q

explain motion parallax

A

near objects pass retinal image plane faster than distance objects

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7
Q

explain kinetic depth effects

A

when a 3D form of an object can be perceived when the object is moving

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8
Q

how do we perceive depth and size?

A

oculomotor cues

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9
Q

what is the monocular oculomotor cue?

A

accommodation

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10
Q

what is the binocular oculomotor cue?

A

convergence

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11
Q

explain how stereopsis is created

A
  • Eyes located at different positions on the head —
  • 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
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12
Q

are binocular disparities always present?

A

when looking at 3D objects - yes

when looking at 2D objects- need to be simulated by presenting 2 different images to each eye

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13
Q

advantages of BSV

A
  • stereopsis
  • binocular summation
  • better space perception
  • hand eye coordination
  • better reading
  • seeing objects in camouflage
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14
Q

what jobs would be difficult without stereopsis

A
  • cannot be pilot by law
  • dentistry
  • sports
  • seamstress
  • jeweller
    etc
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15
Q

define stereo acuity

A

smallest depth difference we can detect

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16
Q

what effect does retinal disparity have on depth effect?

A

Greater the disparity the greater the depth effect

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17
Q

what is the best stereopsis possible

A

2 secs of arc

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18
Q

what is the average stereopsis

A

10 secs of arc

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19
Q

what factors affect stereo thresholds (7)

A
  • practice effects
  • luminance
  • exposure duration
  • retinal eccentricity
  • crowding effects
  • motion in depth
  • monocular blur
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20
Q

what is more detrimental to stereoacuity? mono blur or binocular blur?

A

monocular blur

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21
Q

why is it important to ensure anisemotropia is fully corrected?

A

monocular blur is more detrimental to stereoacuity than binocular blur

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22
Q

when does stereopsis develop?

A

between 3-4 months

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23
Q

when does stereopsis reach normal levels?

A

6 months

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24
Q

at 9 years old, how many seconds of arc of stereopsis on Titmus?

A

40

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25
Q

what is a qualitative method of measuring stereopsis? (total dissociation)

A

using the stereoscope or synoptophore

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26
Q

how does the synoptophore work?

A

each eye has a different viewing tube
two images presented one to each eye
ask px if the arrows are pointing more towards the clinician or the Px
if px says the arrows are pointing more towards themselves- no stereopsis
towards clinicians - stereopsis?

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27
Q

what are the methods of measuring stereopsis? (partial dissociation)

A

polarisation

  • Titmus (wire)
  • randot
  • mallet unit

Red/green
- TNO

Optical
-Lang

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28
Q

titmus test uses polarised glasses, why?

A

to reduce monocular cues

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29
Q

is the titmus test qualitative or quantitative?

A

can be both (fly is qualitative, animals and circles are quantitative)

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30
Q

what distance is the titmus test carried out at

A

40 cm or 16”

31
Q

how many secs of arc is the fly in titmus?

A

3000

32
Q

how many secs of arcs are the animals in titmus?

A

100-500

33
Q

how many secs of arc are the circles in titmus?

A

40-500

34
Q

if you rotate the titmus by 90, will your px have depth perception?

A

no- the wings should be flat - use this as a test to see if they are lying

35
Q

does the randot test have monocular cues?

A

some due to part contour stimuli

36
Q

does the part random dot principle part of the randot test provide monocular cues?

A

no

37
Q

is randot test qualitative or quantitative?

A

quantitative

38
Q

how many secs of arc does the randot test measure ?

A

500- 20

39
Q

what viewing distance do you carry out the randot test at?

A

16” or 40 cm

40
Q

explain the mallet unit test?

A

you have 2 rows of symbols,
try to fuse the two rows using 3 base out prism
when fused the shapes will stick out

41
Q

how many secs of arc does the mallet unit test up to ?

A

10- 30

42
Q

viewing distance of mallet unit ?

A

36 cm

43
Q

why is it important to do the Mallett unit at 36 cm?

A

calibration will change with viewing distance

44
Q

how do you dissociate the 2 eyes in the TNO test

A

use red/green glasses

45
Q

how many screening plates in the TNO test

A

3

46
Q

how many secs of arc do the screening plates in TNO test up to?

A

1980

47
Q

how many quantitative plates are there in TNO test?

A

3
4 presentations on each plate
– 2 presentations at each level

48
Q

how many secs of arc do the quantitative plates test up to?

A

480-15

49
Q

viewing distance of TNO test

A

40 cm

50
Q

who is the TNO test good for?

A

children
people with special needs
wearing glasses

51
Q

advantage of the TNO test

A

it tests up to 15 secs of arc with no monocular cues so good to use to test how good their stereopsis is

52
Q

who is lang test good for?

A

toddlers and children

53
Q

is lang a screening test?

A

yes

54
Q

which shape is a control shop ein lang test?

A

star

55
Q

how do you present lang plates

A

ask them what they can see

56
Q

viewing distance for lang 1 and 2

A

40 cm

57
Q

how many secs of arc does lang 1 test up to?

A

1200-550

58
Q

how many secs of arc does lang 2 test up to?

A

600-200

59
Q

which test have no dissociation

A

free space tests
langs 2 pen
frisby

60
Q

what do free space test entail?

A

perception of real depth

no 2D simulation

61
Q

what does the lang 2 pen test entail?

A

Patient and examiner each hold a pen vertically —
Patient brings points of pens into contact —
Cover one of patients eyes
◦ Repeat test —

If accuracy poorer when using only one eye
indicates presence of stereopsis under binocular conditions —

Equal monocular and binocular response indicates absence of stereopsis

62
Q

why is langs 2 pen test a useful clinical tool

A

test low grade BSV or gross/coarse stereopsis

63
Q

is langs 2 pen quantitative or qualitative?

A

qualitative

64
Q

what does the frisby test entail?

A 
Random array of shapes — 
4 squares of shapes per sheet — 
One square contains a central circle — 
Observe behaviour or ask question
about circles — 
Turn around sheet ask again — 
Responses seen in infants as young as 6 months —
65
Q

what thicknesses of sheets does the frisby test come in?

A

6mm, 3mm and 1 mm

66
Q

which fribky sheet tests better level of stereoacuity

A

1mm

67
Q

what is the disparity of a frisby sheet?

A

875-20”

68
Q

how can you change the level of stereoacuity measurable by the frisby sheets?

A
  • increase viewing distance from 30-80 cm

- change the sheet thickness

69
Q

which test would you use for an under 2 year old?

A

land 1/2 or frisby

70
Q

which test would you use for someone who is about to decompensate?

A

frisby or lang 1/2

71
Q

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

A

TNO

72
Q

which test would you use for a child refusing to wear glasses?

A

lang 1/2 or frisby

73
Q

which test would you use for a home visit and you have no stereo-tests

A

lang 2 pen

binocular vision (10 decks)

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