Lecture 9 - Colour Vision Assessment Flashcards

(41 cards)

1
Q

Why assess CV in someone

A

Job applications - high alert/policman/fireman

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2
Q

What are the different ways to assess CV in practise

A
  • Screen for normal (RG and YB) colour vision
  • Classify class/type of colour vision
    a. Normal trichromatic colour vision
    b. Congenital colour deficiency (Deutan, Protan or Tritan)
    c. Acquired RG and / or YB colour deficiency
    d. Acquired loss on top of congenital deficiency
  1. Quantify severity of RG and YB loss - how bad is it
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3
Q

What does screening do

A

Detects if theres deficiencies or not

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4
Q

How many types of congential colour deficeincy are there

A

3 - deutan, protan, tritan

Depends on which one it effects

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5
Q

What causes acquired CV loss

A

Result of disease later on in life, affect from retina to virtual cortex

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6
Q

What does Holmes - Wright Lantern test do

A

Shines light and have to name R, G or B light

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7
Q

What does Nagel Anomaloscope do

A

Look down circular telescope - see field - illuminating half and half - match the 2 halves - identify

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8
Q

What does City University (2nd ed) with

daylight illumination do

A

5 dots - 1 in centre - 14 outside

Say which is closest in colour to one in middle

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9
Q

CAD test

A
CAD test measurements
carried out in a large
number of observers reveal
a large variability in RG
colour vision
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10
Q

What happens where you’re colour blind

A

See in black and white

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11
Q

How does CVD vary

A
  • Varies on a continous scale, not same as having threshold of 3 = 3x worse than average normal of threshold of 25.
  • Normals: 1,1 for RG and YB
  • Variables can happen genetically and depending on how pigment in eye or how big or narrow cones are
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12
Q

What does CAD test do

A
  • Isolation of colour signals
  • Dynamic luminance contrast noise masks effectively the detection of LC-defined motion, but has no
    effect on the detection of colour-defined motion.
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13
Q

How was CAD test developed and when

A

Marisa’s PHD

2002

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14
Q

What is important when assesing for CV

A

To isolate colour signals as this is what you want to assess. If you show CV test with luminance i.e. with colour and very bright - might not need colour vision to need stimulus but see how bright it is

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15
Q

What is important when assesing for CV

A

To isolate colour signals as this is what you want to assess. If you show CV test with luminance i.e. with colour and very bright - might not need colour vision to need stimulus but see how bright it is
- Make sure colour detectors are not using luminance signals to detect stimulus

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16
Q

How do congentials deficiencies differer from normal

A

Congenital’s CD’s have different luminance sensitivities than normal

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17
Q

What did CAD test involve

A
  • Moving target within this static background of text
  • Put luminance target to find luminance background of dyanmic noise - cant see it
  • Then use colour target - moving in static noise - no effect
  • Then move central target in dynamic noise = no effect
  • If you had target defined by luminacne moving in dyanmic noise it would mask luminance
18
Q

Results for CAD test

A
  • Static pattern - could see it -doesnt matter how much noise you put - can’t see it all the time
  • But when you have dynamic noise, you can mask luminance target using dynamic noise - for colour it doenst make any difference - doenst matter how much noise you put on - can always see the colour
19
Q

What does Ishihara test do

A

Isolate the use of colour signals

Uses isochromatic confusion lines as a base for its design

20
Q

How does ishihara test work

A

Involves numbers on background of different colours
e.g. red/orange 8 on green shades background: Some people see a 3 because this green is similar to orange - same confusion axis

21
Q

What happens in normal trichromat

22
Q

What does relative luminous efficiency show

A

Combination of signals coming from L + M cones

23
Q

Luminance signals in traffic lights

A

Traffic lights designed to be seen by everyone because they have different luminance signals from 3 different colours

24
Q

What happens in Deuteranopia - Luminance discrimination

A
  • Relative luminous efficiency virtually normal as it will follow the L cone - based on 2 L + M cones -
  • Reduced colour discrimination
  • M cone - green missing
  • Someone with green colour deficiency - luminance detection similar to someone with normal colour vision, but have reduced colour discrimination because missing M cone
25
What happens in Protanopia- Luminance discrimination
``` - Note reduced luminous efficiency for long wavelengths (reds look dim) - Reduced colour discrimination - luminance function affected - L cone missing - red lights look dim ```
26
What happens in Protanomaly- Luminance discrimination
Relative deficiency function is according to whatever pigment they have
27
Isochromatic confusion lines
``` CIE-1931 (x,y) colour diagram Typical chromatic discrimination of a normal trichromat Show isochromatic confusion loci ```
28
What is important for efficient assessment of chromatic sensitivity
- A true isolation of colour signals is obtained - Appropriate illumination ( specific lighting ) is used – Daylight D65 or equivalent, - It is based on data that describe the variance in colour discrimination amongst “normal” trichromats, - Has adequate sensitivity and specificity to detect “minimal” deficiencies and to classify them - Can be used to detect and monitor “significant changes” in colour discrimination over time.
29
How can you get an isolation of colour signals
Avoid use of luminance signals - CD's have different to someone with normal CV
30
Why is specific lighting for assessing CV important
If you use different types of white light - all look white but spectral composition is very different and will affect colours and colours available to subject doing CV test
31
D65 light
Has all complete wavelengths, but fluorescent has peaks of wavelenths, not a spread
32
Why use normal trichromats
Need to know how normals behave on CV test to assess someone with congential CV deficiency, to compare - see if someone is abnormal
33
Case Study: aviation
- Concern was expressed by the Civil Aviation Authority UK that the original colour vision standards were too stringent and that the pass/fail limits had been arbitrarily set using colour vision tests that do not quantify well the severity of colour vision loss. - In 2009, the CAA UK introduced more accurate colour assessment procedures using the CAD test and adopted pass/fail limits based on the applicant’s ability to carry out the most demanding, colour-related tasks with the same accuracy as normal trichromats. - As a result, 35% of subjects with congenital colour vision deficiency are now allowed to become pilots.
34
Why did pilots do Ishihara test
To see if its safe to look at colours on runway and land plane If they passed - straight through pilot If failed - 5/6 different CV tests applicants could do and all has different results
35
What are the minimum colour vision requirements
- Visual task analysis to identify the most demanding colour-critical tasks - Assess severity of colour vision loss using a test that quantifies accurately the loss of chromatic sensitivity - Relate subjects’ performance on functional tasks to their colour thresholds and use these findings to establish pass/fail limits which ensure equivalent performance to that measured in normal trichromats - Produce accurate simulations of the most demanding tasks in the laboratory and method for quantifying subjects performance on these functional tasks
36
What is visual task analysis
- Looked at environment pilots have to work in and identified which colour signals are crucial for them to do their job - Identification of most colour critical tasks when no redundancy is involved and the discrimination of colour differences is most difficult.
37
What visual signals that make use of colour were used in visual task analysis
- PAPI lights - Runway lights - Parking lights
38
What does PAPI lights stand for
Precision approach path indicator
39
How do PAPI lights work
- Located on left or right of runway - 2 colour system code - red and white - If on correct light path on landing you will see 2 whites and reds - If too low - see red - If too high - see more whites
40
Laboratory simulation for the PAPI test
- Four stimulus channels derived from one light source - split light into 4 channels, create PAPI stimulator, looked exactly like PAPI lights -Random luminance variation - Viewing distance 4m - Visual angle ~1.4 min arc Corresponds to approach distance ~5.54km - landing plane - Did it 60 times - how many times correct - compared %scores against CAD threshold
41
Results – functional test vs CAD
- Normals - most got 100% | - Some made mistakes - bored - lose concentration