Lecture 9 - Colour Vision Assessment

Question 1

Why assess CV in someone

Answer 1

Job applications - high alert/policman/fireman

Question 2

What are the different ways to assess CV in practise

Answer 2

• 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

3. Quantify severity of RG and YB loss - how bad is it

Question 3

What does screening do

Answer 3

Detects if theres deficiencies or not

Question 4

How many types of congential colour deficeincy are there

Answer 4

3 - deutan, protan, tritan

Depends on which one it effects

Question 5

What causes acquired CV loss

Answer 5

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

Question 6

What does Holmes - Wright Lantern test do

Answer 6

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

Question 7

What does Nagel Anomaloscope do

Answer 7

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

Question 8

What does City University (2nd ed) with

daylight illumination do

Answer 8

5 dots - 1 in centre - 14 outside

Say which is closest in colour to one in middle

Question 9

CAD test

Answer 9

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

Question 10

What happens where you’re colour blind

Answer 10

See in black and white

Question 11

How does CVD vary

Answer 11

• 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

Question 12

What does CAD test do

Answer 12

• 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.

Question 13

How was CAD test developed and when

Answer 13

Marisa’s PHD

2002

Question 14

What is important when assesing for CV

Answer 14

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

Question 15

What is important when assesing for CV

Answer 15

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

Question 16

How do congentials deficiencies differer from normal

Answer 16

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

Question 17

What did CAD test involve

Answer 17

• 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

Question 18

Results for CAD test

Answer 18

• 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

Question 19

What does Ishihara test do

Answer 19

Isolate the use of colour signals

Uses isochromatic confusion lines as a base for its design

Question 20

How does ishihara test work

Answer 20

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

Question 21

What happens in normal trichromat

Answer 21

Have 3 cones

Question 22

What does relative luminous efficiency show

Answer 22

Combination of signals coming from L + M cones

Question 23

Luminance signals in traffic lights

Answer 23

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

Question 24

What happens in Deuteranopia - Luminance discrimination

Answer 24

• 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

Question 25

What happens in Protanopia- Luminance discrimination

Answer 25

- Note reduced luminous
efficiency for long
wavelengths (reds
look dim)
- Reduced colour discrimination - luminance function affected 
- L cone missing - red lights look dim

Question 26

What happens in Protanomaly- Luminance discrimination

Answer 26

Relative deficiency function is according to whatever pigment they have

Question 27

Isochromatic confusion lines

Answer 27

CIE-1931 (x,y) colour diagram
Typical chromatic discrimination of a normal 
trichromat
Show isochromatic
confusion loci

Question 28

What is important for efficient assessment of chromatic sensitivity

Answer 28

• 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.

Question 29

How can you get an isolation of colour signals

Answer 29

Avoid use of luminance signals - CD’s have different to someone with normal CV

Question 30

Why is specific lighting for assessing CV important

Answer 30

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

Question 31

D65 light

Answer 31

Has all complete wavelengths, but fluorescent has peaks of wavelenths, not a spread

Question 32

Why use normal trichromats

Answer 32

Need to know how normals behave on CV test to assess someone with congential CV deficiency, to compare - see if someone is abnormal

Question 33

Case Study: aviation

Answer 33

• 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.

Question 34

Why did pilots do Ishihara test

Answer 34

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

Question 35

What are the minimum colour vision requirements

Answer 35

• 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

Question 36

What is visual task analysis

Answer 36

• 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.

Question 37

What visual signals that make use of colour were used in visual task analysis

Answer 37

• PAPI lights
• Runway lights
• Parking lights

Question 38

What does PAPI lights stand for

Answer 38

Precision approach path indicator

Question 39

How do PAPI lights work

Answer 39

• 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

Question 40

Laboratory simulation for the PAPI test

Answer 40

• 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

Question 41

Results – functional test vs CAD

Answer 41

• Normals - most got 100%

- Some made mistakes - bored - lose concentration