Lecture 9 - Colour Vision Assessment Flashcards
(41 cards)
Why assess CV in someone
Job applications - high alert/policman/fireman
What are the different ways to assess CV in practise
- 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
- Quantify severity of RG and YB loss - how bad is it
What does screening do
Detects if theres deficiencies or not
How many types of congential colour deficeincy are there
3 - deutan, protan, tritan
Depends on which one it effects
What causes acquired CV loss
Result of disease later on in life, affect from retina to virtual cortex
What does Holmes - Wright Lantern test do
Shines light and have to name R, G or B light
What does Nagel Anomaloscope do
Look down circular telescope - see field - illuminating half and half - match the 2 halves - identify
What does City University (2nd ed) with
daylight illumination do
5 dots - 1 in centre - 14 outside
Say which is closest in colour to one in middle
CAD test
CAD test measurements carried out in a large number of observers reveal a large variability in RG colour vision
What happens where you’re colour blind
See in black and white
How does CVD vary
- 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
What does CAD test do
- 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.
How was CAD test developed and when
Marisa’s PHD
2002
What is important when assesing for CV
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
What is important when assesing for CV
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
How do congentials deficiencies differer from normal
Congenital’s CD’s have different luminance sensitivities than normal
What did CAD test involve
- 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
Results for CAD test
- 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
What does Ishihara test do
Isolate the use of colour signals
Uses isochromatic confusion lines as a base for its design
How does ishihara test work
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
What happens in normal trichromat
Have 3 cones
What does relative luminous efficiency show
Combination of signals coming from L + M cones
Luminance signals in traffic lights
Traffic lights designed to be seen by everyone because they have different luminance signals from 3 different colours
What happens in Deuteranopia - Luminance discrimination
- 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