This document discusses colour vision and colour blindness. It begins by explaining that colour vision is mediated by three types of cone cells in the eye that are sensitive to different wavelengths of light corresponding to red, green and blue. It describes theories of colour vision including trichromatic theory. It outlines the pathway of colour vision from the retina to the visual cortex. It discusses concepts such as hue, brightness and saturation. Finally, it describes different types of colour blindness including dichromacy and anomalous trichromacy.

1. Anuraag Singh

2.  Colour vision is the ability of the eye to
discriminate between colours excited by lights
of different wavelengths.
 Colour Vision - Function of cones
 Colour - Perceptual phenomenon
- Spectral composition of light from
the object and visual surroundings
also matter.

3. Sensation of colour is a subjective phenomenon i.e Taught
since childhood
All colours are a result of admixture of Primary colours in
different proportions-
Red ( 723-647)
Green ( 575-492)
Blue ( 492-450)
For any colour there is a complementary colour
- when both mixed properly produce a sensation of white

4. 1.Trichromatic Theory
• It postulates the existence of three kinds of cones
- Each containing different photopigment
- Each sensitive maximally to one of three primary
colours ( Red, Green , Blue )
-Any given colour’s sensation is due to relative
frequency of impulse from each of three cone
system
•

6. 1. Red sensitive cone pigment/erythrolabe/LWS
- Absorbs light maximally in yellow position (peak at 564 nm)
- Its spectrum extends to long wavelength to sense
Red
2. Green Sensitive Cone pigment/chlorolabe/MWS
- Absorbs light maximally in green portion ( peak at
534 nm )
3. Blue sensitive cone pigment/cyanolabe/SWS
-Absorbs maximally in Blue-violet portion with a peak at
420nm

8. • Postulated by Ewald Hering
• Some colours are mutually exclusive
• The cone photoreceptors are linked together to form
three opposing colour pairs: blue/yellow, red/green,
and black/white
• Activation of one member of the pair
inhibits activity in the other
• No two members of a pair can be seen at the same
location to be stimulated
• Never "bluish yellow" or "reddish green“colour
experienced

9. • Cone pigment = 11 cis-retinal + opsin part
• 11 cis-retinal part is similar to rhodopsin
• Priciples of photochemistry of rhodopsin can
be applied to cone pigments
• Difference being that three cone pigments
are bleached by light of different wavelength.

10. Opsins of green and red sensitive cone
pigments show 96% homology ( amino
acid sequence )
Both show 43% homology with blue
pigment
All three i.e Red,Green,Blue show 41%
homology with rod pigment rhodopsin.

11. Photochemical changes
Biochemical changes
Visual signal
( Cone Receptor potential )
Action potential generated is transmitted as
electronic conduction to other cells of retina.

12. A slow graded potential is recorded in these cells
Increase in amplitude of response with increasing
luminosity is also recorded
These cells show two different response
1. Luminosity response:- Hyperpolarizing response with
a broad spectral function
2. Chromatic response:-Hyperpolarizing for a part of a
spectrum and Depolarizing for the remaining part of
spectrum
This represents first stage in visual system where
chromatic interaction’s evidence is noted.

13. Shows Centre-Surround spatial pattern
Red light striking in centre caused hyperpolarisation and
green light in surroundings caused depolarisation.
Amacrine cells
Automatic colour control

14.  There are three distinct groups of ganglion cells:-
1.W
2.X
3.Y
 Colour sensation is mediated by ‘X’ type
 A single ganglion cell may be stimulated by a number
of cones
 When all three types of cones stimulate same
ganglion the resultant signal is White.

15. Two type of colour opponent system is found in
ganglion cells:
1. Opponent colour cell system
Some ganglion cells are excited by one colour type
cone and inhibited by other
Two types of colour opponent ganglion cells:-
1.Red – green opponent colour cells use signals from
red and green cones to detect red/green contrast.
2.Blue – yellow opponent colour cells obtain yellow
signal from summated output of red and green cones
which is contrasted with output from blue cones.

17.  This system is concerned in successive colour system
(Phenomenon of coloured after images )
Example:-when one sees at green spot for several
seconds , then looks at grey card , one
sees a red spot on the card

18. 2. Double opponent colour cell system
These ganglion cells have opponent for both colour
and space.
Example:- Response may be ‘on’ to red in centre and
‘off’ to it in surround, while ‘off’ to green in centre
and ‘on’ to it in surround.

19.  This system is concerned with ‘Simultaneous colour
contrast’ – Phenomenon of perception of a particular
coloured spot against coloured background ( grey
spot appear greenish in red surround and reddish in
green surround ).

20. Trichromatic vision extends 20 to 30 degrees from point of
fixation.
Peripheral to this red and green become indistinguishable.
In far periphery all colour sense is lost.
Very centre of fovea (1/8 degree) is blue blind.

21. All LGB neurons carry information from more than one cone
cell.
Colour information is transmitted from ganglion cells to
parvocellular portion of LGB.
Two type of LGB neurons:-
1. Nonopponent cells ( 30% of total LGB neurons )
Give same response to any monochromatic light
2. Opponent cells ( 60% of total LGB neurons )
Excited by some wavelengths and inhibited by others

22. 1. +R/-G :- Red and green antagonism
2. +G/-R :- Red and green antagonism
3. +B/-Y :- Blue and yellow antagonism
4. +Y/-B :- Blue and yellow anatgonism

23. Colour Signal from parvocellular portion
Layer 4c of striate cortex ( area 17 )
Blobs in layers 2 and 3
( blobs have centre surround cells)
Visual association area
Lingual and fusiform gyri of
occipital lobe

24. Color coded cells are arranged in a hierarchy.
Opponent color cells are found among ganglion cells of retina
and LGB.
Double opponent cells are found in layer 4 of striate
cortex(area 17)

25.  Hue
Identification of colour,dominant spectral colour is determined
by the wavelength of particular colour
 Brightness
Intensity of colour,it depends on the luminosity
of the component wavelength.
In photoptic vision-peak luminosity function at approximately
555 nm and in scotopic vision at about 507 nm.
The Wavelength shift of maximum luminosity from photopic to
scotopic viewing is called Purkinje Shift Phenomenon’

27.  Saturation
It refers to degree of freedom to dilution with white.
It can be estimated by measuring how much of a
particular wavelength must be added to white before
it is distinguishable from white.

28. It describes what mixtures of wavelength can be substituted
for each other without changing the colour.

29. A colour triangle can be drawn to describe
trichromacy of colour mixture.
Three axis are scaled to represent various amounts of
pigment absorption by each of the three cone
pigments.
A particular colour is represented by a line or a
vector.
Length of line identifies brightness.
Angle or direction of line represents hue.
All colours seen by human eye fall inside the colour
triangle.

30. 1. CIE (Commission Internal de Eclairage)
CIE colour space system is based on amounts of three
primary colours necessary to match a specified colour.
CIE chromaticity diagram is constructed by placing the
three reference wavelengths say 450 at X , 520 at Y and
650 at Z of the triangle.

31. *2.The Munsell colour system
 All the colours are represented in a cylinderin terms
of hue and chroma.
 Hue dimension i.e dominant spectral colour is
located on circumference of the cylinder.
 Value dimension i.e lightness is indicated by moving
up or down the cylinder

32. THANK YOU

47. *Standard source A is a defined tungsten lamp
run at a defined current and voltage.
*Standard source C is a substitue for daylight
and consist of a tungsten lamp with a defined
blue filter in front.
*Point E represents a source radiating equal
amount of energy in equal intervals of
wavelength throughout the spectrum.

56. *Colour blindness is also called “Daltonism”
*Defective perception of colour -anomalous
* Absence of colour perception is anopia
*It may be-
*Congenital
*Acquired

57. 1.Monochromacy /Total colour blindness
 When two or all 3 cone pigments are missing.
Types:-
 1.Rod monochromacy
 2.Cone monochromacy
2.Dichromacy - When one of the 3 colour pigment is
absent
 Protanopia - RED retinal photoreceptors absent
 Deuteranopia -GREEN retinal photoreceptors absent.
 Tritanopia -BLUE retinal photoreceptors absent

58. 3.TRICHROMACY [Anomalous Trichromacy]
Colour vision deficiency rather than loss
Protanomaly - RED colour deficiency [Hereditary,
Sex linked, Male1%, ]
Deuteranomaly - GREEN colour
deficiency[Hereditary, Sex linked, Male 5% ]
 Tritanomaly - BLUE colour deficienc [ Rare,Not
hereditary ]

59. *
Gene rhodopsin - chromosome 3.
Gene for blue sensitive cone - chromosome 7
The genes for red and green sensitive cones
are arranged in tandem array on the ‘q’ arm of
x chromosome so defect is inherited as x-
linked recessive
Tritanopia is inherited as an autosomal
dominant defect

60. Congenital colour blindness is two type
Achromatopsia
Dyschromatopsia
More common in male (3-4%)than female(0.4%)
It is x-linked recessive inherited condition.

61. Cone monochromatism:
Presence of only one primary colour
So person is truely colour blind
Rod monochromatism:
Complete or incomplete
Inherited as autosomal recessive trait
Total colour blindness
Day blindness(visual acquity is about 6/60)