3. INTRODUCTION
Colour sense is the ability of the eye to
discriminate between colours excited by light of
different wave lengths.
4. Features Of Colour Vision
Colour vision is a function of
cones. (seen better in photopic
vision)
Our eyes perceive colour with
wavelength of light ranging from
400 to 700nm.
Below 400nm is below violet
wavelength called ultra violet
rays.
Above 720nm is infrared and
beyond visibility.
5. Basic of Colours
Colours are formed from the mixture of basic colours of
Red, Blue and Green.
The colours are appreciated due to different wavelength
of lights.
6. Physics of colours
When beam of light is
passed through a
prism it diffracts rays
into different colours.
The different colours
are due to different
wavelength of light
rays.
7. Types of Vision
Two types of vision they are
1.Achromatic:
Sensation of white
vision with no colour vision
2. Chromatic:
I ) Spectral colour vision
ii) Extra spectral colour
vision
- i.e., Mixing of two spectrum
8. Types of Colours
There are two types of colours.
They are
1. Primary colour :
Blue,
Green, Red and mixing of three
colours
2. Complementary colours:
When
two colours are mixed in
appropriate amount it cancel the
colours and produces white
sensation
9. Physiology of Vision
Perception of colour vision has the combined role of
retina, lateral geniculate nucleus and visual cortex.
Colured light strikes the retina
Produces local potential
Bipolar cells
Activate ganglion cells
Processing in the cones as
10. Physiology of
Vision
L-M Cones – X cells
S cones – X cells
L + M + S Cones – Y Cells
Lateral geniculate nucleus
LMS – relay in parvocells
White and black – relay in magnocells
After processing
Primary visual cortex
Impulse reach layer 2 & 3
11. Physiology of Vision
Has clusters of neurons called blobs and layer 4
Colour information
Projected finally to V8
Converts
Colour input into sensation of colour
12. Theories of Colour Vision
1.Young-Helmholtz theory of colour vision
(trichromatic colour theory)
2. Granits dominator and modulator theory
3. Hering’s opponent colour theory
13. Young-Helmholtz theory of colour vision
(trichromatic colour theory)
There are three primary colours red, green and blue.
There are three types of cones with different pigments.
The three pigments are:
1. Erythrolabe (Porphyropsin -- red)
2. Chlorolabe (Lodopsin-- green)
3. Cyanolabe (Cyanopsin -- blue)
14. Theories of Colour Vision
Sensation of any given colour is determined by the
relative frequency of impulses reaching the brain from
each of the three cone systems.
Colour blindness is classified based on this theory.
This theory fails to explain the black sensation as black is
also considered as a colour.
This also fails to explain how the peripheral colour blind
zones perceive yellow, white or grey sensations.
15. Granits dominator and modulator theory
Granit introduced micro-electrodes into the ganglion cells
and investigate the sensitivity to light of various
wavelengths.
a) Dominator.
b) Modulator cells.
a) Dominators: These respond to the whole visual spectrum.
These are supposed to detect the intensity of the light but
not the colour.
This is due to ‘Y’ ganglion cells.
16. Granits dominator and modulator theory
b) Modulators: These respond
maximum to a narrow
wavelength of light.
There are three groups of
modulators,
blue light of wavelength 450
—470 nm
green light of wavelength 520
—540 nm
red yellow light of 500—600 nm.
17. Granits dominator and modulator
theory
Hence the
modulators are
responsible for colour
vision. According to
the latest concept the
X ganglion cells are
supposed to be the
modulators.
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18. Theories of Colour Vision
Herring's opponent colour
theory
This is an extension of
trichromatic theory and based
on this theory there are four
primary colours—blue, green,
yellow and red.
19. Hering’s opponent colour
theory
According to this
theory the
photochemical
substances give one
sensation on
breakdown and a
different one on
resynthesis.
According to this
theory,
complementary
colours become
antagonistic to its
respective primary
colours.
20. Photo chemical
substance
Hering's opponent colour theory
Sensation
1. White - black - Break down
- Resynthesis
- White
- Black
2. Red - green - Breakdown
- Resynthesis
- Red on & green off
-Green on &Red
-off
3. Yellow - blue - Breakdown
- Resynthesis
- Yellow on & blue off
-Blue on &
- yellow off
21. AFTER IMAGE
After looking at a bright object, if the eyes
are closed, the image remains more distinct
for someone and then fades away gradually.
This phenomenon is called after image.
22. Positive after Image
After looking at a bright
object, if the eyes are
closed or fixed on a
black surface, the after
image appears to be
bright and with same
colour of the object. It
is called Positive after
image
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23. Negative after Image
After looking at bright
object, if the eyes are
fixed on white surface
the after image appears
in the complementary
color. It is called
Negative after image.
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24. Colour Blindness
Insensitive to colours i.e.,
inability on the part of an
individual to recognize the
colours is called colour
blindness
Inheritance of colours
blindness;
Inherited sex linked
anomaly
Due to abnormal gene on
X-chromosomes
Females are the carriers
Incidence in Males – 8%
Females –0.4 %
26. Colour Blindness
The classification of colour blindness is based on
the Young-Helmholtz theory of colour vision
Based on three receptor theory, individuals
suffering from colour blindness are classified
into:
1. Trichromats.
2. Dichromats.
3. Monochromats.
27. Colour Blindness
1. Trichromats These are the people with weakness for
one primary colour. Accordingly, these are classified
into:
a) Protanomolous Weakness to red colour—common
occurrance is 6% and sex-linked.
b) Deuteranomalous Weakness to green colour -
occurance is 6% and sex-linked.
c) Tritanomalous weakness to blue clolour—rare, not
sex-linked.
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28. Colour Blindness
2.Dichromats: These are the
individuals with two cone
systems. These cannot
appreciate one primary colour.
Accordingly they may have:
a) Protanopia — blindness to red.
Phorphyropsin pigment is
absent.
b) Deuteranopia—blindness to
green. lodopsin pigment is
absent.
c) Tritanopia — blindness to blue.
Cyanopsin pigment is absent.
29. Monochromats
They have only one
cone system. These
people can see
black, white and
shades of grey.
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31. Tests For Colour Vision
Ishihara charts:
Charts containing
some numbers made up
of different coloured and
sized dots on a similar
background.
Inability to identity a
number suggests some
defect of colour vision.
32. Tests For Colour Vision
Holmgren wool test:
Different coloured wools
are placed together .
The subject will be given
coloured wool and asked to
pick up a similar coloured
wool.
33. Tests For Colour Vision
Eldridge green lantern:
This consists of different
coloured windows with a light
source in the centre. The subject
should identify the colour of the
window. The effect of mist or fog on
the coloured window can also be
studied. This is used for testing
railway employees.
34. Eldridge green lantern
Importance: Pilots,
navigators, vehicle drivers
and railway employees
require normal colour
vision as they deal with
colours for running their
machines.
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35. Significance of Colour Vision
Pilots, Navigators, vehicle drivers and railway
employees require normal colour vision as they
deal with colours for running their machines.
