Colour Sense

COLOUR SENSE
Presented by-
FARHANA AFRIN
B. OPTOMETRY 1ST YEAR
INTRODUCTION
• It is the ability of the eye to discriminate between difference colour
excited by the light of difference wavelengths.
• Colour vision is a function of cones ( seen better in photopic vision)
• Our eye perceive colour with wavelength of light from 400 to 700 nm.
• In dim light all the colour are seen grey and this phenomenon is
called PURKINJE SHIFT.
THEORIES OF COLOUR VISION
• 1 ) Trichromatic theory:- This theory is originally suggested by Young
and subsequently modified by Helmholtz. So this theory is called
Helmholtz theory.
• It postulates the existence of three kind of cones , each containing a
different photopigment which is maximally sensitive to one of the
three primary colours viz. Red , green and blue . The sensation of any
given colour is determined by the relative frequency of the impulse
from each of the three cone system. In other words , a given colour
consist a admixture of the three primary colour in different
proportion .
RED SENSITIVE CONE PIGMENT
• It is also known as erythrolabe or a long wavelength sensitive cone
pigment , absorbs maximally in a yellow portion with a peak at565nm
. But its spectrum extends far enough into the long wavelength to
sense red.
GREEN SENSITIVE CONE PIGMENT
• It is also known as chlorolabe or medium wavelength sensitive cone
pigment , absorbs maximally in the green portion with in a peak at
535nm
BLUE SENSITIVE CONE PIGMENT
• It is also known as cyanolabe or short wavelength sensitive cone
pigment absorbs maximally in the blue violet portion of the spectrum
with a peak at 440nm
• 2) Opponent colour theory of Hering:- The opponent colour theory of hering
points out that some colour appear to be mutually exclusive . There is no
such colour as reddish-green and such phenomenon can be difficult to explain
on the basis of trichromatic theory alone . In fact it seems that both theories
are useful in that :
• Colour vision in trichromatic at the level of photoreceptors and
• Colour opponency occurs at ganglion cells
• Red green cones to detect red/ green contrast within their receptive field
• Blue yellow opponents colour cells obtain a yellow signal from the summed
output of red and green cones ,which is contrasted with the output from blue
cones within the receptive field.
Colour blindness
• An individual with normal colour vision is known as trichromate. This
is because the normal human eye can appreciate three primary
colours (red, green and blue) due to presence of three different types
of cones, i.e. Red sensitive, green sensitive and blue sensitive. All
colours of the spectrum can be perceived by fusion of these three
primary colours in varying proportions. (Young-Helmholtz trichromatic
theory of colour vision.) In colour blindness, mechanism to appreciate
one or more primary colours is either defective (anomalous) or absent
(anopia). It may be congenital or acquired.
COLOUR VISION TEST
• Pseudoisochrometic test :- It is the most commonly employed test
using Ishihara’s plates , In this there are patterns of coloured and grey
dots which reveal one pattern to the normal individuals and another
to the colour deficient . It is a quick method to screen congenital
proton and deuteron .
• Edridge-green lantern test :- In this test the subject has to name the
various colour shown to him by a lantern and the judgement is made
by the mistake he makes.
• Farnsworth Munsell 100 hue test :- It is a spectroscopic test in which
subject has to be arrange the coloured chips in ascending order . The
colour vision is judged by the error score , i.e greater the score poorer
the colour vision . It is the most sensitive test for both congenital and
acquired colour vision defects . It consists of 85 hue caps and colour
vision is judge by error score( high score means poorer colour vision )
• Farnsworth D15 hue discrimination test :- It is similar test but utilizes
only 15 hue caps .
• City university colour vision test :- It is also a spectroscopic test where
a central coloured plate is to be matched to its closest hue from 4
surrounding colour in each of 10 plates.
• Nagel’s anomaloscope :- In this test the observer is asked to mix red
and green colour is such a proportion that the mixture should match
the given yellow coloured disc . The judgement about the defect is
made from the relative amount of red and green colours and
brightness setting used by the observer .
• Holmgren’s wools test :- In this the subject is asked to make a series of
colour matches from a selection of skeins of coloured wools .
REFERENCE
• Comprehensive OPHTHALMOLOGY by A K Khurana ( page no. 18-19
and 343) 7th Edition
THANK YOU

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