overview of colour blindness and colour vision...

1. COLOUR VISION & COLOUR
BLINDNESS
- AKSHAY.B.K.

2. •It is the ability of the eye to discriminate
between different colours excited by light
of different wavelengths.
COLOURVISION

3. THE PHYSICS OF LIGHT
400 500 600 700
ELECTROMAGNETIC SPECTRUM
VISIBLE SPECTRUM
10
-14
meters 10
6
meters
Wavelength (nm)
Cosmic
Rays
Gamma
Rays X-rays UV Infra-
Red
Micro-
waves TV RadioLight
Light: Electromagnetic energy whose
wavelength is between 400 nm and 700 nm.
(1 nm = 10 meter)

4. •Colour perception by the eye is due to two receptors present
in the layers of retina .
 RODS (scotopic vision)
CONES (photopic vision)
•These cells contain
photosensitive pigments.
•But colour vision is mainly
attributed as function of cone
cells.

5. LAYERS OF RETINA

6. VISUAL PATHWAY

7. THEORIES OF COLOUR VISION
1) TRICHROMATIC THEORY (YOUNG-HELMHOLTZ THEORY)
•This theory proposes the existence of three kinds of cone cells ,each containing a different
photopigment which is maximally sensitive to one of the three primary colours ( 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 systems.
•Three different photosensitive pigments:
1. RED SENSITIVE CONE PIGMENT
2. GREEN SENSITIVE CONE PIGMENT
3. BLUE SENSITIVE CONE PIGMENT
FIG: THOMAS YOUNG & VON HELMHOLTZ

8. RED SENSITIVE CONE PIGMENT
also known as erythrolabe/long
wavelength sensitive cone pigment(LWS).
Max absorption in yellow portion at 564 nm.
GREEN SENSITIVE CONE PIGMENT
also known as Chlorolabe/medium
wavelength sensitive cone pigment (MWS).
Max absorption in green portion at 533nm.
BLUE SENSITIVE CONE PIGMENT
also known as cyanolabe/short
wavelength sensitive cone pigment(SWS).
Max absorption in blue-violet region at
437nm.

9. 2) OPPONENT COLOUR THEORY OF HERING
 According to this theory ,some colours appear to be mutually exclusive i.e there is no such colour as
reddish-green and such phenomenon can be difficult to explain on the basis of trichromatic theory alone.
Therefore HERING proposed the existence of two main types of colour opponent ganglion cells:
1. RED-GREEN OPPONENT COLOUR CELLS
They use signals from red and green cones to detect red/green contrast within their respective field.
2. BLUE-YELLOW OPPONENT COLOUR CELLS
They obtain a yellow signal from the summed output of red and green cones , which is contrasted
with the output from blue cones within the respective field.
fig: EWALD HERING

11. TESTS FOR COLOUR VISION
 OBJECTIVES OF THE TESTS:
•Screening defective colour vision from normal.
•Qualitative classification of colour blindness.(protan,deuteran,tritan)
•Quantitative analysis of deficiency(mild/moderate/marked).
 Different colour vision tests:
•PSEUDO-ISOCHROMATIC CHARTS.
•EDRIDGE-GREEN LANTERN TEST.
•FRANSWORTH-MUNSELL 100 HUE TEST.
•CITY UNIVERSITY COLOUR VISION TEST.
•NAGEL’S ANOMALOSCOPE.
•HOLMGREN’S WOOLS TEST.
Optical illusion.

12. 1.PSEUDO-ISOCHROMATIC CHARTS
•Test done using ISHIHARA PLATES/CHARTS.
•Patterns of coloured and greydots which reveal one pattern to the
normal individuals and another to colour deficients.
•Quick and easy method.
•Ishihara charts are mainly used to detect red-green deficiency.
ISHIHARA CHARTS
INTERPRETATION OF ISHIHARA TEST RESULTS:
•The concise version of ishihara chart contains 14 plates.
•Scoring is made on the basis of first 11 slides.
•10/11 is considered normal.
•7/11or less is abnormal.
•Those scoring 8 or 9/11 need further testing.(fransworth munsell hue
test etc..)
•Patient scoring 10/11 need not be assesed further.

13. HRR PLATES
Other tests based on same principle:
•HARDY –RAND-RITTLER PLATES (HRR).
•AMERICAN OPTICAL COLOUR PLATE TEST.
WHAT DO THE PLATES MEAN???
•Plate 1 is for explaining the test.
•Plates 2-5 , red-green deficient patients may see different numbers.
•“Plate -9”is special i.e is only red-green defecient persons can
appreciate the number in the plate.
•Plates 12-14 are those for red-green deficient persons.(to differentiate
between protanopia and deuteronopia)

14. 2.EDRIDGE GREEN LANTERN TEST
• Subject has to name the various colours shown to him by a lantern &
judgement is made by the mistake he makes.
3.FRANSWORTH-MUNSELL 100 HUE TEST
• Spectroscopic test.
•Subject has to arrange coloured chips in the ascending order
•The colour vision is judged by the error score.

15. 4.CITY UNIVERSITY COLOUR VISION TEST
•Spectroscopic test.
•Central coloured plate is to be matched to its closest hue from
four surrounding colour plates.
5.NAGEL’S ANOMALOSCOPE
•Observer is asked to mix red and green colours in such a proportion that the
mixture should match the given yellow coloured disc. Judgement about defect is
made from the relative amount of red and green colours and the brightness
setting used by the observer.

16. 6.HOLMGRENS WOOLS TEST
•In this the subject is asked to make a series of
colour matches from a selection of skeins of
coloured wools.
•Judgement is made on the basis of colour
matches made by the subject.

17. COLOUR BLINDNESS
•Individuals with normal colour vision are called trichromates.
•In colour blindness, mechanism to appreciate one or more primary colours is either
defective(anomalous) or absent (anopia).
 Broadly classified in two types:
1. CONGENITAL COLOUR BLINDNESS
2. ACQUIRED COLOUR BLINDNESS

18. A. CONGENITAL COLOUR BLINDNESS
•It is an inherited condition.
• X linked recessive disorder.
•Males (3-4%) are more affected than females (0.4%).
 classified in to two types:
1. DYSCHROMATOPSIA.
2. ACHROMATOPSIA.

19. 1.Dyschromatopsia
 it is confusion of colours due to deficiency of mechanism to
perceive colours.
Classified in to three types:
i. ANOMALOUS TRICHROMATIC COLOUR VISION:
Here the mechanism to appreciate all the three primary
colours is present but is defective for one or two of them.
It is further classified in to three types:
a)PROTANOMALOUS: Defective red colour appreciation.
b)DEUTERANOMALOUS: Defective green colour appreciation.
c)TRITANOMALOUS: Defective blue colour appreciation.

20. ii)DICHROMATIC COLOUR VISION:
In this condition the person affected will not be able
to perceive one of the three primary colours. Such individuals
are called DICHROMATES.
Classified in to three types:
a) PROTANOPIA- complete red colour defect.
b) DEUTERANOPIA-complete green colour defect.
c) TRITANOPIA-complete blue colour defect.
RED-GREEN DEFICIENCY
 It is more commonly seen.
 this defect is a source of danger in certain occupations (
drivers , sailors, police etc…)
iii) BLUE CONE MONOCHROMATISM (BCM)
•It is a condition of complete absence of red and green cone
function.

21. 2.ACHROMATOPSIA (2nd variety of congenital colour blindness)
• Extremely rare condition .
•There is rod cell monochromatism.
•It may be of complete type or incomplete type.
•Inherited as an autosomal recessive trait.
•Both sexes (M/f) are affected equally.
•It is characterized by:
 TOTAL COLOUR BLINDNESS.
DAY BLINDNESS ( VISUAL ACUITY 6/60)
NYSTAGMUS.
FUNDUS IS USUALLY NORMAL. ACHROMATOPSIA- BLACK AND WHITE VISION!!!!

22. B. ACQUIRED COLOUR BLINDNESS
•It may follow damage to macula or optic nerve.
•Usually associated with a central scotoma or decreased visual acuity.
BLUE-YELLOW IMPAIRMENT:
• Seen in retinal lesions such as CSR, macular oedema, shallow retinal
detachment.
RED-GREEN DEFICIENCY:
• Seen in optic nerve lesions(optic neuritis),lebers optic atrophy ,
compression of optic nerve.
ACQUIRED BLUE COLOUR DEFECT :
Usually occurs in the old age due to increased sclerosis of the crystalline lens.

23. TREATMENT?????
Colour Blindness Cure
Curing colour blindness is currently impossible. 99% of colour blind males and females are colour blind as a result
of defective genetics on the X chromosome. To cure this colour blindness would require some form of gene therapy,
repairing the damaged chromosome.
Colour Blindness Correction
Recent developments in light filtering lenses have made it possible to provide colour blind people with a greater
ability to distinguish between certain shades that otherwise look the same. Many critics claim they are tailored
specifically to passing the Ishihara tests for colour blindness and have no real world value.
Fig : light filtering glasses.