Color blindness, ishihara book slide, color vision theory

1. Colour vision

2. Contents :
1. Introduction to colour vision
2. Structure of cones
3. Features of colour vision
4. Basic of colour
5. Theories of colour vision
6. Colour blindness
7. Colour vision tests
8. Treatment

3. INTRODUCTION :
• COLOUR VISION – To identify different colour by a light adopted is called
colour vision .

4. STRUCTURE OF CONES -:
1. function of cones .
2. 40 – 80 um long .
3. 45% more on nasal and inferior .
4. Highest in fovea.
5. Largest in fovea .

5. Features of colour vision –
• Our eyes percive colour with wavelength of light
ranging from 400 to 700 nm .
• Below 400nm is below voilet wavelength called ultra
vailet rays .
• Above 720nm is infrared .

6. Basic of colour -
o Colours are formed from the mixture of basic colours of red,
blue and green.
o The colours are appreciated due to different wavelength of
lights.

7. Theories of colour vision -
1. Trichromatic theory
2. Opponent theory
3. Stage theory
1. TRICHROMATIC THEORY -
Suggested – thomas young helmholtz
• three kinds of cones
• each cone containing a different
BLUE CONES --- 440 - 450 nm
GREEN CONES --- 535 – 550 nm
RED CONES --- 570 – 590 nm

8. 2. OPPONENT TheorY -
Suggested – Ewald hering
• Mixing of different colour produces light of yet another colour.
RED + GREEN = YELLOW
GREEN + BLUE = LIGHT BLUE
BLUE + RED = PINK
RED + GREEN + BLUE = WHITE
3. STAGE TheorY –
• Colour vision which incorporates both the trichromatic theory
and the opponent colour theory

9. How do we see colours :
• all frequency of visible light shining.
• light falls on the photoreceptor layer of retina.
• light is converted to neorochemical reaction.
• the phtorecepter cell reads & cones.
• then chemical reaction sends an electrical singnals to the brain.

10. colour blindness –
colour blindness means that you have trouble seeing red , green
blue or a mix of these colours.
NORMAL COLOUR VISION --- TRICHOMATE
ONE OR MORE IS EITHER DEFECTED --- ANOMALOUS
ABSENT --- ANOPIA
COLOUR BLINDNESS ---- DALTONISM
CAUSES
Inherited
Ocular --- Glaucoma
Retinal damage
Diabetic retinopathy
Other causes --- heart problem
nerous disorder
cortical trauma

12. CONGENITAL ACQUIRED
TYPES OF blindness

13. Inherited colour blindness = ( congenital )
there are three types
1. Monochromacy
2. Dichromacy
3. Anomalous Trichromacy
1. MONOCHROMACY
Two colour is absent and one colour is present.
for exp – red + green = blue
2. DICHROMATIS
one colour is absent and two colour is present.
for exp – bule = red + green

14.  PROTANOPIA :
 Complete red colour absent.
 deuteranopia :
 Complete green colour absent.
 TRITANOPIA :
 Complete blue colour absent.
3. trichromacy
These are the people with weakness for one primary colour.
PROTANOMALOUS ---- WEAKNESS TO RED COLOUR
DEUTERANOMALOUS ---- WEAKNESS TO GREEN COLOUR
TRITANOMOLOUS ---- WEAKNESS TO BLUE COLOUR

16. ACQUIRED colour blindness =
CAUSES
Damage to macula
drug incduced
optic nerve damage
tests for colour blindness
 use proper illumination
 explain test for the patient
 patient should use near correction
 monocular examination

17. Ishihara’s test
Designer --- Dr. shinobu ishihara
Professor --- University of tokyo
Published –- 1917
 A test for red- green deficiency.
 75 cm under good illumination.
 Numerals should be answered in not more than 3sec.
 Pathway tracing should be completed
With in 10 sec.
 Three different forms
16 plates
24 plates
38 plates

18. DESIGNED IN FOUR WAYS
1. INTRODUCTARY PLATE [1plates]
for demonstration and malingerer.
2. TRANSFORMATION PLATE [2 - 9plates]
colour normal appear different to colour deficient subject.
3. VANISHING PLATE [ 10 – 17plates]
colour normal appear different to colour deficient subject.
4. HIDDEN DIGIT PLATE [18 – 21plates]
normal person does not see a figure while a CVD will see the fi
5. DIAGNOSTIC PLATE [ 22 – 25plates]

19. 6. TRACKING PLATE
Advantage = protable method
red-green deficency can given
Disadvantage = Degree of deficiency
treatment
• There is currently no treatment.
• x- chrome lens is a monocular CL

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