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Color Vision Fundamentals
Jeff Rabin, OD, PhD
Chief, Visual Function LaboratoryOphthalmology Branch
USAF School of Aerospace Medicine
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Visible light is small part of electromagnetic spectrum.
700 600 500 400
UVIR
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The visible spectrum includes 300
wavelengths (400-700 nm), and in someportions we can discern color differences
of 1 wavelength. The ability to see so
many colors depends on:
a. a separate cone for each wavelength.
b. optic nerve fibers for each color.
c. visual cortex neurons sensitive to eachcolor.
d. difference in stimulation of red, green
and blue sensitive cones.
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y
Red conesy Green cones
y Blue cones
y Brightness = R+ G
y Color = R Gy Color = B (R+G)
y Red cones
outnumber green
cones 2/1y Red + Green cones
outnumber blue
cones 10/1
Retinal ConesNormal Color Vision
Blue cones
absent in
central fovea
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Red, green and
blue cone
sensitivity vs.
wavelength
curves
Retinal ConesNormal Color Vision
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What happens in hereditary
color deficiency?
yRed orgreen cone peak
sensitivity is shifted.
yRed orgreen cones absent.
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B RG
437 nm 564 nm
533 nm
NORMAL CONE SENSITIVITY CURVES
(TRICHROMAT)
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B RG
437 nm 564 nm
Deuteranomaly
(green shifted toward red)
5% of Males
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B RG
437 nm 564 nm
Deutan Dichromat
(no green cones; only red and blue)
1% of Males
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B R
437 nm 564 nm
Deutan Dichromat
(no green cones; only red and blue)
1% of Males (there is no green curve)
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B RG
437 nm
533 nm
Protanomalous
(red shifted toward green)
1% of Males
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B RG
437 nm
533 nm
Protan Dichromat
(no red cones; only green and blue)
1% of Males
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B G
437 nm
533 nm
Protan Dichromat
(no red cones; only green and blue)
1% of Males (there is no red curve)
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Why do colors that
look different to us
appearthe same tocolor deficient
individuals?
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B RG
Color Normal Individual
Large difference
in stimulation of
green and red
cones
Small
difference instimulation
Consider a green vs.
yellowlight
The two spots
appear different
in color because
R-G is large forone, and small
for the other.
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B RG
Deuteranomaly
Small
difference instimulation
Smalldifference in
stimulation
Each spot produces the same R-Gstimulation and thus
looks the same!
(the green sensitivity curve is shifted toward the red)
Look the same!
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Drs. Jay and Maureen Neitz
Department of Cell Biology, Neurobiology & Anatomy
Department of Ophthalmology
Medical College ofWisconsin
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Color Labeling
y Color deficients rely heavilyon context and learning
apple is red because
patient learns to call it red
same hue may appear
gray when presented
without other cues.
y Forwavelengths beyond
545, relative brightness,
context, and learning play a
significant role verbal label
and response.
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Hereditary Color Deficiency
y 8-10% of males and 1/200 females (0.5%) areborn with red or green color deficiency.
y Sex-linked recessive condition (X chromosome).
y Protanomalyred cone peak shifted toward
green (1%)
y Protan Dichromatred cones absent (1%)
y Deuteranomalygreen cone peak shifted
toward red (5%)y Deutan Dichromatgreen cones absent (1%)
y Hereditary tritan defects are rare (0.008%)
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Color Deficiency Males Females
Protanopia 1% 0.01%
Deuteranopia 1% 0.01%
Protanomaly 1% 0.01%
Deuteranomaly 5% 0.4%
Overall (red-green) 8% 0.5%
Tritanopia 0.008% 0.008%
Tritanomaly Rare Rare
Rodmonochromatism
Rare Rare
Cone
monochromatism
Rare Rare
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END SLIDE SHOW
OF COLOR VISION
FUNDIMENTALS