Colour Vision II
The post receptoral basis of colour vision
Prof. Kathy T. Mullen
McGill Vision Research (H4.14)
Dept. of Ophthalmology
kathy.mullen@mcgill.ca
29th Sept 2005
Summary
1. Revision: cone types, the principles of trichromacy,
univariance, and tests for the inherited color vision
deficiencies
2. Connection of cones to retinal neurons: cone opponency
3. Cells types for RG, BY and Ach vision
4. Testing of RG, BY & Ach vision:
1) Farnsworth Munsell
2) Monitor displays and selective color vision tests
5. Examples from Optic Neuritis & Phototoxicity
6. Kollners Rule
29th Sept 2005
Three cones types of human retina:
Log relative sensitivity
Spectral sensitivities of L, M & S
cones
Long
Medium
Short
Wavelength (nm)
Principle of Univariance
• The response of a photoreceptor to any
wavelength can be matched to any other
wavelength simply by adjusting the relative
intensities of the two stimuli
Therefore: any single receptor type is colour
blind
Principle of Trichromacy
• Mixing together three coloured lights in suitable
proportions enables us to make an exact match to any
other colour
• The 3 mixing lights are called ‘primaries’
• The match is called ‘metameric’ - meaning that identical
colour sensations are produced even though the stimuli
are physically different
3 mixing lights
test light to be matched
L1 + L2 + L3
L4
• Colours with different wavelength
distributions will look identical if they
produce the same ratio of quantum
catches in the L, M and S cone types
Trichromats
• One of the three cone types is anomalous
Dichromats
• One of the three cone types is missing
Mixing red and green lights to
match yellow.
A
B
C
A and B. Green and red lights on the top are mixed by the
subject to match the yellow light presented on the bottom.
C. The red-green mixture perfectly matches the yellow.
The same match as it appears to a deuteranomalous observer.
Ishihara test for RG color blindness
45 or spots
29 or spots
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56 in both
6 or spots
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http://www.toledo-bend.com/colorblind/Ishihara
http://www.vischeck.com/daltonize/
How is colour coded?
• Each colour produces a unique
pattern of relative activities in the
three cone types
Connections of cones to retinal neurons
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http://webvision.med.utah.edu/index.html
- -+- -
Cones connect via
retinal neurons into
excitatory and
inhibitory subgroups
http://webvision.med.utah.edu/index.html
Red-green colour visionL/M cone opponent mechanisms
S/(L+M) cone opponent mechanisms: K cells
The luminance mechanism
Retinal cells
Magnocellular (M)
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Parvocellular (P)
S cones and Koniocellular layers of LGN
Koniocellular layers of LGN
Neural pathways for color vision:
L/M (red-green) cone-opponency: P cells of retina & LGN
S cone-opponency: bistratified ganglion cell & K cells of LGN
Luminance (black & white): P cells and M cells.
How do we test these pathways?
Farnsworth Munsell 100 hue or Panel D15
Electronic displays & computer graphics
Farnsworth Munsell
100 Hue Inherited
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and acquired color vision
deficiencies
Red-green, blue-yellow
and non-specific
deficiencies
Show axial effects
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D15
Farnsworth Munsell 100 hue
Protan
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Deutan
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Tritan
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Show over heads for:
F-M 100 hue in Optic Neuritis
F-M 100 hue after intense light exposure
A pattern with colors that
activate only the L/M (‘redgreen’ cone opponent
process
A pattern with colors that
activate only the S/L-M
(‘blue-yellow’) cone
opponent process
Contrast sensitivity of red/green
and luminance gratings
luminance
red/green
Loss of colour and luminance contrast sensitivity
with multiple sclerosis and optic neuritis
T
h
r
e
s
h
o
l
d
RG
BY
Ach
Patrick Flanagan and Connie Markulev
Ophthalmic and Physiological Optics
Volume 25 Issue 1 Page 57 - January
2005
Kollner’s Rule (1912)
Lesions of the outer retinal layers affect blue yellow
vision, lesions of the inner layers and optic nerve
affect red-green vision
Updated version
S cones are physiologically vulnerable and so are
more likely to be damaged by receptoral lesions than
are L or M cones
Post receptoral lesions are more likely to affect both
types of cone opponent neuron: red-green and blueyellow.
Conditions quoted as having tritan (BY)
defects appearing first:
Damage due to high light exposure
Glaucoma
Retinal detachment
Pigmentary degeneration
Myopic retinal degeneration
ARMD
Chorioretinitis
Retinal vascular occlusion
Diabetic retinopathy
Papilledema
Drugs: oral contraceptives, chloroquine
S cones are genetically robust but vulnerable physiologically
Conditions quoted as having RG defects, but
BY defects may also occur:
Lesions of optic nerve/pathway
Retrobulbar neuritis
Leber’s optic atrophy
Compressive lesions of the optic tract
Progressive cone degeneration
L and M cones are physiologically robust but genetically vulnerable
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