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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.

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colour vision ii the post receptoral basis of colour vision
Colour Vision IIThe post receptoral basis of colour vision

Prof. Kathy T. Mullen

McGill Vision Research (H4.14)

Dept. of Ophthalmologykathy.mullen@mcgill.ca

29th Sept 2005

summary
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

spectral sensitivities of l m s cones
Spectral sensitivities of L, M & S cones

Long

Medium

Log relative sensitivity

Short

Wavelength (nm)

principle of univariance
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
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

slide7
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
Trichromats
  • One of the three cone types is anomalous
dichromats
Dichromats
  • One of the three cone types is missing
mixing red and green lights to match yellow
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

Ishihara test for RG color blindness

45 or spots

29 or spots

56 in both

6 or spots

http://www.toledo-bend.com/colorblind/Ishihara

http://www.vischeck.com/daltonize/

how is colour coded
How is colour coded?
  • Each colour produces a unique pattern of relative activities in the three cone types
connections of cones to retinal neurons
Connections of cones to retinal neurons

http://webvision.med.utah.edu/index.html

cones connect via retinal neurons into excitatory and inhibitory subgroups
Cones connect via retinal neurons into excitatory and inhibitory subgroups

-

-

-

-

+

-

-

http://webvision.med.utah.edu/index.html

retinal cells
Retinal cells

Magnocellular (M)

Parvocellular (P)

slide21

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.

Neural pathways for color vision:

How do we test these pathways?

Farnsworth Munsell 100 hue or Panel D15

Electronic displays & computer graphics

farnsworth munsell
Farnsworth Munsell

100 Hue Inherited and acquired color vision deficiencies

Red-green, blue-yellow and non-specific deficiencies

Show axial effects

D15

farnsworth munsell 100 hue
Farnsworth Munsell 100 hue

Protan

Deutan

Tritan

show over heads for
Show over heads for:

F-M 100 hue in Optic Neuritis

F-M 100 hue after intense light exposure

slide25

A pattern with colors that activate only the S/L-M (‘blue-yellow’) cone opponent process

A pattern with colors that activate only the L/M (‘red-green’ cone opponent process

loss of colour and luminance contrast sensitivity with multiple sclerosis and optic neuritis
Loss of colour and luminance contrast sensitivity with multiple sclerosis and optic neuritis

Threshold

RG

BY

Ach

Patrick Flanagan and Connie Markulev Ophthalmic and Physiological Optics Volume 25 Issue 1 Page 57 - January 2005

kollner s rule 1912
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 blue-yellow.

conditions quoted as having tritan by defects appearing first
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
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