Colour Vision II The post receptoral basis of colour vision

1. 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

2. 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

3. Three cones types of human retina:

4. Spectral sensitivities of L, M & S cones Long Medium Log relative sensitivity Short Wavelength (nm)

5. 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

6. 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

7. 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

8. Trichromats • One of the three cone types is anomalous

9. Dichromats • One of the three cone types is missing

10. 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.

11. 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/

12. How is colour coded? • Each colour produces a unique pattern of relative activities in the three cone types

13. Connections of cones to retinal neurons http://webvision.med.utah.edu/index.html

14. Cones connect via retinal neurons into excitatory and inhibitory subgroups - - - - + - - http://webvision.med.utah.edu/index.html

15. Red-green colour vision-L/M cone opponent mechanisms

16. S/(L+M) cone opponent mechanisms: K cells

17. The luminance mechanism

18. Retinal cells Magnocellular (M) Parvocellular (P)

19. S cones and Koniocellular layers of LGN

20. Koniocellular layers of LGN

21. 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

22. Farnsworth Munsell 100 Hue Inherited and acquired color vision deficiencies Red-green, blue-yellow and non-specific deficiencies Show axial effects D15

23. Farnsworth Munsell 100 hue Protan Deutan Tritan

24. Show over heads for: F-M 100 hue in Optic Neuritis F-M 100 hue after intense light exposure

25. 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

26. Contrast sensitivity of red/green and luminance gratings luminance red/green

27. 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

28. 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.

29. 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

30. 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