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Color Vision Dr Taha Sadig Ahmed MBBS. PhD MAANEM.

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Presentation on theme: "Color Vision Dr Taha Sadig Ahmed MBBS. PhD MAANEM."— Presentation transcript:

1 Color Vision Dr Taha Sadig Ahmed MBBS. PhD MAANEM

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4 History of color vision Newton (1704) used a prism to show that sunlight was composed of light with all colors in the rainbow. He defined it as the spectrum.

5 History of color vision Primary colors: 723-647 575-492492-450 Thomas Young 1807: primary colors: when mixed >>> white or any other color

6 Mixing colors

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8 Photopic vision (CONES) Helmholtz..1860: The three primary colors are perceived by three photoreceptor pigments (with broad absorption curves) White light is produced by mixing three colours

9 Cone wavelength ranges SML Wavelength (nm) Relative absorption 400500600 700

10 Photopic vision (CONES) Cone pigments: three kinds 565 535440

11 Photopic vision Young Helmholtz theory Color vision is subserved by three types of cones, each containing a photoreceptor pigment most sensitive to one primary color 1.Cones (contain red-sensitive pigment) 2.Cones (contain green-sensitive pigment) 3.Cones (contain blue-sensitive pigment) in the fovea centralis

12 Cone wavelength ranges SML Wavelength (nm) Relative absorption 400500600 700

13 Color Blindness Weakness or total blindness in detecting a primary color: Definitions: 1.Trichromats: see the 3 1ry colors 2.Dichromats: blind to one 1ry color 3.Monochromats: have color pigment

14 Color Blindness –cont. Prot …… Red Deuter …. Green Trit …… Blue Anamoly …weakness Protanamoly Deuteranamoly Trichromats Tritanamoly

15 Color Blindness –cont. Anamoly …weakness Anopia …. Total loss Protanopia Deuteranopia Dichromats Tritanopia

16 Trichromatic/dichrom atic color vision

17 Color Blindness –cont. Prevalence: males ………….8% females …. 0.4% Inheritance: sex-linked due abnormal gene in the X chromosome

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19 Electrophysiology of Vision

20 Light Change in photopigment Metarhodopsin II Activation of transducin Activation of phophodiesterase Decrease IC cyclic GMP Closure of Na channels Hyperpolarization of receptor Action potential in optic nerve fibres

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22 Photoreception

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24 Figure 17.15 Bleaching and Regeneration of Visual Pigments

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26 Electrophysiology of Vision Electric recording in Retinal cells: Bipolar cells: Hyper- & Depolarization Horizental cells: Hyper- & Depolarization Amacrine cells: Depolarizing potential Ganglion cells: Depolarizing potential

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