color vision dr taha sadig ahmed mbbs. phd maanem
TRANSCRIPT
History of color visionNewton (1704) used a prism to show thatsunlight was composed of light with allcolors in the rainbow. He defined it as the
spectrum.
History of color vision
Primary colors:
723-647 575-492 492-450
Thomas Young 1807:primary colors: when mixed >>>
white or any other color
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
Photopic visionYoung Helmholtz theory
Color vision is subserved bythree 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
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
Color Blindness –cont.
•Prot …… Red•Deuter …. Green•Trit …… Blue•Anamoly …weakness
•Protanamoly •Deuteranamoly Trichromats•Tritanamoly
Color Blindness –cont.
•Anamoly …weakness•Anopia …. Total loss
•Protanopia •Deuteranopia Dichromats•Tritanopia
Color Blindness –cont.
•Prevalence:males ………….8%females …. 0.4%
Inheritance: sex-linked due abnormal gene in the X
chromosome
Light
Change in photopigment
Metarhodopsin II
Activation of transducin
Activation of phophodiesterase
Decrease IC cyclic GMP
Closure of Na channels
Hyperpolarization of receptorAction potential in optic nerve fibres
Electrophysiology of Vision
Electric recording in Retinal cells:•Bipolar cells: Hyper- & Depolarization
•Horizental cells: Hyper- & Depolarization
•Amacrine cells: Depolarizing potential
•Ganglion cells:Depolarizing potential