Colour Vision

1. Colour Vision Sensitivity & Acuity

2. Colour Vision Trichromatic theory of colour vision • There is only one type of rod and this responds strongly to bluish-green light • Cones are divided into three categories, each of which has a different sensitivityto light • There are red light receptors, green light receptors and blue light receptors. • These cone sensitivities support the trichromatic theory as all colours of the visible spectrum can be seen by mixing the 3 primary colours (red, blue and green) • White objects reflect all colours to eye, black absorbs all colours so no light to the eye.

3. Wavelengths of light absorbed by different cones

4. Colour Blindness • If you have normal vision you will see a figure seven in reddish brown dots. • People with red-green colour blindness will not see the 7, why? • These people lack red sensitive cones, but the green stimulated cones are stimulated by the red light, so all dots appear green

5. Sensitivity and Acuity • Rods and cones synapse with bipolar cells • Bipolar cells synapse with ganglion cells • Ganglion cells synapse with neurone fibres • At the fovea each cone synapses individually with a ganglion cell • This gives good Acuity (resolution). N.B Bright light needed • Many Rods synapse with one bipolar neurone – RETINAL CONVERGENCE • Dim light results in small amount of neurotransmitter release • Individually, this would be insufficient to over come the threshold of the bipolar cell, but the total amount of transmitter from several rods is • This gives less acuity but better sensitivity