Cone-shaped retinal cells {cone, cell} have daylight-vision photoreceptors and detect color and visual details.
types
Humans have three cone types. Cone maximum wavelength sensitivities are at indigo 437 nm {short-wavelength cone}, green 534 nm {middle-wavelength cone}, and yellow-green 564 nm {long-wavelength cone}. Shrimp can have eleven cone types.
evolution
Long-wavelength cones evolved first, then short-wavelength cones, and then middle-wavelength cones. Long-wavelength and short-wavelength cones differentiated 30,000,000 years ago. Three cone types and trichromatic vision began in Old World monkeys.
fovea
Fovea has patches of only medium-wavelength or only long-wavelength cones. To improve acuity, fovea has few short-wavelength cones, because different colors focus at different distances. Fovea center has no short-wavelength cones [Curcio et al., 1991] [Roorda and Williams, 1999] [Williams et al., 1981] [Williams et al., 1991].
number
There are five million cones, mostly in fovea. Short-wavelength cones are mostly outside fovea.
size
Cones are smaller than rods.
pigment
Cone light-absorbing pigment is iodopsin. Rods have rhodopsin.
frequency
When rods saturate, cones have approximately same sensitivity to blue and red.
Just above cone threshold {mesopic vision, cone}, rods are more sensitive to short wavelengths, so blue colors are brighter but colorless. Retinal receptors do not detect pure or unmixed colors. Red light does not optimally excite one cone type but makes maximum excitation ratio between two cone types. Blue light excites short-wavelength cones and does not excite other cone types. Green light excites all cone types.
output
Cones send to one ON-center and one OFF-center midget ganglion cell.
Most mammals, including cats and dogs, have two photopigments and two cone types {dichromat}. For dogs, one photopigment has maximum sensitivity at 429 nm, and one photopigment has maximum sensitivity at 555 nm. Early mammals and most mammals are at 424 nm and 560 nm.
Animals can have only one photopigment and one cone type {monochromat} {cone monochromat}. They have limited color range. Animals can have only rods and no cones {rod monochromat} and cannot see color.
Reptiles and birds have four different photopigments {quadchromat}, with maximum sensitivities at near-ultraviolet 370 nm, 445 nm, 500 nm, and 565 nm. Reptiles and birds have yellow, red, and colorless oil droplets, which make wavelength range less, except for ultraviolet sensor.
Women can have two different long-wavelength cones {L-cone} {L photopigment}, one short-wavelength cone {S-cone} {S photopigment}, and one middle-wavelength cone {M-cone} {M photopigment}, and so have four different pigments {tetrachromacy}. Half of men have one or the other long-wavelength cone [Asenjo et al., 1994] [Jameson et al., 2001] [Jordan and Mollon, 1993] [Nathans, 1999].
People with normal color vision have three different photopigments and cones {trichromat}.
1-Consciousness-Sense-Vision-Anatomy-Cells-Retina-Receptors
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Date Modified: 2022.0225