At back inner eyeball, visual receptor-cell layers {retina}| have 90 million rod cells, one million cones, and one million optic nerve axons.
cell types
Retina has 50 cell types.
cell types: clustering
Retina has clusters of same cone type. Retina areas can lack cone types. Fovea has few short-wavelength cones.
development
Retina grows by adding cell rings to periphery. Oldest eye part is at center, near where optic nerve fibers leave retina. In early development, contralateral optic nerve fibers cross over to connect to optic tectum. In early development, optic nerve fibers and brain regions have topographic maps. After maturation, axons can no longer alter connections.
processing
Retina cells separate information about shape, reflectance, illumination, and viewpoint.
Ganglion-cell axons leave retina at region {blindspot}| medial to fovea [DeWeerd et al., 1995] [Finger, 1994] [Fiorani, 1992] [Komatsu and Murakami, 1994] [Komatsu et al., 2000] [Murakami et al., 1997].
Cone cells are Long-wavelength, Middle-wavelength, or Short-wavelength. Outside fovea, cones can form two-dimensional arrays {color-receptor array} with L M S cones in equilateral triangles. Receptor rows have ...S-M-L-S-M-L-S... Receptor rows above, and receptor rows below, are offset a half step: ...-L-S-M-L-S-M-.../...S-M-L-S-M-L-S.../...-L-S-M-L-S-M-...
hexagons
Cones have six different cones around them in hexagons: three of one cone and three of other cone. No matter what order the three cones have, ...S-M-L-S-M..., ...S-L-M-S-L..., or ...M-L-S-M-L..., M and L are beside each other and S always faces L-M pair, allowing red+green brightness, red-green opponency, and yellow-blue opponency. L receptors work with three surrounding M receptors and three surrounding S receptors. M receptors work with three surrounding L receptors and three surrounding S receptors. S receptors work with six surrounding L+M receptor pairs, which are from three equilateral triangles, so each S has three surrounding L and three surrounding M receptors.
In all directions, fovea has alternating long-wavelength and middle-wavelength cones: ...-L-M-L-M-.
Primates have central retinal region {fovea}| that tracks motions and detects self-motion. Retinal periphery detects spatial orientation. Fovea contains 10,000 neurons in a two-degree circle. Fovea has no rods. Fovea center has no short-wavelength cones. Fovea has patches of only medium-wavelength cones or only long-wavelength cones. Fovea has no blood vessels, which pass around fovea.
Retinal layers {inner plexiform layer} can have bipolar-cell and amacrine-cell axons and ganglion-cell dendrites. There are ten inner plexiform layers.
Near retina center is a yellow-pigmented region {macula lutea}| {yellow spot}. Yellow pigment increases with age. If incident light changes spectra, people can briefly see macula image {Maxwell spot}.
1-Consciousness-Sense-Vision-Anatomy-Eye
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Date Modified: 2022.0225