Optic Nerve &
Optical Chiasm
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Rods translate light into monochromic
values, everything inbetween
black and white wheras cones convert them into color.
There are three types of cones,
one of each of the primiary colors of light: red, green and
blue. |
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| Mechanics
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When the light hits the photoreceptors of the retina (cones
and rods), the photoreceptors
send impulses though a maze of specialized intermediary
cells: bipolar, horizontal and
amacrine cells. Bipolar cells receive input from the
receptors which then feeds into the
ganglion cells. The ganglion cells (retinal ganglion
cells), which passes the surface
of the retina, connect and relay signals to the optic
nerve. Horizonal cells link receptors
and bipolar cells by relatively long connections that run
parallel to the layers of the
retina. The amacrine cells are the same, except they link
the bipolar cells and retinal
ganglion cells.
There are two paths the electrical signals may take, a
direct or an indirect path. They
may go from the light receptors to the bipolar cells
connecting with the ganglion cells
then to the retina or they may cross the horizonal and
amacrine cells. The reason for this
being is because there are relatively few bipolars feeding
directly into a ganglion cell.
There are 125 million rods and cones but only 1 million
ganglion cells in each eye.
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| Arrangement
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Humans have eighteen times more rods than cones, but the
arrangement of the cones and rods
in our eye is what makes a formidable tool. Most of our
cones are concentrated in the
fovea. As we get further away from them, the fewer the
cones and more the rods. Because
of this, that's why dim starts are only visible when we
don't look directly at them, instead
just "out of the corner of our eye". Because of this,
that's why the edges of our vision
are predominatly in black and white.
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