Human eyes, which include a Retina
, an iris, and a Cornea
, are some of the most delicate and extraordinary organs in the body.
Through entirely biological processes, they are able to detect frequencies of light via miniscule photoreceptors and convert them into impulses that the brain's neurons are able to process. These impulses are transmitted to the visual cortex of the brain and create an image, which is what we “see.”
The Retina is the part of the eye that essentially captures what you are seeing. If the eye were a video camera, the retina would be the film. It's a thin, transparent tissue on the eye's inner surface that is sensitive to light.
Whenever light hits the eye, thousands of different chemicals are released and funneled up the Optic Nerve.
Based on the composition and saturation of these chemicals, the brain is able to determine exactly what sort of light the eye is reacting to, and thus is able to form an accurate picture of the outside world.
Retinas actually serve two purposes though, and only one of them is directly related to sight. When the light travels through the optic nerve, it's sending information to the brain about sight, but this also sends a very different set of chemicals and impulses through what is known as the retino-hypothamalic tract.
The signals are directly related to circadian rhythm, which is the cycle of light and dark in a 24 hour day. All land organisms on earth are attuned to circadian rhythm, and will either sleep when it's dark and become active during the day or vice versa. This section of the brain is relatively simple and similar variations can be seen in most organisms.
The photoreceptors of the eye are made up of two different types: cones and rods. The average human eye holds an impressive 6 million cones, and a staggering 125 million rods.
Cones are found in the macula and are responsible for most of our vision. They are particularly prominent during the day and are the parts of the eye that detect color. Normal humans have three different types of cones that can detect red, blue, and green, but people who are colorblind may be missing one or more of these cone variations.
Rarely, people will be born with more than three types of cones, sometimes as many as six, and will be able to view an entirely different color spectrum than they would normally be able to see. Their vision has been dubbed tetrachromatic.
Rods reside in the macular region of the this as well but are over a hundred times more receptive to light than cones; they are the parts of the eye that process light at night; this is known by most of the world as night vision.
They're also extremely responsive to movement, and if you've ever seen something move out of the corner of your eye, you've experienced your rods in action. All of these processes combine to create our vision.
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Retina to the Visual Process