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Human eye

Sensory organ of vision / From Wikipedia, the free encyclopedia

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The human eye is an organ of the sensory nervous system that reacts to visible light and allows the use of visual information for various purposes including seeing things, keeping balance, and maintaining circadian rhythm.

Arizona_eye_model.png
Arizona Eye Model. "A" is accommodation in diopters.
Quick facts: Human eye, Details, System, Identifiers, Lati...
Human eye
Human_eye%2C_anterior_view.jpg
The eye of the right side of the face, showing its visible components - a white sclera, a light brown iris, and the black pupil, in its orbit surrounded by the lids and lashes
Eye-diagram_no_circles_border.svg
Details
SystemVisual system
Identifiers
Latinoculus
Greekἀνθρώπινος ὀφθαλμός
MeSHD005123
TA98A01.1.00.007
A15.2.00.001
TA2113, 6734
FMA54448
Anatomical terminology
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The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as the outermost, white part of the eye (the sclera) and one of its inner layers (the pigmented choroid) keeping the eye essentially light tight except on the eye's optic axis. In order, along the optic axis, the optical components consist of a first lens (the cornea—the clear part of the eye) that accounts for most of the optical power of the eye and accomplishes most of the focusing of light from the outside world; then an aperture (the pupil) in a diaphragm (the iris—the coloured part of the eye) that controls the amount of light entering the interior of the eye; then another lens (the crystalline lens) that accomplishes the remaining focusing of light into images; and finally a light-sensitive part of the eye (the retina), where the images fall and are processed. The retina makes a connection to the brain via the optic nerve. The remaining components of the eye keep it in its required shape, nourish and maintain it, and protect it.

Three types of cells in the retina convert light energy into electrical energy used by the nervous system: rods respond to low intensity light and contribute to perception of low-resolution, black-and-white images; cones respond to high intensity light and contribute to perception of high-resolution, coloured images; and the recently discovered photosensitive ganglion cells respond to a full range of light intensities and contribute to adjusting the amount of light reaching the retina, to regulating and suppressing the hormone melatonin, and to entraining circadian rhythm.[1]

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