Eye
- This article refers to the sight organ. See Eye (disambiguation) for other usages.
An
eye is an
organ which has evolved for the purpose of detecting
light. The simplest eyes do nothing but detect whether the surroundings are light or dark. More complex eyes are used to provide the sense of
vision.
Compound eyes are found among the
arthropods (insects and kin), and are composed of many simple facets which give a pixelated image (not multiple images as is often believed).
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\nDiagram of a human eye. Note that not all eyes have the same anatomy as a human eye.
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Light from a distant object and light from a near object being brought to a focus
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\nThe human eye is said to be the window to the soul\n |
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In most
vertebrates and some
mollusks the eye works by projecting images onto a light-sensitive
retina, where the light is detected and transmitted to the
brain via the
optic nerve. The eye is typically roughly spherical, filled with a
transparent gel-like substance called the
vitreous humour, with a focusing
lens and often a muscle called the
iris that controls how much light enters.
Focusing
\nIn order for light rays to be brought to a focus they must be refracted. The amount of refraction required depends on the distance of the object which is being viewed. A distant object will require less bending of light than a nearer one. Most of the refraction occurs at the cornea which has a fixed curvature. The remainder of the required refraction occurs at the lens. The lens can be pulled flatter or rounder by muscles, which adjust the power of the lens. As we age we gain this ability to adjust the focus. Such a condition is known as presbyopia.
See this site for a good diagram on the eye\n
[1]
Parts of the eye
\n* Cornea\n*
Iris\n*
Pupil\n*
Aqueous humour\n*
Lens\n*
Vitreous humour\n*
Retina\n*
Macula\n*
Fovea\n*
Blind spot\n*
Sclera\n*
Tapetum lucidum (not in humans)
Problems
\n*Achromatopsia\n*
Age-related macular degeneration\n*
Aniridia\n*
Amblyopia\n*
Anisometropia\n*
Arc eye\n*
Astigmatism\n*
Blindness\n*
Cataracts\n*
Color blindness\n*
Conjunctivitis\n*Corrective lenses\n*
Floaters\n*
Glaucoma\n*
Hypermetropia\n*
Myopia\n*Nyctalopia\n*
Presbyopia\n*
Retinopathy\n*
Scotoma\n*
Snow blindness\n*
Strabismus\n*Uveitis
See also
\n*Visual perception\n*
Saccade\n*
Persistence of vision\n*
Macropsia\n*
Micropsia\n*
Optometry\n*
Opthamology\n*
Eyeglass prescription\n*
Crystallin\n*
Nictating membrane\n*
Adaptation\n*
Tears\n*
Visual acuity\n*
Snellen chart
External link
\n*Evolution of the Eye
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\n\nCategory:Visual system\nCategory:Optics\nCategory:Computer vision\nCategory:Ophthalmology
