Eye

of the titles of this article is ambiguous. For further meanings see eye (term clarifying).
Menschliches Auge (braun)
Human eye (brown)

the eye (lat. Oculus) is the Sehorgan of humans and animal. The adequate attraction for this sensory organ is with humans electromagnetic radiation with a wavelength of approximately 350 Nm to approximately 750 Nm. In the eye the received attraction produces a change of the excitation in the deriving nerve courses. The eye stands at the beginning of the Sehbahn, those in the brain thisChange of excitation to the visual Cortex passes on. There and in other superordinate centers the excitation samples coming from the eye are finally converted to the feeling by light and color.

For humans is the sense of light of very great importance. It is the guidance sense, thatus a safe orientation makes possible. We lose this security immediately, if we move with closed eyes.

Eyes are sensitive sensory organs. Surrounded by nasal bone, yoke leg and Stirnbein they lie protected, embedded into a fat pad, in the knöchernen eye sockets of theHead. Dust or somewhat the like flies to the lashes, then the lid is closed by the lid reflex and protects against dirt particles. Arrived nevertheless somewhat inside, then it is out-washed with the tear liquid.

Männliches blaues Auge
Male blue eye

table of contents

eyes of the mammals

The human tear apparatus

the Sehorgan (Organon visus) of the mammals and concomitantly humans can be arranged into three subunits:

  1. the eyeball, Bulbus oculi (lat.) or Ophthalmos (griech.),
  2. the appendix organs of the eye (tear apparatus, eye muscles, binding skin and lids) and
  3. the Sehbahn.


Eyeball of the mammals

structure of the mammal eye

the eyeball consists again of three concentric layers:

as well as unite internal structures such as

the wall of the eyeball consist of three skins lying one above the other.

The outside eye skin (Tunica externa bulbi, also Tunica fibrosa bulbi) becomes intwo sections subdivided. The white leather skin (Sclera) lies in the rear eyeball range. At it the outside eye muscles set, which move the eye in the eye socket. Where the light occurs the eye, is the transparent cornea/callosity (cornea).It is constantly moistened with tear liquid.

The 2. Layer, the middle eye skin (Tunica media bulbi or Uvea), consists of three sections. The vein skin is rich at blood vessels and supplies the lying close layers with nutrients and oxygen and possessesa pigment layer. The vein skin changes forward into the ciliary body (also jet body, corpus ciliare), which serves the suspension of the eyepiece and their accommodation. The foremost section of the middle eye skin is the iris (iris). It forms those Pupil and adjusts the beam of light (adaptation).

The internal eye skin (also retina, Tunica interna bulbi or Retina) contains the light cells (Photorezeptoren). In the range of the withdrawal of the Sehnervens are no light cells. One calls this place blind mark. The place of sharpest seeing is the yellow mark.

The interior of the eyeball consists of the glass body (corpus vitreum), the lens (Lens) and the two eye chambers (Camera anterior and posterior bulbi).

Function mechanism of the imaging

in the inside arrives the light by the cornea/callosity and the pupil. It is the circular opening of the colored iris, the iris. The pupil can be increased and made smaller by the muscle fibers in the iris.This procedure, which adapts the eye to the environment, is called adaptation. Behind the iris the flexible eyepiece at volumes is hung up. The lens volumes run to the circular ciliary muscle. The eye inside is fulfilled of the gelatinous glass body. It lends to thatEye the firm and round form, which also eyeball is called.

With humans the range of the electromagnetic spectrum perceptible by the eye is in the wavelength coverage from approximately 380 Nm to 760 Nm, the so-called flash spectrum. On the other hand for example bees seealso shorter-wave light, so-called ultraviolet UV light, while they cannot notice red light for it on the other side. The Sehraum in the eye of the mammals is very many smaller for colored seeing (colored light) than for bright andDarkly (white light). Thus the Farbsehraum lies also within the Weisslichtsehraumes.

In 19. One explained the function of the eye to century similarly the camera in such a way: Reflected light (active) falls into the eye (passive), the illustration of the world on the retina becomesfinally in the brain passed on. In the second half 20. Century was disproved with the help of technical devices for the measurement of the eye movements this idea.

The whole Retina ( retina) is covered with sensory cells, the sharp seeing concentrates however uponly 0.02 per cent of the Retinafläche, the so-called yellow mark. This corresponds about 2 degree ours to approximately 200 degrees of comprehensive horizontal field of vision. We see thus actually only the cutout sharply, which our two eyes with their axes of vision fix. When regarding oneArticle comes off the resting and sharp picture by the fact that the eye muscles, usually unconsciously, move us successively different cutouts of the object before the yellow mark. The eye rests thus when regarding never, it is always in smallest motion understood.One point is fixed for fractions of a second, then jump muscles with a jerky movement (Saccade) to a next point. From this scanning the clear overall view is finally generated. During calm view the individual fixations 0.2 to 0,6 lastSeconds, so that in one second of 2 to 5 Saccaden take place, when fast looking become the Saccaden more frequently and the fixation times more briefly.

The choice of the points of fixation and the sample of the Saccaden are to a considerable degree individual and stand in connection withthe habits and the interest of the viewer or setting of tasks to it. One speaks today of the Intentionalen seeing, an active procedure to the world.

The eye medicine

(Ophthalmologie) is occupied illnesses of the eye with the illnesses of the eye.

Eye of the othersAnimals

although the eyes of vertebrate animals and soft animals in the structure resemble each other strong, have them independently developed. This becomes visible with the formation of the eye with the embryo: During itself the eye with vertebrate animals by a Ausstülpung of the cellsdeveloped, which form the brain later, the eye of the soft animals results from an a inverting of the outside cell layer, which form the skin later. There are estimations that eyes of the most diverse building methods in the course of the evolution about 40 times were again developed.There were the first eyes already before 505 millions Years in the earth age Ordovizium (z. B. with the Nautilus).

The simplest „eyes “are photo-sensitive sensory cells on the outer skin, which function as passive optical systems. They can only recognize whether the environmentbright or dark is. One speaks here of sense of skin light.Insects and other Gliederfüsser have eyes, which are compound from many individual eyes. These compound eyes supply a raster-like picture (, as one to assume would not know repeated pictures).

Beside the described eye types alsoone finds mirror eyes to refractive lenses in nature occasionally also. In the eyes of the comb shell (Pecten) the picture is produced by hollow mirrors, which are arranged behind the retina. Directly before the retina lying the lens serves thatoptical correction of the strongly distorted mirror image. The mirrors are built according to the principle of reflecting glass plates, more for than 30 layers from finest guanine crystals are appropriate closely stacked, each layer into a double membrane enclosed. Also different animals have mirror eyes, among other things thatDeep sea cancer Gigantocypris, lobster and Langusten. This form became generally accepted obviously, where it depends less on the image quality and more on the luminous efficiency.

Light cells

already the single-celled organism Euglena possesses a photo receptor for light dark perception. More highly organism developed howe.g. the earthworm possess at the body end or scatter individual light cells.

Flat eyes

Quallen and sea-stars possess many light cells lying next to each other, which can attach inside to a layer from pigment cells. The concentration of the sensory cells improves the light dark perception.

Pigment cup eyes

the Sehzellen lie ofLight turned away (inverse situation) in a cup from opaque pigment cells. The light can penetrate only by the opening of the cup, in order to stimulate the Sehzellen. Since therefore in each case a small part of the Sehzellen is provoked, can apart from the brightnessalso the direction of arrival of the light to be determined. Such eyes possess among other things vortex worms and snails.

Pit eyes

the pit eye everse from the pigment cup eye by those the light turned () situation of the sensory cells differs and thus that it is filled with secretion pit.In the pit the Sehzellen form a cell layer, which attaches inside to a layer of pigment cells. It is thus an advancement of the flat eye. It makes possible also the regulation for the intensity and the direction of arrival of the light.

Hole eyes

hole eyes are improved pit eyes.The opening of the pit is only a small hole and the cavity is completely filled with secretion. By the increased number of Sehzellen now also picture marriages are possible. The picture is however faint and only schemenhaft. This type findsone with low Tintenfischen. A modification of the hole eye is the blister eye, with which the opening is covered by a transparent skin (occurrences with make kinds of snail). The secretion can be solidified by lens also to a simple kind (with vineyard snails thatCase). These modifications improve the picture slightly.

Lens eye

the lens eye is the highest developed kind of Sehorganen. A multi-level refractive apparatus collects the light and throws it on the retina, which contains now two kinds of sensory cells, to Stäbchen and taps.The attitude on close and remote view is made possible by a flexible lens, stretched those by Zonulafasern and/or. one tosses. One finds the best lens eyes with vertebrate animals.

Compound eyes (complex eyes)

compound eyes consist of a multiplicity of single eyes (Ommatidien), of thoseeach eight sensory cells contains. Each single eye sees only a tiny cutout of the environment, the overall view is a mosaic from all frames. The number of single eyes can lie between some hundreds up to some ten thousand. The dissolution of the compound eye is by the number of single eyes limited and is far smaller therefore than the dissolution of the lens eye. However temporal resolution can be far higher with compound eyes than with lens eyes. It lies for instance with flying insects with 250 pictures per second,which corresponds about the tenfold human eye. This lends an extremely high reaction rate to them. The color sensivity of the compound eye is shifted into the ultraviolet range. In addition Spezien with compound eyes have the largest field of vision of all well-known organisms. To find are these eyes z. B. with spiders and insects. Compound eyes cannot be arranged in the evolution history of the eye!

See also

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