The eye can be called a complicated optical device. Its main task — to "transfer" the right image to the optic nerve.
The eyeball has a spherical shape, its diameter is about 24 mm. Inside it is the aqueous humor, lens and vitreous body. Vitreous limited to three eye membranes. Thick opaque outer shell forming the shape of the eye is called sclera. 6 attached to the sclera of the eye muscles. It is a small number of nerve endings and blood vessels.
At the front, the visible part of the sclera is partially covered conjunctiva and becomes transparent cornea. In no blood vessels in the cornea. Because of its dome-shaped it has a large refractive power. The cornea is the optical system of the eye.
Middle layer —choroid, contains blood vessels that provide the eye with oxygen. In the choroid is the ciliary (ciliary) body with its iris and ciliary belts. Iris— Like shape with a hole circle inside (pupil). The iris consists of muscles, by reduction and relaxation of the pupil size changes. That iris gives the eye its color, depending on the amount of pigment cells. Between the iris and the cornea is space — so-called aqueous chamber,filled with a transparent intraocular fluid (aqueous humor).
The cornea and aqueous humor passes light rays that enter the eyeball through the pupil. Ingestion eyes bright rays of light causes a reflex contraction of the pupil hole. In low light the pupil dilates. Directly behind the pupil is clear crystalline lens, having a convex form. The lens is transparent, elastic — can change its shape, almost instantaneously, "directing focus," whereby a person sees good and near and far. Around it is an annular muscle. Lens as the cornea, including the optical system of the eye.
After the rays pass through the lens, they penetrate vitreous body — A transparent gel-like substance that fills the entire interior of the eyeball. In the end, the light rays fall on the inside, very thin membrane of the eye — retina. The retina is adjacent to the choroid, but on many sites loosely. It was here that she has a tendency to flake off in various diseases of the retina.
The retina has a very complex structure. It consists of photoreceptor (they are sensitive to light), and nerve cells.
In the rods and cones, the enzyme producing rhodopsin converts light energy (photons) into electrical energy nervous tissue, i.e. photochemical reaction. Excitation is conducted on neuronal processes that form visual nerve. According to it, the signals are transmitted from the nerve endings in the brain.