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Visual system is used for perception and analysis of light stimuli. Peripheral part of the system represented by a complex organ - the eye. Eye - peruse all the senses the eye has a special place. If we take 100% of the information you perceive all the senses, together, we will have a share of up to 80% of the information received from outside the body.

This is particularly important in the learning process. No wonder they say that it is better to see once than hear a hundred times. This is indeed the case: a man with vision will recognize objects, perceive their size, shape, location in space and movement. The eye responds to light stimuli, which are electromagnetic oscillations in the visible spectrum.

Eye - paired organ, described as the eyeball. It is located in the orbit. The form of the eye varies from round to oval. Newborn eyes as if squeezed in the anteroposterior direction, so the image extends beyond the eyeball, resulting in a far-sightedness. With the growth of the eyeball is so far-sightedness. It should be noted that the child is born with an already well-developed body of.

Eyeball is a spherical chamber containing a light-guiding medium - the cornea, anterior chamber of moisture, lens, and gelatinous fluid - the vitreous body, whose purpose is to refract the light rays and focus them in the region of the receptors on the retina. The walls of this chamber are three spherical shells. The outer shell is opaque - the sclera - the front moves into the clear cornea. Average or choroid in front of the eye forms the ciliary body and iris, which is linked to eye color. In the middle of the iris is an opening - the pupil, regulating the amount of noise in the eye of light rays. The inner membrane - the retina - the eye contains photoreceptors (rods and cones) and is used to convert light energy into neural excitation.
Light-guiding medium's eyes are involved in the breaking of light rays, providing a clear image on the retina. The major light-refracting media of the human eye are the cornea and lens. The rays coming through the center of the cornea and lens (ie, through the main optical axis of the eye) perpendicular to the surface, do not suffer refraction. All other rays are refracted and converge within the chamber of the eye at one point - focus. Adaptation of the eye to the clear vision of distant objects is different (the focus) is called accommodation. This process is carried out in humans due to changes in the shape of the lens.

Photoreceptors. photoreception process occurs in the retina. The main elements of the retina are the photoreceptors - rods and cones, and connected with bipolar (first neurons in the visual system), and ganglion cells (neurons of the second), giving the fibers of the optic nerve. Photochemical reactions in the receptor leads to the excitation of bipolar and ganglion cells and then, from which nerve impulses are sent to the brain.
Photoreceptors - a highly specialized cells that convert light stimuli into nerve stimulation. Photoreception begins in outer segments, where the disks are the visual pigment molecules (in the sticks - rhodopsin in cones - iodopsin). Under the action of light is a series of very fast reactions and discoloration of the visual pigment. Rods and cones differ in their functions. The rods have a higher sensitivity than the cones, and are the organs of the twilight. They see black and white (colorless) image. Cones are the organs of daylight vision. They provide color vision. There are three types of cones in humans: perceiving predominantly red, green and blue-violet color. Different color of their sensitivity is determined by differences in the visual pigment. Combination of excitations of these receivers in different colors give the feeling of the whole range of colors. Uniform excitation of all three types of cones evokes a sense of white.

Lachrymal fluid. The outer surface of the cornea is constantly covered with a thin layer of tear fluid, which improves the optical properties of the surface of the eye. This fluid is produced by lacrimal glands, and thanks to the regular movements of the age is uniformly distributed over the cornea. Tear fluid protects the cornea and conjunctiva from drying out. Its composition is similar to an ultrafiltrate of blood plasma. Lacrimal fluid contains substances with bactericidal action, and thereby protects the eye from infection.

Spherical aberatsiya - is the inability of the eye to focus light rays that pass through both center and periphery of the eye. For the average person is a typical positive spherical aberatsiya to 0.15 microns. The image blurs because the peripheral light rays focus in front of the cornea.

Refraction - refraction of the optical system of the eye. In ophthalmology accepted the concept of "clinical refraction," which means the location of the focal point relative to the retina. There are three types of clinical refraction: emmetropia, myopia, gipermiopiya.

Emmetropia - a normal adult human eye refraction, in which he distinguishes between good things and far and near. This type of refractive error is more commensurate with the title. This means that the optical apparatus of the eye (cornea and lens) have a focal length equal to the anteroposterior axis of the eye, and the focus in this case falls precisely on the retina.

Ametropia - types of refractive errors that require correction, ie Myopia and hyperopia