Refraction of the eye

The speed of light rays at different refraction: 1-in the myopic eye; 2 - in normal; 3 - in farsighted.

Refraction of the eye - refractive power of the optical system of the eye with the rest of accommodation. Refractive power of the optical system depends on the radius of curvature refractive surfaces (cornea, lens and ostojania them from each other. Svetoprelomlyayuschimi the apparatus of the eye has a complex structure; it consists of the cornea, chamber of moisture, lens and vitreous body. A beam of light on the way to the retina must pass four refractive surface: the front and back surface of the cornea and anterior and posterior surface of the lens. The speed of light rays at different refraction of the eye shown. Refractive power of the optical system of the eye is on average 59,92 D. For eye refraction is set to the length axis of the eye, i.e. the distance from the cornea to the yellow spots. This distance is the average of 25.3 mm So refraction of the eye depends on the ratio between the refractive power and length of the axis, which determines the position of the main focus in relation to the retina and characterizes optical installation eyes.
There are three basic eye refraction: the emmetropia (see), or "normal" eye refraction, hyperopia (see) and myopia (see).
Refraction of the eye changes with age. The newborn is observed mainly farsightedness. In the period of human growth will shift refractive eye towards its strengthening, i.e. myopia. Changes eye refraction caused by the growth of the body, during which the lengthening of the axis of the eye expressed more than a change in the refractive power of the optical system. In old age is a small shift of refraction of the eye towards its weakening due to changes in the lens.
Eye refraction determine subjective and objective methods. Subjective method based on the definition of visual acuity (see) with the aid of glasses. Objective methods for determining eye refraction are skiaskopia (see) and refractometry, i.e., the definition of refraction of the eye with the help of special devices - eye refractometers. These devices eye refraction is determined by the position further points clear of view.