The optical system of the eye. The construction of the image. Accommodation. Refraction, violations

08 january 2017, 22:21

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Eye eyeball is almost spherical shape of about 25 cm in diameter. It consists of several shells, three of them major Fig. 1. Schematic representation of the mechanism of accommodation the left - focus right into the distance - focusing on close objects. The sclera is white in color with a milky tint except for the front part of which is transparent and is called cornea. Through the cornea light enters the eye.

Choroid middle layer contains blood vessels through which blood flows to nourish the eyes. Just under the cornea choroid goes into the iris which determines eye color. In the center is the pupil. The function of this shell to limit the light entering the eye at high brightness. This is achieved by constriction of the pupil in high light and at low extension. Behind the iris is the crystalline lens similar to a biconvex lens which picks up light when it passes through the pupil and focuses it on the retina.

Around the lens the choroid forms the ciliary body which carries the muscle regulating the curvature of the lens that provides clear vision krasnozelenyh items. This is achieved in the following way Fig.1. The pupil is a hole in the center of the iris through which light rays pass into the eye. In the adult, the resting pupil diameter in daylight equal to 15 mm 2 and in the dark increases до75 mm. the Main physiological role of the pupil is to regulate the amount of light entering the retina.

Constriction of the pupil-miosis occurs with the increased light it restricts the flow of light reaching the retina and therefore serves as a protective mechanism when looking at near objects when there is accommodation and the reduction of the visual axes convergence as well as during sleep. Mydriasis mydriasis occurs in low light and increases the illumination of the retina and thereby increases the sensitivity of the eye as well as in the excitation of receptors of afferent nerves in any emotional reactions to the stress associated with increased tone of the sympathetic nervous system in mental excitations suffocation anesthesia. The pupil size is regulated by circular and radial muscles of the iris. Radial muscle extends the pupil is innervated by sympathetic nerve running from the upper cervical node. A circular muscle narrowing a pupil is innervated by parasympathetic fibers of the oculomotor nerve. The reaction of the pupils is always friendly that is, it simultaneously constricts the pupil right and left eye while covering the extension when dimming.

The lens in the eye is suspended on.

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