The optical system of the eye in humans

The shape of the human eye is almost spherical. The average diameter of the organ of vision is about two and a half centimeters.

Anatomy of the human eye

Outside, the organ of vision is surrounded by three shells.

The first, strong and firm (external) is called a sclera (or a protein coat). It provides protection against mechanical damage. The anterior area of the sclera is transparent and is called the cornea (cornea). On the rest of the surface of the eye it is opaque and is called a protein (it has a white color).

To the sclera from the inside adjoins the choroid. It is formed from a fairly complex plexus of blood vessels that feed the blood of the eyes. This shell passes into a rainbow shell, colored in different people in different colors and having a hole in the center. It is called the pupil. The iris has the ability to deform and change the diameter of the pupil. Changes are carried out at the level of reflexes and are associated with the amount of light entering the eye. In bright illumination, the pupil narrows to two millimeters, with slight illumination widening in some cases up to eight millimeters.

The retina (the reticular membrane) is located on the inner side of the vessel. It covers the entire eye fundus, except for the anterior region. The optic nerve, which provides the connection of the brain with the eye, enters the retina behind. In general, the membrane consists of branched nerve fibers, as well as nerve endings. Thus, the supersensitive surface of the eye is formed.

Between the cornea and the iris, there is an anterior chamber filled with chamber moisture.

Directly behind the pupil is the lens. It is represented by a transparent elastic body, which looks like a biconvex lens. The surface of the lens may have different curvatures depending on the effect of the muscle that surrounds it on all sides.

By changing the curvature index, the image of objects located at different distances is clearly shown to the surface of the sensitive layer of the retina. The described process is called accommodation. The eye cavity behind the lens is filled with a gelatinous transparent liquid. It forms a vitreous body.

The optical system of the eye is similar to the corresponding structure in the camera. As an objective, the lens appears in combination with the anterior chamber and the vitreous body, which have refractive properties.

The image is projected on the photosensitive surface of the mesh shell. Sharpness is achieved by accommodation.

The optical system of the eye includes (like the camera system) a diaphragm capable of changing the diameter. The pupil plays the role of the diaphragm.

The ability to accommodation allows you to obtain on the retina clear images of objects located at different distances.

In a quiet state, the optical system of the eye makes it possible to obtain a clear image of distant objects (stars, for example) without effort of accommodation. With the help of the effort of the muscles, which contributes to the increase in the curvature of the lens and the reduction of its focal length, the visual organ implements sharpening of the desired object.

The optical system of the eye undergoes changes with age. By age, the ability to accommodation decreases. The smallest distance at which the optical system of the eye can provide a distinct image ranges from ten (under the age of twenty) to twenty-two centimeters (up to forty years). To old age, the smallest distance increases to thirty or more centimeters - age-long-sightedness develops.

The optical system of the eye contains a point passing through which the rays practically do not refract. This point is located inside the lens, near its posterior plane.