Optic nerve

Each photosensitive cell in a retina is bridged by a nerve to a brain where all information on images, colour and the form gathers and processed. All these nervous fibers gather in a back part of an eye and form one main "cable" known as an optic nerve. It leaves an eyeball through the osteal tunnel in a skull and again arises hardly below a brain in the field of a pituitary body that will join the second optic nerve.

Nerves from both parties then are crossed, so the part of the information from the left eye arrives in the right half of brain and on the contrary. Nerves of the temporal party of each retina are not crossed and remain on the same half of brain whereas fibers from the same part of an eye which performs the basic work of sight, go in different directions a brain.

Optic nerve - not that other as a fascicle of the nervous fibers carrying the smallest electric impulses on tiny cables, each of which is isolated from the myelin next by a layer. In the centre of the main cable there is the large artery going on all its length. It name the central retinal artery. This artery arises in the central part of an eye, and its capillaries cover all surface of a retina. There is a corresponding vein which goes in the opposite direction on an optic nerve near to the central retinal artery and carries away blood from a retina.

The nerves going from a retina, - sensitive nerves; unlike motor nerves which have only one bond the way to a brain, optic nerves are bridged some times. The first occurring occurs just behind that point, the sensory information from different eyes is interchanged the position. This point is called as a visual crossroads, it is close to a pituitary body. Immediately behind this crossroads there is a first communication centre, it is called as a lateralis geniculate body. Here the information from the left eye and the right eye is interchanged the position once again. Function of this bond is bound to reflexes of pupils.

From a lateralis geniculate body nerves a fan disperse on both parties round a temporal part of a brain, forming visual radiance. Then they slightly turn and gather to pass through main "switchboard" - an internal capsule where all impellent and sensory information supplying a body concentrates. From here nerves pass in a back part of a brain to a visual zone of a cortex of a brain.

Short-sightedness

The most widespread reason of short-sightedness - an eyeball which is too long", therefore rays of light form the image before a retina.

Short-sightedness is corrected by concave lenses.

Hyperopia

At a hyperopia the eyeball is too short", so the image cannot turn out in an eye.

Convex lenses focus the image on a retina (the brain places all in the places).