Eyes

The person sees by means of eyes from where the image is transmitted through a hiazma, an optic nerve, visual tracts to special areas of occipital shares of a cerebral cortex. Our sight three-dimensional thanks to existence of two eyes. The right side of a retina transfers "the right part" of the image to the right part of a brain. Similarly happens also to the left side of a retina. And the brain connects these two parts together, receiving the integral image.

At disturbance of the joint movement of the left and right eye solid vision will be upset as each eye sees only "the" image.

Functions of an eye

• The optical function projecting the image;
• Life support function;
• Perception and "coding" of the acquired information for a brain.

Structure

An eye is a difficult optical device which main objective is transfer of the image to an optic nerve. Now the structure of an eye is studied so well that allows to carry out such thin procedures as laser correction of sight.

An eye consists of the following parts:

• Cornea – the transparent cover which is in a front part of an eye. In a cornea there are no blood vessels, it has the big refracting force and borders on a sclera.
• Anterior chamber – the space between an iris and a cornea filled with intraocular liquid.
• Iris which in a form reminds a circle with an opening. The iris consists of muscles which at relaxation or reduction change the pupil sizes. Color of eyes depends on an iris (if on it few pigment cells – it blue and if there is a lot of – hickories). The iris can be compared to the diaphragm in the camera regulating a svetopotok.
• Pupil – an opening in an iris. The sizes of a pupil are influenced by illumination level. The more light, the pupil size is less.
• Crystalline lens – a transparent and elastic lens which can easily change the form, "being almost instantly focused" on something. For this reason the person with good sight can see both with close, and from a long distance. The crystalline lens is located in the special capsule which is kept by a ciliary corbel.
• Vitreous – transparent gel substance which is in back department of an eye. Its main function is keeping fit of an eyeglobe and participation in an intraocular metabolism.
• Retina which consists of nervous cells and photoreceptors, sensitive to light. Receptors of a retina can be divided into two look: sticks and flasks. In them rhodopsin is produced enzyme and energy of light will be transformed to electrical energy of nervous tissue, that is, there is a chemical change. Sticks have a high photosensitivity and allow the person to see well even at weak lighting. Also sticks are responsible for peripheral sight. Flasks, on the contrary, well work only at a large amount of light. Thanks to flasks we can see fine details and distinguish colors.
• Sclera – an external opaque cover of an eyeglobe which in its front part passes into a transparent cornea. Six muscles thanks to which an eye can move are attached to a sclera. Also in it there is a set of vessels and nerve terminations.
• Choroid which is in back department of a sclera. The cover is closely connected with a retina and is responsible for blood supply of intraocular structures. In a choroid there are no nerve terminations therefore at diseases of a cover of people does not feel pain.
• Optic nerve by means of which the image is transferred from nerve terminations to a brain.

Diseases and treatment of eyes

All diseases of eyes can be divided on infectious and noninfectious.

Infectious diseases arise under the influence of different microorganisms: bacteria, viruses, fungi. Important at these diseases to undergo testing of sight and to begin adequate treatment of eyes, otherwise the disease can lead to damage of a cornea and even to sight loss. Conjunctivitis, a blepharitis and barley belong to infectious diseases.

Noninfectious diseases result from an overstrain of sight, genetic predisposition, age changes. The syndrome of a dry eye, a cataract and glaucoma belong to the most widespread noninfectious diseases.

If to reveal noninfectious diseases at early stages, then treatment of eyes has favorable forecasts therefore important time in half a year to undergo testing of sight at the ophthalmologist.

Bags and circles under eyes

In addition to diseases of eyes at people it is often possible to observe existence of circles and baggies lower eyelids. From where they undertake?

The matter is that skin century very gentle and thin. Owing to shortage of oxygen or insufficient blood supply blood in capillaries stagnates and begins to appear through. So there are dark circles under eyes.

Reasons of their emergence set. Circles can be a hereditary factor, feature of a structure of a hypodermic fatty tissue, or to confirm diseases of internals and endocrine system. The stress, a constant sleep debt and chronic fatigue are the most common causes of emergence of circles under eyes.

Hypostases and baggies lower eyelids often develop as a result of the use before going to bed of a large amount of alcohol, tea or coffee. As a result there is a stagnation of circulatory and absorbent vessels and as result – bags on eyes in the mornings.

Besides, baggies lower eyelids can demonstrate bad work of kidneys, existence of allergic reaction, about an inflammation of bosoms of a nose.

For whom is sight check necessary?

• To people with good sight for prevention.
• To people at whom sight falls. In this case comprehensive examination as a result of which the doctor can advise to wear glasses, lenses is necessary or to carry out sight correction.
• To the people carrying contact lenses. As the lens is a foreign body, it can cause undesirable and first hardly noticeable changes which can lead to serious effects (for example, to growing of vessels into a cornea). Besides, check of sight is necessary in order that the doctor could be convinced that the person can carry contact lenses, there are also contraindications to them. In that case the doctor will advise to wear glasses or to make sight correction.
• To the women planning pregnancy. Especially to those women who have a short-sightedness. It will also regularly be necessary to undergo testing during pregnancy. The ophthalmologist can advise to carry out preventive strengthening of a retina by means of barrier laser correction of sight which will significantly reduce risk of its deterioration.
• To people after 40-50 years as in this age category the probability to ache with eye diseases significantly increases (glaucoma, a cataract). That treatment of eyes was successful, it is important to reveal diseases at an early stage.
• To the people having such diseases as a hypertension and a diabetes mellitus.
• Regular check of sight as at them the visual analyzer is at a stage of development and formation is necessary for children, and it is very important to reveal the arising anomalies in development of eyes of the child in time.