Visual acuity is what is in medicine?

It is impossible to overestimate the value that vision has for a person. With it, we get the lion's share of information about the things around us. Several times we are faced with the need to conduct a study of visual acuity: from childhood itself to admission to kindergarten and school, ending with a job placement and medical examination for the military commissariat or obtaining a driver's license.

In the office of the ophthalmologist, the different characteristics of the eyes are checked, including visual acuity. This procedure is called visometry. The method is based on the use of special tables with a set of symbols that are offered to the patient from a certain distance. In Russia, a standard of 5 meters is set. In medicine, visual acuity is the ability to see and distinguish two nearby objects. The norm is when a person can see two points from a distance of several meters, with a distance of 1.45 mm between them.

Vision angle

Defines the visible sizes of objects that are next to each other, as two separate, rather than merged, dots. One object can be seen in the eye in different ways. Everything depends on the distance: when it decreases, the angle of view increases, and, hence, the size of the image on the retina of the eye. About this you will tell an ophthalmologist. At the reception you will be held a definition of visual acuity. All data will be recorded in a medical record.

The sharpness determines the smallest angle of view, in which it is still possible to see the points close to each other separately. This definition of acuity appeared 200 years ago. It is used in modern medicine so far. Based on the conclusion drawn by the English scientist Robert Hooke, the table of the German ophthalmologist Snellen was developed. Doctor for the physiological norm, which corresponds to 100% vision, took a viewing angle equal to one degree.

The Snellen table consists of 11 lines. On top is a large uppercase letter, row down the size of the other decreases. The vision test is performed from a distance of 6 meters. The sharpness is calculated as follows: the number of feet to letters is the numerator, the denominator is the distance that is considered optimal so that the person can read the symbols.

Vision for Sivtsev

Each of us remembers the Sivtsev table in the office of the oculist, which is used by Russian doctors. This simple tool is still very popular. Sivtsev's table is 12 lines with letters, the size of which decreases with each successive line. The patient at the reception sees only the symbols. In fact, there are auxiliary letters on the table. For example, "D" on the left shows the distance from which a person should distinguish signs. For the lower row it is 2.5 meters, for the upper row it is twice as large. On the right, the letter "V" marks the visual acuity in conventional units when reading from 5 meters:

• A number of the bottom - 2.0;
• Only the top row is visible - 0.1;
• Every tenth line is visible from a distance of 5 meters - 1.0 (normal vision).

Visual acuity is an indicator that can be higher than the norm from 1.2 to 3.0. With pathological phenomena, myopia, hyperopia, cataract, astigmatism, glaucoma, acuity can drop to 0.4 and 0.05. The main difference lies in the distance from which a person clearly sees the object. Let's say, with a visual acuity of 1.0, you can consider the car number from 40 meters, at the rate of 0.4 - from 16 m, no more, otherwise the numbers with the letters will merge.

If visual acuity is elevated, in everyday life the benefits of this phenomenon are few. Drivers see early road signs and other objects, but the abilities of such people do not differ from those who have normal vision.

Orlova Table

Used to diagnose children who can not read. Here, instead of letters, images are printed. The principle of operation is the same as with the Sivtsev table - the size of the lines decreases downward. If the child does not recognize the symbols from a distance of 5 meters, then visual acuity is low. In this case, the subject is brought closer to the table by a half-meter, until he calls the images of the upper row correctly. Inspection rules:

1. High level of illumination (700 lux).
2. The first is examined the right eye, the second - the left one.
3. Eyes are not squeezed, but covered with a shutter.
4. In 1-3 lines, errors are not allowed. From the 4th to the 6th line, there is one mistake. From 7-10 two are allowed.
5. It takes no more than three seconds to view the sign.

Projectors of optotypes greatly simplify and accelerate the definition of visual acuity. The angular value of the symbol being played, regardless of the distance to the screen, remains unchanged. It is important that the subject and the device are at the same distance from the screen.

To determine visual acuity in bedridden patients, a special table is used, calculated at a distance of 33 cm from the eye. Control here is the recognition of characters individually and free reading of small text with a note on the distance at which the study was conducted.

What is the eye and how does it work?

Visual acuity is an amazing joint work of the eye, mind and brain. A serious and complex mechanism of operation of gray matter, which ensures the transfer, processing and deciphering of incoming information from the visual organ, has not been studied to this day. It is about unique things - the functioning of the eyes with consciousness. They move sideways, up and down, giving us the widest possible overview.

Compare the work of the eye with a camera, as many people are used to, is completely unfair. Yes, the visual organ is a complex optical system consisting of the cornea, the lens, the vitreous humor and moisture. However, optical devices simply remove the image on the film, and people recognize the information on the retina and, based on this, act.

Interesting Facts

There are a lot of interesting information about the eyes, which, perhaps, is not known to you:

• Every day for 12 hours a person spends 25 minutes blinking.
• Myopia is a disease of the Japanese. Hieroglyphs are perceived harder than letters, so when reading it takes a long time to fix the eye for a short distance. This spoils the eyesight.
• Newborns start blinking at the age of six months.
• Everyone has a gray-blue eye. Only in two years the real color is acquired.
• Only 2% of people on earth have a green eye color.
• The pattern of the iris of the eye in a person, like fingerprints, is individual. On it, too, you can identify the person.
• A person has 150 eyelashes in each century.
• Do not sneeze with your eyes open.

The easiest way to check if the visual acuity is normal is to look at the night sky, to find the constellation Ursa Major. If in the bucket handle next to the middle star another small one is visible, then the sharpness is normal. In this way, studies were carried out among the ancient Arabs.

Human visual acuity: signs of impairment

How often do we find time to visit an ophthalmologist, when the eyes hurt, not to mention preventive purposes? However, the deterioration is gradual. And the person does not notice immediately that the visual acuity is falling.

And you can hope for successful treatment only if the defect is detected in time. The most common types of violations are: hyperopia / myopia, astigmatism, presbyopia, cataract. Symptoms that reduce visual acuity are:

1. It is difficult to fix a glance at objects that used to be seen before. It is important to note which objects are seen worse - those that are near, or those that are far away.
2. You can clearly see the images directly in front of you and it's bad if you move your head slightly to the side. This indicates a partial deterioration in the quality of sight.
3. Pain, itching, foreign body sensation, dryness, burning can not always be signs of visual impairment, but often accompany serious eye diseases and talk about overexertion.

Pathological causes of the development of violations

Cataract is the most common cause in the world for reducing visual acuity. This is a complete or partial violation of the transparency of the lens, which is behind the iris and pupil. In youth, in the absence of congenital diseases, the pupil is completely transparent and elastic, lets in the eye all the rays of light and instantly focuses on distant and intimate objects. With age, the crystalline lens becomes turbid and gradually loses the ability to focus objects at different distances. Cataracts are the main reason for the development of vision and blindness. After 40 years, every 6 people have this condition, after 80 - each. Symptoms of cataract :

• Blurred vision, gradual reduction in severity.
• The appearance of blurriness of objects.
• Reducing the contrast and brightness of the color.
• The color of the pupil becomes white.
• Deterioration of visibility far and near.
• The appearance around the bright light sources of blinding halos.

Improve visual acuity, perhaps in one way - to conduct a microsurgical operation, during which the clouded lens is replaced by an artificial implant. This is a safe operation, after which the absolute majority of patients again acquire a high visual acuity.

Hyperopia and myopia

Hyperopia (hyperopia) is a malaise in which the image forms behind the retina of the eye. The reason for the development of this pathology lies in the short eye axis or the poor refractive power of the lens, which is not enough to create a normal focal length.

Myopia (myopia) - the creation of an object in front of the retina. The disease is refractive and axial. In the first case, the refractive power of the lens or cornea increases, in the second - the length of the eye. Formation of insufficient focal length.

Astigmatism - a violation caused by a change in the shape of the eyeball. It becomes oval, the eye is perfectly round in norm. Pathology develops, as a rule, in childhood and is accompanied by myopia or farsightedness. If you do not start treatment in time - this can lead to a sharp deterioration in visual acuity or strabismus.

Presbyopia

"The disease of short arms" - so this illness is called in another way. Most people suffer from this type of violation after 40 years. With presbyopia, the loss of visual acuity manifests itself in the difficulty of visibility of small objects and the font near. We have to move the newspaper away, embroider it from a distance.

Symptoms and causes of presbyopia

The first thing that should alert a person is the blurriness of objects at close range. You have to strain your eyes to adjust the clarity of the image because of what develops eye fatigue, headaches, asthenopia. All the changes associated with presbyopia are caused by age processes in the structure of the lens and the intraocular muscle.

The most obvious and effective method of correction is reading glasses and progressive lenses, which are used exclusively when working at close range. Surgical intervention is also possible, but this is an extreme measure that involves some risks.

Amblyopia

Pathological disorder, called a "weak eye". A third of all the existing diseases in children associated with the organ of vision. This is a serious illness, leading to dangerous complications. The cause, which caused such a violation of visual acuity, may be acquired defect or congenital anomaly. With amblyopia, one or two eyes deteriorate at the same time.

The pathology often develops against the background of strabismus, cataracts, astigmatism, hyperopia, corneal opacity, nystagmus. The main changes occur in the visual cortex of the brain. Information is received in a distorted form, which enters the eyes, visual acuity falls and is not corrected by glasses.

Auxiliary causes of vision impairment

As additional risk factors that develop pathological processes, distinguish:

1. Long work at the computer.
2. Overexertion of the eye muscles.
3. Poor lighting of the room when working.
4. The presence of visual stimuli (too bright colors or strong lighting, etc.).
5. Abuse of alcohol, smoking.

Visual acuity: treatment and prevention

Mass computerization is the main cause of osteochondrosis and vision problems. No one will give up the computer, but it's not necessary. It is important to properly distribute the load on the eyes. Ophthalmologists recommend installing the monitor so that the main source of light is located on the side, scattering direct glare, and he was not closer than 50 cm to the eyes.

Sunglasses are not only a stylish accessory for the wardrobe, but also a real means of protecting against bright light, helping to preserve sight. In addition to drug therapy and glasses that the ophthalmologist prescribes for the detection of a disorder, you need to take vitamins for the eyes: A, B, C, E. Special gymnastics, a 15-minute rest several times a day from the computer will help to keep the vision for a long time.