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: starting from childhood for admission to kindergarten and school, ending with a job and a medical board for the military enlistment office or obtaining a driver’s license.
In the ophthalmologist’s office, different eye characteristics are checked, including visual acuity. This procedure is called visometry. The method is based on the use of special tables with a set of characters that the patient is invited to consider from a certain distance. In Russia, a standard of 5 meters is set. In medicine, visual acuity is the ability to see and distinguish between two objects nearby. The norm is when a person can see two points from a distance of several meters, with a distance between them of 1.45 mm.
Vision angle
Defines the visible sizes of objects that are nearby, as two separate, not merged points. One subject can be seen by the eye in different ways. It all depends on the distance: when it decreases, the angle of view increases, and, therefore, the size of the image on the retina. An ophthalmologist will tell you about this. At the reception you will be determined by visual acuity. All data will be recorded in a medical record.
The sharpness is determined by the smallest angle of view at which it is still possible to see points close to each other separately. This definition of severity appeared 200 years ago. It is still used in modern medicine. Based on the conclusion drawn by the English scientist Robert Hooke, a table was developed by the German ophthalmologist Snellen. The doctor for the physiological norm, which corresponds to 100% vision, took an angle of view equal to one degree.
Snellen's table consists of 11 rows. Above is a large capital letter, line by line down the size of others decreases. Eye examination is carried out from a distance of 6 meters. The sharpness is calculated as follows: the number of feet to the letters is the numerator, the denominator is the distance that is considered optimal so that a person can read the characters.
Vision examination according to Sivtsev
Each of us remembers Sivtsev’s table in the ophthalmologist’s office, 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 subsequent line. The patient at the reception sees only symbols. In fact, there are auxiliary characters on the table. For example, “D” on the left shows the distance from which a person must distinguish signs. For the lower row it is 2.5 meters, for the upper row - twice as much. On the right, the letter “V” indicates visual acuity in arbitrary units when reading from 5 meters:
- clearly distinguish a row from below - 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 more than the norm from 1.2 to 3.0. With pathological phenomena, myopia, hyperopia, cataracts, astigmatism, glaucoma, the severity can fall to 0.4 and 0.05. The main difference is the distance from which a person clearly sees the object. Suppose, with a visual acuity of 1.0, you can consider the number of the car from 40 meters, with an indicator of 0.4 - from 16 m, not more, otherwise the numbers with letters will merge.
If visual acuity is increased, in everyday life there is little benefit from this phenomenon. Drivers see road signs and other objects early, but the abilities of such people do not differ from those who have normal vision.
Orlova table
Used to diagnose children who cannot read. Here, instead of letters, images are printed. The principle of operation is the same as with the Sivtsev table - the size of the rows decreases downwards. If the child does not recognize the characters from a distance of 5 meters, then visual acuity is low. In this case, the subject is brought closer to the table by half a meter, until he names the images of the upper row correctly. Verification Rules:
- High level of illumination (700 lux).
- The first is the right eye, the second is the left.
- Eyes do not close their eyes, but cover themselves with a shutter.
- In 1-3 lines, errors are unacceptable. From 4-6 lines - one mistake. From 7-10, two are allowed.
- To view the mark is allocated no more than three seconds.
Optotype projectors help greatly simplify and accelerate the determination of visual acuity. The angular value of the character 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. The control here is the recognition of characters separately and the free reading of small text with a note on the distance at which the study was conducted.
What is an eye and how does it work?
Visual acuity is an amazing collaboration of the eye, consciousness and brain. The serious and complex mechanism of the gray matter, providing the transmission, processing and decryption of incoming information from the visual organ, has not been studied so far. We are talking about unique things - the functioning of the eyes with consciousness. They move to the sides, up, down, giving us the widest possible view.
Comparing the eye to the camera, as many are used to, is completely unfair. Yes, the visual organ is a complex optical system consisting of a cornea, lens, vitreous body and moisture. However, optical devices simply capture the image on film, and people recognize information on the retina and, based on this, act.
Interesting Facts
There is a lot of interesting information about the eyes that you may not know:
- Every day for 12 hours a person spends 25 minutes blinking.
- Myopia is a disease of the Japanese. Hieroglyphs are perceived more difficult than letters, so when reading it takes a long time to fix the eye at a short distance. It spoils the eyesight.
- Newborns blink at the age of six months.
- Everyone has gray-blue eyes since birth. Only two years later, real color is acquired.
- Only 2% of people on earth have green eyes.
- The pattern of the iris in a person, like fingerprints, is individual. It can also be used to identify a person.
- A person has 150 eyelashes per eyelid.
- With open eyes you won’t be able to sneeze.
The easiest way to check if visual acuity is normal is to look at the night sky and find the constellation Ursa Major. If another small one is visible in the bucket handle next to the middle star, then the sharpness is normal. In this way, studies were conducted among the ancient Arabs.
Human visual acuity: signs of impairment
How often do we find time to visit an ophthalmologist when our eyes hurt, not to mention preventive purposes? However, deterioration occurs gradually. And a person does not immediately notice that visual acuity is falling.
And successful treatment can only be hoped for in a timely manner to identify a defect. The most common types of disorders are: farsightedness / myopia, astigmatism, presbyopia, cataracts. Symptoms that indicate a decrease in visual acuity are as follows:
- It is difficult to fix the look on objects that were previously well seen. It is important to note which objects began to be seen worse - those that are near, or those that are far away.
- You can clearly see the images right in front of you and it is bad if you take your head a little to the side. This indicates a partial deterioration in the quality of vision.
- Pain, itching, foreign body sensation, dryness, burning sensation may not always be signs of visual acuity, but they often accompany serious eye diseases and indicate an overstrain.
Pathological causes of the development of disorders
Cataract is the most common cause of visual acuity in the world. This is a complete or partial violation of the transparency of the lens, which is located behind the iris and pupil. In youth, in the absence of congenital diseases, the pupil is completely transparent and elastic, passes all rays of light into the eye and instantly focuses on distant and close objects. With age, the lens becomes cloudy and gradually loses the ability to focus objects at different distances. Cataracts are the main reason due to which low vision and blindness develop. After 40 years, every 6 people have this disease, after 80 - each. Symptoms of a cataract:
- Blurred vision, a gradual decrease in severity.
- The appearance of blurry objects.
- Decrease in contrast and color brightness.
- The pupil color turns white.
- Deterioration of visibility far and near.
- The appearance around the bright light sources of blinding halos.
It is possible to improve visual acuity in one way - to conduct a microsurgical operation, during which the clouded lens is replaced with an artificial implant. This is a safe operation, after which the vast majority of patients again gain high visual acuity.
Farsightedness and myopia
Hyperopia (hyperopia) is an ailment in which an image is formed behind the retina. 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. The formation of insufficient focal length.
Astigmatism - a violation caused by a change in the shape of the eyeball . It becomes oval, normally the eye is completely round. Pathology develops, as a rule, in childhood and is accompanied by myopia or farsightedness. If treatment is not started on time, this can lead to a sharp deterioration in visual acuity or strabismus.
Presbyopia
"Disease of short arms" - so this ailment is called differently. Most people suffer from this type of disorder after 40 years. With presbyopia, loss of visual acuity is manifested in difficulty in seeing small objects and typeface near. We have to push the newspaper away, to embroider 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 due to which eye fatigue, headaches, asthenopia develop. All changes associated with presbyopia are caused by age-related processes in the structure of the lens and intraocular muscle.
The most obvious and effective way of correction is reading glasses and progressive lenses, which are used exclusively when working at close range. Surgical intervention is also possible, but it is an extreme measure that carries some risks.
Amblyopia
A pathological disorder called the "weak eye." It makes up a third of all diseases in children associated with the organ of vision. This is a serious illness leading to dangerous complications. The cause of such a violation of visual acuity may be an acquired defect or a congenital anomaly. With amblyopia, one or two eyes worsen at the same time.
Pathology often develops against the background of strabismus, cataracts, astigmatism, hyperopia, clouding of the cornea, nystagmus. Major changes occur in the visual cortex. Information is received in a distorted form, which enters the eyes, visual acuity decreases and is not corrected by glasses.
Auxiliary causes of visual impairment
As additional risk factors that develop pathological processes, there are:
- Long work at the computer.
- Overexertion of the eye muscles.
- Poor lighting at work.
- The presence of visual stimuli (too bright colors or strong lighting, etc.).
- Alcohol abuse, smoking.
Visual acuity: treatment and prevention
To slow down the aging process of the eyes and maintain their health, it is recommended to take complexes containing essential carotenoids, enzymes and antioxidants. For example, the dietary supplement Okuwait® Forte. Its components - lutein, zeaxanthin, vitamins C and E, selenium and zinc, help to cope with eye fatigue, as well as prevent a decrease in visual acuity *.
Massive computerization is the main cause of osteochondrosis and vision problems. No one will refuse a computer, but this is not necessary. It is important to properly distribute the load on the eyes. Ophthalmologists recommend installing the monitor so that the main light source is located on the side, scattering direct glare, and itself is no closer than 50 cm to the eyes.
Sunglasses are not only a stylish accessory of the wardrobe, but also a real means of protection from bright light, which helps to maintain vision. In addition to drug therapy and the glasses that the optometrist will prescribe when a violation is detected, you need to take vitamins for the eyes: A, B, C, E. Special gymnastics, a 15-minute rest several times during the day from the computer will help maintain vision for a long time.
* Instruction for Supplements Okuvayt® Forte