It is impossible to overestimate the importance 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 for admission to kindergarten and school, ending with a job and a medical examination for a military enlistment office or obtaining a driver's license.
In the ophthalmologist's office, various 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 characters that are offered to the patient to consider from a certain distance. In Russia, the standard is 5 meters. In medicine, visual acuity is the ability to see and distinguish between two nearby objects. It is considered normal when a person can see two points from a distance of several meters, with a distance of 1.45 mm between them.
Viewing angle
Defines the visible dimensionsobjects that are nearby, as two separate, not merged points. One object 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 of the eye. The ophthalmologist will tell you about this. At your appointment, your visual acuity will be tested. All data will be recorded in the medical record.
Sharpness is determined by the smallest angle of view at which it is still possible to see points located close to each other separately. This definition of sharpness appeared 200 years ago. It is still used in modern medicine today. 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 the angle of view equal to one degree.
Snellen's table consists of 11 lines. Above is a large capital letter, line by line down the size of others decreases. The vision test is carried out from a distance of 6 meters. Sharpness is calculated as follows: the number of feet to the letters is the numerator, the denominator is the distance that is considered optimal for a person to be able to read the characters.
Vision test according to Sivtsev
Each of us remembers the Sivtsev table in the ophthalmologist's office, which is used by Russian doctors. This simple tool is still very popular today. The Sivtsev table is 12 lines with letters, the size of which decreases with each subsequent line. patient at the receptionsees only characters. 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 bottom row it is 2.5 meters, for the top row it is twice as much. On the right, the letter "V" marks visual acuity in arbitrary units when reading from 5 meters:
- we can clearly see the bottom row – 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 normal from 1.2 to 3.0. With pathological phenomena, myopia, farsightedness, cataracts, astigmatism, glaucoma, visual acuity can drop to 0.4 and 0.05. The main difference lies in the distance from which a person clearly sees the object. For example, with a visual acuity of 1.0, you can see the car number from 40 meters, with an indicator of 0.4 - from 16 m, no more, otherwise the numbers will merge with letters.
If visual acuity is increased, there is little benefit from this phenomenon in everyday life. Drivers see road signs and other objects early, but the ability of such people does not differ from those with normal vision.
Orlova's 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 from a distance of 5 meters the child does not recognize the symbols, then visual acuity is low. In this case, the subject is brought closer to the table by half a meter,until it names the top row images correctly. Validation rules:
- High light level (700 lux).
- The right eye is examined first, the left eye is the second.
- The eyes are not closed, but covered with a shutter.
- Errors in lines 1-3 are not allowed. From 4-6 lines - one mistake. From 7-10 two are allowed.
- No more than three seconds are allowed to view the sign.
Optotype projectors help to significantly simplify and speed up the determination of visual acuity. The angular value of the reproduced character, 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 signs separately and the free reading of small text with a mark on the distance at which the study was carried out.
What is the eye and how does it work?
Visual acuity is an amazing joint work of the eye, consciousness and brain. The serious and most complex mechanism of the work of gray matter, which ensures the transmission, processing and decoding of incoming information from the visual organ, has not yet been studied. We are talking about unique things - the functioning of the eyes together with consciousness. They move sideways, up, down, giving us the widest possible view.
To compare the work of the eye with the camera, as many are accustomed to, is completely unfair. Yes,the visual organ is a complex optical system consisting of the cornea, lens, vitreous body and moisture. However, optical devices simply shoot an image on film, and people recognize the information that has fallen on the retina and, starting from this, act.
Interesting facts
There is a lot of interesting information about 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, you have to fix your eye for a long time at a short distance. It ruins your eyesight.
- Newborns start blinking at the age of six months.
- All have gray-blue eyes from birth. Only after two years is the true color acquired.
- Only 2% of people in the world 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 on each eyelid.
- You can't sneeze with your eyes open.
The easiest way to check if visual acuity is normal is to look at the night sky, find the constellation Ursa Major. If another small star is visible in the bucket handle next to the middle star, 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 the ophthalmologist when the eyes hurt, not to mention preventive purposes? Howeverdeterioration comes gradually. And the person does not immediately notice that visual acuity is falling.
And one can hope for successful treatment only if the defect is detected in time. The most common types of disorders are: farsightedness / nearsightedness, astigmatism, presbyopia, cataracts. Symptoms that indicate a decrease in visual acuity are as follows:
- It's hard to fix your eyes on objects that you used to see well. 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 in front of you and badly if you turn your head a little to the side. This indicates a partial deterioration in the quality of vision.
- Pain, itching, foreign body sensation, dryness, burning may not always be signs of impaired visual acuity, but often accompany serious eye diseases and indicate overexertion.
Pathological causes of the development of disorders
Cataract is the world's most common cause of reduced visual acuity. 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 the 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 cause of low vision and blindness. After 40 years, everyone has 6a person has such a disease, after 80 - in everyone. Cataract symptoms:
- Blurred vision, gradual decrease in acuity.
- The appearance of blurry objects.
- Reduce contrast and color brightness.
- The color of the pupil turns white.
- Deterioration of visibility far and near.
- The appearance of blinding halos around bright light sources.
Improvement of visual acuity can be done in one way - to perform 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 regain high visual acuity.
Hyperopia and myopia
Farsightedness (hypermetropia) 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 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, normally the eye is absolutely round. Pathology develops, as a rule, in childhood and is accompanied by myopia or hyperopia. If treatment is not started on time,can lead to a sharp deterioration in visual acuity or strabismus.
Presbyopia
"Disease of short hands" - this is how this disease is called differently. Most people suffer from this type of disorder after the age of 40. With presbyopia, loss of visual acuity is manifested in the difficulty of seeing small objects and type close up. I have to move the newspaper away, do embroidery at a distance.
Symptoms and causes of presbyopia
The first thing that should alert a person is the blurring of objects at close range. You have to strain your eyes to adjust the clarity of the image, which causes eye fatigue, headaches, and asthenopia. 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 to correct - reading glasses and progressive lenses, which are used exclusively when working at close range. Surgery is also an option, but it is a last resort and comes with some risks.
Amblyopia
A pathological disorder referred to as the "weak eye". It makes up one third of all existing diseases in children associated with the organ of vision. This is a serious disease, leading to dangerous complications. The cause that caused such a violation of visual acuity may be an acquired defect or a congenital anomaly. With amblyopia, one or both eyes deteriorate at the same time.
Pathology often develops against the background of strabismus, cataracts, astigmatism, farsightedness, 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 drops 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.
- Strain of the eye muscles.
- Poor lighting in the room at work.
- 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 keep them he althy, it is recommended to take complexes containing essential carotenoids, enzymes and antioxidants. For example, a biologically active food supplement Okuvayt® Forte. Its components - lutein, zeaxanthin, vitamins C and E, selenium and zinc, help to cope with eye fatigue, as well as prevent visual acuity reduction.
Massive computerization is the main reason for the development of osteochondrosis and vision problems. No one will give up the 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 wardrobe accessory, but also a real means of protection frombright light to help preserve vision. In addition to drug therapy and glasses that an ophthalmologist will prescribe if a violation is detected, you need to take vitamins for the eyes: A, B, C, E. Special gymnastics, 15-minute rest several times during the day from the computer will help maintain vision for a long time.
Dietary supplement instructions for food Okuvayt® Forte
