Visual acuity check: features, table options

"Close your right eye, then the left one ..." - it is this phrase that usually begins the examination of the eyes of an ophthalmologist. The patient should refer to the letters, figures or figures indicated by the doctor, which become smaller with each row.Each of us at least once in life underwent such a check: preventive, for example, before entering school, or forced, in case of manifestation of signs of reduced visual acuity.

Why do I need a vision test?

One of the key factors that help to keep eyesight and avoid eye diseases is timely prevention.

Today the whole world spends most of the time at the computer, in front of the TV. And this affects the eyesight not in the best way.Statistics show a clear decrease in vision in the third part of children even during school-age.

If the eye disease is not detected in time, complications leading to complete or partial blindness will occur.

People working indoors under artificial lighting should regularly do gymnastics for the eyes, frequent breaks to relax the eyes, and try to blink more often.

The second important factor is the timely diagnosis of eye diseases. It is proved thatIn time, the treatment begun in 80% of cases helps to avoid further problems with vision. And if you suddenly noticed that the letters "float" before your eyes, you feel a burning sensation in your eyes, and your eyes water all the time, without delay, run to the oculist.

The doctor will check the visual acuity with the help of a special table, identify the problem and prescribe the necessary medication or one of the forms of vision correction.

Can I check my visual acuity myself?

At home, it is only possible to check the visual acuity. What is visual acuity?

This is the ability of the eye to distinguish two points with a minimum distance between them. The result is considered good if a person sees them with an angular resolution of one minute.

Normal visual acuity is considered to be a value of, (100%). The indicator of visual acuity in a person can be beyond the norm, for example or,. However, most people have indicators below the norm or or, 5.

Existing tables for verification

Despite the emergence of innovative survey technologies, simple test diagnosis in the form of tables is still the most popular among ophthalmologists.What do ophthalmologists use to accurately test how well a person sees?

Check the visual acuity of the special tables with optotypes. There are several such tables, we will consider each of them separately.

Sivtsev's table

In the table Sivtseva, which is used by ophthalmologists since Soviet times, contains 12 lines with capital letters. Their size decreases from row to line in the direction from top to bottom.On the left side of each line is the distance D (in meters) from which a normally seeing person can see and correctly indicate letters (50 meters for the upper row, meter for the bottom row).On the right side of each line is the value V (in conventional units): this is the visual acuity when reading letters from a distance of 5 meters (if the eye sees only the top row, if the lower row is visible). Vision is considered normal (,) if a person sees with each eye the tenth line from a distance of 5 meters.

If a person from 5 meters does not recognize the letters of the upper row, the verified is approached to the table and every meter is asked to name the letters until he calls the letters of the upper row correctly.

The value is calculated using the following formula:

• V = d / D
• V - visual acuity;
• d is the distance from which the study is conducted;
• D is the distance at which the eye sees the given row.

It is noteworthy that only 7 letters of the Russian alphabet are used in the table: Sh, B, M, N, K, Y, I. It is generally accepted that an eye with normal visual acuity (,) can see separately two distant points if the angular distance between them is equal to one angular minute.At a distance of 5 meters, this figure corresponds to 5 millimeters: this should be the distance between the chopsticks of the letter "Ш" in the tenth line on the check table.

It is proved that for the human eye infinity begins at a distance of 5 meters. That's why this distance has become a reference point for testing visual acuity.

Examination of vision according to the Sivtsev table is called visometry. The test cloth is illuminated by two fluorescent lamps in such a way that the illumination is 700 lux. The lower point of the luminaire is 120 cm above the floor.

Eyes are checked alternately: first left, then right. In this case, the second eye is covered by a special shutter. The eyelids of both eyes are open, the head is held straight.All the lines located after the tenth row are intended for people with indicators above the norm: 150 or 200%.Also these series of letters are used in the case if the office for testing the vision is small, and it lacks the required length of 5 meters.

The visual acuity is considered complete if the verified person named absolutely all the letters in the series. The assumption of several errors in the examined person testifies to incomplete visual acuity.

If the final indicator is less, then the doctor determines the presence of myopia (myopia) in the patient. The result, surpassing the line, indicates the presence of farsightedness in the patient.

Normal visual acuity is called emmetropia.

The Snellen table

The Snellen chart is the most common in the world. The table is named so in honor of the Dutch ophthalmologist Hermann Snellen, who developed it in 1862.It contains the lines of uppercase Latin letters, which are called test types.The value of the letters, as in the previous table, decreases from row to line in the direction from top to bottom.

The top line of the table contains the largest letters. A person with normal vision can call them from a distance of 60 meters.

All subsequent lines of the person with good eyesight can also easily read from distances of 36, 24, 18, 12, 9, 6 and 5 meters. The monitor sits at a distance of 6 meters from the table, closes one eye and begins to read the letters from this table.

If he can read only the lines above the line that a person with normal vision can easily read from a distance of 12 meters, then the acuity of his vision is expressed as 6/12. This means that normal visual acuity is considered 6/6. The smaller letters of this table can be used to test a person's near vision.

Orlova's Table

This table is designed to test vision in children who can not read.

The principle of checking the eyes of the Orlova table as a whole is similar to the previous one, only images are used instead of letters. The size of lines with images decreases from top to bottom. Visual acuity is defined in the same way as in the Sivtsev scheme. The norm is considered if the child sees the tenth line from a distance of 5 meters with each eye. If he does not recognize the symbols or figures of the upper row from the specified distance, he begins to approach the table every half a meter and ask what he sees the images.This continues until the child correctly identifies the symbols and pictures of the upper row.

Golovin's Table

Golovin's test of vision is usually used simultaneously with the Sivtsev table.Ophthalmologist Sergei Selivanovich Golovin made it out of ripped rings, lined up in 12 rows.Each row contains rings of reduced size. In the first row there are rings equal in diameter to 70 mm, in the latter mm. Visual acuity is calculated by the same formula as in the case of the Sivtsev table.

Alternative ways of testing eyesight

Now replaced by the above visual inspection tables come transparent devices.The test symbol is not shown on the paper sheet, but on the milk glass behind which the light source is placed.

Modern oculists also use the collimator method when checking the sight, when the letter or sign is next to each other, but they are seen at infinity.Recently, in clinics you can find special projectors with excellent backlighting and clear image transmission.

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conclusions

So, a regular check of vision is one of the most important preventive measures for preventing eye diseases.A timely examination of one of the tables presented in this article will help to identify problems with vision and avoid complications that can lead to blindness.