Human vision is one of the greatest and at the same time fragile abilities. You need to watch her all the time. A trip to an ophthalmologist should be a periodic activity in the life of every person.
Eye examination in modern ophthalmology
In the distant USSR, scientists Sivtsev invented an indispensable tool for modern ophthalmology, which in honor of the author was called the "Sivtsev table." This technique is used to determine visual acuity. To do this, 12 rows of signs were defined: letters and rings with a gap, which, starting from the top row, to the bottom, gradually decrease. From a distance of 5 meters, visual acuity is determined on a scale of 0.1 to 2.0.
What is visual acuity and how is it checked using the Sivtsev table?
Visual acuity is the ability of the human eye to distinguish between two points located at a certain distance from each other. Current standards say that an eye with 100% vision can distinguish between two points that are separated from each other by an angular distance of one minute. Thus, visual acuity can be described as the ability to clearly see and describe such vigilance of the eye with a digital indicator of 100% or 1.0. Sivtsev’s table is just designed in such a way as to determine this digital indicator.
There are situations when a person’s vision is so well developed that his acuity can be estimated at 1.2, 1.5, or even 3.0. While with various diseases of the eye, such as myopia or hyperopia, astigmatism or glaucoma, deviations from the norm can be 0.5 or 0.05.
Often visual acuity is described using percentages. However, it is worth paying attention that only a 100% indicator of acuity corresponds to 100% vision. For example, an acuity index of 0.2 diopters cannot be translated into percentages as 20% vision. This indicator will correspond to 49% of the norm. It is not so easy to translate any indicators into percentages and vice versa. This is what makes the Sivtsev’s table special - the sizes in the columns on the left and on the right are already calculated test results.
How is visual acuity checked by a Sivtsev table?
The standard set of printed signs of various sizes is arranged in 12 rows. All these are letters of the Russian alphabet - W, B, M, N, K, Y. Each bottom row is a smaller letter than the top. Checking should be done in a room with good lighting. It is provided with a special lamp aimed at the table and having diffused light. At a distance of 5 meters from the test is a table of view of Sivtsev. The patient should sit comfortably and, alternately closing the right and left eye, read the letters from the table. If the person tested easily calls letters up to 10 rows, they believe that he has 100% vision. If he stops at any of the above rows, then visual acuity is determined by the indicators in the right row of the table.
The patient can be located closer than 5 meters from the table, but in this case, a special formula will be used to determine the severity:
V = d / d
V in this formula is the value that we need to determine, namely, visual acuity; d is the distance at which the patient is from the table; D - the distance at which the patient distinguishes the symbols of a certain series.
Now in more detail about how the Sivtsev's table should be located. It is placed between two fluorescent lamps, so that the illumination reaches 700 lumens. The bottom edge of the table should be at a height of 120 cm from the floor. The patient sits comfortably, holds his head straight, the eyelids of both eyes are open in the normal position. A special white shield is attached to one eye. Within 3 seconds, the testee is shown the letter that he must name. At the same time, they start from the bottom row and gradually rise to larger signs. If all signs are named, the person being tested has 100% or 1.0 vision. If one or more characters are not recognized, incomplete visual acuity. To determine visual acuity of less than 0.1, the patient gradually approaches the table every 0.5 m until he can determine the signs of the table.
Designations in the Sivtsev table
In addition to the letters of the Russian alphabet, you can notice that there are two more columns that are indicated by the Latin letters D and V. The numbers in the D-column indicate the distance at which a person whose visual acuity is 100% can easily read the left sign. The numbers in the V-column are a numerical characteristic of visual acuity, if this series is readable at a distance of 5 meters.
What other tables are used in ophthalmology?
Since vision is a very important human ability that must be maintained in good condition, there are a number of tests used in ophthalmology that allow you to show a real picture of the condition of the eyes.
- Checking visual acuity - for this, the Sivtseva table was created (as it is called in some sources). Here the letters W, B, M, N, K, S are used. They also use the Orlova table for children, where instead of letters pictures are used (asterisk, fungus, horse, teapot, airplane, duck, elephant, toy car, Christmas tree).
- Checking the contrast of vision - for this, the Golovin table was created. It uses 4 types of optotypes - rings with a gap in one of the 4 sides
- Checking myopia and farsightedness - use the duochrome test, which is two halves of the background in different colors: red and green, the letters (K, H, W, M, I, B, Y) are located on this background. As a result of the test, it is determined whether the vision is normal (the eyes see the letters on both backgrounds the same). If on a red background the letters of one row are sharper than on a green one, then myopia takes place, on the contrary - farsightedness.
- Astigmatism Test - The most common test is called the Siemens Star. The essence of the test is that a person with normal vision sees lines in the picture that, not reaching the center, begin to blur or overlap. In the very center of the line, they again become clearly visible.