Human vision is one of the greatest and at the same time fragile abilities. She needs to be watched all the time. Going to the ophthalmologist should become a periodical activity in the life of every person.
Checking vision in modern ophthalmology
In the distant USSR, the scientist 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. For this, 12 rows of signs were determined: letters and rings with a gap, which, starting from the top row, gradually decrease towards the bottom. From a distance of 5 meters, visual acuity is determined on a scale from 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 one minute apart from each other. 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. The Sivtsev table is just designed in such a wayway to determine this digital indicator.
There are situations when a person's vision is so well developed that its sharpness can be estimated at 1, 2 or 1, 5 and even 3, 0. While with various eye diseases, such as myopia or hyperopia, astigmatism or glaucoma, deviations from the norm can be 0.5 or 0.05.
Visual acuity is often described using percentages. However, it is worth noting that only 100% acuity corresponds to 100% vision. For example, a sharpness index of 0.2 diopters cannot be converted into percentages as 20% vision. This indicator will correspond to 49% of the norm. It is not so easy to convert any indicators to percentages and vice versa. This is what makes Sivtsev's table special - the sizes in the columns on the left and right are already calculated results of the check.
How is visual acuity checked with the Sivtsev table?
The standard set of printed characters of various sizes is lined up in 12 rows. All these are the letters of the Russian alphabet - Sh, B, M, N, K, Y. Each bottom row is smaller letters than the top row. Testing must be done in a well-lit room. It is provided by a special lamp directed at the table and having diffused light. Sivtsev's table of vision is located at a distance of 5 meters from the person being checked. The patient should sit comfortably and, alternately closing the right and left eyes, read the letters from the table. If the person being checked easily names letters up to 10 rows, they consider thatHe 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 row.
Now more details about how the Sivtsev 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 usual position. A special white shield is attached to one eye. Within 3 seconds, the person being checked 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 the signs are named, the person being checked has 100% or 1.0 vision. If one or more signs are not recognized - incomplete visual acuity. To determine visual acuity less than 0, 1 patient gradually approaches the table every 0.5 m until he can determine the signs of the table.
Notation in Sivtsev's table
In addition to the letters of the Russian alphabet, you can see that there are two more columns, which are denoted by the Latin letters D and V. The numbers inThe D-column indicates the distance at which a person whose visual acuity is 100% from the table can easily read the sign on the left. The numbers in the V-column are a numerical characteristic of visual acuity, if this row is readable by a test at a distance of 5 meters.
What other tables are used in ophthalmology?
Since vision is a very important human ability that needs to 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). The letters W, B, M, H, K, Y are used here. They also use the Orlova table for children, where pictures are used instead of letters (asterisk, fungus, horse, kettle, plane, duck, elephant, 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 a duochrome test, which is two halves of a background of different colors: red and green, letters (K, H, W, M, I, B, S) 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 as the same). If, on a red background, the letters of one row are clearer than on green, then there is myopia, on the contrary, farsightedness.
- Astigmatism test is the mosta test called the Siemens star is common. The essence of the test is that a person with normal vision sees lines in the drawing, which, not reaching the center, begin to blur or overlap with each other. In the very center, the lines become clearly visible again.
