Each person faced situations when, at an appointment with an ophthalmologist, they had to close one eye and name the letters from the table in front of them. Probably, many wondered why they are located that way. This was told by the ophthalmologist Marina Ilyukhina.
The purpose of the tables is to help the doctor assess the visual acuity of the patient. They are called optotypes. These are special blanks with the image of letters or numbers. For children, drawings in the form of Christmas trees or other images can be used. When evaluating symbols, doctors take into account the following main parameters.
- minimally visible;
- Simply recognizable.
“Letters and small symbols, as well as figures, can act as optotypes. They stand in rows: larger ones on top, smaller ones below.the specialist said.
She also notes that the national visual acuity table appeared in 1928. It is called the “Sivtsev Table” and is a variant of the Snellen table.
It is based on seven letters of the Russian alphabet. They are different in size, but the same in width and height. The following letters are used – W, B, M, N, K, Y, I. There are 12 lines in such a table. Each line corresponds to an indicator of visual acuity – it is written on the right side of the board and is indicated by the symbol V.