According to the World Health Organization，the problem of hearing impairment affects about 650 million people—this is every ninth inhabitant of the planet，and more than half of them suffer from disabling hearing loss.More than 13 million people with hearing impairment live in Russia，including more than 1 million children ^{[ 1 ] ．}In the study of patients with hearing impairments，visual defects were found in more than a quarter of cases，in the structure of which various refractive errors prevailed ^{[ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ] ．}Vision plays a central role in the development of newborns and children，and early and visual disorders can affect the formation of motor skills，cognitive functions，social and communicative abilities and the formation of social relationships ^{[ 10 ] ．}It should be noted that when assessing visual functions in children，one of the main diagnostic indicators is the acuity of central vision.The subjective component，which presupposes the verbal participation of children in the assessment of optotypes，complicates the assessment of visual acuity in deaf-mute children.

As is known，the world standard for determining visual acuity in preschool children is the Lea chart.On the territory of the Russian Federation and other post-Soviet countries，it is customary to use the Orlova chart for visometry in children of this age group，which is essentially an analogue of the Lea chart.The Orlova chart is a single sheet of paper with a 580×520 cm format，which depicts optotypes (drawings) of various sizes in the form of a star，mushroom，Christmas tree，circle，chicken，car，horse，airplane，elephant，motorcycle.The optotypes are grouped into two sheets：there are 5 rows in the left，and 7 in the right.The optotypes in the rows from top to bottom gradually decrease in size.Visual acuity is marked opposite each row：in the left column from 0.1 to 0.3，in the right column from 0.4 to 1.0.With a visual acuity of 0.1－0.2，there are three optotypes in each row，at 0.3-four optotypes，at 0.4－0.5-five，at 0.6－0.7-six，at 0.8－0.9-seven，at 1.0-eight.The background of the chart is white，and the letters are black ( Figure 1 ) ^{[ 11 , 12 , 13 , 14 , 15 , 16 ] ．}

The most common method of visometry in patients with hearing impairments and the mute remains a study using the Golovin diagram ( Figure 2 )，which shows Landolt rings with breaks directed up，down，left or right.On the territory of the Russian Federation and other post-Soviet countries，various methods are used for this：printed Golovin-Sivtsev chart，transparent devices and projectors.The Golovin-Sivtsev chart (Russian：Таблица Головина-Сивцева) is a standardized chart for testing visual acuity，which was developed in 1923 by Soviet ophthalmologists Sergei Golovin and D．A.Sivtsev.In the Union of Soviet Socialist Republics，it was the most common chart of its kind，and as of 2022 its use is still widespread in several post-Soviet states.The chart consists of two parts with 12 rows each，representing visual acuity values between 0.1 and 2.0.The left part consists of series of the Cyrillic letters Ш，Б，М，Н，К，Ы，and И in a definite order，and the right part of the chart consists of a series of Landolt C symbols.The width of each character is equal to its height，and the contours have standard 1/5 gaps of the overall size.The value D，indicated to the left of each row，gives the distance in meters from which a person with a visual acuity of 1.0 can read the corresponding row.The value V，indicated to the right，gives the minimum visual acuity needed to read the row from a distance of 5 meters.The first row contains symbols 70 mm in size (V＝0.1)；the second row，35 mm；the bottom third row，7 mm (V＝1.0)；the bottom row，3.5 mm (V＝2.0)．Black and white pattern identification at 1 arcminute angle is considered to be visual acuity of 1.0，which is around 1 mm per 3.44 m distance.A character 7 mm in size has 1.4 mm pattern gaps，so over the 5 m view distance it gives an angle of around 1 arcminute (atan(0.007/5/5)≈0.963') ( Figure 2 ) ^{[ 17 , 18 ] ．}

Our own clinical experience testifies to certain disadvantages of visometry according to the Golovin chart in children，due to the difficulty of correctly assessing the orientation of Landolt rings due to insufficient development of left-right orientation.