[Visual acuity assessment: historical overview and current trends]

[Visual acuity charts in the Russian Empire, the USSR and modern Russia]

Visual acuity is the quantitative parameter of the visual system characterizing its functional spatial resolution. Special test charts are commonly used for visual acuity assessment. The development of foreign tests for visual acuity is comprehensively covered in the literature, while the history of improving visual acuity charts in modern Russia, the USSR, and in the territory of the Russian Empire is only considered fragmentarily. In particular, there are almost no mentions of D.A. Sivtsev's work on proper letter-signs selection, and of A.A. Kryukov's tests. The purpose of this article is to review the history of developing visual acuity assessment methods in the Russian Empire, the USSR and modern Russia. One of the first sets of tests for visual acuity assessment available in the Russian Empire was developed by A.A. Kryukov; it was republished several times, but some criticism of the test can be encountered in the literature of that period. Subsequently, a task of developing a more accurate method was presented, which was implemented in the form of several editions of the visual acuity charts by D.A. Sivtsev and S.S. Golovin. The authors put a lot of effort into selecting the letters for the most reliable results of visual acuity assessment, excluded some unsuccessful characters (Cyrillic letters 'Ж' and 'Ю') and changed the size levels of the chart (the lines corresponding to the visual acuity levels of 1.25 and 1.5 were substituted by 1.5 and 2.0). Around the same period, A. Holina's chart appeared in print, but due to its poor structure the chart did not gain popularity, although it had a number of advantages. The review also considers some modern tests: the RORBA chart (named after the authors Rosenbaum, Ovechkin, Roslyakov, Bershanskiy, Aizenshtat), the vanishing optotypes by S.A. Koskin et al., the three-bar optotypes by the Institute for Information Transmission Problems (IITP), and the "Quartet" optotypes. Despite a large number of options, the search for the best method of measuring visual acuity for various medical and scientific tasks continues.

[Comparison of visometry by Sivtsev and ETDRS charts]

Most foreign authors currently recommend the protocol and charts developed for the Early Treatment Diabetic Retinopathy Study (ETDRS) as the gold standard for evaluation of visual acuity (VA) in clinical trials and studies. Not every medical facility has equipment required for performing visometry by that method, while Sivtsev tables are found universally.

OBJECTIVE

To compare ETDRS and the more common Sivtsev visometry methods.

MATERIAL AND METHODS

The study included 100 volunteers - students of the Sechenov University. All participants were examined for VA in both eyes without correction using ETDRS "R" chart and Sivtsev table. Visometry with "R" ETDRS chart involved calculation of the number of named letters, then the number was translated into logarithmic notation by the conventional method. Sivtsev visometry findings were translated into logarithmic notation by two methods: first - standard, line-by-line, second - experimental, letter-by-letter. Subjects were divided into two groups: high VA (higher than 0.4 in decimal scale) and low VA - everyone else.

RESULTS

The best agreement with ETDRS was found in letter-by-letter method of Sivtsev table interpretation, especially in the group with high VA with the lowest 95% limits of agreement (LoA) of ±0.157 logMAR, or 8 letters on ETDRS. Clinically significant were also LoA in comparison of ETDRS with line-by-line calculation method in the group with high VA and in letter-by-letter method without dividing groups by VA.

CONCLUSION

The use of Sivtsev table in standardized multicenter studies is only reasonable when the ETDRS charts are unavailable.