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2. V. V. Volkov, Yu. E. Shelepin, V. B. Makulov, L. N. Kolesnikova, and V. N. Pauk, “New letter-based tests for measurement of visual acuity,” Oftal’mol. Zh., 5, 294–296 (1987).
3. V. V. Volkov, Yu. E. Shelepin, V. B. Makulov, L. N. Kolesnikova, and V. N. Pauk, Methods for Visual Contrast Perimetry: Methodological Recommendations and Atlas [in Russian], Moscow (1988), p. 14.
4. S. S. Golovin, Clinical Ophthalmology [in Russian], State Press, Moscow, Leningrad (1923).
5. S. S. Golovin, Russian Isognostic Tables for Studies of Visual Acuity [in Russian], State Press, Moscow, Leningrad (1925).