Volume 35 #3

Contents

1. AN OVERVIEW OF THE VISUAL ACUITY ASSESSMENT. 1. PRIMARY MEASURES AND VARIOUS NOTATIONS
2. Analysis of the functions of binocular visual systems in schoolchildren
3. Oculomotor activity in solving visual cognitive tasks under different time conditions
4. Discrimination of rippled sound signals with overlapping additional signals
5. THE ROLE OF PROJECTIVE TRANSFORMATIONS IN IMAGE NORMALIZATION

The paper presents a brief overview and analysis of various approaches to assessment of visual acuity (VA). It aims to explicate the reasons of disparity of opinions among experts on the methods of assessing VA by reflecting on advantages and shortcomings of individual methods and the corresponding VA notations. In the course of time, the number of methods and procedures of VA assessing was increasing; they became more diverse and complex. In parallel, the number of professionals who assessed VA for different purposes was also increasing. Such state of affairs has resulted in certain difference between the views on the interpretation of outcomes of VA measurement and to introducing different VA notations. Currently, however, reaching a consensus among experts is becoming crucial since numerous research projects require cooperation of professionals from different areas and, also, involve international collaboration. In search of the common ground for the consensus and the unified terminology and notation, it is reasonable to appraise the crux of the VA assessment problem and, as well, rationales for a great variety of current viewpoints on solving the problem in practice. An overview of contemporary approaches to assessment of VA points out that there exists the sole primary measure of VA that can be obtained by a direct measurement and expressed by the base unit of spatial metrics – the minimum angle of resolution (MAR, αm) – defined as the minimum angle at which two points are just perceived as separate. There exists one more measure, in place of MAR, – the critical spatial frequency (Fc) – which can be gauged directly when one employs gratings of varying spatial frequency to estimate the maximum (critical) spatial frequency above which periods of a grating can no longer be distinguished. It is reasonable to consider all other VA measures as secondary, or derived, since these are calculated as functions of α m. Introduction of various secondary measures, such as Snellen fraction, decimal units, logMAR, visual efficiency (VE), visual acuity rating (VAR), and others, was stipulated by the demand of developing alternative notations of VA, which are more convenient and comprehensible, than αm, for practitioners who assess VA in applied areas for various purposes, such as screening, diagnostics, monitoring, rehabilitation, disability determination, population statistical evaluations, designing of new VA tests, etc. We conclude that, in view of substantial differences of the purposes, requirements and criteria among experts in various areas, the quest for a unique measure of VA, which would be optimal in all contexts, is probably unresolvable, as is establishing of the ultimate, “gold standard”, practical method of VA assessment.

Key words: human vision, visual acuity, scales of measurement, MAR, Snellen fraction, decimal units, logMAR, VAR

DOI: 10.31857/S0235009221030033

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