Shortened Measurement Time of Functional Visual Acuity for Screening Visual Function

Abstract

The functional visual acuity test which is the average of the visual acuities measured during a specific time frame (standard, 60 seconds) has been used recently to assess the visual function in various conditions. The availability of a shorter version of the functional visual acuity test promises to be patient friendly in that it is a simple screening test performed in a shorter period of time than the standard test. The results of measurements of the FVA test between the 30-second measurement time (short-version FVA test) and the standard 60-second measurement are compared, and the feasibility of the short-version FVA test instead of the standard FVA test is investigated. Twenty-eight healthy volunteers (25 men and 3 women) were enrolled in this prospective observational study. All subjects underwent measurement of the binocular distance-corrected visual acuity and the binocular distance-corrected FVA with the 60-second and 30-second measurement times. The interchangeability of the corrected-distance FVA, maximal VA, visual maintenance ratio, and average response time in the short-version and the standard FVA tests was evaluated using the Bland-Altman method, and the results showed agreements of the two tests except for the minimal VA. The short-version FVA test is equivalent to the standard method except for evaluating the visual acuity fluctuations and promises to be a simple visual screening test that can be performed in a shorter time.

Figure 1

The functional visual acuity (FVA) measurement system and results of typical cases. (a) The FVA measurement system. (b) A representative printout of the results of the FVA test using the standard method. The blue line denotes the Landolt corrected visual acuity. The red line shows the timewise changes in the visual acuity during testing. The green line denotes the mean logarithm of the minimum angle of resolution (logMAR) visual acuity during the measurement (defined as the FVA). The yellow circles indicate the number of correct responses; the blue triangles indicate spontaneous blinks. FVA (logMAR), −0.09; visual maintenance ratio, 0.95; and maximal/minimal logMAR visual acuities, −0.18/0.10, respectively; average response time, 1.39 seconds. (c) A representative printout of the results of the FVA test using the short-version method in the same subject as in B FVA (logMAR), −0.10; visual maintenance ratio, 0.95; maximal/minimal logMAR visual acuities, −0.18/0.00, respectively; average response time, 1.30 seconds.

Figure 2

The Bland–Altman plot shows the agreement between the FVA in the logarithm of the minimum angle of resolution (logMAR) measured using the standard- and short-version methods. The solid line shows the mean difference, and the dashed lines show the 95% limits of agreement. Several plots overlap. 30 FVA = FVA measured using the short-version method; 60 FVA = FVA using the standard-version method.

Figure 3

The Bland–Altman plot shows the agreement between the maximal visual acuity in logarithm of the minimum angle of resolution (logMAR) measured using the standard- and short-version methods. The solid line shows the mean difference, and the dashed lines show the 95% limits of agreement. Several plots overlap. 30 maximal VA = maximal VA measured using the short-version method; 60 maximal VA = maximal VA using the standard-version method.

Figure 4

The Bland–Altman plot shows the agreement between the visual maintenance ratio (VMR) measured using the standard- and short-version methods. The solid line shows the mean difference, and the VMR dashed lines show the 95% limits of agreement. Several plots overlap. 30 VMR = VMR measured using the short-version method; 60 VMR = VMR measured using the standard-version method.

Figure 5

The Bland–Altman plot shows agreement between the average response time (ART) measured using the standard- and short-version methods. The solid line shows the mean difference, and dashed lines show the 95% limits of agreement. Several plots overlap. 30 ART = ART measured using the short-version method; 60 ART = ART measured using the standard-version method.

Figure 6

The relationship between the BUT and the minimal VA of the standard FVA test. The BUT and the minimal VA of the standard FVA test are correlated significantly (r = −0.416; P=0.028). logMAR = logarithm of the minimum angle of resolution.