Mesopic Functional Visual Acuity in Normal Subjects

<div><p>To evaluate mesopic functional visual acuity (FVA) with a newly developed system in normal subjects and to compare the results with photopic FVA, sixty-eight healthy volunteers (24.03 ± 4.42 [mean ± standard deviation] years) were enrolled in this study. A commercially available FVA measurement system (AS-28; Kowa, Aichi, Japan) was modified to measure FVA under mesopic conditions as well as photopic conditions. Measurements were performed monocularly in photopic conditions during 60 seconds. After dark adaptation for 15 minutes, the same measurements were repeated in mesopic conditions. Outcomes included starting visual acuity (VA), FVA (the average of VAs), visual maintenance ratio (VMR), maximum VA, minimum VA, and numbers of blinks during the 60-second measurement session, and were compared between mesopic and photopic conditions. Starting VA was –0.11 ± 0.08 and 0.39 ± 0.12 logarithm of the minimum angle of resolution (logMAR) in photopic and mesopic conditions, respectively. FVA was –0.06 ± 0.09 and 0.52 ± 0.14 logMAR, VMR was 0.98 ± 0.02 and 0.94 ± 0.04, maximum VA was –0.15 ± 0.06 and 0.33 ± 0.12 logMAR, the minimum VA was 0.05 ± 0.12 and 0.78 ± 0.20 logMAR, and the number of blinks was 8.23 ± 7.54 and 7.23 ± 6.20, respectively. All these parameters except the number of blinks were significantly different between the two conditions (<i>P</i> < 0.001). Besides, the difference between maximum and minimum VAs and standard deviation of VA were significantly larger in mesopic than in photopic conditions (<i>P</i> < 0.001). This study revealed that not only overall visual function decline but also instability of vision under mesopic conditions even in healthy subjects.</p></div

Results of functional visual acuity testing in both photopic and mesopic conditions in a representative subject (22 year old female).

<p>All visual outcomes in mesopic conditions were apparently worse than those in photopic conditions. In addition, it should be noted that line graph of visual acuity during 60 seconds remarkably fluctuated in mesopic conditions. VA = visual acuity, max = maximum, min = minimum, SD = standard deviation, logMAR = logarithm of the minimum angle of resolution.</p

Various parameters of functional visual acuity testing.

<p>Sequential visual acuities measured over a 60-second measurement session are denoted by continuous red line. Yellow dots show correct responses. Average of all visual acuity values is calculated as functional visual acuity, which is shown as green line. Blue line denotes starting visual acuity. Visual maintenance ratio refers to area beneath time-wise change in visual acuity (red line) divided by area beneath starting visual acuity (blue line). Maximum and minimum visual acuities imply the best and worst value of visual acuity over the testing period.</p

Comparison of visual function parameters between photopic and mesopic conditions.

<p>VA = visual acuity, logMAR = logarithm of the minimum angle of resolution, SD = standard deviation.</p><p>*: Significant difference by Wilcoxon’s signed rank test.</p><p>Comparison of visual function parameters between photopic and mesopic conditions.</p