Mesopic Functional Visual Acuity in Normal Subjects.

Takahiro Hiraoka,Fumiki Okamoto,Yoshifumi Okamoto,Tetsuro Oshika,Sujin Hoshi,Wayne Iwan Lee Davies

doi:10.1371/journal.pone.0134505

Abstract

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 (P < 0.001). Besides, the difference between maximum and minimum VAs and standard deviation of VA were significantly larger in mesopic than in photopic conditions (P < 0.001). This study revealed that not only overall visual function decline but also instability of vision under mesopic conditions even in healthy subjects.

Highlights

Standard visual acuity (VA), which relies on a patient’s recognition of familiar, high contrast letters or Landolt rings, is an excellent measure of visual function
We developed and tested a new method to measure mesopic functional visual acuity (FVA) using a commercially available FVA measurement system
The measurements were performed after dark adaptation for 15 minutes, because numerous studies have evaluated mesopic visual functions after dark adaptation for 5–20 minutes [37,38,39] and there has been a report which showed better and more stable results after 15 minutes of adaptation compared to 5 minutes in some subjects [40]

Summary

Introduction

Standard visual acuity (VA), which relies on a patient’s recognition of familiar, high contrast letters or Landolt rings, is an excellent measure of visual function. Visual acuity is only one aspect of actual visual function. Contrast sensitivity and glare testing provide additional important details of visual function. Commonly used tests to measure these aspects of visual function only detect the maximum value of each parameter. Results are expressed as one value and may not accurately reflect the entire spectrum of results. In many situations of daily life, continuous gazing tasks

Methods

Results

Conclusion