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Takahiro Hiraoka, Yoshifumi Okamoto, Fumiki Okamoto, Tetsuro Oshika; Mesopic functional visual acuity in normal subjects. Invest. Ophthalmol. Vis. Sci. 2014;55(13):164.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate mesopic functional visual acuities (FVA) with a newly developed measurement system in normal subjects, and to compare the results with photopic FVA.
Sixty-eight healthy volunteers were enrolled in this study. Their age was 24.03 ± 4.42 [mean ± SD]) years. A commercially available FVA measurement system (AS-28; Kowa, Aichi, Japan) was modified to measure FVA in a mesopic condition as well as photopic condition. First, the test was performed monocularly in a photopic condition with background luminance of 250 ± 25 cd/m2. Subjects delineate the direction of the automatically presented Landolt rings by handling the joystick, and the size of optotypes changes by one step depending on the responses. They enlarge when the response is incorrect and become smaller when it is correct. This testing is continuously performed for 60 seconds under natural blinking. Subsequently, the above measurements were repeated in a mesopic condition after dark adaptation for 15 minutes. In mesopic FVA measurements, the background luminance was switched to 0.1 ± 0.01 cd/m2. When each testing is completed, the result is recorded as a line graph, which is made up of points joining the correct answers only. The outcome parameters of this system included starting (baseline) VA, FVA (the average of VAs), visual maintenance ratio (VMR), maximal and minimal visual VAs, and blink numbers during the 60-second measurement session.
The starting VA was -0.11 ± 0.08 logMAR in a photopic condition and 0.39 ± 0.12 logMAR in a mesopic condition. The FVA was -0.06 ± 0.09 and 0.52 ± 0.14 logMAR in the photopic and mesopic conditions, the VMR was 0.98 ± 0.02 and 0.94 ± 0.04, the maximal VA was -0.15 ± 0.06 and 0.33 ± 0.12 logMAR, the minimal VA was 0.05 ± 0.12 and 0.78 ± 0.20 logMAR, and the blink number during the 60-second testing period was 8.23 ± 7.54 and 7.23 ± 6.20, respectively. All these parameters except blink number were significantly different between the two conditions (P < 0.0001).
This is the first attempt to assess mesopic FVA. The results showed that not only VA but also VMR deteriorated in mesopic conditions in normal subjects. This means that it becomes difficult for human eyes to maintain the decreased visual function in mesopic conditions. This device may be sensitive to detect early and tiny changes in visual function in various eye diseases, and helpful for better understanding of unidentified visual complaint.
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