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. 2016 Jun;254(6):1091-7.
doi: 10.1007/s00417-016-3329-7. Epub 2016 Apr 22.

Fiat Lux: the effect of illuminance on acuity testing

Laurence P Tidbury  1 , Gabriela Czanner  2   3 , David Newsham  4   5
Affiliations

Fiat Lux: the effect of illuminance on acuity testing

Laurence P Tidbury et al. Graefes Arch Clin Exp Ophthalmol. 2016 Jun.

Abstract

Purpose: To determine the effect of changing illuminance on visual and stereo acuity.

Methods: Twenty-eight subjects aged 21 to 60 years were assessed. Monocular visual acuity (ETDRS) of emmetropic subjects was assessed under 15 different illuminance levels (50-8000 lux), provided by a computer controlled halogen lighting rig. Three levels of myopia (-0.50DS, -1.00DS & 1.50DS) were induced in each subject using lenses and visual acuity (VA) was retested under the same illuminance conditions. Stereoacuity (TNO) was assessed under the same levels of illuminance.

Results: A one log unit change in illuminance level (lx) results in a significant change of 0.060 LogMAR (p < 0.001), an effect that is exacerbated in the presence of induced myopic refractive error (p < 0.001). Stereoacuity scores demonstrate statistically significant overall differences between illuminance levels (p < 0.001).

Conclusions: The findings of this study demonstrate that changes in illuminance have a statistically significant effect on VA that may contribute to test/retest variability. Increases in illuminance from 50 to 500 lx resulted in an improved VA score of 0.12 LogMAR. Differences like these have significant clinical implications, such as false negatives during vision screening and non-detection of VA deterioration, as the full magnitude of any change may be hidden. In research where VA is a primary outcome measure, differences of 0.12 LogMAR or even less could affect the statistical significance and conclusions of a study. It is recommended that VA assessment always be performed between 400 lx and 600 lx, as this limits any effect of illuminance change to 0.012 LogMAR.

Keywords: Illumination; Lighting; Myopia; Stereoacuity; Vision; Visual acuity.

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Figures

Fig. 1
Fig. 1
Mean VA change from the baseline 500 lx. The bars are 95 % family-wise confidence intervals
Fig. 2
Fig. 2
Changes of VA (LogMAR) from reference VA at 500 lx (2.7 in logarithmic scale) in three typical subjects. The data indicate possible effects of Rx state, illuminance, interaction and subject specific baseline (500 lx) values
Fig. 3
Fig. 3
Mean VA change from the baseline 500 lx. The bars are 95 % family-wise confidence intervals
See this image and copyright information in PMC

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