A Novel Measure of Vision Competence by Assessing the Visual Acuity Space at Different Levels of Contrast and Ambient Luminance

Abstract

Visual acuity is a key parameter in the assessment of vision. It determines everyday vision, which is influenced by constantly changing contrast and lighting conditions. In clinical applications, however, these conditions are only poorly reflected by measuring visual acuity only at a single specific luminance and maximum contrast, leaving the actual visual performance under other everyday lighting conditions undetected. For this purpose, a setup has been developed that allows the presentation of optotypes at different contrasts and ambient luminance levels, the major determinants of spatial vision. In an automated test run, visual acuity was determined for a wide range of contrasts and luminance levels using an adaptive staircase algorithm and evaluated in a three-dimensional visual acuity space. The focus was on people with normal vision and patients with achromatopsia, an inherited autosomal recessive retinal disease that results in extreme sensitivity to glare and reduced visual acuity. In both cases, the standard tests of visual acuity differed enormously from their vision capabilities in daily living conditions. While the visual acuity of people with normal vision improved to a certain extent with increasing luminance, the visual acuity of people with achromatopsia dropped into range of legal blindness with increasing luminance. To counteract glare, achromatopsia patients use so-called edge filter glasses in everyday life, which alleviate their vision problems. Hence, as a further step, the benefit of these filter glasses was investigated quantitatively by measuring the visual acuity of the participants at the critical contrast luminance combinations with and without wearing the filter glass. For people with healthy eyes, this had a negative effect, as their visual acuity worsened in almost all conditions. For achromatopsia patients, the edge filter had a beneficial effect, improving their previously severe visual impairment to moderate. To quantify vision competence reflected in the visual acuity space, a new score was developed as a unified measure of vision for rapid assessment of visual acuity in daily living tasks. This score can be used as a novel endpoint to assess changes in vision competence after interventions in clinical trials. Finally, the new method and the device have been converted into a smaller version with optimized testing time for clinical use. Overall, this study presents a novel method for assessing visual acuity at different contrasts and luminance levels to provide a single measure of vision competence for typical conditions of daily living.