The Impact of Glare Type and Intensity on Objective and Subjective Visual Performance

PurposeTo compare the effects of spatially uniform glare and point light sources on visual acuity (VA) of individuals with normal vision under everyday contrast and illuminance conditions, and to investigate the related subjective perception of glare. MethodsVA was assessed with spatially uniform glare (120 cm x 120 cm) lighting (VA-CAL test) and with four point light sources in either the paracentral (13.3{degrees}) or the near-peripheral visual field (23.5{degrees}). For all conditions, the illuminance and the optotype contrast (Landolt rings) were varied in four steps from 25 to 2200 lux and five steps from 20% to 80%, respectively. In addition to visual acuity testing, the subjective glare discomfort score was assessed for each illuminance using the Photoaversion Severity Questionnaire (PSQ). ResultsTwelve volunteers with normal vision (22 to 32 years, 6 women, 6 men) were enrolled in the study. Overall, regardless of the type of glare, increasing illuminance improved VA, while decreasing the contrast reduced VA. A statistically significant difference of 0.06 logMAR for the different types of glare was found only between uniform and point light glare in the near-periphery. The discomfort scores increased with illuminance, but did not differ statistically significantly between the different types of glare. ConclusionsBoth uniform and point light sources are a good way to measure daily visual performance in glare and show comparable results in influencing VA and subjective discomfort in everyday conditions. Translational RelevanceUniform light sources are just as suitable for testing visual acuity under glare as point light sources, although we recommend using uniform light for assessing daytime performance and punctual light for testing fitness to drive at night.