The effects of glare, luminance and contrast on visual acuity (VA)

Abstract

"Purpose: Clinical measurements of VA are typically obtained under optimal conditions using high contrast optotypes. However, these conditions are not representative of real-life environments where observers are frequently faced with low contrast, low luminance targets accompanied by significant degrees of glare. Accordingly, the aim of the present study was to measure VA under both optimal and suboptimal conditions in younger and older adults.

Method: The study was performed on 30 older (ages 50-71 years) and 30 younger (21-28 years) subjects. High (0.0 log unit) and low (1.05 log unit) contrast VAs were tested using the Adhikari Carter Feigl Zele logMAR chart. VA was measured both with and without a 0.3 neutral density (ND) filter to create low luminance conditions, as well as both with and without an LED glare source being directed into the eye.

Results: The average change in VA under the low contrast and low luminance conditions were 1.22 logMAR (p < 0.001) and 0.94 (p < 0.001), respectively. Average VA changed by -0.77 in the presence of glare (p < 0.001). There were no significant age effects noted between the two groups (p=0.25). Interaction effects were significant between luminance and contrast (p < 0.001) as well as between luminance, contrast and the presence of glare (p < 0.001) in both age groups.

Conclusions: The results demonstrate that reducing contrast and luminance produced a significant decline in VA in younger and older adults. This finding has considerable clinical significance, for example when driving at night, where a subject with excellent VA in the examination room might exhibit very poor VA under degraded conditions. Clinical measurements should include assessment of visual performance under sub-optimal conditions. "