Effect of Luminance on Visual Acuity Measurement

Abstract

Background/Objective: In clinical settings, poor chart luminance can cause eyestrain and glare which can be a source of discomfort to the patient giving rise to errors in visual acuity measurement. The aim of this study was to determine the effect of luminance on visual acuity measurement at distance (6m). Materials and Methods: This was an experimental study in which a light meter was used to measure different luminance reflecting from the visual acuity chart while a total number of 30 subjects (16 males and 14 females) within the ages 15 to 40 were asked to verbally respond to the most detailed optotypes recognized while viewing a 3m logMAR acuity chart. A repeated measure ANOVA, was conducted to assess whether there were differences between the average logMAR visual acuity for each of the five luminance levels. Results: Participants identified the optotypes differently under different luminance condition (F_{2.36, 68.3}= 104.144, p < 0.001). There was also a significant linear trend, (F_{1, 29} = 185.93, p < 0.001) and quadratic trend, (F_{1, 29} = 4.87, P < 0.001) increase in visual acuity. In addition, increasing the luminance from 10cd/m² to 90cd/m², produced 1.5 times increase in visual acuity. Conclusion: The application of this result will help to establish an optimum chart luminance for comfortable visual acuity measurement for clinical examination and also to provide information and guidance regarding luminance to chart designers and manufacturers.