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David Evans, Kaydee L McCray, Michelle M Hammond, Pinakin Gunvant Davey; Luminance and visual acuity: 20/20 may not always mean 20/20!. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1077.
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© ARVO (1962-2015); The Authors (2016-present)
Various computerized visual acuity units (CVA unit) are routinely utilized in eye care practices to measure visual acuity. Due to multiple factors, including electronic circuitry aging, variances in input line voltages, screen durability, office humidity, etc. CVA units undergo luminance change and degradation. We sought to investigate the variances in luminance that exist across different examination lanes in different clinical facilities, and if the differences in luminance impact measured visual acuity.
The luminance levels on the central screen area of CVA units were measured in 25 examination rooms at various clinics. Visual acuity measurements were performed by one investigator under five luminance conditions. Three of the luminance levels were obtained by adjusting one CVA unit to 40, 85 and 150 cd/m2. Two additional levels (204 and 402 cd/m2) were obtained from two CVA units that were purchased for the study and incorporated without adjustment. . The order of presentation of the luminance levels was randomized. Fifty eyes of fifty participants (mean age 37.5 SD 12.9 years), that had no known pathology and visual acuity 20/20 or better on a standardized ETDRS chart, were included in the study. The visual acuity threshold was measured three times, each time with a different set of randomized Sloan letters.
Luminance varied significantly across the CVA unit, adjusted to 38 to 161.5 cd/m2, and from the preset levels found with newly purchased units from 204 to 402 cd/m2 .The logMAR acuity values measured at the five luminance levels were -0.061, -0.077, -0.83, -0.102 and -0.128 for 40, 85, 150, 204 and 402 cd/m2 respectively. The level of luminance significantly influenced measured visual acuity (repeated measures ANOVA with Bonferroni correction (F=42.87, p=2.2 E-20)). The visual acuity measured at 40 cd/m2 was significantly different than for 150, 204 and 402 cd/m2 (p=.00001, 6.5 E-7, 6.7 E-14). The visual acuity measured at 85 and 150 cd/m2 were significantly different than 204 and 402 cd/m2 (p=0.002 & 1.6 E-9 and p=0.01 & 1.5 E-10).
Commercially available CVA units differ significantly in luminance, even when newly purchased from manufacturers. The visual acuity measured under these different luminance levels is significantly different. The luminance levels in CVA units should be standardized with continuous monitoring as they tend to vary and are prone to degradation over time.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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