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The effect of room illumination on distance visual acuity using a projected chart

1 May 1999


Historically distance visual acuity (DVA) has been measured in darkened conditions and the assumption has been that different exam room illuminations do not affect DVA in individuals. Recently, there has been some evidence that a particularly dark exam room may degrade acuity in some individuals. This DVA degradation in healthy individuals could be due to night myopia effects or increased optical aberrations. However, a bright exam room may cause reduced chart contrast resulting in lowered DVA as well. The purpose of this study was to determine whether changes in general room illumination can have a significant affect upon DVA. In this study, the DVA's of 37 healthy subjects between the ages of 12 and 49 were measured at three statistically different room illumination levels (300-440 lux, 100-200 lux, and 1-50 lux, p=0.0001) with a projected Flom (or S-) chart. The three subject groups mean DVA's for the three room illumination levels were compared using ANOVA repeated measures test. No significant differences were found between the three mean DV A's (LogMAR -0.078, -0.097, and -0.100 at bright, medium, and dim lighting levels respectively, p=0.234). This suggests that DVA was not affected by changes in general room illumination. However, there was a small subgroup of subjects whose DVA was significantly reduced at the lower room illuminations. The possibility that these subjects represent a clinically significant subgroup of patients who are night myopes is explored.


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