Visual Acuity, Contrast, and Flicker, as Measures of Retinal Sensitivity*†

Abstract

Visual acuity at three contrasts and two brightnesses, and critical flicker frequency (CFF) at two brightnesses, were measured morning and evening on 24 subjects for five successive days. During the days the subjects drove automobiles for several hours, in the brilliant sunshine of the Arizona desert. Statistical analysis of the results shows that the acuity and flicker measurements have high correlation, but that the inherent variance of visual acuity measurements is great, while that of CFF is small. The CFF can be used to develop a logarithmic index of retinal sensitivity. Application of this index to the effect of exposure to sunlight is exemplified. Other applications are suggested.