The effect of glare on visibility depends on spatial frequency

AGUIRRE R.C.; BARRAZA J.F.; COLOMBO E.M.

Sarasota, Florida, USA

Congreso; 7th Annual Meeting of the Vision Sciences Society; 2007

VisionSciences Society

Purpose. The increment of contrast threshold due to glare is modeled by adding a uniform veiling luminance (Lv) to the stimulus. This veil imitates the masking effect produced by the scattering of light in the ocular media. We showed that the effect of glare on reaction times depends on the spatial frequency of the stimulus. We wondered whether this dependence is linked with the contrast sensitivity. In this study, we investigated the reduction of contrast sensitivity (CS) produced by glare. Methods. Experiment 1: we measured the CS for mesopic achromatic sinusoidal gratings for four glare intensities. We performed an orientation discrimination experiment with an adaptive 2AFC procedure to determine the contrast thresholds. Experiment 2: we determined the Lv that added to the stimuli produced the same thresholds for each spatial frequency. Two subjects participated in this experiment. Viewing was monocular with natural pupil. Results. Contrast threshold measurements show that the effect of glare is strongest for those spatial frequencies whose CS is maximal. The effect almost disappears for high spatial frequencies. The same effects are obtained when glare is replaced by the equivalent Lv. Conclusions. First, we show that the effect of glare on visibility cannot be only explained by intraocular scattering because this optical effect does not depend on stimuli spatial frequency. Second, the Lv catches the dependence of the effect of glare on spatial frequency suggesting that there is not a unique value of Lv for each glare intensity. Third, the effect of glare on contrast thresholds suggests that RTs are closely related to contrast sensitivity.