The influence of target size on the contrast sensitivity function determined with the Vistech VCTS 6500 Chart

The Vistech Vision Contrast Test System is a convenient method to determine the contrast sensitivity function clinically. To assess the effect of increased target size on the contrast sensitivity function of 14 healthy volunteers, we halved the viewing distance from 3 to 1.5 m. In this way the size of the targets of the Vistech VCST 6500 chart is increased from 1.4 to 2.8 deg. The contrast sensitivity functions obtained at the two distances revealed an increase of contrast sensitivity for the lowest spatial frequency at the reduced viewing distance. We presume that this effect is due to the insufficient number of cycles in the targets with the lowest spatial frequency.