Contrast sensitivity (i.e., the ability to detect objects by distinguishing them from their background) was assessed monocularly with the subject's best spectacle correction under mesopic (low, but not quite dark) conditions at a distance of 8 (2.45 m) feet from the eye at a spatial frequency of 1.5, 3, 6, and 12 cycles per degree (cpd) using the Vector Vision CSV 1000-HGT with and without a glare source. Raw scores from contrast sensitivity testing were transformed to log units. A higher numeric value represented better contrast sensitivity. This analysis was prespecified for the first operative eye. No formal statistical hypothesis testing was planned.