New approaches for assessment of vision in refractive surgery and cataract

The purpose of this study was to test new methods of evaluating contrast sensitivity (CS) and disability glare. These measurements are particularly useful in evaluating the effects of cataract and refractive surgery on the visual system. In this study we compared the right eye of 20 subjects and both eyes of eight subjects who had bilateral LASIK. We tested contrast sensitivity and visual acuity (VA) in normal and low photopic luminance conditions. VA measurements were taken using high (96%) and low (5%) contrast logarithmic charts. CS measurements were taken using prototype charts with 20/50 and 20/40 demands. Disability glare was simulated by using a dark filter cut to cover only the letters, so that the luminance was 10 cd/m2 in the center with 100 cd/m2 surrounding it, resulting in a diffuse surrounding glare. Under photopic viewing conditions, visually normal observers demonstrated VA and CS values with well-defined confidence intervals. Between-subject variability with 20/50 letters was less than that observed with 20/40, making the 20/50 letter size more desirable for clinical application. In visually normal subjects we observed a significant decrease in performance with a modest decrease in photopic luminance. This effect was most apparent for low contrast acuity and 20/50 CS, demonstrating the potential usefulness of these measurements as clinical tools. While the most LASIK patients performed within normal limits on this test, there was a tendency for decreased performance. The debilitating effects of glare were observed in normal subjects as well as LASIK patients. The addition of diffuse surrounding glare to our low photopic CS stimulus led to a significant decrease in performance. Our approach to measuring disability glare produced a reliable decrease in performance evident in visually normal observer as well as in our non-symptomatic LASIK patients. While these findings are significant, further studies are underway to explore the utility of this methodology