A comparison of clinical acuity and contrast sensitivity charts: effect of uncorrected myopia.

We have examined the effect of corrected and uncorrected myopia on visual acuity and contrast sensitivity using a standard acuity chart and two commercially available printed contrast sensitivity charts (Vistech and Pelli-Robson). We tested 140 eyes of 70 young adults. Most subjects were myopic and were tested with and without their optimum spectacle or contact lens correction. We found no effect of myopia, if well corrected, on acuity or contrast sensitivity. All three test scores were sensitive to uncorrected myopia. The Pelli-Robson contrast sensitivity chart, which was designed to be insensitive to defocus, required more than three diopters of refractive error to elicit a two line change in performance, and it was generally very insensitive to uncorrected myopia. Although the Vistech chart was sensitive to uncorrected myopia, the large step sizes used in the chart, and the higher inter- and intra-subject variability in scores reduces its potential value for refraction. The Snellen letter chart gave the most sensitive and reliable changes in performance with uncorrected myopia.