Contrast reduction and reading: assessment and reliability with the Reading Explorer test

PURPOSE. To investigate the reliability of the Reading Explorer (REX) charts and to assess the impact of text contrast reduction (1.5 cycle/degree) on reading speed in subjects with normal and low vision. METHODS. Standard visual acuity (ETDRS charts), reading speed (MNread charts), and contrast sensitivity (Pelli-Robson charts) measurements were obtained in 3 groups of subjects stratified by visual acuity level in the better eye from 0.0 to 1.0 logMAR, with intermediate cutoffs at 0.3 and 0.6 logMAR. Measurements of reading speed for decreasing levels of text contrast were obtained with the REX charts using a 1.5 cycle/degree text. RESULTS. Since in many patients with lower vision a plateau of maximum reading speed across different levels of text contrast was not found, reliability indexes were computed for average reading speed and reading contrast threshold. In the group with lower visual acuity, 95\% limits of agreement were +/- 0.134 log word/minute and +/- 0.175 log contrast sensitivity, suggesting good reliability. The proportion of subjects with a 20\% loss of reading speed from 90\% to 45\% text contrast was estimated to be 1/3 at 0.6 logMAR visual acuity level and 2/3 at 1.0 logMAR. CONCLUSIONS. The adverse effect of decreased text contrast, which may be found in ordinary reading material, on the reading performance of subjects with advanced and initial low vision is probably underestimated. The REX test proved to be a reliable investigation tool for this phenomenon.