Contrast Sensitivity, Visual Acuity, Reading Speed and Macular Visual Field Damage in Glaucoma

Abstract

Abstract: : Purpose: To investigate the relationship between visual field (VF) loss, letter chart contrast sensitivity (CS), visual acuity and reading speed in glaucoma patients. Specifically, to determine if letter chart CS tests can reliably identify patients with visual field loss close to fixation. Methods: Twenty seven open–angle glaucoma patients (mean age 67, range 41–89 yrs) with a wide spectrum of visual field damage (mean MD –6.3, range +1.4 to –31.1 dB) were examined twice within one month. At each session, the VF of the study eye was tested with SITA Standard 24–2 and 10–2 tests (stimulus size III). CS was measured with the Pelli–Robson (PR) charts and the Lighthouse (LH) letter contrast test (Mars Perceptrix Corp, 2003). Reading speed (at newsprint size) and critical print size were estimated with the Bailey–Lovie reading charts (Berkeley 10–word version W1). Data from the 2 sessions were averaged to reduce variability. Results:Letter chart CS measurements related most closely to the highest VF sensitivity estimate within the central 1.5 degrees of fixation (foveal test point and its 4 neighbors on 10–2 test; Pearson r=0.77 [PR] and 0.82 [LH], p<0.001). In comparison, the relationship between the CS scores and the worst point within 1.5 degrees of fixation was much weaker (r=0.44 [PR] and 0.43 [LH], p<0.05%). Two of 3 patients with deep paracentral visual field loss (sensitivity < 10 dB within 1.5° of fixation) had near–normal CS scores (log CS>1.60) with both Pelli–Robson and Lighthouse tests. While the critical print size was best predicted by distance visual acuity and the mean VF sensitivity within the central 1.5 degrees of fixation (R²=0.26), reading speed was best predicted by letter chart CS (R²=0.25 [PR] and 0.22 [LH]). Conclusions: Letter chart CS tests are unlikely to reliably identify all patients with glaucomatous visual field loss close to fixation. However, they are important and practical ancillary tests in patients with field loss near fixation, not least because they improve our understanding of the bearing of glaucomatous field loss on real–world vision, in particular reading performance.

Keywords: contrast sensitivity • visual fields • reading