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MiYoung Kwon, Bhavika Patel, Rong Liu, Christopher A Girkin; The shrinking visual span may explain glaucomatous reading deficits. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1945.
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© 2017 Association for Research in Vision and Ophthalmology.
Glaucoma is a leading cause of world blindness, characterized by typical visual field defects. Patients with bilateral glaucoma read slower than normal cohorts (e.g. Ramulu et al. 2009). The purpose of the current study is to examine visual factors that might limit reading ability in glaucoma patients and to identify the best predictor for glaucomatous reading impairment.
This study tested four visual factors: binocular visual acuity (BVA), binocular contrast sensitivity (BCS), stereoacuity, and the visual span (i.e. the number of letters recognizable in a glance) known to limit reading speed (Legge et al., 2001). The visual span likely reflects a decrease in field of view in glaucomatous vision. Patients with primary open-angle glaucoma (mean age =64.8±11.1 yrs; n=15; mean MD and VFI for the better eye =−5.72±5.31 and 84.00±15.20; mean MD and VFI for the worse eye =−11.58±9.14 and 67.51±28.74) and age-matched normal controls (mean age =57.9±7.7 yrs; n=10) were recruited. Visual span was measured by asking subjects to recognize letters in trigrams (strings of random three letters) flashed briefly at varying letter positions left and right of the fixation point. Over a block of trials, a profile was built showing letter recognition accuracy versus letter position. The area under this profile was defined as the size of the visual span. Oral reading speed was measured with short blocks of text. For each subject, BVA (ETDRS charts), BCS (Pelli-Robson chart), and stereoacuity (Stereo Fly test) were also assessed.
Compared to normal controls, glaucoma patients showed significantly slower reading speed (by 31%, t(23)=3.06, p <0.01). While no significant deficit was found in BVA (t(23)=1.40, p=0.18), glaucoma patients showed pronounced deficits in BCS (t(23)=3.37, p<0.01), stereoacuity (t(23)=2.17, p=0.04), and visual span size (t(23)=2.34, p=0.03). Multiple regression analysis further revealed that the glaucomatous reading impairment was best predicted by the size of the visual span (p=0.01).
Our findings showed that despite relatively normal acuity, reading is considerably impaired in glaucoma patients. Visual span shrinkage associated with glaucomatous visual field loss may explain reading impairment in glaucoma patients.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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