Relation of Reading Performance to Visual Acuity and Perceived Reading Ability in Low Vision

Abstract

Abstract: : Purpose: To determine the relationship of reading speed vs. print size function parameters to visual acuity and to perceived reading ability. Methods: Reading speed vs. print size was measured on 50 low vision patients using MNRead at a distance of 40 cm with the patient's habitual correction and binocular viewing. Presenting binocular visual acuity was measured using the rear-illuminated ETDRS visual acuity chart with the patient's habitual correction. Perceived reading ability was estimated with a questionnaire for which patients rated the difficulty of performing specific reading tasks using a 4-category ordinal response scale. Results: Each set of reading speed vs. print size data was fit with the function R=R_max*(1-exp{-2.3(P-P₀)/(P_c-P ₀)}), where R is the reading rate in words per minute, R_max is the maximum reading rate, P is the print size in MAR, P₀ is the threshold print size, and P_c is the critical print size (i.e., the print size that yields a reading rate 90% of R_max). Perceived reading ability on an interval scale was estimated from difficulty ratings of reading tasks using Rasch analysis. Log MAR acuity ranged from 0 to 1.2; R_max ranged from 19 to 265 words/min.; P₀ ranged from 0 to 1.2 log MAR; and P_c ranged from 0.45 to 1.7 log MAR. There was a strong correlation between log P₀ and log P_c (r = 0.77), log P₀ and log MAR acuity (r = 0.59), and log P_c and log MAR acuity (r = 0.66). The linear regression between log MAR acuity and log P₀ had a slope of 1 and an intercept of 0, whereas the linear regression between log MAR acuity and log P_c had a slope of 1 and an intercept of 0.47. The correlations between R_max and log MAR visual acuity, log P₀, and log P_c were weak (0.16, -0.25, and 0.18, respectively). Perceived reading ability was moderately correlated with R_max, log P₀, and log P_c (0.48, -0.46, and -0.41, respectively). Conclusions: Maximum reading rate is nearly independent of visual acuity, whereas reading threshold and critical print size are strongly associated with acuity. Critical print size is 3 times the reading threshold. Although maximum reading rate is not correlated with threshold or critical print size, perceived reading ability is associated with all three parameters.

Keywords: reading • low vision • visual acuity