Development of a scale to measure reading ability

Abstract

PURPOSE: The Guide for Evaluation of Visual Impairment has argued the case for developing “ability scales” that reflect the impact of visual impairment on important everyday “abilities” including reading. We propose a reading ability scale with anchoring values of 0 for no reading ability and 100 for normal reading ability, to represent the reading ability of subjects with age-related macular degeneration (AMD) and other forms of low vision. METHODS: We analyzed MNREAD data for 46 subjects with AMD and 46 young adults with normal vision. The raw data were fitted with a nonlinear mixed effects model to estimate the log reading speeds at 11 print sizes (0 to 1.0 logMAR). An individual’s reading ability score (RAS) is defined to be the sum of the estimated log reading speeds across this set of print sizes, divided by the mean summed value for the group of young, normal adults, and multiplied by 100. RAS was evaluated by Rasch analysis and Principal Component Analysis. We compared the RAS values of the AMD subjects for unaided reading and for reading with a prescribed stand magnifier across the same range of physical print size. The goal of this comparison was to evaluate the change in overall reading function due to magnifier use. RESULTS: Psychometric analysis indicated that the RAS was monotonically related to a hypothetical (latent) reading-ability variable. RAS values for unaided reading by our AMD subjects ranged from 5 to 89 (with a median of 42.5). Their RAS values were significantly correlated with critical print size, reading acuity, distance visual acuity, and contrast sensitivity (p<0.05). With the use of magnifiers, the median RAS values increased significantly from 42.6 to 72.2 (p<0.01). CONCLUSION: RAS values on the new reading ability scale provide a single-valued score that represents an individual AMD subject’s reading ability with reference to standard normally sighted readers. The RAS is responsive to changes in reading performance with the use of magnifiers. It may be a useful outcome measure for evaluating the merits of rehabilitation or therapeutic interventions intended to improve visual function.