Abstract
PurposeLow vision reduces text visibility and causes difficulties in reading. A valid low-vision simulation could be used to evaluate the accessibility of digital text for readers with low vision. We examined the validity of a digital simulation for replicating the text visibility and reading performance of low-vision individuals.MethodsLow-vision visibility was modeled with contrast sensitivity functions (CSFs) with parameters to represent reduced acuity and contrast sensitivity. Digital filtering incorporating these CSFs were applied to digital versions of the Lighthouse Letter Acuity Chart and the Pelli-Robson Contrast Sensitivity Chart. Reading performance (reading acuity, critical print size, and maximum reading speed) was assessed with filtered versions of the MNREAD reading acuity Chart. Thirty-six normally sighted young adults completed chart testing under normal and simulated low-vision conditions. Fifty-eight low-vision subjects (thirty with macular pathology and twenty-eight with non-macular pathology) and fifteen normally sighted older subjects completed chart testing with their habitual viewing. We hypothesized that the performance of the normally sighted young adults under simulated low-vision conditions would match the corresponding performance of actual low-vision subjects.ResultsWhen simulating low-vision conditions with visual acuity better than 1.50 logMAR (Snellen 20/630) and contrast sensitivity better than 0.15 log unit, the simulation adequately reduced the acuity and contrast sensitivity in normally sighted young subjects to the desired low-vision levels. When performing the MNREAD test with simulated low vision, the normally sighted young adults had faster maximum reading speed than both the Non-macular and Macular groups, by an average of 0.07 and 0.12 log word per minute, respectively. However, they adequately replicated the reading acuity as well as the critical print size, up to 2.00 logMAR of both low-vision groups.ConclusionA low-vision simulation based on clinical measures of visual acuity and contrast sensitivity can provide good estimates of reading performance and the accessibility of digital text for a broad range of low-vision conditions.
Highlights
Low vision refers to any vision impairment that cannot be corrected by glasses or contact lenses
The simulation is based on image filtering that uses transformations of the normal contrast sensitivity function (CSF) to represent reduced visibility associated with low vision
We evaluated the validity of the simulation by testing normally sighted subjects on filtered images of text to determine if measures of acuity, contrast sensitivity and reading performance match the performance of people with actual low vision
Summary
Low vision refers to any vision impairment that cannot be corrected by glasses or contact lenses. Other factors affecting vision, such as field loss, light level and glare, often add to the difficulties in lowvision function (Fletcher et al, 1999; Turano et al, 2004; Kiser et al, 2005). The simulation is based on image filtering that uses transformations of the normal contrast sensitivity function (CSF) to represent reduced visibility associated with low vision. We evaluated the validity of the simulation by testing normally sighted subjects on filtered images of text to determine if measures of acuity, contrast sensitivity and reading performance match the performance of people with actual low vision. A valid simulation of lowvision visibility could be useful to eye-care clinicians, display designers, website creators, and family members in evaluating the accessibility of digital rendering of text or graphics for people with low vision
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