Reading Arabic Under Simulated Low Vision: Orthographic Complexity Shapes the Effect of Contrast Polarity

Reading is a critical visual task that depends on the resolution of fine character features, and how these features are affected by display variables under degraded viewing conditions remains an important question in clinical psychophysics. While contrast polarity effects on reading have been documented in Latin scripts, evidence from non-Latin orthographies is limited. This study investigated the effect of contrast polarity on Arabic reading performance under simulated visual impairment.

Reading acuity (RA), maximum reading speed (MRS) and critical print size (CPS) were assessed in 47 normally sighted adults using the Balsam Alabdulkader-Leat (BAL) reading chart. Testing was conducted under baseline and simulated visual impairment using a Bangerter filter, with both black-on-white and white-on-black charts.

The simulation significantly degraded all reading measures (MRS, p = 0.001; RA, p < 0.0001; CPS, p < 0.0001). A significant simulation × polarity interaction was found for RA (p < 0.0001), with black-on-white charts producing better visual acuity at baseline and white-on-black producing better visual acuity under simulated impairment. Chart polarity did not affect MRS (p = 0.38) or CPS (p = 0.82) significantly.

Arabic relies on small, high-spatial-frequency features such as dots for letter discrimination, which appear to modulate how contrast polarity interacts with optical degradation at threshold. These findings provide preliminary evidence that may guide future studies of reading performance in Arabic-speaking patients with visual impairment.