We investigated how dioptric blur affected word acuity thresholds for targets presented at different retinal eccentricities.
Word thresholds were measured at 0, 5, and 10 degrees and for different Weber contrast levels of 4, 10, 45, and 90%.
We find that increasing optical blur increased word acuity thresholds, but the extent of change was dependent on retinal eccentricity and stimulus contrast. In particular, the resolution reduction per diopter of blur (as indicated by the slope of lines fitted to data) was significantly less at peripheral locations (0 degrees vs. 5 and 10 degrees) and for low-contrast targets.
These findings provide useful guidelines to predict how patients with contrast loss and/or those that rely upon an eccentric retinal location for reading respond to the introduction of optical blur in a clinical setting.