Eye movements and reading with simulated visual impairment

The purpose of this study was to investigate the effects of simulated visual impairment on the reading speed and reading eye movements of young, normally-sighted observers. Afocal diffusing filters (Ryser occlusion foils) were used to create three levels of impairment and eye movements were recorded using a spectacle-mounted, infra-red limbal reflection system. Reading speed decreased significantly (P < 0.01) as the level of impairment increased. Eye movement analysis revealed the main contributory factors to be increased fixation durations, shorter saccades (resulting in increased numbers of forward saccades per line) and, to a lesser extent, increased time required for page navigation. The results suggest that in order to achieve optimal reading speeds, print size should be at least four times the acuity threshold and that print contrast should be at least twenty times contrast threshold.