Influence of contrast polarity on the accommodative response.

PURPOSE To assess the changes in the accommodative response of the eye while reading a text under different contrast polarity conditions: black letters on white background (BoW condition) and white letters on black background (WoB condition). METHODS Eighteen subjects with ages ranging from 21 to 41 years participated in this experimental study. The accommodative response (AR) of the eye while reading a text with BoW or WoB contrast polarity was obtained objectively with an adaptive optics system that corrected all aberrations but subject's own. Two different letter sizes (visual acuity conditions), shown on a microdisplay, were tested. The AR of each eye was measured with its natural pupil diameter at 0-3D of accommodative demand from the far point of the eye, with a step of 0.5D. The slope of the stimulus-response curve was calculated for each subject and condition. RESULTS The averaged maximum pupil size was bigger for reverse (WoB) than for normal (BoW) contrast with statistical significance. The slopes for the ARs of the four conditions were not significantly different from each other. CONCLUSIONS Contrast polarity does not seem to influence the accommodative response when reading text from an electronic microdisplay.