Differences in visual acuity between the eyes: determination of normal limits in a clinical population

We determined the difference in visual acuity between the right and left eyes of patients and also determined the maximal level of acuity expected in a group of visually normal individuals. Visual acuity was measured in the right and left eyes of 72 subjects aged from 16 to 67 years using Bailey-Lovie type charts. The chart was read until fewer than three letters were read on a line and acuities were based on each letter correct contributing -0.02 to the overall score. For 1 2 of these subjects, visual acuity was measured a further four times. Average visual acuities for right and left eyes were -0.137 and -0.126 log MAR, respectively. The signed visual acuity difference was normally distributed and had a standard deviation of 0.050 log MAR. The mean visual acuity difference for the 12 subjects for whom the measures were repeated was 0.033 log MAR (SD of the signed visual acuity difference: 0.049 log MAR). We conclude that if a patient has a difference in visual acuity between the two eyes of more than 5 letters on a Bailey-Lovie style chart, further investigation is indicated.