Study of chart designs and optotypes for preschool vision screening--I. Comparability of chart designs.

Design variations in children's distance vision screening charts contribute to inconsistencies noted in preschool vision screening programs. This study compares children's distance visual acuity on two chart designs: logarithm of the minimal angle of resolution (LOGMAR) vs a chart of 'standard' design. In theory, the LOGMAR chart offers the advantages of improved precision in measuring inter-patient differences and greater consistency of follow-up measurements. Our findings indicate the following: 1) the ability to complete a test depends upon the child's age, not on chart design; 2) isolation of symbols is required more frequently for the LOGMAR charts than for the standard charts; and 3) on average, children have slightly poorer visual acuity scores on LOGMAR charts than on standard charts.