New visual acuity chart: modification for clinical practice and research.
The authors created numeric optotypes by steps following the standard Sloan letters and developed a visual acuity test chart using Logarithm of the Minimal Angle of Resolution (Log MAR) such as the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. Legibility of new numeric optotypes was presented in per cent of correct response at threshold. Only seven numbers (0, 2, 3, 5, 6, 8, 9) were used as optotypes and the average of per cent of correct response at threshold equal to 80.7 which was slightly less than standard Sloan letters (82%). The comparison between results of visual acuity level from the new chart and ETDRS showed that the ETDRS chart was slightly more legible than the new chart. It can be used universally especially with Thai people for clinical practice and research.