Logmar 4m ETDRS Chart 3 Revised 4 metre viewing. Acuity range 40m to 2M. Will fit illuminated cabinets SDT-392-LSV and SDT-396-LPV These revised charts incorporate a slight change in the difficulty score for each of the ten Sloan letters derived from the best visual acuity examinations of 7420 eyes during the ETDRS study. The original charts difficulty scores were derived from the examination of 234 eyes. In addition to the revised arrangement of letters which resulted in the ultimate homogeneity of difficulty per line, the three charts are balanced so that in each
chart the ten letters are represented at least once in every position.