4 Meter 2000 Series Revised ETDRS Chart "1" from Precision Vision®

This "revised" ETDRS chart incorporates a slight change in difficulty score for each of the ten Sloan optotypes. These difficulty levels were derived from the best corrected visual acuity examinations of 7,420 eyes during the ETDRS study. The difficulty scores from the "original" charts were derived from the examination of 234 eyes. This further testing helped to pinpoint difficulty levels and further calibrate this already reliable test.