Visual acuity is the quantifiable measure of the ability to identify black symbols on a white background at a standardized test distance. The most commonly measured type, recognition visual acuity, is defined as the ability to discern certain optotypes (letters, numbers, or figures) at a specified distance. Ideally, tests of visual acuity should have the same number of optotypes for each acuity level and the same proportional decrease in size from one acuity level to the next smaller level in logMAR progression.(32)
For visual acuity testing, appropriately scaled (logMAR) single crowded HOTV letters or Lea symbols surrounded by crowding bars at a 5-foot (1.5 meter) test distance with the child matching or reading the optotypes aloud should be used.
A passing score is the correct identification of 3 of 3 or 3 of 4 optotypes with each eye at the 20/50 level for children 36 through 47 months and at the 20/40 level for children 48 to <72 months.
Acceptable practices are to use the HOTV or LEA symbols calibrated for a 10-foot (3 meter) test distance or to use a single line of these optotypes surrounded by a rectangular crowding bar on all four sides.
Other optotypes like Allen pictures and the Tumbling E should not be used.