Everyone knows the Snellen chart, standardized in the 1860s by Herman Snellen, MD, who defined the formula expressing how well a person sees in the form of a fraction. His ratio of 20/20 is well known but he left the door open in terms of visual acuity tests. Although most people know the standard assessment with its pyramid of letters, there were numerous attempts to improve its function, especially for young children who didn’t yet know the alphabet. The test, above left, dates to 1950 and includes a two-sided Snellen chart for youngsters and people who can’t read. One side has the rotating “E” and the second side has pictures. The black wooden box, above right, was used in the ’20s to ’40s, and contains a flip chart with 20 different shapes in a range of sizes and matching wooden blocks. To test a young patient’s visual acuity, eyecare professionals would place the flip chart on the wall and ask a child to choose which block matches the shape on the chart.
Courtesy of The Museum of Vision, museumofvision.org.