Keystone Telebinocular Tests of Visual Efficiency #11, DB-6D: A Test for Stereopsis
Test 11, DB-6D: A Test for Stereopsis (cross-eyedness)
This is one of Keystone's more unusual stereograms, a test for stereopsis (or "cross-eyedness") that boasts less than 50% accuracy, but makes up in aesthetic what's lacking in efficacy.
Keystone View Company (Meadville, PA) published several series of stereoscopic images promoted as optical diagnostic and therapeutic tools in the 1930s and '40s—including the "Eye-Skill Series," "Comfort and Depth Perception Series," and "Betts Ready To Read Tests."
Card slightly bowed (as typical), otherwise VG; 3.5 X 7 inches. Housed in mylar sleeve for safekeeping.