Keystone Telebinocular Tests of Visual Efficiency #6, DB-2B A Test of the Visual Efficiency of the Left Eye under a normal fusion situation.
Test 5, DB-1B: A Test of the Visual Efficiency of the Left Eye under a normal fusion situation.
This stereograph appears in several of Keystone's optical series; this particular card belonging to the Keystone Telebinocular Tests of Visual Efficiency, "for use with Keystone Ophthalmic Telebinocular, Visual Survey Telebinocular, or Keystone Tel-EYE-Trainer."
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, with edgewear and sticker; 3.5 X 7 inches. Housed in mylar sleeve for safekeeping.