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This vintage Keystone Diagnostic Series DB-12 Blue-Yellow Color Blind Test Card was produced by the Keystone View Company as part of their professional eye-training and diagnostic sets. The card displays multiple dot-matrix number plates designed to evaluate blue-yellow color discrimination, a less common but clinically important form of color-blind screening.
The front of the card features numbered test squares containing patterned digits such as 1, 4, and 8, each rendered with color-contrast techniques used in early color-vision diagnostics. Designed for use in Keystone eye-training stereoscopic systems, these cards were traditionally used in schools, clinics, and optometry offices.
This piece is ideal for collectors of optical devices, medical history, and Keystone stereoview material, or for anyone assembling a complete Keystone diagnostic or training set.
Condition:
This is a specialized diagnostic Keystone card, part of a professional optometric testing set—more desirable than standard stereoviews.
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