Printed pseudoisochromatic plates are the most widely used type of color vision test to screen for color vision deficiency. The principle is that the color of a target (digit or letter) embedded in a background of another color appears “falsely of the same color” to color-deficient people. Target and background chromacities are chosen carefully to be the ones confused by people with color vision deficiency.
Design of Pseudoisochromatic Plates
Pseudoisochromatic plates must be carefully designed in order to be effective. As a result of the printing process, minor misalignments between a figure of one chromaticity and the uniform background of another undistinguishable chromaticity may reveal the shape of the digits or letters. In addition, the relative luminous efficiency of the eye varies considerably within normal trichromats and even more so in color-deficient observers. Hence, a figure and...