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Eriko Miyahara, Patrick C. Hwang; Misreading patterns of Ishihara plates by normal trichromats. Journal of Vision 2006;6(6):235. doi: 10.1167/6.6.235.
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© ARVO (1962-2015); The Authors (2016-present)
Ishihara Pseudoisochromatic Plates have been known to be one of the best screening tools for red-green color vision deficiencies. Although majority of the normal trichromats read all the plates correctly, it has been known that some normal trichromats make mistakes in reading the plates. The purpose of this study was to obtain reading results of Ishihara plates by normal trichromats and analyze the misreading patterns to seek potential explanations.
Methods. Reading data on Ishihara plates (abbreviated version, 2001) and the anomaloscope setting were obtained from 249 normal trichromats as part of color vision screening procedure for psychophysical experiments. The spectral reflectance of each color of dots in the Ishihara plates was measured by GretagMacbeth Spectrolino Spectrophotometer and plotted in the DKL cone-excitation space. Each plate was scanned into a digital image file and colored dots were put into separate layers to simulate various combinations of reading patterns.
Results. Out of 249 normal trichromats, 111 individuals (45%) misread at least one plate. The common misreading patterns generally followed the reading behavior of color vision defectives. Otherwise, the misreading patterns appear to originate in the cognitive aspect. For instance, the plate number 13 that should read “73” was misread as none (response by color defectives), 7, 13, 18, 23, 28, or 78. These misreading patterns cannot be predicted by chromaticity coordinates of the colored dots. Rather, the interpretation of “7” (can be read as 1 or 2 due to the unique Ishihara style) or “3” seem to induce various misreading patterns.
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