These color vision tests have been designed by Dr Hahn for the screening, classifying the type and estimating the grade of color deficiency. These plates are designed to measure Red, Green, Blue, Yellow. They provide classification of strong, medium and mild color deficiencies. Screening is accomplished using the initial 12 plates. Nine diagnostic plates use numbers and ‘winding lines’. Total plates for type A and B is 21 plates.
The tests were designed according to the Pitt’s and Judd’s Isocolor Theories for color defectives using the C.I.E. chromaticity diagram and Standard color paper (JIS Z8721-1964). Clinical testing over the past 12 years has shown that these Isochromatic tests yield a more accurate results compared to the Ishihara tests which were designed in 1917.. Dr Ohta has shown the misdiagnosis of the Ishihara test to exceed 12%. Further, the Ishihara test only tests for Red/Green and does not categorize the defect to strong, medium or mild defect.