Studies on pseudoisochromatic plates for classification of degrees of color vision deficiency

Tokyo Medical College (TMC) plates and Okuma plates were evaluated as tools to classify degrees of color deficiency. These two pseudoisochromatic plates are most widely used in Japan. One hundred and twenty-eight protanopes, 427 deuteranopes, 187 protanomals and 445 deuteranomals, that is, 1187 cases in total were tested using several kinds of pseudoisochromatic plates, Panel D-15 test, JFC lantern test and anomaloscope. The results of TMC plates and Okuma plates were studied. Generally speaking, classification of degree with TMC plates was significantly more severe than that with Okuma plates. For instance, 96.9% of protanopes and 74.5% of deuteranopes were diagnosed as severe degree by TMC plates, while by Okuma plates, only 30% of protanopes and 53% of deuteranopes were the cases. Consequently, classifications of the two plates are inconsistent in majority. It is because the basis of classification differs from each other; hue discrimination in yellowred to yellow-green in TMC plates, while grade of desaturation in neutral colors in Okuma plates. Furthermore, the color differences used in the pseudoisochromatic plates are not sufficient enough to separate severe, moderate and mild ones, therefore individual variation or slight changes of test condition are likely to make the results confusing. After all, pseudoisochromatic plates alone are not valid for classification of degrees of color deficiency. Some other color vision tests should be combined for the purpose.