SCREENING OF RED‐GREEN DEFECTS OF COLOUR VISION WITH PSEUDOISOCHROMATIC TESTS

Abstract

Fifty red-green defective and 100 normal human subjects were examined with the 2nd edition of the Bostrom-Kugelberg (BK II, 1972) series and the Ishihara complete edition (1976) of pseudoisochromatic plates. The results are related to those obtained with the 1st edition of the Bostrom-Kugelberg test (BK I, 1944) and the Bostrom test (II B, 1950) and to the classification of defects obtained with the Nagel anomaloscope. The 50 red-green defectives were originally selected by using a combination of the BK I and II B tests. The normal subjects also, passed this preliminary test, and an examination with the Nagel anomaloscope. In the final examinations performed under standardized conditions, 3 red-green defectives passed both the BK II and the BK I test, while 8 defectives passed the Ishihara test. Combination of BK II or BK I test with the Ishihara test does not improve the result. Only 1 defective (a borderline case of protanomaly) passed the separate II B test. Normal subjects were not classified as colour defectives with any of the 4 pseudoisochromatic tests used. All normal subjects passed both the BK II and the Ishihara test. Classified as suspected red-green defectives (1 misreading made in standardized conditions) were 5 normal subjects with the II B test and 1 normal subject with the BK I test. In the 2nd edition of Bostrom-Kugelberg series, the plates numbered 3, 5, 11, 16 and 18 are clearly less effective than respective plates of the 1st edition. Only the plates numbered 1 and 10 have markedly improved in the 2nd edition. Red-green defectives made on average 0.54 misreadings per plate in the BK II test as compared with respective 0.62 in BK I, 0.69 in the Ishihara and 0.56 in the II B test.