Hahn's New Pseudoisochromatic Colour Vision of colour vision deficiencies. They have been less success-Test contains provision for screening red-green and blueful in differentiating protans from deutans. Few have been yellow colour vision deficiencies, a qualitative diagnosis designed to provide a quantitative diagnosis, and even as protan and deutan, and a quantitative diagnosis of fewer of those are still currently available. The benchmark red-green deficiencies. In this study 58 colour vision defiis undoubtedly Ishihara's Test, which, despite being decient and 68 colour vision normal subjects were examined signed over 80 years ago, seems to continue to be the using a battery of colour vision tests. The screening and most widely used colour vision screening test worldwide. classification ability of the Hahn test was compared with Many assessments have shown a high level of achieve-Ishihara's Test and the Standard Pseudoisochromatic ment in separating normal from colour vision deficient Plates (SPP). The quantitative diagnosis ability was assubjects (for summaries see Refs. 1-3). sessed by comparison with the Farnsworth-Munsell D-Many other PIC plate tests have come in the meantime 15 Test, the Farnsworth Lantern, and the Anomaloscope and many have gone. Often they appear to gain currency range. The Hahn proved to have a colour vision screening in their country of origin (for instance, Stilling in Gerperformance comparable with the two other PIC tests. Its many, Tokyo Medical College in Japan, American Optical classification ability was poor compared with the other and Dvorine in the U.S.A. Bostro ยจm-Kugelberg in Swe-PIC tests, one design in the SPP plates was markedly den) without gaining a wider usage. One notable excepsuperior. The Hahn's quantitative diagnosis plates did tion was the American Optical Hardy-Rand-Rittler not produce a useful classification; more than 50% of plates. They achieved wide acceptance and provided a subjects made the full six errors and only 3 of 58 colour quantitative diagnosis more thorough and systematic than vision deficient subjects made less than 3 errors out of any other PIC plate test. Unfortunately, the H-R-R plates the 6 plates. The colorimetric measurements are used to have been long unavailable. illustrate the design features and are consistent with these The availability of a PIC plate test that purports to performances. แญง 1998 John Wiley & Sons, Inc. Col Res Appl, 23, carry out identification of colour deficiencies, protan and 69-77, 1998 deutan differentiation, and a quantitative diagnosis (not Key words: colour vision; colour vision deficiencies; to mention a tritan screening plate) is, therefore, of some pseudoisochromatic plates; clinical assessment significance and, if it performs well, widespread use is likely to eventuate. The ''New Pseudoisochromatic Colour Vision Test'' by Hahn 4 is designed with these four