Performance of colour-deficient people on the Holmes-Wright lantern (type A): consistency of occupational colour vision standards in aviation

Introduction: The Holmes-Wright lantern type A (H-W A) is an occupational colour vision test used by the UK Civil Aviation Authority (CAA) and approved by Joint Aviation Requirements (JAR) to select aircrew. Pass, to obtain a CAA Class 1 Aviation medical certificate, can be achieved at three stages of the examination. The Commission Internationale d'Eclairage (CIE) recommends that the Falant pass criteria are used with all approved lanterns. A pass to obtain CIE Colour Vision Standard 2 can be achieved at two stages of the examination. This study examines the consistency of these pass criteria. Methods: One hundred and twenty-five men with red-green colour deficiency were examined. All subjects completed three runs of the nine colour pairs shown on the H-W A at high brightness, in photopic and scotopic viewing. Results: Ten of 78 deuteranomalous trichromats examined passed to obtain a CAA Class 1 Aviation medical certificate at the first stage of the examination but only two of these subjects were successful at all three stages. Seventeen deuteranomalous trichromats passed to obtain CIE Colour Vision Standard 2 in photopic viewing and 20 subjects (one protanope and 19 deuteranomalous trichromats) passed in scotopic viewing. Only 50% of subjects who passed at the first stage of the examination were also successful at the second stage in either viewing condition. Ten deuteranomalous trichromats passed to obtain CIE Colour Vision Standard 2 in both photopic and scotopic viewing. Forty-three per cent of subjects made red-green errors and 79% made red-white errors at some stage of the examination. Conclusions: The staged pass criteria used by the CAA and the CIE lack internal consistency when applied to the H-W A. Colour-deficient people who pass to a standard at the first stage of the examination are unlikely to be successful if the examination is continued. The staged pass criteria do not identify individuals with superior colour discrimination ability and it is difficult to justify selection of personnel for high risk occupations in aviation on this basis.