The clinical use of the Holmes—Wright lantern

Abstract

The Holmes—Wright colour perception lantern is an occupational colour vision test given to recruits in the Royal Navy, RAF and the Civil Aviation Authority in the United Kingdom. A standardised examination procedure is followed which involves the presentation of 27 paired red, green and white ‘signal’ lights subtending approximately one minute of arc at a distance of 20 feet (6 metres). The examination is first performed in normal room illumination (photopic viewing) and then in the dark after fifteen minutes dark adaptation (scotopic viewing). Failure of the test is considered as any incorrect response including misnaming white as ‘green’ and green as ‘white’. The standard examination procedure and the pass/fail criterion differs significantly from that described in other studies of Lantern tests. Results are presented for 28 colour deficient observers, previously classified with the Nagel Anomaloscope, and 20 normal trichromats. All the colour deficient observers failed the test in both viewing conditions. All the normal trichromats passed the test in photopic viewing conditions but 9 people (45%) failed in scotopic conditions and were denied the optimum colour perception rating (CP1) required for careers as pilots in the British Armed Forces. Eighteen normal trichromats (90%) failed an additional examination under scotopic conditions viewing through +0.50D spherical lenses. The role of vocational lantern tests is discussed in relation to these findings.