Performance of red-green color deficient subjects on the Holmes-Wright lantern (Type A) in photopic viewing

Abstract

Background: The Holmes-Wright lantern (Type A) is an approved occupational color vision test for airline pilots in the European Economic Community and for specific occupations in the British Armed Forces. The colors shown are red, green and white signal lights.

Hypothesis: The Holmes-Wright lantern is a sensitive screening test for red-green color deficiency in photopic viewing and the pass/fail level is similar to that of the Farnsworth Lantern (Falant) if the same scoring method is applied.

Method: There were 138 color deficient subjects identified with the Ishihara plates and diagnosed with the Nagel anomaloscope, completed a color vision test battery which included three runs of the nine color pairs of the Holmes-Wright lantern at high brightness in normal room illumination.

Results: Screening sensitivity on a single error was found to be 97% compared with the Ishihara plates. Using the Falant scoring method, 20 subjects passed. These were 1 deuteranope, 2 protanomalous trichromats and 17 deuteranomalous trichromats (22% of 88 anomalous trichromats). The mean error score was greater for protans than for deutans but the mean number of qualitative error categories was smaller. Green/white confusions were the most frequent errors. It was not possible to predict who would pass the lantern test from other test results but all subjects with a Nagel anomaloscope matching range > 15 scale units who failed the Farnsworth D15 test or were grading as moderate/severe with the American Optical Company (Hardy, Rand and Rittler) plates failed.

Conclusions: The Holmes-Wright lantern is a sensitive screening test for red-green color deficiency. Although a similar percentage of anomalous trichromats fail the Holmes-Wright lantern as fail the Falant, if the same scoring method is used, the superior correlation between the Holmes-Wright result and other color vision tests designed to grade the severity of color deficiency suggests that the two lantern results are not equivalent.