Introduction: The Ishihara plates are commonly used as an initial occupational screening test for color vision. While effective at detecting red-green deficiencies, the color deficient subject can learn the test using different techniques. Some medical standards such as the European Aviation Safety Agency (EASA) require plate randomization and apply a stricter pass/fail requirement than suggested by Ishihara. This has been reported to increase the false positive rate up to ∼50%.
Method: Two modifications to the Ishihara protocol are investigated. These involved allowing subjects a second attempt where one or two reading errors were made and the presentation of rotated Ishihara plates.
Results: A reduction of false positive rate to 5.9% was found. Correct identification of certain rotated Ishihara plates was not affected.
Discussion: By using a modified Ishihara protocol, fewer color normal subjects would require unnecessary advanced color vision examination. Further, additional safeguards would be in place to ensure that no subject with a color vision deficiency could pass the Ishihara test.