Survey of the accuracy of new pseudoisochromatic plates

The accuracy of three new pseudoisochromatic tests for detecting red-green colour deficiency was assessed. These were the Ishihara plates, the Ishihara test for 'unlettered persons' and Ohkuma's test cards. We examined 500 subjects; 471 normal trichromats and 29 colour-deficient people. Results obtained for the 1989 edition of the Ishihara plates were compared with the 9th edition and the most efficient plates identified. Although normal trichromats may be expected to make several interpretive misreadings, the Ishihara plates were found to be superior to the 9th edition and to the Ohkuma test (1986) for colour vision screening. The new symbol designs of the Ishihara plates for 'unlettered persons' (1990) were found to be very effective for colour vision screening, and a further study with young children is proposed. The 38 plate 1989 edition of the Ishihara test is recommended for use in clinical practice. The designs included in the concise 24 plate edition and the new abbreviated 14 plate edition are not selected from the point of view of accuracy and more reliable results are obtained if the full test is given or if the practitioner shows only the most efficient designs.