Screening for congenital colour vision defects. A comparison between the Ohkuma and Ishihara plates.

A prospective comparison between the Ohkuma and Ishihara pseudoisochromatic (PIC) plates was carried out in a group of 400 patients attending a general ophthalmology practice. The sensitivity of the Ohkuma test was compared to the Ishihara test, and the specificity of both was determined by reference to anomaloscopy as a gold standard. Both tests correctly identified the same group of 24 patients as having a red/green confusion axis, and the Ohkuma test was equally as sensitive as the Ishihara. The grading plates in both tests are unreliable, but the Ohkuma test is quicker, easier to administer, gives less ambiguous responses and has a clearer cut-off score for abnormality. On the basis of this experience the Ohkuma test is recommended as more appropriate for routine colour vision screening than either the 24 or 38 plate Ishihara tests.