Pseudoisochromatic plate testing: are we measuring color vision or something else?

Color vision testing with pseudoisochromatic (PIP) plates [Hardy-Rand-Ritter (HRR), Ishihara] is a typical part of the neuro-ophthalmologic examination, and abnormal responses are often used as evidence of optic neuropathy. However, color disc arrangement tests such as the Farnsworth D-15 are the gold standard for detecting and classifying color vision deficits. The aim of this study was to determine if apparent color vision deficits on HRR and Ishihara plate testing represent truly aberrant color vision or indicate a decrement of other psychovisual parameters.