Divides the electroretinogram components in a sequence of their disappearance, that is, PI, PII, and PIII. The PI component is a slow cornea-positive wave. In contrast, although the PII is a cornea-positive wave, it rises relatively fast to the amplitude during its peak before recovering to a midway potential with the stimulus light still on. The PIII corneal-negative wave progresses faster than PI and PII and remains a negative potential with the stimulus light on.