Photoreceptors Practice Test

Under photopic (cone-driven) conditions, the ERG shows a distinct positive deflection at light offset called the d-wave, which reflects the OFF responses of cone pathways (cone OFF bipolar and related cells) when the light is turned off. This OFF response is characteristic of cone-mediated activity and becomes prominent only when the retina is in a photopic state. In scotopic (rod-driven) testing, the waveform is dominated by rod responses and the d-wave is not a prominent feature. So the d-wave is associated with the photopic ERG.