In a scotopic ERG, which waveform is labeled as "c"?

• A. A-wave
• B. B-wave
• C. C-wave
• D. D-wave

Answer: (C)

In an ERG, the different waves reflect activity from distinct retinal layers, especially in scotopic (rod-dominated) responses. The initial negative deflection comes from photoreceptors (rods) responding to light. The following positive deflection arises mainly from ON-bipolar cells (with Müller cells contributing as well). The waveform labeled as c is the slow, late-positive component that follows the b-wave and is generated by the retinal pigment epithelium in response to changes in photoreceptor activity and subretinal ion flux. This c-wave is typically slower and can be more prominent under certain stimulus conditions, which is why it’s identified separately from the earlier a- and b-waves.