Which waves are found on a photopic ERG?

• A. a, c, d
• B. b, c, d
• C. a, b, d
• D. a, b, c

Answer: (C)

In a photopic ERG, which records cone-driven activity under bright light, you mainly see three components: the a-wave, the b-wave, and the d-wave. The a-wave comes first and reflects the initial hyperpolarization of cone photoreceptors in response to the flash. The subsequent b-wave is produced by bipolar cells (and influenced by Müller cells) as the inner retina responds to that cone input. When the light is turned off, an additional deflection called the d-wave can appear, representing activity in the OFF pathway as the retina returns toward baseline.

The c-wave, on the other hand, is a slow potential largely tied to the retinal pigment epithelium and changes in subretinal potassium during and after illumination. It is not a typical feature of standard photopic recordings, which focus on the immediate cone-driven responses. Therefore, the waves you’d expect in a photopic ERG are the a-, b-, and d-waves.