Is the c-wave positive or negative?

Is the c-wave positive or negative?

• A. Positive
• B. Negative
• C. Zero
• D. Undefined

Answer: (A)

The c-wave is a slow, positive deflection seen in the electroretinogram, mainly produced by the retinal pigment epithelium’s response to light. When light changes photoreceptor activity, ions in the subretinal space shift and the RPE adjusts its transepithelial potential. This coordinated response creates a net positive change in the extracellular potential that the recording electrode picks up, so it appears as a positive wave on the ERG trace after the initial a- and b-waves. In normal recordings, this c-wave is clearly positive and slower than the earlier waves; its magnitude can drop with certain retinal diseases affecting the RPE or outer retina, but the sign remains positive under normal conditions.

The c-wave is a slow, positive deflection seen in the electroretinogram, mainly produced by the retinal pigment epithelium’s response to light. When light changes photoreceptor activity, ions in the subretinal space shift and the RPE adjusts its transepithelial potential. This coordinated response creates a net positive change in the extracellular potential that the recording electrode picks up, so it appears as a positive wave on the ERG trace after the initial a- and b-waves. In normal recordings, this c-wave is clearly positive and slower than the earlier waves; its magnitude can drop with certain retinal diseases affecting the RPE or outer retina, but the sign remains positive under normal conditions.