Fig. 3(b) shows a comparison between the IOSs recorded from the OS-RPE layer and the ERG trace. The OS-RPE trace shows a slow decrease in tissue reflectivity between 5 ms and after stimulus onset, a subsequent faster decrease, and a negative peak at 34 ms after stimulus on-set. This behavior was followed by a fast increase in reflectivity, which peaked at 67 ms after stimulus onset. The negative peak in the OS-RPE IOS appears to correlate with the end of the steep rise of the B-wave and the positive peak in the IOSs recorded from the inner retinal layers, whereas the positive peak appears to correlate with the end of the oscillatory potentials in the ERG and the negative peak in the IOSs measured in the inner retinal layers. Considering the fact that the ERG trace is an integrated electrical response of different retinal cells comprising the retinal layers, it is likely that the difference between the timing of the positive and negative peaks in the IOSs from various retinal layers and the a- and b-waves in the ERG trace is due to a combination of the electrical responses that occur simultaneously in different retinal layers. For example, the slow PIII response, the cornea-negative wave potential that is maintained for the duration of the light flash in the ERG recording, is masked by the simultaneous positive electrical activity in the inner retina arising from the bipolar and Müller cells, thus defining the timing and magnitude of the a- and b-wave peaks.1 In contrast, fOCT measures the individual optical responses from the various retinal layers that correspond to physiological processes such as cell membrane de- or hyperpolarization, cell swelling or deswelling resulting from ion exchange and water in- and efflux between the intra- and extracellular matrix, metabolic activity, etc. Although these physiological processes develop in parallel over time, fOCT in contrast to ERG, is able to resolve the spatial location in the retina (in depth) where these processes occur.