Advance in ERG Analysis: From Peak Time and Amplitude to Frequency, Power, and Energy

Figure 4

(a) ERG traces (averaged from up to 100 responses) obtained at seven time points in the right (OD) eye and left (OS) eye of a male patient affected with retinitis pigmentosa (both eyes presented with nonrecordable scotopic ERGs, constricted visual fields, pigmentary deposits, and decreased visual acuity) in a time span of 3 decades. The horizontal (time) and vertical (voltage) scale bars apply to both eyes and some traces have been magnified (×2, ×5, or ×10 times) for visualization purposes. The flash onset is indicated by the black vertical arrow. ERG progression is shown in years since the first visit on the left-hand side. (b) Scalograms computed for each pathological ERG waveform (presented in the same order than in panel (a)) in which we quantified the 20b and 40b descriptors. Note that, in some scalograms, the position of the 40b descriptors was delayed (i.e., delayed latency of the b-wave) compared to normals (see Figure 3) and the 40b descriptors were always more severely attenuated than the 20b. (c) Progression of the TD b-wave amplitudes from both eyes. Because of the noise contaminants the 4th and 5th ERG were imprecisely measured (indicated by the lighter gray background on the graph), while the last two ERGs were nonmeasurable, thus preventing the quantification of disease progression from that point (indicated by the darker gray background). (d) Using the DWT descriptors of the b-wave (20b + 40b) allowed us to monitor the disease progression more precisely and for the whole time span (additional 16 years of monitoring: see zoomed box). (e) Using the inverse DWT, we reconstructed the low-frequency bands (i.e., 20 and 40 Hz bands), obtaining the biological denoised responses which are shown, in red, on top of the unprocessed gray tracings.