Intra-sessional and inter-sessional variability of multifocal electroretinogram

The aim of this study was to investigate the intra-sessional and inter-sessional variability of the multifocal electroretinogram (mfERG). Right eyes of 20 healthy adult subjects with uncorrected visual acuity of 1.0 were studied. mfERG recordings were obtained in two sessions by using jet corneal electrodes. The responses were averaged over five retinal regions, the central hexagon (CH: 0.0–2.3°) and four concentric rings [ring 1 (R1: 2.3–7.4°), ring 2 (R2: 7.4–12.0°), ring 3 (R3: 12.0–19.4°), and ring 4 (R4: 19.4–30.0°)]. In the first session, recordings were repeated while the electrodes stayed in place (the first and the second recordings). Second sessions (third recordings) were performed 1 week later. Individual coefficient of variation (CV; standard deviation/mean) for P1 and N1 amplitudes and implicit times were calculated for the first to second and first to third recordings to assess intra-sessional and inter-sessional variability, respectively, and were evaluated by Wilcoxon-paired samples test. Regarding implicit time and amplitude of mfERG recordings, there was no significant difference between the first to second and first to third recordings (P > 0.05, Bonferroni-corrected Wilcoxon test). CV values significantly decreased with eccentricity in both intra-sessional and inter-sessional comparisons (P < 0.05, Wilcoxon test). However, partial ring averaging showed no significant difference (P > 0.05) between CV values for single hexagons in each ring. Intra-sessional CV values were significantly lower than corresponding inter-sessional values (P < 0.05, Wilcoxon test). Our results support the importance of electrode replacement on variability. The increased number of hexagons that are averaged is the main factor that explains the lower variability in the more peripheral rings.