The mean amplitude of the a-waves, b-waves, and OPs of the fmERGs recorded in the 37 eyes with ERM were significantly smaller than the corresponding waves in the normal fellow eyes (
P < 0.0001, Wilcoxon signed rank test;
Table 1 ). The preoperative relative amplitudes (affected eye and normal fellow eye) of the a-waves, b-waves, and the OPs were 75%, 69%, and 45%, respectively. These ratios showed that the OPs were the most affected component of the fmERGs.
In the 37 eyes, the mean b/a ratio in the affected eyes (2.49 ± 0.13) was not significantly different from that in the fellow eyes (2.64 ± 0.09). However, a careful examination of the b/a ratios showed that the size of the ratio depended on the a-wave amplitude. The ratios significantly decreased with increasing the a-wave amplitude (
r = −0.548,
P = 0.0003). To analyze this relationship more carefully, the eyes were divided into two groups: eyes with a-wave amplitude was more than 70% of the fellow eyes (22 eyes) and eyes with a-wave amplitude less than 70% of the fellow eyes (15 eyes). Typical examples of the two groups are shown as case 1 and case 2, respectively, in
Figure 1 . In the first group, there was a significant lower b/a ratio of 2.15 ± 0.15 in the affected eyes than the 2.61 ± 0.13 in the fellow eyes (
P = 0.003, Wilcoxon signed rank test;
Fig. 2 ). In the second group, the difference in the b/a ratio was not significant between the affected and normal eyes (2.99 ± 0.18 vs. 2.67 ± 0.10;
P = 0.08, Wilcoxon signed rank test).
We wanted to determine whether the preoperative visual acuity correlates with the degree of amplitude reduction of the a-wave, b-wave, or OPs and found that the correlations were not significant. However, the preoperative a-wave amplitude correlated significantly with postoperative visual acuity (
r = 0.543,
P = 0.0019;
Fig. 3 ).
The preoperative implicit times of the a- and b-waves in the affected eyes were significantly longer than those in the fellow eyes (P < 0.0001, Wilcoxon signed rank test).
In the 29 eyes that underwent surgery and were observed for more than 6 months, the mean amplitudes of the a-waves, b- waves, and the OPs were significantly larger after surgery (P = 0.0003, P = 0.0051, and P < 0.0001, respectively, Wilcoxon signed rank test). In these eyes, the amplitude of the affected eye versus the fellow eyes was 102% for the a-wave, 81% for the b-wave, and 71% for the OPs. The difference in the mean amplitude of a-wave of the affected eyes from that of the normal eye was not significant (P = 0.596, Wilcoxon signed rank test). However, the postoperative b-waves and OPs were still significantly smaller than their corresponding waves in the normal fellow eyes (P < 0.0001, P = 0.0001, respectively, Wilcoxon signed rank test). Only three eyes showed more than 90% recovery of the amplitudes of all components of the fmERGs.
In 17 of the 29 eyes under observation for more than 6 months and with less severely reduced a-wave amplitude, the mean b/a ratio in the fellow eyes was 2.77 ± 0.24, which was significantly higher than that in the affected eyes before surgery at 2.06 ± 0.19. After surgery, the b/a ratio was still significantly lower at 2.14 ± 0.17. (
P = 0.0004, Wilcoxon signed rank test). In the other 12 eyes with markedly reduced a-wave amplitudes, the mean b/a ratio before surgery was 2.96 ± 0.22 which then decreased after surgery to 2.21 ± 0.13. This ratio was significantly lower than that in normal fellow eyes (2.74 ± 0.14;
P = 0.0047, Wilcoxon signed rank test). The recovery of the fmERGs and macula morphology in the representative two cases in
Figure 1 are shown in
Figure 4 .
The postoperative implicit times of the a- and b-waves were shorter than the preoperative ones, although the differences were not significant. However, the implicit time of each component was still longer than that in normal fellow eyes (
P = 0.0002,
P = 0.0111, respectively, Wilcoxon signed rank test;
Table 1 ).