The magnitude of RNFL thickness at baseline was 101.1 ± 9.4 μm and 101.2 ± 9.8, respectively, in the group of eyes assigned to be EG and fellow control eyes (
P = 0.80). At the final available time point, RNFL thickness had declined to 86.7 ± 15.1 μm in EG eyes (
P < 0.0001) but had not changed in fellow control eyes (101.9 ± 10.9,
P = 0.20,
Fig. 1A). Retinal nerve fiber layer retardance at baseline was 58.5 ± 5.2 μm and 58.6 ± 5.2, respectively, in the group of eyes assigned to be EG and fellow control eyes (
P = 0.92). At the final available time point, RNFL retardance had declined to 46.6 ± 7.2 μm in EG eyes (
P < 0.0001) but had not changed in fellow control eyes (58.9 ± 6.3,
P = 0.50,
Fig. 1B). The mfERG HFC amplitude at baseline was 94.8 ± 15.4 nV and 96.3 ± 16.8 nV, respectively, in the group of eyes assigned to be EG and fellow control eyes (
P = 0.13). At the final available time point, mfERG HFC amplitude had declined to 66.8 ± 19.3 nV in EG eyes (
P < 0.0001) and also declined slightly in fellow control eyes (to 87.8 ± 15.8 nV,
P = 0.0001,
Fig. 1C). The average change from baseline in EG eyes was −14.1 ± 14.1% for RNFL thickness (range, +8.8% to −52.1%), −20.2 ± 11.2% for RNFL retardance (range, −4.4% to −44.1%), and −29.7 ± 16.6% for mfERG HFC amplitude (range, +10.4% to −54.4%). The decline in the control eye group for mfERG HFC amplitude represented a −8.2 ± 12.2% change from their baseline amplitudes. The amplitudes of the mfERG LFC features also declined slightly from baseline in both EG and fellow control eye groups: N1 decreased by 10.3 ± 16.7% and 4.8 ± 16.3% in EG and control eyes, respectively, but there was no significant difference in the magnitude of change between EG and control eyes (
P = 0.10,
Fig. 1D); P1 decreased by 9.0 ± 17.1% and 8.5 ± 12.0% in EG and control eyes, respectively, but again there was no significant difference in the magnitude of change between EG and control eyes (
P = 0.88,
Fig. 1E); N2 decreased by 19.4 ± 17.8% and 9.5 ± 13.7% in EG and control eyes, respectively, a difference that was greater in EG as compared to control eyes (
P = 0.006,
Fig. 1F). The longitudinal changes observed in the fellow control eye group for all mfERG parameters suggest possible effects of chronic exposure to anesthesia, frequency of the testing protocol, and perhaps aging, which appear to impact EG and control eyes equally for the LFC features N1 and P1.