Figures 3A and
3B illustrate ERG a-wave amplitudes across the study in all groups. In unoperated control eyes, a-wave amplitudes dropped rapidly between 4 and 8 weeks of age (over 50% amplitude loss), compared with the initial ERGs in this group. Amplitude reduction rates then slowed and by the end of the study were 63.2% ± 9.4% less than the initial values (
P < 0.001). A similar pattern was observed in the inactive IDDI-treated eyes, whose end point amplitudes were 58.7% ± 8.0% lower than their initial values (
P < 0.001). No statistically significant difference was found in the end point values between these two groups (
P > 0.59). ERG a-wave amplitude loss was significantly lower in both FA-treated groups, with better preservation seen in the eyes treated with the lower daily FA dose. End point a-wave amplitudes in the FA 0.2-μg/d–treated eyes were 22.3% ± 15.5% lower than initial ERGs; the difference was not statistically significant (
P = 0.09). In the FA 0.5-μg/d–treated eyes, end point a-wave amplitudes showed 37.7% ± 10.7% reduction compared with the initial ERGs, which appeared to be significant (
P = 0.029). There was no statistically significant difference in end point ERG a-wave amplitudes between the two FA groups (
P > 0.1). End point a-wave amplitudes were significantly greater in the FA 0.2-μg/d–treated eyes compared with the unoperated control eyes (
P < 0.001) and with the inactive IDDI-treated eyes (
P < 0.01). However, end point a-wave amplitudes of the FA 0.5-μg/d–treated eyes were significantly greater only compared with the unoperated control eyes (
P < 0.05) and did not show statistically significant differences compared with the inactive IDDI-treated eyes (
P = 0.118). In addition, left (unoperated) eyes of the FA 0.2-μg/d–treated animals also showed significant preservation of the ERG a-wave amplitudes compared with both control groups (
P < 0.05). ERG a-wave implicit times (
Figs. 4A,
4B) did not show statistically significant changes during the study within or between groups.