When the effects of gene therapy on preserving RGCs were quantitated, we found that although treatment with AAV-
ECSOD suppressed RGC loss by 9% with a mean of 1274 ± 230 cells/mm
2 compared with 1156 ± 254 cells/mm
2 for control EAE eyes injected with AAV-
GFP, this difference was not significant (
P = 0.44;
Fig. 6A ). Although AAV-
CAT–treated eyes had 13% more RGCs with a mean of 1332 ± 171 cells/mm
2 compared with 1163 ± 87 cells/mm
2 for EAE control eyes inoculated with AAV-
GFP, this difference was not significant (
P = 0.08;
Fig. 6A ). However, for eyes that received both antioxidant genes, we found ganglion cell loss was suppressed by 29% with a mean RGC count of 1613 ± 248 cells/mm
2 compared with 1142 ± 139 cells/mm
2 for
GFP-inoculated EAE controls. This difference was highly significant (
P = 0.009;
Fig. 6A ). Compared with the normal optic nerves of mice that were not sensitized for EAE, AAV-
ECSOD–treated eyes had a 27% loss of RGCs (
P = 0.006). In eyes that received AAV-
CAT, ganglion cell loss was 24% (
P = 0.004). With combined antioxidant gene treatment, RGC loss was limited to 9% compared with the normal optic nerve (
P = 0.22); this difference was not statistically significant. Therefore, combined ROS scavenging preserved the normal complement of RGCs 6 months after sensitization for EAE, whereas neither ECSOD nor catalase did.