APOE and endothelial dysfunction: Third, total cell number in the RGC layer and axon number in the optic nerve was not affected by the lack of apolipoprotein E. These findings illustrate that apolipoprotein E deficiency causes oxidative stress and endothelial dysfunction in retinal arterioles, but no oxidative damage in nonvascular retinal tissue probably by effective buffering of excessive ROS and RNS generation by antioxidant redox enzymes.