To investigate whether or not the aging phenotype has increased vulnerability to axonal injury in vivo, we quantitated the loss of retinal ganglion cells (RGCs) after optic nerve crush. After crush, young animals lost 20% in 3 days and 50% of their RGCs in 7 days; however, old animals lost 40% in 3 days and 70% of their RGCs in 7 days. Our results showed that the time course in the loss of RGCs after crush in old mice is faster than that in young mice. Thus, old age increases susceptibility for the loss of RGCs following axonal damage.