Scatter plot of X-Gal staining scores for individual retinas from aged DBA/2J R3/+ mice compared to aged C57BL/6R3/+ animals. Loss of X-Gal staining correlates to the loss of retinal ganglion cells . A majority of DBA/2J mice older than 10.5 months exhibit reduced staining, relative to younger animals (closed circles). Although these mice develop progressively more damage as they age, there is a high degree of variability in the amount of damage exhibited by mice at the older ages. Retinal disease is associated with the DBA/2J genetic background, since no cell loss was observed in C57BL/6 mice (open circles) at any age examined.