With age many retinal neurons are lost. In humans the rod
photoreceptor population in the perimacular region is subject to
approximately 30% loss over life. Those that remain have been reported to
suffer from extensive convolutions and localized swellings of their outer
segments abnormally increasing their disc content and outer segment
length. Here we examine quantitatively age-related changes in rat rod
photoreceptors. The rat retina is ∼97% rod dominated. Here, aged rods
showed significant reductions in outer segment length. The discs in their
outer segments had a similar density, irrespective of whether they were
young or old, however, in aged animals a higher proportion were
misregistered. Surprisingly, in all of the tissue examined, we found no
evidence for any convolution of outer segments or localized swelling as
reported in humans, rather all remained straight. There are methodological
differences between the research reported here and that undertaken on
human retinae. There are also major differences in overall retinal
architecture between humans and rodents that could contribute to
differences in the aging process of individual cells. If it is the case
that individual photoreceptors age differently in rodents compared to
humans, it may pose significant problems for the use of this animal model
in studies of ageing and age related outer retinal disease.