Effects of age on nerve fibers in the rhesus monkey optic nerve

Abstract

During normal aging there is a reduction in white matter volume in the cerebral hemispheres and structural abnormalities in myelin in some parts of the central nervous system, but whether nerve fibers are lost with age and whether the myelin changes are ubiquitous is not known. Studying the optic nerve, which is a circumscribed bundle of nerve fibers, offers an opportunity to gain further insight into the effects of normal aging on white matter. The present study examined the optic nerves from young (4-10 years) and old (27-33 years) rhesus monkeys using light and electron microscopy. These nerves had been perfused transcardially to obtain optimal preservation of the tissue. Varying degrees of degeneration were encountered in all the optic nerves from the old monkeys. The changes included myelin abnormalities, similar to those reported in other parts of the central nervous system; the presence of degenerating axons and their sheaths; changes in neuroglial cells; and thickening of the trabeculae of connective tissue in the nerve. The total number of nerve fibers was reduced from an average of 1.6 x 10(6) in the young optic nerves to as few as 4 x 10(5) in one old monkey, and with one exception in all of the old optic nerves the packing density of nerve fibers was less than in any of the young optic nerves. The degenerative changes were most marked in those optic nerves that contained the fewest nerve fibers.

Age-related changes in the thickness of the human lamina cribrosa

“…6 Our results confirm this difference in beam thickness through the lamina cribrosa and also that beam thickness increased with increasing age in a subset of eyes. Several studies on human and primate optic nerves have found a thickening of the trabeculae of the fibrous connective tissue fascicles of the optic nerve with increasing age, [15][16][17] so it would be reasonable to find a similar increase in CBT with increasing age.…”

Age-related changes in human and non-human primate white matter: from myelination disturbances to cognitive decline

“…At these splits, large inclusions of fluidfilled balloons or of dense inclusions were observed. These forms of myelin pathology were observed in subcortical WM of the primary visual cortex (Peters et al 2000), prefrontal cortex, and the corpus callosum (Peters and Sethares 2002), as well as the anterior commissure (Sandell and Peters 2003) and in the optic nerve (Sandell and Peters 2001). Additionally, there was significant evidence of remyelination, as reflected by the presence of redundant myelin and of increased frequency of paranodes that could reflect a shortening of internodal myelin lengths as damaged myelin was replaced by new myelin .…”

Age-related ocular vascular changes

“…Age-related changes to the optic nerve include a decrease in the number of axons [12], axonal swelling at the level of the lamina cribrosa [13], thickening of lamina cribrosa [14] and an increase in elastic fibers [15]. Harwerth et al reported a mean decline of 3 µm in retinal nerve fiber layer per decade, which represents a loss of approximately 60,000 retinal ganglion cells; furthermore, on average the retina of a 25-year-old has twice as many retinal ganglion cells as that of a 95-year-old patient [16].…”