the optic nerve is ensheathed in all three meningeal layers (dura, arachnoid, and pia mater) rather than the epineurium, perineurium, and endoneurium found in peripheral nerves. fiber tracts of the mammalian central nervous system have only limited regenerative capabilities compared to the peripheral nervous system. therefore, in most mammals, optic nerve damage results in irreversible blindness. the fibers from the retina run along the optic nerve to nine primary visual nuclei in the brain, from which a major relay inputs into the primary visual cortex.