“…once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In adult centres the nerve paths are something fixed, ended, immutable. Everything may die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree. Inspired with high ideals, it must work to impede or moderate gradual decay of neurons, to overcome the almost invincible rigidity of their connections, and to re-establish normal nerve paths, when disease has severed centres that were intimately associated.” (Santiago Ramon y Cajal, 1913-14).
A discussion of the restoration of visual functions, from WebVision.