The origin of most cases of optic nerve atrophy is certainly obscure. There can be no doubt, when the amblyopia and characteristic disk changes follow traumatism, peripheral disease, or there is positive diagnosis of cerebral disease, or following the continued action of some virus or poison in the system, that is known to affect the optic nerve. The occurrence of optic nerve atrophy in general disease always brings with it doubt as to the causative relation. The statements of patients are unreliable especially as regards nature, duration and severity of preëxisting diseases and an element of doubt is always attached to the relation of such a chronic process as nerve atrophy which may have begun months or years after an apparently well authenticated cause.
The atrophy may involve the whole structure of the optic nerve for its whole length, or may be complete in only a portion; it may effect