Ascending and descending optic atrophy produced experimentally in squirrel monkeys.

The axons that make up the optic nerve originate from the retinal ganglion cells and extend from there to the lateral geniculate body. If cellular integrity is interrupted by disease anywhere along the course of an axon, degeneration occurs in both directions from the point of insult. Thus, axon frag­ ments between the site of injury and the lat­ eral geniculate body are separated from their nuclei (retinal ganglion cells) and degener­ ate. As an example, the optic nerve degener­ ates when the retinal disease affects the nerve fiber layer or ganglion cells (ascending optic atrophy). On the other hand, the por­ tion of the axon still attached to its cell body in the retina will also degenerate. For exam­ ple, the optic nerve degenerates when seg­ ments of the axons are destroyed intracranially or at the orbital apex (descending optic atrophy). Such descending optic atrophy ex­ tends all the way into the retinal nerve fiber layer and in fact includes disappearance of the retinal ganglion cells. Reported here are observations on the de­ velopment of ascending and descending optic atrophy produced experimentally in squirrel monkeys. To obtain descending optic atro­ phy, I severed the optic nerve as far poste­ rior in the orbit as was feasible. To obtain ascending atrophy, I destroyed nerve fibers coursing toward the disk by full-thickness photocoagulation in a ring around the disk.