For four weeks after severance of the optic nerve at the apex of the orbit, the axons in the optic nerve, optic disk, and retinal nerve fiber layer, as well as the ganglion cells, appeared normal. Between four and five weeks, the nerve fibers disappeared from view by fundus photographs, and the disk turned pale. By electron microscopy, the axons simply disintegrated and disappeared simultaneously along the whole axon with practically no inflammation or macrophagic activity except where the nerve had been incised. The myelin collapsed and disintegrated very slowly over subsequent months, and remnants were still present six months later. The scaffolding of septa and glia simply collapsed onto the empty space left by the axons, leaving the microscopic picture of columnar optic atrophy (isomorphic). Ascending atrophy followed the same morphologic sequence, but it began within two weeks after destruction of the retinal nerve fibers by photocoagulation.
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