• The number and distribution of human optic nerve axons were compared with clinical measurements available in the same eyes, including visual acuity, disc appearance, and visual field studies. Definite loss of axons occurs prior to reproducible visual field defects in some patients suspected of having glaucoma. In glaucoma, the superior and inferior poles of the nerve lose nerve fibers at a selectively greater rate, leading to an hourglass-shaped atrophy. Cavernous degeneration of the retrobulbar optic nerve is rarely observed in chronic glaucoma. The pattern of atrophy in examples of toxic amblyopia, ischemic optic neuropathy, and chronic papilledema differs from that of glaucoma, suggesting different mechanisms of damage in these conditions.
Quigley HA, Addicks EM, Green WR. Optic Nerve Damage in Human GlaucomaIII. Quantitative Correlation of Nerve Fiber Loss and Visual Field Defect in Glaucoma, Ischemic Neuropathy, Papilledema, and Toxic Neuropathy. Arch Ophthalmol. 1982;100(1):135-146. doi:10.1001/archopht.1982.01030030137016