We have examined by light and electron microscopy the retina, optic nervehead, and optic nerves of 21 human eyes from glaucoma patients in whom clinical information was available for comparison. In several cases it was possible to correlate the degree and distribution of optic nerve damage with the clinical appearance of the optic disc and visual field studies. There was no selective loss of astrocytes of the optic nervehead in early glaucoma cupping. Acquired increases in optic disc cup size prior to detectable visual field loss probably represent loss of ganglion cell axonal fibers which is not yet significant enough to produce field defects. It is unlikely that the mechanism of axonal damage in chronic human glaucoma involves early loss of astrocytic glial cells at the optic nervehead. At the level of the retrobulbar optic nerve, the ganglion cell axonal fibers of the superior and inferior quadrants seem to be lost earlier than the fibers of the nasal and temporal nerve periphery. Since the superior and inferior poles of the optic nerve may contain the fibers of arcuate area ganglion cells, these data confirm the presumption from visual field testing that arcuate area ganglion cell fibers are selectively more susceptible to damage in chronic glaucoma.