We compared the clinical appearance of the retinal nerve fiber layer (NFL) and its histology in primate eyes. In 12 eyes with NFL lesions induced by orbital optic nerve trauma, clinical detection of NFL atrophy was possible after loss of 50% of the neural tissue in a given area. Some retinal areas with no visible NFL striations had remaining nerve fibers. The detectability of NFL atrophy was directly affected both by the pattern of nerve fiber loss as well as by the zone of the retina in which the loss occurred. While each nerve bundle gives rise to a single light striation nasal and temporal to the nerve head, this one-to-one correspondence is not true above and below the disc, where bundles are thicker and incompletely divided by glial septa.