Aging in the Human Optic Nerve

The human optic nerve parallel processes a myriad of visual functions in addition to Snellen visual acuity. Visual functions such as color vision, perimetry, contrast sensitivity and brightness-sense may be disproportionately involved in certain diseases. For example, we have demonstrated that brightness-sense is particularly impaired by optic nerve conduction blocks (Arch. Ophthalmol. 1985). Animal studies have demonstrated anatomically and physiologically distinct categories of retinal ganglion cell types ('X,' 'Y,' 'W,' cell responses in cats). In man, psychophysical tests such as Enoch's QLLP Testing have shown both sustained and transient type retinal responses. We have demonstrated size classes of axons in a human optic nerve which project in a differential distribution to six primary visual nuclei.