Forever young: Visual functions not affected or minimally affected by aging: A review

Sir visual functions, once developed to adult levels of performance, have b een noted to exhibit little or no alteration with aging (also see Appendix, Note I). Those selected for more substantial discussions in this article a re: (a) the Stiles-Crawford effect of the first kind (SCE-I) also known as the "directional sensitivity of the retina" (b) specific vernier acuity par adigms (including alignment of two lines one with the other, and two- and t hree-point vernier alignment tasks); and (c) color vision-related perceptua l constancies. Each of these functions has rather different origins in the visual system. The SCE incorporates optical waveguide photoreceptor propert ies and has both physical and physiological origins; vernier (acuity tone o f the hyperacuities) is largely the result of neural data processing mechan isms; and the color vision-related effects have their origins in retinal ne ural processes. Descriptions of additional visual functions minimally affec ted by age are presented as well This recent research raises many questions . How care these visual responses be so stable, when so many other visual r esponses show decrements with aging? What does it mean if anomalous respons es within the more stable functions are encountered in individuals? Can the se age-resistant functions be employed to help sustain other functions in a ging individuals? Are such relatively invariant functions limited to the vi sual system? Because of the stability of the reported responses with aging, these same relationships can be used as test controls for other studies of aging, and as benchmarks to distinguish between "nonmal" aging and disease processes.