Real-world evaluation of visual function.
Visual function declines with age in a variety of ways. It must also be kept in mind, however, that the results reported here are primarily group findings. When evaluating the performance of older persons, there is extremely wide variability, and even though average performance may decline as a function of age, many older adults maintain excellent visual function throughout their lifetimes. It is important to keep the variability of individual performance in mind to avoid ageist stereotypes. Although declines in age-related vision are well documented, it is less clear why these declines have occurred. Most recent studies have controlled for criterion differences by using forced-choice methods. These studies confirm that even after correcting for differences in threshold criteria, age-related declines persist. Many other studies have controlled for optical changes using a variety of techniques. Again, some age-related declines still exist Although it is widely believed that the neuroanatomy and physiology of the visual pathways are affected by aging, there is still relatively little understanding of how these changes impact visual function. Thus, there is a need for further studies to link potential neural mechanisms to observed changes in functional visual performance. Furthermore, there is also a possibility that there may be multiple sites of decline within a given person and that these sites of decline may vary across persons. Thus, the use of an individual-differences approach is needed to evaluate the many potential explanations for sensory decline. Finally, there is frequently a discrepancy between performance in the laboratory and real-world performance. In trying to predict the performance of real-world tasks and in designing the best environments for the elderly, sensory function should not be considered in isolation. Rather contributing factors such as cognitive ability, expectations, distractions, and other health-related and motor problems must also be considered. Traditional clinical measures of visual function, though appropriate for evaluating the presence of disease, are often inadequate in explaining everyday performance impairments. Thus, further research is needed to fully understand the complex interactions between sensory, cognitive, motor, economic, and physical factors that together determine one's level of ability or disability in everyday tasks.