Vision changes in normal aging have been studied by a number of research groups; an excellent summary can be found in the 2011 review in Vision Research by Owsley.
7 Normal aging brings about changes in the intraocular transmission and scatter of light, density of photoreceptors, efficacy of phototransduction and photopigment regeneration, and quality of synaptic transmission and signal processing in the retina and beyond. Most studies of vision and aging have examined a limited set of vision measures in small groups of older individuals, and compared these to normal adult values. The largest sample of very old individuals followed longitudinally can be found in the SKI study, and one of its most important findings is summarized in
Figure 1, drafted using SKI study data kindly provided by G. Haegerstrom-Portnoy for this paper; VA and contrast sensitivity data from that study have been published previously.
5 Figure 1 shows, on a logarithmic scale, how the thresholds for a variety of vision measures change with age, compared to the normal adult value. As indicated by these regression lines, thresholds increase proportionally from year to year, starting at the age where the line intersects the horizontal axis. The age of onset and the annual rate of change appear to vary markedly, depending on the measure of interest. The review by Owsley
7 cites several studies that have hypothesized that the detection of second order visual stimuli (those thought to require the involvement of multiple detection mechanisms in visual cortex) are more severely affected by aging than simple stimuli, such as flicker detection (temporal contrast sensitivity [TCS] in
Fig. 1), and this certainly could explain why TCS has the shallowest increase with age. Other measures in
Figure 1, such as color vision and stereoacuity, may have artificially steep regression lines due to the poor discrimination abilities of the stereo cards and D-15 test used to measure them. What seems clear from this Figure is that the rise of high contrast VA starts close to a decade later than other measures, possibly because it is less affected by optical factors, such as yellowing of the lens and scatter in the intraocular media.
A secondary effect of aging, not visible in
Figure 1, but widely reported in studies of visual function in the elderly, is the increased range of values. While some elderly individuals appear to have the vision of a 30-year-old, others have markedly increased thresholds, even in the absence of overt pathology. In an analysis of psychophysical and electrophysiologic measures taken from a range of peer-reviewed papers, Johnson and Choy
8 concluded that increasing variability with age may account for an important fraction of the overall average threshold increase seen in the population. They speculated that this may be due to latent pathology in many elderly individuals or to natural variability of the aging process.
One might expect a high degree of correlation between changes in different visual function measures within a single person, and, thus, hypothesize that elderly patients with good visual acuities would not show large changes in other measures. To test this hypothesis, Haegerstrom-Portnoy et al.
5 performed a separate analysis limited to participants with best-corrected VA better than 20/40, that is, near normal, and determined the number of these near-normally sighted individuals showing a 10-fold worsening in other visual function measures increased rapidly with age, for almost every measure tested. This finding supports the notion that large changes in most of the vision measures shown in
Figure 1 are part of normal aging rather than caused by undiagnosed eye pathology.
While the measures in
Figure 1 all refer to basic psychophysical visual functions, changes with age in the performance of activities of daily living (ADL) have been studied in the SKI and SEE studies as well, in addition to smaller studies by other groups. As part of the SKI study, Lott et al.
9 measured the distance, as a function of age, at which participants could recognize faces and/or facial expressions, and also asked the participants how often in daily life they had difficulty recognizing familiar faces from across a room or in dim light. They found a high correlation between the self reports and test data, and a steady decline of these abilities after age 65, with more pronounced losses after age 80.
Driving is another visual ADL that has been studied extensively in the last decade, both in simulators and on the open road, in the latter case with either a driving instructor in the vehicle, or with multiple camcorders set up to record the drivers actions, and the relation of the vehicle to other traffic, and to road markers and signals. Most vision studies find correlations between driving performance and driver age, but the role of vision is uncertain. In the Salisbury Eye Evaluation Driving Study (SEEDS), an increase in visual field defects was associated with increased wait times at stop signs in urban drivers
10 and with self-restrictions in night driving,
11 which also correlated with reduced contrast sensitivity; running red lights correlated with a reduction in attentional visual field.
12 These and other aberrant driving behaviors, such as running stop signs or making unsafe lane changes, were correlated primarily with cognitive factors, suggesting that vision changes have a relatively minor role in accounting for age-related worsening in the performance of complex tasks, such as driving.
Considering these findings in normally sighted elderly populations, it becomes clear that the effects of vision loss due to eye disease in the elderly can be understood and addressed only in the context of the many changes associated with aging, including nonvisual disabilities and comorbidities that affect many elderly individuals