Weak correlations between visual abilities in healthy older adults, despite long-term performance stability.

Using batteries of visual tests, most studies have found that there are only weak correlations between the performance levels of the tests. Factor analysis has confirmed these results. This means that a participant excelling in one test may rank low in another test. Hence, there is very little evidence for a common factor in vision. In visual aging research, cross-sectional studies have repeatedly found that healthy older adults' performance is strongly deteriorated in most visual tests compared to young adults. However, also within the healthy older population, there is no evidence for a visual common factor. To investigate whether the weak between-tests correlations are due to fluctuations in individual performance throughout time, we conducted a longitudinal study. Healthy older adults performed a battery of eight visual tests, with two re-tests after approximately four and seven years. Pearson's, Spearman's and intraclass correlations of most visual tests were significant across the three testing, indicating that the tests are reliable and individual differences are stable across years. Yet, we found low between-tests correlations at each visit, which is consistent with previous studies finding no evidence for a visual common factor. Our results exclude the possibility that the weak correlations between tests are due to high within-individual variance across time.