Vision and cognition in Alzheimer’s disease

Abstract

Alzheimer’s disease (AD) is known to affect visual pathways, but potential concomitant effects on vision and cognitive performance are not well understood. We studied 43 individuals with AD of mild severity and 22 individuals without dementia on a battery of tests designed to measure multiple aspects of basic and higher-order visual perception and cognition. All subjects performed on the same visual and cognitive test batteries. The results showed no differences between groups on tests of static visual acuity, stereoacuity, dynamic visual acuity or motion direction discrimination. However, individuals with AD performed significantly worse on tests of static spatial contrast sensitivity, visual attention, shape-from-motion, color, visuospatial construction and visual memory. Correlation analyses showed strong relationships between visual and cognitive scores. The findings show that AD affects several aspects of vision and are compatible with the hypothesis that visual dysfunction in AD may contribute to performance decrements in other cognitive domains. The pattern of involvement indicates that AD affects multiple visual neural pathways and regions. It is possible that better understanding of vision-related dysfunction could aid diagnosis and interventions to improve functional capacity in patients with dementia.

Introduction

Alzheimer’s disease (AD) is the most common cause of abnormal cognitive decline in older adults [89], and neuropathological changes underlying AD involve visual pathways [61], [63], [111]. As sight is “the first door of the intellect” (Paccioli, ca 1445–ca 1514 [11]), it is reasonable to suspect that visual decline may contribute to intellectual deterioration in AD. AD is now reported to impair visual sensory functions including spatial contrast sensitivity [32], [43], [49], color, stereopsis, temporal resolution [23], [25] and motion [33], [103]. AD can also affect visual attention [68], [74] and “higher” visual functions such as reading, route finding, object localization and recognition [24], [48], [60], [73], [101]. Better understanding of these vision-related deficits could aid diagnosis, interpretation of cognitive scores, and interventions to improve functional capacity in patients with AD [22].

The selectivity of visual deficits and relation to disease stage and locus of CNS impairment in AD remain uncertain. Recent polemic concerns selectivity of “ventral” (“what” or “temporal”) vs “dorsal” (“where” or “parietal”) visual pathway deficits in AD [40], [48] including movement perception deficits [6], [46], [83], [91], [95], [96]. Moreover, Kurylo et al. [48] suggested that visual dysfunction does not follow overall disease progression in AD but rather reflects sporadic involvement in certain cases. Visual function in AD is an issue of theoretical and practical importance that requires further investigation.

The purpose of this study was to investigate visual and cognitive abilities in older individuals with and without AD. We tested the hypotheses that AD produces both ventral and dorsal visual pathway deficits while sparing basic sensory functions, and that these visual function deficits correlate with overall severity of AD.