The Nature and Impact of Visual Perceptual Changes in Ageing and Dementia

The purpose of this thesis was to assess the impact of healthy older age and older age with Alzheimer’s disease (AD) on the structural and functional integrity of the visual system and on key associated measures of visual performance. A systematic review of the literature (Chapter 2) revealed a significant impact of AD on the retina, where significant thinning in the ganglion cell layer of the retina, most commonly in superior and inferior retinal nerve fibre layer (RNFL) quadrants is consistently reported. Evidence of amyloid-β plaques in the lateral geniculate nuclei of the thalamus and in primary visual cortices (area V1) was also identified, accompanied by some evidence of gliosis in the magnocellular visual pathways and by neuron and glial cell loss in the parvocellular visual pathway. Reduced neural activation in areas V1 and V5/MT was also noted. In the context of visual performance, age and AD-related deficits have been reported in several visual domains including sensitivity to contrast, colour, depth, and motion. Self-report studies confirmed that dementia is associated with visual impairment and reduced vision-related quality of life beyond that experienced as part of the ‘typical’ aging process and that people with dementia are aware of the visual changes they experience (Chapter 3). The experiences of visual impairment by people with dementia were confirmed by their carers (Chapter 4). A series of clinical and psychophysical assessments of visual performance confirmed deleterious effects of AD on the visual system beyond that observed in healthy older age. This included AD-related deficits on fundamental aspects of visual perception, reflected by deficits on tests of colour discrimination and motion perception (Chapter 5). These effects extended to visual cognition, in particular to stimulus identification and visual search performance (Chapter 6).