Visual symptoms in Parkinson's disease and Parkinson's disease dementia

Abstract

Non-motor symptoms such as dementia and visual hallucinations are key determinants of long-term outcome and quality of life in Parkinson’s disease (PD). Attempting to understand these issues better was the motivation behind this thesis. A major aim of the study was to characterise the visual symptoms experienced by patients with PD and PD dementia, focussing not just on complex visual hallucinations, whose prognostic implications are already well-described, but also on a range of other visual symptoms including illusory misperceptions, sensations of passage and presence and double vision. A major objective was to define key measures of visual exploration strategy during visuocognitive assessment and examine the link between strategy, cognition and visual and motor symptoms. We also set out to examine the utility of retina-specific visual assessment techniques to define the potential role of retinal dysfunction in visual impairment and symptomatology. A major finding of this study was that not all visual symptoms share a common pathophysiological basis. Our results argue in favour of splitting hallucinations into separate phenomenological groups in order to better define causation and predictive value in future longitudinal studies. In addition, exploration strategy on a variety of visual tasks was demonstrated to be significantly less efficient in subjects with perceptual difficulties, providing insight into the interaction between cognition and eye movements in PD. Retinal structure, as assessed by optical coherence tomography, was not significantly altered in PD and our results would caution against the use of this technique as a disease biomarker until more is known about the limitations of this method. Finally, our neurophysiological assessment hints at the retina as the site of diminished visual acuity in PD despite there being no striking differences in central and peripheral retinal responses between control and PD subjects.