Visual Function During Gait in Parkinson's Disease: Impact of Cognition and Response to Visual Cues

Parkinson's disease (PD) is associated with problems of gait such as veering, difficulty turning, an inability to perceive doorways or obstacles, and negotiate uneven terrain. Gait problems, especially veering, may be exacerbated by visuospatial dysfunction which predispose to falls, freezing and festination of gait. Visuospatial dysfunction is common in PD and likely involves peripheral features (e.g. contrast sensitivity) as well as central cognitive mechanisms (e.g. attention). Central neuro-degeneration in PD, PD dementia, and dementia with Lewy Bodies may influence visual function, as impaired visual sampling has been reported in these conditions. Visual sampling is measured via saccadic (fast eye movement) activity, as saccades are the mechanisms through which people orientate and explore the environment. The use of objective devices to reliably measure saccades is important to detect disease related eye movement changes. Emerging visuomotor research has measured visual sampling in PD using devices such as electrooculography and infra-red eye tracking, revealing reduced amplitude, speed and frequency of saccades during various tasks. Despite recent increases in visuomotor research it remains unclear how PD influences visual sampling of the environment during gait and the influence of attentional and cognitive deficits. Recent work demonstrated that people with PD sample their environment less frequently than controls, despite a slower gait. Saccadic timing was unchanged in response to environmental cues. Despite this, environmental visual cues (transverse lines on the floor) have been shown to increase the number of fixations made during gait. However the mechanisms of this response remain unclear. Cognition is likely of importance, with response potentially influenced by attentional control. This observational study aims to examine the influence of cognition on visuomotor control during gait in PD. This aim will be achieved by observation of visual sampling under several environmental challenges (straight walk, doorways, turns, visual cue) and a dual task.