Figure 2. Change in saccade frequency (without vs with a visual cue) People with Parkinson’s disease increase visual sampling during gait in response to visual cues Stuart S, Galna B, Lord S, and Rochester L Institute for Ageing and Health, Newcastle University Methods Introduction Visual sampling was measured in 7 subjects with PD and 7 healthy older adults (>50 years) (controls). The data was collected using an infra-red mobile eye-tracker (50Hz) (Dikablis), which was synchronised with a 3D motion capture system (Vicon). Participants walked straight under 4 conditions; with and without a door and with and without a visual cue (transverse tape lines). The primary outcome measure for this study was visual sampling; specifically saccadic frequency (number of saccades per second) during gait. A saccade (fast eye movement) was classed as an eye movement with a velocity threshold of ≥240 degrees/second (~5° amplitude). Gait impairments are intrinsic to Parkinson’s disease (PD) and driven at least in part by visual and cognitive deficits [1]. Therapeutic interventions such as visual cues (e.g. coloured transverse tape lines) are used to alleviate walking disturbances associated with PD. However, the mechanisms by which cues work and who they are best suited to remains unknown, although intact attention is likely to be required. This study describes preliminary work assessing visual sampling in PD during walking under different conditions (i.e. without and with visual cues), and reports preliminary, descriptive results. Trial duration (%) Start Door 0% 100% Left and Up Saccade Up Saccade Horizontal Vertical Results Figure 2 Layout of walking conditions Figure 3 Eye-tracker positioning Figure 1 Example of eye tracker data trace PD (n=7) and control (n=7) participants had normal cognition (MoCA >26). PD participants had poorer scores for attention, executive function and visual functions, which are commonly impaired in PD [2]. Saccade frequency Control participants made more frequent saccades during walking without a visual cue than PD participants (Figure 1), but did not change their saccadic frequency with a visual cue. PD participants increased their saccadic frequency in response to a visual cue (Figure 2). Table 1.   Demographic, clinical, cognitive and visual characteristics of PD and control participants. Characteristic PD (n=7) Mean (SD) Control (n=7) Mean (SD) Demographic Age (years) 67 (5.6) 55.6 (3.5) Sex 6 m, 1 f 3 m, 4 f Clinical Hoehn & Yahr stage 2 (0.8) - UPDRS Part III 29.7 (12.6) Disease duration (years) 3.5 (3.5) Freezing of gait questionaire 1.3 (3.9) Geriatric Depression Scale 2.7 (3) 0.7 (.9) Falls efficacy scale 22.6 (5.9) 17.3 (1.5) Cognitive Montreal Cognitive Assessment 27 (1.6) 28.6 (.5) Addenbrookes cognitive examination 90.4 (5.4) 93.9 (3.6) CDR: Power of attention 1456.12 (277.8) 1203.8 (71.2) Judgement of line orientation 23.5 (4.95) 24 (4.3) Royals CLOX 1 12.2 (1.23) 13 (1.1) Royals CLOX 2 13.2 (1.23) 13.4 (1.1) VOSP - Incomplete letters 19.6 (0.7) 19.3 (.5) VOSP - Dot counting 9.90 (0.32) 10 (0) VOSP - Position discrimination 17.4 (5.91) 19.3 (1.03) Vision Visual acuity (logMAR) 0.00 (0.08) -0.1 (.11) Contrast sensitivity (logCS) 1.59 (0.10) 1.65 (0.07) Figure 2. Change in saccade frequency (without vs with a visual cue) Conclusions In contrast to healthy controls, people with PD respond positively to visual cues. Response to visual cues is evidenced by increasing saccadic frequency - possibly mediated by attention. In non-cued conditions people with PD present make fewer saccades compared with controls. Further work on a larger sample (n = 40 controls, 60 PD) will provide more definitive results. References Galna S, Lord S, Daud D, Archibald N, Burn D and Rochester L. Visual sampling during walking in people with Parkinson’s disease and the influence of environment and dual-task. Brain Research. 1473(2012) 35-43. Stuart, S., et al., The measurement of visual sampling during real-world activity in Parkinson's disease and healthy controls: A structured literature review. J Neurosci Methods, 2014. 222: p. 175-88. Acknowledgements This is a summary of independent research funded by the National Institute for Health Research (NIHR)'s Doctoral Fellowship Programme, the Newcastle Biomedical Research Unit based at Newcastle Hospitals NHS Foundation Trust and Newcastle University. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health."