Investigators/Authors: Mark Hallett, MD; Codrin Lungu, MD
Objective/Rationale: Difficulties with walking is often a significant problem for patients with Parkinson disease. Not only is walking slow, but there are also occasional falls and freezing (getting “stuck” in place). Freezing, in particular, is often refractory to medication and even Deep Brain Stimulation (DBS). Freezing is sometimes precipitated by visual stimuli (like encountering a doorway) or relieved by visual stimuli. One of the difficulties in understanding this is that there is no information on where patients are looking while they are walking. With this project, we will study where patients are looking and determine how that influences walking.
Project Description/Methods/Design: The aim is to see where patients with Parkinson disease look when walking. An eye tracking device will be used that allows patients to walk freely. The system will record a video of what is in front of the patient and then indicate exactly what the eyes are focused on in that scene. A comparison will be done between patients and age/sex matched healthy subjects. Exploratory studies will be done first to develop detailed hypotheses. We will study subjects walking in various situations including a plain corridor, a corridor with many objects, a corridor with horizontal lines on the floor, and a corridor with a door to go through. A door often makes walking more difficult, while horizontal lines on the floor might be helpful. Some variability of influence might depend on where the patient is looking.
Relevance to Treatment of Parkinson’s Disease: It is clearly critical in walking to know what lies ahead and how to deal with it. If it is determined that there are systematic abnormalities in where patients are looking, then it might be possible to improve walking by training patients to look differently. The biggest impact could be on freezing of gait where visual stimuli are known to be important.
Expected Outcome: The first outcome is basic knowledge about the coupling of vision and walking in patient with Parkinson disease. Certain types of visual-motor coordination are known to be impaired in patients, and this might be another example, with bad consequences. The second outcome is a set of ideas of how to improve physical therapy gait training. It might also be possible to develop new ideas for devices that would aid vision to help improve gait.
September 2014 Project Update:
Study Progress: By using an eye-tracker while walking, our project explores the presence of visual exploration differences between patients with Parkinson’s disease (PD) and healthy volunteers (HV). The participants are asked to wear the SMI Eye Tracking Glasses while waking through a corridor. Information regarding the areas of visual fixation is obtained and the percentages of time spent looking at specific areas are compared between different populations (Healthy Volunteers, patients with Parkinson’s Disease with and without Freezing of Gait).
Our study has enrolled a total of 24 participants:
15 patients with PD without freezing of gait
2 patients with PD and freezing of gait
7 healthy volunteers
Preliminary results: Our preliminary analysis demonstrates increased fixation duration and decreased saccade velocity on patients with PD when compared with HVs. More importantly, there are sight differences on the percentages of time spent looking at specific areas between the two populations. The differences are not statistically significant at this time, likely due to the small sample size.
- Continue patient enrollment and analysis.
- Evaluate differences on area scanned in different static environments and the translation into dynamic tasks (walking). Additionally, assess the influence of therapeutic visual exploration strategies.
- Development of detailed hypothesis based on our current explorations.
September 2015 Project Update:
Methods Used and Research Subjects: We used the SensoMotoric Instruments Eye Tracking Glasses (SMI ETG) set-up. This records eye position binocularly, and superimposes the results on the recording from a front-facing camera. The result is a map of the explored visual environment. We used custom created software scripts to separate the visual scene into areas of interest (AOI). The analysis was performed using SPSS and MATLAB software, analyzing the relative percentage of time spent fixating on different AOIs, over the duration of the task. The resulting output offers an effective summary of where the patients are looking during gait.
A total of 19 PD patients without freezing of gait (PD), 9 PD patients with freezing of gait (FG) and 18 healthy volunteers (HV) participated in the study. The study had two components: for the dynamic task, patients walked in a realistic environment, consisting of a corridor in the NIH clinical center, including a doorway – which is particularly relevant, as freezing episodes often occur in doorways. In the “Static” experiment, patients explored static images in a fixed position.
Results: The data analysis is still being finalized and the manuscript is in preparation.
The crucial finding is that in patients with freezing of gait there is significantly less fixation on the “target” region, defined as the area of the opposing wall towards which the subjects are walking. This is specific only to FG subjects, i.e., occurring only in patients with PD with a history of freezing (determined by the FOG questionnaire), and not in the patients with PD who do not experience freezing (~30% of time vs ~65% of time).
On further analysis, it appears that FG patients fixate more on the ground. This does not appear related to posture or ability to explore relevant areas of the target – interestingly, the same pattern of visual exploration occurs in the static task, where the head is fixated in the same position for all subjects.
Significance: Our data may identify a clinic marker specific to freezing of gait. This is the first time a visual exploration paradigm has been applied in this manner. The results highlight specific visual exploration differences in patients with freezing of gait, that separate them not only from healthy volunteers, but also from PD patients who do not experience freezing of gait. This supports the notion that freezing is characterized by a distinct abnormality of gaze that may be a physiological factor contributing to the disorder.
- We are continuing additional data analysis. In addition to the results mentioned here, we are further parsing the patterns of visual exploration, the relation with obstacles, correlations with other clinical features etc. A manuscript is in preparation reporting these results.
- We plan to recruit additional subjects and refine the paradigm while exploring various subtypes of PD, as well as perform testing with and without various treatments.
- We plan to combine the visual exploration experiment, similar to the one performed in this project, with instrumented analyses of gait.
- We are considering the development of rehabilitation and training paradigms based on further findings with this experimental approach.
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