Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Health and Rehabilitation Sciences

Supervisor

Dickey, James P.

2nd Supervisor

Graham, Laura J.

Co-Supervisor

Abstract

Concussions are complex conditions that are difficult to manage medically. Variations in symptom presentation, intricate neurophysiological processes, and the availability of a variety of possible assessment tools may contribute to this complexity. Clinicians must use a broad approach, employing both subjective symptom assessment and objective assessments to confirm a diagnosis and/or monitor progression and recovery. Oculomotor function after concussion may be an important indicator of injury, given the interconnectedness of oculomotor function, vestibulo-ocular and visual systems, and even cognition. Oculomotor function may be assessed objectively or indirectly using patient-reported symptom checklists as part of subjective assessments. One way of objectively assessing oculomotor function is the observation of saccades: rapid movement of eyes between targets. Two types of saccades were studied: prosaccades, where the eyes move toward a target, and antisaccades, where the eyes move to the mirror opposite location of the target. Antisaccades require inhibition of prosaccades, reflecting a component of executive function. Measuring the reaction time and directional errors of saccades can give insight into the status of some aspects of executive function. Chapter 2 compared objective electroencephalography (EEG) and saccadic eye movements to assess changes in neurological function with accumulated head impacts throughout a season of men’s hockey. EEG was sensitive to minor changes in executive function, whereas saccades were not. Subjective measures, such as symptom checklists, provide a standardized protocol for assessing concussion symptoms and severity. Chapter 3 tracked saccades and patient-reported symptom measures to assess changes in the function and symptomology following a 16-week interdisciplinary outpatient rehabilitation intervention for patients with persistent post-concussion symptoms. Improvement in patient function was measured by improved standard outcome measures. These improvements were associated with saccadic eye movement measurements. Chapter 4 investigated the relationship between a patient’s initial vestibulo-ocular symptoms and their length of recovery from acute concussion. This study demonstrated that the presence of any vestibulo-ocular symptoms led to 19 times greater odds of not being discharged four weeks after their assessment. This builds on existing research in which patients with vestibulo-ocular symptoms on other diagnostic tests were shown to have delayed recovery. Using the SCAT5 to collect vestibulo-ocular symptoms is easier for clinicians and less provocative for patients. Together these findings show that oculomotor assessments may be useful in hockey athletes with acute concussions and adults with persistent post-concussion symptoms. Further research is needed to determine their utility in subconcussive head impacts.

Summary for Lay Audience

Our eyes provide us with a constant stream of information about the world around us and our actions within it. The process of controlling our eye movements, known as oculomotor function, is complex and involves communication between many areas of the brain. Oculomotor function may reveal changes in the brain following head impacts and concussions. All contact sports athletes will experience head impacts. Therefore, there is concern about the large impacts that lead to concussions as well as the potential neurological consequences of accumulated head impacts. Most athletes with concussion recover within two weeks, but some individuals experience prolonged symptoms, termed persistent post-concussion symptoms. This thesis investigated the use of oculomotor assessments across the continuum of concussion (subconcussive impacts, acute concussion and persistent post-concussion symptoms). In the subconcussion study, helmet-mounted sensors, rapid eye movements and electroencephalograms were collected before, during, and after the season to evaluate players’ brain function. In a separate study, symptom data were retrospectively collected from hockey players in southwestern Ontario to evaluate the relationship between initial vestibulo-ocular symptoms and time to discharge from physician’s care. Finally, rapid eye movements were collected before and after a 16-week concussion therapy program for individuals with delayed recovery from concussion. This thesis determined that rapid eye movements are not sensitive enough to detect changes in brain function from subconcussive head impacts. Saccades can measure improvement during therapy for patients with delayed recovery from concussion. Also, initial vestibulo- ocular symptoms are associated with extended time to discharge after concussion for hockey players. These results show that assessing visual symptoms may support prognosis planning for hockey athletes and that eye tracking can monitor recovery for persistent concussion symptoms.

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