Effect of Chiropractic Intervention on Oculomotor and Attentional Visual Outcomes in Young Adults With Long-Term Mild Traumatic Brain Injury: A Randomized Controlled Trial

Objective:   This study aimed to establish if chiropractic care can improve oculomotor and cognitive symptoms in individuals with persistent postconcussion syndrome (PPCS).

Methods:   A single-blind, randomized controlled intervention study recorded baseline computerized eye-tracker assessment (CEA) outcomes in 40 young adults with PPCS following mild traumatic brain injury. Participants were randomly allocated to either a chiropractic or age-matched active control intervention, and the change in CEA outcomes following intervention was compared between the chiropractic and control groups. A battery of CEAs including egocentric localization, fixation stability, pursuit, saccades, Stroop, and the vestibulo-ocular reflex, were used to assess oculomotor function, visual attention/processing, and selective attention.

Results:   Relative to the control group, participants receiving the chiropractic intervention scored better in the Stroop test (P < .001), had improved gaze stability during both vestibulo-ocular reflex (P < .001) and fixation stability (P = .009), and a lower vertical error in egocentric localization (P < .001). However, performance was poorer in pursuits, where they had an increased tracking error (P < .001).

Conclusion:   Chiropractic care in participants with PPCS significantly improved static and dynamic gaze stability, and performance in the Stroop test, compared with a control intervention. These results suggest that chiropractic care can offer a novel avenue for alleviating certain visual and cognitive symptoms in patients with PPCS. It also adds to the growing evidence that suggests that some longstanding PPCS visual symptoms may have a spinal or proprioceptive basis.

Keywords:   Brain Concussion; Chiropractic; Eye-Tracking Technology; Postconcussion Syndrome; Proprioception.

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Introduction

Traumatic brain injury (TBI) is a change in typical brain function that affects neurologic function after an external force to the head. [1, 2] Diagnosis and categorization of TBI severity is currently subjective, open to bias, and predicting an individual’s outcome after injury is challenging. [3, 4] Although symptoms can vary depending on the neurologic area of injury, visual symptoms are common following even mild TBI (MTBI) owing to the many areas of the brain involved in processing vision [5] and controlling the eyes. Visual symptoms can include oculomotor dysfunction including disorders of convergence and accommodation, poorer fixation, slower or less accurate saccades, poorer pursuit movements, and modification of the vestibulo-ocular reflex (VOR). [6]

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Other common symptoms are less specific, but impact tasks that tax attentional, inhibitive, or visuospatial processing. [7, 8] To gain accurate and objective measures of eye gaze behaviors, computerized eye-tracker assessments (CEAs) have become increasingly common. [6] Previous work using CEAs has suggested that changes in vision after mTBI may be, in addition to the primary neurologic insult, due to proprioceptive changes from cervical spine dysfunction or damage. [9, 10] This is supported by other research that shows altering proprioceptive drive with vibration changes CEA outcomes in those with mTBI. [11] Further augmenting this dual site of injury concept is those with mTBI have a higher incidence of neck pain [12, 13] and significantly worse objective measures of cervical spine function. [11]

Altering proprioceptive drive to the brain with either whole body or localized cervical spine vibration [11] has been shown to improve CEA performance in mTBI, and cognitive performance in a range of other conditions, including Alzheimer’s disease, [14] Parkinson’s disease, [15] and stroke, [16] and improves performance on the Stroop test in young adults. [17]

Although the exact process remains unclear, enhancing proprioceptive input to the brain is believed to aid in the integration of vestibular and sensorimotor functions, as well as improve cognitive performance. [14, 18] A drawback of vibration therapies is the transitory nature, so another proprioceptive based intervention—chiropractic care — was investigated as a potential pathway to manage visual deficits post mTBI. Chiropractic is a type of manual therapy whose aim is to manage spinal articular dysfunction and the altered neurologic component associated with it. [19]

Spinal joint dysfunction can result in altered afferent input to the central nervous system, which modifies the way it processes and integrates sensory and proprioceptive input. [20, 21] Once spinal dysfunction is corrected, the sensorimotor integration and cognitive function can improve. [22–24] Theoretically, if participants with mTBI have symptoms (as assessed by CEAs) that were caused or worsened by a related spinal injury, then managing the spinal dysfunction could, in turn, improve CEA outcomes and potentially their symptomology.

As an initial step in investigating this therapeutic intervention, this study aimed to investigate whether a chiropractic intervention intended at reducing spinal proprioceptive dysregulation can alter some of the commonly reported defects in eye-tracking function and spatial awareness that occur following mTBI.

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