Functional Mechanism of Neural Control in Post-Concussion Convergence Insufficiency

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Project Summary/Abstract: During the past 6 years, our study team investigated the neural mechanism of typically-occurring convergence insufficiency (TYP-CI), the most common binocular vision disorder in children and young adults (3.4% to 12.7%5–11) leading to 20 publications12–31 with 4 more in review and 6 in preparation. We conducted the only randomized clinical trial (RCT) integrating objective eye movement and fMRI outcome measures, achieving 100% planned enrollment and retention of 100 young adults.28 Our results localized the reduction in functional activity for TYP-CI compared to controls within the oculomotor vermis (OVM) and the cuneus. Functional activity in the OVM and cuneus was significantly correlated to convergence peak velocity providing the first mechanistic identification of these deficits that create significant burden to those afflicted. 23 Our longitudinal results discovered that the neural mechanistic change stimulated by office-based vergence /accommodative therapy (OBVAT) is an increase in the frontal eye field (FEF) and thalamus functional activity. Increased functional activity from the FEF and thalamus significantly correlates to convergence peak velocity. 23,32,33 Results are leading to personalized point-of-care therapies remediating the debilitating symptoms for TYP-CI patients. While our research and results of other RCTs show that OBVAT is the most effective treatment for remediating symptoms and improving vision function in both TYP-CI children 34–36 and adults, 37,38 none of these participants had a history of head injury, a pathology that has been linked to CI. Our research team has demonstrated that the prevalence of CI is higher (38% to 49%) in children 39,40 and adults 41,42 with persistent post-concussive symptoms (PPCS-CI), than in the non-concussed population. Currently, there is no validated treatment for PPCS-CI. This difference in prevalence, mode of onset (longstanding versus sudden onset), and severity of the condition has led to a debate about whether the diagnostic and management procedures effective for TYP-CI should be utilized for PPCS-CI, and strongly suggests that new research is needed to optimize PPCS-CI management. We are uniquely positioned to provide answers to these questions by building on our work establishing the neurofunctional mechanism of TYP-CI and OBVAT administered to TYP-CI. Such research is of great importance because PPCS-CI is associated with debilitating visual symptoms impacting the return to school/sports, 43–47 work, 48–51 or driving. 52 We have identified three significant gaps for the treatment of PPCS-CI that must be addressed to determine its most effective management. First, given the obvious differences in etiology, are there significant differences between TYP-CI and PPCS-CI related to objective eye movement measures (peak velocity, final amplitude, and repeatability) due to underlying neural mechanistic differences? Second, what is the underlying neural mechanism of OBVAT for PPCS-CI compared to TYP-CI? Third, how effective is OBVAT for PPCS-CI and is the dosage of administration different than TYP-CI? This renewal addresses these gaps in clinical science.