Ocular Motor Control and Cognitive Function in Military Veterans With Chronic Mild Traumatic Brain Injury

Ocular motor control (OMC) and cognitive dysfunction are common persistent sequelae in persons with mild traumatic brain injury (mTBI). Combat and training operations frequently expose military Service Members to biomechanical and blast events that render them susceptible to mTBI, and problems such as OMC disturbances and cognitive dysfunction are frequent long after injury. However, these problems can be difficult to detect, often only becoming clinically evident with physical or psychological stress. Knowledge of the relationship between OMC and cognitive dysfunction in chronic mTBI, and of clinical tools to assess this issue, is limited.

Setting: Academic laboratory; Marcus Institute for Brain Health, University of Colorado; Design: 2-arm, examiner-blinded cross-sectional observational study. Participants: Military Veterans with chronic mTBI (experimental; n = 38) whose most recent mTBI was more than 3 months before enrolment, and Veterans without a history of TBI (control; n = 40); Measures: The computerized King-Devick (K-D) test assessed rapid number naming tasks; the Right Eye computerized eye tracker system measured antisaccade tasks; the Conners' Continuous Performance Test (CPT) tested aspects of selective and sustained attention and impulsivity; the FAS test measured the ability to name as many common nouns that start with "F," "A," and "S" as a method to assess phonemic verbal fluency, attention, and initiation; and the Posttraumatic Stress Disorder (PTSD) Checklist for DSM-5 (PCL-5) was used as a self-report of posttraumatic stress-related symptoms.

Veterans in the experimental group had a median of 2 mTBIs, and these occurred approximately 11 years before the study. On the K-D Test, the experimental group had significantly more errors and took significantly more time (51.32 seconds) compared with the control group (43.00 seconds). Significantly greater antisaccade latencies were found in the experimental group for target only, on target distractor, and ipsilateral proximal distractor paradigms, and antisaccade error rates were significantly greater in the experimental group for the contralateral proximal distractor paradigm. Significantly greater PCL-5, and worse FAS test scores and CPT commissions and omissions scores were found in the experimental group. For the experimental group, time since most recent TBI correlated with antisaccade on target distractor error rates. Regression modeling showed that FAS test scores were a significant determinant of K-D test performance. Separate regression modeling for each of the antisaccade task paradigms indicated that group status was significantly associated with antisaccade latency scores for the ipsilateral proximal distractor paradigm. PCL-5 was a significant factor for the on target distractor paradigm, and age and cognitive function denoted by FAS test and CPT scores were significant factors contributing to error rates in multiple specified antisaccade paradigm task performances.

Results support the conclusion that OMC and cognitive performance are persistent co-occurring problems in Veterans with chronic mTBI. Notably, these deficits can be detected even after as few as 2 mTBIs that occurred 11 years earlier, indicating that an OMC-cognition axis of sequelae may exist in the chronic stage of mTBI. The results also identify cognitive correlates of the OMC task paradigms, aiding in the clinical application and interpretation of these tests in chronic mTBI.