Vertical Heterophoria and Vestibular Symptoms in Military Personnel with Chronic mTBI

Among the most common sequelae of mild traumatic brain injury (mTBI) are visual and vestibular complaints, particularly in military populations exposed to blast injuries and repetitive concussive events. This study aimed to investigate the prevalence of vestibular symptoms (dizziness, imbalance, visual motion hypersensitivity, and motion sickness) and their association with subjective vertical heterophoria (SVH) and vertical vergence imbalance (VVI) in military service members with chronic mTBI.

This study was a retrospective analysis of patients with chronic mTBI treated at the National Intrepid Center of Excellence, Walter Reed National Military Medical Center (WRNMMC), from July 2024 to January 2025. The study was approved by the WRNMMC Institutional Review Board before data collection. Written informed consent was obtained from all participants. Patients who had been diagnosed with strabismus or other ocular pathologies that could confound the results were excluded. Clinical data were collected from standard assessment during the Neuro-Optometry appointment. Data analysis included the following variables: (1) Vestibular symptoms, assessed via a binary self-report (yes/no) indicating the presence or absence of dizziness, imbalance, visual motion hypersensitivity, and motion sickness; (2) Total vestibular symptom score, representing the total number of symptoms reported; (3) SVH, a patient-reported measure of vertical misalignment of the visual axes obtained through the alternating cover test; and (4) VVI, defined as the absolute difference (in prism diopters, Δ) between the right and left eyes in the breakpoint of vertical fusional vergence ranges. Descriptive statistics, logistic regression, Mann-Whitney U tests, and Spearman's rank correlation were used for the analysis.

A total of 84 subjects were included in the analysis with mean age of 40.3 ± 5.1 years, and 100% of the participants were male. The prevalence of vestibular symptoms was as follows: dizziness (40.5%), imbalance (23.8%), visual motion hypersensitivity (13.1%), and motion sickness (17.9%). Overall, 71.4% of subjects (60/84) had at least one vestibular symptom. SVH was reported in 54.8% of participants; 54.8% had VVI ≥ 0.5Δ, and 23.8% had VVI ≥ 1.0Δ. No significant correlations were found between SVH/VVI and individual vestibular symptoms (all P > .05); however, there was a significant positive correlation between the vestibular symptom score and VVI (ρ = .27, P = .01).

In this population of military personnel with a history of chronic mTBI, both persistent vestibular complaints and vertical heterophoria were prevalent. The study showed that elevated vertical vergence imbalance between the two eyes was significantly correlated with more vestibular symptoms in patients with chronic mTBI. Vertical heterophoria may be a useful clinical technique; however, effectiveness of vertical heterophoria correction for the management of symptomatic mTBI requires further investigation.