Casey S. Gilmore, Kelvin O. Lim, Mona K. Garvin, Jui-Kai Wang, Johannes Ledolter, Alicia L. Fenske, Carolyn L. Gentz, Julie Nellis, Michael T. Armstrong, Randy H. Kardon
JAMA Network Open, 3(12), e2030824
Abstract
Importance: Mild traumatic brain injury (mTBI) may predispose individuals to progressive neurodegeneration.
Objective: To identify evidence of neurodegeneration through longitudinal evaluation of changes in retinal layer thickness using Optical Coherence Tomography (OCT) in veterans with a history of mTBI.
Design: Longitudinal cohort study
Setting: Minneapolis Veterans Affairs Health Care System
Participants: Participants were 139 veterans who were receiving services in the Minneapolis VA Health Care System (MVAHCS). Participants in the TBI group (n=69) were diagnosed with symptomatic or mild TBI based on the Mayo TBI Severity Classification System. Participants in the age-matched control group (n=70) had no history of TBI. Participants with any history or evidence of retinal or optic nerve disease that could affect retinal thickness were excluded.
Exposures: Presence and severity of mTBI was determined through consensus review of self-report responses during the Minnesota Blast Exposure Screening Tool (MN-BEST) semi-structured interview.
Main Outcome and Measures: Change over time of retinal nerve fiber layer (RNFL) thickness.
Results: Compared to controls, veterans with mTBI showed significantly greater RNFL thinning (p=0.004, Cohen’s d=0.52). Functionally, veterans with mTBI showed greater declines in visual field mean deviation and pattern standard deviation and high spatial frequency (12 cycles/degree) contrast sensitivity (all p-values<0.05), compared to controls. Cognitively, there was a significantly greater decrease in the number of errors over time during the Groton Maze Learning Test (GMLT) in controls compared to mTBI (p=0.04, d=0.37). RNFL tissue loss was significantly correlated with 1) worsening performance on the GMLT over time (Spearman’s ρ=-0.20, p=0.03), and 2) mTBI severity (ρ=-0.25, p=.006). The more severe the mild TBI (larger MN-BEST severity score), the faster the reduction in RNFL thickness (i.e. the more negative the slope) across time.
Conclusions and Relevance: There was longitudinal evidence for significant, progressive neural degeneration over time in veterans with mTBI, as indicated by greater RNFL tissue loss in mTBI vs controls as well as measures of function. Results suggest that these longitudinal measures may be useful biomarkers of neurodegeneration. Changes in this biomarker may provide early detection of subsequent cognitive and functional deficits that may impact veterans’ independence and need for care.
Casey Gilmore, PhD 