Progressive Neurodegeneration of the Retinal Nerve Fiber Layer in Veterans with Mild Traumatic Brain Injury

Abstract

Purpose : The purpose of this investigation was to prospectively evaluate the structural and functional changes over time in the visual and central nervous system in veterans with a history of mild traumatic brain injury compared to age-matched control group of veterans. There is concern for progressive neurodegeneration after traumatic brain injury leading to Chronic Traumatic Encephalopathy (CTE), resulting in dementia, depression and suicide.

Methods : 69 veterans with mild TBI and 70 age-matched control veterans are being evaluated every 6 months. Optical Coherence Tomography (OCT) was recorded as well as tests of visual function, cognition and MRI. A linear trend statistical model was used to estimate slope of subject retinal nerve fiber layer (RNFL) thickness, visual acuity, contrast sensitivity, visual field sensitivity and tests of cognitive function. Changes in structural MRI (cortical thickness) at an 18-month time point, was completed in 88 of the subjects. Outcome measures were evaluated for slope, accounting for number of time points (at least 4 visits; 870 different visits on 139 subjects).

Results : To date a highly significant difference between the negative slopes of RNFL in mild TBI (1.5 microns/year) and normal subjects (0.35 microns/year) was found (p=0.001). This was associated with a small, but significant loss of visual acuity of one letter loss/year (p=0.04), low spatial frequency contrast sensitivity (p=0.008) and visual field mean sensitivity of 0.5 decibels loss per year (p=0.03) compared to normal. A mildly significant increase in errors on the cognitive maze test was found in the TBI group compared to normal (p-0.05). A significant decrease in percent change in cortical thickness at visual cortex (V1) was found for mild TBI vs. control group (t = -2.45, p = 0.016) with a medium Cohen’s d effect size = 0.544.

Conclusions : To date, we have found evidence for a significant, progressive neural degeneration over time with the greatest significant change in RNFL thinning in veterans with mild TBI, indicating that retinal thickness analysis may be useful for predicting neurodegeneration. Functional tests of vision are showing small, but significant changes over the current time period of study. Continued evaluation of subjects will determine if extent of functional deterioration in the visual and cognitive pathways follow structural loss in the retina and visual cortex.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.