Research reveals hidden visual deficits and neural pathway alterations in mild TBI patients

Vanderbilt University Medical Center-led research reveals subtle changes in the visual pathways of individuals with chronic mild traumatic brain injury (TBI), even when standard eye examinations show no abnormalities. These findings include structural and functional deficits despite participants showing normal visual acuity during clinical examination.

Mild TBI accounts for approximately 3 million cases in the U.S. each year. Up to 85% of TBI patients, regardless of injury severity, report visual disturbances such as light sensitivity, blurred vision, or difficulty reading. Persistent symptoms including memory problems, irritability, or slowed thinking often impact quality of life. Despite these symptoms, many individuals display no abnormalities during routine clinical evaluations such as fundus examinations.

In a case-control study, “Primary Visual Pathway Changes in Individuals With Chronic Mild Traumatic Brain Injury,” published in JAMA Ophthalmology, researchers reported that 78% of participants with mild TBI exhibited visual deficits when evaluated with a comprehensive battery of tests.

Machine-learning analyses revealed subtle changes in the optic radiations and occipital lobe regions in 70% of participants, independent of self-reported visual symptoms.

A cohort of 28 individuals with a history of mild TBI and 28 controls with no history of brain injury underwent a range of tests and assessments. These included oculomotor function, visual field performance, contrast sensitivity, visual evoked potentials, retinal structure via optical coherence tomography, and magnetic resonance imaging (MRI) of the brain.

A machine-learning model was applied to data from MRI diffusion imaging and tractography to evaluate microstructural and macrostructural differences in the optic radiations and cortical regions of the visual pathway.

Individuals with mild TBI demonstrated reduced prism convergence test breakpoints and recovery points, indicating ocular motor function deficits. Contrast sensitivity was decreased and binocular summation index in VEPs increased. Subsets of participants exhibited reduced peripapillary retinal nerve fiber layer thickness, increased optic nerve/sheath size, and cortical volume changes in occipital regions.

Findings suggest that mild TBI is associated with chronic alterations in the visual pathway, including measurable deficits in oculomotor function and subtle structural changes in the retina and brain.

Changes were present in varying degrees across participants and often independent of their self-reported visual symptoms. The hidden nature of the changes and the noticeable effect they can have on patient vision suggests the importance of including comprehensive diagnostic assessments for evaluating visual dysfunction in mild TBI.

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