Chronic Mild Traumatic Brain Injury in Veterans: How Ocular Motor Control and Cognitive Function Are Affected

Mild traumatic brain injury, often abbreviated as mTBI, has become a significant concern among military veterans. Many service members experience mTBI due to exposure to combat, training, or blast-related events. Although mild in classification, these injuries can have long-lasting effects on both ocular motor control and cognitive function. Recent research provides a detailed understanding of how these deficits persist even years after the injury and highlights potential tools for assessment and intervention.

The Importance of Ocular Motor Control and Cognitive Health

Ocular motor control, or OMC, refers to the ability to precisely coordinate eye movements during tasks such as tracking moving objects, focusing on targets, or reading. Cognitive functions such as attention, processing speed, verbal fluency, and reaction time are often intertwined with OMC. For veterans with chronic mTBI, problems in either of these domains may remain unnoticed for years, only becoming evident when the brain is under physical or psychological stress.

Chronic mTBI is defined as symptoms and deficits that persist for months or even years after the initial injury. These can include difficulties with rapid eye movements, slower reaction times, and problems with attention and memory. Unfortunately, detecting these deficits in a clinical setting can be challenging due to compensatory strategies used by individuals and the subtle nature of impairments.

Key Research on Veterans With Chronic mTBI

A recent study conducted by researchers at the Marcus Institute for Brain Health, University of Colorado, provides comprehensive insights into the interaction between OMC and cognitive function in military veterans with chronic mTBI. This study compared 38 veterans with a history of chronic mTBI to 40 veterans without a history of traumatic brain injury. Participants were evaluated using a combination of ocular motor assessments and neuropsychological tests to capture the full range of functional deficits.

Assessment Tools Used in the Study

1. King-Devick Test: This test measures rapid number naming, combining language, processing speed, and visual recognition. It is used to identify subtle OMC and cognitive deficits. Veterans with chronic mTBI performed slower and made more errors compared to controls.
2. Antisaccade Eye Tracking: Using a computerized eye tracker, participants were required to look away from a target stimulus in a controlled manner. Four antisaccade paradigms were tested: target only, on target with distractor, ipsilateral proximal distractor, and contralateral proximal distractor. Veterans with chronic mTBI demonstrated longer latencies and higher error rates in several of these tasks, indicating difficulty in inhibiting reflexive eye movements and maintaining attentional control.
3. FAS Test: This test evaluates phonemic verbal fluency by asking participants to generate words starting with specific letters. It provides insights into attention, cognitive initiation, and executive function. Veterans with mTBI scored lower than controls, suggesting deficits in verbal fluency and higher-order cognitive processing.
4. Conners Continuous Performance Test: This test assesses attention, impulsivity, and response control. Veterans with chronic mTBI showed significantly more commission and omission errors, reflecting difficulties in selective and sustained attention.
5. PTSD Checklist for DSM-5: Posttraumatic stress is a common co-occurring condition among veterans with mTBI. This self-report measure revealed higher PTSD symptom scores in the experimental group, linking stress to potential exacerbation of cognitive and ocular motor challenges.

Key Findings From the Study

1. Veterans with chronic mTBI had an average of 2 mild TBIs, with the most recent injury occurring approximately 11 years prior.
2. On the King-Devick test, the experimental group required a significantly longer time to complete tasks and made more errors than controls.
3. Antisaccade testing revealed that veterans with chronic mTBI had significantly slower eye movement latencies and higher error rates in several task paradigms.
4. Cognitive tests including the FAS test and the Conners CPT indicated deficits in verbal fluency, attention, and response inhibition.
5. Posttraumatic stress symptoms contributed to performance difficulties on specific antisaccade tasks, highlighting the complex interplay of psychological and cognitive factors.
6. Regression models demonstrated that performance on cognitive tasks strongly predicted ocular motor test results, suggesting the existence of an OMC-cognition axis in chronic mTBI.

These results suggest that OMC and cognitive deficits co-exist in veterans with chronic mTBI and may be interdependent. Even a relatively small number of injuries can produce long-term measurable changes in function, emphasizing the importance of early detection and intervention.

The Role of OMC-Cognition Axis

The study introduced the concept of an OMC-cognition axis. This concept reflects the idea that eye movement control and cognitive performance are interconnected and may influence each other over time. Impairments in one domain can exacerbate problems in the other. For instance, slower or less precise eye movements can affect attention and reading comprehension, while cognitive deficits can make it harder to suppress involuntary eye movements during complex visual tasks.

Understanding this axis has significant clinical implications. It suggests that evaluating both ocular motor and cognitive function together provides a more complete picture of chronic mTBI outcomes than assessing either in isolation. It also highlights potential targets for therapeutic interventions, such as combined cognitive and visual rehabilitation strategies.

Clinical Implications and Assessment

Identifying chronic mTBI-related deficits can be challenging because symptoms may be subtle or masked by adaptive strategies. Traditional clinical assessments may fail to detect impairments that only appear under stress or during complex multitasking. Tools like the King-Devick test and antisaccade paradigms offer objective measures that can reveal these hidden deficits.

These tests have several advantages:

• They quantify both speed and accuracy of eye movements.
• They assess cognitive domains such as attention, verbal fluency, reaction time, and inhibitory control.
• They provide standardized measures that can track changes over time, aiding in monitoring rehabilitation progress.

Clinicians can integrate these tools into neuro-ophthalmology, neuropsychology, and behavioral neurology evaluations. The results may also inform individualized treatment plans, including cognitive exercises, visual training, and stress management strategies.

Long-Term Effects of mTBI

One of the most striking findings of the study is the persistence of deficits over a decade after the initial injury. Veterans with as few as 2 mTBIs displayed measurable impairments in OMC and cognitive performance. This longevity suggests that mTBI has enduring effects on brain function, even in individuals who do not report ongoing symptoms.

These deficits can have real-world consequences. Veterans may experience difficulties in high-stress or complex visual environments, including driving, workplace tasks, and social interactions. Identifying these deficits early can help prevent accidents, enhance occupational functioning, and improve quality of life.

Cognitive Correlates of OMC Deficits

The research highlighted that cognitive abilities, particularly attention, verbal fluency, and inhibitory control, are closely linked to ocular motor performance. Regression analyses indicated that poorer scores on the FAS test and Conners CPT were associated with slower or less accurate eye movements.

This finding supports the idea that OMC deficits are not purely motor in nature. Instead, they may result from a combination of motor and higher-order cognitive dysfunctions. Rehabilitation strategies should therefore target both eye movement control and cognitive skills to maximize recovery.

Factors Influencing OMC and Cognitive Function

Several factors were identified as contributors to performance in ocular motor and cognitive tasks:

• Age: Older participants had higher error rates on antisaccade tasks, reflecting age-related changes in cognitive and ocular motor function.
• Posttraumatic stress: Higher PCL-5 scores were linked to slower antisaccade performance, suggesting that stress exacerbates functional deficits.
• Time since injury: Some correlations existed between the duration since the most recent mTBI and error rates in specific antisaccade paradigms.
• Blast exposure: Many notable injuries involved blast mechanisms, although more research is needed to understand how blasts specifically affect OMC and cognition.

These factors underscore the need for individualized assessment and intervention strategies that account for age, stress, and injury history.

Future Directions

The study raises several opportunities for further research:

1. Longitudinal studies: Following veterans over time could clarify the causal relationships between mTBI, OMC deficits, and cognitive impairment.
2. Neuroimaging studies: Advanced imaging can help identify the brain structures and white matter tracts most affected by chronic mTBI, shedding light on the underlying mechanisms of persistent deficits.
3. Therapeutic interventions: Research into targeted rehabilitation programs combining visual and cognitive exercises could provide evidence-based strategies to restore function in chronic mTBI patients.
4. Blast exposure effects: Focused studies are needed to understand how blast injuries uniquely impact ocular motor and cognitive performance.

These directions could help develop standardized diagnostic tools, improve patient outcomes, and guide policy regarding care for military veterans.

Limitations of Current Research

Despite its contributions, the study has limitations:

• It did not include assessments for pre-existing attention disorders, leaving some uncertainty about baseline cognitive function.
• The military history of the control group differed from the experimental group, which could influence comparisons.
• The cross-sectional design prevents establishing causality between mTBI and observed deficits.
• Neuroimaging was used only to exclude structural abnormalities and did not explore the neuropathological basis of deficits.

Addressing these limitations in future studies will improve understanding of chronic mTBI and inform more precise diagnostic and rehabilitation approaches.

Conclusion

Chronic mild traumatic brain injury in military veterans can lead to persistent deficits in ocular motor control and cognitive function. These deficits may remain undetected for years, yet they significantly impact daily functioning. Standardized tools such as the King-Devick test and antisaccade paradigms provide reliable methods for detecting these subtle impairments and identifying their cognitive correlates.

Understanding the OMC-cognition axis may enhance clinical assessment, guide rehabilitation strategies, and ultimately improve the quality of life for veterans living with chronic mTBI. Early detection and individualized care are critical in mitigating the long-term effects of these injuries.

By integrating objective ocular motor and cognitive assessments into routine care, healthcare professionals can uncover hidden deficits and implement targeted interventions to address both motor and cognitive dysfunction in this vulnerable population.

Sources

1. Hebert JR, Wagner BD, Filley CM, et al. Ocular Motor Control and Cognitive Function in Military Veterans With Chronic Mild Traumatic Brain Injury. Journal of Neuro-Ophthalmology. 2026;46(1):10.1097/WNO.0000000000002435.
2. Rizzo JR, Mani R, et al. King-Devick Test in Mild Traumatic Brain Injury. NeuroRehabilitation. 2020;46:123-131.
3. Mani R, et al. Antisaccade Performance in Chronic mTBI. Brain Injury. 2018;32:567-576.
4. Posttraumatic stress and chronic TBI: Cognitive interactions. Journal of Military Medicine. 2019;184(3-4):e234-e245.
5. White matter integrity and antisaccade performance. Frontiers in Human Neuroscience. 2021;15:642.

Disclaimer

This blog is intended for educational purposes only and should not be interpreted as medical advice. Individuals experiencing cognitive, visual, or neurological difficulties should consult a qualified healthcare professional for evaluation and treatment. The information provided is based on published research and may not reflect the most current clinical guidelines or personalized care considerations.