Increased oculomotor deficits during target blanking as an indicator of mild traumatic brain injury

Eye Movements in Mild Traumatic Brain Injury: Ocular Biomarkers

Mild traumatic brain injury (mTBI, or concussion), results from direct and indirect trauma to the head (i.e. a closed injury of transmitted forces), with or without loss of consciousness. The current method of diagnosis is largely based on symptom assessment and clinical history. There is an urgent need to identify an objective biomarker which can not only detect injury, but inform prognosis and recovery. Ocular motor impairment is argued to be ubiquitous across mTBI subtypes and may serve as a valuable clinical biomarker with the recent advent of more affordable and portable eye tracking technology. Many groups have positively correlated the degree of ocular motor impairment to symptom severity with a minority attempting to validate these findings with diffusion tract imaging and functional MRI. However, numerous methodological issues limit the interpretation of results, preventing any singular ocular biomarker from prevailing. This review will comprehensively describe the anatomical susceptibility, clinical measurement, and current eye tracking literature surrounding saccades, smooth pursuit, vestibulo-ocular reflex, vergence, pupillary light reflex, and accommodation in mTBI.

Vestibulo-ocular dysfunction in mTBI: Utility of the VOMS for evaluation and management – A review

BACKGROUND: Individuals who have suffered a concussion/mild traumatic brain injury (mTBI) frequently report symptoms associated with vestibular and/or oculomotor dysfunction (VOD) like dizziness, nausea, fatigue, brain fog, headache, gait and neurocognitive impairments which are associated with the development of chronic symptoms. The Vestibular/Ocular Motor Screening (VOMS) tool has been established as a reliable and clinically relevant complement to use alongside a battery of post-concussion tests to improve screening and referral for further evaluation and treatment of VOD. OBJECTIVES: This paper will review the pathoanatomy and symptomatology of common vestibular and oculomotor disorders after concussion, as well as the utility of the VOMS to assist in diagnosis, referral, and management. METHODS: Primary articles were identified using a search via PubMed, Google Scholar, OneSearch, and CINAHL. Search key terms were combinations of “mild traumatic brain injury” or “concussion” or “pursuit” or “accommodation” or “vergence” or “convergence insufficiency” or “saccades” or “vestibulo-ocular reflex” or “vestibular ocular motor screen” or “vestibular rehabilitation”, or “vision rehabilitation” including adult and pediatric populations that were published in print or electronically from 1989 to 2021 in English. Classic papers on anatomy of eye movements, vestibular system and pathological changes in mTBI were also included, regardless of publication date. RESULTS: Objective impairments are commonly found during testing of smooth pursuit, saccades, vergence, accommodation, vestibular ocular reflex, and visual motion sensitivity after mTBI. These deficits can be actively treated with vestibular physical therapy and oculomotor/neuro-optometric vision therapy. VOMS is an efficient and reliable tool that can be used by all healthcare and rehabilitation providers to aid in diagnosis of post-concussion VOD, to help facilitate the decision to refer for further evaluation and treatment to expedite symptomatic post-concussion recovery. CONCLUSIONS: VOD is common after concussion in acute, post-acute, and chronic phases. Once areas of impairments are identified through proper assessment, clinicians can maximize recovery by referring to vestibular physical therapy and/or neuro-optometry to design a targeted treatment program to address individual deficits.

Smooth Pursuit Eye Movements as a Biomarker for Mild Concussion within 7-Days of Injury

AIM

Deficits in smooth-pursuit eye movements (SPEM) are often associated with mild traumatic brain injury(TBI). Eye tracking tests serve as a quick objective clinical tool to assess such predictive visual tracking. In this study, SPEM was assessed along circular, horizontal and vertical trajectories in adolescents with concussion and age-matched controls.

METHODS

Ninety-one young adolescents with concussion and 140 visually healthy age-matched controls with a mean age of 14 years performed a computerized test of circular, horizontal and vertical tracking task using an eye tracker. Oculomotor tracking was assessed by computing the rate of fixation, saccades and SPEM made while performing the tasks.

RESULTS

The predictive visual tracking task was able to differentiate the TBI group from the non-TBI group. The TBI group showed a significant difference in the fixation, saccades and SPEM percentages for circular tracking movement compared to the controls. There was a significant difference in fixation and SPEM % for horizontal and vertical tracking.

CONCLUSIONS

Predictive visual tracking, assessed using eye tracking technology, is able to differentiate deficits in oculomotor functions in individuals with and without concussion. The eye tracking technology may serve as a quick objective tool to detect and monitor neural deficits due to TBI.

Saccade and Fixation Eye Movements During Walking in People With Mild Traumatic Brain Injury

Background: Clinical and laboratory assessment of people with mild traumatic brain injury (mTBI) indicate impairments in eye movements. These tests are typically done in a static, seated position. Recently, the use of mobile eye-tracking systems has been proposed to quantify subtle deficits in eye movements and visual sampling during different tasks. However, the impact of mTBI on eye movements during functional tasks such as walking remains unknown.

Objective: Evaluate differences in eye-tracking measures collected during gait between healthy controls (HC) and patients in the sub-acute stages of mTBI recovery and to determine if there are associations between eye-tracking measures and gait speed.

Methods: Thirty-seven HC participants and 67individuals with mTBI were instructed to walk back and forth over 10-m, at a comfortable self-selected speed. A single 1-min trial was performed. Eye-tracking measures were recorded using a mobile eye-tracking system (head-mounted infra-red Tobbii Pro Glasses 2, 100 Hz, Tobii Technology Inc. VA, United States). Eye-tracking measures included saccadic (frequency, mean and peak velocity, duration and distance) and fixation measurements (frequency and duration). Gait was assessed using six inertial sensors (both feet, sternum, right wrist, lumbar vertebrae and the forehead) and gait velocity was selected as the primary outcome. General linear model was used to compare the groups and association between gait and eye-tracking outcomes were explored using partial correlations.

Results: Individuals with mTBI showed significantly reduced saccade frequency (p = 0.016), duration (p = 0.028) and peak velocity (p = 0.032) compared to the HC group. No significant differences between groups were observed for the saccade distance, fixation measures and gait velocity (p > 0.05). A positive correlation was observed between saccade duration and gait velocity only for participants with mTBI (p = 0.025).

Conclusion: Findings suggest impaired saccadic eye movement, but not fixations, during walking in individuals with mTBI. These findings have implications in real-world function including return to sport for athletes and return to duty for military service members. Future research should investigate whether or not saccade outcomes are influenced by the time after the trauma and rehabilitation.

Rehabilitation of visual disorders

While there is a long history of rehabilitation for motor deficits following cerebral lesions, less is known about our ability to improve visual deficits. Vision therapy, prisms, occluders, and filters have been advocated for patients with mild traumatic brain injury, on the premise that some of their symptoms may reflect abnormal visual or ocular motor function, but the evidence for their efficacy is modest. For hemianopia, attempts to restore vision have had unimpressive results, though it appears possible to generate blindsight through training. Strategic approaches that train more efficient use of visual search in hemianopia have shown consistent benefit in visual function, while prism aids may help some patients. There are many varieties of alexia. Strategic adaptation of saccades can improve hemianopic alexia, but there has been less work and mixed results for pure alexia, neglect dyslexia, attentional dyslexia, and the central dyslexias. A number of approaches have been tried in prosopagnosia, with recent studies of small groups suggesting that face perception of prosopagnosic subjects can be enhanced through perceptual learning.

Oculomotor Behavior as a Biomarker for Differentiating Pediatric Patients With Mild Traumatic Brain Injury and Age Matched Controls

IMPORTANCE

Children have the highest incidence of mild traumatic brain injury (mTBI) in the United States. However, mTBI, specifically pediatric patients with mTBI, are notoriously difficult to detect, and with a reliance on traditional, subjective measurements of eye movements, the subtle but key oculomotor deficits are often missed.

OBJECTIVE

The purpose of this project is to determine if the combined measurement of saccades, smooth pursuit, fixations and reaction time represent a biomarker for differentiating pediatric patients with mild traumatic brain injury compared to age matched controls.

DESIGN

This study used cross-sectional design. Each participant took part in a suite of tests collectively labeled the "Brain Health EyeQ" to measure saccades, smooth pursuit, fixations and reaction time.

PARTICIPANTS

The present study recruited 231 participants - 91 clinically diagnosed with a single incident mTBI in the last 2 days as assessed by both the Glasgow Coma Scale (GCS) and Graded Symptoms Checklist (GSC), and 140 age and gender-matched controls (n = 165 male, n = 66 female, M age = 14.20, SD = 2.78).

RESULTS

One-way univariate analyses of variance examined the differences in performance on the tests between participants with mTBI and controls. ROC curve analysis examined the sensitivity and specificity of the tests. Results indicated that together, the "Brain Health EyeQ" tests were successfully able to identify participants with mTBI 75.3% of the time, providing further validation to a growing body of literature supporting the use of eye tracking technology for mTBI identification and diagnosis.

Oculomotor, Vestibular, and Reaction Time Effects of Sports-Related Concussion: Video-Oculography in Assessing Sports-Related Concussion

Objective:

The purpose of the study was to test the ability of oculomotor, vestibular, and reaction time (OVRT) metrics to serve as a concussion assessment or diagnostic tool for general clinical use.

Setting and Participants:

Patients with concussion were high school-aged athletes clinically diagnosed in a hospital setting with a sports-related concussion (n = 50). Control subjects were previously recruited male and female high school student athletes from 3 local high schools (n = 170).

Design:

Video-oculography was used to acquire eye movement metrics during OVRT tasks, combined with other measures. Measures were compared between groups, and a subset was incorporated into linear regression models that could serve as indicators of concussion.

Measures:

The OVRT test battery included multiple metrics of saccades, smooth pursuit tracking, nystagmoid movements, vestibular function, and reaction time latencies.

Results:

Some OVRT metrics were significantly different between groups. Linear regression models distinguished control subjects from concussion subjects with high accuracy. Metrics included changes in smooth pursuit tracking, increased reaction time and reduced saccade velocity in a complex motor task, and decreased optokinetic nystagmus (OKN) gain. In addition, optokinetic gain was reduced and more variable in subjects assessed 22 or more days after injury.

Conclusion:

These results indicate that OVRT tests can be used as a reliable adjunctive tool in the assessment of concussion and that OKN results appear to be associated with a prolonged expression of concussion symptoms.

Clinical validation of an optimized multimodal neurocognitive assessment of chronic mild TBI

OBJECTIVE

Previous laboratory-based studies have shown that neurocognitive eye-tracking metrics are sensitive to chronic effects of mild traumatic brain injury (mTBI), even in individuals with normal performance on traditional neuropsychological measures. In this study, we sought to replicate and extend these findings in a military medical environment. We expected that metrics from the multimodal Fusion n-Back test would successfully distinguish chronic mTBI participants from controls, particularly eye movement metrics from the more cognitively challenging "1-Back" subtest.

METHODS

We compared performance of participants with chronic mTBI (n = 46) and controls (n = 33) on the Fusion n-Back test and a battery of conventional neuropsychological tests. Additionally, we examined test reliability and the impact of potential confounds to neurocognitive assessment.

RESULTS

Our results supported hypotheses; Fusion 1-Back metrics were successful in multimodal (saccadic and manual) classification of chronic mTBI versus control. In contrast, conventional neuropsychological measures could not distinguish these groups. Additional findings demonstrated the reliability of Fusion n-Back test metrics and provided evidence that saccadic metrics are resistant to confounding influences of age, intelligence, and psychiatric symptoms.

INTERPRETATION

The Fusion n-Back test could provide advantages in differential diagnosis for complex brain injury populations. Additionally, the rapid administration of this test could be valuable for screening patients in clinical settings where longer test batteries are not feasible.

The Measurement of Eye Movements in Mild Traumatic Brain Injury: A Structured Review of an Emerging Area

Mild traumatic brain injury (mTBI), or concussion, occurs following a direct or indirect force to the head that causes a change in brain function. Many neurological signs and symptoms of mTBI can be subtle and transient, and some can persist beyond the usual recovery timeframe, such as balance, cognitive or sensory disturbance that may pre-dispose to further injury in the future. There is currently no accepted definition or diagnostic criteria for mTBI and therefore no single assessment has been developed or accepted as being able to identify those with an mTBI. Eye-movement assessment may be useful, as specific eye-movements and their metrics can be attributed to specific brain regions or functions, and eye-movement involves a multitude of brain regions. Recently, research has focused on quantitative eye-movement assessments using eye-tracking technology for diagnosis and monitoring symptoms of an mTBI. However, the approaches taken to objectively measure eye-movements varies with respect to instrumentation, protocols and recognition of factors that may influence results, such as cognitive function or basic visual function. This review aimed to examine previous work that has measured eye-movements within those with mTBI to inform the development of robust or standardized testing protocols. Medline/PubMed, CINAHL, PsychInfo and Scopus databases were searched. Twenty-two articles met inclusion/exclusion criteria and were reviewed, which examined saccades, smooth pursuits, fixations and nystagmus in mTBI compared to controls. Current methodologies for data collection, analysis and interpretation from eye-tracking technology in individuals following an mTBI are discussed. In brief, a wide range of eye-movement instruments and outcome measures were reported, but validity and reliability of devices and metrics were insufficiently reported across studies. Interpretation of outcomes was complicated by poor study reporting of demographics, mTBI-related features (e.g., time since injury), and few studies considered the influence that cognitive or visual functions may have on eye-movements. The reviewed evidence suggests that eye-movements are impaired in mTBI, but future research is required to accurately and robustly establish findings. Standardization and reporting of eye-movement instruments, data collection procedures, processing algorithms and analysis methods are required. Recommendations also include comprehensive reporting of demographics, mTBI-related features, and confounding variables.

Vertical smooth pursuit as a diagnostic marker of traumatic brain injury

AIM

Neural deficits were measured via the eye tracking of vertical smooth pursuit (VSP) as markers of traumatic brain injury (TBI). The present study evaluated the ability of the eye tracking tests to differentiate between different levels of TBI severity and healthy controls.

METHODOLOGY

Ninety-two individuals divided into four groups (those with mild, moderate or severe TBI and healthy controls) participated in a computerized test of VSP eye movement using a remote eye tracker.

RESULTS

The VSP eye tracking test was able to distinguish between severe and moderate levels of TBI but unable to detect differences in the performance of participants with mild TBI and healthy controls.

CONCLUSION

The eye-tracking technology used to measure VSP eye movements is able to provide a timely and objective method of differentiating between individuals with moderate and severe levels of TBI.

Vestibular and Balance Dysfunction Following Sport-Related Concussion

Purpose

Sport-related concussion is a significant public health concern that requires a multidisciplinary team to appropriately manage. Athletes often report dizziness and imbalance following concussion, and these symptoms can predict increased time to recover. Vestibular diagnostic evaluations provide important information regarding the athlete's oculomotor, gaze stability, and balance function in order to identify deficits for rehabilitation. These measures also describe objective function helpful for determining when an athlete is ready to return to play. The purpose of this clinical focus article is to provide background on the current understanding of the effects of concussion on the peripheral and central vestibular system, as well as information on a protocol that can be used for acute concussion assessment. Case studies describing 3 common postconcussion presentations will highlight the usefulness of this protocol.

Conclusion

Sport-related concussion is a highly visible disorder with many symptoms that may be evaluated in the vestibular clinic. A thoughtful protocol evaluating the typical presentation of these patients may help guide the multidisciplinary team in determining appropriate management and clearance for return to sport.

Toward development of clinically translatable diagnostic and prognostic metrics of traumatic brain injury using animal models: A review and a look forward

Traumatic brain injury is a leading cause of cognitive and behavioral deficits in children in the US each year. There is an increasing interest in both clinical and pre-clinical studies to discover biomarkers to accurately diagnose traumatic brain injury (TBI), predict its outcomes, and monitor its progression especially in the developing brain. In humans, the heterogeneity of TBI in terms of clinical presentation, injury causation, and mechanism has contributed to the many challenges associated with finding unifying diagnosis, treatment, and management practices. In addition, findings from adult human research may have little application to pediatric TBI, as age and maturation levels affect the injury biomechanics and neurophysiological consequences of injury. Animal models of TBI are vital to address the variability and heterogeneity of TBI seen in human by isolating the causation and mechanism of injury in reproducible manner. However, a gap between the pre-clinical findings and clinical applications remains in TBI research today. To take a step toward bridging this gap, we reviewed several potential TBI tools such as biofluid biomarkers, electroencephalography (EEG), actigraphy, eye responses, and balance that have been explored in both clinical and pre-clinical studies and have shown potential diagnostic, prognostic, or monitoring utility for TBI. Each of these tools measures specific deficits following TBI, is easily accessible, non/minimally invasive, and is potentially highly translatable between animals and human outcomes because they involve effort-independent and non-verbal tasks. Especially conspicuous is the fact that these biomarkers and techniques can be tailored for infants and toddlers. However, translation of preclinical outcomes to clinical applications of these tools necessitates addressing several challenges. Among the challenges are the heterogeneity of clinical TBI, age dependency of some of the biomarkers, different brain structure, life span, and possible variation between temporal profiles of biomarkers in human and animals. Conducting parallel clinical and pre-clinical research, in addition to the integration of findings across species from several pre-clinical models to generate a spectrum of TBI mechanisms and severities is a path toward overcoming some of these challenges. This effort is possible through large scale collaborative research and data sharing across multiple centers. In addition, TBI causes dynamic deficits in multiple domains, and thus, a panel of biomarkers combining these measures to consider different deficits is more promising than a single biomarker for TBI. In this review, each of these tools are presented along with the clinical and pre-clinical findings, advantages, challenges and prospects of translating the pre-clinical knowledge into the human clinical setting.

Working memory load improves diagnostic performance of smooth pursuit eye movement in mild traumatic brain injury patients with protracted recovery

Smooth pursuit eye movements have been investigated as a diagnostic tool for mild traumatic brain injury (mTBI). However, the degree to which smooth pursuit differentiates mTBI patients from healthy controls (i.e. its diagnostic performance) is only moderate. Our goal was to establish if simultaneous performance of smooth pursuit and a working memory task increased the diagnostic performance of pursuit metrics following mTBI. We integrated an n-back task with two levels of working memory load into a pursuit target, and tested single- and dual-task pursuit in mTBI patients and healthy controls. We assessed pursuit using measures of velocity accuracy, positional accuracy and positional variability. The mTBI group had higher pursuit variability than the control group in all conditions. Performing a concurrent 1-back task decreased pursuit variability for both the mTBI and control groups. Performing a concurrent 2-back task produced differential effects between the groups: Pursuit variability was significantly decreased in the control group, but not in the mTBI group. Diagnostic indices were improved when pursuit was combined with the 2-back task, and increased by 20% for the most sensitive variable. Smooth pursuit with simultaneous working memory load may be a superior diagnostic tool for mTBI than measuring smooth pursuit alone.

Saccadic impairment in chronic traumatic brain injury: examining the influence of cognitive load and injury severity

OBJECTIVE

Previous research suggests that saccadic eye movements can be uniquely sensitive to impairment in chronic traumatic brain injury (TBI). This study was conducted to examine saccadic eye movements across varying levels of cognitive load and TBI history/severity. We hypothesized that saccadic impairment in chronic mild and moderate-severe TBI would be most pronounced under conditions of high cognitive load.

METHODS

In total, 61 participants (including n = 20 with chronic mild TBI, n = 15 with chronic moderate-severe TBI, and 26 uninjured controls) completed a battery of conventional neuropsychological tests and the Fusion n-Back Test, which measures manual and saccadic response time (RT) across varying cognitive load and cueing conditions.

RESULTS

Consistent with our hypotheses, chronic mild and moderate-severe TBI were associated with substantial saccadic impairment under conditions of high cognitive load. Participants with moderate-severe TBI also demonstrated saccadic impairment at low levels of cognitive load. TBI groups and uninjured controls did not differ significantly on manual metrics or conventional neuropsychological measures.

CONCLUSIONS

This study provides additional support for the value of eye tracking for enhanced assessment of TBI. Additionally, findings suggest that TBI is associated with greatest susceptibility to oculomotor interference under high levels of cognitive load.

Deficits in saccades and smooth-pursuit eye movements in adults with traumatic brain injury: a systematic review and meta-analysis

PURPOSE

To conduct a review of literature and quantify the effect that traumatic brain injury (TBI) has on oculomotor functions (OM).

METHODS

A systematic review and meta-analysis was conducted from papers that objectively measured saccades and smooth-pursuit eye movements in mild and severe TBI.

RESULTS

The overall impact of TBI on OM functions was moderate and significant with an effect size of 0.42 from 181 OM case-control comparisons. The heterogeneity, determined using the random effect model, was found to be significant (Q (180) = 367, p < 0.0001, I² = 51) owing to the variety of OM functions (reflexive saccades, antisaccades, memory-guided saccades, self-paced saccades and pursuits) measured and varying post-injury periods.The overall effect on OM functions were similar in mild and severe TBI despite differences in combined effect size of various OM functions. OM functions involving complex cognitive skills such as antisaccades (in mild and severe TBI) and memory-guided saccades (in mild TBI) were the most adversely affected, suggesting that OM deficits may be associated with cognitive deficits in TBI.

CONCLUSION

TBI often results in long-standing OM deficits. Experimental measures of OM assessment reflect neural integrity and may provide a sensitive and objective biomarker to detect OM deficits following TBI.

Oculomotor-Based Vision Assessment in Mild Traumatic Brain Injury: A Systematic Review

OBJECTIVE

The purpose of this article is to synthesize and appraise the evidence regarding the use of oculomotor-based vision assessment to identify and monitor recovery from mild traumatic brain injury (mTBI). Specific objectives are to (1) identify changes in oculomotor-based vision following mTBI; (2) distinguish methods of assessment; (3) appraise the level and quality of evidence; and, if warranted, (4) determine clinical recommendations for assessment.

METHODS

A systematic review was undertaken to identify and appraise relevant literature. A search was conducted of 7 databases of peer-reviewed literature from January 1990 to January 2015. Articles were included if study populations were clearly identified as having mTBI and used an assessment of oculomotor-based vision. Articles with pooled data (eg, mTBI and stroke), addressing afferent visual function (eg, visual field deficits) or using single case designs, were excluded.

RESULTS

Twenty articles were selected for inclusion. Exploratory findings suggest that measurements of saccades, smooth pursuit, and vergence are useful in detecting changes associated with mTBI. Assessment methods included eye tracker protocols, optometric assessment, and the King-Devick test.

CONCLUSION

The strength of this evidence is not yet sufficient to warrant clinical recommendations. Research using rigorous methods is required to develop reliable, valid, and clinically useful assessment protocols.

Neuro-ophthalmologic disorders following concussion

Visual symptoms, such as photophobia and blurred vision, are common in patients with concussion. Such symptoms may be accompanied by abnormalities of specific eye movements, such as saccades and convergence, or accommodation deficits. The high frequency of visual involvement in concussion is not surprising, since more than half of the brain's pathways are dedicated to vision and eye movement control. These areas include many that are most vulnerable to head trauma, including the frontal and temporal lobes. Vision and eye movement testing is important at the bedside and on the sidelines of athletic events, where brief performance measures that require eye movements, such as rapid number naming, are reliable and sensitive measures for concussion detection. Tests of vision and eye movements are also being explored clinically to identify and monitor patients with symptoms of both sport- and nonsport-related concussion. Evaluation of vision and eye movements can assist in making important decisions after concussion, including the prognosis for symptom recovery, and to direct further visual rehabilitation as necessary.

Feasibility of using normobaric hypoxic stress in mTBI research

Studies of mild traumatic brain injury (mTBI) recovery generally assess patients in unstressed conditions that permit compensation for impairments through increased effort expenditure. This possibility may explain why a subgroup of individuals report persistent mTBI symptoms yet perform normally on objective assessment. Accordingly, the development and utilization of stress paradigms may be effective for enhancing the sensitivity of mTBI assessment. Previous studies, discussed here, indirectly but plausibly support the use of normobaric hypoxia as a stressor in uncovering latent mTBI symptoms due to the overlapping symptomatology induced by both normobaric hypoxia and mTBI. Limited studies by our group and others further support this plausibility through proof-of-concept demonstrations that hypoxia reversibly induces disproportionately severe impairments of oculomotor, pupillometric, cognitive and autonomic function in mTBI individuals.

Oculometric Assessment of Sensorimotor Impairment Associated with TBI

Supplemental digital content is available in the text.

Purpose

Diffuse tissue damage from impact or blast traumatic brain injury (TBI) degrades information processing throughout the brain, often resulting in impairments in sensorimotor function. We have developed an eye-movement assessment test, consisting of a simple, appropriately randomized, radial tracking task together with a broad set of oculometric measures that can be combined to yield a sensitive overall indicator of sensorimotor functional status. We show here that this multidimensional method can be used to detect and characterize sensorimotor deficits associated with TBI.

Methods

To compare dynamic visuomotor processing of TBI subjects (n = 34) with a separate control population (n = 41), we used the Comprehensive Oculometric Behavioral Response Assessment (COBRA) method (Liston & Stone, J Vision. 14:12, 2014) to quantify 10 performance metrics for each subject. Each TBI subject's set of oculometrics was then combined to compute a single TBI impairment vector whose magnitude we refer to as the impairment index.

Results

In our TBI population, several individual oculometrics were significantly degraded, including pursuit latency, initial pursuit acceleration, pursuit gain, catch-up saccade amplitude, proportion smooth tracking, and speed responsiveness. Furthermore, the TBI impairment index discriminated TBI subjects from controls with an 81% probability that increased with self-reported TBI severity; although the 9 subjects self-reporting “little-to-no” residual impairment were statistically indistinguishable from controls (58% probability), the remaining 25 subjects were easily detectable (91% probability). Given the demonstrated link between higher-order visual perception/cognition and eye movements, we interpret the observed TBI-related impairments as degradations in the speed, accuracy, and precision of information processing within cortical circuits supporting higher-order visual processing and sensorimotor control, not just low-level brainstem motor deficits.

Conclusions

We conclude that multidimensional oculometric testing could be used as a sensitive screen for subtle neurological signs of subclinical neurological insults, to quantify functional impairment, to monitor deterioration or recovery, and to evaluate treatment efficacy.

Eye Control Deficits Coupled to Hand Control Deficits: Eye-Hand Incoordination in Chronic Cerebral Injury

It is widely accepted that cerebral pathology can impair ocular motor and manual motor control. This is true in indolent and chronic processes, such as neurodegeneration and in acute processes such as stroke or those secondary to neurotrauma. More recently, it has been suggested that disruptions in these control systems are useful markers for prognostication and longitudinal monitoring. The utility of examining the relationship or the coupling between these systems has yet to be determined. We measured eye and hand-movement control in chronic, middle cerebral artery stroke, relative to healthy controls, in saccade-to-reach paradigms to assess eye-hand coordination. Primary saccades were initiated significantly earlier by stroke participants relative to control participants. However, despite these extremely early initial saccades to the target, reaches were nevertheless initiated at approximately the same time as those of control participants. Control participants minimized the time period between primary saccade onset and reach initiation, demonstrating temporal coupling between eye and hand. In about 90% of all trials, control participants produced no secondary, or corrective, saccades, instead maintaining fixation in the terminal position of the primary saccade until the end of the reach. In contrast, participants with stroke increased the time period between primary saccade onset and reach initiation. During this temporal decoupling, multiple saccades were produced in about 50% of the trials with stroke participants making between one and five additional saccades. Reaches made by participants with stroke were both longer in duration and less accurate. In addition to these increases in spatial reach errors, there were significant increases in saccade endpoint errors. Overall, the magnitude of the endpoint errors for reaches and saccades were correlated across participants. These findings suggest that in individuals with otherwise intact visual function, the spatial and temporal relationships between the eye and hand are disrupted poststroke, and may need to be specifically targeted during neurorehabilitation. Eye-hand coupling may be a useful biomarker in individuals with cerebral pathology in the setting of neurovascular, neurotraumatic, and neurodegenerative pathology.

Visual system pathology in humans and animal models of blast injury

Injury from blast exposure is becoming a more prevalent cause of death and disability worldwide. The devastating neurological impairments that result from blasts are significant and lifelong. Progress in the development of effective therapies to treat injury has been slowed by its heterogeneous pathology and the dearth of information regarding the cellular mechanisms involved. Within the last decade, a number of studies have documented visual dysfunction following injury. This brief review examines damage to the visual system in both humans and animal models of blast injury. The in vivo use of the retina as a surrogate to evaluate brain injury following exposure to blast is also highlighted.

The Intersection between Ocular and Manual Motor Control: Eye-Hand Coordination in Acquired Brain Injury

Acute and chronic disease processes that lead to cerebral injury can often be clinically challenging diagnostically, prognostically, and therapeutically. Neurodegenerative processes are one such elusive diagnostic group, given their often diffuse and indolent nature, creating difficulties in pinpointing specific structural abnormalities that relate to functional limitations. A number of studies in recent years have focused on eye-hand coordination (EHC) in the setting of acquired brain injury (ABI), highlighting the important set of interconnected functions of the eye and hand and their relevance in neurological conditions. These experiments, which have concentrated on focal lesion-based models, have significantly improved our understanding of neurophysiology and underscored the sensitivity of biomarkers in acute and chronic neurological disease processes, especially when such biomarkers are combined synergistically. To better understand EHC and its connection with ABI, there is a need to clarify its definition and to delineate its neuroanatomical and computational underpinnings. Successful EHC relies on the complex feedback- and prediction-mediated relationship between the visual, ocular motor, and manual motor systems and takes advantage of finely orchestrated synergies between these systems in both the spatial and temporal domains. Interactions of this type are representative of functional sensorimotor control, and their disruption constitutes one of the most frequent deficits secondary to brain injury. The present review describes the visually mediated planning and control of eye movements, hand movements, and their coordination, with a particular focus on deficits that occur following neurovascular, neurotraumatic, and neurodegenerative conditions. Following this review, we also discuss potential future research directions, highlighting objective EHC as a sensitive biomarker complement within acute and chronic neurological disease processes.

Assessment and rehabilitation of central sensory impairments for balance in mTBI using auditory biofeedback: a randomized clinical trial

Background

Complaints of imbalance are common non-resolving signs in individuals with post-concussive syndrome. Yet, there is no consensus rehabilitation for non-resolving balance complaints following mild traumatic brain injury (mTBI). The heterogeneity of balance deficits and varied rates of recovery suggest varied etiologies and a need for interventions that address the underlying causes of poor balance function. Our central hypothesis is that most chronic balance deficits after mTBI result from impairments in central sensorimotor integration that may be helped by rehabilitation. Two studies are described to 1) characterize balance deficits in people with mTBI who have chronic, non-resolving balance deficits compared to healthy control subjects, and 2) determine the efficacy of an augmented vestibular rehabilitation program using auditory biofeedback to improve central sensorimotor integration, static and dynamic balance, and functional activity in patients with chronic mTBI.

Methods

Two studies are described. Study 1 is a cross-sectional study to take place jointly at Oregon Health and Science University and the VA Portland Health Care System. The study participants will be individuals with non-resolving complaints of balance following mTBI and age- and gender-matched controls who meet all inclusion criteria. The primary outcome will be measures of central sensorimotor integration derived from a novel central sensorimotor integration test. Study 2 is a randomized controlled intervention to take place at Oregon Health & Science University. In this study, participants from Study 1 with mTBI and abnormal central sensorimotor integration will be randomized into two rehabilitation interventions. The interventions will be 6 weeks of vestibular rehabilitation 1) with or 2) without the use of an auditory biofeedback device. The primary outcome measure is the daily activity of the participants measured using an inertial sensor.

Discussion

The results of these two studies will improve our understanding of the nature of balance deficits in people with mTBI by providing quantitative metrics of central sensorimotor integration, balance, and vestibular and ocular motor function. Study 2 will examine the potential for augmented rehabilitation interventions to improve central sensorimotor integration.

Trial registration

This trial is registered at clinicaltrials.gov (NCT02748109)

Clinical evaluation of concussion: the evolving role of oculomotor assessments

Sports-related concussion is a change in brain function following a direct or an indirect force to the head, identified in awake individuals and accounting for a considerable proportion of mild traumatic brain injury. Although the neurological signs and symptoms of concussion can be subtle and transient, there can be persistent sequelae, such as impaired attention and balance, that make affected patients particularly vulnerable to further injury. Currently, there is no accepted definition or diagnostic criteria for concussion, and there is no single assessment that is accepted as capable of identifying all patients with concussion. In this paper, the authors review the available screening tools for concussion, with particular emphasis on the role of visual function testing. In particular, they discuss the oculomotor assessment tools that are being investigated in the setting of concussion screening.

The Craig Hospital Eye Evaluation Rating Scale (CHEERS)

BACKGROUND

Oculomotor deficits in smooth pursuit, saccades, vestibular-ocular reflex (VOR), vergence, and fixation are common problems seen after moderate to severe traumatic brain injury (TBI). No scale currently exists to rate all of these together. The Craig Hospital Eye Evaluation Rating Scale (CHEERS) was designed to systematically quantify frequency and severity of eye movement deficits in TBI.

OBJECTIVE

To assess the intra- and interrater reliability of a new rating scale for detecting the presence and degree of 5 oculomotor abnormalities after TBI.

DESIGN

A reliability study.

SETTING

This was an institution-based study at Craig Rehabilitation Hospital.

PARTICIPANTS

English-speaking patients between ages 18 and 65 years with a primary diagnosis of moderate to severe mechanical TBI and who were not blind in either eye were eligible.

METHODS

Between October 2013 and March 2014, a total of 11 TBI patients and 9 non-TBI controls were enrolled in the study. The median age was 30 years (range, 18-74 years) for subjects and 52 years (range, 28-63 years) for controls. All patients were male, and 8 of 9 controls were female. Eye movements (fixation, smooth pursuit, saccade, convergence, and vestibular-ocular reflex) were recorded for each on digital video. They were rated on 2 separate occasions by each of the 2 raters.

MAIN OUTCOME MEASUREMENTS

Inter- and intrarater reliability tests.

RESULTS

Median elapsed time between the first and second ratings was 7 days (range, 5-44 days). Intrarater agreement was very strong (Spearman ρ ≥ 0.900) for pursuit, saccades, and VOR for both raters, and strong (Spearman ρ ≥ 0.710) for vergence and fixation. The interrater agreement for detecting presence of any oculomotor abnormality was substantial (unweighted κ = 0.63). The interrater concordance on the full range of scale scoring was strongest on the VOR test (weighted κ = 0.98), was substantial for vergence, pursuit, saccades, and total score (weighted κ > 0.60), and was moderate for fixation. For TBI patients, every eye movement rated was found to be more abnormal than compared to those in the controls.

CONCLUSIONS

CHEERS is a reliable scale for assessing and quantifying oculomotor deficits commonly observed in moderate to severe TBI. Further studies to validate the scale's utility in outcome prediction, and its applicability to broader brain injury populations, are warranted.

LEVEL OF EVIDENCE

IV.

Ocular motor assessment in concussion: Current status and future directions

Mild head injury such as concussions and subconcussive repetitive impact may lead to subtle changes in brain function and it is imperative to find sensitive and reliable tests to detect such changes. Tests involving the visual system, in particular eye movements, can incorporate higher cortical functioning and involve diffuse pathways in the brain, including many areas susceptible to head impact. With concussions, the clinical neuro-ophthalmic exam is important for detecting abnormalities in vergence, saccades, pursuit, and visual fixation. On the sidelines, the King-Devick test has been used as a visual performance measure that incorporates eye movements and increases the sensitivity in detecting possible concussions in conjunction with standard sideline tests of cognition, symptom checklists, and balance. Much promise lies in the eye movement laboratory to quantitate changes in saccades and pursuit with concussions using video-oculography. A combination of eye movement tasks coupled with neuroimaging techniques and other objective biomarkers may lead to a better understanding of the anatomical and physiological consequences of concussion and to better understand the natural history of this condition.

Sensitivity and specificity of an eye movement tracking-based biomarker for concussion

Object:

The purpose of the current study is to determine the sensitivity and specificity of an eye tracking method as a classifier for identifying concussion.

Methods:

Brain injured and control subjects prospectively underwent both eye tracking and Sport Concussion Assessment Tool 3. The results of eye tracking biomarker based classifier models were then validated against a dataset of individuals not used in building a model. The area under the curve (AUC) of receiver operating characteristics was examined.

Results:

An optimal classifier based on best subset had an AUC of 0.878, and a cross-validated AUC of 0.852 in CT- subjects and an AUC of 0.831 in a validation dataset. The optimal misclassification rate in an external dataset (n = 254) was 13%.

Conclusion:

If one defines concussion based on history, examination, radiographic and Sport Concussion Assessment Tool 3 criteria, it is possible to generate an eye tracking based biomarker that enables detection of concussion with reasonably high sensitivity and specificity.

Individual differences in oscillatory brain activity in response to varying attentional demands during a word recall and oculomotor dual task

Every day, we face situations that involve multi-tasking. How our brain utilizes cortical resources during multi-tasking is one of many interesting research topics. In this study, we tested whether a dual-task can be differentiated in the neural and behavioral responses of healthy subjects with varying degree of working memory capacity (WMC). We combined word recall and oculomotor tasks because they incorporate common neural networks including the fronto-parietal (FP) network. Three different types of oculomotor tasks (eye fixation, Fix-EM; predictive and random smooth pursuit eye movement, P-SPEM and R-SPEM) were combined with two memory load levels (low-load: five words, high-load: 10 words) for a word recall task. Each of those dual-task combinations was supposed to create varying cognitive loads on the FP network. We hypothesize that each dual-task requires different cognitive strategies for allocating the brain's limited cortical resources and affects brain oscillation of the FP network. In addition, we hypothesized that groups with different WMC will show differential neural and behavioral responses. We measured oscillatory brain activity with simultaneous MEG and EEG recordings and behavioral performance by word recall. Prominent frontal midline (FM) theta (4-6 Hz) synchronization emerged in the EEG of the high-WMC group experiencing R-SPEM with high-load conditions during the early phase of the word maintenance period. Conversely, significant parietal upper alpha (10-12 Hz) desynchronization was observed in the EEG and MEG of the low-WMC group experiencing P-SPEM under high-load conditions during the same period. Different brain oscillatory patterns seem to depend on each individual's WMC and varying attentional demands from different dual-task combinations. These findings suggest that specific brain oscillations may reflect different strategies for allocating cortical resources during combined word recall and oculomotor dual-tasks.

Filling in the gaps: Anticipatory control of eye movements in chronic mild traumatic brain injury

A barrier in the diagnosis of mild traumatic brain injury (mTBI) stems from the lack of measures that are adequately sensitive in detecting mild head injuries. MRI and CT are typically negative in mTBI patients with persistent symptoms of post-concussive syndrome (PCS), and characteristic difficulties in sustaining attention often go undetected on neuropsychological testing, which can be insensitive to momentary lapses in concentration. Conversely, visual tracking strongly depends on sustained attention over time and is impaired in chronic mTBI patients, especially when tracking an occluded target. This finding suggests deficient internal anticipatory control in mTBI, the neural underpinnings of which are poorly understood. The present study investigated the neuronal bases for deficient anticipatory control during visual tracking in 25 chronic mTBI patients with persistent PCS symptoms and 25 healthy control subjects. The task was performed while undergoing magnetoencephalography (MEG), which allowed us to examine whether neural dysfunction associated with anticipatory control deficits was due to altered alpha, beta, and/or gamma activity. Neuropsychological examinations characterized cognition in both groups. During MEG recordings, subjects tracked a predictably moving target that was either continuously visible or randomly occluded (gap condition). MEG source-imaging analyses tested for group differences in alpha, beta, and gamma frequency bands. The results showed executive functioning, information processing speed, and verbal memory deficits in the mTBI group. Visual tracking was impaired in the mTBI group only in the gap condition. Patients showed greater error than controls before and during target occlusion, and were slower to resynchronize with the target when it reappeared. Impaired tracking concurred with abnormal beta activity, which was suppressed in the parietal cortex, especially the right hemisphere, and enhanced in left caudate and frontal–temporal areas. Regional beta-amplitude demonstrated high classification accuracy (92%) compared to eye-tracking (65%) and neuropsychological variables (80%). These findings show that deficient internal anticipatory control in mTBI is associated with altered beta activity, which is remarkably sensitive given the heterogeneity of injuries.

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Neuropsychological test performance was impaired in mTBI patients.

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Visual tracking was impaired in the gap task, where targets were randomly occluded.

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Impaired visual tracking concurred with abnormal MEG beta activity.

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Beta was suppressed in parietal and enhanced in caudate and frontal–temporal areas.

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Regional MEG beta-amplitude demonstrated high classification accuracy (92%).

Vision concerns after mild traumatic brain injury

OPINION STATEMENT

Mild traumatic brain injury (mTBI) can manifest with visual dysfunction including deficits in accommodation, vergence movements, versions, and field of vision as well increased photosensitivity and a decline in ocular and overall health. Patients with incomitant strabismus should be referred to an ophthalmologist for intervention. Patients with mTBI who experience photosensitivity, or deficits in accommodation, versions, vergences, or field of vision may benefit from vision rehabilitation. These therapies may include spectacles with tinting and a variety of prism combinations. Patients with chronic visual dysfunction following mTBI may benefit from occupational, vestibular, cognitive, and other forms of physical therapy.

Detection of third and sixth cranial nerve palsies with a novel method for eye tracking while watching a short film clip

OBJECT

Automated eye movement tracking may provide clues to nervous system function at many levels. Spatial calibration of the eye tracking device requires the subject to have relatively intact ocular motility that implies function of cranial nerves (CNs) III (oculomotor), IV (trochlear), and VI (abducent) and their associated nuclei, along with the multiple regions of the brain imparting cognition and volition. The authors have developed a technique for eye tracking that uses temporal rather than spatial calibration, enabling detection of impaired ability to move the pupil relative to normal (neurologically healthy) control volunteers. This work was performed to demonstrate that this technique may detect CN palsies related to brain compression and to provide insight into how the technique may be of value for evaluating neuropathological conditions associated with CN palsy, such as hydrocephalus or acute mass effect.

METHODS

The authors recorded subjects' eye movements by using an Eyelink 1000 eye tracker sampling at 500 Hz over 200 seconds while the subject viewed a music video playing inside an aperture on a computer monitor. The aperture moved in a rectangular pattern over a fixed time period. This technique was used to assess ocular motility in 157 neurologically healthy control subjects and 12 patients with either clinical CN III or VI palsy confirmed by neuro-ophthalmological examination, or surgically treatable pathological conditions potentially impacting these nerves. The authors compared the ratio of vertical to horizontal eye movement (height/width defined as aspect ratio) in normal and test subjects.

RESULTS

In 157 normal controls, the aspect ratio (height/width) for the left eye had a mean value ± SD of 1.0117 ± 0.0706. For the right eye, the aspect ratio had a mean of 1.0077 ± 0.0679 in these 157 subjects. There was no difference between sexes or ages. A patient with known CN VI palsy had a significantly increased aspect ratio (1.39), whereas 2 patients with known CN III palsy had significantly decreased ratios of 0.19 and 0.06, respectively. Three patients with surgically treatable pathological conditions impacting CN VI, such as infratentorial mass effect or hydrocephalus, had significantly increased ratios (1.84, 1.44, and 1.34, respectively) relative to normal controls, and 6 patients with supratentorial mass effect had significantly decreased ratios (0.27, 0.53, 0.62, 0.45, 0.49, and 0.41, respectively). These alterations in eye tracking all reverted to normal ranges after surgical treatment of underlying pathological conditions in these 9 neurosurgical cases.

CONCLUSIONS

This proof of concept series of cases suggests that the use of eye tracking to detect CN palsy while the patient watches television or its equivalent represents a new capacity for this technology. It may provide a new tool for the assessment of multiple CNS functions that can potentially be useful in the assessment of awake patients with elevated intracranial pressure from hydrocephalus or trauma.

The neuro-ophthalmology of head trauma

SUMMARY

Traumatic brain injury (TBI) is a major cause of morbidity and mortality. Concussion, a form of mild TBI, might be associated with long-term neurological symptoms. The effects of TBI and concussion are not restricted to cognition and balance. TBI can also affect multiple aspects of vision; mild TBI frequently leads to disruptions in visual functioning, while moderate or severe TBI often causes structural lesions. In patients with mild TBI, there might be abnormalities in saccades, pursuit, convergence, accommodation, and vestibulo-ocular reflex. Moderate and severe TBI might additionally lead to ocular motor palsies, optic neuropathies, and orbital pathologies. Vision-based testing is vital in the management of all forms of TBI and provides a sensitive approach for sideline or post-injury concussion screening. One sideline test, the King-Devick test, uses rapid number naming and has been tested in multiple athlete cohorts.

Individual differences in working memory capacity determine the effects of oculomotor task load on concurrent word recall performance

In this study, the interaction between individual differences in working memory capacity, which were assessed by the Korean version of the California Verbal Learning Test (K-CVLT), and the effects of oculomotor task load on word recall performance are examined in a dual-task experiment. We hypothesized that varying levels of oculomotor task load should result in different demands on cognitive resources. The verbal working memory task used in this study involved a brief exposure to seven words to be remembered, followed by a 30-second delay during which the subject carried out an oculomotor task. Then, memory performance was assessed by having the subjects recall as many words as possible. Forty healthy normal subjects with no vision-related problems carried out four separate dual-tasks over four consecutive days of participation, wherein word recall performances were tested under unpredictable random SPEM (smooth pursuit eye movement), predictive SPEM, fixation, and eyes-closed conditions. The word recall performance of subjects with low K-CVLT scores was significantly enhanced under predictive SPEM conditions as opposed to the fixation and eyes-closed conditions, but performance was reduced under the random SPEM condition, thus reflecting an inverted-U relationship between the oculomotor task load and word recall performance. Subjects with high K-CVLT scores evidenced steady word recall performances, regardless of the type of oculomotor task performed. The concurrent oculomotor performance measured by velocity error did not differ significantly among the K-CVLT groups. However, the high-scoring subjects evidenced smaller phase errors under predictive SPEM conditions than did the low-scoring subjects; this suggests that different resource allocation strategies may be adopted, depending on individuals' working memory capacity.

The predictive brain state: asynchrony in disorders of attention?

It is postulated that a key function of attention in goal-oriented behavior is to reduce performance variability by generating anticipatory neural activity that can be synchronized with expected sensory information. A network encompassing the prefrontal cortex, parietal lobe, and cerebellum may be critical in the maintenance and timing of such predictive neural activity. Dysfunction of this temporal process may constitute a fundamental defect in attention, causing working memory problems, distractibility, and decreased awareness.