George T. Gitchel

Differential eye movements in mild traumatic brain injury versus normal controls.

Objectives:Objective measures to diagnose and to monitor improvement of symptoms following mild traumatic brain injury (mTBI) are lacking. Computerized eye tracking has been advocated as a rapid, user friendly, and field-ready technique to meet this need. Design:Eye-tracking data collected via a head-mounted, video-based binocular eye tracker was used to examine saccades, fixations, and smooth pursuit movement in military Service Members with postconcussive syndrome (PCS) and asymptomatic control subjects in an effort to determine if eye movement differences could be found and quantified. Participants:Sixty Military Service Members with PCS and 26 asymptomatic controls. Outcome Measures:The diagnosis of mTBI was confirmed by the study physiatrists history, physical examination, and a review of any medical records. Various features of saccades, fixation and smooth pursuit eye movements were analyzed. Results:Subjects with symptomatic mTBI had statistically larger position errors, smaller saccadic amplitudes, smaller predicted peak velocities, smaller peak accelerations, and longer durations. Subjects with symptomatic mTBI were also less likely to follow a target movement (less primary saccades). In general, symptomatic mTBI tracked the stepwise moving targets less accurately, revealing possible brain dysfunction. Conclusions:A reliable, standardized protocol that appears to differentiate mTBI from normals was developed for use in future research. This investigation represents a step toward objective identification of those with PCS. Future studies focused on increasing the specificity of eye movement differences in those with PCS are needed.

Slowed Saccades and Increased Square Wave Jerks in Essential Tremor

Background Eye movements in essential tremor (ET) are poorly described and may present useful information on the underlying pathophysiology of the disorder. Methods Sixty patients with ET, including 15 de novo untreated patients, and 60 age-matched controls constitute the study population. A video-based eye tracker was used to assess binocular eye position. Oculomotor function was assessed while subjects followed random horizontally and vertically step-displaced targets. Results For all reflexive saccades, latencies were increased in ET subjects by a mean of 16.3% (p<0.01). Saccades showed reduced peak velocities with a lengthy, wavering velocity plateau, followed by slowed decelerations. For larger 30°+ saccades, peak velocities were decreased by a mean of 25.2% (p<0.01) and durations increased by 31.8% (p<0.01). The frequency of square wave jerks (SWJs) in patients was more than triple that of controls (p<0.0001). Despite frequent interruptions by SWJs, fixations were otherwise stable and indistinguishable from controls (root mean square [RMS] velocity, p = 0.324). The abnormal eye movement parameters were independent of disease duration, tremor severity, and medication therapy. Discussion In contrast to normally swift onset and efficient acceleration/deceleration movements, saccades in ET are characterized by abnormally prolonged latencies and slowed velocity profiles. Although ET subjects maintain highly stable fixations, they are interrupted by increased numbers of SWJs. This study reveals novel oculomotor deficits in ET, which are distinct from the eye movement dysfunction of other movement disorders, supporting a role for eye tracking to assist in the differential diagnoses of not only atypical, but also more common movement disorders.

Pervasive Ocular Tremor in Patients With Parkinson Disease

OBJECTIVE To further assess oculomotor control of patients with Parkinson disease (PD) during fixation and with movement. DESIGN Case-control study. SETTING A Parkinson disease research, education, and clinical center. PATIENTS One hundred twelve patients with PD, including 18 de novo untreated patients, and 60 age-matched controls. INTERVENTION Modern, precise eye tracking technology was used to assess oculomotor parameters. Oculomotor function was compared between groups during fixation and while tracking a randomly displaced target on a PC monitor. MAIN OUTCOME MEASURES Fixation stability and saccadic parameters. RESULTS All patients with PD and 2 of 60 control subjects showed oscillatory fixation instability (ocular tremor), with an average fundamental frequency of 5.7 Hz and average magnitude of 0.27°. Saccadic parameters and occurrences of square wave jerks did not differ between subjects with PD and controls. The amplitude and frequency of fixation instability did not correlate with disease duration, clinical Unified Parkinsons Disease Rating Scale scores, or dopa-equivalent dosing. No differences in oculomotor parameters were found between medicated and unmedicated patients with PD. CONCLUSIONS All patients with PD exhibited persistent ocular tremor that prevented stability during fixation. The pervasiveness and specificity of this feature suggest that modern, precise oculomotor testing could provide a valuable early physiological biomarker for diagnosing PD.

Effects of hyperbaric oxygen on eye tracking abnormalities in males after mild traumatic brain injury

The effects of hyperbaric oxygen (HBO2) on eye movement abnormalities in 60 military servicemembers with at least one mild traumatic brain injury (TBI) from combat were examined in a single-center, randomized, double-blind, sham-controlled, prospective study at the Naval Medicine Operational Training Center. During the 10 wk of the study, each subject was delivered a series of 40, once a day, hyperbaric chamber compressions at a pressure of 2.0 atmospheres absolute (ATA). At each session, subjects breathed one of three preassigned oxygen fractions (10.5%, 75%, or 100%) for 1 h, resulting in an oxygen exposure equivalent to breathing either surface air, 100% oxygen at 1.5 ATA, or 100% oxygen at 2.0 ATA, respectively. Using a standardized, validated, computerized eye tracking protocol, fixation, saccades, and smooth pursuit eye movements were measured just prior to intervention and immediately postintervention. Between and within groups testing of pre- and postintervention means revealed no significant differences on eye movement abnormalities and no significant main effect for HBO2 at either 1.5 ATA or 2.0 ATA equivalent compared with the sham-control. This study demonstrated that neither 1.5 nor 2.0 ATA equivalent HBO2 had an effect on postconcussive eye movement abnormalities after mild TBI when compared with a sham-control.

Experimental support that ocular tremor in Parkinson's disease does not originate from head movement

INTRODUCTION Our recent report of ocular tremor in Parkinsons disease (PD) has raised considerable controversy as to the origin of the tremor. Using an infrared based eye tracker and a magnetic head tracker, we reported that ocular tremor was recordable in PD subjects with no apparent head tremor. However, other investigators suggest that the ocular tremor may represent either transmitted appendicular tremor or subclinical head tremor inducing the vestibulo-ocular reflex (VOR). The present study aimed to further investigate the origin of ocular tremor in PD. METHODS Eye movements were recorded in 8 PD subjects both head free, and with full head restraint by means of a head holding device and a dental impression bite plate. Head movements were recorded independently using both a high sensitivity tri-axial accelerometer and a magnetic tracking system, each synchronized to the eye tracker. RESULTS Ocular tremor was observed in all 8 PD subjects and was not influenced by head free and head fixed conditions. Both magnetic tracking and accelerometer recordings supported that the ocular tremor was fully independent of head position. CONCLUSION The present study findings support our initial findings that ocular tremor is a fundamental feature of PD unrelated to head movements. Although the utility of ocular tremor for diagnostic purposes requires validation, current findings in large cohorts of PD subjects suggest its potential as a reliable clinical biomarker.

Ocular tremor in Parkinson's disease is due to eye, not head oscillation

to head shaking arising from transmitted armtremor and, in turn, inducing a vestibular ocular reflex.Despite their resolve, the authors provide absolutely nosupportive data for this speculation. Most conspicuously, intheir figure, when the head is fully restrained (evidentby the flat accelerometer reading), the ocular tremorpersists. Thus, the only relevant data refute the authors’hypothesis.Using a magnetic tracker, we consistently recorded nohead tremor in a subset of 20 patients

Eye Tracking Results in Postconcussive Syndrome Versus Normative Participants

Purpose Standard physical, neurologic, and neuropsychologic examinations may not detect abnormalities after mild traumatic brain injury (mTBI). An analysis of eye movements may be more sensitive to neurologic dysfunction. Methods We performed eye tracking assessments in 71 active duty and veteran military personnel with persistent postconcussive symptoms (3 months to 5 years after mTBI) and 75 volunteers with no history of brain injury. Both eyes were sampled at 500 Hz and analyzed for various eye measurement parameters during visual tasks involving the saccadic and smooth systems. Results No difference between mTBI and normal participants in main sequence profiles was observed. On the circular task, intersaccadic interval duration was shorter in mTBI compared with normal subjects (horizontal: Cohens D = -0.65; vertical: Cohens D = -0.75). For reading, absolute saccadic amplitudes (Cohens D = -0.76) and average forward saccadic amplitudes were lower (Cohens D = -0.61). Absolute fixation velocity was higher (Cohens D = 1.02), and overall fixation durations (Cohens D = 0.58), regression durations (Cohens D = 0.49), and forward saccadic durations (Cohens D=0.54) were longer. mTBI participants had more fixations (Cohens D = 0.54) and regressions per line (Cohens D = 0.70) and read fewer lines (Cohens D = -0.38) than normal subjects. On the horizontal ramp task, mTBI participants had lower weighted smooth pursuit gains (Cohens D = -0.55). On the horizontal step task, mTBI participants had shorter mean fixation times (Cohens D = -0.55). Conclusions These results suggest vulnerability of the smooth pursuit and saccadic systems in mTBI. Eye tracking shows promise as an objective, sensitive assessment of damage after mTBI. (ClinicalTrials.gov number, NCT01611194, NCT01925963.).