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Jonathan B. Jacobs, Ken Hrovat, King Yi, Margaret Skelly; Evaluation Of MTBI Subjects Using An Eye-movement-based Testing Suite. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4851.
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© ARVO (1962-2015); The Authors (2016-present)
Mild Traumatic Brain Injury (MTBI) is the "signature injury" of the wars in Iraq and Afghanistan (OIF/OEF). In contrast to impact injuries, which are generally focal, blast-induced MTBI damage is diffuse, affecting multiple portions of the brain, in particular axonal connectivity. The result can be diminishment of higher operations involving memory, impulse control and prediction/planning, important parts of "executive function." Currently the testing for detecting MTBI relies heavily on self-reporting and questionnaires, necessitating a large degree of subjectivity. It has been estimated that up to 25% of brain-injured veterans are not being properly diagnosed, and therefore are not being directed towards appropriate treatment. We propose to develop an objective, quantitative testing suite to aid the diagnosis of MTBI by measuring subjects’ performance during a series of visual tasks that depend on this higher-order processing.
We compared twenty control subjects with no history of blast or impact closed-head injury, and ten age-matched MTBI subjects who had been involved in at least one close-proximity explosion. Subjects were excluded if they were taking medications that affected eye movements, or if they were abusing alcohol or other drugs. Eye movements were calibrated monocularly and recorded using high-speed digital video oculography. Subjects tracked a high-contrast laser or LED through a series of tests designed to evaluate components of executive function. The trials included: self-paced saccades; anti-saccades; memory-guided saccades; and fixation with and without a visual target.
With the fixation target visible, both groups could keep within one foveal radius of the target, though the MTBI subjects had greater scatter. With the target extinguished MTBI subjects’ attempts at refixation failed to correct drift errors, resulting in large excursions from the target. MTBI subjects were more likely to make initial direction errors for the antisaccade task, and less likely to correct the error than controls. Both groups made accurate, regularly spaced saccades in the self-paced task, though the MTBI group made fewer saccades. The MTBI subjects were also more likely to make runs of square-wave jerks.
MTBI subjects had poorer control over fixation and saccadic performance for non-visible targets when compared to controls. This translated into increases in latency, likely due to increased cognitive load; errors in amplitude, generally overshooting the imagined target; and made more spontaneous or inappropriate saccades. The MTBI subjects frequently performed as well as the control subjects on one or more of the tests, but were far more likely to show substandard performance overall.
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