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Jonathan Jacobs, Margaret Skelly; Comparison of Smooth Pursuit and Saccadic Testing in Screening for Mild Traumatic Brain Injury. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1921. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Mild Traumatic Brain Injury (MTBI) is a signature injury of modern warfare. Unlike impact injuries, which are focal, blast-induced MTBI damage is diffuse, affecting multiple portions of the brain via impaired axonal connectivity, impairing operations involving memory, impulse control and prediction/planning (“executive function.”). Current MTBI testing uses highly subjective self-reporting and questionnaires. It is estimated that up to 25% of brain-injured veterans are not properly diagnosed, and may not receive treatment. Previously, we presented a saccade-based test that effectively detected decreased performance in MTBI. Here we present results for these same subjects on smooth pursuit tasks designed to evaluate executive function deficits, and compare their diagnostic value to saccadic testing.
We compared 11 controls with no history of closed-head injury, and 11 MTBI subjects 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 drugs. Eye movements were recorded using 500Hz video. Subjects tracked a laser or LED through the following trials: predictable linear pursuit; unpredictable stop-and-start targets; and one- and two-dimensional pursuit of predictably moving targets with unpredictable invisibility gaps.
Both the MTBI and control subjects had similar pursuit gains, approaching 1.0, with minimal need for corrective saccades. Their latency to initiate pursuit was also not significantly different. On the more complex tests, the MTBI subjects demonstrated reduced accuracy and increased reaction times than the controls for the unpredictable targets than did the control group. However, the differences in performance were less definitive for the smooth pursuit test battery than when these two groups performed the saccadic tests.
MTBI subjects had poorer performance on the pursuit tasks. But the differences were not as large nor as easy to detect as found in the saccadic trials. Pursuit gain is unaffected, as expected, as it is a basic task, not dependent on higher cortical function. Decreases in accuracy and latency may point to reduced ability to predict target trajectory; however this is also a challenging task for uninjured subjects. The minimal deficits seen in pursuit testing suggest the use of saccadic measures for MTBI screening.
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