Abstract Text: Heavy weapons training exposes Soldiers to blast overpressure, often repeatedly. It is not uncommon for Soldiers to report symptoms including headache, dizziness, and difficulty thinking following these exposures. Although these symptoms suggest adverse neurological changes associated with concussions, these overpressure exposure effects are almost always subclinical, difficult to detect, and insufficient for clinical diagnosis. The subjective nature of symptom reporting inventories means that self-reporting is often unreliable for detection of neurotrauma. Thus, there is interest in identifying objective biomarkers of neurotrauma that are reliable, easy to administer, and require minimal testing time. One such tool that may meet these requirements is oculomotor testing using eye-tracking technologies. The Environmental Sensors in Training (ESiT) team at Walter Reed Army Institute of Research (WRAIR) partnered with a military unit to determine the relation between overpressure exposure experienced by service members during routine training and oculomotor assessment. This endeavor was completed over three separate visits that involved completion of outcome measures in the morning prior to training activities, recording of overpressure exposure levels during training activities, and repeating outcome measures following conclusion of training for the day. All oculomotor testing was performed with the DX-100 system (Neurolign, Pittsburgh, PA), which was selected for its test customization capability. For this effort, the DX-100 test protocol required six and a half minutes to execute and included spontaneous nystagmus, horizontal/vertical smooth pursuits, self-paced saccades (horizontal), predictive saccades (horizontal), vertical random saccades, vergence pursuit, and light reflex tests (pupillometry). Results for the first two data-collection efforts are presented here. For the first effort, participants were 5 un-exposed controls and 15 exposed service members. Cumulative overpressure impulse exposures ranged from 148 psi*ms to 590 psi*ms. To minimize false positives, a positive finding with the DX-100 was defined as three or more of the tests being flagged as showing an adverse change from pre-exposure to post-exposure values. When this criterion was used, exposed participants were more likely to present with positive findings on eye-tracking tests (r=.66, p=.002). Three or more positive findings were present for 13 of 15 exposed participants and not for any controls. The second effort was performed in a different training environment that was executed within a constructed enclosure that resulted in much higher cumulative overpressure impulse exposure values that ranged from 436 psi*ms to 1014 psi*ms. Here, 13 service members participated as exposed subjects and 5 as un-exposed controls. Using the same criterion discussed previously, exposed participants were more likely to have findings on eye-tracking tests (r=.85, p<.001) as 11 of 13 exposed participants presented with three or more findings. No control participants met this criterion. If these findings continue to be replicated with the data from the third effort, they will support a growing body of evidence that the use of eye-tracking tests can be sensitive to neurotrauma following exposure to blast overpressure. It is interesting that a stronger correlation was observed between exposure level and eye-tracking test findings for the second data collection effort, which is where increased cumulative overpressure impulse exposure level was experienced by all exposed participants. This observation suggests that there may be a threshold exposure level at which eye-tracking testing sensitivity is optimal due to the increase in signal and decrease in noise. That being said, if a safety exposure level can be identified and agreed upon, the eye-tracking test criterion could potentially be adjusted such that the eye-tracking tests can be optimized to determine when an individual has exceeded a pre-defined safety exposure level, which would be useful for situations where exposure data is unavailable.