Measurement of force changes along visual pathway in a biofidelic instrumented headform (BIH) during exposure to blasts

Abstract

Purpose : Soldiers who specialize in artillery, breaching, and explosives-based activities are exposed to repeated blast forces that can result in neurological symptoms including visual dysfunction. There is a need to determine the exposure levels which induce these symptoms. This study investigates the use of fiber optic strain sensors embedded in a biofidelic headform as a means to estimate the strain experienced by the eye, optic nerve, and visual pathways when exposed to blast forces.

Methods : Biosimilarity between the 3D printed skull and a human skull was determined by modal testing. Biosimilarity of the brain was determined by magnetic resonance elastography (MRE). Two, distributed arrays of fiber Bragg grating-based strain sensors were embedded into the resulting BIH in the locations of the two eyes and through the simulated optic nerves and brain. Finally, the BIH was covered in simulated skin. The BIH was exposed to repeated blast forces under two conditions: with and without a barrier in between the BIH and the source of the blast forces. Tests were repeated for two standoff distances of the source.

Results : A comparison of the modal response of the model skull with that of a human skull showed good agreement. The MRE of the model brain showed a shear stiffness at the high end of normal range for human brains. The peak strain values measured with the barrier in place were on average 4.7 times less than the strain values measured without the barrier. Peak values were less when the source was farther away from the BIH. In addition, by comparing the relative strain values along the length of each sensor array, the motion of the optic nerve when exposed to the blast forces was estimated and animated.

Conclusions : The viability of the BIH and fiber optic strain sensor arrays to model the response of the visual pathways when exposed to blast forces was demonstrated. The sensors were sensitive enough to discriminate between two test configurations: with and without a barrier between the BIH and the source. Future work will correlate the measured strain levels with neuron damage (animal studies) and neurological effects (clinical studies) reported at equivalent exposure levels. Once this correlation is established, the measurements can be used to establish exposure limits to help minimize the negative effects of blast exposure on soldiers.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.