Eric A. Kennedy

Evaluation of different projectiles in matched experimental eye impact simulations.

Eye trauma results in 30,000 cases of blindness each year in the United States and is the second leading cause of monocular visual impairment. Eye injury is caused by a wide variety of projectile impacts and loading scenarios with common sources of trauma being motor vehicle crashes, military operations, and sporting impacts. For the current study, 79 experimental eye impact tests in literature were computationally modeled to analyze global and localized responses of the eye to a variety of blunt projectile impacts. Simulations were run with eight different projectiles (airsoft pellets, baseball, air gun pellets commonly known as BBs, blunt impactor, paintball, aluminum, foam, and plastic rods) to characterize effects of the projectile size, mass, geometry, material properties, and velocity on eye response. This study presents a matched comparison of experimental test results and computational model outputs including stress, energy, and pressure used to evaluate risk of eye injury. In general, the computational results agreed with the experimental results. A receiver operating characteristic curve analysis was used to establish the stress and pressure thresholds that best discriminated for globe rupture in the matched experimental tests. Globe rupture is predicted by the computational simulations when the corneoscleral stress exceeds 17.21 MPa or the vitreous pressure exceeds 1.01 MPa. Peak stresses were located at the apex of the cornea, the limbus, or the equator depending on the type of projectile impacting the eye. A multivariate correlation analysis revealed that area-normalized kinetic energy was the best single predictor of peak stress and pressure. Additional incorporation of a relative size parameter that relates the projectile area to the area of the eye reduced stress response variability and may be of importance in eye injury prediction. The modeling efforts shed light on the injury response of the eye when subjected to a variety of blunt projectile impacts and further validate the eye models ability to predict globe rupture. Results of this study are relevant to the design and regulation of safety systems and equipment to protect against eye injury.

The effects of the extraocular muscles on eye impact force–deflection and globe rupture response

There are over 1.9 million eye injuries per year in the United States, with blunt impacts the cause of approximately one-half of all civilian eye injuries. No previous experimental studies have investigated the effects of the extraocular muscles on the impact response of the eye. A spring-powered blunt impactor was used to determine the effects that the extraocular muscles have on the force-deflection and injury response of the eye to blunt trauma. A total of 10 dynamic impact tests were performed at 8.2+/-0.1m/s on five human cadaver heads. With the extraocular muscles left intact, the average peak force was found to be 271+/-51N at 7.5+/-0.9mm posterior translation; with the muscles transected, the average peak force was 268+/-26N at 7.6+/-1.3mm of posterior translation. From the data available from this study, the peak impact force and overall amount of translation during the impact are not affected by the extraocular muscles. Additionally, from the data presented in this study, the eyes with the extraocular muscles left intact do not rupture with a different injury pattern or display an increased risk for rupture than the eyes with the extraocular muscles transected. Therefore, it is believed that the effect of the extraocular muscles is not sufficient to drastically alter the response of the eye under dynamic impact. This information is useful to characterize the boundary conditions that dictate the eye response from blunt impact and can be used to define the biofidelity requirements for the impact response of synthetic eyes.

Rib fracture timing in dynamic belt tests with human cadavers

The purpose of this article is to present data from dynamic belt loading tests on the thorax of human cadavers where the exact timing of all rib fractures is known. To quantify rib fracture timing, a total of 47 strain gages were placed throughout the thorax of two human cadavers (one male, one female). To simulate thoracic loading observed in a severe car crash, a custom table‐top belt loading device was developed. The belt loading pulse was configured to result in approximately 40% chest compression during a 150 ms load and unload cycle. The time histories of each strain gage were analyzed to determine the time of each rib fracture which was then directly compared with the reaction loads and chest displacements at that exact time, thereby creating a noncensored data set. In both cadavers, all rib fractures occurred within the first 35% compression of the thorax. As a general trend, fractures on the left side of the thorax, where the passenger belt passed over the abdomen, occurred first followed by fractures to the upper ribs on the right side of the thorax. By utilizing this technique, the exact timing of each injury level can be characterized relative to the mechanical parameters. For example, using rib fractures as the parameter for Abbreviated Injury Scale (AIS) scores in the female test, it was shown that AIS 1 injury occurred at a chest compression of 21.1%, AIS 2 at 21.6%, AIS 3 at 22.0%, and AIS 4 at 33.3%. Clin. Anat. 24:327–338, 2011.

Eye injuries from electrical weapon probes: Incidents, prevalence, and legal implications

PURPOSE While generally reducing morbidity and mortality, electrical weapons have risks associated with their usage, including burn injuries and trauma associated with uncontrolled fall impacts. However, the prevalence of significant eye injury has not been investigated. METHODS We searched for incidents of penetrating eye injury from TASER® conducted electrical weapon (CEW) probes via open source media, litigation filings, and a survey of CEW law-enforcement master instructors. RESULTS We report 20 previously-unpublished cases of penetrating eye injury from electrical weapon probes in law-enforcement field uses. Together with the 8 previously published cases, there are a total of 28 cases out of 3.44 million field uses, giving a demonstrated CEW field-use risk of penetrating eye injury of approximately 1:123 000. Confidence limits [85 000, 178 000] by Wilson score interval. There have been 18 cases of total unilateral blindness or enucleation. We also present legal decisions on this topic. CONCLUSIONS The use of electrical weapons presents a rare but real risk of total or partial unilateral blindness from electrical weapon probes. Catastrophic eye injuries appear to be the dominant non-fatal complication of electronic control.

Eye injury from electrical weapon probes: Mechanisms and treatment

Purpose While generally reducing morbidity and mortality, TASER® electrical weapons have risks associated with their usage, including burn injuries and head and cervical trauma associated with uncontrolled falls. The primary non‐fatal complications appear to be significant eye injury but no analysis of the mechanisms or suggested treatments has been published. Methods We used a biomechanical model to predict the risk of eye injury as a function of distance from the weapon muzzle to the eye. We compared our model results to recently published epidemiological findings. We also describe the typical presentation and suggest treatment options. Results The globe rupture model predicted that a globe rupture can be expected (50% risk) when the eye is within 6 m of the muzzle and decreases rapidly beyond that. This critical distance is 9 m for lens and retinal damage which is approximately the range of the most common probe cartridges. Beyond 9 m, hyphema is expected along with a perforation by the dart portion of the probe. Our prediction of globe rupture out to 6 m (out of a typical range of 9 m) is consistent with the published risk of enucleation or unilateral blindness being 69 ± 18%, with an eye penetration. Conclusions Significant eye injury is expected from a penetration by an electrical weapon probe at close range. The risk decreases rapidly at extended distances from the muzzle. Not all penetrating globe injuries from electrical weapon probes will result in blindness.

Evaluation of Globe Rupture Injury Mechanisms and Pressure Response of the Eye During Projectile Impact

In the United States, over 1.9 million civilian eye injuries occur annually [1]. Furthermore, with the recent conflict, the military has experienced a dramatic 17%–26% increase in rate of injury to the eyes [2]. Risk functions for various eye injuries, particularly globe rupture, have already been developed and show area-normalized energy (based on the mass, size, and velocity of the projectile) to be most highly correlated to injury [3–5]. However, it remains desirable to further investigate the relationship between area-normalized energy and the eye injury mechanism.© 2011 ASME