High rate internal pressurization of the human eye to determine dynamic rupture pressure.

Over 1.9 million people suffer from eye injuries in the United States, occurring from automobile accidents, sports related impacts, and military combat. The purpose of the current study is to analyze the rupture pressure of human eyes using a high rate pressurization system. Internal pressure was dynamically induced into the eye with a drop tower pressurization system. The rupture pressure was measured with a small pressure sensor inserted into the optic nerve. A total of 10 human eye dynamic pressure tests were performed to determine rupture pressure and to compare the results with previous data. It was found that the average high rate rupture pressure of human eyes is 0.89+/- 0.25 MPa. In comparing these data with previous studies, it is concluded that as the loading rate increases the rupture pressure also increases.

Dynamic material property measurements of human eyes.

As a result of trauma, approximately 30,000 people become blind in one eye every year in the United States. A common injury prediction tool used for eye injuries is computational modeling, which requires accurate material properties to produce reliable results. The purpose of this study is to determine the dynamic material properties of the human sclera. A high rate pressurization system was used to create a dynamic pressure event to the point of rupture in 5 human eyes. Measurements were obtained for the internal pressure, the diameter of the globe, and the changing coordinates of the optical markers. A relationship between true stress and Green-Lagrangian strain was determined for each test specimen in the x and y direction to show directional effects. It was found that the average maximum true stress was 10.45 +/- 2.28 MPa, the average maximum Green-Lagrangian strain in the x-direction was 0.041 +/- 0.012, and the average maximum Green-Lagrangian strain in the y-direction was 0.073 +/- 0.015. In comparing these data with previous studies, it is concluded that the human eye is both anisotropic and viscoelastic. This study presents dynamic material properties that can be used for establishing injury criteria to help prevent eye injuries in the future.

The effect of frontal air bags on eye injury patterns in automobile crashes.

OBJECTIVE: To investigate eye injuries resulting from frontal automobile crashes and to determine the effects of frontal air bags. METHODS: The National Automotive Sampling System database files from January 1, 1993, through December 31, 1999, were examined in a 3-part study that included an investigation of 22 236 individual crashes that occurred in the United States. A new 4-level eye injury severity scale that quantifies injuries based on recovery time, need for surgery, and possible loss of sight was developed. RESULTS: Of all occupants who were exposed to an air bag deployment, 3% sustained an eye injury. In contrast, 2% of occupants not exposed to an air bag deployment sustained an eye injury. A closer examination of the type of eye injuries showed that there was a statistically significant increase in the risk of corneal abrasions for occupants who were exposed to an air bag compared with those who were not (P =.03). Of occupants exposed to an air bag deployment, 0.5% sustained a corneal abrasion compared with 0.04% of occupants who were not exposed to an air bag. CONCLUSIONS: Using the new injury levels, it was shown that although occupants exposed to an air bag deployment had a higher risk of sustaining minor eye injuries, the air bag appears to have provided a beneficial exchange by reducing the number of severe eye injuries.

Computer modeling of airbag-induced ocular injury in pilots wearing night vision goggles.

BACKGROUND: Airbags have saved lives in automobile crashes for many years and are now planned for use in helicopters. The purpose of this study was to investigate the potential for ocular injuries to helicopter pilots wearing night vision goggles when the airbag is deployed. METHODS: A nonlinear finite element model of the human eye was created. Ocular structures such as the fatty tissue, extraocular muscles, and bony orbit were included. The model was imported into Madymo (Mathematical Dynamical Models) and used to determine the worst-case position of a helicopter pilot wearing night vision goggles. This was evaluated as the greatest Von Mises stress in the eye when the airbag was deployed. RESULTS: The worst-case position was achieved by minimizing the distance between the eyes and goggles, having the occupant look directly into the airbag, and making initial contact with the airbag halfway through its full deployment. Simulations with the goggles both remaining fastened to and breaking away from the aviator helmet were performed. Finally, placing a protective lens in front of the eyes was found to reduce the stress to the eye but increase the force experienced by the surrounding orbital bones. CONCLUSION: The finite element model of the eye proved effective for evaluating the experimental parameters.