High Rate Internal Pressurization of the Human Eye to Determine Dynamic Material Properties

Over 1.9 million people suffer from eye injuries in the United States each year, occurring mainly from automobile accidents, sports related impacts, and military combat. 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 create a high rate pressurization system to analyze the rupture pressure of human eyes and to determine the dynamic material properties of human sclera. A high rate pressurization system was used to create a dynamic pressure event to the point of rupture in 12 human eyes. The internal pressure was dynamically induced into the eye with a drop tower while the rupture pressure was measured with a small pressure sensor inserted through the optic nerve. Measurements were obtained for the diameter of the globe, the thickness, and the changing coordinates of the optical markers. A relationship between true stress and true strain was determined for each test specimen in the equatorial and meridional direction to show any directional effects. It was found that the average rupture stress was 13886 ± 4807 kPa, the average maximum true strain in the equatorial direction was 0.041 ± 0.014, and the average maximum true strain in the meridional direction was 0.058 ± 0.018. It was also found that the average rupture pressure for the human eye was 836 ± 130 kPa. In comparing these data with previous studies, it is concluded that the loading rate directly affects the rupture pressure and that the human eye is both anisotropic and viscoelastic.