Blast Injury Biomechanics

droppedImageOcular injuries from blasts have increased in recent engagements caused by increasing prevalence of improvised explosive devices (IEDs). Such injuries are classified as primary and secondary injuries and are caused respectively by blast over pressures and fragments from debris. Several factors are hypothesized to influence the severity of primary eye injury in the literature: the high pressure shock front and the subsequent wave of lower sub-atmospheric pressure, threshold overpressure, and reflection of the shock wave by the orbit. There is, however, a dearth of clinical data that could verify the hypotheses above and establish the mechanism of the injury. Measuring and assessing the influence of these factors is difficult because survivable primary blast injuries are likely accompanied by injuries from fragments and blunt-force trauma and are thus more difficult to distinguish and enumerate. Moreover, the severity of the blast injuries and distance of the tertiary care facility from the injury site means that often patients are unable to recount the injury event, and witnesses are unavailable. The same limitations hinder clinical studies of the effectiveness of current eye armor, developed for ballistic and laser protection, in preventing blast injuries.

The overall goal of this project is to develop an experimentally validated computational model of the eye and apply the model to evaluate the stresses and deformations incurred by the eye-wall and critical ocular components from blast overpressures, and to investigate the interaction between the standard issue eye armor and the blast wave, and its effect on the mechanical loading of the eye. The model will be developed based on the following working hypotheses. 1) The anisotropic mechanical properties of the cornea and sclera as derived from the collagen structure, are critical to modeling the interaction of the blast wave and the globe.  2) The mechanical behavior of the cornea and sclera under dynamic (high-rate) loading is significantly different than the under quasistatic (slow-rate) loading. 3) The surrounding environment of the globe, including the extraocular tissues of the orbit and bony facial features is important in determining the effects of blast loading on the eye. 

In addition to computational models, we are developing dynamic inflation experiments to characterize the high-rate behavior of the eye-wall and tissue simulates.  The experiments uses 3D-DIC and a high-speed camera setup to capture the full-field elastodynamic displacement and strain response, then apply both analytical  and computational models of structural vibration to determine material properties.

Current and former students and postdoctoral fellows

Collaborators

  • Rajneesh Bhardwaj, PhD – Assistant Professor, Department of Mechanical Engineering, IIT Bombay
  • Kaliat T. Ramesh, PhD – Alonzo G. Decker Jr. Professor of Science & Engineering, Department of Mechanical Engineering, Johns Hopkins University
  • Oliver Schein, MD – Burton E. Grossman Professor of Ophthalmology, Director, Comprehensive Eye Service, Cornea and Anterior Segment Service, Johns Hopkins Medical School
  • Gehard Grimm, Adam Fournier PhD  – Army Aberdeen Test Center.