Modeling of the Eye and Orbit to Simulate Shaken Baby Syndrome

Abstract

Abstract: : Purpose: The mechanism of injury to the eyes in "Shaken Baby Syndrome" is poorly understood. We are using experimental and computational models of the eye to investigate the mechanism of injuries in violent shaking. Methods: We have developed a finite element model that incorporates the eye and the most important intra–orbital structures. We represented the eye as a sphere with three layers: the sclera, the retina, and the vitreous body. The orbital bone was modelled as a rigid body filled with fat tissue. Extra–ocular muscles were represented as active one–dimensional components. Geometric and material properties for all model components were taken from the literature [1]. We used acceleration profiles from an earlier experimental study (performed on crash test dummies) as the model loading, and performed simulations using the LS–DYNA (Livermore Software Technology Corporation) explicit finite–element software for dynamic simulations. The model was informed by data from semi–quantitative in–vitro anatomical traction experiments on in–situ rabbit eyes. Results: The results of these anatomical and computer experiments suggest that the interaction between the eye and the intra–orbital fat determines the motion of the eye in high acceleration situations. This is fundamentally important when modelling the dynamics of motions and forces in accidental or induced trauma. Computer simulations incorporating this functional anatomical relationship show that deceleration of the head leads to different pressure gradients inside and outside the eye. Simulations also show that oscillating the bone of the orbit may result in a resonant effect causing increasing displacement and increasing shear stress within the eye. Conclusions: It is this shear stress which we believe can damage the retina and its blood vessels. This may be the mechanism whereby violent shaking with its oscillatory motion results in severe ocular damage.

Keywords: computational modeling • trauma • orbit