Numerical Simulation Analysis Of Blunt Orbital Trauma

The human eye is a valuable and exquisite organ. Over90%of humansensory signals received by the brain are channeled through the eyes. Currently,external injury to the eyes is a major factor on visual health. When an impactingobject is bigger than the orbital rim, the resulting injury is called external blunttrauma. The extent of injury depends on the force and the direction of impact.Light injury may include edema or bleeding, and injury to the soft issues around theglobe. More serious injury can lead to orbital rim fracture, globe dislocation, lossof ocular motility, globe rupture and other complications. Research on the impactof external force on ocular function, the consequences of injuries, and themechanism of injuries, all have both academic and clinical significance.This study utilizes spiral CT（computed tomography）imaging of the orbitaltissues to measure their CT numbers. Using empirical formulae, the biologicalmatters of the orbital wall and their material constants are measured. Through theaxis of the globe, a two dimensional model is constructed using axial and sagittalslices, as well as the axial slices of optic foramen and ethmoid. A2-D model,while simple, still leads to meaningful finite element analysis. Static pressure wasapplied to the soft tissues of the eyelid, forward and backward movement of theorbital rim was restrained. The resulting finite element analysis shows:1. Themedial wall deforms more than the lateral wall; the inferior wall has largerdeformation relative to the superior wall. They match clinical data that states“injury to the medial wall and inferior wall is more frequently observed, while lessso in superior wall and lateral wall.”2. Where the posterior globe and the opticnerves are connected, the equivalent stress and the equivalent strain are relativelylarge, suggesting that this area is more susceptible to injury.This study further constructs a3-D model of the orbital region, using thecoronary slice coronal sections as the basis. The model includes the orbital cavity,the globe and the intra ocular soft issues. Restraining orbital rim movement alongthe front to back vector, applying positive pressure to the eyelid and orbital margin.The finite element analysis also indicates:1. The medial wall and the inferior wall,under blunt force, are more easily fractured than the other two walls.2. Asdetermined from the deformation of the globe, the global issues that are easier to injure are the iris, the iridocomeal angle, the lens and other anterior global tissues.3. In the orbit, the more easily injured tissues are the muscles located between theglobe, the medial wall and the inferior wall, which control global motion-theinferior rectus muscle, the medial rectus muscle and the inferior oblique muscle.All these match clinical data. The study can be a reference for the clinician,provide recommendations for areas of emphasis during patient evaluation, andprevent errors in diagnosis of patient with external injuries.