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S. Schutte, S.P. van den Bedem, F. van Keulen, F.C. van der Helm, H.J. Simonsz; First Application of Finite-Element (FE) Modeling to Investigate Orbital Mechanics . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2128.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To reach a full understanding of the suspension of the eye, a model of orbital mechanics based upon FE analysis and in vivo data is developed. In most studies the way the eye is suspended in the orbit remains undefined, i.e. the center of rotation of the eye is fixed and distributed loads are reduced to single force vectors. The focus of this study is on validation of the FE model and on analyzing disorders of eye motility. Methods: Contours of bony orbit, eye muscles and eye were determined from MRI employing a region-growing algorithm. A mathematical 5th order surface was fitted through the contours to describe the geometrically accurate 3D-boundaries. A tetrahedral mesh was constructed in each solid and in the remaining volume, the latter comprising fat including connective-tissue septa. In this study spatial inhomogenities were extended and at several points sliding surfaces were introduced, e.g. tendons over sclera, medial rectus over orbital wall and Tenon's capsule over sclera. The material properties for muscles and fat were modeled using a non-linear Mooney-Rivlin material model. Results: Simulations of active horizontal eye movement, of single-point passive forced duction and dual-point passive forced duction yielded different centers of rotation and different values of stiffness, largely corresponding to literature data. Torsional forced duction showed no sideways displacement of the muscle belly at the level of the posterior pole, despite the lack of explicit connective-tissue structures to keep the muscle bellies in place. Eye motility in orbital wall fracture was modeled by adhering the medial rectus to the orbital wall. Duane's leash motility was simulated by co contraction after elevation or depression with decreased elasticity of orbital fat. Conclusions: The FE model offers unique possibilities to examine complex disorders of eye motility and enables a full understanding of the suspension of the eye in the orbit. More in vivo measurements are needed, however, for a sound basis of the model.
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