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F.-W. Goudsmit, J. W. Moerkerken, S. Schutte, F. C. T. van der Helm, F. van Keulen, H. J. Simonsz; Analysis of the Extra-Ocular Muscle Paths with the Delft Finite Element Model of Orbital Mechanics. Invest. Ophthalmol. Vis. Sci. 2009;50(13):657.
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© ARVO (1962-2015); The Authors (2016-present)
This investigation studied the importance of sliding surfaces, pressure distribution and the muscle path with the Delft Finite Element Model of Orbital Mechanics (DFEM). The path of the EOMs is determined by the tension in the muscle, the stiffness of the muscle itself and by external forces on the muscle. We investigated, with the DFEM, whether the curved path could be explained solely by interaction with the fat surrounding the rectus muscles, rather than through focal mechanical effects.
The DFEM was extended to incorporate the oblique muscles and optical nerve. Geometries were obtained from MRI and meshed using 4-noded tetrahedral elements. A fine mesh was used in areas subjected to large deformations (behind the insertions of the EOM) and in the narrow area in the apex subjected to large reaction forces. The use of a fine tetrahedral mesh facilitated calculation and prevented distortion of elements. A contact algorithm (with zero friction) was employed to model sliding between the interacting tissues. Sliding was permitted between the fat and EOM, between the fat and optic nerve, between the fat and the eye. With the model both pressure distribution and muscle paths were studied.
Sliding permitted more eye rotation than in the previous versions of the model. The model predicted the pressure distribution in the fat behind the eye (Fig): due to the use of isotropic homogenous orbital fat, the pressure distribution was more gradual in the area between the tendon and eye than in reality. During muscle contraction high pressure gradients were found in the fat between EOM and eye. This resulted in a force orthogonal to the muscle line of action causing sharp bending ("lateral inflections") of the muscle anteriorly.
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