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Xiaofei Wang, Mani Baskaran, Helmut Rumpel, Shamira Perera, Winston Eng Hoe Lim, Monisha Esther Nongpiur, Tin Aung, Dan Milea, Michael J A Girard; Finite element analysis predicts high optic nerve head strains during horizontal eye movements. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© 2017 Association for Research in Vision and Ophthalmology.
(1) To combine finite element (FE) analysis and dynamic magnetic resonance imaging (MRI) to estimate optic nerve head (ONH) strains (deformations) during eye movements, and identify factors influencing such strains; (2) To compare ONH strains induced by eye movements with those induced by intraocular pressure (IOP) which are critical in glaucoma.
The eyes and orbital tissues of a healthy subject were visualized during visually-guided horizontal eye movements, using dynamic MRI. A baseline FE model of the left eye was reconstructed in the primary gaze position and included details from the orbital tissues (visualized with MRI; Figure 1A) and from the ONH tissues (using measurements from the literature). The effect of a lateral eye movement of 13° was then simulated, based on the MRI findings. ONH strains due to eye movements were compared with those resulting from an IOP of 50 mmHg. Finally, a sensitivity study was performed, in which we varied the stiffness of all connective tissues to understand their influence on the ONH during eye movements.
The baseline FE model matched the MRI scan well (Figure 1A). Our models predicted that, during eye movements, the retrobulbar portion of optic nerve had a pulling action on the ONH, which resulted in large strains within the ONH tissues. Specifically, the strains generated within the prelamina (mean: 0.027), the lamina cribrosa (0.018), and the retrolamina (0.041) following an eye movement were higher than those resulting from an IOP of 50 mmHg (Figure 1B). These results held true even when considering variations in connective tissue stiffness. In addition, we found that stiff scleras reduced lamina cribrosa and prelamina strains during eye movements, but stiff dura and pia maters significantly increased those strains.
This study is the first to combine FE with MRI to estimate ONH strains during eye movements. Our models predict high ONH strains during eye movements, which were aggravated with stiffer optic nerve sheaths. Further studies are needed to explore a possible link between ONH strains induced by eye movements and axonal loss in glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure 1. (A) FE model in primary and left gaze positions of a left globe (yellow outlines) superimposed on the MRI scan indicating a good match. (B) Predicted ONH strains for various loading scenarios.
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