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J. Stitzel, A. Kemper, S. Duma; Myopia and Hyperopia’s Effect on Probability of Globe Rupture Due To a Foreign Body Impact . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5028.
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Purpose: The purpose of this study was to investigate the effects of foreign body impacts on a myopic, emmetropic, and hyperopic eye using the most recent and most advanced finite element eye model for trauma. The Virginia Tech Eye Model (VTEM) was developed based on dimensions from LeGrand’s theoretical eye, and validated with experimental impact tests on pressurized post mortem human eyes. Methods: For this study the axial length and equatorial diameter of the VTEM were scaled to simulate a myopic, hyperopic, and emmetropic eye. The dimensions used for these eyes were the outer range of values from a study by Miller et al at the University of California Berkeley, employing MRI technology to measure the antero–posterior length and equatorial diameter of numerous myopic, hyperopic, and emmetropic eyes. The modified VTEM, embedded in a simulated orbit with surrounding tissue, was impacted with a finite element baseball traveling at two velocities (30.1 m/s and 41.2 m/s), and the maximum first principal stress was reported as a rupture predictor. The velocities and impact object were chosen to match experimental validation testes that resulted in no rupture (30.1 m/s) and rupture (41.2 m/s) in previous studies. Results: The simulations showed that the maximum stress increased significantly with increasing antero–posterior length and equatorial diameter of the eye for both impact speeds (0.01<p<0.07). Based on experimental validation tests, rupture was reported to occur at 22.15 MPa. Although none of the cases for the 30.1 m/s impact reported in this paper reached this value, the myopic case was very close to rupture (21.33 MPa). Similarly, in the 41.2 m/s impact all the cases reported in this paper were larger than the rupture criteria, but the hyperopic case was close to no rupture (23.61 MPa). Conclusions: These results indicate that the changes in antero–posterior length and equatorial diameter have a significant influence on whether rupture is caused by a foreign body impact to the eye. They suggest that the myopic eye, with increasing antero–posterior and equatorial dimensions, may be at increased risk of rupture due to impact with blunt objects compared to the emmetropic eye. Similarly, the hyperopic eye may be at decreased risk. When there is a danger of blunt impact, all persons should be encouraged to wear protective eyewear, but myopes may be particularly at risk.
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