Bovine Eye Finite Element Modeling And IOP Research Of Biomechanics

OBJECTIVE:To establish a finite element model which accords with normal and true bovine anatomical and physiological eye as far as possible. By using the model it seeks to explore the changes of internal stress in different parts of eye under different conditions of intraocular pressure, especially the change of internal stress of lamina cribrosa, and to establish a mathematical model for the experimental study of glaucoma.METHOD:(1) The fresh bovine ocular perienchyma was cleared. After the clearance of perienchyma and muscles of eyeball, we used ophthalmic scissor to cut sclera and cornea into strips. The sclera was cut into the strip sample with the radial width of3.8mm and the length of14.5mm. The cornea was cut into the strip sample with the radial width of9.5mm and the length of10mm;(2) The anterior tissue of the cribriform plate was removed, the sclera was fixed, the naso-temporal length of lamina cribrosa and superior-inferior length of lamina cribrosa were measured by vernier caliper;(3) Using858Mini BionixII biomechanical loading instrument, we extended the sclera and cornea. The velocity of extension of sclera being0.3mm/s,3mm,30mm/s,300mm/s respectively, and the rate of extension of corneal was0.3mm/s and30mm/s respectively. The deformation-stress curve was measured;(4) The fresh bovine eyeball was scanned accurately by micro-CT, to obtain geometrical images and measurement data of bovine eyeball, then geometric shape of bovine eyeball was built by using3dimensional reconstruction for these images and data;(5) The intraocular pressure of finite element model was set. The eyeball wall was regarded as mechanical bearing part. We set as10mmHg,30mmHg,60mmHg,100mmHg respectively to simulate and calculate, which is to obtain the force conditions of the various parts of the eye under different intraocular pressure.RESULTS:(1) Using model parametric optimization method of reverse engineering, we got more accurate access to the complex nonlinear viscoelastic and super-elastic parameters and more accord with physiological mechanics of material parameters settings, then got the more real eye model.(2)With the gradual increase of intraocular pressure, the stress change of the anterior half of the sclera, also called the front of the eye axis, is not obvious, while the stress of the posterior half sclera is smaller. Meanwhile, we also found that with the increase of simulated intraocular pressure, the force of the central portion of lamina cribrosa is the most obvious.CONCLUSION:(1) This research established a finite element model based on normal bovine ball, considering the morphology and mechanical properties of cornea, sclera and lamina cribrosa and the actual morphology;(2) Using this finite element model, we found that the stress was obviously increased in the center of the front portion of the sclera and the lamina cribrosa with the increased intraocular pressure. It indicated that the stress increased in homogeneously with the change of intraocular pressure may be related to disparities in the retina ganglion cell death. Graph16,Table2,References67.