Three Dimensional Model

A Three-Dimensional (3D) FE model of the human eye has been established via the explicit dynamics finite element code LS-DYNA 970 (LSTC, Livermore, CA, United States) (27). Briefly, the morphological characteristics of the human eye (a normal/healthy male) along with intraconal and extraconal fats were obtained from Magnetic Resonance Imaging (MRI)/Computed Tomography (CT) data. The donor declared his agreement to employ the images of his head for medical research purposes under the ethical rules of Tehran University of Medical Sciences based on the 2008 Declaration of Helsinki. Subsequently, these images were brought in a personal computer using MIMICS software (MIMICS 10.0, Materialise Inc., Belgium) to establish a smooth mesh for the surfaces

The model of the human eye in the current study was accompanied by some simplifications, i.e., symmetric cornea which could be a rational assumption to mirror the shape of a real healthy cornea as employed previously (15, 30, 31). Deformation of the cornea under various IOPs (10, 20, and 30 mmHg) were considered to be comparatively minor in comparison with the cornea’s radius of curvature (32). Third, the mechanical behavior of the corneal tissue assumed to be approximately incompressible as well as linear elastic. Indeed, as the deformation of the cornea in the eye would not exceed profoundly to the applied load, its deformation can be considered as small deformation and, as a result, linear elastic (33). In the computational model, the outer and inner radii of curvature of the corneal were set as 7.8 and 6.6 mm, respectively (33, 34). In addition, the horizontal and base diameters (including the limbus parts and a part of the sclera) of the cornea were set as 11 and 15.3 mm, respectively

The results revealed the surface of the iris at a higher stress was profoundly affected by a higher IOP (30 mmHg) while there is a less amount of stress distribution in the iris surface at the IOP of 10 mmHg (Fig. 4). The vitreous body, regardless of the variations in the IOP, showed almost the same amount of stress with the same distribution (Fig. 5). The amount of stress in the retina and sclera which act as holder pressure applied from the external load was different by variation of the IOPs. That is, by increasing the pressure in the aqueous body the stress in the retina and sclera are increased and decreased, respectively (Fig. 6). The crucial role of the optic nerve is to link the eye to the brain for image interpretation. In this study, the stresses and deformations of the optic nerve at various IOPs were also calculated (Fig. 7b). The results illustrated that by increasing the IOP the stress in this component is amplified. The same pattern was observed in the resultant displacement of the optic nerve as a result of IOP increasing, since there was no dramatic alteration in the amount of displacement in the optic nerve head which can be lead to detachment from its site to sclera