Simulation model of an eyeball based on finite element analysis on a supercomputer

Abstract

Background/aims: A simulation model of the human eye was developed. It was applied to the determination of the physical and mechanical conditions of impacting foreign bodies causing intraocular foreign body (IOFB) injuries.

Methods: Modules of the Hypermesh (Altair Engineering, Tokyo, Japan) were used for solid modelling, geometric construction, and finite element mesh creation based on information obtained from cadaver eyes. The simulations were solved by a supercomputer using the finite element analysis (FEA) program PAM-CRASH (Nihon ESI, Tokyo, Japan). It was assumed that rupture occurs at a strain of 18.0% in the cornea and 6.8% in the sclera and at a stress of 9.4 MPa for both cornea and sclera. Blunt-shaped missiles were shot and set to impact on the surface of the cornea or sclera at velocities of 30 and 60 m/s, respectively.

Results: According to the simulation, the sizes of missile above which corneal rupture occurred at velocities of 30 and 60 m/s were 1.95 and 0.82 mm. The missile sizes causing scleral rupture were 0.95 and 0.75 mm at velocities of 30 and 60 m/s.

Conclusions: These results suggest that this FEA model has potential usefulness as a simulation tool for ocular injury and it may provide useful information for developing protective measures against industrial and traffic ocular injuries.

Figure 1

Stress-strain curves for cornea and sclera. Each line represents the value from 12 corneal or scleral samples (A). Stress-strain curve for the simulation model is derived from experimental values and the data of past reports. Penetrating ocular injury is assumed to occur at a strain of 18.0% in cornea and 6.8% in sclera (B).

Figure 2

Meshing principles of the eye. The model of the human eye is composed of three layers, outer (A; cornea and sclera (superficial layer)), middle (B; cornea and sclera (deep layer), iris, ciliary body, choroid, and retina), and inner (C; aqueous humour, lens, and vitreous). Mesh principle in the cross sectional view is indicated (D).

Figure 3

Missile shape. The missile shape used in the simulation is blunt. Size of the missile is indicated as d.

Figure 4

Axial strain and axial size curve of cornea (A) and sclera (B). The threshold of rupture is 18.0% for cornea and 6.8% for sclera as indicated by the broken line. The two conditions of different velocities of missiles, 30 m/s (H) and 60 m/s (J), are demonstrated.

Figure 5

Example of missile impacts on cornea and sclera. Simulation in four situations, 3.0, 60, cornea (size (mm), velocity (m/s), impacted tissue) (A), 0.5, 60, cornea (B), 3.0, 60, sclera (C) and 0.5, 60, sclera (D), is displayed. Colour bar indicates axial strain. Rupture is represented in A and C.