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What causes damage in blunt trauma- validation of finite element modelling (FEM)

Session Details

Session Title: Quick Fire Free Paper 5

Session Date/Time: Sunday 14/09/2014 | 11:00-13:00

Paper Time: 11:40

Venue: Boulevard B

First Author: : T.Rossi ITALY

Co Author(s): :                  

Abstract Details

Purpose:

according to classic theories, direct blunt trauma to the eyeball causes retinal injury due to scleral strain and vitreous traction. We developed a numerical model simulating the classic experiment of a BB pellet impacting the eye and a blast injury, where no strain is involved and published both. FEM analysis showed that the pressure wave traveling through the eye and the orbit is responsible for peak values that can damage both the retina and optic nerve in both cases. Present presentation deals with the deployment of an ex-vivo setting developed to validate our model.

Setting:

Experimental ex-vivo setting

Methods:

freshly enucleated pig eyes were inserted into a bony orbit model reproduced by means of a 3D printer from a real CT scan. The orbit was filled with ballistic gel of the same elastic modulus than the orbital fat. Two different experiments were setup to reproduce 1) a BB pellet injury and 2) a primary blast wave injury. In experiment 1, a steam gun fired a BB pellet perpendicular to the cornea and a pressure sensor located inside the vitreous chamber measured pressure waves. In experiment 2, a commercially available firecracker was ignited at known distance from the eye-orbit model and two pressure sensors were located within the eye and at the orbit apex.

Results:

Experiment 1 yielded a pressure wave that travelled the eye causing significant macular traction that could be responsible for macular hole formation well before bulb deformation occurs. Experiment 2 validated the FEM model of a steady wave resonating within the orbit, caused by constructive interference of elastic waves traveling the orbit and resonating in between the bony orbit walls, due to impendance mismatch.

Conclusions:

The pathogenesis of macular holes associated to blunt eye trauma and of optic nerve damage secondary to blast injury, might deserve thorough revision, since the mechanical properties of the eye and orbit allow elastic wave reverberation that determines high pressures. The peculiar pyramid-like orbit geometry allows a 5-fold amplification of pressure waves at the orbit apex justifying selective optic nerve damage at this location.

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