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W. Gray, W. E. Sponsel; Lens Displacement Mechanism in Dynamic Blunt Trauma Events. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2778.
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© ARVO (1962-2015); The Authors (2016-present)
Modeling of paintball ocular trauma in an effort to develop improved blunt trauma predictive capability: Paintball injuries are an increasing source of clinical pathology, and share dynamic characteristics with other forms of civilian and military blunt intraorbital impact injury.
Sixty fresh abattoir porcine globes were implanted in Knox gelatin within Perspex model orbits of human dimensions, and subjected to paintball impact through a range of velocities 25-100 m/s. In an effort to identify intraocular injury mechanisms, anatomically-correct models of the eye were developed and implemented into CTH, an Eulerian impact-physics computer code.
Detailed pathology of porcine eye specimens following paintball impact experiments revealed ubiquitous zonular rupture and posterior displacement of the lens. Although severity of the trauma varied, these characteristics were observed over the full range of impact energies evaluated (1-13 J). In some cases lens capsule detachment was observed, and in the highest energy impacts, the lens was deposited into the anterior chamber following forward rebound. The numerical simulations revealed that hydrostatic pressurization of the anterior chamber resulting from impact-induced deformation was largely responsible for lens displacement. Peak dynamic pressures predicted in the anterior chamber varied from approximately 1 MPa (1 J) to 6 MPa (13 J). In all cases, pressure loading was sufficient to initiate posterior displacement in advance of the deformation, i.e., physical contact between the cornea and lens is not necessary.
The choice of a paintball as the trauma producing device was fortuitous as early rupture of its thin outer shell facilitated a more uniform distribution of the impact energy allowing for large inward deformations of the cornea and sclera without perforation and penetration into the anterior chamber. The numerical model also predicts high strains (50-100%) in the angle region of each zonule consistent with the ubiquitous angle recessions observed in the pathology. Thus, angle recession can also be explained by high hydrostatic pressures in the anterior chamber.
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