PURPOSE. Primary blast injury (PBI) mostly affects air-filled organs, although it is sporadically reported in fluid-filled organs, including the eye. The purpose of the present paper is to explain orbit blast injury mechanisms through finite element modeling (FEM).METHODS. FEM meshes of the eye, orbit, and skull were generated. Pressure, strain, and strain rates were calculated at the cornea, vitreous base, equator, macula, and orbit apex for pressures known to cause tympanic rupture, lung damage, and 50% chance of mortality. RESULTS.Pressures within the orbit ranged between þ0.25 and À1.4 MegaPascal (MPa) for tympanic rupture, þ3 and À1 MPa for lung damage, and þ20 and À6 MPa for 50% mortality. Higher trinitrotoluene (TNT) quantity and closer explosion caused significantly higher pressures, and the impact angle significantly influenced pressure at all locations. Pressure waves reflected and amplified to create steady waves resonating within the orbit. Strain reached 20% along multiple axes, and strain rates exceeded 30,000 s À1 at all locations even for the smallest amount of TNT.CONCLUSIONS. The orbit's pyramidlike shape with bony walls and the mechanical impedance mismatch between fluidlike content and anterior air-tissue interface determine pressure wave reflection and amplification. The resulting steady wave resonates within the orbit and can explain both macular holes and optic nerve damage after ocular PBI. (Invest Ophthalmol Vis Sci. 2012;53:8057-8066) DOI:10.1167/iovs.12-10591 P rimary blast injury (PBI) refers to biological damage caused by the peak incident overpressure (PIO) wave generated by an explosion. Initially described exclusively in hollow, air-filled organs, 1,2 the spectrum of PBI progressively enlarged to encompass fluid-filled organs, including the central nervous system 3,4 and the eye. 3-6Macular holes, choroidal rupture, and optic nerve damage occur relatively frequently after blunt trauma, 7 and although the pathogenic mechanism remains unclear, vitreous traction, 8 globe deformation, differential eye layer stiffness, 9 shockwave propagation, and multiaxial strain 10 likely participate.Finite element modeling (FEM) is a numerical analysis method largely used to simulate multiphysics problems. Previous applications to ophthalmology [11][12][13] and, specifically, to blunt eye trauma 10 have been reported. The purpose of the present paper is to create a computational model of ocular PBI, simulate the propagation of blast waves through the orbit, and explain its pathogenesis. The study was prompted by the observation of macular holes, multiple choroidal ruptures, subretinal bleeding, and optic atrophy after blast exposure, in the absence of any contact with splinters and/or flying objects (Fig. 1). MATERIALS AND METHODS Finite Element ModelingThe eye model has been previously described, 10,14 while orbit and retrobulbar fat tissue were reconstructed based on patient computed tomography scan and magnetic resonance imaging ( Fig. 2; see the Appendix for further technical details on FEM). C...
Primary blast injury (PBI) is the general term that refers to injuries resulting from the mere interaction of a blast wave with the body. Although few instances of primary ocular blast injury, without a concomitant secondary blast injury from debris, are documented, some experimental studies demonstrate its occurrence. In order to investigate PBI to the eye, a finite element model of the human eye using simple constitutive models was developed. The material parameters were calibrated by a multi-objective optimisation performed on available eye impact test data. The behaviour of the human eye and the dynamics of mechanisms occurring under PBI loading conditions were modelled. For the generation of the blast waves, different combinations of explosive (trinitrotoluene) mass charge and distance from the eye were analysed. An interpretation of the resulting pressure, based on the propagation and reflection of the waves inside the eye bulb and orbit, is proposed. The peculiar geometry of the bony orbit (similar to a frustum cone) can induce a resonance cavity effect and generate a pressure standing wave potentially hurtful for eye tissues.
Understanding the mechanisms of traumatic ocular injury is helpful to make accurate diagnoses before the symptoms emerge and to develop specific eye protection. The comprehension of the dynamics of primary blast injury mechanisms is a challenging issue. The question is whether the pressure wave propagation and reflection alone could cause ocular damage. To date, there are dissenting opinions and no conclusive evidence thereupon. A previous numerical investigation of blast trauma highlighted the dynamic effect of pressure propagation and its amplification by the geometry of the bony orbit, inducing a resonance cavity effect and a standing wave hazardous for eye tissues. The objective of the current work is to find experimental evidence of the numerically identified phenomenon. Therefore, tests aimed at evaluating the response of porcine eyes to blast overpressure generated by firecrackers explosion were performed. The orbital cavity effect was considered mounting the enucleated eyes inside a dummy orbit. The experimental measurements obtained during the explosion tests presented in this paper corroborate the numerical evidence of a high-frequency pressure amplification, enhancing the loading on the ocular tissues, attributable to the orbital bony walls surrounding the eye.
Abstract. Human eye subjected to non penetrating impact (blunt-impact) may experience severe damage. The most common type is partial tearing of the retina at specific eye locations. In ophthalmology, based on impact experiment performed by Delori et al. (1967), it is commonly accepted that the mechanism responsible for retinal damage is the vitreous pull-traction action and the equatorial expansion of the sclera. Based on the evidence of a vitrectomized patient who reported retinal damage after blunt impact, an investigation on the possible role of shockwave dynamics in the retinal damage has been performed by means of hydrocode numerical simulation. A FEM model of the eye has been developed and the experiment of Delori et al. has been reproduced. Soft tissues constitutive response has been determined by means of reverse engineering approach. It has been demonstrated that release waves at the retina-choroid interface are generated in the early time of the blunt impact and can cause retina tearing when the eye bulb is still undeformed. This result has been also confirmed for the case of blast-load exposure.
The paper introduces exploratory research that examines the effects of participation in interdisciplinary and international service-learning in forest fire management. Service-learning was interpreted as an educational device capable of supporting employability pathways within higher education. This theoretical proposition informed qualitative research that collected students’ perceptions of their service-learning experience. The research findings confirm the positive relationship between service-learning participation and the development of key soft skills. Moreover, the findings indicate how service-learning participation fosters labor market knowledge and skills, and opportunities for identifying and exploring academic and professional opportunities and cultivating authentic relationships. Service-Learning internazionali per la gestione degli incendi boschivi e l’employability nell’alta formazione: una ricerca qualitativa. Il contributo presenta una ricerca esplorativa che esamina gli effetti di partecipazione a progetti di service-learning interdisciplinari e internazionali sulla prevenzione degli incendi. Il service-learning è qui interpretato come un dispositivo educativo capace di sostenere percorsi di employability all’interno di contesti europei di alta formazione. Questa prospettiva teoretica è il punto di avvio di questa ricerca qualitativa che ha raccolto le percezioni degli studenti sull’esperienza di service-learning a cui hanno partecipato. I risultati dello studio confermano il rapporto positivo tra la partecipazione al service-learning e lo sviluppo di soft skills. Viene inoltre rilevato come questa partecipazione possa favorire l’acquisizione di conoscenze e competenze sul mercato del lavoro, per identificare ed esplorare opportunità accademiche e professionali post-laurea e coltivare relazioni autentiche utili alla pianificazione continua del proprio percorso professionale e personale.
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