Mechanistic hypothesis for eye injury in infant shaking
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The terms abusive head injury and shaken baby syndrome are used to describe a unique pattern of nonaccidental traumatic injuries occurring in children that many clinicians and researchers have good reason to believe is caused by violent shaking. Typical injuries include severe brain injury, with intracranial and retinal hemorrhages, but the pathogenesis of injuries is poorly understood. A major paradox in head trauma in infants is that the injuries induced by a shaking event are much more severe than those caused by even very violent single-impact head trauma, despite the relatively low accelerations in shaking.
We have developed a finite element computer model of the eye, orbit, and orbital bone and used it to simulate the effects of single-impact and oscillatory motion inputs. The model was informed by data from semiquantitative in vitro anatomical traction experiments on in situ rabbit eyes. The new results reported here strongly suggest that suction between the eye and its surrounding fat dominates the dynamical stability of the system composed of the eye, its socket, and the components and material supporting the eye. Computer simulations incorporating this functional anatomical relationship show that deceleration of the head generates pressure gradients inside and outside the eye; these could cause damaging shear stresses in structures such as the retina and blood vessels. Simulations also show that oscillating the bone of the orbit causes the eye to move anteriorly and posteriorly with an increasing amplitude, building up the stresses within the eye over time. This is the first time that any biomechanical mechanism has been identified that might explain the disproportionally severe injuries caused by an oscillatory mechanism such as violent shaking of an abused infant. However, further study is required and this conclusion is therefore preliminary and provisional.
Key WordsEye injury child abuse computational modeling finite element analysis
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- 2.Levin AV. Retinal hemorrhages and child abuse, in Recent Advances in Pediatrics. (David TJ, ed.), Churchill Livingstone, Edinburgh. 2000; pp. 151–219.Google Scholar
- 3.The Ophthalmology Child Abuse Working Party. Child abuse and the eye. Eye 1999;13:3–10.Google Scholar
- 17.Bron AJ, Tripathi RC, Tripathi BJ. The bony orbit and paranasal sinuses, in Wolff’s Anatomy of the Eye and the Orbit. Bron AJ, Tripathi RC, Tripathi BJ. 8th ed., Chapman & Hall Medical, London, 1997; pp. 1–29.Google Scholar
- 21.Welsh TJ, Gilman M. (1969), Voluntary propulsion of the eyes. Am J Ophthalmol 1969;67:583–585.Google Scholar
- 22.Duke-Elder S, Wybar K. The mechanics of the movement of the eyes. in System of Ophthalmology Vol VI Ocular Motility and Strabismus (Duke-Elder S. ed.), Henry Kimpton, London, 1973; pp. 136–144.Google Scholar
- 24.Goldsmith W. Biomechanics of head injury. in Biomechanics:its foundations and objectives (Fung YC, Perrone N, and Anliker M, eds), Prentice-Hall, Hemel Hempstead, 1972; pp. 585–634.Google Scholar