A Computational study of the passive mechanisms of eye restraint during head impact trauma

Authors: Cirovic, Srdjan¹; Bhola, R. M.²; Hose, D. R.³; Howard, I. C.¹; Lawford, P. V³; Parsons, M. A.⁴

Source: Computer Methods in Biomechanics and Biomedical Engineering, Volume 8, Number 1, February, 2005 , pp. 1-6(6)

Publisher: Taylor and Francis Ltd

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Abstract:

A finite element model of the eye and the orbit was used to examine the hypothesis that the orbital fat provides an important mechanism of eye stability during head trauma. The model includes the globe, the orbital fat, the extra-ocular muscles, and the optic nerve. MRI images of an adult human orbit were used to generate an idealized geometry of the orbital space. The globe was approximated as a sphere 12mm in radius. The optic nerve and the sclera were represented as thin shells, whereas the vitreous and the orbital fat were represented as nearly incompressible solids of low stiffness. The orbital bone was modelled as a rigid shell. Frontal head impact resulting from a fall onto a hard floor was simulated by prescribing to the orbital bone a triangular acceleration pulse of 200g (1962 m/s 2 ) peak for a duration of 4.5ms. The results show that the fat provides the crucial passive mechanism of eye restraint. The mechanism is a consequence of the fact that the fat is incompressible and that its motion is restricted by the rigidity of the orbital walls. Thus, the acceleration loads of short duration cannot generate significant distortion of the fat. In contrast, the passive muscles provide little support to the globe. When the connection between the orbital fat and the eye is absent the eye is held mainly by the optic nerve. We discuss the possible role that this loss of contact may have in some cases of the evulsion of the eye and the optic nerve.

Keywords: Head trauma; Orbital fat; Impact; Eye mechanics; Globe motion

Document Type: Research article

DOI: http://dx.doi.org/10.1080/10255840500062989

Affiliations: 1: Department of Mechanical Engineering, The University of Sheffield, Mappin Street, Sheffield, S1 3JD, UK 2: Academic Unit of Ophthalmology and Orthoptics, The University of Sheffield, O-Floor, Royal Hallamshire Hospital, Sheffield, S10 2JF, UK 3: Academic Unit of Medical Physics and Clinical Engineering, The University of Sheffield, I-Floor, Royal Hallamshire Hospital, Sheffield, S10 2JF, UK 4: Ophthalmic Sciences Unit, Academic Unit of Ophthalmology and Orthoptics, The University of Sheffield, O-Floor, Royal Hallamshire Hospital, Sheffield, S10 2JF, UK

Publication date: 2005-02-01

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A Computational study of the passive mechanisms of eye restraint during head impact trauma

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