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Computer modeling of ocular injury in infants exposed to acceleration

Computer modeling of ocular injury in infants exposed to acceleration. N. Rangarajan, S. Kamalakkannnan, T. Shams. GESAC Inc, Boonsboro, MD. Alex Levin, MD, MHSc, FAAP, FAAO, FRCSC. Sickkids Hospital, Toronto. Carole Jenny, MD, MBA. Brown University, Providence, RI. Objective.

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Computer modeling of ocular injury in infants exposed to acceleration

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  1. Computer modeling of ocular injury in infants exposed to acceleration N. Rangarajan, S. Kamalakkannnan, T. Shams. GESAC Inc, Boonsboro, MD. Alex Levin, MD, MHSc, FAAP, FAAO, FRCSC. Sickkids Hospital, Toronto. Carole Jenny, MD, MBA. Brown University, Providence, RI.

  2. Objective • To develop a finite element model of the infant eye. • To evaluate the level of stresses and strains when the head is exposed to an acceleration pulse. • Model to be exercised with acceleration pulses obtained from Aprica 2.5 kg infant dummy shaking tests. GESAC, Inc

  3. Presentation Road Map • Description of the model • Parametric study • Discussion of results • Conclusions • Limitations • Work in progress GESAC, Inc

  4. The Model • LS Dyna model consists of orbit, fatty tissue, extra-ocular muscles, sclera, retina, and vitreous. GESAC, Inc

  5. Model Description • Key dimensions • Sclera, diameter = 20 mm • Rectus muscle length = 50 mm • Contact definitions • Surfaces for orbit/fat/sclera/retina tied together • Nodes on retina tied to vitreous surface GESAC, Inc

  6. Shaking experiment with Aprica 2.5 dummy. Click on picture to see baby being shaken. Large AVI file Data for Prescribed Motion GESAC, Inc

  7. Prescribed motion • Applied motion - rotational oscillations • Represents average data from shaking tests with Aprica 2.5kg dummy GESAC, Inc

  8. Eye ball with muscles GESAC, Inc

  9. The Model – Vitreous and Retina Attachment GESAC, Inc

  10. Parametric Study • Parametric study was conducted to evaluate the effect of variation in material models and properties of vitreous and fat on the maximum stress and stress distribution. • Six cases were simulated. GESAC, Inc

  11. Simulation Matrix GESAC, Inc

  12. Results • Results of the simulation study are discussed • Stresses on retina • Stresses on the sclera GESAC, Inc

  13. Stress on Retina – Case 2 Stress on one of the elements in case 2 GESAC, Inc

  14. Stress on Retina – Case 3 Stress on one of the elements in case 3 GESAC, Inc

  15. Stress on Retina – Case 5 Stress on one of the elements in case 5 GESAC, Inc

  16. Simulation – Case 2 Click on picture to see animation of simulation results. Large AVI file. GESAC, Inc

  17. Simulation – Case 5 • Click on picture to see animation of simulation results. Large AVI file. GESAC, Inc

  18. Stress Distribution on Sclera– Case 2 GESAC, Inc

  19. Stress Distribution on Retina – Case 2 GESAC, Inc

  20. Stress Distribution on Vitreous – Case 2 GESAC, Inc

  21. Stress Distribution on Sclera – Case 5 GESAC, Inc

  22. Stress Distribution on Retina – Case 5 GESAC, Inc

  23. Stress Distribution on Vitreous – Case 5 GESAC, Inc

  24. Comparison of Maximum Stress on Retina * The calculation reaches an infinite loop at 0.94 sec, when case 5 has a maximum of 0.0964 GESAC, Inc

  25. Conclusions - 1 • Stress on retina and sclera accumulates (increases) as the shaking continues for certain material models for vitreous, e.g. viscoelastic or fluid. • Maximum stress occurs around the vitreous-retina contact area both in front and back. • Property of vitreous has great effect on maximum stress and stress distribution. GESAC, Inc

  26. Conclusions - 2 • When using viscoelastic material for vitreous, smaller bulk modulus value shows a clearer stress accumulation effect. Rate of change of stress is more evident. • When using fluid for vitreous, the viscosity coefficient does not show significant effect on maximum stress, stress accumulation effect, and stress distribution. GESAC, Inc

  27. Limitations - 1 • Current model does not include several important structures,such as lens, choroid, ciliary body, and cornea. • Definition of distribution of fat and orbit geometry was approximated. GESAC, Inc

  28. Limitations - 2 • Input motion was purely rotational at centre of the orbit. • All model input data were obtained from literature, material data not verified by experimentation. • Material property data were scaled and appropriateness of scaling has to evaluated. GESAC, Inc

  29. Limitations - 3 • Effect of variation of mesh size, integration intervals and integration procedures have not been fully evaluated. GESAC, Inc

  30. Limitations - 4 • All the material models used in this study are currently available in LS-Dyna material library. It may be necessary to develop new material models to fully describe the material used in this model. • This is a preliminary study to provide a qualitative picture of what happens within the infant eye under repeated motion and results should be interpreted with caution. GESAC, Inc

  31. Work in Progress - 1 • Study influence of additional features such as lens, choroid and ciliary body on model response. • Develop a more accurate orbit geometry and fatty tissue distribution. • Change center of motion to head CG. Both linear and angular motion will be used as input. GESAC, Inc

  32. Work in Progress - 2 • Evaluate effect of mesh size change. • Evaluate effect of meshing axis. • Examine response under purely linear deceleration like a typical frontal crash pulse. This will be an indirect method of validation of the model. GESAC, Inc

  33. Component models under development - 1 Sclera and cornea Choroid Pars plana and pars plicata Retina GESAC, Inc

  34. Component models under development - 2 Vitreous Lens Orbit Fat GESAC, Inc

  35. Component models under development - 3 Extra-ocular muscles Eye assembly GESAC, Inc

  36. Acknowledgements • This work was supported by Aprica, inc. Japan. We thank Aprica project managers, Ms. P. Kawasaki and Dr. R.Bigge, MD, PhD. • Dr. Levin, MD provided invaluable guidance and a push when needed! GESAC, Inc

  37. THANK YOU GESAC, Inc

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