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.
1/17/2019
GESAC, Inc

3. Presentation Road Map Description of the model Parametric study
Discussion of results
Conclusions
Limitations
Work in progress
1/17/2019
GESAC, Inc

4. The Model
LS Dyna model consists of orbit, fatty tissue, extra-ocular muscles, sclera, retina, and vitreous.
Oribt modelled as rigid shell
Fatty tissue is either viscoelastic or elastic 8 noded brick elements
Extra occular muscles are spring and dampers in parallel
Sclera is thick shell elements
Retina was a thick shell elements
Vitreous is solid brick 8-noded brick elements
1/17/2019
GESAC, Inc

5. Model Description Key dimensions Contact definitions
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
Data for sclera and muscle length obtained from Eric Powers’ thesis at
VA Tech. Scaled for infants after consultation with Levin.
Oribt surface nodes tied to sclera nodes. Allows shear but cannot detach.
1/17/2019
GESAC, Inc

6. Data for Prescribed Motion
Shaking experiment with Aprica 2.5 dummy. Click on picture to see baby being shaken. Large AVI file
1/17/2019
GESAC, Inc

7. Prescribed motion Applied motion - rotational oscillations
Represents average data from shaking tests with Aprica 2.5kg dummy
Angular acceleration data obtained from tess. So, was angular
Displacement.
Angular velocity was obtained by differentiating angular displacement.
Average peak velocity was plotted with time and average duration.
Pulse is repetitive, same amplitude and duration.
Positive – Negative angular motion was degrees in each
Direction. This is typical.
1/17/2019
GESAC, Inc

8. Eye ball with muscles
1/17/2019
GESAC, Inc

9. The Model – Vitreous and Retina Attachment
Attachments were made in the back between vitreous and retina.
This is because most blood vessals occur there.
Attachments were also made in the front. The sclera surround the
Vitreous.
Picture horizontally from front [left ] to back
Top of the eye is on top of the picture.
1/17/2019
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.
1/17/2019
GESAC, Inc

11. Simulation Matrix Case Vitreous Fat V.E. Fluid Elastic1 2 3 4 5 6
Vitreous
BK, G0 & Gi in MPa
V.E.
BK=0.7
PR=0.49
G0=0.014
Gi=0.012
BK=7.0
G0=0.14
Gi=0.12
Fluid
VC=0.5
VC=0.3
VC=0.1
Fat
E, BK, G0 & Gi in MPa
Elastic
E=0.047
V.E. (Viscoelastic)
Material properties obtained from Powers thesis.
Vitreous is a viscous gel.
Fat could be elastic or viscoelastic. It turned out that VE model of
Fat resulted in better control of motion but did not make much
Difference in the strains under similar excitation.
For the fluid model the vitreous and retina are attached all nodes.
PR = Poissons ratio is close to 0.5 or imcompressible.
1/17/2019
GESAC, Inc

12. Results Results of the simulation study are discussed
Stresses on retina
Stresses on the sclera
1/17/2019
GESAC, Inc

13. Stress on Retina – Case 2 Stress on one of the elements in case 2
1/17/2019
GESAC, Inc

14. Stress on Retina – Case 3 Stress on one of the elements in case 3
1/17/2019
GESAC, Inc

15. Stress on Retina – Case 5 Stress on one of the elements in case 5
1/17/2019
GESAC, Inc

16. Simulation – Case 2
Click on picture to see animation of simulation results. Large AVI file.
1/17/2019
GESAC, Inc

17. Simulation – Case 5
Click on picture to see animation of simulation results. Large AVI file.
1/17/2019
GESAC, Inc

18. Stress Distribution on Sclera– Case 2
1/17/2019
GESAC, Inc

19. Stress Distribution on Retina – Case 2
1/17/2019
GESAC, Inc

20. Stress Distribution on Vitreous – Case 2
1/17/2019
GESAC, Inc

21. Stress Distribution on Sclera – Case 5
1/17/2019
GESAC, Inc

22. Stress Distribution on Retina – Case 5
1/17/2019
GESAC, Inc

23. Stress Distribution on Vitreous – Case 5
1/17/2019
GESAC, Inc

24. Comparison of Maximum Stress on Retina
Case 1 2 3 4 5 6
Maximum Stress (MPa) *
Fat
Vitreous
Elastic
V.E.
Fluid
* The calculation reaches an infinite loop at 0.94 sec, when case 5 has a maximum of
1/17/2019
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.
1/17/2019
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.
1/17/2019
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.
1/17/2019
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.
1/17/2019
GESAC, Inc

29. Limitations - 3
Effect of variation of mesh size, integration intervals and integration procedures have not been fully evaluated.
1/17/2019
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.
1/17/2019
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.
1/17/2019
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.
1/17/2019
GESAC, Inc

33. Component models under development - 1
Sclera and cornea
Choroid
Pars plana and pars plicata
Retina
1/17/2019
GESAC, Inc

34. Component models under development - 2
Vitreous
Lens
Orbit
Fat
1/17/2019
GESAC, Inc

35. Component models under development - 3
Extra-ocular muscles
Eye assembly
1/17/2019
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!
1/17/2019
GESAC, Inc

37. THANK YOU
1/17/2019
GESAC, Inc