A finite element infant eye model to investigate retinal forces in shaken baby syndrome
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Published on: September 13, 2016
Steven Alex Hans1, Sebastian Y Bawab, Michael L Woodhouse
1Department of Mechanical Engineering, Old Dominion University, Norfolk, VA 23529-0247, USA. shans001@odu.edu
Insights
Shaken baby syndrome (SBS) may cause retinal hemorrhaging due to sustained, high forces on the posterior retina during shaking motions. These forces exceed those from impact, suggesting shaking alone is a significant risk factor for infant injury.
Area of Science:
- Biomechanics
- Pediatric Trauma
- Ophthalmology
Background:
- Shaken baby syndrome (SBS) involves infant abuse with acceleration-deceleration forces.
- Bilateral retinal hemorrhaging is a key indicator of SBS.
- Computational eye models can assess retinal forces during simulated abuse.
Purpose of the Study:
- To computationally model an infant eye using finite element analysis.
- To assess posterior retinal forces during simulated shaking and impact motions.
- To compare the biomechanical effects of shaking versus impact on the infant eye.
Main Methods:
- Developed a finite element computational model of an infant eye based on literature.
- Simulated a four-cycle shaking motion and a 100 ms impact pulse (60G).
- Compared retinal forces and impulses generated by shaking versus impact.
Main Results:
- Shaking motion produced sustained mean retinal forces (~0.08 N) with peaks over 0.2 N.
- Impact simulation resulted in lower mean forces (~0.025 N) and peak forces (~0.11 N).
- The impulse from shaking was 13 times greater than from impact.
Conclusions:
- Shaking alone may generate sufficient force to cause retinal hemorrhaging.
- Sustained and localized posterior retinal forces from shaking exceed those from impact.
- The optic nerve's role in localized stress may contribute to retinal injury during shaking.
Background:
Shaken baby syndrome (SBS) is a form of abuse in which an infant, typically 6 months or less, is held and submitted to repeated acceleration-deceleration forces. One of the indicators of abuse is bilateral retinal hemorrhaging. A computational model of an infant eye, using the finite element method, is built in order to assess forces at the posterior retina for a shaking and an impact motions.
Method:
The eye model is based on histological studies, diagrams, and materials from previous literature. Motions are applied to the model to simulate a four-cycle shaking motion in 1 second with maximum extension/flexion of the neck. The retinal forces of the shaking motion, at the posterior eye, are compared to an impact pulse (60G) simulating a fall for a total duration of 100 ms.
Results:
The shaking motion, for the first cycle, shows retinal force means at the posterior eye to be around 0.08 N sustained from the time range of 50 to 200 ms, into the shake, with a peak in excess of 0.2 N. The impulse, area under the curve, is 15 N-ms for 250 msec for the first cycle. The impact simulation reveals a mean retinal force around 0.025 N for a time range of 0 to 26 ms, with a peak force around 0.11 N. Moreover, the impulse for the impact simulation is 13 times lower than the shaking motion.
Conclusion:
The results suggest that shaking alone may be enough to cause retinal hemorrhaging, as there are more sustained and higher forces in the posterior retina, compared to an impact due to a fall. This is in part due to the optic nerve causing more localized stresses in a shaking motion than an impact.
