Abstract
Purpose :
Abusive head trauma (AHT), formerly known as Shaken Baby Syndrome (SBS), is the leading cause of infant death and long-term morbidity from injury. Controversy abounds in discussions involving ocular consequences following AHT, and the pathophysiology of the diagnosis is not well understood. When comparing an oscillatory event with a single traumatic impact, there are qualitative and quantitative differences in clinical presentation. Given these parameters, we postulate the rotational shearing forces between the vitreous and retina result in multilayered and multifocal retinal hemorrhages (RH) that are exclusive to AHT.
Methods :
A finite element model was developed to computationally measure stress and shear on an anatomic model with maximum biofidelity, in the context of force, displacement, acceleration/deceleration, and frequency, to mimic shaking in vivo. To empirically corroborate our finite element model, young sheep eyes (Sierra Medical, Whitter) harvested at 6-9 months of age were utilized to isolate the forces within the vitreoretinal adhesion and measured by a biaxial planar materials analyzer (CellScale, Ontario).
Results :
Calculated shear stress from our finite element model ranged from 3-16 kPa throughout one cycle of shaking. Maximal stress was observed peripherally, corresponding to areas of arterial bifurcations and globe equator, as well as at the posterior pole of the eye. Stress values were also nearly equivalent throughout all three layers of the retina (preretinal, intraretinal, and subretinal spaces). Seven replicates of the ex vivo animal model confirmed that the initial tear between neuroretina layer and the vitreous occurs at stress pressures between 2-5 kPa.
Conclusions :
Ocular manifestations from shaking an infant show unique characteristics. Our data suggests nearly 360° of variable RH in AHT is likely due to repeated cycles of multi-axial oscillatory shaking, producing tangential shearing from rotational forces. Preretinal, intraretinal, and subretinal involvement implies both central retinal artery bifurcations as well as choroidal capillaries are implicated in the formation of multifocal hemorrhages. Previous studies have shown a stress value of 2 kPa is likely sufficient to cause vitreoretinal tears in a shaken infant, and we look to incorporate our calculations into a working virtual reality (VR) eye model for public educational uses.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.