Abstract
Purpose :
Motor Vehicle Accidents (MVA) are the leading cause of death for children worldwide. Retinal hemorrhage (RH) was exhibited in 17% of these fatal cases. We hypothesize that MVA induced retinal stresses are correlated with the RH injury. Computer models were developed to investigate the mechanical responses of a child’s eye during two MVA scenarios, and their direct associations with RH.
Methods :
A 3D model of the human child ocular globe (Fig.1) during two representative MVA scenarios (vehicle traversing a speed bump and non-impact abrupt stop) was mimicked using finite element analysis (FEA). Geometric parameters and material properties from each intraocular structure were obtained from the literature. Displacement and rotation profiles derived from an analytical vehicle model traversing a speed bump at 45 kph were used as critical loading conditions. Vehicular dynamic parameters such as sprung mass, suspension stiffness, damping coefficients, weight distribution, and moment of inertia were considered. An abrupt stop from 70 kph with a braking time of 1.5 s and a constant deacceleration profile of 1G was also analyzed. Stresses were quantified in both scenarios.
Results :
The quadratic mean acceleration experienced during the speed bump event was 1.967 m/s2, causing a “very uncomfortable” level for the young passenger based on the ISO 2631-1’s levels of discomfort. Acceleration frequency spectra showed peaks at 4 Hz and 9 Hz. Although these loading values are sufficient to transmit vibrations to the human body, they are far less than average accelerations of 32.4 m/s2 at 2.2 Hz during abusive head traumas (AHT). A peak stress of 0.655 kPa was experienced by the retina (Fig.2a). Results from the abrupt stop simulation showed higher retinal stresses with a peak value of 1.434 kPa (Fig.2b). Stresses found in both MVA scenarios are located at the posterior pole of the ocular globe, which coincides with the majority RH observations in AHT.
Conclusions :
We identified a correlation between higher retinal stress regions induced in MVA and RH damage location. Only the peak retinal stress from the abrupt stop event exceeded the 1 kPa traction stress necessary for vitreoretinal separation and subsequent RH. These results assert the irregularity of RH in different MVA compared to AHT and help build a basis for further RH findings in severe MVA.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.