Cases of child abuse, specifically abusive head trauma (AHT) or shaken-baby syndrome (SBS), have long been associated clinically with retinal hemorrhages (RH). Previous research has shown that the vast majority (~85%) of AHT cases present with some type of RH. Traumatic RH is initiated by an external application of forces and accelerations to the head, but the mechanism by which this causes RH in infants is still unknown. The most prominent theory suggests that collagen-mediated adhesion between the vitreous and retina causes traction on the retina during rapid head rotation, damaging retinal blood vessels. To date, this theory has never been proven.
In order to better understand the mechanisms of traumatic RH in infants, agerelated changes of the vitreous and vitreoretinal interface were investigated. First, dynamic shear tests were conducted using a novel rheological interconversion technique to characterize the changes in material properties with developmental age of porcine vitreous. Next, scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDS) studies were performed on specimens from the vitreoretinal interface to quantitatively evaluate changes in collagen with age and in different regions of the eye.
In dynamic shear, there was a statistically significant difference among the three age groups at varying shear rates (frequencies) for both storage (G′) and loss (G″) shear modulus. In particular, younger porcine vitreous had significantly higher (G′) and (G″) than vitreous from older animals. Given the unavoidable time degradation of vitreous, the interconversion technique used to characterize the porcine vitreous dynamic properties provided more reliable data over a wider range of frequencies (0.01 Hz - 1 Hz) than previous studies.
SEM image analysis of the vitreoretinal interface resulted in a significantly higher percent collagen in eyes from 3- to 5-day-old piglets compared to 4-week-old piglets (p=0.002). Statistically significant regional differences were hindered by large variances due to charging artifacts and extraneous collagen from the vitreous body. The EDS analysis resulted in significant differences in carbon (p=0.009), nitrogen (p=0.025), silicon (p≤0.001), and sulfur (p=0.007) with respect to age. Regional significant differences were also found for sulfur (p=0.002).