Racial differences in human scleral material properties

Purpose:To determine the racial differences in the material properties of posterior scleral shells from human donors of European (n=20 eyes) and African (n=11 eyes) descent. Methods:Posterior scleral shells were subjected to IOP elevations from 5 to 45 mmHg and the resulting fullfield displacements were recorded using laser speckle interferometry. Eye-specific finite element models were generated based on experimentally measured scleral shell surface geometry and thickness. Inverse numerical analyses were performed to identify material parameters for each eye by matching experimental deformation measurements to model predictions using a microstructure-based constitutive formulation that incorporates the crimp response and anisotropic architecture of scleral collagen fibrils. Generalized Estimating Equation models were constructed to determine whether there was a significant effect of race on the fitted material parameters while accounting for age and intra-donor correlations. Results:The age-dependent scleral shear modulus is significantly higher (p=0.019) and the collagen fibril crimp angle is lower in donors from African descent, although this did not reach conventional statistical significance (p=0.057, Fig. 1). The IOP-dependent in-plane strains in the peripapillary sclera are significantly lower in donors from African descent (p<0.015 for all IOP levels, Fig. 2). Conclusions:Results show that posterior sclera of donors of African descent are stiffer compared to donors of European descent due to both a higher shear stiffness of the nonfibrillar matrix and a lower level of stretch at which the collagen fibrils uncrimp and stiffen. These differences may be due to a higher collagen cross-linking density in donors of African descent and relate to a higher susceptibility to glaucoma.