Age and race significantly impact the IOP-induced mechanical energy absorpion in the posterior human sclera

The purpose of this study was to establish if age and race were influential factors in the peripapillary human sclera’s ability to absorb mechanical energy from IOP-induced deformation in normal donors of African (AD) and European (ED) descent. Mechanical inflation testing was performed on 28 pairs of normal eyes from human donors (9 AD, 19 ED) aged 20 to 90 years. The intact posterior scleral shell of each eye was pressurized while the full-field, three-dimensional displacements of the outer scleral surface were measured using laser speckle interferometry (ESPI). By analytical differentiation of the displacement field, the mean maximum principal (tensile) strain was computed at 10 discrete pressure levels from 5 to 45 mmHg within the ~2-mm-wide band of peripapillary sclera surrounding the optic nerve head. An asymptotic functional form (strain = a + b*IOP + IOP/c) was used to fit the variation of strain with increasing IOP (R2=0.99). The area under the strain-IOP curve, representing the total mechanical energy absorbed by the peripapillary sclera when inflated from 5 to 45 mmHg, was computed by analytical integration. We observed that the ability of the peripapillary sclera to absorb IOP-induced deformation decreased significantly with age in both the AD and ED groups (p<0.001), and was more pronounced in the AD group (p=0.0481). In conclusion, the peripapillary sclera exhibits a significant loss in its ability to absorb mechanical energy from IOP-induced deformations with age, and the AD eyes showed a significantly more rapid decline in energy absorption with age than ED eyes. These differences may increase the magnitude of transient IOP elevations and thereby contribute to the increased susceptibility of the elderly and persons of AD to glaucoma.