Age-related variations in the biomechanical properties of human sclera

This study examined age-related changes in biomechanical behaviour in the anterior, equatorial and posterior regions of the human sclera (white of the eye). Circumferential strip specimens were extracted from areas close to the limbus, equator and posterior pole in 45 donor scleras ranging in age between 51 and 84 years. The strips were subjected to cycles of uniaxial tension loading at a strain rate of 8% per minute while monitoring their load-deformation behaviour. All specimens demonstrated nonlinear behaviour with an initially low tangent modulus (a measure of material stiffness) increasing under higher stresses. The average ratios between the tangent modulus at a high stress of 1 MPa and that at a low stress of 0.05 MPa were 11.2±1.7, 12.0±1.7 and 12.4±1.5 for anterior, equatorial and posterior specimens, respectively. Stiffening was observed with age in all regions, but it was statistically significant only in the anterior region (P<0.01). Anterior specimens showed the largest stiffness growth with advancing age in both the initial, matrix regulated phase of behaviour (0.32 MPa/decade), and the final, collagen regulated phase (3.97 MPa/decade), followed by equatorial (0.27 and 2.15 MPa/decade) then posterior specimens (0.14 and 0.26 MPa/decade). The stress-strain behaviour of scleral tissue exhibits increasing stiffness with higher age. In addition to a regional variation of material stiffness, the rate of stiffness growth with age also varies between regions.