Age- and race-related differences in human scleral material properties.
OBJECTIVE
We tested the hypothesis that there are age- and race-related differences in posterior scleral material properties, using eyes from human donors of European (20-90 years old, n = 40 eyes) and African (23-74 years old, n = 22 eyes) descent.


METHODS
Inflation tests on posterior scleral shells were performed while full-field, three-dimensional displacements were recorded using laser speckle interferometry. Scleral material properties were fit to each eye using a microstructure-based constitutive formulation that incorporates the collagen fibril crimp and the local anisotropic collagen architecture. The effects of age and race were estimated using Generalized Estimating Equations, while accounting for intradonor correlations.


RESULTS
The shear modulus significantly increased (P = 0.038) and collagen fibril crimp angle significantly decreased with age (P = 0.002). Donors of African descent exhibited a significantly higher shear modulus (P = 0.019) and showed evidence of a smaller collagen fibril crimp angle (P = 0.057) compared to donors of European descent. The in-plane strains in the peripapillary sclera were significantly lower with age (P < 0.015) and African ancestry (P < 0.015).


CONCLUSIONS
The age- and race-related differences in scleral material properties result in a loss of scleral compliance due to a higher shear stiffness and a lower level of stretch at which the collagen fibrils uncrimp. The loss of compliance should lead to larger high frequency IOP fluctuations and changes in the optic nerve head (ONH) biomechanical response in the elderly and in persons of African ancestry, and may contribute to the higher susceptibility to glaucoma in these at-risk populations.
Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States.
Rafael
R
Grytz
Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States.
Massimo A
MA
Fazio
Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States.
Vincent
V
Libertiaux
Mechanical Engineering, University of Calabria, Calabria, Italy.
Luigi
L
Bruno
Discoveries in Sight Research Laboratories, Devers Eye Institute, Portland, Oregon, United States.
Stuart
S
Gardiner
Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States.
Christopher A
CA
Girkin
Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States.
J Crawford
JC
Downs
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001696:Biomechanical Phenomena; D044383:Black People; D003094:Collagen / Q000032:analysis; D004548:Elasticity / Q000502:physiology*; D005260:Female; D006801:Humans; D007368:Interferometry / Q000379:methods; D008297:Male; D008875:Middle Aged; D057972:Posterior Eye Segment / Q000502:physiology; D012590:Sclera / Q000502:physiology*; D044465:White People; D055815:Young Adult
D003094:Collagen
computational modeling; extracellular matrix; glaucoma posterior segment