Abstract
Purpose :
This study aims to experimentally characterize and numerically model the depth-dependent material properties of the human corneal stroma. Quantifying the mechanical properties at known depths will allow building material models with accurate microstructure representation, which can further be used for treatment developments or testing surgical interventions.
Methods :
Five Descemet’s Membrane Endothelial Keratoplasty (DMEK) corneal transplants were obtained in less than 24 hours after transplantation. The corneas were cut into strips of 6 mm x 2 mm x 0.15 mm using a femtosecond laser in the central cornea; 150µm thick samples were taken at 50 µm (D1), 300 µm (D2), and 550 µm (D3) depth and tested by a uniaxial extension (CellScale, UStretch & Biorakes). (Fig 1). The samples were stored and tested in a hydration-preserving culture media containing 5 % Dextran. The samples were pre-stretched with a force of 10mN and pre-conditioned with 5 cycles of 10 % strain. The last cycle of force-displacement data was recorded for analysis. For the initial estimation of mechanical strength, the tangent elastic modulus was calculated at 10 % strain.
Results :
The human cornea shows a depth-dependent mechanical variability, with its stiffness decreasing continuously from the anterior to the posterior surfaces. Our measurements have shown that the stiffness of the posterior cornea (D3) is less than 40% of the stiffness of the anterior cornea (D1) at 10% strain (Fig. 2).
Conclusions :
In this study, we quantify the decrease in the mechanical strength of the human cornea in depth. The main limitation of the study is the lack of orientation markers on the specimens obtained from the clinic, which would give us additional insight into the orientation dependence of corneal biomechanics. While the anterior part of the cornea is known to be isotropic, the lack of orientation markers could explain the high variability observed in the anisotropic posterior part of the cornea. In a next step, a depth-dependent anisotropic numerical human cornea can be constructed using this information after more samples are collected.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.