Depth-Dependent Out-of-Plane Young’s Modulus of the Human Cornea

<p><b>Purpose/Aim</b>: Despite their importance in accurate mechanical modeling of the cornea, the depth-dependent material properties of the cornea have only been partially elucidated. In this work, we characterized the depth-dependent out-of-plane Young’s modulus of the central and peripheral human cornea with high spatial resolution.</p> <p><b>Materials and Methods</b>: Central and peripheral corneal buttons from human donors were subjected to unconfined axial compression followed by stress relaxation for 30 min. Sequences of fluorescent micrographs of full-thickness corneal buttons were acquired throughout the experiment to enable tracking of fluorescently labeled stromal keratocyte nuclei and measurements of depth-dependent infinitesimal strains. The nominal (gross) out-of-plane Young’s modulus and drained Poisson’s ratio for each whole specimen was computed from the equilibrium stress and overall tissue deformation. The depth-dependent (local) out-of-plane Young’s modulus was computed from the equilibrium stress and local tissue strain based on an anisotropic model (transverse isotropy).</p> <p><b>Results</b>: The out-of-plane Young’s modulus of the cornea exhibited a strong dependence on in-plane location (peripheral versus central cornea), but not depth. The depth-dependent out-of-plane Young’s modulus of central and peripheral specimens ranged between 72.4–102.4 kPa and 38.3–58.9 kPa. The nominal out-of-plane Young’s modulus was 87 ± 41.51 kPa and 39.9 ± 15.28 kPa in the central and peripheral cornea, while the drained Poisson’s ratio was 0.05 ± 0.02 and 0.07 ± 0.04.</p> <p><b>Conclusions</b>: The out-of-plane Young’s modulus of the cornea is mostly independent of depth, but not in-plane location (i.e. central vs. peripheral). These results may help inform more accurate finite element computer models of the cornea.</p>