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Abstract
Purpose To investigate the anisotropic characteristics of the normal human corneal stroma using fresh corneal tissue. Methods Sixty-four corneal specimens extracted from stromal lenticules were included in this study. The specimens were cut in the temporal-nasal (horizontal) or superior-inferior (vertical) direction. Strip specimens were subjected to uniaxial tensile testing. The tensile properties of the specimens were measured and compared in the two directions. Results The low-strain tangent modulus was statistically significantly greater in the vertical direction than in the horizontal direction (1.32 ± 0.50 MPa vs 1.17 ± 0.43 MPa; P=0.035), as was the high-strain tangent modulus (51.26 ± 8.23 MPa vs 43.59 ± 7.96 MPa; P ≤ 0.001). The elastic modulus in the vertical direction was also higher than that in horizontal direction at stresses of 0.01, 0.02, and 0.03 MPa, but not statistically significant; so, P=0.338, 0.373, and 0.417, respectively. Conclusions The biomechanical behavior in normal human corneal stroma tissue is slightly stiffer in the vertical direction than in the horizontal direction. This information may aid our understanding of the biomechanical properties of the cornea and related diseases.
Highlights
Uniaxial tensile testing has been used to compare the mechanical behavior of porcine and cadaveric human cornea strips from different directions and showed that the elastic response differs according to the cutting direction [9, 10]
While the material parameters of the corneal stromal lenticules have be measured through uniaxial tensile test in the previous study [12], the purpose of this study was to investigate the mechanical anisotropy of the normal human corneal stroma using stromal lenticules extracted during small incision lenticule extraction (SMILE) as part of an effort to elucidate the biomechanical behavior of the human cornea
A typical stress-strain curve is shown in Figure 2. e curve can be divided into four sections. e first section is the linear elastic OA segment, in which the load changes are very small and deformation increases rapidly. e second section is the AB segment, in which the load increases exponentially with an increase in deformation, reflecting a nonlinear relationship. e third section is the BC segment, which is an approximately straight line, where the maximum stress is reached at point C. e fourth section is D, which is the fracture point. e elastic modulus (E) of the OA segment is defined as the low-strain tangent modulus (LSTM) and that of the BC segment is defined as the highstrain tangent modulus (HSTM) [15]
Summary
Uniaxial tensile testing has been used to compare the mechanical behavior of porcine and cadaveric human cornea strips from different directions and showed that the elastic response differs according to the cutting direction [9, 10] This test cannot describe the mechanical anisotropy of the normal human cornea accurately. While the material parameters of the corneal stromal lenticules have be measured through uniaxial tensile test in the previous study [12], the purpose of this study was to investigate the mechanical anisotropy of the normal human corneal stroma using stromal lenticules extracted during SMILE as part of an effort to elucidate the biomechanical behavior of the human cornea
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