Preliminary Investigation of the Mechanical Anisotropy of the Normal Human Corneal Stroma

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.

Direct Evidence of Symmetry between Bilateral Human Corneas in Biomechanical Properties: A Comparison Study with Fresh Corneal Tissue

“…Although the tensile tests were conducted in saline solution in the present study, the experiment was accomplished in a very short time; therefore, it is unlikely that significant swelling occurred during the experiments. [16].…”

“…e thickness of the cap was 120 μm. After the creation of the refractive lenticule and small incision, the surgeon dissected the lenticule from the surrounding tissue and extracted it through the small incision [16].…”

“…All patients underwent a systematic ophthalmologic examination, including slit-lamp microscopy, corneal topography, and intraocular pressure (IOP) measurement, to ensure a healthy cornea. Exclusion criteria were keratoconus or suspected keratoconus, active ocular and systemic disease, prior clinical history of ocular surgery or trauma, and any other condition that can affect the health of the cornea [16].…”

“…e tests were performed using an In Situ Bidirectional Tension and Compression Testing System (IBTC-50, Tianjin Care Measure and Control Co., Ltd., Tianjin, China) in a water bath apparatus filled with normal saline at room temperature. e strain rate was 0.01 mm/s [16].…”

“…e BC segment is a high-strain region and approximately a straight line. D is the fracture point [16].…”