Measuring Human Corneal Stromal Biomechanical Properties Using Tensile Testing Combined With Optical Coherence Tomography

Abstract

Purpose: To investigate the ex vivo elastic modulus of human corneal stroma using tensile testing with optical coherence tomography (OCT) imaging and its correlation with in vivo measurements using corneal visualization Scheimpflug technology.Methods: Twenty-four corneal specimens extracted from stromal lenticules through small incision lenticule extraction were cut into strips for uniaxial tensile tests. In vivo corneal biomechanical responses were evaluated preoperatively using the corneal visualization Scheimpflug technology (CorVis ST). The correlation of the elastic modulus with clinical characteristics and dynamic corneal response parameters were analyzed using Spearman’s correlation analysis.Results: The mean low strain tangent modulus (LSTM) of the human corneal stroma was 0.204 ± 0.189 (range 0.010–0.641) MPa, and high strain tangent modulus (HSTM) 5.114 ± 1.958 (range 2.755–9.976) MPa. Both LSTM (r = 0.447, p = 0.029) and HSTM (r = 0.557, p = 0.005) were positively correlated with the stress-strain index (SSI). LSTM was also positively correlated with the A1 deflection length (r = 0.427, p = 0.037) and A1 deflection area (r = 0.441, p = 0.031). HSTM was positively correlated with spherical equivalent (r = 0.425, p = 0.038).Conclusions: The correlation of corneal elastic modulus with A1 deflection parameters and SSI may indicate a relationship between these parameters and tissue elasticity. The HSTM decreased with the degree of myopia. Combining tensile test with OCT may be a promising approach to assess corneal biomechanical properties.

The alteration of the structure and macroscopic mechanical response of porcine patellar tendon by elastase digestion

“…The tensile stress and strain were calculated using Eqs 3 , 4 , respectively. The slopes of the low- and high-strain linear regions on the stress-strain curve were obtained by bidirectional curve fitting and were recorded as low (E LT ) and high (E HT ) tensile moduli, respectively ( Herbert et al, 2016 ; Song et al, 2022 ). The intersection of the two tangents defined a transition point, with the abscissa of the transition strain and the ordinate of the transition stress, and the intersection of the tangent of the high-strain linear region and the X -axis was recorded as the ductility index ε *.…”

Ex vivo, in vivo and in silico studies of corneal biomechanics: a systematic review

“…All the samples considered in the studies were extracted in healthy corneal conditions without any active pathological condition affecting the tissue. Animal corneas were generally obtained from pigs aged between 4 and 6 months from slaughterhouse [ 11 – 17 , 19 , 20 , 23 – 26 , 29 , 30 , 32 ], while human corneal specimens were harvested from cadaver donor eyes as full-thickness samples [ 12 , 13 , 22 , 29 , 30 ], or removed as stromal lenticules from the central cornea during surgery [ 5 , 10 , 21 , 27 , 46 ].…”

“…For strain less than 20%, low-strain tangent modulus 1.17 ± 0.43 MPa in NT direction and 1.32 ± 0.50 MPa in SI direction. For strain between 35% and 55%, high-strain tangent modulus 43.59 ± 7.96 MPa in NT direction and 51.26 ± 8.23 MPa in SI direction [ 5 ] Tensile H stromal lenticules removed from cornea during the SMILE surgery (7 males, 15 females, age 23.96 ± 5.27 years) No. of strips: 24 Length: 6.60 mm Width: 1.00 mm Specimens underwent 2 loading/ unloading cycles for preconditioning.…”

“…The thickness was obtained by surgery data [ 10 , 21 , 22 , 46 ] or measured by pachymetry [ 11 , 13 , 20 , 25 , 26 , 29 , 30 ], digital calliper [ 14 , 24 ], ultrasonic thickness measurement [ 32 ], optical-magnifying scale [ 12 ] or microscope [ 23 ]. All these methods have some limitations in terms of accuracy due to thickness variation between central and peripherical regions and to tissue swelling during all the experimental procedures for sample preservation and preparation [ 5 , 23 ]. Only in two studies [ 5 , 47 ], the exact thickness was acquired during the testing with an optical coherence tomography (OCT) imaging.…”

“…Both the thickness and structural organization ensure the corneal mechanical properties needed to guarantee its functionality as protection for the inner ocular components and major refractive power of the ocular system. It has been shown that corneal biomechanics is impaired in myopic patients [ 4 , 5 ], as well as in patients affected by other ocular diseases (such as keratoconus [ 6 , 7 ], glaucoma [ 8 ], dry eye disease [ 9 ]). Therefore, assessing the mechanical behaviour of the cornea is clinically crucial for understanding first of all the physiological behaviour of the tissue and, in this respect, for diagnosing potential pathologies responsible for the weaking, thinning or curvature variation, and quantifying the success of refractive surgery and therapeutic treatments.…”