scholarly journals Time-varying regularity of changes in biomechanical properties of the corneas after removal of anterior corneal tissue

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Di Zhang ◽  
Xiao Qin ◽  
Haixia Zhang ◽  
Lin Li
Keyword(s):  
Elastic Modulus ◽  
Stress Relaxation ◽  
Refractive Surgery ◽  
Biomechanical Properties ◽  
Collagen Fibrils ◽  
Uniaxial Tensile ◽  
Control Group ◽  
Corneal Tissue ◽  
Corneal Refractive Surgery ◽  
Corneal Biomechanical Properties

Abstract Background The corneal biomechanical properties with the prolongation of time after corneal refractive surgery are important for providing a mechanical basis for the occurrence of clinical phenomena such as iatrogenic keratectasia and refractive regression. The aim of this study was to explore the changes of corneal elastic modulus, and stress relaxation properties from the 6-month follow-up observations of rabbits after a removal of anterior corneal tissue in simulation to corneal refractive surgery. Methods The anterior corneal tissue, 6 mm in diameter and 30–50% of the original corneal thickness, the left eye of the rabbit was removed, and the right eye was kept as the control. The rabbits were normally raised and nursed for 6 months, during which corneal morphology data, and both of corneal hysteresis (CH) and corneal resistance factor (CRF) were gathered. Uniaxial tensile tests of corneal strips were performed at months 1, 3, and 6 from 7 animals, and corneal collagen fibrils were observed at months 1, 3, and 6 from 1 rabbit, respectively. Results Compared with the control group, there were statistical differences in the curvature radius at week 2 and month 3, and both CH and CRF at months 1, 2, and 6 in experiment group; there were statistical differences in elastic modulus at 1, 3, and month 6, and stress relaxation degree at month 3 in experiment group. The differences in corneal elastic modulus, stress relaxation degree and the total number of collagen fibrils between experiment and control groups varied gradually with time, and showed significant changes at the 3rd month after the treatment. Conclusions Corneas after a removal of anterior corneal tissue undergo dynamic changes in corneal morphology and biomechanical properties. The first 3 months after treatment could be a critical period. The variation of corneal biomechanical properties is worth considering in predicting corneal deformation after a removal of anterior corneal tissue.

The Changes of the Corneal Tissue Structures and Biomechanical Properties in the Process of Cornea Post-Embryonic Development

2014 ◽  
Vol 934 ◽  
pp. 3-7
Author(s):  
Shuang Hao ◽  
Ai Jun Deng ◽  
Guo Hui Wang
Keyword(s):  
Electron Microscope ◽  
Elastic Modulus ◽  
Collagen Fiber ◽  
Morphological Structure ◽  
Biomechanical Properties ◽  
Collagen Fibrils ◽  
Corneal Tissue ◽  
Corneal Fibroblasts ◽  
New Zealand White Rabbits ◽  
Biomechanical Experiment

To investigate the changes of corneal tissues morphological structure and biomechanical properties in different month age rabbits, the eyeballs of the 1 month, 2 month and 3 month-old-New Zealand white rabbits were obtained and getting the cornea tissues, and then measured the thickness of the cornea tissues. The first part of the corneal tissue was used to observe cornea structure with HE staining. The second part was used to observe collagen fibrils by electron microscope. The third part of the cornea tissues were cut into strips and used to test the elastic modulus of the cornea on Instron5544 tester. The thickness of the cornea was increased with month age. HE staining observation shows that the numbers of corneal fibroblasts were decreased and the fiber bundle increased with month age. Electron microscope observation shows that the diameters of collagen fibrils were increased at 2 and 3 month. Biomechanical experiment results reveal that cornea tissues elastic modulus was increased with month age. In the post-embryonic stages, the structure of cornea, the structure and number of collagen fiber, the number of corneal fibroblasts and the biomechanical properties of cornea were changed continually.

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

2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Chao Xue ◽  
Yaoqi Xiang ◽  
Yi Song ◽  
Min Shen ◽  
Di Wu ◽  
...  
Keyword(s):  
Biomechanical Properties ◽  
Tangent Modulus ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Corneal Tissue ◽  
Significant Difference ◽  
Lenticule Extraction ◽  
The Difference ◽  
First Time ◽  
Corneal Biomechanical Properties

Purpose. To investigate the difference between the eyes from the same human with respect to the biomechanical properties of fresh corneal tissues and investigate the assumption of similarity of the corneal biomechanical properties between the eyes. Methods. Strip specimens extracted through a small incision lenticule extraction (SMILE) surgery were tested using a uniaxial tensile test. The specimens were extracted vertically. Low-strain tangent modulus (LSTM), high-strain tangent modulus (HSTM), and tensile strength ( σ b ) were the biomechanical parameters used in the comparison of the eyes from the same human. Results. Ninety corneal specimens from 45 persons were included in this study. The LSTM of the left and right eyes were 1.34 ± 0.52 and 1.37 ± 0.46 MPa, while the HSTM were 50.53 ± 7.51 and 49.41 ± 7.01 MPa, respectively. There was no significant difference between the eyes in terms of LSTM, HSTM, and σ b P = 0.813 ,   0.335 ,   and  0.605 ,   resp . . The LSTM and HSTM were significantly correlated with the spherical equivalent (SE) ( P ≤ 0.01 ,   P = 0.001 , resp.). Conclusions. The assumption that the corneal biomechanical properties of the eyes from the same human are similar has been confirmed for the first time using fresh human corneal tissue. This finding may be useful in further biomechanical studies.

Evaluation of Biomechanically Corrected Intraocular Pressure Measurements in Keratoconus and Forme Fruste Keratoconus

2020 ◽  
Vol 63 (6) ◽  
pp. 541-549
Author(s):  
Tomoya Nishida ◽  
Takashi Kojima ◽  
Takahiro Kataoka ◽  
Naoki Isogai ◽  
Yoko Yoshida ◽  
...  
Keyword(s):  
Intraocular Pressure ◽  
Biomechanical Properties ◽  
Control Group ◽  
Pressure Measurements ◽  
Altman Plot ◽  
Significant Difference ◽  
The Difference ◽  
The Right ◽  
Corneal Biomechanical Properties ◽  
Forme Fruste Keratoconus

<b><i>Introduction:</i></b> Although biomechanically corrected intraocular pressure (bIOP) is available, the effectiveness of intraocular pressure (IOP) correction in keratoconus and forme fruste keratoconus (FFK) eyes has not been investigated. <b><i>Objective:</i></b> Evaluation of bIOP measurements in eyes with keratoconus and FFK. <b><i>Methods:</i></b> Forty-two eyes in 21 patients with keratoconus in one eye and FFK in the fellow eye were examined (KC/FFK group; mean age 24.62 ± 8.6 years; 16 males and 5 females). The control group consisted of 62 eyes in 31 unaffected subjects (mean age 26.26 ± 3.64 years; 15 males and 16 females). The bIOP was determined using a Scheimpflug-based tonometer (Corvis Scheimpflug Technology [Corvis ST®]) after measuring the IOP with a conventional non-contact tonometer (NIOP). The agreement between NIOP and bIOP values was examined using the Bland-Altman plot. The difference between NIOP and bIOP (bIOP correction amount) was compared between keratoconus and FFK eyes. <b><i>Results:</i></b> In the control group, there were no significant differences between right and left eyes in both NIOP and bIOP values (<i>p</i> = 0.975 and <i>p</i> = 0.224, respectively). In the KC/FFK group, NIOP values were significantly lower in the keratoconus eyes (9.93 ± 1.96 mm Hg) than in the FFK eyes (12.23 ± 3.03 mm Hg; <i>p</i> = 0.0003). There was no significant difference in bIOP values between the right and left eyes of the KC/FFK group (<i>p</i> = 0.168). The bIOP correction amount was significantly increased in keratoconus eyes (3.58 ± 2.12 mm Hg) compared to in FFK eyes (1.80 ± 3.32 mm Hg; <i>p</i> = 0.011). <b><i>Conclusions:</i></b> For eyes with keratoconus and FFK, the bIOP method is effective to adjust IOP measurements based on corneal biomechanical properties.

scholarly journals Influence of dextran solution and corneal collagen crosslinking on Corneal Biomechanical Parameters Evaluated by Corvis ST

2021 ◽  
Author(s):  
Xiao Qin ◽  
Lei Tian ◽  
Hui Zhang ◽  
Di Zhang ◽  
Li-Li Guo ◽  
...  
Keyword(s):  
Biomechanical Properties ◽  
Control Group ◽  
Corvis St ◽  
Collagen Crosslinking ◽  
Corneal Collagen Crosslinking ◽  
Biomechanical Parameters ◽  
Dextran Solution ◽  
Corneal Biomechanical Properties ◽  
Porcine Eyes ◽  
Corneal Collagen

Abstract Purpose: To analyze the influence of dextran solution and corneal collagen crosslinking (CXL) on corneal biomechanical parameters evaluated by Corneal Visualization Scheimpflug Technology (Corvis ST). Materials and Methods: Forty porcine eyes were included in this study. Twenty porcine eyes were soaked in dextran solution for 30 minutes (10 eyes in 2% dextran solution and 10 eyes in 20% dextran solution). CXL treatment was performed in 10 porcine eyes, the other 10 porcine eyes were regarded as a control group. Each eye was fixed on an experimental inflation platform to carry out Corvis measurements at different IOPs. Corneal biomechanical parameters were calculated based on Corvis measurement. Statistical analysis was used to analyze the influence of dextran solution and CXL on corneal biomechanical parameters based on Corvis parameters. Results: Corneal energy absorbed area (Aabsorbed) decreased after being soaked in dextran solution under IOP of 15 mmHg; Corneal elastic modulus (E) decreased after being soaked in 2% dextran solution and increased after being soaked in 20% dextran solution; SP-A1 increased after CXL. Conclusion: Both dextran solution and CXL can change corneal biomechanical properties; SP-A1 may be used as an effective parameter for the evaluation of CXL.

EFFECTS OF CULTURE PERIODS AND LOADING ON BIOMECHANICAL PROPERTIES OF SHEEP COLLAGEN FASCICLES

2014 ◽  
Vol 14 (06) ◽  
pp. 1440010
Author(s):  
AHMET C. CILINGIR
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Soft Tissues ◽  
Culture Media ◽  
Experimental Studies ◽  
Biomechanical Properties ◽  
Collagen Fibrils ◽  
Tangent Modulus ◽  
Control Group ◽  
Stress Strain

Soft tissues (e.g., tendon, skin, cartilage) change their dimensions and properties in response to applied mechanical stress/strain, which is called remodeling. Experimental studies using tissue cultures were performed to understand the biomechanical properties of collagen fascicles under mechanical loads. Collagen fascicles were dissected from sheep Achilles tendons and loaded under 1, 2, and 3 kg for 2, 4, and 6 days under culture. The mechanical properties of collagen fascicles after being loaded into the culture media were determined using tensile tester, and resultant stress–strain curves, tangent modulus, tensile strength, and strain at failure values were compared with those in a non-loaded and non-cultured control group of fascicles. The tangent modulus and tensile strength of the collagen fascicles increased with the increasing remodeling load after two days of culture. However, these values gradually decreased with the increasing culture period compared with the control group. According to the results obtained in this study, the mechanical properties of collagen fascicles were improved by loading at two days of culture, most likely due to the remodeling of collagen fibers. However, after a period of remodeling, local strains on the collagen fibrils increased, and finally, the collagen fibrils broke down, decreasing the mechanical properties of the tissue.

scholarly journals Corneal Biomechanical Properties after FS-LASIK with Residual Bed Thickness Less Than 50% of the Original Corneal Thickness

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Haixia Zhang ◽  
Muhammad Ahmad Khan ◽  
Di Zhang ◽  
Xiao Qin ◽  
Ding Lin ◽  
...  
Keyword(s):  
Elastic Moduli ◽  
Corneal Thickness ◽  
Tensile Tests ◽  
Biomechanical Properties ◽  
Uniaxial Tensile ◽  
Stress Region ◽  
Bed Thickness ◽  
Limit Stress ◽  
The Right ◽  
Corneal Biomechanical Properties

Background. The changes in corneal biomechanical properties after LASIK remain an unknown but important topic for surgical design and prognostic evaluation. This study aims to observe the postoperative corneal biomechanical properties one month after LASIK with amount of corneal cutting (ACC) greater than 50% of the central corneal thickness (CCT). Methods. FS-LASIK was performed in 10 left rabbit eyes with ACC being 60% (L60) and 65% (L65) of the CCT, while the right eyes (R) were the control. After 4 weeks, rabbits were executed and corneal strip samples were prepared for uniaxial tensile tests. Results. At the same strain, the stresses of L65 and L60 were larger than those of R. The elastic moduli of L60 and L65 were larger than those of R when the stress was 0.02 MPa, while they began to be less than those of R when stress exceeds the low-stress region. After 10 s relaxation, the stress of specimens L65, L60, and R increased in turn. Conclusion. The elastic moduli of the cornea after FS-LASIK with ACC greater than 50% of the CCT do not become less under normal rabbit IOP. The limit stress grows with the rise of ACC when relaxation becomes stable.

scholarly journals Investigation of corneal biomechanical properties using the CORVIS ST device (Oculus, Germany) in patients with myopia and myopic astigmatism

2020 ◽  
pp. 20-28
Author(s):  
V.D. Antonuk ◽  
◽  
T.S. Kuznetsova ◽  
Keyword(s):  
Excimer Laser ◽  
Refractive Surgery ◽  
Corneal Thickness ◽  
Biomechanical Properties ◽  
Corvis St ◽  
Vision Correction ◽  
Laser Vision ◽  
Laser Refractive Surgery ◽  
Myopic Astigmatism ◽  
Corneal Biomechanical Properties

Purpose. To evaluate the corneal biomechanical properties using the CORVIS ST device (Oculus, Germany) in patients with myopia and myopic astigmatism with intact cornea as well as in patients with myopia and myopic astigmatism who underwent excimer laser refractive surgery using femtolaser or microkeratome. Material and methods. Totally the study included 65 patients aged 18 years to 56 years with myopia and myopic astigmatism of various degrees were examined. They were scheduled for excimer laser refractive surgery after laser refractive surgery in different periods from 5 days to 5 years. Among the additional methods of examination, all patients were measured the biomechanical properties of the cornea using a CORVIS ST device (Oculus, Germany). Results. After excimer laser refractive surgery performing for myopia and myopic astigmatism correction, indicators of the corneal biomechanical properties, namely indicators describing stiffness and elasticity were changed, as well as IOP indicators. Conclusion. The biomechanical properties of the cornea, such as stiffness and elasticity, can be assessed using the CORVIS ST device (Oculus, Germany). After excimer laser vision correction of myopia and myopic astigmatism, corneal stiffness and elasticity decreases. IOP value in patients after excimer laser correction of myopia and myopic astigmatism decreases. It is associated with a decrease in corneal thickness but is not associated with a true decrease in IOP. Key words: biomechanical properties of the cornea, refractive surgery, excimer laser vision correction, femtolaser vision correction, myopia, myopic astigmatism.

scholarly journals P.096 Evaluation of Poly Vinyl Alcohol Cryogel (PVA-C) composites for mimicking biomechanical properties of the lumbar interverterbral disc

2017 ◽  
Vol 44 (S2) ◽  
pp. S38-S38
Author(s):  
BH Wang ◽  
K Gurr ◽  
C Bailey ◽  
G Campbell
Keyword(s):  
Elastic Modulus ◽  
Stress Relaxation ◽  
Annulus Fibrosus ◽  
Symptom Relief ◽  
Biomechanical Properties ◽  
Poly Vinyl Alcohol ◽  
Solution Synthesis ◽  
Lumbar Intervertebral Disc ◽  
Reinforced Composite ◽  
Simple Compression

Background: Current lumbar intervertebral disc prostheses provide suboptimal symptom relief with little natural load-cushioning. PVA-C is a promising biocompatible material, and our previous study finds that it can closely mimic the properties of nucleus pulposus. However, pure PVA-C does not possess adequate stiffness to mimic the annulus fibrosus. Methods: Composite particle-reinforced PVA-C formulations were tested to identify methods that could increase the elastic modulus. This included: sephadex, hydroxyapatite (stock) and hydroxyapatite (in-solution synthesis). All formulations were tested using 15% PVA-C and 5% reinforcing agent. Indentation and durometer tests were performed as well as simple compression, compressive stress relaxation and creep. Results: Indentation and durometer results did not clearly reveal any specific formulations that significantly improved stiffness. The addition of in-solution synthesized hydroxyapatite resulted in 1.15 to 2 time increase in elastic modulus (0.3-0.9 MPa) and associated decrease in stress relaxation and creep. The addition of stock hydroxyapatite and spehadex (G100f and G50sf) lowered the elastic modulus and increased stress relaxation and creep. Conclusions: In-solution synthesized hydroxyapatite is the only particle-reinforced composite PVA-C formulation that exhibited greater stiffness than pure PVA-C. The elastic modulus will need to be increased by 5-10x to adequately mimic the annulus fibrosus. A fiber-reinforced composite will likely be needed to accomplish this.

scholarly journals Experimental Analysis of Plantar Fascia Mechanical Properties in Subjects with Foot Pathologies

2021 ◽  
Vol 11 (4) ◽  
pp. 1517
Author(s):  
Silvia Todros ◽  
Carlo Biz ◽  
Pietro Ruggieri ◽  
Piero G. Pavan
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Stress Relaxation ◽  
Healthy Subjects ◽  
Human Subjects ◽  
Fibrous Tissue ◽  
Plantar Fascia ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Foot Biomechanics

Plantar Fascia (PF) is a fibrous tissue that plays a key role in supporting the foot arch; it can be affected by several pathologies that can alter foot biomechanics. The present study aims at investigating the mechanical behavior of PF and evaluating possible correlations between mechanical properties and specific pathologies, namely diabetes and plantar fibromatosis (Ledderhose syndrome). PF samples were obtained from 14 human subjects, including patients with Ledderhose syndrome, patients affected by diabetes and healthy subjects. Mechanical properties of PF tissues were evaluated on three samples from each subject, by cyclic uniaxial tensile tests up to 10% of maximum strain and stress relaxation tests for 300 s, in hydrated conditions at room temperature. In tensile tests, PF exhibits non-linear stress–strain behavior, with a higher elastic modulus (up to 25–30 MPa) in patients affected by Ledderhose syndrome and diabetes with respect to healthy subjects (elastic modulus 10 ÷ 14 MPa). Stress-relaxation tests show that PF of patients affected by Ledderhose syndrome and diabetes develop more intense viscous phenomena. The results presented in this work represent the first experimental data on the tensile mechanical propertied of PF in subjects with foot diseases and can provide an insight on foot biomechanics in pathological conditions.

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