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Villegas L, Zvietcovich F, Marcos S, Birkenfeld JS. Revealing regional variations in scleral shear modulus in a rabbit eye model using multi-directional ultrasound optical coherence elastography. Sci Rep 2024; 14:21010. [PMID: 39251655 PMCID: PMC11384758 DOI: 10.1038/s41598-024-71343-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2024] [Accepted: 08/27/2024] [Indexed: 09/11/2024] Open
Abstract
The mechanical properties of the sclera play a critical role in supporting the ocular structure and maintaining its shape. However, non-invasive measurements to quantify scleral biomechanics remain challenging. Recently introduced multi-directional optical coherence elastography (OCE) combined with an air-coupled ultrasound transducer for excitation of elastic surface waves was used to estimate phase speed and shear modulus in ex vivo rabbit globes (n = 7). The scleral phase speed (12.1 ± 3.2 m/s) was directional-dependent and higher than for corneal tissue (5.9 ± 1.4 m/s). In the tested locations, the sclera proved to be more anisotropic than the cornea by a factor of 11 in the maximum of modified planar anisotropy coefficient. The scleral shear moduli, estimated using a modified Rayleigh-Lamb wave model, showed significantly higher values in the circumferential direction (65.4 ± 31.9 kPa) than in meridional (22.5 ± 7.2 kPa); and in the anterior zone (27.3 ± 9.3 kPa) than in the posterior zone (17.8 ± 7.4 kPa). The multi-directional scanning approach allowed both quantification and radial mapping of estimated parameters within a single measurement. The results indicate that multi-directional OCE provides a valuable non-invasive assessment of scleral tissue properties that may be useful in the development of improved ocular models, the evaluation of potential myopia treatment strategies, and disease characterization and monitoring.
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Affiliation(s)
- Lupe Villegas
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
| | - Fernando Zvietcovich
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain
- Department of Engineering, Pontificia Universidad Católica del Peru, Lima, Peru
| | - Susana Marcos
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain
- The Center for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, Rochester, NY, USA
| | - Judith S Birkenfeld
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain
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Zhang Y, Wang Y, Han X, Luo J, Lin C, Zhang Q, He X. Characterization of Limbus Biomechanical Properties Using Optical Coherence Elastography. JOURNAL OF BIOPHOTONICS 2024:e202400275. [PMID: 39225054 DOI: 10.1002/jbio.202400275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2024] [Revised: 07/31/2024] [Accepted: 08/19/2024] [Indexed: 09/04/2024]
Abstract
The elasticity of the limbus is crucial for ocular health, yet it remains inadequately explored. This study employs acoustic radiation force optical coherence elastography (ARF-OCE) to evaluate the biomechanical properties of the limbus under varying intraocular pressures. The method was validated using a heterogeneous phantom and subsequently applied to ex vivo porcine limbus samples. Elastic wave velocity at specific locations within the limbus was calculated, and the corresponding Young's modulus values were obtained. Spatial elasticity distribution maps were generated by correlating Young's modulus values with their respective locations in the two-dimensional structural images. The results indicate that ARF-OCE enhances the understanding of limbus biomechanical behavior and holds potential for diagnosing regional variations caused by ocular diseases.
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Affiliation(s)
- Yubao Zhang
- Key Laboratory for Optoelectronic Information Perception and Instrumentation of Jiangxi Province, Nanchang Hangkong University, Nanchang, People's Republic of China
| | - Yue Wang
- Faculty of Artificial Intelligence in Education, Central China Normal University, Wuhan, People's Republic of China
- Jiangxi Xinjian No.2 Secondary School, Nanchang, People's Republic of China
| | - Xiao Han
- Key Laboratory for Optoelectronic Information Perception and Instrumentation of Jiangxi Province, Nanchang Hangkong University, Nanchang, People's Republic of China
| | - Jiahui Luo
- Key Laboratory for Optoelectronic Information Perception and Instrumentation of Jiangxi Province, Nanchang Hangkong University, Nanchang, People's Republic of China
| | - Chuanqi Lin
- Key Laboratory for Optoelectronic Information Perception and Instrumentation of Jiangxi Province, Nanchang Hangkong University, Nanchang, People's Republic of China
| | - Qin Zhang
- Key Laboratory for Optoelectronic Information Perception and Instrumentation of Jiangxi Province, Nanchang Hangkong University, Nanchang, People's Republic of China
| | - Xingdao He
- Key Laboratory for Optoelectronic Information Perception and Instrumentation of Jiangxi Province, Nanchang Hangkong University, Nanchang, People's Republic of China
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Chao C, Lema C, Redfern R, Richdale K. Changes in tear glucose and insulin concentrations following an oral glucose tolerance test. Clin Exp Optom 2023; 106:752-758. [PMID: 35977531 DOI: 10.1080/08164622.2022.2111204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Revised: 07/15/2022] [Accepted: 08/03/2022] [Indexed: 10/15/2022] Open
Abstract
CLINICAL RELEVANCE Tear glucose and insulin are responsible for the health of the ocular surface; thus, it is important for clinicians to detect the tear glucose and insulin using point-of-care methods. AIM To determine if changes in blood glucose and insulin levels following an oral glucose tolerance test are reflected in the tears and to test the association between gene expression and tear insulin and glucose. METHODS Twenty healthy young adults were enrolled. Basal tears and peripheral blood samples were collected to assess glucose and insulin using a point-of-care glucometer and ELISA assays in fasted subjects, and 1.5 and 3 h after an oral glucose challenge. Conjunctival impression cytology was collected to determine gene expression of insulin receptor (INSR) and glucose transporters (GLUT1 and GLUT4). Changes were examined using non-parametric one-way ANOVA. Spearman tests were conducted to examine associations between variables. RESULTS Glucose and insulin levels increased 1.5 h after oral glucose in both blood (P < 0.001) and tears (P < 0.049) and returned to near baseline values after 3 h. There was a positive correlation between glucose levels in the blood and tears (rho = 0.57, P < 0.001), but not between blood and tear insulin levels (P = 0.18). Glucose and insulin levels in tears were correlated (rho = 0.32, P = 0.048). Tear glucose concentration at 1.5 h after oral glucose was associated with INSR expression (rho = 0.49, P = 0.03), and there was a trend with GLUT1 (P = 0.06) but not GLUT4. CONCLUSION Tear glucose reflected blood glucose levels but this correspondence was not observed for insulin. Further studies are required to determine the role of glucose and insulin on the ocular surface in both health and diabetes.
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Affiliation(s)
- Cecilia Chao
- College of Optometry, University of Houston, Houston, TX, USA
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
| | - Carolina Lema
- College of Optometry, University of Houston, Houston, TX, USA
| | - Rachel Redfern
- College of Optometry, University of Houston, Houston, TX, USA
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Makarem A, Abass A, Bao F, Elsheikh A. Assessment of age-related change of the ocular support system. Front Bioeng Biotechnol 2023; 11:1146828. [PMID: 37492801 PMCID: PMC10363727 DOI: 10.3389/fbioe.2023.1146828] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 06/23/2023] [Indexed: 07/27/2023] Open
Abstract
To estimate the material stiffness of the orbital soft tissue in human orbits using an inverse numerical analysis approach, which could be used in future studies to understand the behaviour under dynamic, non-contact tonometry or simulate various ophthalmological conditions. Clinical data were obtained for the left eye of 185 Chinese participants subjected to a complete ophthalmic examination, including tests by the Corvis ST and Pentacam. 185 numerical models of the eye globes were built with idealised geometry of the sclera while considering the corneal tomography measured by the Pentacam. The models were extended to include representations of the orbital soft tissue (OST), which were given idealised geometry. The movement of the whole eye in response to an air-puff directed at the central cornea was examined and used in an inverse analysis process to estimate the biomechanical stiffness parameters of the OST. The results indicated a weak correlation of E t with the progression of age, regardless of the stress at which E t was calculated. However, there was evidence of significant differences in E t between some of the age groups. There was statistical evidence of significant differences between E t in the age range 20< years < 43 relative to E t in OST with age ranges 43< years < 63 (p = 0.022) and 63< years < 91 (p = 0.011). In contrast, E t in OST with age ranges 43< years < 63 and 63< years < 91 were not significantly different (p = 0.863). The optimised mechanical properties of the OST were found to be almost four times stiffer than properties of fatty tissue of previous experimental work. This study consolidated previous findings of the role of extraocular muscles on the ocular suppor system. In addition, the rotation of the globe during corvis loading is suggested to be of posterior components of the globe and shall be further investigated.
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Affiliation(s)
- Ahmed Makarem
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Ahmed Abass
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- Faculty of Engineering, Port Said University, Port Fouad, Egypt
| | - Fangjun Bao
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, China
- National Institute for Health Research (NIHR), Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust, UCL Institute of Ophthalmology, London, United Kingdom
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Marzec E, Pięta P, Olszewski J. Dielectric properties of the non-glycated and in vitro methylglyoxal-glycated cornea of the rabbit eye. Bioelectrochemistry 2023; 150:108333. [PMID: 36463591 DOI: 10.1016/j.bioelechem.2022.108333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Revised: 11/21/2022] [Accepted: 11/27/2022] [Indexed: 12/02/2022]
Abstract
The dielectric properties of the non-glycated and in vitro methylglyoxal-glycated cornea of the rabbit eye were tested in the frequency range of 200 Hz to 100 kHz of the electric field and at temperatures of 25 to 140 °C. The denaturation temperature (Td) for the non-glycated cornea and the non-enzymatically glycated cornea are approximately 45 and 55 °C, respectively. The mechanism of proton conduction up to Td in a glycated cornea requires more energy, i.e. more than twice the activation energy (ΔH) than in non-glycated tissue. The dielectric spectra for both examined tissues showed the same characteristic frequency of about 7 kHz assigned to the orientation relaxation time of the polar side groups inside the corneal stroma. These results may be useful in the surgical treatment of the cornea using conductive keratoplasty and in tissue engineering for clinical applications to regenerate this tissue. The medical use of these physico-biological techniques is important because the human cornea protects all eye tissues from various environmental factors.
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Affiliation(s)
- E Marzec
- Department of Bionics and Experimental Medical Biology, Poznan University of Medical Sciences, Parkowa 2, 60-775 Poznań, Poland.
| | - P Pięta
- Department of Bionics and Experimental Medical Biology, Poznan University of Medical Sciences, Parkowa 2, 60-775 Poznań, Poland
| | - J Olszewski
- Department of Bionics and Experimental Medical Biology, Poznan University of Medical Sciences, Parkowa 2, 60-775 Poznań, Poland
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Zhao Y, Hu G, Yan Y, Wang Z, Liu X, Shi H. Biomechanical analysis of ocular diseases and its in vitro study methods. Biomed Eng Online 2022; 21:49. [PMID: 35870978 PMCID: PMC9308301 DOI: 10.1186/s12938-022-01019-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2022] [Accepted: 07/13/2022] [Indexed: 12/25/2022] Open
Abstract
Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the structure and function of ocular tissue is beneficial to reveal the pathological processes. Studying the pathogenesis of various ocular diseases will be helpful for the diagnosis and treatment of ocular diseases. We provide a critical review of recent biomechanical analysis of ocular diseases including glaucoma, high myopia, and diabetes. And try to summarize the research about the biomechanical changes in ocular tissues (e.g., optic nerve head, sclera, cornea, etc.) associated with those diseases. The methods of ocular biomechanics research in vitro in recent years are also reviewed, including the measurement of biomechanics by ophthalmic equipment, finite element modeling, and biomechanical analysis methods. And the preparation and application of microfluidic eye chips that emerged in recent years were summarized. It provides new inspiration and opportunity for the pathogenesis of eye diseases and personalized and precise treatment.
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Ohn K, Noh YH, Moon JI, Jung Y. Measurement of corneal biomechanical properties in diabetes mellitus using the Corvis ST. Medicine (Baltimore) 2022; 101:e30248. [PMID: 36086751 PMCID: PMC10980441 DOI: 10.1097/md.0000000000030248] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 07/13/2022] [Indexed: 11/26/2022] Open
Abstract
We sought to assess changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with those among healthy controls using Corvis ST (CST). The study group included 209 eyes from healthy control subjects and 33 eyes from diabetic subjects, respectively. Following an ophthalmological examination, measurements with CST were taken. Additionally, hemoglobin A1c and blood glucose values were collected. Results were then compared to those of the control group after adjusting for potential confounding factors, including age-, intraocular pressure (IOP)-, central corneal thickness (CCT)-, spherical equivalent (SE)- and axial length (AL). After adjusting for potential confounding factors, including the age, IOP, CCT, SE, and AL, patients with DM presented significantly lower whole-eye movement (WEM) (ms) values than patients without DM (21.71 ± 0.84 vs. 22.15 ± 0.64 ms; P < .001). There was a significant and negative correlation between WEM (ms) and hemoglobin A1c in DM patients (r = -0.733; P = .001). In univariate and multivariate general linear mixed model (GLMM) analyses, IOP (P < .001 and P < .001, respectively) and the presence of DM (P = .001 and P < .001, respectively) significantly affected WEM (ms). In DM, significant changes in corneal biomechanical properties were detectable. The DM group showed significantly less deformable cornea and sclera than did the normal controls, even after adjusting for age, IOP, CCT, SE, and AL. These findings may cause misinterpretation of IOP measurements in diabetic patients. Therefore, the measurement of corneal biomechanics should be taken into consideration in clinical practice.
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Affiliation(s)
- Kyoung Ohn
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Young Ho Noh
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Jung Il Moon
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Younhea Jung
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
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Zheng X, Weng Y, Wang Y, Xin Y, Wu J, Ziad Masoud Abu Said A, Nguelemo Mayopa K, Akiti S, Li X, Wang C, Wang J, Eliasy A, Bao F, Chen S, Elsheikh A. Long-term Effects of Riboflavin Ultraviolet-A-Induced CXL With Different Irradiances on the Biomechanics of In Vivo Rabbit Corneas. J Refract Surg 2022; 38:389-397. [PMID: 35686711 DOI: 10.3928/1081597x-20220425-01] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To evaluate the long-term effects of ultraviolet-A corneal cross-linking (CXL) with different irrandiances on the biomechanical properties of rabbit corneas and the corresponding changes in stromal microstructure. METHODS The study involved the left eyes of 85 healthy white Japanese rabbits, randomly divided into five groups (n = 16 to 18 each). After removing the epithelium, the first four groups were exposed to riboflavin (0.22% concentration by volume) and ultraviolet-A (370 nm) at different CXL irradiations but with the same total dose (5.4 J/cm2). The four groups were defined as standard CXL (SCXL; 3 mW/cm2 for 30 minutes, n = 17), accelerated CXL1 (ACXL1; 9 mW/cm2 for 10 minutes, n = 16), accelerated CXL2 (ACXL2; 18 mW/cm2 for 5 minutes, n = 17), and accelerated CXL3 (ACXL3; 30 mW/cm2 for 3 minutes, n = 17). The control group (n = 18) was treated with riboflavin without ultraviolet-A exposure. Nine months after CXL, 10 corneas from each group were tested ex vivo under inflation, and the tangent modulus (Et) was estimated using an inverse analysis process. The remaining six to eight specimens in each group were examined by electron microscopy to determine the mean fibril diameter and interfibrillar spacing. RESULTS The SCXL and ACXL1 groups showed statistically significant differences in Et at all stresses (0.005, 0.010, and 0.015 MPa) analyzed compared to the control group (all P < .01), but the differences were non-significant in the ACXL3 group (P = 1.000, .785, and .679, respectively). For the ACXL2 group, there was no statistical difference in Et under the low stress of 0.005 MPa (P = .155), but the differences became significant at 0.010 and 0.015 MPa when compared with the control group (all P < .05). CONCLUSIONS CXL had a significant effect on corneal biomechanics in both standard and accelerated procedures. However, standard CXL was the most effective, and this effectiveness decreased gradually with increasing ultraviolet-A power intensity. [J Refract Surg. 2022;38(6):389-397.].
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Wang J, Zhao Y, Yu AY, Wu J, Zhu M, Jiang M, Li X, Zhu D, Zhang P, Zheng X, Bao F, Elsheikh A. Effect of travoprost, latanoprost and bimatoprost PGF2α treatments on the biomechanical properties of in-vivo rabbit cornea. Exp Eye Res 2022; 215:108920. [PMID: 35007519 DOI: 10.1016/j.exer.2022.108920] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Revised: 12/07/2021] [Accepted: 12/31/2021] [Indexed: 11/04/2022]
Abstract
Prostaglandin F2α analogues (PGF2α), one of the most commonly prescribed classes of hypotensive agents, could decrease collagen fibril density and remodel the extracellular matrix in cornea. We hypothesized that PGF2α's would induce corneal softening, reduce the accuracy of intraocular pressure (IOP) measurement and lead to uncertainty in the effectiveness of the therapy. We determined the stress-strain behavior of rabbit cornea after PGF2α usage and evaluated the effect of biomechanical changes associated with PGF2α treatment on IOP measurements by Goldmann Applanation Tonometry (GAT). The tangent modulus decreased after PGF2α treatment, while the stromal interfibrillar spacing increased. PGF2α was shown to also affect the lateral eye with lower effect, which did not undergo direct eyedrop treatment. Significant decreases in the numerical predictions of GAT-IOP were predicted in all treated groups relative to control groups. Different PGF2α's (travoprost, latanoprost and bimatoprost) were associated with different extents of reduction in tissue stiffness and changes in corneal microstructure. PGF2α-induced changes in corneal mechanical properties could reduce the accuracy of IOP measurement and may cause an overestimation of the effect of PGF2α in lowering IOP, possibly leading to uncertainties in glaucoma management.
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Affiliation(s)
- JunJie Wang
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China; The Institute of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, 325027, China
| | - YiPing Zhao
- Department of Ophthalmology, Ninth People's Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, 200025, China
| | - AYong Yu
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China
| | - Jie Wu
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China
| | - ManMan Zhu
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China
| | - MuChen Jiang
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China
| | - Xuefei Li
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China
| | - DaTian Zhu
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China
| | - PeiPei Zhang
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China
| | - XiaoBo Zheng
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China; The Institute of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, 325027, China.
| | - FangJun Bao
- Eye Hospital, Wenzhou Medical University, Wenzhou, 325027, China; The Institute of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, 325027, China.
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, L69 3GH, UK; National Institute for Health Research (NIHR) Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK; Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, China
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Zhang D, Zhang H, Tian L, Zheng Y, Fu C, Zhai C, Li L. Exploring the Biomechanical Properties of the Human Cornea In Vivo Based on Corvis ST. Front Bioeng Biotechnol 2021; 9:771763. [PMID: 34869287 PMCID: PMC8637821 DOI: 10.3389/fbioe.2021.771763] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/21/2021] [Indexed: 11/18/2022] Open
Abstract
Purpose: The aim of this study was to provide a method to determine corneal nonlinear viscoelastic properties based on the output data of corneal visualization Scheimpflug technology (Corvis ST). Methods: The Corvis ST data from 18 eyes of 12 healthy humans were collected. Based on the air-puff pressure and the corneal displacement from the Corvis ST test of normal human eyes, the work done by the air-puff attaining the whole corneal displacement was obtained. By applying a visco-hyperelastic strain energy density function of the cornea, in which the first-order Prony relaxation function and the first-order Ogden strain energy were employed, the corneal strain energy during the Corvis ST test was calculated. Then the work done by the air-puff attaining the whole corneal displacement was completely regarded as the strain energy of the cornea. The identification of the nonlinear viscoelastic parameters was carried out by optimizing the sum of difference squares of the work and the strain energy using the genetic algorithm. Results: The visco-hyperelastic model gave a good fit to the data of corneal strain energy with time during the Corvis ST test (R2 > 0.95). The determined Ogden model parameter μ ranged from 0.42 to 0.74 MPa, and α ranged from 32.76 to 55.63. The parameters A and τ in the first-order Prony function were 0.09–0.36 and 1.21–1.95 ms, respectively. Conclusion: It is feasible to determine the corneal nonlinear viscoelastic properties based on the corneal contour information and air-puff pressure of the Corvis ST test.
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Affiliation(s)
- Di Zhang
- Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, China.,School of Biomedical Engineering, Capital Medical University, Beijing, China
| | - Haixia Zhang
- Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, China.,School of Biomedical Engineering, Capital Medical University, Beijing, China
| | - Lei Tian
- Beijing Tongren Eye Center, Beijing Tongren Hospital, Beijing Ophthalmology and Visual Sciences Key Laboratory, Beijing Institute of Ophthalmology, Capital Medical University, Beijing, China.,Beijing Advanced Innovation Center for Big Data-Based Precision Medicine, Beijing Tongren Hospital, Beihang University and Capital Medical University, Beijing, China
| | - Yan Zheng
- Beijing Tongren Eye Center, Beijing Tongren Hospital, Beijing Ophthalmology and Visual Sciences Key Laboratory, Capital Medical University, Beijing, China
| | - Caiyun Fu
- Beijing Tongren Eye Center, Beijing Tongren Hospital, Beijing Ophthalmology and Visual Sciences Key Laboratory, Capital Medical University, Beijing, China
| | - Changbin Zhai
- Beijing Tongren Eye Center, Beijing Tongren Hospital, Beijing Ophthalmology and Visual Sciences Key Laboratory, Capital Medical University, Beijing, China
| | - Lin Li
- Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, China.,School of Biomedical Engineering, Capital Medical University, Beijing, China
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Bao F, Chen W, Zheng X, Miao Y, Zhu M, Akiti S, Li Y, Weng Z, Wang J, Zhang P, Chen S, Elsheikh A. Changes in Corneal Biomechanical Properties in PRK Followed by Two Accelerated CXL Energy Doses in Rabbit Eyes. J Refract Surg 2021; 37:853-860. [PMID: 34914559 DOI: 10.3928/1081597x-20210830-03] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE To evaluate whether photorefractive keratectomy (PRK) combined with the two commonly delivered energy doses in accelerated corneal cross-linking (A-CXL) could help the cornea maintain its preoperative stiffness level. METHODS A total of 72 corneas of 36 healthy white Japanese rabbits were randomly divided into four equal groups. The groups included an untreated control group and three that had undergone PRK. After tissue ablation, one of the latter three groups (PRK group) was left untreated, whereas the other two were exposed to riboflavin (0.22% concentration by volume) and ultraviolet-A (370 nm) with the same irradiation (30 mW/cm2) but different CXL energy doses of 1.8 J/cm2 (PXL group) and 2.7 J/cm2 (PXH group). Dynamic Scheimpflug analyzer (Corvis ST; Oculus Optikgeräte GmbH) measurements of stiffness parameter at first applanation (SP-A1), Stress-Strain Index (SSI), and other dynamic corneal response parameters were taken 3 days preoperatively and 1 month postoperatively. Subsequently, ex vivo inflation testing was performed and the tangent modulus of each specimen was estimated using an inverse analysis process. RESULTS In comparison to the control group, the tangent modulus at a stress of 10 kPa decreased by 8.9% in the PRK group and increased by 10.6% and 22.4% in the PXL and PXH groups, respectively. SP-A1 decreased postoperatively in the PRK group (P < .05), indicating an overall stiffness reduction of -7.4, -3.5, and -5.3 mm Hg/mm in PRK, PXL, and PXH groups, respectively. The material stiffness parameter SSI remained almost unchanged in the PRK group (P = .989), increased slightly in the PXL group (8.3%, P = .077), and increased significantly in the PXH group (11.1%) (P < .05). CONCLUSIONS Biomechanical deterioration following PRK was significant and could not be fully compensated for by ACXL with either 1.8 or 2.7 J/cm2 doses. The increased value of corneal overall stiffness was higher in A-CXL with 2.7 J/cm2 energy than with 1.8 J/cm2 energy. [J Refract Surg. 2021;37(12):853-860.].
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Aboulatta A, Abass A, Makarem A, Eliasy A, Zhou D, Chen D, Liu X, Elsheikh A. Experimental evaluation of the viscoelasticity of porcine vitreous. J R Soc Interface 2021; 18:20200849. [PMID: 33530856 DOI: 10.1098/rsif.2020.0849] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
This study aims to estimate the material properties of the porcine vitreous while testing it in close to its natural physiological conditions. Eighteen porcine eyes were tested within 48 h post-mortem. A custom-built computer-controlled test rig was designed to support, load and monitor the behaviour of eye globes while being subjected to dynamic rotation cycles mimicking saccade eye movement. Specimens were glued to the base of a container, surrounded by gelatin, frozen and cut in half to expose the vitreous. After thawing, the container was subjected to concentric dynamic rotations of up to 5°, 10° or 15°, while taking 50 MP photos of the specimen every 2 ms. The images were analysed by a digital image correlation algorithm to trace the movement of marked points on the vitreous surface with different radii from the centre of the posterior chamber. The initial camera image was used in building a finite-element model of the test set-up, which was used in an inverse analysis exercise to estimate the material properties of the vitreous. Angular displacements of the monitored points were up to 3.3°, 4.1° and 3.9° in response to eye rotations of 5°, 10° and 15°, respectively. With the experimental relationships between eye rotation and angular displacements used as target behaviour, the inverse analysis exercise estimated the initial shear modulus, the long-term shear modulus and the viscoelastic decay constant of the porcine vitreous as 2.10 ± 0.15 Pa, 0.50 ± 0.04 Pa and 1.20 ± 0.09 s-1, respectively. Consideration of the viscoelasticity of the vitreous was essential to represent its experimental behaviour. Testing the vitreous in close to its normal physiological conditions produced estimations of the initial shear modulus and long-term shear modulus that were, respectively, smaller and larger than reported values (Zimberlin et al. 2010 Soft Matter 6, 3632-3635. (doi:10.1039/b925407b), Liu et al. 2013 J. Biomech. 46, 1321-7. (doi:10.1016/j.jbiomech.2013.02.006), Rossi et al. 2011 Invest. Ophthalmol. Vis. Sci. 52, 3994-4002. (doi:10.1167/iovs.10-6477)).
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Affiliation(s)
- Ali Aboulatta
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Ahmed Abass
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Ahmed Makarem
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Ashkan Eliasy
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Dong Zhou
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Duo Chen
- Key Laboratory for Biomechanics and Mechanobiology of the Ministry of Education, School of Biological Science and Medical Engineering, Beihang University, People's Republic of China
| | - Xiaoyu Liu
- Key Laboratory for Biomechanics and Mechanobiology of the Ministry of Education, School of Biological Science and Medical Engineering, Beihang University, People's Republic of China.,Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing 100083, People's Republic of China
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK.,Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing 100083, People's Republic of China.,NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
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14
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Zhu R, Zheng X, Guo L, Zhao Y, Wang Y, Wu J, Yu AY, Wang J, Bao F, Elsheikh A. Biomechanical Effects of Two Forms of PGF2α on Ex-vivo Rabbit Cornea. Curr Eye Res 2020; 46:452-460. [PMID: 32795212 DOI: 10.1080/02713683.2020.1805771] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE To investigate the biomechanical effects of two synthetic prostaglandin F2α analogues (PGF2α), namely Travoprost and Tafluprost, on the ex-vivo rabbit cornea. MATERIALS AND METHODS Ninety-six eyes of 48 Japanese white rabbits were divided into 3 equal groups randomly; the Travoprost treated group (Tra), the Tafluprost treated group (Taf) and the control group (Co). Eyes in Tra and Taf groups were preserved in storage medium for 10 days with 1:10 Travoprost and Tafluprost diluents, respectively; while the Co eyes were preserved in a similar but PGF2α-free medium. Twenty-four corneas of each group were tested under inflation conditions with up to 30 mmHg posterior pressure. The pressure-deformation data obtained experimentally were used in an inverse analysis process to derive the stress-strain behavior of the tissue, using which the tangent modulus, a direct measure of the tissue's material stiffness, was calculated. The remaining eight specimens of each group were analyzed using electron microscopy for fibril diameter and interfibrillar spacing. RESULTS Although the central corneal thickness increased significantly in the three groups after storage (p < .01), it was similar in all groups both before (p = .598) and after storage (p = .181). After treatment with Travoprost and Tafluprost, the corneas exhibited lower tangent modulus (by 29.2% and 29.8%, respectively, at 6 kPa stress) and larger stromal interfibril spacing (by 21.9% and 23.6%) compared with the control group. There was no significant change in fibril diameter with either Travoprost or Tafluprost treatment (p = .769). CONCLUSIONS The results demonstrated significant reductions in tangent modulus and increases in interfibrillar spacing, which were of similar magnitudes, with the application of two different forms of PGF2α.
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Affiliation(s)
- Rong Zhu
- Eye Hospital, Wenzhou Medical University, Wenzhou, China
| | - XiaoBo Zheng
- Eye Hospital, Wenzhou Medical University, Wenzhou, China.,The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, China
| | - LiLi Guo
- Eye Hospital, Wenzhou Medical University, Wenzhou, China
| | - YiPing Zhao
- Department of Ophthalmology, Ninth People's Hospital, Shanghai JiaoTong University School of Medicine, Shanghai, China
| | - Yuan Wang
- Eye Hospital, Wenzhou Medical University, Wenzhou, China
| | - Jie Wu
- Eye Hospital, Wenzhou Medical University, Wenzhou, China
| | - AYong Yu
- Eye Hospital, Wenzhou Medical University, Wenzhou, China
| | - JunJie Wang
- Eye Hospital, Wenzhou Medical University, Wenzhou, China.,The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, China
| | - FangJun Bao
- Eye Hospital, Wenzhou Medical University, Wenzhou, China.,The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, China
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, UK.,National Institute for Health Research (NIHR) Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK.,Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, China
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15
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Priyadarsini S, Whelchel A, Nicholas S, Sharif R, Riaz K, Karamichos D. Diabetic keratopathy: Insights and challenges. Surv Ophthalmol 2020; 65:513-529. [PMID: 32092364 PMCID: PMC8116932 DOI: 10.1016/j.survophthal.2020.02.005] [Citation(s) in RCA: 64] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Revised: 02/10/2020] [Accepted: 02/11/2020] [Indexed: 12/11/2022]
Abstract
Ocular complications from diabetes mellitus are common. Diabetic keratopathy, the most frequent clinical condition affecting the human cornea, is a potentially sight-threatening condition caused mostly by epithelial disturbances that are of clinical and research attention because of their severity. Diabetic keratopathy exhibits several clinical manifestations, including persistent corneal epithelial erosion, superficial punctate keratopathy, delayed epithelial regeneration, and decreased corneal sensitivity, that may lead to compromised visual acuity or permanent vision loss. The limited amount of clinical studies makes it difficult to fully understand the pathobiology of diabetic keratopathy. Effective therapeutic approaches are elusive. We summarize the clinical manifestations of diabetic keratopathy and discuss available treatments and up-to-date research studies in an attempt to provide a thorough overview of the disorder.
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Affiliation(s)
- S Priyadarsini
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - A Whelchel
- Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - S Nicholas
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - R Sharif
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - K Riaz
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - D Karamichos
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA; Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
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16
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Wang X, Xu G, Wang W, Wang J, Chen L, He M, Chen Z. Changes in corneal biomechanics in patients with diabetes mellitus: a systematic review and meta-analysis. Acta Diabetol 2020; 57:973-981. [PMID: 32201905 DOI: 10.1007/s00592-020-01481-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 01/10/2020] [Indexed: 02/07/2023]
Abstract
AIMS To determine the changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with controls. METHODS Pertinent studies were identified by comprehensively search of PubMed, Embase, the Web of Science, the Cochrane Library, Scopus, the China National Knowledge Infrastructure and the Chinese biomedical disc (CBM) databases. Pooling analyses by random models using the D-L method were performed for corneal hysteresis (CH), the corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated intraocular pressure (IOPg). RESULTS A total of 15 studies were included in the final analysis, involving 1506 eyes in the diabetic group and 2190 eyes in the control group. The diabetic group had significantly higher CH, CRF, IOPg and IOPcc values than the control group. The pooled mean differences were 1.34 mmHg (95% confidence interval [CI] 0.60-2.08 mmHg, P < 0.001) for IOPg and 0.85 mmHg (95% CI 0.18-1.51 mmHg, P = 0.013) for IOPcc, 0.38 mmHg (95% CI 0.01-0.75, P = 0.047) for CH and 0.63 mmHg (95% CI 0.27-0.98, P = 0.001) for the CRF. Sensitivity analyses using the leave-one-out method showed a consistent significant difference between the groups (all P < 0.001). CONCLUSIONS Corneal biomechanics changed in the patients with DM. High CH, CRF, IOPcc and IOPg values may be associated factors for diabetes mellitus. Future studies are warranted to clarify the underlying mechanisms and explore the relationship between corneal biomechanics, glaucoma and diabetes mellitus. REGISTRATION PROSPERO registration No CRD4201705465.
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Affiliation(s)
- Xiaoyi Wang
- Department of Ophthalmology Center, Huizhou Municipal Central Hospital, Huizhou, Guangdong Province, People's Republic of China
| | - Guihua Xu
- Department of Ophthalmology Center, Huizhou Municipal Central Hospital, Huizhou, Guangdong Province, People's Republic of China
| | - Wei Wang
- Zhongshan Ophthalmic Center, State Key Laboratory of Ophthalmology, Sun Yat-Sen University, Guangzhou, People's Republic of China
| | - Juanjuan Wang
- Department of Ophthalmology Center, Huizhou Municipal Central Hospital, Huizhou, Guangdong Province, People's Republic of China
| | - Lili Chen
- Department of Ophthalmology Center, Huizhou Municipal Central Hospital, Huizhou, Guangdong Province, People's Republic of China
| | - Mingguang He
- Zhongshan Ophthalmic Center, State Key Laboratory of Ophthalmology, Sun Yat-Sen University, Guangzhou, People's Republic of China
| | - Zilin Chen
- Department of Ophthalmology Center, Huizhou Municipal Central Hospital, Huizhou, Guangdong Province, People's Republic of China.
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17
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18
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Richdale K, Chao C, Hamilton M. Eye care providers' emerging roles in early detection of diabetes and management of diabetic changes to the ocular surface: a review. BMJ Open Diabetes Res Care 2020; 8:8/1/e001094. [PMID: 32299899 PMCID: PMC7199150 DOI: 10.1136/bmjdrc-2019-001094] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 03/20/2020] [Accepted: 03/24/2020] [Indexed: 12/16/2022] Open
Abstract
US adults visit eye care providers more often than primary healthcare providers, placing these doctors in a prime position to help identify and manage patients with prediabetes and diabetes. Currently, diabetes is identified in eye clinics in an advanced stage, only after visible signs of diabetic retinopathy. Recent ophthalmic research has identified multiple subclinical and clinical changes that occur in the anterior segment of the eye with metabolic disease. The corneal epithelium exhibits increased defects and poor healing, including an increased risk of neurotrophic keratitis. Increased thickness and stiffness of the cornea artificially alters intraocular pressure. There is damage to the endothelial cells and changes to the bacterial species on the ocular surface, both of which can increase risk of complications with surgery. Decreased corneal sensitivity due to a loss of nerve density predispose patients with metabolic disease to further neurotrophic complications. Patients with diabetes have increased Meibomian gland dysfunction, blepharitis and reduced tear production, resulting in increased rates of dry eye disease and discomfort. Early detection of metabolic disease may allow eye care providers to be more proactive in recommending referral and intervention in order to reduce the risk of blindness and other diabetes-related morbidity. Continued research is needed to better understand the time course of changes to the anterior segment and what can be done to better detect and diagnose patients with prediabetes or undiagnosed diabetes and provide improved care for these patients.
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Affiliation(s)
- Kathryn Richdale
- College of Optometry, University of Houston, Houston, Texas, USA
| | - Cecilia Chao
- College of Optometry, University of Houston, Houston, Texas, USA
- School of Optometry and Vision Science, University of New South Wales-Kensington Campus, Sydney, New South Wales, Australia
| | - Marc Hamilton
- Health and Human Performance, University of Houston, Houston, Texas, USA
- Biology and Biochemistry, University of Houston, Houston, Texas, USA
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19
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Ramm L, Spoerl E, Pillunat LE, Terai N. Is the Corneal Thickness Profile Altered in Diabetes Mellitus? Curr Eye Res 2020; 45:1228-1234. [PMID: 32180465 DOI: 10.1080/02713683.2020.1741009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Purpose: To investigate the influence of chronic hyperglycemia in diabetes mellitus (DM) on spatial corneal thickness distribution and to analyze the influence of disease-specific factors. Methods: DM patients and healthy subjects were matched according to age and intraocular pressure (IOP). In diabetics, disease duration, DM type, and HbA1c value were assessed. Spatially resolved corneal thickness was measured by Pentacam HR. Thinnest corneal thickness (TCT) and peripheral pachymetry of concentric circles around TCT were determined. The Dynamic Scheimpflug Analyzer Corvis ST (CST) was used to measure the parameter pachy slope, which is an indicator of the change of corneal thickness from the apex to the periphery. Results: 59 DM patients and 57 healthy subjects were included. Age (P = .486) and IOP (P = .154) were not different between the groups. In DM, pachy slope was significantly higher than in healthy subjects (41.1 ± 9.87 vs. 35.18 ± 10.64 μm, P = .004). Also, the differences between TCT and the average of peripheral corneal thickness of concentric circles with a diameter of 2 mm (10.3 ± 1.7 vs. 9.3 ± 3.8 μm, P < .001) to 6 mm (82.2 ± 12.4 vs. 76.8 ± 12.6 μm, P = .011) were increased in patients. Changes in thickness profile were associated with HbA1c value and presence of diabetic retinopathy or maculopathy. Conclusion: In DM, a stronger peripheral corneal thickness increase was detectable. This change was shown using the novel CST parameter pachy slope and confirmed by Pentacam readings. These alterations might affect IOP and biomechanical measurements, and influence refractive procedures.
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Affiliation(s)
- Lisa Ramm
- Department of Ophthalmology, University Hospital Dresden , Dresden, Germany
| | - Eberhard Spoerl
- Department of Ophthalmology, University Hospital Dresden , Dresden, Germany
| | - Lutz E Pillunat
- Department of Ophthalmology, University Hospital Dresden , Dresden, Germany
| | - Naim Terai
- Department of Ophthalmology, University Hospital Dresden , Dresden, Germany
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20
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Ramm L, Herber R, Spoerl E, Pillunat LE, Terai N. Intraocular pressure measurements in diabetes mellitus. Eur J Ophthalmol 2019; 30:1432-1439. [PMID: 31779470 DOI: 10.1177/1120672119890517] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
PURPOSE To investigate the impact of diabetes mellitus-induced changes on intraocular pressure measurements using Goldmann applanation tonometry, Ocular Response Analyzer, and Corvis ST. METHODS Measurements were done using Goldmann applanation tonometry, Ocular Response Analyzer, and Corvis ST in 69 diabetic patients. Biomechanical-corrected intraocular pressure values by Ocular Response Analyzer (IOPcc) and Corvis ST (bIOP) were used. In addition, biometry and tomography were performed and information on diabetes mellitus specific factors was collected. Results were compared to an age-matched group of 68 healthy subjects. RESULTS In diabetes mellitus, Goldmann applanation tonometry intraocular pressure (P = 0.193) and central corneal thickness (P = 0.184) were slightly increased. Also, IOPcc (P = 0.075) and bIOP (P = 0.542) showed no significant group difference. In both groups, IOPcc was higher than Goldmann applanation tonometry intraocular pressure (P = 0.002, P < 0.001), while bIOP was nearly equal to Goldmann applanation tonometry intraocular pressure (P = 0.795, P = 0.323). Central corneal thickness showed a tendency to higher values in poorly controlled than in controlled diabetes mellitus (P = 0.059). Goldmann applanation tonometry intraocular pressure correlated to central corneal thickness, while IOPcc and bIOP were independent from central corneal thickness in both groups. All intraocular pressure values showed significant associations to corneal biomechanical parameters. Only in diabetes mellitus, bIOP was correlated to Pachy slope (P = 0.023). CONCLUSION In diabetes mellitus, Goldmann applanation tonometry intraocular pressure was slightly, but not significantly, increased, which might be caused by a higher central corneal thickness and changes in corneal biomechanical properties. However, intraocular pressure values measured by Ocular Response Analyzer and Corvis ST were not significantly different between diabetes mellitus patients and healthy subjects. The bIOP showed a higher agreement with Goldmann applanation tonometry than IOPcc and was independent from central corneal thickness.
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Affiliation(s)
- Lisa Ramm
- Department of Ophthalmology, University Hospital Carl Gustav Carus, TU Dresden, Germany
| | - Robert Herber
- Department of Ophthalmology, University Hospital Carl Gustav Carus, TU Dresden, Germany
| | - Eberhard Spoerl
- Department of Ophthalmology, University Hospital Carl Gustav Carus, TU Dresden, Germany
| | - Lutz E Pillunat
- Department of Ophthalmology, University Hospital Carl Gustav Carus, TU Dresden, Germany
| | - Naim Terai
- Department of Ophthalmology, University Hospital Carl Gustav Carus, TU Dresden, Germany
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McKay TB, Priyadarsini S, Karamichos D. Mechanisms of Collagen Crosslinking in Diabetes and Keratoconus. Cells 2019; 8:cells8101239. [PMID: 31614631 PMCID: PMC6830090 DOI: 10.3390/cells8101239] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Revised: 10/09/2019] [Accepted: 10/10/2019] [Indexed: 12/14/2022] Open
Abstract
Collagen crosslinking provides the mechanical strength required for physiological maintenance of the extracellular matrix in most tissues in the human body, including the cornea. Aging and diabetes mellitus (DM) are processes that are both associated with increased collagen crosslinking that leads to increased corneal rigidity. By contrast, keratoconus (KC) is a corneal thinning disease associated with decreased mechanical stiffness leading to ectasia of the central cornea. Studies have suggested that crosslinking mediated by reactive advanced glycation end products during DM may protect the cornea from KC development. Parallel to this hypothesis, riboflavin-mediated photoreactive corneal crosslinking has been proposed as a therapeutic option to halt the progression of corneal thinning by inducing intra- and intermolecular crosslink formation within the collagen fibrils of the stroma, leading to stabilization of the disease. Here, we review the pathobiology of DM and KC in the context of corneal structure, the epidemiology behind the inverse correlation of DM and KC development, and the chemical mechanisms of lysyl oxidase-mediated crosslinking, advanced glycation end product-mediated crosslinking, and photoreactive riboflavin-mediated corneal crosslinking. The goal of this review is to define the biological and chemical pathways important in physiological and pathological processes related to collagen crosslinking in DM and KC.
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Affiliation(s)
- Tina B McKay
- Schepens Eye Research Institute/Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, Boston, MA 02114, USA.
| | - Shrestha Priyadarsini
- Department of Ophthalmology/Dean McGee Eye Institute, University of Oklahoma Health Science Center, Oklahoma City, OK 73104, USA.
| | - Dimitrios Karamichos
- Department of Ophthalmology/Dean McGee Eye Institute, University of Oklahoma Health Science Center, Oklahoma City, OK 73104, USA.
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The Mechanical Interpretation of Ocular Response Analyzer Parameters. BIOMED RESEARCH INTERNATIONAL 2019; 2019:5701236. [PMID: 31380431 PMCID: PMC6662474 DOI: 10.1155/2019/5701236] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 06/03/2019] [Accepted: 06/20/2019] [Indexed: 11/17/2022]
Abstract
Purpose Ocular Response Analyzer (ORA) is one of the most widely used devices in clinic, while the mechanical interpretations of parameters obtained from ORA have not been understood completely. The aim of this research is to explore the mechanical interpretation of ORA parameters. Methods Rabbits aged 3-24 months were measured with ORA in vivo and corneal strips uniaxial tensile tests to get ORA parameters and corneal biomechanical parameters (corneal elastic modulus, relaxation time, and relaxation limit). The mechanical interpretation of ORA parameters was cognized preliminarily by analyzing the correlation between ORA parameters and corneal biomechanical parameters. On the other hand, finite element method was applied to simulate ORA measurements with different corneal biomechanical parameters to obtain quantitative relationship between ORA parameters and corneal biomechanical parameters further. Results Biomechanical experimental results showed that Corneal Resistance Factor (CRF) was correlated with corneal elastic modulus and relaxation limit significantly, while the significant correlations between Corneal Hysteresis (CH) and corneal biomechanical parameters were not observed. Results of finite element analysis showed that both CH and CRF were correlated with corneal elastic modulus, relaxation limit, and relaxation time significantly. Besides, corneal elastic modulus was positively correlated with upslop1 and upslop2 and negatively correlated with w2. Conclusions For all ORA parameters, CH, CRF, the upslope, and the width of the peaks are parameters which may reflect corneal elastic properties. It is viable to cognize mechanical interpretation of ORA parameters by the comparisons of the data from ORA and biomechanical tests of rabbits with different ages and the simulations of ORA based on finite element methods. Further studies are needed to confirm the mechanical interpretation.
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Barrientez B, Nicholas SE, Whelchel A, Sharif R, Hjortdal J, Karamichos D. Corneal injury: Clinical and molecular aspects. Exp Eye Res 2019; 186:107709. [PMID: 31238077 DOI: 10.1016/j.exer.2019.107709] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 06/03/2019] [Accepted: 06/21/2019] [Indexed: 12/13/2022]
Abstract
Currently, over 10 million people worldwide are affected by corneal blindness. Corneal trauma and disease can cause irreversible distortions to the normal structure and physiology of the cornea often leading to corneal transplantation. However, donors are in short supply and risk of rejection is an ever-present concern. Although significant progress has been made in recent years, the wound healing cascade remains complex and not fully understood. Tissue engineering and regenerative medicine are currently at the apex of investigation in the pursuit of novel corneal therapeutics. This review uniquely integrates the clinical and cellular aspects of both corneal trauma and disease and provides a comprehensive view of the most recent findings and potential therapeutics aimed at restoring corneal homeostasis.
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Affiliation(s)
- Brayden Barrientez
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Sarah E Nicholas
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Amy Whelchel
- Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Rabab Sharif
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Jesper Hjortdal
- Department of Ophthalmology, Aarhus University Hospital, Aarhus, Denmark
| | - Dimitrios Karamichos
- Department of Ophthalmology, Dean McGee Eye Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA; Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA.
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24
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An Update on Corneal Biomechanics and Architecture in Diabetes. J Ophthalmol 2019; 2019:7645352. [PMID: 31275634 PMCID: PMC6589322 DOI: 10.1155/2019/7645352] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Accepted: 05/02/2019] [Indexed: 12/12/2022] Open
Abstract
In the last decade, we have witnessed substantial progress in our understanding of corneal biomechanics and architecture. It is well known that diabetes is a systemic metabolic disease that causes chronic progressive damage in the main organs of the human body, including the eyeball. Although the main and most widely recognized ocular effect of diabetes is on the retina, the structure of the cornea (the outermost and transparent tissue of the eye) can also be affected by the poor glycemic control characterizing diabetes. The different corneal structures (epithelium, stroma, and endothelium) are affected by specific complications of diabetes. The development of new noninvasive diagnostic technologies has provided a better understanding of corneal tissue modifications. The objective of this review is to describe the advances in the knowledge of the corneal alterations that diabetes can induce.
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25
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Qin X, Tian L, Zhang H, Chen X, Li L. Evaluation of corneal elastic modulus based on Corneal Visualization Scheimpflug Technology. Biomed Eng Online 2019; 18:42. [PMID: 30947733 PMCID: PMC6449989 DOI: 10.1186/s12938-019-0662-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2019] [Accepted: 03/27/2019] [Indexed: 11/11/2022] Open
Abstract
BACKGROUND Corneal biomechanical properties are important for the diagnosis of corneal diseases, individualized design and prognosis of corneal surgery. Clinical available devices such as Ocular Response Analyzer (ORA) and Corneal Visualization Scheimpflug Technology (Corvis ST) can provide corneal biomechanics related parameters, while corneal elastic modulus cannot be extracted directly from them at present. The aim of this study is to suggest a method to determine corneal elastic modulus based on the results of Corvis ST test according to Reissner's theory on the relation between stress and small displacement in shallow spherical shell. RESULTS Five rabbits (10 eyes) and 10 healthy humans (20 eyes) were measured with Corvis ST to obtain the normal range of corneal elastic modulus. Results showed Corneal elastic modulus of rabbit was 0.16 MPa to 0.35 MPa, human corneal elastic modulus was 0.16-0.30 MPa. Rabbit corneas were also measured at different intraocular pressures (IOP), and results showed corneal elastic modulus, first applanation time (A1T) and stiffness parameter (SP-A1) were positively correlated with IOP. Deformation amplitude (DA), the second applanations time (A2T), and peak distance (PD) were negatively correlated with IOP. Finite element method was used to simulate the Corvis measurements according to the calculated elastic modulus and the simulated corneal apical displacements were agreement with experimental results in general. CONCLUSIONS The method to determine corneal elastic modulus based on Corvis test according to the relationship between force and displacements of shallow spherical shell is convenient and effective.
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Affiliation(s)
- Xiao Qin
- Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069 China
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069 China
| | - Lei Tian
- Beijing Ophthalmology & Visual Sciences Key Laboratory, Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Haixia Zhang
- Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069 China
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069 China
| | - Xinyan Chen
- Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069 China
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069 China
| | - Lin Li
- Beijing Key Laboratory of Fundamental Research on Biomechanics in Clinical Application, Capital Medical University, Beijing, 100069 China
- School of Biomedical Engineering, Capital Medical University, Beijing, 100069 China
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Measurement of Corneal Biomechanical Properties in Diabetes Mellitus Using the Ocular Response Analyzer and the Corvis ST. Cornea 2019; 38:595-599. [DOI: 10.1097/ico.0000000000001879] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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Bao F, Zheng Y, Liu C, Zheng X, Zhao Y, Wang Y, Li L, Wang Q, Chen S, Elsheikh A. Changes in Corneal Biomechanical Properties With Different Corneal Cross-linking Irradiances. J Refract Surg 2018; 34:51-58. [PMID: 29315442 DOI: 10.3928/1081597x-20171025-01] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Accepted: 10/19/2017] [Indexed: 11/20/2022]
Abstract
PURPOSE To evaluate whether different corneal cross-linking (CXL) irradiances, all with the same delivered total energy, achieve similar increases in corneal material stiffness. METHODS One hundred twenty-six healthy white Japanese rabbits were randomly divided into seven groups (n = 18 each). After removing the epithelium of the left corneas, six groups were exposed to riboflavin (0.22% concentration by volume) and ultraviolet-A (370 nm) at different CXL irradiations, all with the same total dose (5.4 J/cm2), ranging from 3 mW/cm2 for 30 minutes to 90 mW/cm2 for 1 minute. The left corneas of the seventh group were exposed to riboflavin without irradiation. Twelve corneas of each group were prepared for inflation testing, where they were subjected to internal hydrostatic pressure simulating intraocular pressure, whereas the other six specimens were processed for electron microscopy measurements of fibril diameter and interfibrillar spacing. The inverse modeling process was used to estimate the tangent modulus of the tissue, which is considered an accurate measure of the material stiffness. RESULTS The stiffening effect of CXL decreased when using high irradiation/short duration settings. Compared with the group with no irradiation (NUVA group), the tangent modulus increases reduced from 212.5% in the 3mW/30min group to 196.8% in the 90mW/1min group. These increases were significant (P < .05) in the 3mW/30min and 9mW/10min groups, but became insignificant in other CXL groups. The interfibrillar spacing in the anterior 50 μm of the corneal stroma also reduced with high irradiation/short duration settings, changing from 20.05 ± 1.89 nm in the NUVA group down to 13.06 ± 2.07 and 14.37 ± 1.90 nm in the 3mW/30min and 9mW/10min groups, respectively. These changes were significant (P < .05) between non-adjacent groups, but became non-significant otherwise. The corresponding changes in fibril diameter were small and nonsignificant in all cases (P > .05). CONCLUSIONS Because the effect of CXL in stiffening the tissue and reducing the interfibrillar spacing consistently decreased with reducing the irradiance duration, the Bunsen-Roscoe law may not be readily applicable in the CXL of corneal tissue. [J Refract Surg. 2018;34(1):51-58.].
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Ma J, Wang Y, Wei P, Jhanji V. Biomechanics and structure of the cornea: implications and association with corneal disorders. Surv Ophthalmol 2018; 63:851-861. [PMID: 29857022 DOI: 10.1016/j.survophthal.2018.05.004] [Citation(s) in RCA: 72] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Revised: 05/17/2018] [Accepted: 05/21/2018] [Indexed: 12/14/2022]
Abstract
Recent studies have shown that alterations in corneal biomechanical properties are associated with corneal pathologies, particularly corneal ectasia. Moreover, these alterations may have implications with regard to the outcomes of therapeutic modalities and corneal refractive surgeries. We address corneal anatomy and its relevance to corneal biomechanical characteristics, as well as ocular and systemic conditions associated with changes in corneal biomechanics.
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Affiliation(s)
- Jiaonan Ma
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China
| | - Yan Wang
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China; Tianjin Eye Hospital, Tianjin Eye Institute, Tianjin Key Laboratory of Ophthalmology and Visual Science, Naikai University, Tianjin Medical University, Tianjin, China.
| | - Pinghui Wei
- Tianjin Eye Hospital, Tianjin Eye Institute, Tianjin Key Laboratory of Ophthalmology and Visual Science, Naikai University, Tianjin Medical University, Tianjin, China
| | - Vishal Jhanji
- UPMC Eye Center, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
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Continuous-light versus pulsed-light accelerated corneal crosslinking with ultraviolet-A and riboflavin. J Cataract Refract Surg 2018; 44:382-389. [DOI: 10.1016/j.jcrs.2017.12.028] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Revised: 10/17/2017] [Accepted: 12/09/2017] [Indexed: 11/21/2022]
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