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Intraocular pressure measurement: A Review. Surv Ophthalmol 2022; 67:1319-1331. [DOI: 10.1016/j.survophthal.2022.03.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 02/16/2022] [Accepted: 03/01/2022] [Indexed: 11/21/2022]
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Ferguson TJ, Singuri S, Jalaj S, Ford MR, De Stefano VS, Seven I, Dupps WJ. Depth-resolved Corneal Biomechanical Changes Measured Via Optical Coherence Elastography Following Corneal Crosslinking. Transl Vis Sci Technol 2021; 10:7. [PMID: 34313710 PMCID: PMC8322708 DOI: 10.1167/tvst.10.5.7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Purpose To evaluate depth-resolved changes of corneal biomechanical properties in eyes with corneal ectasia after corneal crosslinking (CXL) using optical coherence elastography. Methods In a prospective pilot series of eyes with corneal ectasia, a custom high-speed swept source optical coherence tomography system was used to image the cornea before and 3 months after CXL during a low-speed applanating deformation while monitoring applanation force. Cross-correlation was applied to track frame-by-frame two-dimensional optical coherence tomography speckle displacements, and the slope of force versus local axial displacement behavior during the deformation was used to produce a two-dimensional array of axial stiffness (k). These values were averaged for anterior (ka) and posterior (kp) stromal regions and expressed as a ratio (ka/kp) to assess depth-dependent differences in stiffness. CXL was performed according to the Dresden protocol with a system approved by the U.S. Food and Drug Administration. Results Four eyes from four patients with keratoconus (n = 3) or post-LASIK ectasia (n = 1) underwent optical coherence elastography before and 3 months after CXL. The mean ka/kp was 1.03 ± 0.07 before CXL compared with 1.34 ± 0.17 after the CXL procedure. All four eyes demonstrated at least a 20% increase in the ka/kp. Conclusions Preferential stiffening of the anterior stroma with the standard CXL protocol was demonstrated with optical coherence elastography in live human subjects. Translational Relevance Although ex vivo studies have demonstrated anterior stiffening effects after CXL using various destructive and nondestructive methods, this report presents the first evidence of such changes in serial live human measurements.
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Affiliation(s)
| | - Srinidhi Singuri
- Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of CWRU, Cleveland, Ohio, USA
| | - Sanjai Jalaj
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - Matthew R Ford
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | | | - Ibrahim Seven
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - William J Dupps
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA.,Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of CWRU, Cleveland, Ohio, USA.,Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA.,Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA
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Blackburn BJ, Rollins AM, Dupps WJ. Biomechanics of Ophthalmic Crosslinking. Transl Vis Sci Technol 2021; 10:8. [PMID: 34328498 PMCID: PMC8327749 DOI: 10.1167/tvst.10.5.8] [Citation(s) in RCA: 9] [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: 04/25/2021] [Accepted: 06/19/2021] [Indexed: 12/12/2022] Open
Abstract
Crosslinking involves the formation of bonds between polymer chains, such as proteins. In biological tissues, these bonds tend to stiffen the tissue, making it more resistant to mechanical degradation and deformation. In ophthalmology, the crosslinking phenomenon is being increasingly harnessed and explored as a treatment strategy for treating corneal ectasias, keratitis, degenerative myopia, and glaucoma. This review surveys the multitude of exogenous crosslinking strategies reported in the literature, both "light" (involving light energy) and "dark" (involving non-photic chemical processes), and explores their mechanisms, cytotoxicity, and stage of translational development. The spectrum of ophthalmic applications described in the literature is then discussed, with particular attention to proposed therapeutic mechanisms in the cornea and sclera. The mechanical effects of crosslinking are then discussed in the context of their proposed site and scale of action. Biomechanical characterization of the crosslinking effect is needed to more thoroughly address knowledge gaps in this area, and a review of reported methods for biomechanical characterization is presented with an attempt to assess the sensitivity of each method to crosslinking-mediated changes using data from the experimental and clinical literature. Biomechanical measurement methods differ in spatial resolution, mechanical sensitivity, suitability for detecting crosslinking subtypes, and translational readiness and are central to the effort to understand the mechanistic link between crosslinking methods and clinical outcomes of candidate therapies. Data on differences in the biomechanical effect of different crosslinking protocols and their correspondence to clinical outcomes are reviewed, and strategies for leveraging measurement advances predicting clinical outcomes of crosslinking procedures are discussed. Advancing the understanding of ophthalmic crosslinking, its biomechanical underpinnings, and its applications supports the development of next-generation crosslinking procedures that optimize therapeutic effect while reducing complications.
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Affiliation(s)
- Brecken J. Blackburn
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
| | - Andrew M. Rollins
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
| | - William J. Dupps
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
- Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA
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4
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Singh M, Nair A, Aglyamov SR, Larin KV. Compressional Optical Coherence Elastography of the Cornea. PHOTONICS 2021; 8:111. [PMID: 37727230 PMCID: PMC10508915 DOI: 10.3390/photonics8040111] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Assessing the biomechanical properties of the cornea is crucial for detecting the onset and progression of eye diseases. In this work, we demonstrate the application of compression-based optical coherence elastography (OCE) to measure the biomechanical properties of the cornea under various conditions, including validation in an in situ rabbit model and a demonstration of feasibility for in vivo measurements. Our results show a stark increase in the stiffness of the corneas as IOP was increased. Moreover, UV-A/riboflavin corneal collagen crosslinking (CXL) also dramatically increased the stiffness of the corneas. The results were consistent across 4 different scenarios (whole CXL in situ, partial CXL in situ, whole CXL in vivo, and partial CXL in vivo), emphasizing the reliability of compression OCE to measure corneal biomechanical properties and its potential for clinical applications.
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Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Rd., Room N207, Houston, TX 77204, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, BCM335, Houston, TX 77030, USA
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5
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Chong J, Dupps WJ. Corneal biomechanics: Measurement and structural correlations. Exp Eye Res 2021; 205:108508. [PMID: 33609511 DOI: 10.1016/j.exer.2021.108508] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 02/09/2021] [Accepted: 02/12/2021] [Indexed: 02/02/2023]
Abstract
The characterization of corneal biomechanical properties has important implications for the management of ocular disease and prediction of surgical responses. Corneal refractive surgery outcomes, progression or stabilization of ectatic disease, and intraocular pressure determination are just examples of the many key clinical problems that depend highly upon corneal biomechanical characteristics. However, to date there is no gold standard measurement technique. Since the advent of a 1-dimensional (1D) air-puff based technique for measuring the corneal surface response in 2005, advances in clinical imaging technology have yielded increasingly sophisticated approaches to characterizing the biomechanical properties of the cornea. Novel analyses of 1D responses are expanding the clinical utility of commercially-available air-puff-based instruments, and other imaging modalities-including optical coherence elastography (OCE), Brillouin microscopy and phase-decorrelation ocular coherence tomography (PhD-OCT)-offer new opportunities for probing local biomechanical behavior in 3-dimensional space and drawing new inferences about the relationships between corneal structure, mechanical behavior, and corneal refractive function. These advances are likely to drive greater clinical adoption of in vivo biomechanical analysis and to support more personalized medical and surgical decision-making.
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Affiliation(s)
- Jillian Chong
- Cleveland Clinic Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - William J Dupps
- Cleveland Clinic Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA; Dept. of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve Univ, Cleveland, OH, USA; Dept. of Biomedical Engineering, Lerner Research Institute and Case Western Reserve Univ, Cleveland, OH, USA.
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6
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Mechanical Stability of Cryopreserved Split-Thickness Tectonic Corneal Grafts. Cornea 2020; 39:1151-1156. [PMID: 32558731 DOI: 10.1097/ico.0000000000002399] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE To evaluate the influence of cryopreservation on the pressure-strain relationship of microkeratome dissected anterior stromal grafts (ASGs). METHODS Partial thickness ASGs were created from 7 pairs of human corneas and randomized to immediate grafting or grafting after 3 months of cryopreservation at -80°C into a whole globe ex vivo corneal perforation model. High frequency ultrasound speckle tracking was used to calculate the cross-sectional axial and lateral strains in each graft at increasing intraocular pressure (IOP) from 5 to 30 mm Hg. The mean axial and lateral strains were compared between the paired groups. RESULTS The mean axial and lateral strains were not significantly different between the cryopreserved and noncryopreserved ASGs. The mean lateral strains at 30 mm Hg in the noncryopreserved and cryopreserved grafts were 2.4% ± 2.1% and 1.4% ± 0.7% (P = 0.294), respectively. The mean axial strains at 30 mm Hg in the noncryopreserved and cryopreserved grafts were -7.8% ± 3.3% and -5.5% ± 3.0% (P = 0.198), respectively. A linear pressure-strain relationship was found for all grafts at physiologic IOP. CONCLUSIONS ASGs cryopreserved at -80°C maintain their IOP-strain relationship compared with noncryopreserved ASGs at physiologic pressures, supporting the potential use of cryopreserved human corneal stroma for patch grafting procedures.
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De Stefano VS, Ford MR, Seven I, Dupps WJ. Depth-Dependent Corneal Biomechanical Properties in Normal and Keratoconic Subjects by Optical Coherence Elastography. Transl Vis Sci Technol 2020; 9:4. [PMID: 32832211 PMCID: PMC7414661 DOI: 10.1167/tvst.9.7.4] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 04/07/2020] [Indexed: 12/15/2022] Open
Abstract
Purpose Compare depth-resolved biomechanical properties in normal and keratoconic corneas in live human subjects using optical coherence elastography (OCE). Methods In a prospective series of normal and keratoconus (KC) eyes, a corneal perturbation was applied by a custom swept-source OCE system using a transparent flat lens coupled to force transducers. Cross-correlation was applied to track frame-by-frame OCT speckle displacement. Regional displacements for the anterior and posterior stroma were plotted in force versus displacement (k) graphs. A spatial biomechanical property ratio (ka/kp ) was defined by dividing the maximum total displacement by the maximum force for the anterior (ka ) and posterior cornea (kp) and was compared between normal and KC groups with the Mann-Whitney U test. Area under the receiver operating characteristics curve (AUROC) for differentiating normal and KC eyes was calculated for ka/kp , kmax, and thinnest point of corneal thickness (TPCT). Results Thirty-six eyes were analyzed (21 eyes of 12 normal subjects and 15 KC eyes of 12 subjects). The ka/kp for the normal group was 1.135 ± 0.07 (mean ± standard deviation) and 1.02 ± 0.08 for the KC group (P < 0.001), indicating a relative deficit in anterior stromal stiffness in KC eyes. AUROC was 0.91 for ka /kp , 0.95 for kmax, and 1 for TPCT. Conclusions Significant differences in depth-dependent corneal biomechanical properties were observed between normal and KC subjects. Translational Relevance OCE was applied for the first time to human KC subjects and revealed alterations in the normal anterior-to-posterior stromal stiffness gradient, a novel and clinically accessible disease biomarker.
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Affiliation(s)
- Vinicius S De Stefano
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA.,Department of Ophthalmology and Visual Sciences, Federal University of Sao Paulo, Sao Paulo, Brazil
| | - Matthew R Ford
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Ibrahim Seven
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - William J Dupps
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA.,Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.,Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA
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Clayson K, Pavlatos E, Pan X, Sandwisch T, Ma Y, Liu J. Ocular Pulse Elastography: Imaging Corneal Biomechanical Responses to Simulated Ocular Pulse Using Ultrasound. Transl Vis Sci Technol 2020; 9:5. [PMID: 32509440 PMCID: PMC7255625 DOI: 10.1167/tvst.9.1.5] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 11/08/2019] [Indexed: 12/14/2022] Open
Abstract
Purpose In vivo evaluation of corneal biomechanics holds the potential for improving diagnosis and management of ocular diseases. We aimed to develop an ocular pulse elastography (OPE) technique to quantify corneal strains generated by naturally occurring pulsations of the intraocular pressure (IOP) using high-frequency ultrasound. Methods Simulated ocular pulses were induced in whole porcine and human donor globes to investigate the effects of physiologic variations in baseline IOP, ocular pulse amplitude, and frequency on corneal strains. Ocular pulse-induced strains were measured in additional globes before and after UVA-riboflavin-induced corneal crosslinking. The central cornea in each eye was imaged with a 50-MHz ultrasound imaging system and correlation-based speckle tracking of radiofrequency data was used to calculate tissue displacements and strains. Results Ocular pulse-induced corneal strains followed the cyclic changes of IOP. Both baseline IOP and ocular pulse amplitude had a significant influence on strain magnitude. Variations in pulse frequency within the normal human heart rate range did not introduce detectable changes in corneal strains. A significant decrease of corneal strain, as quantified by the OPE technique, was observed after corneal crosslinking. The extent of corneal stiffening (i.e., strain reduction) seemed to correlate with the initial strain magnitude. Conclusions This ex vivo study demonstrated the feasibility of the OPE method to quantify corneal strains generated by IOP pulsation and detect changes associated with corneal crosslinking treatment. Translational Relevance Integrating in vivo measurement of IOP and ocular pulse amplitude, the OPE method may lead to a new clinical tool for safe and quick biomechanical evaluations of the cornea.
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Affiliation(s)
- Keyton Clayson
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA.,Biophysics Interdisciplinary Group, The Ohio State University, Columbus, OH, USA
| | - Elias Pavlatos
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
| | - Xueliang Pan
- Department of Biomedical Informatics, The Ohio State University, Columbus, OH, USA
| | - Thomas Sandwisch
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
| | - Yanhui Ma
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
| | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA.,Biophysics Interdisciplinary Group, The Ohio State University, Columbus, OH, USA.,Department of Ophthalmology and Visual Science, The Ohio State University, Columbus, OH, USA
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9
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Clayson K, Pavlatos E, Pan X, Sandwisch T, Ma Y, Liu J. Ocular Pulse Elastography: Imaging Corneal Biomechanical Responses to Simulated Ocular Pulse Using Ultrasound. Transl Vis Sci Technol 2020. [DOI: 10.1167/tvst.210.1.1802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- Keyton Clayson
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
- Biophysics Interdisciplinary Group, The Ohio State University, Columbus, OH, USA
| | - Elias Pavlatos
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
| | - Xueliang Pan
- Department of Biomedical Informatics, The Ohio State University, Columbus, OH, USA
| | - Thomas Sandwisch
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
| | - Yanhui Ma
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
| | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University, Columbus, OH, USA
- Biophysics Interdisciplinary Group, The Ohio State University, Columbus, OH, USA
- Department of Ophthalmology and Visual Science, The Ohio State University, Columbus, OH, USA
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10
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Pye DC. A clinical method for estimating the modulus of elasticity of the human cornea in vivo. PLoS One 2020; 15:e0224824. [PMID: 31914133 PMCID: PMC6948750 DOI: 10.1371/journal.pone.0224824] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Accepted: 10/22/2019] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND To develop a method, using current clinical instrumentation, to estimate the Young's modulus of the human cornea in vivo. METHODS Central corneal curvature (CCC), central corneal thickness(CCT), intraocular pressure (IOP) was measured with the Goldmann tonometer (IOPG) and the Pascal Dynamic Corneal Tonometer(PDCT) in one eye of 100 normal young human subjects (21.07 ± 2.94 years) in vivo. The Orssengo and Pye algorithm was used to calculate the Young's modulus of the corneas of these subjects. RESULTS The Young's modulus(E) of the corneas of the subjects using the PDCT and IOPG results (Ecalc) was 0.25 ± 0.10MPa, and without the PDCT results (Eiopg) was 0.29 ± 0.06MPa. The difference in these results is due to the difference in tonometry results between the two instruments, as the mean PDCT result for the subjects was 16.89 ± 2.49mmHg and the IOPG result 15.06 ± 2.71mmHg. E was affected by the CCC of the subjects but more particularly by the CCT and IOP measurements. Corneal stiffness results are also presented. CONCLUSION Two methods have been developed to estimate the Young's modulus of the human cornea in vivo using current clinical instrumentation. One method (Ecalc) is applicable to the general corneal condition, and Eiopg to the normal cornea, and these results can be used to calculate corneal stiffness.
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Affiliation(s)
- David C. Pye
- School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
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11
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Pant AD, Dorairaj SK, Amini R. Appropriate Objective Functions for Quantifying Iris Mechanical Properties Using Inverse Finite Element Modeling. J Biomech Eng 2019; 140:2676340. [PMID: 29570756 DOI: 10.1115/1.4039679] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Indexed: 01/08/2023]
Abstract
Quantifying the mechanical properties of the iris is important, as it provides insight into the pathophysiology of glaucoma. Recent ex vivo studies have shown that the mechanical properties of the iris are different in glaucomatous eyes as compared to normal ones. Notwithstanding the importance of the ex vivo studies, such measurements are severely limited for diagnosis and preclude development of treatment strategies. With the advent of detailed imaging modalities, it is possible to determine the in vivo mechanical properties using inverse finite element (FE) modeling. An inverse modeling approach requires an appropriate objective function for reliable estimation of parameters. In the case of the iris, numerous measurements such as iris chord length (CL) and iris concavity (CV) are made routinely in clinical practice. In this study, we have evaluated five different objective functions chosen based on the iris biometrics (in the presence and absence of clinical measurement errors) to determine the appropriate criterion for inverse modeling. Our results showed that in the absence of experimental measurement error, a combination of iris CL and CV can be used as the objective function. However, with the addition of measurement errors, the objective functions that employ a large number of local displacement values provide more reliable outcomes.
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Affiliation(s)
- Anup D Pant
- Department of Biomedical Engineering, The University of Akron, Akron, OH 44325 e-mail:
| | - Syril K Dorairaj
- Department of Ophthalmology, Mayo Clinic, Jacksonville, FL 32224 e-mail:
| | - Rouzbeh Amini
- Mem. ASME Department of Biomedical Engineering, The University of Akron, Akron, OH 44325 e-mail:
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12
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Effects of Thickness on Corneal Biomechanical Properties Using Optical Coherence Elastography. Optom Vis Sci 2019; 95:299-308. [PMID: 29561496 DOI: 10.1097/opx.0000000000001193] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
SIGNIFICANCE Measured corneal biomechanical properties are driven by intraocular pressure, tissue thickness, and inherent material properties. We demonstrate tissue thickness as an important factor in the measurement of corneal biomechanics that can confound short-term effects due to UV riboflavin cross-linking (CXL) treatment. PURPOSE We isolate the effects of tissue thickness on the measured corneal biomechanical properties using optical coherence elastography by experimentally altering the tissue hydration state and stiffness. METHODS Dynamic optical coherence elastography was performed using phase-sensitive optical coherence tomography imaging to quantify the tissue deformation dynamics resulting from a spatially discrete, low-force air pulse (150-μm spot size; 0.8-millisecond duration; <10 Pa [<0.08 mmHg]). The time-dependent surface deformation is characterized by a viscoelastic tissue recovery response, quantified by an exponential decay constant-relaxation rate. Ex vivo rabbit globes (n = 10) with fixed intraocular pressure (15 mmHg) were topically instilled every 5 minutes with 0.9% saline for 60 minutes and 20% dextran for another 60 minutes. Measurements were made after every 20 minutes to determine the central corneal thickness (CCT) and the relaxation rates. Cross-linking treatment was performed on another 13 eyes, applying isotonic riboflavin (n = 6) and hypertonic riboflavin (n = 7) every 5 minutes for 30 minutes, followed by UV irradiation (365 nm, 3 mW/cm) for 30 minutes while instilling riboflavin. Central corneal thickness and relaxation rates were obtained before and after CXL treatment. RESULTS Corneal thickness was positively correlated (R = 0.9) with relaxation rates. In the CXL-treated eyes, isotonic riboflavin did not affect CCT and showed a significant increase in relaxation rates (+10%; P = .01) from 2.29 ms to 2.53 ms. Hypertonic riboflavin showed a significant CCT decrease (-31%; P = .01) from 618 μm to 429 μm but showed little change in relaxation rates after CXL treatment. CONCLUSIONS Corneal thickness and stiffness are correlated positively. A higher relaxation rate implied stiffer material properties after isotonic CXL treatment. Hypertonic CXL treatment results in a stiffness decrease that offsets the stiffness increase with CXL treatment.
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13
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Blackburn BJ, Gu S, Ford MR, de Stefano V, Jenkins MW, Dupps WJ, Rollins AM. Noninvasive Assessment of Corneal Crosslinking With Phase-Decorrelation Optical Coherence Tomography. Invest Ophthalmol Vis Sci 2019; 60:41-51. [PMID: 30601930 PMCID: PMC6322634 DOI: 10.1167/iovs.18-25535] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Purpose There is strong evidence that abnormalities in corneal biomechanical play a causal role in corneal ectasias, such as keratoconus. Additionally, corneal crosslinking (CXL) treatment, which halts progression of keratoconus, directly appeals to corneal biomechanics. However, existing methods of corneal biomechanical assessment have various drawbacks: dependence on IOP, long acquisition times, or limited resolution. Here, we present a method that may avoid these limitations by using optical coherence tomography (OCT) to detect the endogenous random motion within the cornea, which can be associated with stromal crosslinking. Methods Phase-decorrelation OCT (PhD-OCT), based in the theory of dynamic light scattering, is a method to spatially resolve endogenous random motion by calculating the decorrelation rate, Γ, of the temporally evolving complex-valued OCT signal. PhD-OCT images of ex vivo porcine globes were recorded during CXL and control protocols. In addition, human patients were imaged with PhD-OCT using a clinical OCT system. Results In both the porcine cornea and the human cornea, crosslinking results in a reduction of Γ (P < 0.0001), indicating more crosslinks. This effect was repeatable in ex vivo porcine corneas (change in average Γ = −41.55 ± 9.64%, n = 5) and not seen after sham treatments (change in average Γ = 2.83 ± 12.56%, n = 5). No dependence of PhD-OCT on IOP was found, and correctable effects were caused by variations in signal-to-noise ratio, hydration, and motion. Conclusions PhD-OCT may be a useful and readily translatable tool for investigating biomechanical properties of the cornea and for enhancing the diagnosis and treatment of patients.
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Affiliation(s)
- Brecken J Blackburn
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
| | - Shi Gu
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
| | - Matthew R Ford
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States
| | | | - Michael W Jenkins
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States.,Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio, United States
| | - William J Dupps
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States.,Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, United States.,Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, United States
| | - Andrew M Rollins
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States
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14
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Kazaili A, Lawman S, Geraghty B, Eliasy A, Zheng Y, Shen Y, Akhtar R. Line-Field Optical Coherence Tomography as a tool for In vitro characterization of corneal biomechanics under physiological pressures. Sci Rep 2019; 9:6321. [PMID: 31004101 PMCID: PMC6474860 DOI: 10.1038/s41598-019-42789-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Accepted: 04/03/2019] [Indexed: 12/02/2022] Open
Abstract
There has been a lot of interest in accurately characterising corneal biomechanical properties under intraocular pressure (IOP) to help better understand ocular pathologies that are associated with elevated IOP. This study investigates the novel use of Line-Field Optical Coherence Tomography (LF-OCT) as an elastographic tool for accurately measuring mechanical properties of porcine corneas based on volumetric deformation following varying IOPs. A custom-built LF-OCT was used to measure geometrical and corneal surface displacement changes in porcine corneas under a range of IOPs, from 0-60 mmHg. Corneal thickness, elastic properties and hysteresis were calculated as a function of pressure. In addition, the effects of hydration were explored. We found that the elastic modulus increased in a linear fashion with IOP. Corneal thickness was found to reduce with IOP, decreasing 14% from 0 to 60 mmHg. Prolonged hydration in phosphate buffered saline (PBS) was found to significantly increase the elastic modulus and corneal hysteresis. Our study demonstrates that LF-OCT can be used to accurately measure the elastic properties based on volumetric deformation following physiological pressures. Furthermore, we show that prolonged hydration in PBS has a significant effect on the measured corneal properties.
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Affiliation(s)
- Ahmed Kazaili
- Department of Mechanical, Materials and Aerospace Engineering, School of Engineering, University of Liverpool, Liverpool, L69 3GH, UK
- Department of Biomedical Engineering, College of Engineering, University of Babylon, Hillah, Iraq
| | - Samuel Lawman
- Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, UK
- Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, L7 8TX, UK
| | - Brendan Geraghty
- Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, L7 8TX, UK
| | - Ashkan Eliasy
- Department of Mechanical, Materials and Aerospace Engineering, School of Engineering, University of Liverpool, Liverpool, L69 3GH, UK
| | - Yalin Zheng
- Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, L7 8TX, UK
| | - Yaochun Shen
- Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, L69 3GJ, UK
| | - Riaz Akhtar
- Department of Mechanical, Materials and Aerospace Engineering, School of Engineering, University of Liverpool, Liverpool, L69 3GH, UK.
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Blackburn BJ, Jenkins MW, Rollins AM, Dupps WJ. A Review of Structural and Biomechanical Changes in the Cornea in Aging, Disease, and Photochemical Crosslinking. Front Bioeng Biotechnol 2019; 7:66. [PMID: 31019909 PMCID: PMC6459081 DOI: 10.3389/fbioe.2019.00066] [Citation(s) in RCA: 78] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 03/07/2019] [Indexed: 12/27/2022] Open
Abstract
The study of corneal biomechanics is motivated by the tight relationship between biomechanical properties and visual function within the ocular system. For instance, variation in collagen fibril alignment and non-enzymatic crosslinks rank high among structural factors which give rise to the cornea's particular shape and ability to properly focus light. Gradation in these and other factors engender biomechanical changes which can be quantified by a wide variety of techniques. This review summarizes what is known about both the changes in corneal structure and associated changes in corneal biomechanical properties in aging, keratoconic, and photochemically crosslinked corneas. In addition, methods for measuring corneal biomechanics are discussed and the topics are related to both clinical studies and biomechanical modeling simulations.
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Affiliation(s)
- Brecken J. Blackburn
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, United States
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
- Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of CWRU, Cleveland, OH, United States
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States
| | - Michael W. Jenkins
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States
- Department of Pediatrics, Case Western Reserve University, Cleveland, OH, United States
| | - Andrew M. Rollins
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States
| | - William J. Dupps
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, United States
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States
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Maczynska E, Karnowski K, Szulzycki K, Malinowska M, Dolezyczek H, Cichanski A, Wojtkowski M, Kaluzny B, Grulkowski I. Assessment of the influence of viscoelasticity of cornea in animal ex vivo model using air-puff optical coherence tomography and corneal hysteresis. JOURNAL OF BIOPHOTONICS 2019; 12:e201800154. [PMID: 30239154 PMCID: PMC7065616 DOI: 10.1002/jbio.201800154] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Accepted: 09/19/2018] [Indexed: 05/29/2023]
Abstract
Application of the air-puff swept source optical coherence tomography (SS-OCT) instrument to determine the influence of viscoelasticity on the relation between overall the air-puff force and corneal apex displacement of porcine corneas ex vivo is demonstrated. Simultaneous recording of time-evolution of the tissue displacement and air pulse stimulus allows obtaining valuable information related in part to the mechanical properties of the cornea. A novel approach based on quantitative analysis of the corneal hysteresis of OCT data is presented. The corneal response to the air pulse is assessed for different well-controlled intraocular pressure (IOP) levels and for the progression of cross-linking-induced stiffness of the cornea. Micrometer resolution, fast acquisition and noncontact character of the air-puff SS-OCT measurements have potential to improve the in vivo assessment of mechanical properties of the human corneas.
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Affiliation(s)
- Ewa Maczynska
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
| | - Karol Karnowski
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
| | - Krzysztof Szulzycki
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
| | - Monika Malinowska
- Laboratory of Molecular and Systemic Neuromorphology, Department of NeurophysiologyNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Hubert Dolezyczek
- Laboratory of Molecular and Systemic Neuromorphology, Department of NeurophysiologyNencki Institute of Experimental Biology, Polish Academy of SciencesWarsawPoland
| | - Artur Cichanski
- Institute of Mechanics and Machine Design, Faculty of Mechanical EngineeringUTP University of Science and TechnologyBydgoszczPoland
| | - Maciej Wojtkowski
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
- Institute of Physical ChemistryPolish Academy of SciencesWarsawPoland
| | - Bartlomiej Kaluzny
- Department of Optometry, Collegium MedicumNicolaus Copernicus UniversityBydgoszczPoland
| | - Ireneusz Grulkowski
- Institute of Physics, Faculty of Physics, Astronomy and InformaticsNicolaus Copernicus UniversityTorunPoland
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Sánchez-Barahona C, Bolívar G, Mikropoulos DG, Konstas AG, Teus MA. Effect of Acute Increases in Intraocular Pressure on Corneal Pachymetry in Rabbit Eyes Treated with Timolol Maleate. Open Ophthalmol J 2018. [DOI: 10.2174/1874364101812010314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Objective:
To evaluate in an in vivo rabbit model, the effect of topical timolol maleate therapy on the central corneal thickness response to acute intraocular pressure increases.
Method:
In this prospective and interventional controlled study, the central corneal thickness and intraocular pressure were measured in vivo in 12 rabbit eyes treated with topical timolol maleate for 1 month and in 12 controls at baseline, and after the intraocular pressure (measured by direct cannulation of the anterior chamber) was increased to 15 and 30 mmHg using a forced saline infusion into the anterior chamber.
Results:
There were no significant differences in the basal central corneal thickness values (control group, 373.2±12.9 µm; study group, 377.5±19.2 µm, p=0.5) or the central corneal thickness values when the intraocular pressure was increased to 15 mmHg (control group, 335.2±14.3 µm; study group, 330.0±32.1 µm, p=0.6) and to 30 mmHg (study group, 318.8±25.3 µm; control group, 329.8±21.0 µm, p=0.3).
Conclusion:
Rabbit corneas treated with topical timolol maleate for 1 month did not show a strain response to acute intraocular pressure increases that differed from control eyes. This is in contrast to a previous finding in which rabbit eyes treated with prostaglandin analogues had a greater decrease in central corneal thickness in response to a sudden intraocular pressure increase compared with untreated corneas.
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De Stefano VS, Ford MR, Seven I, Dupps WJ. Live human assessment of depth-dependent corneal displacements with swept-source optical coherence elastography. PLoS One 2018; 13:e0209480. [PMID: 30592752 PMCID: PMC6310362 DOI: 10.1371/journal.pone.0209480] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Accepted: 12/06/2018] [Indexed: 01/01/2023] Open
Abstract
Purpose To assess depth-dependent corneal displacements in live normal subjects using optical coherence elastography (OCE). Methods A corneal elastography method based on swept-source optical coherence tomography (OCT) was implemented in a clinical prototype. Low amplitude corneal deformation was produced during OCT imaging with a linear actuator-driven lens coupled to force transducers. A cross-correlation algorithm was applied to track frame-by-frame speckle displacement across horizontal meridian scans. Intra-measurement force and displacement data series were plotted against each other to produce local axial stiffness approximations, k, defined by the slope of a linear fit to the force/displacement data (ignoring non-axial contributions from corneal bending). Elastographic maps displaying local k values across the cornea were generated, and the ratio of mean axial stiffness approximations for adjacent anterior and posterior stromal regions, ka/kp, was calculated. Intraclass correlation coefficients (ICC) were used to estimate repeatability. Results Seventeen eyes (ten subjects) were included in this prospective first-in-humans translational study. The ICC was 0.84. Graphs of force vs. displacement demonstrated that, for simultaneously acquired measurements involving the same applied force, anterior stromal displacements were lower (suggesting stiffer behavior) than posterior stromal displacements. Mean ka was 0.016±0.004 g/mm and mean kp was 0.014±0.004 g/mm, giving a mean ka/kp ratio of 1.123±0.062. Conclusion OCE is a clinically feasible, non-invasive corneal biomechanical characterization method capable of resolving depth-dependent differences in corneal deformation behavior. The anterior stroma demonstrated responses consistent with stiffer properties in compression than the posterior stroma, but to a degree that varied across normal eyes. The clinical capability to measure these differences has implications for assessing the biomechanical impact of corneal refractive surgeries and for ectasia risk screening applications.
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Affiliation(s)
- Vinicius S. De Stefano
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, United States of America
- Dept. of Ophthalmology and Visual Sciences, Federal University of Sao Paulo, Sao Paulo, Brazil
| | - Matthew R. Ford
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, United States of America
| | - Ibrahim Seven
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, United States of America
| | - William J. Dupps
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, United States of America
- Dept. of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States of America
- Dept. of Ophthalmology, Cleveland Clinic Lerner College of Medicine of CWRU, Cleveland, OH, United States of America
- * E-mail:
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Pant AD, Gogte P, Pathak-Ray V, Dorairaj SK, Amini R. Increased Iris Stiffness in Patients With a History of Angle-Closure Glaucoma: An Image-Based Inverse Modeling Analysis. ACTA ACUST UNITED AC 2018; 59:4134-4142. [DOI: 10.1167/iovs.18-24327] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- Anup Dev Pant
- Department of Biomedical Engineering, The University of Akron, Akron, Ohio, United States
| | | | | | - Syril K. Dorairaj
- Department of Ophthalmology, Mayo Clinic, Jacksonville, Florida, United States
| | - Rouzbeh Amini
- Department of Biomedical Engineering, The University of Akron, Akron, Ohio, United States
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Singh M, Han Z, Li J, Vantipalli S, Aglyamov SR, Twa MD, Larin KV. Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography. J Cataract Refract Surg 2018; 44:1023-1031. [PMID: 30049567 DOI: 10.1016/j.jcrs.2018.03.036] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 02/17/2018] [Accepted: 03/20/2018] [Indexed: 01/08/2023]
Abstract
PURPOSE To quantify the effects of the hydration state on the Young's modulus of the cornea. SETTING Biomedical Optics Laboratory, University of Houston, Houston, Texas, USA. DESIGN Experimental study. METHODS Noncontact, dynamic optical coherence elastography (OCE) measurements were taken of in situ rabbit corneas in the whole eye-globe configuration (n = 10) and at an artificially controlled intraocular pressure of 15 mm Hg. Baseline OCE measurements were taken by topically hydrating the corneas with saline for 1 hour. The corneas were then dehydrated topically with a 20% dextran solution for another hour, and the OCE measurements were repeated. A finite element method was used to quantify the Young's modulus of the corneas based on the OCE measurements. RESULTS The thickness of the corneas shrank considerably after topical addition of the 20% dextran solution (∼680 μm to ∼370 μm), and the OCE-measured elastic-wave speed correspondingly decreased (∼3.2 m/s to ∼2.6 m/s). The finite element method results showed an increase in Young's modulus (500 kPa to 800 kPa) resulting from dehydration and subsequent thinning. CONCLUSION Young's modulus increased significantly as the corneas dehydrated and thinned, showing that corneal geometry and hydration state are critical factors for accurately quantifying corneal biomechanical properties.
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Affiliation(s)
- Manmohan Singh
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Zhaolong Han
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Jiasong Li
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Srilatha Vantipalli
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Salavat R Aglyamov
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Michael D Twa
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Kirill V Larin
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia.
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Pavlatos E, Chen H, Clayson K, Pan X, Liu J. Imaging Corneal Biomechanical Responses to Ocular Pulse Using High-Frequency Ultrasound. IEEE TRANSACTIONS ON MEDICAL IMAGING 2018; 37:663-670. [PMID: 29408793 PMCID: PMC5826553 DOI: 10.1109/tmi.2017.2775146] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Imaging corneal biomechanical changes or abnormalities is important for better clinical diagnosis and treatment of corneal diseases. We propose a novel ultrasound-based method, called ocular pulse elastography (OPE), to image corneal deformation during the naturally occurring ocular pulse. Experiments on animal and human donor eyes, as well as synthetic radiofrequency (RF) data, were used to evaluate the efficacy of the OPE method. Using very high-frequency ultrasound (center frequency = 55 MHz), correlation-based speckle tracking yielded an accuracy of less than 10% error for axial tissue displacements of or above. Satisfactory speckle tracking was achieved for out-of-plane displacements up to . Using synthetic RF data with or without a pre-defined uniform strain, the OPE method detected strains down to 0.0001 axially and 0.00025 laterally with an error less than 10%. Experiments in human donor eyes showed excellent repeatability with an intraclass correlation of 0.98. The measurement outcome from OPE was also shown to be highly correlated with that of standard inflation. These results suggest the feasibility of OPE as a potential clinical tool for evaluating corneal biomechanics in vivo.
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Clayson K, Pavlatos E, Ma Y, Liu J. 3D Characterization of corneal deformation using ultrasound speckle tracking. JOURNAL OF INNOVATIVE OPTICAL HEALTH SCIENCES 2017; 10:1742005. [PMID: 29399203 PMCID: PMC5794035 DOI: 10.1142/s1793545817420056] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The three-dimensional (3D) mechanical response of the cornea to intraocular pressure (IOP) elevation has not been previously reported. In this study, we use an ultrasound speckle tracking technique to measure the 3D displacements and strains within the central 5.5 mm of porcine corneas during the whole globe inflation. Inflation tests were performed on dextran-treated corneas (treated with a 10% dextran solution) and untreated corneas. The dextran-treated corneas showed an inflation response expected of a thin spherical shell, with through-thickness thinning and in-plane stretch, although the strain magnitudes exhibited a heterogeneous spatial distribution from the central to more peripheral cornea. The untreated eyes demonstrated a response consistent with swelling during experimentation, with through-thickness expansion overriding the inflation response. The average volume ratios obtained in both groups was near 1 confirming general incompressibility, but local regions of volume loss or expansion were observed. These results suggest that biomechanical measurements in 3D provide important new insight to understand the mechanical response of ocular tissues such as the cornea.
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Affiliation(s)
- Keyton Clayson
- Department of Biomedical Engineering, The Ohio State University Columbus, OH 43210, USA
- Biophysics Interdisciplinary Group, The Ohio State University Columbus, OH 43210, USA
| | - Elias Pavlatos
- Department of Biomedical Engineering, The Ohio State University Columbus, OH 43210, USA
| | - Yanhui Ma
- Department of Biomedical Engineering, The Ohio State University Columbus, OH 43210, USA
| | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University Columbus, OH 43210, USA
- Biophysics Interdisciplinary Group, The Ohio State University Columbus, OH 43210, USA
- Department of Ophthalmology and Visual Science The Ohio State University, Columbus, OH 43210, USA
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Singh M, Li J, Vantipalli S, Han Z, Larin KV, Twa MD. Optical coherence elastography for evaluating customized riboflavin/UV-A corneal collagen crosslinking. JOURNAL OF BIOMEDICAL OPTICS 2017; 22:91504. [PMID: 28055060 PMCID: PMC5995143 DOI: 10.1117/1.jbo.22.9.091504] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 11/15/2016] [Indexed: 05/02/2023]
Abstract
UV-induced collagen cross-linking is a promising treatment for keratoconus that stiffens corneal tissue and prevents further degeneration. Since keratoconus is generally localized, the efficacy of collagen cross-linking (CXL) treatments could be improved by stiffening only the weakened parts of the cornea. Here, we demonstrate that optical coherence elastography (OCE) can spatially resolve transverse variations in corneal stiffness. A short duration ( ? 1 ?? ms ) focused air-pulse induced low amplitude ( ? 10 ?? ? m ) deformations in the samples that were detected using a phase-stabilized optical coherence tomography system. A two-dimensional map of material stiffness was generated by measuring the damped natural frequency (DNF) of the air-pulse induced response at various transverse locations of a heterogeneous phantom mimicking a customized CXL treatment. After validation on the phantoms, similar OCE measurements were made on spatially selective CXL-treated in situ rabbit corneas. The results showed that this technique was able to clearly distinguish the untreated and CXL-treated regions of the cornea, where CXL increased the DNF of the cornea by ? 51 % . Due to the noncontact nature and minimal excitation force, this technique may be valuable for in vivo assessments of corneal biomechanical properties.
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Affiliation(s)
- Manmohan Singh
- University of Houston, Biomedical Engineering, 3517 Cullen Boulevard, Room 2027, Houston, Texas 77204, United States
| | - Jiasong Li
- University of Houston, Biomedical Engineering, 3517 Cullen Boulevard, Room 2027, Houston, Texas 77204, United States
| | - Srilatha Vantipalli
- University of Houston, Department of Optometry, 4901 Calhoun Road, Houston, Texas 77204, United States
| | - Zhaolong Han
- University of Houston, Biomedical Engineering, 3517 Cullen Boulevard, Room 2027, Houston, Texas 77204, United States
| | - Kirill V. Larin
- University of Houston, Biomedical Engineering, 3517 Cullen Boulevard, Room 2027, Houston, Texas 77204, United States
- Baylor College of Medicine, Molecular Physiology and Biophysics, One Baylor Plaza, Houston, Texas 77030, United States
- Samara State Aerospace University, Electrical and Computer Engineering, 34, Moskovskoye shosse, Samara 443086, Russia
| | - Michael D. Twa
- University of Alabama at Birmingham, School of Optometry, 1716 University Boulevard, Birmingham, Alabama 35233, United States
- Address all correspondence to: Michael D. Twa,
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Singh M, Li J, Han Z, Vantipalli S, Liu CH, Wu C, Raghunathan R, Aglyamov SR, Twa MD, Larin KV. Evaluating the Effects of Riboflavin/UV-A and Rose-Bengal/Green Light Cross-Linking of the Rabbit Cornea by Noncontact Optical Coherence Elastography. Invest Ophthalmol Vis Sci 2017; 57:OCT112-20. [PMID: 27409461 PMCID: PMC4968774 DOI: 10.1167/iovs.15-18888] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Purpose The purpose of this study was to use noncontact optical coherence elastography (OCE) to evaluate and compare changes in biomechanical properties that occurred in rabbit cornea in situ after corneal collagen cross-linking by either of two techniques: ultraviolet-A (UV-A)/riboflavin or rose-Bengal/green light. Methods Low-amplitude (≤10 μm) elastic waves were induced in mature rabbit corneas by a focused air pulse. Elastic wave propagation was imaged by a phase-stabilized swept source OCE (PhS-SSOCE) system. Corneas were then cross-linked by either of two methods: UV-A/riboflavin (UV-CXL) or rose-Bengal/green light (RGX). Phase velocities of the elastic waves were fitted to a previously developed modified Rayleigh-Lamb frequency equation to obtain the viscoelasticity of the corneas before and after the cross-linking treatments. Micro-scale depth-resolved phase velocity distribution revealed the depth-wise heterogeneity of both cross-linking techniques. Results Under standard treatment settings, UV-CXL significantly increased the stiffness of the corneas by ∼47% (P < 0.05), but RGX did not produce statistically significant increases. The shear viscosities were unaffected by either cross-linking technique. The depth-wise phase velocities showed that UV-CXL affected the anterior ∼34% of the corneas, whereas RGX affected only the anterior ∼16% of the corneas. Conclusions UV-CXL significantly strengthens the cornea, whereas RGX does not, and the effects of cross-linking by UV-CXL reach deeper into the cornea than cross-linking effects of RGX under similar conditions.
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Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Jiasong Li
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Zhaolong Han
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | | | - Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Chen Wu
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Raksha Raghunathan
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas, United States
| | - Michael D Twa
- School of Optometry, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States 5Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk, Russia
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Larin KV, Sampson DD. Optical coherence elastography - OCT at work in tissue biomechanics [Invited]. BIOMEDICAL OPTICS EXPRESS 2017; 8:1172-1202. [PMID: 28271011 PMCID: PMC5330567 DOI: 10.1364/boe.8.001172] [Citation(s) in RCA: 203] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Revised: 01/18/2017] [Accepted: 01/19/2017] [Indexed: 05/18/2023]
Abstract
Optical coherence elastography (OCE), as the use of OCT to perform elastography has come to be known, began in 1998, around ten years after the rest of the field of elastography - the use of imaging to deduce mechanical properties of tissues. After a slow start, the maturation of OCT technology in the early to mid 2000s has underpinned a recent acceleration in the field. With more than 20 papers published in 2015, and more than 25 in 2016, OCE is growing fast, but still small compared to the companion fields of cell mechanics research methods, and medical elastography. In this review, we describe the early developments in OCE, and the factors that led to the current acceleration. Much of our attention is on the key recent advances, with a strong emphasis on future prospects, which are exceptionally bright.
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Affiliation(s)
- Kirill V Larin
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Blvd., Houston, Texas 77204-5060, USA; Department of Molecular Physiology and Biophysics, Baylor College of Medicine, 1 Baylor Plaza, Houston, Texas 77030, USA;
| | - David D Sampson
- Optical + Biomedical Engineering Laboratory, School of Electrical, Electronic & Computer Engineering, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia; Centre for Microscopy, Characterisation & Analysis, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia;
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Nunes V, Cross J, Speich JE, Morgan DR, Strauss JF, Ramus RM. Fetal membrane imaging and the prediction of preterm birth: a systematic review, current issues, and future directions. BMC Pregnancy Childbirth 2016; 16:387. [PMID: 27938341 PMCID: PMC5148829 DOI: 10.1186/s12884-016-1176-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Accepted: 12/01/2016] [Indexed: 01/08/2023] Open
Abstract
Background Preterm premature rupture of membranes (PPROM) is the largest identifiable cause of preterm birth. There is currently no good screening test for PPROM in low-risk asymptomatic patients. Our goal was to identify how imaging methods can be utilized for examining the risks for PPROM in asymptomatic patients. Methods This paper is a systematic review of the literature on fetal membrane thickness and its use for the prediction of PPROM. Four key studies are identified and reviewed; two in vitro studies and two in vivo ultrasound studies each using differing methodologies. Additionally reviewed is a study using Optical Coherence Tomography, an emerging technique using near-infrared technology to produce high-resolution images. Results There is currently insufficient data to determine the association between fetal membrane thickness and PPROM by ultrasound. Conclusions Fetal membrane thickness could have relevant clinical ramifications for the prediction of PPROM. Suggested improvements in study methodology and design will lead to progress in this area of research, as well as the use of newer technologies. Larger sample sizes, histological comparison, uniform methodologies for data collection, longitudinal study design and expanding data analysis beyond fetal membrane thickness to other properties would expand our knowledge in this field. In addition, transvaginal ultrasound should be utilized to improve resolution, as well as emerging methodologies such as MRI fusion imaging using ultrasound and Shear Wave Elastography.
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Affiliation(s)
- Vanessa Nunes
- Department of Obstetrics & Gynecology, Virginia Commonwealth University, Richmond, VA, USA
| | - Jennifer Cross
- Department of Obstetrics & Gynecology, Virginia Commonwealth University, Richmond, VA, USA
| | - John E Speich
- Department of Mechanical and Nuclear Engineering, School of Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Danielle R Morgan
- Department of Obstetrics & Gynecology, Virginia Commonwealth University, Richmond, VA, USA
| | - Jerome F Strauss
- Department of Obstetrics & Gynecology, Virginia Commonwealth University, Richmond, VA, USA
| | - Ronald M Ramus
- Department of Obstetrics & Gynecology, Virginia Commonwealth University, Richmond, VA, USA.
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Han Z, Li J, Singh M, Wu C, Liu CH, Raghunathan R, Aglyamov SR, Vantipalli S, Twa MD, Larin KV. Optical coherence elastography assessment of corneal viscoelasticity with a modified Rayleigh-Lamb wave model. J Mech Behav Biomed Mater 2016; 66:87-94. [PMID: 27838594 DOI: 10.1016/j.jmbbm.2016.11.004] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Revised: 10/27/2016] [Accepted: 11/02/2016] [Indexed: 01/22/2023]
Abstract
The biomechanical properties of the cornea play a critical role in forming vision. Diseases such as keratoconus can structurally degenerate the cornea causing a pathological loss in visual acuity. UV-A/riboflavin corneal collagen crosslinking (CXL) is a clinically available treatment to stiffen the cornea and restore its healthy shape and function. However, current CXL techniques do not account for pre-existing biomechanical properties of the cornea nor the effects of the CXL treatment itself. In addition to the inherent corneal structure, the intraocular pressure (IOP) can also dramatically affect the measured biomechanical properties of the cornea. In this work, we present the details and development of a modified Rayleigh-Lamb frequency equation model for quantifying corneal biomechanical properties. After comparison with finite element modeling, the model was utilized to quantify the viscoelasticity of in situ porcine corneas in the whole eye-globe configuration before and after CXL based on noncontact optical coherence elastography measurements. Moreover, the viscoelasticity of the untreated and CXL-treated eyes was quantified at various IOPs. The results showed that the stiffness of the cornea increased after CXL and that corneal stiffness is close to linear as a function of IOP. These results show that the modified Rayleigh-Lamb wave model can provide an accurate assessment of corneal viscoelasticity, which could be used for customized CXL therapies.
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Affiliation(s)
- Zhaolong Han
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Jiasong Li
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Chen Wu
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Raksha Raghunathan
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712, United States
| | - Srilatha Vantipalli
- College of Optometry, University of Houston, Houston, TX 77204, United States
| | - Michael D Twa
- School of Optometry, University of Alabama at Birmingham, Birmingham, AL 35233, United States
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States; Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk, Russia; Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, United States.
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30
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Singh M, Li J, Vantipalli S, Wang S, Han Z, Nair A, Aglyamov SR, Twa MD, Larin KV. Noncontact Elastic Wave Imaging Optical Coherence Elastography for Evaluating Changes in Corneal Elasticity Due to Crosslinking. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS : A PUBLICATION OF THE IEEE LASERS AND ELECTRO-OPTICS SOCIETY 2016. [PMID: 27547022 DOI: 10.1109/jqe.2016.2585338] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The mechanical properties of tissues can provide valuable information about tissue integrity and health and can assist in detecting and monitoring the progression of diseases such as keratoconus. Optical coherence elastography (OCE) is a rapidly emerging technique, which can assess localized mechanical contrast in tissues with micrometer spatial resolution. In this work we present a noncontact method of optical coherence elastography to evaluate the changes in the mechanical properties of the cornea after UV-induced collagen cross-linking. A focused air-pulse induced a low amplitude (μm scale) elastic wave, which then propagated radially and was imaged in three dimensions by a phase-stabilized swept source optical coherence tomography (PhS-SSOCT) system. The elastic wave velocity was translated to Young's modulus in agar phantoms of various concentrations. Additionally, the speed of the elastic wave significantly changed in porcine cornea before and after UV-induced corneal collagen cross-linking (CXL). Moreover, different layers of the cornea, such as the anterior stroma, posterior stroma, and inner region, could be discerned from the phase velocities of the elastic wave. Therefore, because of noncontact excitation and imaging, this method may be useful for in vivo detection of ocular diseases such as keratoconus and evaluation of therapeutic interventions such as CXL.
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Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77204 USA
| | - Jiasong Li
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77204 USA
| | | | - Shang Wang
- Department of Molecular Physiology and Biophysics at Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 USA
| | - Zhaolong Han
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77204 USA
| | - Achuth Nair
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77004 USA
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78731 USA
| | - Michael D Twa
- School of Optometry at the University of Alabama at Birmingham, Birmingham, AL 35924
| | - Kirill V Larin
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77004 USA and and the Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk 634050, Russia, phone: 832-842-8834; fax: 713-743-0226
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31
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Singh M, Li J, Vantipalli S, Wang S, Han Z, Nair A, Aglyamov SR, Twa MD, Larin KV. Noncontact Elastic Wave Imaging Optical Coherence Elastography for Evaluating Changes in Corneal Elasticity Due to Crosslinking. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS : A PUBLICATION OF THE IEEE LASERS AND ELECTRO-OPTICS SOCIETY 2016; 22:6801911. [PMID: 27547022 PMCID: PMC4990138 DOI: 10.1109/jstqe.2015.2510293] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The mechanical properties of tissues can provide valuable information about tissue integrity and health and can assist in detecting and monitoring the progression of diseases such as keratoconus. Optical coherence elastography (OCE) is a rapidly emerging technique, which can assess localized mechanical contrast in tissues with micrometer spatial resolution. In this work we present a noncontact method of optical coherence elastography to evaluate the changes in the mechanical properties of the cornea after UV-induced collagen cross-linking. A focused air-pulse induced a low amplitude (μm scale) elastic wave, which then propagated radially and was imaged in three dimensions by a phase-stabilized swept source optical coherence tomography (PhS-SSOCT) system. The elastic wave velocity was translated to Young's modulus in agar phantoms of various concentrations. Additionally, the speed of the elastic wave significantly changed in porcine cornea before and after UV-induced corneal collagen cross-linking (CXL). Moreover, different layers of the cornea, such as the anterior stroma, posterior stroma, and inner region, could be discerned from the phase velocities of the elastic wave. Therefore, because of noncontact excitation and imaging, this method may be useful for in vivo detection of ocular diseases such as keratoconus and evaluation of therapeutic interventions such as CXL.
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Affiliation(s)
| | | | | | - Shang Wang
- Department of Molecular Physiology and Biophysics at Baylor College
of Medicine, One Baylor Plaza, Houston, TX 77030 USA
| | - Zhaolong Han
- Department of Biomedical Engineering at the University of Houston,
Houston, TX 77204 USA
| | - Achuth Nair
- Department of Biomedical Engineering at the University of Houston,
Houston, TX 77004 USA
| | - Salavat R. Aglyamov
- Department of Biomedical Engineering, University of Texas at
Austin, Austin, TX 78731 USA
| | - Michael D. Twa
- School of Optometry at the University of Alabama at Birmingham,
Birmingham, AL 35924
| | - Kirill V. Larin
- Department of Biomedical Engineering at the University of Houston,
Houston, TX 77004 USA and and the Interdisciplinary Laboratory of
Biophotonics, Tomsk State University, Tomsk 634050, Russia, phone:
832-842-8834; fax: 713-743-0226
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Hatami-Marbini H, Rahimi A. Interrelation of Hydration, Collagen Cross-Linking Treatment, and Biomechanical Properties of the Cornea. Curr Eye Res 2015; 41:616-22. [PMID: 26126201 DOI: 10.3109/02713683.2015.1042546] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
PURPOSE The present study was designed to investigate the effects of hydration and collagen cross-linking treatment on biomechanical properties of the cornea. METHODS The original corneal collagen cross-linking protocol was used to induce cross-links in bovine corneas. The thickness of samples was used as a measure of their hydration and five different thickness groups (n = 5 each) were considered. The cross-linked corneal strips were allowed to hydrate/dehydrate until their thickness reached 500, 700, 900, 1100, and 1500 μm. The tensile behavior of specimens in each thickness group was characterized by conducting uniaxial tensile experiments. The experiments were done in mineral oil in order to keep the thickness of samples constant and minimize hydration changes. RESULTS It was observed that collagen cross-linking treatment significantly increased both the maximum tensile stress and the equilibrium (relaxed) stress of the bovine cornea (p < 0.01). Furthermore, with increasing the thickness (hydration) of the collagen cross-linked samples, their tensile stiffness significantly decreased (p < 0.01). An exponential relation and a logarithmic expression successfully represented experimentally measured stress-strain behavior and relaxation response of all groups (r(2 )> 0.99), respectively. CONCLUSION Hydration and collagen cross-linking treatment concomitantly affect biomechanical properties of the cornea. Therefore, an accurate estimate of stiffening effects of collagen cross-linking treatment option using uniaxial tensile experiments is only possible if the hydration of specimens is fully controlled.
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Affiliation(s)
- Hamed Hatami-Marbini
- a Computational Biomechanics Laboratory, School of Mechanical and Aerospace Engineering, Oklahoma State University , Stillwater , OK , USA
| | - Abdolrasol Rahimi
- a Computational Biomechanics Laboratory, School of Mechanical and Aerospace Engineering, Oklahoma State University , Stillwater , OK , USA
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Effects of corneal cross-linking on ocular response analyzer waveform-derived variables in keratoconus and postrefractive surgery ectasia. Eye Contact Lens 2015; 40:339-44. [PMID: 25365551 DOI: 10.1097/icl.0000000000000090] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
PURPOSE To assess changes in Ocular Response Analyzer (ORA) waveforms after UVA/riboflavin corneal collagen cross-linking (CXL) using investigator-derived and manufacturer-supplied morphometric variables in patients with keratoconus (KC) and postrefractive surgery ectasia. DESIGN Prospective randomized trial of a standard epithelium-off CXL protocol. PARTICIPANTS Patients with progressive KC (24 eyes of 21 patients) or postrefractive surgery ectasia (27 eyes of 23 patients) were enrolled. METHODS Replicate ORA measurements were obtained before and 3 months after CXL. Pretreatment and posttreatment waveform variables were analyzed for differences by paired Student t tests using measurements with the highest waveform scores. MAIN OUTCOME MEASURES Corneal hysteresis, corneal resistance factor, 37-s generation manufacturer-supplied ORA variables, and 15 investigator-derived ORA variables. RESULTS No variables were significantly different 3 months after CXL in the KC group, and no manufacturer-supplied variables changed significantly in the postrefractive surgery ectasia group. Four custom variables (ApplanationOnsetTime, P1P2avg, Impulse, and Pmax) increased by small but statistically significant margins after CXL in the postrefractive surgery ectasia group. CONCLUSIONS Changes in a small subset of investigator-derived variables suggested an increase in corneal bending resistance after CXL. However, the magnitudes of these changes were low and not commensurate with the degree of clinical improvement or prior computational estimates of corneal stiffening in the same cohort over the same period. Available air-puff-derived measures of the corneal deformation response underestimate the biomechanical changes produced by CXL.
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Brown SE, Simmasalam R, Antonova N, Gadaria N, Asbell PA. Progression in keratoconus and the effect of corneal cross-linking on progression. Eye Contact Lens 2015; 40:331-8. [PMID: 25320958 DOI: 10.1097/icl.0000000000000085] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Ultraviolet corneal collagen cross-linking (CXL) has been shown to possibly delay, halt, or even reverse disease progression in keratoconus. Understanding of keratoconic progression in untreated eyes, however, is still incomplete and is hampered by the varying definitions and metrics used to evaluate corneal changes. As a result, the CXL literature varies widely in criteria for progression and parameters for successful outcomes. To date, there have been few long-term, well-controlled clinical trials supporting the efficacy of CXL to prevent progression in keratoconus. Review of our data on keratoconus suggests the course of corneal change is difficult to predict and that many keratoconic eyes appear stable once the eyes begin to exhibit frank changes in corneal curvature typical of keratoconus. Better-defined metrics for progression in keratoconus are needed. Larger, long-term randomized clinical trials may more clearly establish the efficacy and safety of CXL in the management of keratoconus and determine which patients are the best candidates for this procedure.
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Affiliation(s)
- Sarah E Brown
- Department of Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, NY
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35
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Kim J, Brown W, Maher JR, Levinson H, Wax A. Functional optical coherence tomography: principles and progress. Phys Med Biol 2015; 60:R211-37. [PMID: 25951836 PMCID: PMC4448140 DOI: 10.1088/0031-9155/60/10/r211] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In the past decade, several functional extensions of optical coherence tomography (OCT) have emerged, and this review highlights key advances in instrumentation, theoretical analysis, signal processing and clinical application of these extensions. We review five principal extensions: Doppler OCT (DOCT), polarization-sensitive OCT (PS-OCT), optical coherence elastography (OCE), spectroscopic OCT (SOCT), and molecular imaging OCT. The former three have been further developed with studies in both ex vivo and in vivo human tissues. This review emphasizes the newer techniques of SOCT and molecular imaging OCT, which show excellent potential for clinical application but have yet to be well reviewed in the literature. SOCT elucidates tissue characteristics, such as oxygenation and carcinogenesis, by detecting wavelength-dependent absorption and scattering of light in tissues. While SOCT measures endogenous biochemical distributions, molecular imaging OCT detects exogenous molecular contrast agents. These newer advances in functional OCT broaden the potential clinical application of OCT by providing novel ways to understand tissue activity that cannot be accomplished by other current imaging methodologies.
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Affiliation(s)
- Jina Kim
- Department of Surgery, Duke University, Durham, NC 27710, USA
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36
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Understanding the Correlation between Tomographic and Biomechanical Severity of Keratoconic Corneas. BIOMED RESEARCH INTERNATIONAL 2015; 2015:294197. [PMID: 25945330 PMCID: PMC4402575 DOI: 10.1155/2015/294197] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/31/2014] [Revised: 10/14/2014] [Accepted: 10/15/2014] [Indexed: 11/26/2022]
Abstract
Purpose. To evaluate correlation between tomographic gradation of keratoconus (KC) and its corresponding air-puff induced biomechanical response. Methods. Corneal tomography and biomechanics were measured with Scheimpflug imaging in 44 normal and 92 KC corneas. Deformation waveform was also analyzed with Fourier series. A custom KC severity scale was used from 1 to 3 with 3 as the most severe grade. Tomographic and biomechanical variables were assessed among the grades. Sensitivity and specificity of the variables were assessed using receiver operating characteristics (ROC). Results. Curvature variables were significantly different between normal and disease (P < 0.05) and among grades (P < 0.05). Biomechanical variables were significantly different between normal and disease (P<0.05) but similar among grades 1 and 2 (P > 0.05). All variables had an area under the ROC curve greater than 0.5. The root mean square of the Fourier cosine coefficients had the best ROC (0.92, cut-off: 0.027, sensitivity: 83%, specificity: 88.6%). Spearman correlation coefficient was significant between most variables (P < 0.05). However, tomographic segregation of keratoconus did not result in concomitant biomechanical segregation of the grades. Conclusions. There was lack of significant biomechanical difference between mild disease grades, despite progressive corneal thinning. Mathematical models that estimate corneal modulus from air-puff deformation may be more useful.
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Sinha Roy A, Kurian M, Matalia H, Shetty R. Air-puff associated quantification of non-linear biomechanical properties of the human cornea in vivo. J Mech Behav Biomed Mater 2015; 48:173-182. [PMID: 25955559 DOI: 10.1016/j.jmbbm.2015.04.010] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Revised: 04/05/2015] [Accepted: 04/09/2015] [Indexed: 11/30/2022]
Abstract
With the advent of newer techniques to correct refraction such as flapless laser procedure and collagen crosslinking, in vivo estimation of corneal biomechanical properties has gained importance. In this study, a new 3-D patient specific inverse finite element method of estimating corneal biomechanical properties from air-puff applanation was developed. The highlight of the model was inclusion of patient-specific corneal tomography, fiber dependent hyperelastic model, cross links between collagen lamellae and epithelium layer. A lumped mass, spring and dashpot model was included to model the resistance to motion and deformation of the eye globe caused by air-puff applanation. 10 normal eyes of 10 human subjects were used for the study. 3-D finite element models were constructed and custom routines were scripted for performing the inverse calculations. The model for each eye was perturbed to estimate the effect of measured intraocular pressure on the estimated biomechanical variables. The study demonstrated that the inverse method was effective in quantification of material properties and was sensitive to intraocular pressure alterations. Specifically, in vivo fiber dependent hyperelastic biomechanical properties of human corneas were estimated for the first time.
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Affiliation(s)
- Abhijit Sinha Roy
- Imaging, Biomechanics and Mathematical Modeling Solutions, Narayana Nethralaya, Bangalore, India.
| | - Mathew Kurian
- Cornea and Cataract Services, Narayana Nethralaya, Bangalore, India
| | - Himanshu Matalia
- Corneal and Refractive Services, Narayana Nethralaya, Bangalore, India
| | - Rohit Shetty
- Corneal and Refractive Services, Narayana Nethralaya, Bangalore, India; Narayana Nethralaya, Bangalore, India
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Hatami-Marbini H, Rahimi A. Evaluation of hydration effects on tensile properties of bovine corneas. J Cataract Refract Surg 2015; 41:644-51. [DOI: 10.1016/j.jcrs.2014.07.029] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 06/12/2014] [Accepted: 07/11/2014] [Indexed: 11/27/2022]
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Torricelli AAM, Ford MR, Singh V, Santhiago MR, Dupps WJ, Wilson SE. BAC-EDTA transepithelial riboflavin-UVA crosslinking has greater biomechanical stiffening effect than standard epithelium-off in rabbit corneas. Exp Eye Res 2014; 125:114-7. [PMID: 24929203 DOI: 10.1016/j.exer.2014.06.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 05/12/2014] [Accepted: 06/04/2014] [Indexed: 10/25/2022]
Abstract
Studies suggest that standard corneal collagen crosslinking (CXL) is a safe and effective treatment to stiffen the cornea for keratoconus and other ectatic corneal disorders. The purpose of the present study was to compare the biomechanical effects of transepithelial benzalkonium chloride-EDTA (BAC-EDTA) riboflavin-UVA crosslinking to standard epithelium-off riboflavin-UVA crosslinking in a rabbit model. Corneal stiffness was quantified using optical coherence elastography at two months after treatment. The mean lateral-to-axial displacement ratio for the BAC-EDTA transepithelial CXL group was lower (greater stiffness) [0.062 ± 0.042, mean ± SD] than epithelium-off CXL (mean ± SD: 0.065 ± 0.045) or untreated control eyes (0.069 ± 0.044). Using ANOVA with Tukey correction, a statistically significant difference was found between the BAC-EDTA transepithelial CXL group and standard epithelium-off CXL (p = 0.0019) or the untreated control (p < 0.0001) groups. A graph of the probability density functions for biomechanical stiffness also showed a greater shift in stiffening in the BAC-EDTA transepithelial CXL group than the standard epithelium-off CXL or untreated control group. These results demonstrated that the biomechanical stiffening effect produced by BAC-EDTA transepithelial CXL was greater than that produced by standard epithelium-off CXL in a rabbit model.
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Affiliation(s)
- Andre A M Torricelli
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA; University of Sao Paulo, Sao Paulo, Brazil
| | - Matthew R Ford
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Vivek Singh
- LV Prasad Eye Institute, HERF, Hyderabad, AP, India
| | - Marcony R Santhiago
- University of Sao Paulo, Sao Paulo, Brazil; Federal University of Rio de Janeiro, Brazil
| | - William J Dupps
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA; Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, OH, USA
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