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Mekonnen TT, Zevallos-Delgado C, Hatami M, Singh M, Aglyamov SR, Larin KV. Acute alcohol consumption modulates corneal biomechanical properties as revealed by optical coherence elastography. J Biomech 2024; 169:112155. [PMID: 38761746 DOI: 10.1016/j.jbiomech.2024.112155] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 05/03/2024] [Accepted: 05/14/2024] [Indexed: 05/20/2024]
Abstract
Acute alcohol ingestion has been found to impact visual functions, including eye movement, but its effects on corneal biomechanical properties remain unclear. This study aimed to investigate the influence of acute alcohol consumption on corneal biomechanical properties using optical coherence elastography (OCE). An air-coupled ultrasound transducer induced elastic waves in mice corneas in vivo, and a high-resolution phase-sensitive optical coherence tomography (OCT) system tracked the mechanical waves to quantify the elastic wave speed. In vivo measurements were performed on three groups of age- and gender-matched mice: control, placebo (administered saline), and alcohol (administered ethanol) groups. Longitudinal measurements were conducted over a one-hour period to assess acute temporal changes in wave speeds, which are associated with inherent biomechanical properties of the cornea. The results showed a significant decrease in wave speed for the alcohol group after 10 min of ingestion in comparison to pre-ingestion values (p = 0.0096), whereas the temporal wave speed changes for the placebo group were statistically insignificant (p = 0.076). In contrast, the control group showed no significant changes in elastic wave speed and corneal thickness. Furthermore, a significant difference was observed between the wave speeds of the placebo and alcohol groups at each measurement time point between 10 and 50 min (p < 0.05), though both groups exhibited a similar trend in corneal thickness change. The findings of this study have important implications for clinical assessments and research in corneal disorders, highlighting the potential of OCE as a valuable tool for evaluating such changes.
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Affiliation(s)
- Taye Tolu Mekonnen
- Department of Biomedical Engineering, University of Houston, Houston, TX, USA
| | | | - Maryam Hatami
- Department of Biomedical Engineering, University of Houston, Houston, TX, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX, USA
| | - Salavat R Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX, USA
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX, USA.
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Wang C, Zhu J, Ma J, Meng X, Ma Z, Fan F. Optical coherence elastography and its applications for the biomechanical characterization of tissues. JOURNAL OF BIOPHOTONICS 2023; 16:e202300292. [PMID: 37774137 DOI: 10.1002/jbio.202300292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Revised: 09/19/2023] [Accepted: 09/27/2023] [Indexed: 10/01/2023]
Abstract
The biomechanical characterization of the tissues provides significant evidence for determining the pathological status and assessing the disease treatment. Incorporating elastography with optical coherence tomography (OCT), optical coherence elastography (OCE) can map the spatial elasticity distribution of biological tissue with high resolution. After the excitation with the external or inherent force, the tissue response of the deformation or vibration is detected by OCT imaging. The elastogram is assessed by stress-strain analysis, vibration amplitude measurements, and quantification of elastic wave velocities. OCE has been used for elasticity measurements in ophthalmology, endoscopy, and oncology, improving the precision of diagnosis and treatment of disease. In this article, we review the OCE methods for biomechanical characterization and summarize current OCE applications in biomedicine. The limitations and future development of OCE are also discussed during its translation to the clinic.
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Affiliation(s)
- Chongyang Wang
- Key Laboratory of the Ministry of Education for Optoelectronic Measurement Technology and Instrument, Beijing Information Science and Technology University, Beijing, China
| | | | - Jiawei Ma
- Key Laboratory of the Ministry of Education for Optoelectronic Measurement Technology and Instrument, Beijing Information Science and Technology University, Beijing, China
| | - Xiaochen Meng
- Key Laboratory of the Ministry of Education for Optoelectronic Measurement Technology and Instrument, Beijing Information Science and Technology University, Beijing, China
| | - Zongqing Ma
- Key Laboratory of the Ministry of Education for Optoelectronic Measurement Technology and Instrument, Beijing Information Science and Technology University, Beijing, China
| | - Fan Fan
- Key Laboratory of the Ministry of Education for Optoelectronic Measurement Technology and Instrument, Beijing Information Science and Technology University, Beijing, China
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Frigelli M, Büchler P, Kling S. Optomechanical assessment of photorefractive corneal cross-linking via optical coherence elastography. Front Bioeng Biotechnol 2023; 11:1272097. [PMID: 38026898 PMCID: PMC10680454 DOI: 10.3389/fbioe.2023.1272097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 10/20/2023] [Indexed: 12/01/2023] Open
Abstract
Purpose: Corneal cross-linking (CXL) has recently been used with promising results to positively affect corneal refractive power in the treatment of hyperopia and mild myopia. However, understanding and predicting the optomechanical changes induced by this procedure are challenging. Methods: We applied ambient pressure modulation based optical coherence elastography (OCE) to quantify the refractive and mechanical effects of patterned CXL and their relationship to energy delivered during the treatment on porcine corneas. Three different patterned treatments were performed, designed according to Zernike polynomial functions (circle, astigmatism, coma). In addition, three different irradiation protocols were analyzed: standard Dresden CXL (fluence of 5.4 J/cm2), accelerated CXL (fluence of 5.4 J/cm2), and high-fluence CXL (fluence of 16.2 J/cm2). The axial strain distribution in the stroma induced by ocular inflation (Δp = 30 mmHg) was quantified, maps of the anterior sagittal curvature were constructed and cylindrical refraction was assessed. Results: Thirty minutes after CXL, there was a statistically significant increase in axial strain amplitude (p < 0.050) and a reduction in sagittal curvature (p < 0.050) in the regions treated with all irradiation patterns compared to the non-irradiated ones. Thirty-6 hours later, the non-irradiated regions showed compressive strains, while the axial strain in the CXL-treated regions was close to zero, and the reduction in sagittal curvature observed 30 minutes after the treatment was maintained. The Dresden CXL and accelerated CXL produced comparable amounts of stiffening and refractive changes (p = 0.856), while high-fluence CXL produced the strongest response in terms of axial strain (6.9‰ ± 1.9‰) and refractive correction (3.4 ± 0.9 D). Tripling the energy administered during CXL resulted in a 2.4-fold increase in the resulting refractive correction. Conclusion: OCE showed that refractive changes and alterations in corneal biomechanics are directly related. A patient-specific selection of both, the administered UV fluence and the irradiation pattern during CXL is promising to allow customized photorefractive corrections in the future.
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Affiliation(s)
- Matteo Frigelli
- Computational Bioengineering Group, ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
| | - Philippe Büchler
- Computational Bioengineering Group, ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
| | - Sabine Kling
- Computational Bioengineering Group, ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
- Institute for Biomedical Engineering, ITET Department, ETH Zürich, Zürich, Switzerland
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Mekonnen T, Zevallos-Delgado C, Singh M, Aglyamov SR, Larin KV. Multifocal acoustic radiation force-based reverberant optical coherence elastography for evaluation of ocular globe biomechanical properties. JOURNAL OF BIOMEDICAL OPTICS 2023; 28:095001. [PMID: 37701876 PMCID: PMC10494982 DOI: 10.1117/1.jbo.28.9.095001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 08/01/2023] [Accepted: 08/28/2023] [Indexed: 09/14/2023]
Abstract
Significance Quantifying the biomechanical properties of the whole eye globe can provide a comprehensive understanding of the interactions among interconnected ocular components during dynamic physiological processes. By doing so, clinicians and researchers can gain valuable insights into the mechanisms underlying ocular diseases, such as glaucoma, and design interventions tailored to each patient's unique needs. Aim The aim of this study was to evaluate the feasibility and effectiveness of a multifocal acoustic radiation force (ARF) based reverberant optical coherence elastography (RevOCE) technique for quantifying shear wave speeds in different ocular components simultaneously. Approach We implemented a multifocal ARF technique to generate reverberant shear wave fields, which were then detected using phase-sensitive optical coherence tomography. A 3D-printed acoustic lens array was employed to manipulate a collimated ARF beam generated by an ultrasound transducer, producing multiple focused ARF beams on mouse eye globes ex vivo. RevOCE measurements were conducted using an excitation pulse train consisting of 10 cycles at 3 kHz, followed by data processing to produce a volumetric map of the shear wave speed. Results The results show that the system can successfully generate reverberant shear wave fields in the eye globe, allowing for simultaneous estimation of shear wave speeds in various ocular components, including cornea, iris, lens, sclera, and retina. A comparative analysis revealed notable differences in wave speeds between different parts of the eye, for example, between the apical region of the cornea and the pupillary zone of the iris (p = 0.003 ). Moreover, the study also revealed regional variations in the biomechanical properties of ocular components as evidenced by greater wave speeds near the apex of the cornea compared to its periphery. Conclusions The study demonstrated the effectiveness of RevOCE based on a non-invasive multifocal ARF for assessing the biomechanical properties of the whole eyeball. The findings indicate the potential to provide a comprehensive understanding of the mechanical behavior of the whole eye, which could lead to improved diagnosis and treatment of ocular diseases.
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Affiliation(s)
- Taye Mekonnen
- University of Houston, Department of Biomedical Engineering Houston, Texas, United States
| | | | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering Houston, Texas, United States
| | - Salavat R. Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, Texas, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering Houston, Texas, United States
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Techniques for In Vivo Assessment of Corneal Biomechanics: Brillouin Spectroscopy and Hydration State - Quo Vadis? Klin Monbl Augenheilkd 2022; 239:1427-1432. [PMID: 35977709 DOI: 10.1055/a-1926-5249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
To assess the structural integrity of the cornea, non-invasive methods are needed for the local measurement of its mechanical properties. Among a number of established techniques and their associated advantages and disadvantages, Brillouin spectroscopy is still a relatively new technique, capable of determining the compressive modulus of biological tissue, specifically the cornea, in vivo. In the present paper, these various existing and developing technologies for corneal biomechanics are discussed and correlated.
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Singh M, Zvietcovich F, Larin KV. Introduction to optical coherence elastography: tutorial. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2022; 39:418-430. [PMID: 35297425 PMCID: PMC10052825 DOI: 10.1364/josaa.444808] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Accepted: 01/25/2022] [Indexed: 06/03/2023]
Abstract
Optical coherence elastography (OCE) has seen rapid growth since its introduction in 1998. The past few decades have seen tremendous advancements in the development of OCE technology and a wide range of applications, including the first clinical applications. This tutorial introduces the basics of solid mechanics, which form the foundation of all elastography methods. We then describe how OCE measurements of tissue motion can be used to quantify tissue biomechanical parameters. We also detail various types of excitation methods, imaging systems, acquisition schemes, and data processing algorithms and how various parameters associated with each step of OCE imaging can affect the final quantitation of biomechanical properties. Finally, we discuss the future of OCE, its potential, and the next steps required for OCE to become an established medical imaging technology.
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Affiliation(s)
- Manmohan Singh
- Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Fernando Zvietcovich
- Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
- Department of Engineering, Pontificia Universidad Catolica del Peru, San Miguel, Lima 15088, Peru
| | - Kirill V. Larin
- Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA
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Ge GR, Tavakol B, Usher DB, Adler DC, Rolland JP, Parker KJ. Assessing corneal cross-linking with reverberant 3D optical coherence elastography. JOURNAL OF BIOMEDICAL OPTICS 2022; 27:026003. [PMID: 35166086 PMCID: PMC8843360 DOI: 10.1117/1.jbo.27.2.026003] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Accepted: 01/27/2022] [Indexed: 06/14/2023]
Abstract
SIGNIFICANCE Corneal cross-linking (CXL) is a well-known procedure for treating certain eye disorders such as keratoconus. However, characterization of the biomechanical changes in the cornea as a result of this procedure is still under active research. Specifically, there is a clinical need for high-resolution characterization of individual corneal layers. AIM A high-resolution elastography method in conjunction with a custom optical coherence tomography system is used to track these biomechanical changes in individual corneal layers. Pre- and post-treatment analysis for both low-dose and high-dose CXL experiments are performed. APPROACH A recently developed elastography technique that utilizes the theory of reverberant shear wave fields, with optical coherence tomography as the modality, is applied to pig corneas ex vivo to evaluate elasticity changes associated with corneal CXL. Sets of low-dose and high-dose CXL treatments are evaluated before and after treatments with three pairs of pig corneas per experiment. RESULTS The reverberant three-dimensional (3D) optical coherence elastography (OCE) technique can identify increases in elasticity associated with both low-dose and high-dose CXL treatments. There is a notable graphical difference between low-dose and high-dose treatments. In addition, the technique is able to identify which layers of the cornea are potentially affected by the CXL procedure and provides insight into the nonlinearity of the elasticity changes. CONCLUSIONS The reverberant 3D OCE technique can identify depth-resolved changes in elasticity of the cornea associated with CXL procedures. This method could be translated to assess and monitor CXL efficacy in various clinical settings.
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Affiliation(s)
- Gary R. Ge
- University of Rochester, The Institute of Optics, Rochester, New York, United States
| | - Behrouz Tavakol
- Glaukos Corporation, San Clemente, California, United States
| | - David B. Usher
- Glaukos Corporation, San Clemente, California, United States
| | | | - Jannick P. Rolland
- University of Rochester, The Institute of Optics, Rochester, New York, United States
- University of Rochester, Department of Biomedical Engineering, Rochester, New York, United States
- University of Rochester, Center for Visual Science, Rochester, New York, United States
| | - Kevin J. Parker
- University of Rochester, Department of Biomedical Engineering, Rochester, New York, United States
- University of Rochester, Department of Electrical and Computer Engineering, Rochester, New York, United States
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Sun MG, Son T, Crutison J, Guaiquil V, Lin S, Nammari L, Klatt D, Yao X, Rosenblatt MI, Royston TJ. Optical coherence elastography for assessing the influence of intraocular pressure on elastic wave dispersion in the cornea. J Mech Behav Biomed Mater 2022; 128:105100. [PMID: 35121423 PMCID: PMC8904295 DOI: 10.1016/j.jmbbm.2022.105100] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 01/17/2022] [Accepted: 01/21/2022] [Indexed: 10/19/2022]
Abstract
The cornea is a highly specialized organ that relies on its mechanical stiffness to maintain its aspheric geometry and refractive power, and corneal diseases such as keratoconus have been linked to abnormal tissue stiffness and biomechanics. Dynamic optical coherence elastography (OCE) is a clinically promising non-contact and non-destructive imaging technique that can provide measurements of corneal tissue stiffness directly in vivo. The method relies on the concepts of elastography where shear waves are generated and imaged within a tissue to obtain mechanical properties such as tissue stiffness. The accuracy of OCE-based measurements is ultimately dependent on the mathematical theories used to model wave behavior in the tissue of interest. In the cornea, elastic waves propagate as guided wave modes which are highly dispersive and can be mathematically complex to model. While recent groups have developed detailed theories for estimating corneal tissue properties from guided wave behavior, the effects of intraocular pressure (IOP)-induced prestress have not yet been considered. It is known that prestress alone can strongly influence wave behavior, in addition to the associated non-linear changes in tissue properties. This present study shows that failure to account for the effects of prestress may result in overestimations of the corneal shear moduli, particularly at high IOPs. We first examined the potential effects of IOP and IOP-induced prestress using a combination of approximate mathematical theories describing wave behavior in thin plates with observations made from data published in the OCE literature. Through wave dispersion analysis, we deduce that IOP introduces a tensile hoop stress and may also influence an elastic foundational effect that were observable in the low-frequency components of the dispersion curves. These effects were incorporated into recently developed models of wave behavior in nearly incompressible, transversely isotropic (NITI) materials. Fitting of the modified NITI model with ex vivo porcine corneal data demonstrated that incorporation of the effects of IOP resulted in reduced estimates of corneal shear moduli. We believe this demonstrates that overestimation of corneal stiffness occurs if IOP is not taken into consideration. Our work may be helpful in separating inherent corneal stiffness properties that are independent of IOP; changes in these properties and in IOP are distinct, clinically relevant issues that affect the cornea health.
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Zvietcovich F, Larin KV. Wave-based optical coherence elastography: The 10-year perspective. PROGRESS IN BIOMEDICAL ENGINEERING (BRISTOL, ENGLAND) 2022; 4:012007. [PMID: 35187403 PMCID: PMC8856668 DOI: 10.1088/2516-1091/ac4512] [Citation(s) in RCA: 27] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
After 10 years of progress and innovation, optical coherence elastography (OCE) based on the propagation of mechanical waves has become one of the major and the most studied OCE branches, producing a fundamental impact in the quantitative and nondestructive biomechanical characterization of tissues. Preceding previous progress made in ultrasound and magnetic resonance elastography; wave-based OCE has pushed to the limit the advance of three major pillars: (1) implementation of novel wave excitation methods in tissues, (2) understanding new types of mechanical waves in complex boundary conditions by proposing advance analytical and numerical models, and (3) the development of novel estimators capable of retrieving quantitative 2D/3D biomechanical information of tissues. This remarkable progress promoted a major advance in answering basic science questions and the improvement of medical disease diagnosis and treatment monitoring in several types of tissues leading, ultimately, to the first attempts of clinical trials and translational research aiming to have wave-based OCE working in clinical environments. This paper summarizes the fundamental up-to-date principles and categories of wave-based OCE, revises the timeline and the state-of-the-art techniques and applications lying in those categories, and concludes with a discussion on the current challenges and future directions, including clinical translation research.
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Affiliation(s)
- Fernando Zvietcovich
- University of Houston, Biomedical Engineering, Houston, TX, United States, 77204
| | - Kirill V. Larin
- University of Houston, Biomedical Engineering, Houston, TX, United States, 77204,
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Hepfer RG, Chen P, Shi C, Rocha KM, Waring GO, Slate EH, Yao H. Depth- and direction-dependent changes in solute transport following cross-linking with riboflavin and UVA light in ex vivo porcine cornea. Exp Eye Res 2021; 205:108498. [PMID: 33600810 DOI: 10.1016/j.exer.2021.108498] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 01/15/2021] [Accepted: 02/08/2021] [Indexed: 11/15/2022]
Abstract
Diffusion is an important mechanism of transport for nutrients and drugs throughout the avascular corneal stroma. The purpose of this study was to investigate the depth- and direction-dependent changes in stromal transport properties and their relationship to changes in collagen structure following ultraviolet A (UVA)-riboflavin induced corneal collagen cross-linking (CXL). After cross-linking in ex vivo porcine eyes, fluorescence recovery after photobleaching (FRAP) was performed to measure fluorescein diffusion in the nasal-temporal (NT) and anterior-posterior (AP) directions at corneal depths of 100, 200, and 300 μm. Second harmonic generation (SHG) imaging was also performed at these three corneal depths to quantify fiber alignment. For additional confirmation, an electrical conductivity method was employed to quantify ion permeability in the AP direction in corneal buttons and immunohistochemistry (IHC) was used to image collagen structure. Cross-linked corneas were compared to a control treatment that received the riboflavin solution without UVA light (SHAM). The results of FRAP revealed that fluorescein diffusivity decreased from 23.39 ± 11.60 μm2/s in the SHAM group to 19.87 ± 10.10 μm2/s in the CXL group. This change was dependent on depth and direction: the decrease was more pronounced in the 100 μm depth (P = 0.0005) and AP direction (P = 0.001) when compared to the effect in deeper locations and in the NT direction, respectively. Conductivity experiments confirmed a decrease in solute transport in the AP direction (P < 0.0001). FRAP also detected diffusional anisotropy in the porcine cornea: the fluorescein diffusivity in the NT direction was higher than the diffusivity in the AP direction. This anisotropy was increased following CXL treatment. Both SHG and IHC revealed a qualitative decrease in collagen crimping following CXL. Analysis of SHG images revealed an increase in coherency in the anterior 200 μm of CXL treated corneas when compared to SHAM treated corneas (P < 0.01). In conclusion, CXL results in a decrease in stromal solute transport, and this decrease is concentrated in the most anterior region and AP direction. Solute transport in the porcine cornea is anisotropic, and an increase in anisotropy with CXL may be explained by a decrease in collagen crimping.
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Affiliation(s)
- R Glenn Hepfer
- Clemson-MUSC Bioengineering Program, Department of Bioengineering, Clemson University, Charleston, SC, USA; Department of Oral Health Science, Medical University of South Carolina, Charleston, SC, USA
| | - Peng Chen
- Clemson-MUSC Bioengineering Program, Department of Bioengineering, Clemson University, Charleston, SC, USA
| | - Changcheng Shi
- Clemson-MUSC Bioengineering Program, Department of Bioengineering, Clemson University, Charleston, SC, USA
| | - Karolinne M Rocha
- Storm Eye Institute, Department of Ophthalmology, Medical University of South Carolina (MUSC), Charleston, SC, USA
| | | | - Elizabeth H Slate
- Department of Statistics, Florida State University, Tallahassee, FL, USA
| | - Hai Yao
- Clemson-MUSC Bioengineering Program, Department of Bioengineering, Clemson University, Charleston, SC, USA; Department of Oral Health Science, Medical University of South Carolina, Charleston, SC, USA.
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Direct Evidence of Symmetry between Bilateral Human Corneas in Biomechanical Properties: A Comparison Study with Fresh Corneal Tissue. J Ophthalmol 2021. [DOI: 10.1155/2021/8891412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Purpose. To investigate the difference between the eyes from the same human with respect to the biomechanical properties of fresh corneal tissues and investigate the assumption of similarity of the corneal biomechanical properties between the eyes. Methods. Strip specimens extracted through a small incision lenticule extraction (SMILE) surgery were tested using a uniaxial tensile test. The specimens were extracted vertically. Low-strain tangent modulus (LSTM), high-strain tangent modulus (HSTM), and tensile strength () were the biomechanical parameters used in the comparison of the eyes from the same human. Results. Ninety corneal specimens from 45 persons were included in this study. The LSTM of the left and right eyes were 1.34 ± 0.52 and 1.37 ± 0.46 MPa, while the HSTM were 50.53 ± 7.51 and 49.41 ± 7.01 MPa, respectively. There was no significant difference between the eyes in terms of LSTM, HSTM, and. The LSTM and HSTM were significantly correlated with the spherical equivalent (SE) (, resp.). Conclusions. The assumption that the corneal biomechanical properties of the eyes from the same human are similar has been confirmed for the first time using fresh human corneal tissue. This finding may be useful in further biomechanical studies.
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Zvietcovich F, Nair A, Singh M, Aglyamov SR, Twa MD, Larin KV. Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus. Invest Ophthalmol Vis Sci 2020; 61:7. [PMID: 33141893 PMCID: PMC7645208 DOI: 10.1167/iovs.61.13.7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Purpose Currently, the biomechanical properties of the corneo-scleral limbus when the eye-globe deforms are largely unknown. The purpose of this study is to evaluate changes in elasticity of the cornea, sclera, and limbus when subjected to different intraocular pressures (IOP) using wave-based optical coherence elastography (OCE). Special attention was given to the elasticity changes of the limbal region with respect to the elasticity variations in the neighboring corneal and scleral regions. Methods Continuous harmonic elastic waves (800 Hz) were mechanically induced in the sclera near the corneo-sclera limbus of in situ porcine eye-globes (n = 8). Wave propagation was imaged using a phase-sensitive optical coherence tomography system (PhS-OCT). The eyes were subjected to five different IOP-levels (10, 15, 20, 30, and 40 mm Hg), and spatially distributed propagation velocities were calculated along corneal, limbal, and scleral regions. Finite element analysis (FEA) of the same regions under the same excitation conditions were conducted for further validation of results. Results FEA demonstrated that the stiffness of the heterogeneous cornea-limbus-sclera transition can be characterized by phase velocity measurements of the elastic waves produced at 800 Hz in the anterior eye. Experimental results revealed that the wave speed in the limbus (cL = 6.5 m/s) is between the cornea (cc = 2.9 m/s) and sclera (cs = 10.0 m/s) at a physiological IOP level (15 mm Hg) and rapidly increases as the IOP level is increased, even surpassing the wave speed in the sclera. Finally, the change in elastic wave speed in the limbus (ΔcL∼18.5 m/s) was greater than in the cornea (Δcc ∼12.6 m/s) and sclera (Δcs∼8.1 m/s) for the same change in IOP. Conclusions We demonstrated that wave-based OCE can be utilized to assess limbus biomechanical properties. Moreover, experimental evidence showed that the corneo-scleral limbus is highly nonlinear compared to the cornea and sclera when the eye-globe is deformed by an increase of IOP. This may suggest that the limbus has enough structural flexibility to stabilize anterior eye shape during IOP changes.
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Affiliation(s)
- Fernando Zvietcovich
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Salavat R Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, Texas, United States
| | - Michael D Twa
- College of Optometry, University of Houston, Houston, Texas, United States
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
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13
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Pitre JJ, Kirby MA, Li DS, Shen TT, Wang RK, O'Donnell M, Pelivanov I. Nearly-incompressible transverse isotropy (NITI) of cornea elasticity: model and experiments with acoustic micro-tapping OCE. Sci Rep 2020; 10:12983. [PMID: 32737363 PMCID: PMC7395720 DOI: 10.1038/s41598-020-69909-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 07/21/2020] [Indexed: 12/28/2022] Open
Abstract
The cornea provides the largest refractive power for the human visual system. Its stiffness, along with intraocular pressure (IOP), are linked to several pathologies, including keratoconus and glaucoma. Although mechanical tests can quantify corneal elasticity ex vivo, they cannot be used clinically. Dynamic optical coherence elastography (OCE), which launches and tracks shear waves to estimate stiffness, provides an attractive non-contact probe of corneal elasticity. To date, however, OCE studies report corneal moduli around tens of kPa, orders-of-magnitude less than those (few MPa) obtained by tensile/inflation testing. This large discrepancy impedes OCE's clinical adoption. Based on corneal microstructure, we introduce and fully characterize a nearly-incompressible transversely isotropic (NITI) model depicting corneal biomechanics. We show that the cornea must be described by at least two shear moduli, contrary to current single-modulus models, decoupling tensile and shear responses. We measure both as a function of IOP in ex vivo porcine cornea, obtaining values consistent with both tensile and shear tests. At pressures above 30 mmHg, the model begins to fail, consistent with non-linear changes in cornea at high IOP.
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Affiliation(s)
- John J Pitre
- Department of Bioengineering, University of Washington, Seattle, WA, USA.
| | - Mitchell A Kirby
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - David S Li
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Department of Chemical Engineering, University of Washington, Seattle, WA, USA
| | - Tueng T Shen
- Department of Ophthalmology, University of Washington, Seattle, WA, USA
| | - Ruikang K Wang
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Department of Ophthalmology, University of Washington, Seattle, WA, USA
| | - Matthew O'Donnell
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Ivan Pelivanov
- Department of Bioengineering, University of Washington, Seattle, WA, USA
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14
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Nair A, Singh M, Aglyamov SR, Larin KV. Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography. JOURNAL OF BIOMEDICAL OPTICS 2020; 25:1-9. [PMID: 32372574 PMCID: PMC7199791 DOI: 10.1117/1.jbo.25.5.055001] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Accepted: 04/24/2020] [Indexed: 05/04/2023]
Abstract
SIGNIFICANCE It is generally agreed that the corneal mechanical properties are strongly linked to many eye diseases and could be used to assess disease progression and response to therapies. Elastography is the most notable method of assessing corneal mechanical properties, but it generally requires some type of external excitation to induce a measurable displacement in the tissue. AIM We present Heartbeat Optical Coherence Elastography (Hb-OCE), a truly passive method that can measure the elasticity of the cornea based on intrinsic corneal displacements induced by the heartbeat. APPROACH Hb-OCE measurements were performed in untreated and UV-A/riboflavin cross-linked porcine corneas ex vivo, and a distinct difference in strain was detected. Furthermore, a partially cross-linked cornea was also assessed, and the treated and untreated areas were similarly distinguished. RESULTS Our results suggest that Hb-OCE can spatially map displacements in the cornea induced by small fluctuations in intraocular pressure, similar to what is induced by the heartbeat. CONCLUSIONS The described technique opens the possibility for completely passive and noncontact in vivo assessment of corneal stiffness.
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Affiliation(s)
- Achuth Nair
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Salavat R. Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, Texas, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
- Address all correspondence to Kirill V. Larin, E-mail:
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15
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Kazaili A, Geraghty B, Akhtar R. Microscale assessment of corneal viscoelastic properties under physiological pressures. J Mech Behav Biomed Mater 2019; 100:103375. [DOI: 10.1016/j.jmbbm.2019.103375] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2019] [Revised: 07/21/2019] [Accepted: 07/26/2019] [Indexed: 10/26/2022]
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Zvietcovich F, Pongchalee P, Meemon P, Rolland JP, Parker KJ. Reverberant 3D optical coherence elastography maps the elasticity of individual corneal layers. Nat Commun 2019; 10:4895. [PMID: 31653846 PMCID: PMC6814807 DOI: 10.1038/s41467-019-12803-4] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Accepted: 09/24/2019] [Indexed: 12/01/2022] Open
Abstract
The elasticity mapping of individual layers in the cornea using non-destructive elastography techniques advances diagnosis and monitoring of ocular diseases and treatments in ophthalmology. However, transient Lamb waves, currently used in most dynamic optical coherence and ultrasound elastography techniques, diminish the translation of wave speed into shear/Young’s modulus. Here, we present reverberant 3D optical coherence elastography (Rev3D-OCE), a novel approach leveraging the physical properties of diffuse fields in detecting elasticity gradients not only in the lateral direction, but also along the depth axis of the cornea. A Monte Carlo analysis, finite element simulations, and experiments in layered phantoms are conducted to validate the technique and to characterize the axial elastography resolution. Experiments in ex vivo porcine cornea at different intraocular pressures reveal that Rev3D-OCE enables the elastic characterization of single layers that matches the anatomical description of corneal layers with unprecedented contrast in the dynamic OCE field. Elastic mapping of individual layers of the cornea with elastography uses Lamb waves, which are dependent on the thickness of each layer and the direction of propagation. Here the authors present Reverberant 3D Optical Coherence Elastography to measure elasticity of single layers using waves propagating in all directions.
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Affiliation(s)
- Fernando Zvietcovich
- Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY, 14627-0126, USA
| | | | - Panomsak Meemon
- Suranaree University of Technology, Nakhon Ratchasima, Thailand, 30000
| | - Jannick P Rolland
- The Institute of Optics, University of Rochester, Rochester, NY, 14627-0186, USA
| | - Kevin J Parker
- Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY, 14627-0126, USA.
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17
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Li Y, Zhu J, Chen JJ, Yu J, Jin Z, Miao Y, Browne AW, Zhou Q, Chen Z. Simultaneously imaging and quantifying in vivo mechanical properties of crystalline lens and cornea using optical coherence elastography with acoustic radiation force excitation. APL PHOTONICS 2019; 4:106104. [PMID: 32309636 PMCID: PMC7164808 DOI: 10.1063/1.5118258] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The crystalline lens and cornea comprise the eye's optical system for focusing light in human vision. The changes in biomechanical properties of the lens and cornea are closely associated with common diseases, including presbyopia and cataract. Currently, most in vivo elasticity studies of the anterior eye focus on the measurement of the cornea, while lens measurement remains challenging. To better understand the anterior segment of the eye, we developed an optical coherence elastography system utilizing acoustic radiation force excitation to simultaneously assess the elasticities of the crystalline lens and the cornea in vivo. A swept light source was integrated into the system to provide an enhanced imaging range that covers both the lens and the cornea. Additionally, the oblique imaging approach combined with orthogonal excitation also improved the image quality. The system was tested through first ex vivo and then in vivo experiments using a rabbit model. The elasticities of corneal and lens tissue in an excised normal whole-globe and a cold cataract model were measured to reveal that cataractous lenses have a higher Young's modulus. Simultaneous in vivo elasticity measurements of the lens and cornea were performed in a rabbit model to demonstrate the correlations between elasticity and intraocular pressure and between elasticity and age. To the best of our knowledge, we demonstrated the first in vivo elasticity of imaging of both the lens and cornea using acoustic radiation force-optical coherence elastography, thereby providing a potential powerful clinical tool to advance ophthalmic research in disorders affecting the lens and the cornea.
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Affiliation(s)
- Yan Li
- Beckman Laser Institute, University of California, Irvine, Irvine, California 92612, USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, California 92617, USA
| | - Jiang Zhu
- Beckman Laser Institute, University of California, Irvine, Irvine, California 92612, USA
| | - Jason J. Chen
- Beckman Laser Institute, University of California, Irvine, Irvine, California 92612, USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, California 92617, USA
| | - Junxiao Yu
- Beckman Laser Institute, University of California, Irvine, Irvine, California 92612, USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, California 92617, USA
| | - Zi Jin
- Beckman Laser Institute, University of California, Irvine, Irvine, California 92612, USA
| | - Yusi Miao
- Beckman Laser Institute, University of California, Irvine, Irvine, California 92612, USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, California 92617, USA
| | - Andrew W. Browne
- Department of Biomedical Engineering, University of California, Irvine, Irvine, California 92617, USA
- Department of Ophthalmology, School of Medicine, University of California, Irvine, Irvine, California 92617, USA
- Gavin Herbert Eye Institute, University of California, Irvine, Irvine, California 92697, USA
| | - Qifa Zhou
- Department of Ophthalmology and Biomedical Engineering, University of Southern California, Los Angeles, California 90089, USA
- Roski Eye Institute, University of Southern California, Los Angeles, California 90007, USA
| | - Zhongping Chen
- Beckman Laser Institute, University of California, Irvine, Irvine, California 92612, USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, California 92617, USA
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18
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Vekilov DP, Singh M, Aglyamov SR, Larin KV, Grande-Allen KJ. Mapping the spatial variation of mitral valve elastic properties using air-pulse optical coherence elastography. J Biomech 2019; 93:52-59. [PMID: 31300156 PMCID: PMC10575695 DOI: 10.1016/j.jbiomech.2019.06.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 05/18/2019] [Accepted: 06/14/2019] [Indexed: 10/26/2022]
Abstract
The mitral valve is a highly heterogeneous tissue composed of two leaflets, anterior and posterior, whose unique composition and regional differences in material properties are essential to overall valve function. While mitral valve mechanics have been studied for many decades, traditional testing methods limit the spatial resolution of measurements and can be destructive. Optical coherence elastography (OCE) is an emerging method for measuring viscoelastic properties of tissues in a noninvasive, nondestructive manner. In this study, we employed air-pulse OCE to measure the spatial variation in mitral valve elastic properties with micro-scale resolution at 1 mm increments along the radial length of the leaflets. We analyzed differences between the leaflets, as well as between regions of the valve. We found that the anterior leaflet has a higher elastic wave velocity, which is reported as a surrogate for stiffness, than the posterior leaflet, most notably at the annular edge of the sample. In addition, we found a spatial elastic gradient in the anterior leaflet, where the annular edge was found to have a greater elastic wave velocity than the free edge. This gradient was less pronounced in the posterior leaflet. These patterns were confirmed using established uniaxial tensile testing methods. Overall, the anterior leaflet was stiffer and had greater heterogeneity in its mechanical properties than the posterior leaflet. This study measures differences between the two mitral leaflets with greater resolution than previously feasible and demonstrates a method that may be suitable for assessing valve mechanics following repair or during the engineering of synthetic valve replacements.
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Affiliation(s)
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, TX, United States
| | - Salavat R Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, TX, United States; University of Texas at Austin, Department of Biomedical Engineering, Austin, TX, United States
| | - Kirill V Larin
- University of Houston, Department of Biomedical Engineering, Houston, TX, United States
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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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20
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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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21
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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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Preliminary Investigation of the Mechanical Anisotropy of the Normal Human Corneal Stroma. J Ophthalmol 2018; 2018:5392041. [PMID: 30416826 PMCID: PMC6207891 DOI: 10.1155/2018/5392041] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 07/20/2018] [Accepted: 09/16/2018] [Indexed: 11/17/2022] Open
Abstract
Purpose To investigate the anisotropic characteristics of the normal human corneal stroma using fresh corneal tissue. Methods Sixty-four corneal specimens extracted from stromal lenticules were included in this study. The specimens were cut in the temporal-nasal (horizontal) or superior-inferior (vertical) direction. Strip specimens were subjected to uniaxial tensile testing. The tensile properties of the specimens were measured and compared in the two directions. Results The low-strain tangent modulus was statistically significantly greater in the vertical direction than in the horizontal direction (1.32 ± 0.50 MPa vs 1.17 ± 0.43 MPa; P=0.035), as was the high-strain tangent modulus (51.26 ± 8.23 MPa vs 43.59 ± 7.96 MPa; P ≤ 0.001). The elastic modulus in the vertical direction was also higher than that in horizontal direction at stresses of 0.01, 0.02, and 0.03 MPa, but not statistically significant; so, P=0.338, 0.373, and 0.417, respectively. Conclusions The biomechanical behavior in normal human corneal stroma tissue is slightly stiffer in the vertical direction than in the horizontal direction. This information may aid our understanding of the biomechanical properties of the cornea and related diseases.
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Ang M, Baskaran M, Werkmeister RM, Chua J, Schmidl D, Aranha dos Santos V, Garhöfer G, Mehta JS, Schmetterer L. Anterior segment optical coherence tomography. Prog Retin Eye Res 2018; 66:132-156. [DOI: 10.1016/j.preteyeres.2018.04.002] [Citation(s) in RCA: 216] [Impact Index Per Article: 36.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 02/20/2018] [Accepted: 04/04/2018] [Indexed: 02/03/2023]
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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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25
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Wang S, Singh M, Tran TT, Leach J, Aglyamov SR, Larina IV, Martin JF, Larin KV. Biomechanical assessment of myocardial infarction using optical coherence elastography. BIOMEDICAL OPTICS EXPRESS 2018; 9:728-742. [PMID: 29552408 PMCID: PMC5854074 DOI: 10.1364/boe.9.000728] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 12/26/2017] [Accepted: 12/27/2017] [Indexed: 05/18/2023]
Abstract
Myocardial infarction (MI) leads to cardiomyocyte loss, impaired cardiac function, and heart failure. Molecular genetic analyses of myocardium in mouse models of ischemic heart disease have provided great insight into the mechanisms of heart regeneration, which is promising for novel therapies after MI. Although biomechanical factors are considered an important aspect in cardiomyocyte proliferation, there are limited methods for mechanical assessment of the heart in the mouse MI model. This prevents further understanding the role of tissue biomechanics in cardiac regeneration. Here we report optical coherence elastography (OCE) of the mouse heart after MI. Surgical ligation of the left anterior descending coronary artery was performed to induce an infarction in the heart. Two OCE methods with assessment of the direction-dependent elastic wave propagation and the spatially resolved displacement damping provide complementary analyses of the left ventricle. In comparison with sham, the infarcted heart features a fibrotic scar region with reduced elastic wave velocity, decreased natural frequency, and less mechanical anisotropy at the tissue level at the sixth week post-MI, suggesting lower and more isotropic stiffness. Our results indicate that OCE can be utilized for nondestructive biomechanical characterization of MI in the mouse model, which could serve as a useful tool in the study of heart repair.
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Affiliation(s)
- Shang Wang
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
- Equal contribution
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
- Equal contribution
| | - Thuy Tien Tran
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - John Leach
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Road, Houston, Texas 77204, USA
| | - Irina V. Larina
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - James F. Martin
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
- The Texas Heart Institute, 6770 Bertner Avenue, Houston, Texas 77030, USA
| | - Kirill V. Larin
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
- Interdisciplinary Laboratory of Biophotonics, Tomsk State University, 36 Lenin Ave., Tomsk 634050, Russia
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26
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Kirby MA, Pelivanov I, Song S, Ambrozinski Ł, Yoon SJ, Gao L, Li D, Shen TT, Wang RK, O’Donnell M. Optical coherence elastography in ophthalmology. JOURNAL OF BIOMEDICAL OPTICS 2017; 22:1-28. [PMID: 29275544 PMCID: PMC5745712 DOI: 10.1117/1.jbo.22.12.121720] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Accepted: 12/14/2017] [Indexed: 05/03/2023]
Abstract
Optical coherence elastography (OCE) can provide clinically valuable information based on local measurements of tissue stiffness. Improved light sources and scanning methods in optical coherence tomography (OCT) have led to rapid growth in systems for high-resolution, quantitative elastography using imaged displacements and strains within soft tissue to infer local mechanical properties. We describe in some detail the physical processes underlying tissue mechanical response based on static and dynamic displacement methods. Namely, the assumptions commonly used to interpret displacement and strain measurements in terms of tissue elasticity for static OCE and propagating wave modes in dynamic OCE are discussed with the ultimate focus on OCT system design for ophthalmic applications. Practical OCT motion-tracking methods used to map tissue elasticity are also presented to fully describe technical developments in OCE, particularly noting those focused on the anterior segment of the eye. Clinical issues and future directions are discussed in the hope that OCE techniques will rapidly move forward to translational studies and clinical applications.
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Affiliation(s)
- Mitchell A. Kirby
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
| | - Ivan Pelivanov
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
| | - Shaozhen Song
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
| | - Łukasz Ambrozinski
- Akademia Górniczo-Hutnicza University of Science and Technology, Krakow, Poland
| | - Soon Joon Yoon
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
| | - Liang Gao
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
| | - David Li
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
- University of Washington, Department of Chemical Engineering, Seattle, Washington, United States
| | - Tueng T. Shen
- University of Washington, Department of Ophthalmology, Seattle, Washington, United States
| | - Ruikang K. Wang
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
- University of Washington, Department of Ophthalmology, Seattle, Washington, United States
| | - Matthew O’Donnell
- University of Washington, Department of Bioengineering, Seattle, Washington, United States
- Address all correspondence to: Matthew O’Donnell, E-mail:
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27
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Liu CH, Schill A, Raghunathan R, Wu C, Singh M, Han Z, Nair A, Larin KV. Ultra-fast line-field low coherence holographic elastography using spatial phase shifting. BIOMEDICAL OPTICS EXPRESS 2017; 8:993-1004. [PMID: 28270998 PMCID: PMC5330560 DOI: 10.1364/boe.8.000993] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 01/16/2017] [Accepted: 01/16/2017] [Indexed: 05/02/2023]
Abstract
Optical coherence elastography (OCE) is an emerging technique for quantifying tissue biomechanical properties. Generally, OCE relies on point-by-point scanning. However, long acquisition times make point-by-point scanning unfeasible for clinical use. Here we demonstrate a noncontact single shot line-field low coherence holography system utilizing an automatic Hilbert transform analysis based on a spatial phase shifting technique. Spatio-temporal maps of elastic wave propagation were acquired with only one air-pulse excitation and used to quantify wave velocity and sample mechanical properties at a line rate of 200 kHz. Results obtained on phantoms were correlated with data from mechanical testing. Finally, the stiffness of porcine cornea at different intraocular pressures was also quantified in situ.
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Affiliation(s)
- Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
| | - Alexander Schill
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
| | - Raksha Raghunathan
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
| | - Chen Wu
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
| | - Zhaolong Han
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
- Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk, Russia
- Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77584, USA
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28
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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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29
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Singh M, Han Z, Nair A, Schill A, Twa MD, Larin KV. Applanation optical coherence elastography: noncontact measurement of intraocular pressure, corneal biomechanical properties, and corneal geometry with a single instrument. JOURNAL OF BIOMEDICAL OPTICS 2017; 22:20502. [PMID: 28241272 PMCID: PMC5316890 DOI: 10.1117/1.jbo.22.2.020502] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Accepted: 01/30/2017] [Indexed: 05/18/2023]
Abstract
Current clinical tools provide critical information about ocular health such as intraocular pressure (IOP). However, they lack the ability to quantify tissue material properties, which are potent markers for ocular tissue health and integrity. We describe a single instrument to measure the eye-globe IOP, quantify corneal biomechanical properties, and measure corneal geometry with a technique termed applanation optical coherence elastography (Appl-OCE). An ultrafast OCT system enabled visualization of corneal dynamics during noncontact applanation tonometry and direct measurement of micro air-pulse induced elastic wave propagation. Our preliminary results show that the proposed Appl-OCE system can be used to quantify IOP, corneal biomechanical properties, and corneal geometry, which builds a solid foundation for a unique device that can provide a more complete picture of ocular health.
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Affiliation(s)
- Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Zhaolong Han
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Achuth Nair
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Alexander Schill
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Michael D. Twa
- University of Alabama at Birmingham, School of Optometry, Birmingham, Alabama, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
- Tomsk State University, Interdisciplinary Laboratory of Biophotonics, Tomsk, Russia
- Baylor College of Medicine, Molecular Physiology and Biophysics, Houston, Texas, United States
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