1
|
Li GY, Feng X, Yun SH. In Vivo Optical Coherence Elastography Unveils Spatial Variation of Human Corneal Stiffness. IEEE Trans Biomed Eng 2024; 71:1418-1429. [PMID: 38032780 PMCID: PMC11086014 DOI: 10.1109/tbme.2023.3338086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2023]
Abstract
OBJECTIVE The mechanical properties of corneal tissues play a crucial role in determining corneal shape and have significant implications in vision care. This study aimed to address the challenge of obtaining accurate in vivo data for the human cornea. METHODS We have developed a high-frequency optical coherence elastography (OCE) technique using shear-like antisymmetric (A0)-mode Lamb waves at frequencies above 10 kHz. RESULTS By incorporating an anisotropic, nonlinear constitutive model and utilizing the acoustoelastic theory, we gained quantitative insights into the influence of corneal tension on wave speeds and elastic moduli. Our study revealed significant spatial variations in the shear modulus of the corneal stroma on healthy subjects for the first time. Over an age span from 21 to 34 (N = 6), the central corneas exhibited a mean shear modulus of 87 kPa, while the corneal periphery showed a significant decrease to 44 kPa. The central cornea's shear modulus decreases with age with a slope of -19 +/- 8 kPa per decade, whereas the periphery showed non-significant age dependence. The limbus demonstrated an increased shear modulus exceeding 100 kPa. We obtained wave displacement profiles that are consistent with highly anisotropic corneal tissues. CONCLUSION Our approach enabled precise measurement of corneal tissue elastic moduli in situ with high precision (<7%) and high spatial resolution (<1 mm). Our results revealed significant stiffness variation from the central to peripheral corneas. SIGNIFICANCE The high-frequency OCE technique holds promise for biomechanical evaluation in clinical settings, providing valuable information for refractive surgeries, degenerative disorder diagnoses, and intraocular pressure assessments.
Collapse
|
2
|
Zhang X, Sun L, Chen L, Zhang C, Xian Y, Aruma A, Wei R, Shen Y, Chen W, Zhou X. Corneal biomechanical stiffness and histopathological changes after in vivo repeated accelerated corneal cross-linking in cat eyes. Exp Eye Res 2023; 227:109363. [PMID: 36584907 DOI: 10.1016/j.exer.2022.109363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Revised: 11/09/2022] [Accepted: 12/20/2022] [Indexed: 12/29/2022]
Abstract
Corneal cross-linking (CXL) has been proved efficiency for treating progressive keratoconus and other corneal ectasia diseases by stabilizing corneal geometry and biomechanics. However, the necessity of repeated CXL treatment in patients is unknown. This study aimed to investigate corneal biomechanical stiffness and change in corneal histopathological characteristics after repeated accelerated CXL (A-CXL) in cat eyes. A-CXL was performed with 0.1% riboflavin applied for 10 min, followed by ultraviolet A irradiation at 30 mW/cm2 for 3 min at 365 nm in 15 domestic cats. Corneas (n = 30) were divided into three groups: one-time accelerated corneal cross-linking (A-CXL*1 group), repeated accelerated corneal cross-linking (A-CXL*2 group), and an untreated control group. In A-CXL*2 group, A-CXL was repeated at 1-month intervals. In vivo ocular examinations were performed pre- and postoperatively. Biomechanical analysis was performed using a biotester biaxial testing system. We used the Mooney-Rivlin strain-energy function to describe corneal material properties. No infection in any case after A-CXL was observed. Biomechanical tests showed that the stress-strain curves of the two A-CXL groups were significantly different from those of the control group (P < 0.01), whereas stress-strain curve of the A-CXL*2 group was similar to that of the A-CXL*1 group (P > 0.05). Delayed epithelial healing and haze were observed 1 month after surgery. Stromal demarcation line depth measured with anterior spectral-domain optical coherence tomography was 187.6 ± 20.4 and 197.1 ± 11.5 μm for the A-CXL*1 and A-CXL*2 groups, respectively (P > 0.05). These results show that A-CXL can increase corneal biomechanics in cat eyes. The biomechanical enhancement of cat corneas treated with repeated A-CXL at 1-month intervals was similar to that of performing a one-time A-CXL. Repeated cross-linking procedures at short intervals may increase the risk of adverse reactions, and more caution should be taken in clinical applications.
Collapse
Affiliation(s)
- Xiaoyu Zhang
- Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, China; Shanghai Research Center of Ophthalmology and Optometry, Shanghai, 200031, China; Shanghai Engineering Research Center of Laser and Autostereoscopic 3D for Vision Care (20DZ2255000), Shanghai, 200031, China
| | - Ling Sun
- Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, China; Shanghai Research Center of Ophthalmology and Optometry, Shanghai, 200031, China; Shanghai Engineering Research Center of Laser and Autostereoscopic 3D for Vision Care (20DZ2255000), Shanghai, 200031, China
| | - Lingfeng Chen
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, China
| | - Chaoqin Zhang
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, China
| | - Yiyong Xian
- Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, China; Shanghai Research Center of Ophthalmology and Optometry, Shanghai, 200031, China; Shanghai Engineering Research Center of Laser and Autostereoscopic 3D for Vision Care (20DZ2255000), Shanghai, 200031, China
| | - Aruma Aruma
- Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, China; Shanghai Research Center of Ophthalmology and Optometry, Shanghai, 200031, China; Shanghai Engineering Research Center of Laser and Autostereoscopic 3D for Vision Care (20DZ2255000), Shanghai, 200031, China
| | - Ruoyan Wei
- Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, China; Shanghai Research Center of Ophthalmology and Optometry, Shanghai, 200031, China; Shanghai Engineering Research Center of Laser and Autostereoscopic 3D for Vision Care (20DZ2255000), Shanghai, 200031, China
| | - Yang Shen
- Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, China; Shanghai Research Center of Ophthalmology and Optometry, Shanghai, 200031, China; Shanghai Engineering Research Center of Laser and Autostereoscopic 3D for Vision Care (20DZ2255000), Shanghai, 200031, China
| | - Weiyi Chen
- College of Biomedical Engineering, Taiyuan University of Technology, Taiyuan, Shanxi, 030024, China
| | - Xingtao Zhou
- Eye Institute and Department of Ophthalmology, Eye & ENT Hospital, Fudan University, Shanghai, 200031, China; NHC Key Laboratory of Myopia (Fudan University), Key Laboratory of Myopia, Chinese Academy of Medical Sciences, Shanghai, 200031, China; Shanghai Research Center of Ophthalmology and Optometry, Shanghai, 200031, China; Shanghai Engineering Research Center of Laser and Autostereoscopic 3D for Vision Care (20DZ2255000), Shanghai, 200031, China.
| |
Collapse
|
3
|
Abstract
PURPOSE The relevance of corneal biomechanics and the importance of including it in the clinical assessment of corneal ectasias are being increasingly recognized. The connection between corneal ultrastructure, biomechanical properties, and optical function is exemplified by a condition like keratoconus. Biomechanical instability is seen as the underlying basis for the secondary morphological changes in the cornea. Asymmetric biomechanical weakening is believed to drive progressive corneal steepening and thinning. Biomechanical strengthening is the principle of collagen crosslinking that has been shown to effectively arrest progression of the keratoconus. Corneal biomechanics has therefore ignited the interest of researchers and clinicians alike and has given us new insights into the cause and course of the disease. This article is an overview of the extensive work published, predominantly in the last two decades, on the biomechanical aspect of keratoconus. METHODS Published articles on corneal biomechanics in the specific context of keratoconus were reviewed, based on an electronic search using PubMed, Elsevier, and Science Direct. The search terms used included "Corneal Biomechanics," "Mechanical properties of the cornea," "Corneal ultrastructure," "Corneal Collagen," and "Keratoconus". Articles pertaining to refractive surgery, keratoplasty, collagen crosslinking, or intrastromal rings were excluded. RESULTS The electronic search revealed more than 500 articles, from which 80 were chosen for this article. CONCLUSIONS The structural and organizational pattern of the corneal stroma determines its mechanical properties and are responsible for the maintenance of the normal shape and function of the cornea. Changes in the ultrastructure are responsible for the biomechanical instability that leads to corneal ectasia. As non-invasive methods for evaluating corneal biomechanics in vivo evolve, our ability to diagnose subclinical keratoconus will improve, allowing identification of patients at risk to develop ectasia and to allow early treatment to arrest progression of the disease.
Collapse
Affiliation(s)
- Prema Padmanabhan
- Department of Cornea and Refractive Surgery, Medical Research Foundation, Sankara Nethralaya, Chennai, India
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, UK.,Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, China.,NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
| |
Collapse
|
4
|
Zhang J, Murgoitio-Esandi J, Qian X, Li R, Gong C, Nankali A, Hao L, Xu BY, Kirk Shung K, Oberai A, Zhou Q. High-Frequency Ultrasound Elastography to Assess the Nonlinear Elastic Properties of the Cornea and Ciliary Body. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2022; 69:2621-2629. [PMID: 35820015 PMCID: PMC9547080 DOI: 10.1109/tuffc.2022.3190400] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Mechanical properties of the anterior anatomical structures of the eye, such as the cornea and ciliary body, play a key role in the ocular function and homeostasis. However, measuring the biomechanical properties of the anterior ocular structures, especially deeper structures, such as the ciliary body, remains a challenge due to the lack of high-resolution imaging tools. Herein, we implement a mechanical shaker-based high-frequency ultrasound elastography technique that can track the induced elastic wave propagation to assess the linear and nonlinear elastic properties of anterior ocular structures. The findings of this study advance our understanding of the role of anterior ocular structures in the pathogenesis of different ocular disorders, such as glaucoma.
Collapse
|
5
|
Bontzos G, Douglas VP, Douglas KAA, Kapsala Z, Drakonaki EE, Detorakis ET. Ultrasound Elastography in Ocular and Periocular Tissues: A Review. Curr Med Imaging 2021; 17:1041-1053. [PMID: 33319691 DOI: 10.2174/1573405616666201214123117] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Revised: 08/31/2020] [Accepted: 10/15/2020] [Indexed: 11/22/2022]
Abstract
Ultrasound elastography has become available in everyday practice, allowing direct measurement of tissue elasticity with important and expanding clinical applications. Several studies that have evaluated pathological and non-pathological tissues have demonstrated that ultrasound elastography can actually improve the diagnostic accuracy of the underlying disease process by detecting differences in their elasticity. Ocular and periocular tissues can also be characterized by their elastic properties. In this context, a comprehensive review of literature on ultrasound elastography as well as its current applications in Ophthalmology is presented.
Collapse
Affiliation(s)
- Georgios Bontzos
- Department of Ophthalmology, University Hospital of Heraklion, Crete, Greece
| | | | | | - Zoi Kapsala
- Department of Ophthalmology, University Hospital of Heraklion, Crete, Greece
| | | | | |
Collapse
|
6
|
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: 30] [Impact Index Per Article: 10.0] [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.
Collapse
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.
| |
Collapse
|
7
|
Ashofteh Yazdi A, Melchor J, Torres J, Faris I, Callejas A, Gonzalez-Andrades M, Rus G. Characterization of non-linear mechanical behavior of the cornea. Sci Rep 2020; 10:11549. [PMID: 32665558 PMCID: PMC7360609 DOI: 10.1038/s41598-020-68391-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2019] [Accepted: 06/23/2020] [Indexed: 11/24/2022] Open
Abstract
The objective of this study was to evaluate which hyperelastic model could best describe the non-linear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasal-temporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress–strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R2 > 0.95). Moreover, Hamilton-Zabolotskaya model showed the highest discriminative capability of the non-linear model parameter (Parameter A) for the tissue structural changes between the two sample groups (p = 0.0005). The present work determines the best hyperelastic model with the highest discriminative capability in description of the non-linear mechanical behavior of the cornea.
Collapse
Affiliation(s)
- A Ashofteh Yazdi
- Ultrasonics Lab, Department of Structural Mechanics, University of Granada, Politécnico de Fuentenueva, 18071, Granada, Spain.,Department of Biomedical Engineering, Islamic Azad University, Mashhad Branch, Mashhad, Iran
| | - J Melchor
- Department of Statistics and Operations Research, University of Granada, Granada, Spain.,Instituto de Investigación Biosanitaria, Ibs.GRANADA, Granada, Spain.,Excellence Research Unit, "Modelling Nature" (MNat), University of Granada, Granada, Spain
| | - J Torres
- Ultrasonics Lab, Department of Structural Mechanics, University of Granada, Politécnico de Fuentenueva, 18071, Granada, Spain.,Instituto de Investigación Biosanitaria, Ibs.GRANADA, Granada, Spain
| | - I Faris
- Ultrasonics Lab, Department of Structural Mechanics, University of Granada, Politécnico de Fuentenueva, 18071, Granada, Spain.,Instituto de Investigación Biosanitaria, Ibs.GRANADA, Granada, Spain
| | - A Callejas
- Ultrasonics Lab, Department of Structural Mechanics, University of Granada, Politécnico de Fuentenueva, 18071, Granada, Spain.,Instituto de Investigación Biosanitaria, Ibs.GRANADA, Granada, Spain
| | - M Gonzalez-Andrades
- Maimonides Biomedical Research Institute of Cordoba (IMIBIC), Department of Ophthalmology, Reina Sofia University Hospital and University of Cordoba, Edificio IMIBIC, Av. Menéndez Pidal, s/n. 14004, Cordoba, Spain. .,Massachusetts Eye and Ear and Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, Boston, MA, USA.
| | - G Rus
- Ultrasonics Lab, Department of Structural Mechanics, University of Granada, Politécnico de Fuentenueva, 18071, Granada, Spain. .,Instituto de Investigación Biosanitaria, Ibs.GRANADA, Granada, Spain. .,Excellence Research Unit, "Modelling Nature" (MNat), University of Granada, Granada, Spain.
| |
Collapse
|
8
|
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.
Collapse
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
| |
Collapse
|
9
|
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
| |
Collapse
|
10
|
Qian X, Li R, Li Y, Lu G, He Y, Humayun MS, Chen Z, Zhou Q. In vivo evaluation of posterior eye elasticity using shaker-based optical coherence elastography. Exp Biol Med (Maywood) 2020; 245:282-288. [PMID: 31910651 DOI: 10.1177/1535370219897617] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Age-related macular degeneration (AMD) is a progressive retinal disease and becomes the leading cause of blindness. It is well established that early detection is the key to preservation of functional vision. However, it is very difficult to diagnose AMD in very early stages, before structural changes are evident. Consequently, investigating the biomechanical properties of the retina maybe essential for understanding its physiological function. In this study, we present a shear wave-based quantitative method for estimating the elasticity of the posterior eye using shaker-based optical coherence elastography. This technique has been developed and validated on both a homogeneous phantom and a healthy rabbit in vivo. The shear wave speed from the ganglion side to the photoreceptor side of the rabbit eye is 4.1 m/s, 4.9 m/s, and 6.7 m/s, respectively. In addition, the most stiff sclera region has an average shear wave speed of 9.1 m/s. The results demonstrate the feasibility of using this technique to quantify biomechanical properties of the posterior eye and its potential translation to the clinical study. Impact statement Herein, we propose a potentially clinical applicable shaker-based optical coherence elastography (OCE) technique to characterize the biomechanical properties of the posterior eye, including different layers of the retina. Compared with either acoustic radiation force OCE or air-puff OCE, the newly developed method can induce sufficient shear wave propagation at the posterior eye with high resolution and large field of view.
Collapse
Affiliation(s)
- Xuejun Qian
- Department of Biomedical Engineering and NIH Ultrasonic Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, USA.,USC Roski Eye Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Runze Li
- Department of Biomedical Engineering and NIH Ultrasonic Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, USA.,USC Roski Eye Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Yan Li
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612, USA
| | - Gengxi Lu
- Department of Biomedical Engineering and NIH Ultrasonic Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, USA.,USC Roski Eye Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Youmin He
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612, USA
| | - Mark S Humayun
- Department of Biomedical Engineering and NIH Ultrasonic Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, USA.,USC Roski Eye Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Zhongping Chen
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612, USA
| | - Qifa Zhou
- Department of Biomedical Engineering and NIH Ultrasonic Transducer Resource Center, University of Southern California, Los Angeles, CA 90089, USA.,USC Roski Eye Institute, University of Southern California, Los Angeles, CA 90033, USA
| |
Collapse
|
11
|
Koruk H, Choi JJ. Displacement of a bubble located at a fluid-viscoelastic medium interface. THE JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 2019; 145:EL410. [PMID: 31153355 DOI: 10.1121/1.5108678] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 04/29/2019] [Indexed: 06/09/2023]
Abstract
A model for estimating the displacement of a bubble located at a fluid-viscoelastic medium interface in response to acoustic radiation force is presented by extending the model for a spherical object embedded in a bulk material. The effects of the stiffness and viscosity of the viscoelastic medium and the amplitude and duration of the excitation force on bubble displacement were investigated using the proposed model. The results show that bubble displacement has a nonlinear relationship with excitation duration and viscosity. The time at which the steady state is reached increases with increasing medium viscosity and decreasing medium stiffness.
Collapse
Affiliation(s)
- Hasan Koruk
- Mechanical Engineering Department, MEF University, Istanbul 34396,
| | - James J Choi
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United
| |
Collapse
|
12
|
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.
Collapse
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
| |
Collapse
|
13
|
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.
Collapse
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:
| |
Collapse
|
14
|
High-Resolution Shear Wave Imaging of the Human Cornea Using a Dual-Element Transducer. SENSORS 2018; 18:s18124244. [PMID: 30513950 PMCID: PMC6308409 DOI: 10.3390/s18124244] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Revised: 11/22/2018] [Accepted: 11/30/2018] [Indexed: 12/23/2022]
Abstract
Estimating the corneal elasticity can provide valuable information for corneal pathologies and treatments. Ophthalmologic pathologies will invariably cause changes to the elasticity of the cornea. For example, keratoconus and the phototoxic effects of ultraviolet radiation usually increase the corneal elasticity. This makes a quantitative estimation of the elasticity of the human cornea important for ophthalmic diagnoses. The present study investigated the use of a proposed high-resolution shear wave imaging (HR-SWI) method based on a dual-element transducer (comprising an 8-MHz element for pushing and a 32-MHz element for imaging) for measuring the group shear wave velocity (GSWV) of the human cornea. An empirical Young’s modulus formula was used to accurately convert the GSWV to Young’s modulus. Four quantitative parameters, bias, resolution, contrast, and contrast-to-noise ratio (CNR), were measured in gelatin phantoms with two different concentrations (3% and 7%) to evaluate the performance of HR-SWI. The biases of gelatin phantoms (3% and 7%) were 5.88% and 0.78%, respectively. The contrast and CNR were 0.76, 1.31 and 3.22, 2.43 for the two-side and two-layer phantoms, respectively. The measured image resolutions of HR-SWI in the lateral and axial directions were 72 and 140 μm, respectively. The calculated phase SWV (PSWV) and their corresponding Young’s modulus from six human donors were 2.45 ± 0.48 m/s (1600 Hz) and 11.52 ± 7.81 kPa, respectively. All the experimental results validated the concept of HR-SWI and its ability for measuring the human corneal elasticity.
Collapse
|
15
|
Qian X, Ma T, Shih CC, Heur M, Zhang J, Shung KK, Varma R, Humayun MS, Zhou Q. Ultrasonic Microelastography to Assess Biomechanical Properties of the Cornea. IEEE Trans Biomed Eng 2018; 66:647-655. [PMID: 29993484 DOI: 10.1109/tbme.2018.2853571] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
OBJECTIVE To both qualitatively and quantitatively investigate corneal biomechanical properties through an ultrasonic microelastography imaging system, which is potentially useful in the diagnosis of diseases, such as keratoconus, postrefractive keratectasia, and tracking treatment such as cross-linking surgery. METHODS Our imaging system has a dual-frequency configuration, including a 4.5 MHz ring transducer to push the tissue and a confocally aligned 40 MHz needle transducer to track micron-level displacement. Two-dimensional/three-dimensional acoustic radiation force impulse (ARFI) imaging and Young's modulus in the region of interest were performed on ex vivo porcine corneas that were either cross-linked using formalin solution or preloaded with intraocular pressure (IOPs) from 5 to 30 mmHg. RESULTS The increase of corneal stiffness and the change in cross-linked volume following formalin crosslinking could be precisely observed in the ARFI images and reflected by the reconstructed Young's modulus while the B-mode structural images remained almost unchanged. In addition, the relationship between the stiffness of the cornea and IOPs was investigated among 12 porcine corneas. The corneal stiffness is significantly different at various IOPs and has a tendency to become stiffer with increasing IOP. CONCLUSION Our results demonstrate the principle of using ultrasonic microelastography techniques to image the biomechanical properties of the cornea. Integrating high-resolution ARFI imaging labeled with reconstructed Young's modulus and structural imaging of the cornea can potentially lead to a routinely performed imaging modality in the field of ophthalmology.
Collapse
|
16
|
Axial mechanical and structural characterization of keratoconus corneas. Exp Eye Res 2018; 175:14-19. [PMID: 29842851 DOI: 10.1016/j.exer.2018.05.019] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 04/13/2018] [Accepted: 05/18/2018] [Indexed: 11/23/2022]
Abstract
PURPOSE Previous studies indicate that there is an axial gradient of collagen lamellar branching and anastomosing leading to regional differences in corneal tissue stiffness that may control corneal shape. To further test this hypothesis we have measured the axial material stiffness and quantified the collagen lamellar complexity in ectatic and mechanically weakened keratoconus corneas (KC). METHODS Acoustic radiation force elastic microscopy (ARFEM) was used to probe the axial mechanical properties of the cone region of three donor KC buttons. 3 Dimensional second harmonic generation microscopy (3D-SHG) was used to qualitatively evaluate lamellar organization in 3 kC buttons and quantitatively measure lamellar branching point density (BPD) in a separate KC button that had been treated with epikeratophakia (Epi-KP). RESULTS The mean elastic modulus for the KC corneas was 1.67 ± 0.44 kPa anteriorly and 0.970 ± 0.30 kPa posteriorly, substantially below that previously measured for normal human cornea. 3D-SHG of KC buttons showed a simplified collagen lamellar structure lacking noticeable angled lamellae in the region of the cone. BPD in the anterior, posterior, central and paracentral regions of the KC cornea were significantly lower than in the overlying Epi-KP lenticule. Additionally, BPD in the cone region was significantly lower than the adjacent paracentral region in the KC button. CONCLUSIONS The KC cornea exhibits an axial gradient of mechanical stiffness and a BPD that appears substantially lower in the cone region compared to normal cornea. The findings reinforce the hypothesis that collagen architecture may control corneal mechanical stiffness and hence corneal shape.
Collapse
|
17
|
Evolution of the vertebrate corneal stroma. Prog Retin Eye Res 2018; 64:65-76. [DOI: 10.1016/j.preteyeres.2018.01.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 01/12/2018] [Accepted: 01/15/2018] [Indexed: 12/14/2022]
|
18
|
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.
Collapse
|
19
|
Rogala MM, Danielewska ME, Antończyk A, Kiełbowicz Z, Rogowska ME, Kozuń M, Detyna J, Iskander DR. In-vivo corneal pulsation in relation to in-vivo intraocular pressure and corneal biomechanics assessed in-vitro. An animal pilot study. Exp Eye Res 2017; 162:27-36. [PMID: 28689748 DOI: 10.1016/j.exer.2017.07.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Revised: 06/30/2017] [Accepted: 07/05/2017] [Indexed: 01/27/2023]
Abstract
The aim was to ascertain whether the characteristics of the corneal pulse (CP) measured in-vivo in a rabbit eye change after short-term artificial increase of intraocular pressure (IOP) and whether they correlate with corneal biomechanics assessed in-vitro. Eight New Zealand white rabbits were included in this study and were anesthetized. In-vivo experiments included simultaneous measurements of the CP signal, registered with a non-contact method, IOP, intra-arterial blood pressure, and blood pulse (BPL), at the baseline and short-term elevated IOP. Afterwards, thickness of post-mortem corneas was determined and then uniaxial tensile tests were conducted leading to estimates of their Young's modulus (E). At the baseline IOP, backward stepwise regression analyses were performed in which successively the ocular biomechanical, biometric and cardiovascular predictors were separately taken into account. Results of the analysis revealed that the 3rd CP harmonic can be statistically significantly predicted by E and central corneal thickness (Models: R2 = 0.662, p < 0.005 and R2 = 0.832, p < 0.001 for the signal amplitude and power, respectively). The 1st CP harmonic can be statistically significantly predicted by the amplitude and power of the 1st BPL harmonic (Models: R2 = 0.534, p = 0.015 and R2 = 0.509, p < 0.018, respectively). For elevated IOP, non-parametric analysis indicated significant differences for the power of the 1st CP harmonic (Kruskal-Wallis test; p = 0.031) and for the mean, systolic and diastolic blood pressures (p = 0.025, p = 0.019, p = 0.033, respectively). In conclusion, for the first time, the association between parameters of the CP signal in-vivo and corneal biomechanics in-vitro was confirmed. In particular, spectral analysis revealed that higher amplitude and power of the 3rd CP harmonic indicates higher corneal stiffness, while the 1st CP harmonic correlates positively with the corresponding harmonic of the BPL signal.
Collapse
Affiliation(s)
- Maja M Rogala
- Wroclaw University of Science and Technology, Department of Mechanics, Materials Science and Engineering, Faculty of Mechanical Engineering, ul. Smoluchowskiego 25, 50-370 Wroclaw, Poland.
| | - Monika E Danielewska
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
| | - Agnieszka Antończyk
- Wroclaw University of Environmental and Life Sciences, Department of Surgery, Faculty of Veterinary Medicine, pl. Grunwaldzki 51, 50-366 Wroclaw, Poland.
| | - Zdzisław Kiełbowicz
- Wroclaw University of Environmental and Life Sciences, Department of Surgery, Faculty of Veterinary Medicine, pl. Grunwaldzki 51, 50-366 Wroclaw, Poland.
| | - Marta E Rogowska
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
| | - Marta Kozuń
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Faculty of Mechanical Engineering, ul. Lukasiewicza 7/9, 50-371 Wroclaw, Poland.
| | - Jerzy Detyna
- Wroclaw University of Science and Technology, Department of Mechanics, Materials Science and Engineering, Faculty of Mechanical Engineering, ul. Smoluchowskiego 25, 50-370 Wroclaw, Poland.
| | - D Robert Iskander
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
| |
Collapse
|
20
|
Mikula ER, Jester JV, Juhasz T. Measurement of an Elasticity Map in the Human Cornea. Invest Ophthalmol Vis Sci 2017; 57:3282-6. [PMID: 27327584 PMCID: PMC4961063 DOI: 10.1167/iovs.15-18248] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose The biomechanical properties of the cornea have an important role in determining the shape of the cornea and visual acuity. Since the cornea is a nonhomogeneous tissue, it is thought that the elastic properties vary throughout the cornea. We aim to measure a map of corneal elasticity across the cornea. Methods An acoustic radiation force elasticity microscope (ARFEM) was used to create a map of corneal elasticity in the human cornea. This ARFEM uses a low frequency, high intensity acoustic force to displace a femtosecond laser-generated microbubble, while using a high frequency, low intensity ultrasound to monitor the position of the microbubble within the cornea. From the displacement of the bubble and the magnitude of the acoustic radiation force, the local value of corneal elasticity is calculated in the direction of the displacement. Measurements were conducted at 6 locations, ranging from the central to peripheral cornea at anterior and posterior depths. Results The mean anterior elastic moduli were 4.2 ± 1.2, 3.4 ± 0.7, and 1.9 ± 0.7 kPa in the central, mid, and peripheral regions, respectively, while the posterior elastic moduli were 2.3 ± 0.7, 1.6 ± 0.3, and 2.9 ± 1.2 kPa in the same radial locations. Conclusions We found that there is a unique distribution of elasticity axially and radially throughout the cornea.
Collapse
Affiliation(s)
- Eric R Mikula
- Gavin Herbert Eye Institute, University of California, Irvine, California, United States
| | - James V Jester
- Gavin Herbert Eye Institute, University of California, Irvine, California, United States 2Department of Biomedical Engineering, University of California, Irvine, California, United States
| | - Tibor Juhasz
- Gavin Herbert Eye Institute, University of California, Irvine, California, United States 2Department of Biomedical Engineering, University of California, Irvine, California, United States
| |
Collapse
|
21
|
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.
Collapse
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.
| |
Collapse
|
22
|
Abstract
OBJECTIVES To determine the effect of hydration media on ex vivo corneal elasticity. METHODS Experiments were conducted on 40 porcine eyes retrieved from an abattoir (10 eyes each for phosphate-buffered saline (PBS), balanced salt solution, Optisol, 15% dextran). The epithelium was removed, and the cornea was excised with an intact scleral rim and placed in 20% dextran overnight to restore its physiological thickness. For each hydration media, corneas were evenly divided into two groups: one with an intact scleral rim and the other without. Corneas were mounted onto a custom chamber and immersed in a hydration medium for elasticity testing. Although in each medium, corneal elasticity measurements were performed for 2 hr: at 5-min intervals for the first 30 min and then 15-min intervals for the remaining 90 min. Elasticity testing was performed using nanoindentation with spherical indenters, and Young modulus was calculated using the Hertz model. Thickness measurements were taken before and after elasticity testing. RESULTS The percentage change in corneal thickness and elasticity was calculated for each hydration media group. Balanced salt solution, PBS, and Optisol showed an increase in thickness and Young moduli for corneas with and without an intact scleral rim. Fifteen percent dextran exhibited a dehydrating effect on corneal thickness and provided stable maintenance of corneal elasticity for both groups. CONCLUSIONS Hydration media affects the stability of corneal thickness and elasticity measurements over time. Fifteen percent dextran was most effective in maintaining corneal hydration and elasticity, followed by Optisol.
Collapse
|
23
|
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.
Collapse
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
| |
Collapse
|
24
|
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.
Collapse
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
| |
Collapse
|
25
|
Application of Elastography for the Noninvasive Assessment of Biomechanics in Engineered Biomaterials and Tissues. Ann Biomed Eng 2016; 44:705-24. [PMID: 26790865 DOI: 10.1007/s10439-015-1542-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Accepted: 12/18/2015] [Indexed: 12/11/2022]
Abstract
The elastic properties of engineered biomaterials and tissues impact their post-implantation repair potential and structural integrity, and are critical to help regulate cell fate and gene expression. The measurement of properties (e.g., stiffness or shear modulus) can be attained using elastography, which exploits noninvasive imaging modalities to provide functional information of a material indicative of the regeneration state. In this review, we outline the current leading elastography methodologies available to characterize the properties of biomaterials and tissues suitable for repair and mechanobiology research. We describe methods utilizing magnetic resonance, ultrasound, and optical coherent elastography, highlighting their potential for longitudinal monitoring of implanted materials in vivo, in addition to spatiotemporal limits of each method for probing changes in cell-laden constructs. Micro-elastography methods now allow acquisitions at length scales approaching 5-100 μm in two and three dimensions. Many of the methods introduced in this review are therefore capable of longitudinal monitoring in biomaterials and tissues approaching the cellular scale. However, critical factors such as anisotropy, heterogeneity and viscoelasity-inherent in many soft tissues-are often not fully described and therefore require further advancements and future developments.
Collapse
|
26
|
Koruk H, El Ghamrawy A, Pouliopoulos AN, Choi JJ. Acoustic particle palpation for measuring tissue elasticity. APPLIED PHYSICS LETTERS 2015; 107:223701. [PMID: 26869723 PMCID: PMC4718564 DOI: 10.1063/1.4936345] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 11/11/2015] [Indexed: 05/07/2023]
Abstract
We propose acoustic particle palpation-the use of sound to press a population of acoustic particles against an interface-as a method for measuring the qualitative and quantitative mechanical properties of materials. We tested the feasibility of this method by emitting ultrasound pulses across a tunnel of an elastic material filled with microbubbles. Ultrasound stimulated the microbubble cloud to move in the direction of wave propagation, press against the distal surface, and cause deformations relevant for elasticity measurements. Shear waves propagated away from the palpation site with a velocity that was used to estimate the material's Young's modulus.
Collapse
Affiliation(s)
| | - Ahmed El Ghamrawy
- Noninvasive Surgery and Biopsy Laboratory, Department of Bioengineering, Imperial College London , London SW7 2AZ, United Kingdom
| | - Antonios N Pouliopoulos
- Noninvasive Surgery and Biopsy Laboratory, Department of Bioengineering, Imperial College London , London SW7 2AZ, United Kingdom
| | - James J Choi
- Noninvasive Surgery and Biopsy Laboratory, Department of Bioengineering, Imperial College London , London SW7 2AZ, United Kingdom
| |
Collapse
|
27
|
Singh M, Wu C, Liu CH, Li J, Schill A, Nair A, Larin KV. Phase-sensitive optical coherence elastography at 1.5 million A-Lines per second. OPTICS LETTERS 2015; 40:2588-91. [PMID: 26030564 PMCID: PMC5451255 DOI: 10.1364/ol.40.002588] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Shear-wave imaging optical coherence elastography (SWI-OCE) is an emerging method for 3D quantitative assessment of tissue local mechanical properties based on imaging and analysis of elastic wave propagation. Current methods for SWI-OCE involve multiple temporal optical coherence tomography scans (M-mode) at different spatial locations across tissue surface (B- and C-modes). This requires an excitation for each measurement position leading to clinically unacceptable long acquisition times up to tens of minutes. In this Letter, we demonstrate, for the first time, noncontact true kilohertz frame-rate OCE by combining a Fourier domain mode-locked swept source laser with an A-scan rate of ∼1.5 MHz and a focused air-pulse as an elastic wave excitation source. The propagation of the elastic wave in the sample was imaged at a frame rate of ∼7.3 kHz. Therefore, to quantify the elastic wave propagation velocity in a single direction, only a single excitation was needed. This method was validated by quantifying the elasticity of tissue-mimicking agar phantoms as well as of a porcine cornea ex vivo at different intraocular pressures. The results demonstrate that this method can reduce the acquisition time of an elastogram to milliseconds.
Collapse
Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA
| | - Chen Wu
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA
| | - Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA
| | - Jiasong Li
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA
| | - Alexander Schill
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77004, USA
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA
- Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk 634050, Russia
- Corresponding author:
| |
Collapse
|
28
|
Bao F, Deng M, Wang Q, Huang J, Yang J, Whitford C, Geraghty B, Yu A, Elsheikh A. Evaluation of the relationship of corneal biomechanical metrics with physical intraocular pressure and central corneal thickness in ex vivo rabbit eye globes. Exp Eye Res 2015; 137:11-7. [PMID: 26026878 DOI: 10.1016/j.exer.2015.05.018] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2015] [Revised: 05/14/2015] [Accepted: 05/26/2015] [Indexed: 10/23/2022]
Abstract
The relationship of corneal biomechanical metrics provided by the Ocular Response Analyzer (ORA) and Corvis ST (CVS) with physical intraocular pressure (IOPp) and central corneal thickness (CCT) was evaluated. Thirty fresh enucleated eyes of 30 rabbits were used in ex vivo whole globe inflation experiments. IOPp was measured with a pressure transducer and increased from 7.5 to 37.5 mmHg in steps of 7.5 mmHg while biomechanical data was acquired using the ORA and CVS. At least 3 examinations were performed at each pressure level, where CCT and twelve biomechanical metrics were recorded and analyzed as a function of IOPp. The biomechanical metrics included corneal hysteresis (CH) and corneal resistance factor (CRF), obtained by the ORA. They also included the applanation times (A1T, A2T), lengths (A1L, A2L) and velocities (A1V, A2V), in addition to the highest concavity time (HCT), peak distance (PD), radius (HR) and deformation amplitude (DA), obtained by the CVS. The variation of CCT and the twelve biomechanical metrics for the 30 rabbit eyes tested across the 5 pressure stages considered (inter-pressure differences) were statistically significant (P = 0.00). IOPp was highly to moderately correlated with most biomechanical metrics, especially CRF, A1T, A1V, A2V, PD and DA, while the relationships with CH, A2T, A1L and HCT were poor. IOP has important influences on most corneal biomechanical metrics provided by CVS and ORA. Two biomechanical metrics A1V and HR were influenced by CCT after correcting for the effect of IOP in most pressure stages, while the correlation with others were weak. Comparisons of research groups based on ORA and CVS with different IOPs and CCTs may lead to possible misinterpretations if both or one of which are not considered in the analysis.
Collapse
Affiliation(s)
- FangJun Bao
- The Affiliated Eye Hospital of WenZhou Medical University, Wenzhou, 325027, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province, 325027, China
| | - ManLi Deng
- The Affiliated Eye Hospital of WenZhou Medical University, Wenzhou, 325027, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province, 325027, China
| | - QinMei Wang
- The Affiliated Eye Hospital of WenZhou Medical University, Wenzhou, 325027, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province, 325027, China
| | - JinHai Huang
- The Affiliated Eye Hospital of WenZhou Medical University, Wenzhou, 325027, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province, 325027, China
| | - Jing Yang
- The Affiliated Eye Hospital of WenZhou Medical University, Wenzhou, 325027, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province, 325027, China
| | - Charles Whitford
- School of Engineering, University of Liverpool, Liverpool, L69 3GH, UK
| | - Brendan Geraghty
- School of Engineering, University of Liverpool, Liverpool, L69 3GH, UK
| | - Ayong Yu
- The Affiliated Eye Hospital of WenZhou Medical University, Wenzhou, 325027, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, Zhejiang Province, 325027, China.
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, L69 3GH, UK; National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, UK
| |
Collapse
|