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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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2
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Dua HS, Freitas R, Mohammed I, Ting DSJ, Said DG. The pre-Descemet's layer (Dua's layer, also known as the Dua-Fine layer and the pre-posterior limiting lamina layer): Discovery, characterisation, clinical and surgical applications, and the controversy. Prog Retin Eye Res 2023; 97:101161. [PMID: 36642673 DOI: 10.1016/j.preteyeres.2022.101161] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 12/22/2022] [Accepted: 12/28/2022] [Indexed: 01/15/2023]
Abstract
The pre-Descemet's layer/Dua's layer, also termed the Dua-Fine layer and the pre-posterior limiting lamina layer, lies anterior to the Descemet's membrane in the cornea, is 10 μm (range 6-16) thick, made predominantly of type I and some type VI collagen with abundant elastin, more than any other layer of the cornea. It has high tensile strength (bursting pressure up to 700 mm of Hg), is impervious to air and almost acellular. At the periphery it demonstrates fenestrations and ramifies to become the core of the trabecular meshwork, with implications for intraocular pressure and glaucoma. It has been demonstrated in some species of animals. The layer has assumed considerable importance in anterior and posterior lamellar corneal transplant surgery by improving our understanding of the behaviour of corneal tissue during these procedures, improved techniques and made the surgery safer with better outcomes. It has led to the innovation of new surgical procedures namely, pre-Descemet's endothelial keratoplasty, suture management of acute hydrops, DALK-triple and Fogla's mini DALK. The discovery and knowledge of the layer has introduced paradigm shifts in our age old concepts of Descemet's membrane detachment, acute corneal hydrops in keratoconus and Descemetoceles, with impact on management approaches. It has been shown to contribute to the pathology and clinical signs observed in corneal infections and some corneal dystrophies. Early evidence suggests that it may have a role in the pathogenesis of keratoconus in relation to its elastin content. Its contribution to corneal biomechanics and glaucoma are subjects of current investigations.
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Affiliation(s)
- Harminder S Dua
- Larry A Donoso Laboratory for Eye Research, Academic Unit of Ophthalmology and Visual Sciences, University of Nottingham, The Queens Medical Centre, Nottingham University Hospitals, NHS Trust, Nottingham, England, UK.
| | - Rui Freitas
- Larry A Donoso Laboratory for Eye Research, Academic Unit of Ophthalmology and Visual Sciences, University of Nottingham, The Queens Medical Centre, Nottingham University Hospitals, NHS Trust, Nottingham, England, UK; Life and Health Sciences Research Institute (ICVS), School of Medicine, University of Minho, Portugal.
| | - Imran Mohammed
- Larry A Donoso Laboratory for Eye Research, Academic Unit of Ophthalmology and Visual Sciences, University of Nottingham, The Queens Medical Centre, Nottingham University Hospitals, NHS Trust, Nottingham, England, UK.
| | - Darren S J Ting
- Larry A Donoso Laboratory for Eye Research, Academic Unit of Ophthalmology and Visual Sciences, University of Nottingham, The Queens Medical Centre, Nottingham University Hospitals, NHS Trust, Nottingham, England, UK.
| | - Dalia G Said
- Larry A Donoso Laboratory for Eye Research, Academic Unit of Ophthalmology and Visual Sciences, University of Nottingham, The Queens Medical Centre, Nottingham University Hospitals, NHS Trust, Nottingham, England, UK; Research Institute of Ophthalmology, Cairo, Egypt.
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3
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Wagner FM, Sekundo W. Iatrogenic Keratectasia after Refractive Surgery - Causes, Prophylaxis, Therapy. Klin Monbl Augenheilkd 2023; 240:783-794. [PMID: 37348513 DOI: 10.1055/a-2073-8478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/24/2023]
Abstract
Iatrogenic keratectasia is induced thinning and protrusion of the cornea after laser refractive surgery. Known risk factors include an excessively thin postoperative residual stromal bed, a thicker flap, or preoperatively undetected evidence of preexisting subclinical keratoconus. The rate of post-refractive ectasia in eyes without identifiable preoperative risk factors is 20 per 100 000 eyes for photorefractive keratectomy, 90 per 100 000 eyes for laser in situ keratomileusis, and 11 per 100 000 eyes for small incision lenticule extraction. Traditional screening tools for preoperative risk include the ectasia risk score system and percentage of tissue alteration. More recent methods include corneal elastography and epithelial mapping, in addition to Artificial Intelligence methods for data analysis. Therapy includes contact lenses, cross-linking, implantation of intracorneal ring segments, penetrating or lamellar keratoplasty, and, in early studies, implantation of corneal lenticules.
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Affiliation(s)
- Felix Mathias Wagner
- Universitätsaugenklinik Mainz, Mainz, Deutschland
- Universitätsaugenklinik Marburg, Marburg, Deutschland
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4
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Mirzayev I, Gündüz AK, Aydın Ellialtıoğlu P, Gündüz ÖÖ. Clinical applications of anterior segment swept-source optical coherence tomography: A systematic review. Photodiagnosis Photodyn Ther 2023; 42:103334. [PMID: 36764640 DOI: 10.1016/j.pdpdt.2023.103334] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Revised: 01/25/2023] [Accepted: 02/07/2023] [Indexed: 02/11/2023]
Abstract
Optical coherence tomography (OCT) is a non-invasive method that provides the opportunity to examine tissues by taking cross-sectional images. OCT is increasingly being used to evaluate anterior segment (AS) pathologies. Swept-source (SS) OCT allows greater penetration and achieves better visualization of the internal configuration of AS tissues due to the longer wavelength employed and high scan speeds. We reviewed the utilization of AS SS-OCT in various conditions including glaucoma, ocular surface pathologies, iris tumors, refractive surgery, cataract surgery, and scleral diseases. A systematic literature search was carried out on PubMed, Scopus, and Web of Science databases between January 1, 2008, and September 1, 2022 using the following keywords: AS SS-OCT; dry eye and SS-OCT; ocular surface and SS-OCT; cornea and SS-OCT; dystrophy and SS-OCT; glaucoma and SS-OCT; ocular surface tumors and SS-OCT; conjunctival tumors and SS-OCT; refractive surgery and SS-OCT; cataract and SS-OCT; biometry and SS-OCT; sclera and SS-OCT; iris and SS-OCT; ciliary body and SS-OCT; artificial intelligence and SS-OCT. A total of 221 studies were included in this review. Review of the existing literature shows that SS-OCT offers several advantages in the diagnosis of AS diseases. Exclusive features of SS-OCT including rapid scanning, deeper tissue penetration, and better image quality help improve our understanding of various AS pathologies.
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Affiliation(s)
- Ibadulla Mirzayev
- Department of Ophthalmology, Ankara University Faculty of Medicine, Ankara, Turkey; Halil Şıvgın Çubuk State Hospital, Ophthalmology Clinic, Ankara, Turkey
| | - Ahmet Kaan Gündüz
- Department of Ophthalmology, Ankara University Faculty of Medicine, Ankara, Turkey; Private Eye Clinic, Ankara, Turkey.
| | | | - Ömür Özlenen Gündüz
- Department of Ophthalmology, Ankara University Faculty of Medicine, Ankara, Turkey
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5
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Lopes BT, Elsheikh A. In Vivo Corneal Stiffness Mapping by the Stress-Strain Index Maps and Brillouin Microscopy. Curr Eye Res 2023; 48:114-120. [PMID: 35634717 DOI: 10.1080/02713683.2022.2081979] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The study of corneal stiffness in vivo has numerous clinical applications such as the measurement of intraocular pressure, the preoperative screening for iatrogenic ectasia after laser vision correction surgery and the diagnosis and treatment of corneal ectatic diseases such as keratoconus. The localised aspect of the microstructure deterioration in keratoconus leading to local biomechanical softening, corneal bulging, irregular astigmatism and ultimately loss of vision boosted the need to map the corneal stiffness to identify the regional biomechanical failure. Currently, two methods to map the corneal stiffness in vivo are integrated into devices that are either already commercially available or about to be commercialised: the stress-strain index (SSI) maps and the Brillouin Microscopy (BM). The former method produces 2D map of stiffness across the corneal surface, developed through numerical simulations using the corneal shape, its microstructure content, and the deformation behaviour under air-puff excitation. It estimates the whole stress-strain behaviour, making it possible to obtain the material tangent modulus under different intraocular pressure levels. On the other hand, BM produces a 3D map of the corneal longitudinal modulus across the corneal surface and thickness. It uses a low-power near-infrared laser beam and through a spectral analysis of the returned signal, it assesses the mechanical compressibility of the tissue as measured by the longitudinal modulus. In this paper, these two techniques are reviewed, and their advantages and limitations discussed.
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Affiliation(s)
- Bernardo T Lopes
- School of Engineering, University of Liverpool, Liverpool, UK.,Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, UK.,Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, China.,National Institute for Health Research (NIHR) Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
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6
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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.
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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
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7
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Li F, Wang K, Liu Z. In Vivo Biomechanical Measurements of the Cornea. BIOENGINEERING (BASEL, SWITZERLAND) 2023; 10:bioengineering10010120. [PMID: 36671692 PMCID: PMC9854753 DOI: 10.3390/bioengineering10010120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/03/2022] [Revised: 01/11/2023] [Accepted: 01/13/2023] [Indexed: 01/18/2023]
Abstract
In early corneal examinations, the relationships between the morphological and biomechanical features of the cornea were unclear. Although consistent links have been demonstrated between the two in certain cases, these are not valid in many diseased states. An accurate assessment of the corneal biomechanical properties is essential for understanding the condition of the cornea. Studies on corneal biomechanics in vivo suggest that clinical problems such as refractive surgery and ectatic corneal disease are closely related to changes in biomechanical parameters. Current techniques are available to assess the mechanical characteristics of the cornea in vivo. Accordingly, various attempts have been expended to obtain the relevant mechanical parameters from different perspectives, using the air-puff method, ultrasound, optical techniques, and finite element analyses. However, a measurement technique that can comprehensively reflect the full mechanical characteristics of the cornea (gold standard) has not yet been developed. We review herein the in vivo measurement techniques used to assess corneal biomechanics, and discuss their advantages and limitations to provide a comprehensive introduction to the current state of technical development to support more accurate clinical decisions.
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Affiliation(s)
- Fanshu Li
- Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Health Science Center, Peking University, Beijing 100191, China
| | - Kehao Wang
- Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine, Beihang University, Beijing 100191, China
| | - Ziyuan Liu
- Beijing Key Laboratory of Restoration of Damaged Ocular Nerve, Health Science Center, Peking University, Beijing 100191, China
- Correspondence:
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Zhao Y, Zhu Y, Wang Y, Yang H, He X, Alvarez-Arenas TG, Li Y, Huang G. Quantitative Evaluation of In Vivo Corneal Biomechanical Properties after SMILE and FLEx Surgery by Acoustic Radiation Force Optical Coherence Elastography. SENSORS (BASEL, SWITZERLAND) 2022; 23:s23010181. [PMID: 36616779 PMCID: PMC9823345 DOI: 10.3390/s23010181] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 12/20/2022] [Accepted: 12/22/2022] [Indexed: 05/28/2023]
Abstract
The purpose of this study is to quantitatively evaluate the differences in corneal biomechanics after SMILE and FLEx surgery using an acoustic radiation force optical coherence elastography system (ARF-OCE) and to analyze the effect of the corneal cap on the integrity of corneal biomechanical properties. A custom ring array ultrasound transducer is used to excite corneal tissue to produce Lamb waves. Depth-resolved elastic modulus images of the in vivo cornea after refractive surgery were obtained based on the phase velocity of the Lamb wave. After refractive surgery, the average elastic modulus of the corneal flap decreased (71.7 ± 24.6 kPa), while the elastic modulus of the corneal cap increased (219.5 ± 54.9 kPa). The average elastic modulus of residual stromal bed (RSB) was increased after surgery, and the value after FLEx (305.8 ± 48.5 kPa) was significantly higher than that of SMILE (221.3 ± 43.2 kPa). Compared with FLEx, SMILE preserved most of the anterior stroma with less change in corneal biomechanics, which indicated that SMILE has an advantage in preserving the integrity of the corneal biomechanical properties. Therefore, the biomechanical properties of the cornea obtained by the ARF-OCE system may be one of the essential indicators for evaluating the safety of refractive surgery.
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Affiliation(s)
- Yanzhi Zhao
- School of Medical, Nanchang University, Nanchang 330031, China
- Department of Ophthalmology, The Third Affiliated Hospital of Nanchang University, Nanchang 330008, China
| | - Yirui Zhu
- School of Physics, Nanjing University, Nanjing 210093, China
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province, Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang 330063, China
| | - Yongbo Wang
- School of Medical, Nanchang University, Nanchang 330031, China
- Department of Ophthalmology, The Third Affiliated Hospital of Nanchang University, Nanchang 330008, China
| | - Hongwei Yang
- School of Medical, Nanchang University, Nanchang 330031, China
- Department of Ophthalmology, The Third Affiliated Hospital of Nanchang University, Nanchang 330008, China
| | - Xingdao He
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province, Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang 330063, China
| | - Tomas Gomez Alvarez-Arenas
- Institute for Physical and Information Technologies, Spanish National Research Council, Serrano 144, 28006 Madrid, Spain
| | - Yingjie Li
- Department of Ophthalmology, The Third Affiliated Hospital of Nanchang University, Nanchang 330008, China
| | - Guofu Huang
- School of Medical, Nanchang University, Nanchang 330031, China
- Department of Ophthalmology, The Third Affiliated Hospital of Nanchang University, Nanchang 330008, China
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9
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In Vivo Evaluation of the Effects of SMILE with Different Amounts of Stromal Ablation on Corneal Biomechanics by Optical Coherence Elastography. Diagnostics (Basel) 2022; 13:diagnostics13010030. [PMID: 36611322 PMCID: PMC9818797 DOI: 10.3390/diagnostics13010030] [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: 11/22/2022] [Revised: 12/18/2022] [Accepted: 12/18/2022] [Indexed: 12/24/2022] Open
Abstract
This work aims to depth-resolved quantitatively analyze the effect of different stromal ablation amounts on the corneal biomechanical properties during small incision lenticule extraction (SMILE) using optical coherence elastography (OCE). A 4.5-MHz ultrasonic transducer was used to excite elastic waves in the corneal tissue. The OCE system combined with the antisymmetric Lamb wave model was employed to achieve a high-resolution, high-sensitivity, and depth-resolved quantitative detection of the corneal Young's modulus. Eighteen rabbits were randomly divided into three groups; each group had six rabbits. The first and second groups underwent -3D and -6D SMILE surgeries, and the third group was the control group, respectively. Young's modulus of the corneal cap and residual stromal bed (RSB) were both increased after SMILE, which shared the stress under intraocular pressure (IOP). Furthermore, the Young's modulus of both the corneal cap and RSB after 3D SMILE group were significantly lower than that in the -6D group, which indicated that the increases in the post-operative corneal Young's modulus were positively correlated with the amount of stromal ablation. The OCE system for quantitative spatial characterization of corneal biomechanical properties can provide useful information on the extent of safe ablation for SMILE procedures.
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Nair A, Singh M, Aglyamov SR, Larin KV. Multimodal Heartbeat and Compression Optical Coherence Elastography for Mapping Corneal Biomechanics. Front Med (Lausanne) 2022; 9:833597. [PMID: 35479957 PMCID: PMC9037093 DOI: 10.3389/fmed.2022.833597] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Accepted: 02/28/2022] [Indexed: 11/13/2022] Open
Abstract
The biomechanical properties of the cornea have a profound influence on the health, structural integrity, and function of the eye. Understanding these properties may be critical for diagnosis and identifying disease pathogenesis. This work demonstrates how two different elastography techniques can be combined for a multimodal approach to measuring corneal biomechanical properties. Heartbeat optical coherence elastography (Hb-OCE) and compression OCE were performed simultaneously to measure the stiffness of the cornea in an in vivo rabbit model. Measurements were further performed after collagen crosslinking to demonstrate how the combined technique can be used to measure changes in corneal stiffness and map mechanical contrast. The results of this work further suggest that measurements from Hb-OCE and compression OCE are comparable, meaning that Hb-OCE and compression OCE may be used interchangeably despite distinct differences in both techniques.
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Affiliation(s)
- Achuth Nair
- Biomedical Engineering, University of Houston, Houston TX, United States
| | - Manmohan Singh
- Biomedical Engineering, University of Houston, Houston TX, United States
| | | | - Kirill V. Larin
- Biomedical Engineering, University of Houston, Houston TX, United States
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, United States
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11
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Alexandrovskaya Y, Baum O, Sovetsky A, Matveyev A, Matveev L, Sobol E, Zaitsev V. Optical Coherence Elastography as a Tool for Studying Deformations in Biomaterials: Spatially-Resolved Osmotic Strain Dynamics in Cartilaginous Samples. MATERIALS 2022; 15:ma15030904. [PMID: 35160851 PMCID: PMC8838169 DOI: 10.3390/ma15030904] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 01/14/2022] [Accepted: 01/20/2022] [Indexed: 12/15/2022]
Abstract
This paper presents a recently developed variant of phase-resolved Optical Coherence Elastography (OCE) enabling non-contact visualization of transient local strains of various origins in biological tissues and other materials. In this work, we demonstrate the possibilities of this new technique for studying dynamics of osmotically-induced strains in cartilaginous tissue impregnated with optical clearing agents (OCA). For poroelastic water-containing biological tissues, application of non-isotonic OCAs, various contrast additives, as well as drug solutions administration, may excite transient spatially-inhomogeneous strain fields of high magnitude in the tissue bulk, initiating mechanical and structural alterations. The range of the strain reliably observed by OCE varied from ±10−3 to ±0.4 for diluted and pure glycerol, correspondingly. The OCE-technique used made it possible to reveal previously inaccessible details of the complex spatio-temporal evolution of alternating-sign osmotic strains at the initial stages of agent diffusion. Qualitatively different effects produced by particular hydrophilic OCAs, such as glycerol and iohexol, are discussed, as well as concentration-dependent differences. Overall, the work demonstrates the unique abilities of the new OCE-modality in providing a deeper insight in real-time kinetics of osmotically-induced strains relevant to a broad range of biomedical applications.
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Affiliation(s)
- Yulia Alexandrovskaya
- Institute of Photon Technologies, Federal Scientific Research Center “Crystallography and Photonics”, Russian Academy of Sciences, 2 Pionerskaya Street, Troitsk, 108840 Moscow, Russia;
- Correspondence:
| | - Olga Baum
- Institute of Photon Technologies, Federal Scientific Research Center “Crystallography and Photonics”, Russian Academy of Sciences, 2 Pionerskaya Street, Troitsk, 108840 Moscow, Russia;
| | - Alexander Sovetsky
- Institute of Applied Physics of the Russian Academy of Sciences, 46 Uljanova Street, 603950 Nizhny Novgorod, Russia; (A.S.); (A.M.); (L.M.); (V.Z.)
| | - Alexander Matveyev
- Institute of Applied Physics of the Russian Academy of Sciences, 46 Uljanova Street, 603950 Nizhny Novgorod, Russia; (A.S.); (A.M.); (L.M.); (V.Z.)
| | - Lev Matveev
- Institute of Applied Physics of the Russian Academy of Sciences, 46 Uljanova Street, 603950 Nizhny Novgorod, Russia; (A.S.); (A.M.); (L.M.); (V.Z.)
| | - Emil Sobol
- UCI Health Beckman Laser Institute & Medical Clinic, 1002 Health Sciences Rd., Irvine, CA 92612, USA;
| | - Vladimir Zaitsev
- Institute of Applied Physics of the Russian Academy of Sciences, 46 Uljanova Street, 603950 Nizhny Novgorod, Russia; (A.S.); (A.M.); (L.M.); (V.Z.)
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12
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Kling S. In-Vivo Measurement of Ocular Deformation in Response to Ambient Pressure Modulation. Front Bioeng Biotechnol 2021; 9:759588. [PMID: 34869269 PMCID: PMC8634479 DOI: 10.3389/fbioe.2021.759588] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Accepted: 10/26/2021] [Indexed: 11/20/2022] Open
Abstract
A novel approach is presented for the non-invasive quantification of axial displacement and strain in corneal and anterior crystalline lens tissue in response to a homogenous ambient pressure change. A spectral domain optical coherence tomography (OCT) system was combined with a custom-built set of swimming goggles and a pressure control unit to acquire repetitive cross-sectional scans of the anterior ocular segment before, during and after ambient pressure modulation. The potential of the technique is demonstrated in vivo in a healthy human subject. The quantification of the dynamic deformation response, consisting of axial displacement and strain, demonstrated an initial retraction of the eye globe (−0.43 to −1.22 nm) and a subsequent forward motion (1.99 nm) in response to the pressure change, which went along with a compressive strain induced in the anterior crystalline lens (−0.009) and a tensile strain induced in the cornea (0.014). These mechanical responses appear to be the result of a combination of whole eye motion and eye globe expansion. The latter simulates a close-to-physiologic variation of the intraocular pressure and makes the detected mechanical responses potentially relevant for clinical follow-up and pre-surgical screening. The presented measurements are a proof-of-concept that non-contact low-amplitude ambient pressure modulation induces tissue displacement and strain that is detectable in vivo with OCT. To take full advantage of the high spatial resolution this imaging technique could offer, further software and hardware optimization will be necessary to overcome the current limitation of involuntary eye motions.
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Affiliation(s)
- Sabine Kling
- OPTIC Team, Computer Vision Laboratory, ITET Department, ETH Zürich, Zürich, Switzerland
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13
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Real-Time Strain and Elasticity Imaging in Phase-Sensitive Optical Coherence Elastography Using a Computationally Efficient Realization of the Vector Method. PHOTONICS 2021. [DOI: 10.3390/photonics8120527] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
We present a real-time realization of OCT-based elastographic mapping local strains and distribution of the Young’s modulus in biological tissues, which is in high demand for biomedical usage. The described variant exploits the principle of Compression Optical Coherence Elastography (C-OCE) and uses processing of phase-sensitive OCT signals. The strain is estimated by finding local axial gradients of interframe phase variations. Instead of the popular least-squares method for finding these gradients, we use the vector approach, one of its advantages being increased computational efficiency. Here, we present a modified, especially fast variant of this approach. In contrast to conventional correlation-based methods and previously used phase-resolved methods, the described method does not use any search operations or local calculations over a sliding window. Rather, it obtains local strain maps (and then elasticity maps) using several transformations represented as matrix operations applied to entire complex-valued OCT scans. We first elucidate the difference of the proposed method from the previously used correlational and phase-resolved methods and then describe the proposed method realization in a medical OCT device, in which for real-time processing, a “typical” central processor (e.g., Intel Core i7-8850H) is sufficient. Representative examples of on-flight obtained elastographic images are given. These results open prospects for broad use of affordable OCT devices for high-resolution elastographic vitalization in numerous biomedical applications, including the use in clinic.
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14
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Desissaire S, Schwarzhans F, Steiner S, Vass C, Fischer G, Pircher M, Hitzenberger CK. Temporal phase evolution OCT for measurement of tissue deformation in the human retina in-vivo. BIOMEDICAL OPTICS EXPRESS 2021; 12:7092-7112. [PMID: 34858702 PMCID: PMC8606136 DOI: 10.1364/boe.440893] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 10/13/2021] [Accepted: 10/13/2021] [Indexed: 05/08/2023]
Abstract
We demonstrate the use of temporal phase evolution (TPE-) OCT methods to evaluate retinal tissue deformation in-vivo over time periods of several seconds. A custom built spectral domain (SD)-OCT system with an integrated retinal tracker, ensuring stable imaging with sub-speckle precision, was used for imaging. TPE-OCT measures and images phase differences between an initial reference B-scan and each of the subsequent B-scans of the evaluated temporal sequence. In order to demonstrate the precision and repeatability of the measurements, retinal nerve fiber (RNF) tissue deformations induced by retinal vessels pulsating with the heartbeat were analyzed in several healthy subjects. We show TPE maps (M-scans of phase evolution as a function of position along B-scan trace vs. time) of wrapped phase data and corresponding deformation maps in selected regions of the RNF layer (RNFL) over the course of several cardiac cycles. A reproducible phase pattern is seen at each heartbeat cycle for all imaged volunteers. RNF tissue deformations near arteries and veins up to ∼ 1.6 µm were obtained with an average precision for a single pixel of about 30 nm. Differences of motion induced by arteries and veins are also investigated.
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Affiliation(s)
- Sylvia Desissaire
- Center for Medical Physics and Biomedical
Engineering, Medical University of Vienna,
Vienna, 1090, Austria
| | - Florian Schwarzhans
- Center for Medical Statistics, Informatics
and Intelligent Systems, Medical University of
Vienna, Vienna, 1090, Austria
| | - Stefan Steiner
- Department of Ophthalmology and Optometry,
Medical University of Vienna, Vienna, 1090,
Austria
| | - Clemens Vass
- Department of Ophthalmology and Optometry,
Medical University of Vienna, Vienna, 1090,
Austria
| | - Georg Fischer
- Center for Medical Statistics, Informatics
and Intelligent Systems, Medical University of
Vienna, Vienna, 1090, Austria
| | - Michael Pircher
- Center for Medical Physics and Biomedical
Engineering, Medical University of Vienna,
Vienna, 1090, Austria
| | - Christoph K. Hitzenberger
- Center for Medical Physics and Biomedical
Engineering, Medical University of Vienna,
Vienna, 1090, Austria
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15
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Ferguson TJ, Singuri S, Jalaj S, Ford MR, De Stefano VS, Seven I, Dupps WJ. Depth-resolved Corneal Biomechanical Changes Measured Via Optical Coherence Elastography Following Corneal Crosslinking. Transl Vis Sci Technol 2021; 10:7. [PMID: 34313710 PMCID: PMC8322708 DOI: 10.1167/tvst.10.5.7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Purpose To evaluate depth-resolved changes of corneal biomechanical properties in eyes with corneal ectasia after corneal crosslinking (CXL) using optical coherence elastography. Methods In a prospective pilot series of eyes with corneal ectasia, a custom high-speed swept source optical coherence tomography system was used to image the cornea before and 3 months after CXL during a low-speed applanating deformation while monitoring applanation force. Cross-correlation was applied to track frame-by-frame two-dimensional optical coherence tomography speckle displacements, and the slope of force versus local axial displacement behavior during the deformation was used to produce a two-dimensional array of axial stiffness (k). These values were averaged for anterior (ka) and posterior (kp) stromal regions and expressed as a ratio (ka/kp) to assess depth-dependent differences in stiffness. CXL was performed according to the Dresden protocol with a system approved by the U.S. Food and Drug Administration. Results Four eyes from four patients with keratoconus (n = 3) or post-LASIK ectasia (n = 1) underwent optical coherence elastography before and 3 months after CXL. The mean ka/kp was 1.03 ± 0.07 before CXL compared with 1.34 ± 0.17 after the CXL procedure. All four eyes demonstrated at least a 20% increase in the ka/kp. Conclusions Preferential stiffening of the anterior stroma with the standard CXL protocol was demonstrated with optical coherence elastography in live human subjects. Translational Relevance Although ex vivo studies have demonstrated anterior stiffening effects after CXL using various destructive and nondestructive methods, this report presents the first evidence of such changes in serial live human measurements.
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Affiliation(s)
| | - Srinidhi Singuri
- Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of CWRU, Cleveland, Ohio, USA
| | - Sanjai Jalaj
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - Matthew R Ford
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | | | - Ibrahim Seven
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA
| | - William J Dupps
- Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, USA.,Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of CWRU, Cleveland, Ohio, USA.,Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, USA.,Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA
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16
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Abdelghany AA, D’Oria F, Alio Del Barrio J, Alio JL. The Value of Anterior Segment Optical Coherence Tomography in Different Types of Corneal Infections: An Update. J Clin Med 2021; 10:jcm10132841. [PMID: 34199039 PMCID: PMC8267702 DOI: 10.3390/jcm10132841] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2021] [Revised: 06/03/2021] [Accepted: 06/26/2021] [Indexed: 11/06/2022] Open
Abstract
Anterior segment optical coherence tomography (AS-OCT) is a modality that uses low-coherence interferometry to visualize and assess anterior segment ocular features, offering several advantages of being a sterile and noncontact modality that generates high-resolution cross-sectional images of the tissues. The qualitative and quantitative information provided by AS-OCT may be extremely useful for the clinician in the assessment of a wide spectrum of corneal infections, guiding in the management and follow-up of these patients. In clinical practice, infections are routinely evaluated with slit-lamp biomicroscopy, an examination and imaging modality that is limited by the physical characteristics of light. As a consequence, the depth of pathology and the eventually associated corneal edema cannot be accurately measured with the slit-lamp. Therefore, it represents a limit for the clinician, as in vivo information about corneal diseases and the response to treatment is limited. Resolution of corneal infection is characterized by an early reduction in corneal edema, followed by a later reduction in infiltration: both parameters can be routinely measured with standardized serial images by AS-OCT.
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Affiliation(s)
- Ahmed A. Abdelghany
- Ophthalmology Department, Faculty of Medicine, Minia University, Minia 61519, Egypt;
| | - Francesco D’Oria
- Section of Ophthalmology, Department of Basic Medical Sciences, Neurosciences and Sense Organs, University of Bari, 70124 Bari, Italy;
| | | | - Jorge L. Alio
- Vissum Miranza, Miguel Hernandez University, c/Cabañal, 1, 03016 Alicante, Spain;
- Correspondence:
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17
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Atalay E, Özalp O, Yıldırım N. Advances in the diagnosis and treatment of keratoconus. Ther Adv Ophthalmol 2021; 13:25158414211012796. [PMID: 34263132 PMCID: PMC8246497 DOI: 10.1177/25158414211012796] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 04/07/2021] [Indexed: 01/31/2023] Open
Abstract
Keratoconus had traditionally been considered a rare disease at a time when the imaging technology was inept in detecting subtle manifestations, resulting in more severe disease at presentation. The increased demand for refractive surgery in recent years also made it essential to more effectively detect keratoconus before attempting any ablative procedure. Consequently, the armamentarium of tools that can be used to diagnose and treat keratoconus has significantly expanded. The advances in imaging technology have allowed clinicians and researchers alike to visualize the cornea layer by layer looking for any early changes that might be indicative of keratoconus. In addition to the conventional geometrical evaluation, efforts are also underway to enable spatially resolved corneal biomechanical evaluation. Artificial intelligence has been exploited in a multitude of ways to enhance diagnostic efficiency and to guide treatment. As for treatment, corneal cross-linking treatment remains the mainstay preventive approach, yet the current main focus of research is on increasing oxygen availability and developing new strategies to improve riboflavin permeability during the procedure. Some new combined protocols are being proposed to simultaneously halt keratoconus progression and correct refractive error. Bowman layer transplantation and additive keratoplasty are newly emerging alternatives to conventional keratoplasty techniques that are used in keratoconus surgery. Advances in tissue engineering and regenerative therapy might bring new perspectives for treatment at the cellular level and hence obviate the need for invasive surgeries. In this review, we describe the advances in the diagnosis and treatment of keratoconus primarily focusing on newly emerging approaches and strategies.
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Affiliation(s)
- Eray Atalay
- Department of Ophthalmology, Medical School, Eskişehir Osmangazi University, Meşelik Kampüsü, Odunpazarı, Eskişehir 26040, Turkey
| | - Onur Özalp
- Department of Ophthalmology, Medical School, Eskişehir Osmangazi University, Eskişehir, Turkey
| | - Nilgün Yıldırım
- Department of Ophthalmology, Medical School, Eskişehir Osmangazi University, Eskişehir, Turkey
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18
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Wilson A, Marshall J. A review of corneal biomechanics: Mechanisms for measurement and the implications for refractive surgery. Indian J Ophthalmol 2021; 68:2679-2690. [PMID: 33229643 PMCID: PMC7856929 DOI: 10.4103/ijo.ijo_2146_20] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Detailed clinical assessment of corneal biomechanics has the potential to revolutionize the ophthalmic industry through enabling quicker and more proficient diagnosis of corneal disease, safer and more effective surgical treatments, and the provision of customized and optimized care. Despite these wide-ranging benefits, and an outstanding clinical need, the provision of technology capable of the assessment of corneal biomechanics in the clinic is still in its infancy. While laboratory-based technologies have progressed significantly over the past decade, there remain significant gaps in our knowledge regarding corneal biomechanics and how they relate to shape and function, and how they change in disease and after surgical intervention. Here, we discuss the importance, relevance, and challenges associated with the assessment of corneal biomechanics and review the techniques currently available and underdevelopment in both the laboratory and the clinic.
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Affiliation(s)
- Abby Wilson
- Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, UK
| | - John Marshall
- Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, UK
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19
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Rippy JR, Singh M, Aglyamov SR, Larin KV. Ultrasound Shear Wave Elastography and Transient Optical Coherence Elastography: Side-by-Side Comparison of Repeatability and Accuracy. IEEE OPEN JOURNAL OF ENGINEERING IN MEDICINE AND BIOLOGY 2021; 2:179-186. [PMID: 34179823 PMCID: PMC8224461 DOI: 10.1109/ojemb.2021.3075569] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Objective: We compare the repeatability and accuracy of ultrasound shear wave elastography (USE) and transient optical coherence elastography (OCE). Methods: Elastic wave speed in gelatin phantoms and chicken breast was measured with USE and OCE and compared with uniaxial mechanical compression testing. Intra- and Inter-repeatability were analyzed using Bland-Altman plots and intraclass correlation coefficients (ICC). Results: OCE and USE differed from uniaxial testing by a mean absolute percent error of 8.92% and 16.9%, respectively, across eight phantoms of varying stiffness. Upper and lower limits of agreement for intrasample repeatability for USE and OCE were ±0.075 m/s and −0.14 m/s and 0.13 m/s, respectively. OCE and USE both had ICCs of 0.9991. In chicken breast, ICC for USE was 0.9385 and for OCE was 0.9924. Conclusion: OCE and USE can detect small speed changes and give comparable measurements. These measurements correspond well with uniaxial testing.
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20
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Brodie F, Repka M, Burns SA, Prakalapakorn SG, Morse C, Schuman JS, Duenas MR, Afshari N, Pollack JS, Thorne JE, Vitale A, Sen HN, Myung D, Blumenkranz MS, Tu E, Hammer DX, Tarver M, Cunningham B, Kagemann L, Sadda S, Sarraf D, Jaffe GJ, Eydelman M. Development, Validation, and Innovation in Ophthalmic Laser-Based Imaging: Report From a US Food and Drug Administration-Cosponsored Forum. JAMA Ophthalmol 2021; 139:113-118. [PMID: 33211074 DOI: 10.1001/jamaophthalmol.2020.4994] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In April 2019, the US Food and Drug Administration, in conjunction with 11 professional ophthalmic, vision science, and optometric societies, convened a forum on laser-based imaging. The forum brought together the Food and Drug Administration, clinicians, researchers, industry members, and other stakeholders to stimulate innovation and ensure that patients in the US are the first in the world to have access to high-quality, safe, and effective medical devices. This conference focused on the technology, clinical applications, regulatory issues, and reimbursement issues surrounding innovative ocular imaging modalities. Furthermore, the emerging role of artificial intelligence in ophthalmic imaging was reviewed. This article summarizes the presentations, discussion, and future directions.
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Affiliation(s)
- Frank Brodie
- Byers Eye Institute, Stanford University, Stanford, California.,Now with Vitreoretinal Surgery Fellowship Program, Duke Ophthalmology, Duke University School of Medicine, Durham, North Carolina
| | - Michael Repka
- American Academy of Ophthalmology, San Francisco, California
| | | | - S Grace Prakalapakorn
- American Association for Pediatric Ophthalmology and Strabismus, San Francisco, California
| | - Christie Morse
- American Association for Pediatric Ophthalmology and Strabismus, San Francisco, California
| | | | | | - Natalie Afshari
- American Society of Cataract and Refractive Surgeons, Fairfax, Virginia
| | - John S Pollack
- American Society of Retinal Specialists, Chicago, Illinois
| | | | | | - H Nida Sen
- American Uveitis Society, Birmingham, Alabama
| | - David Myung
- Byers Eye Institute, Stanford University, Stanford, California
| | | | - Elmer Tu
- Cornea Society, Fairfax, Virginia
| | - Daniel X Hammer
- Center for Devices and Radiological Health Food and Drug Administration, Silver Spring, Maryland
| | - Michelle Tarver
- Center for Devices and Radiological Health Food and Drug Administration, Silver Spring, Maryland
| | - Bradley Cunningham
- Center for Devices and Radiological Health Food and Drug Administration, Silver Spring, Maryland
| | - Larry Kagemann
- Center for Devices and Radiological Health Food and Drug Administration, Silver Spring, Maryland
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21
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Singh M, Nair A, Aglyamov SR, Larin KV. Compressional Optical Coherence Elastography of the Cornea. PHOTONICS 2021; 8:111. [PMID: 37727230 PMCID: PMC10508915 DOI: 10.3390/photonics8040111] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Assessing the biomechanical properties of the cornea is crucial for detecting the onset and progression of eye diseases. In this work, we demonstrate the application of compression-based optical coherence elastography (OCE) to measure the biomechanical properties of the cornea under various conditions, including validation in an in situ rabbit model and a demonstration of feasibility for in vivo measurements. Our results show a stark increase in the stiffness of the corneas as IOP was increased. Moreover, UV-A/riboflavin corneal collagen crosslinking (CXL) also dramatically increased the stiffness of the corneas. The results were consistent across 4 different scenarios (whole CXL in situ, partial CXL in situ, whole CXL in vivo, and partial CXL in vivo), emphasizing the reliability of compression OCE to measure corneal biomechanical properties and its potential for clinical applications.
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Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Rd., Room N207, Houston, TX 77204, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, BCM335, Houston, TX 77030, USA
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22
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Chong J, Dupps WJ. Corneal biomechanics: Measurement and structural correlations. Exp Eye Res 2021; 205:108508. [PMID: 33609511 DOI: 10.1016/j.exer.2021.108508] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 02/09/2021] [Accepted: 02/12/2021] [Indexed: 02/02/2023]
Abstract
The characterization of corneal biomechanical properties has important implications for the management of ocular disease and prediction of surgical responses. Corneal refractive surgery outcomes, progression or stabilization of ectatic disease, and intraocular pressure determination are just examples of the many key clinical problems that depend highly upon corneal biomechanical characteristics. However, to date there is no gold standard measurement technique. Since the advent of a 1-dimensional (1D) air-puff based technique for measuring the corneal surface response in 2005, advances in clinical imaging technology have yielded increasingly sophisticated approaches to characterizing the biomechanical properties of the cornea. Novel analyses of 1D responses are expanding the clinical utility of commercially-available air-puff-based instruments, and other imaging modalities-including optical coherence elastography (OCE), Brillouin microscopy and phase-decorrelation ocular coherence tomography (PhD-OCT)-offer new opportunities for probing local biomechanical behavior in 3-dimensional space and drawing new inferences about the relationships between corneal structure, mechanical behavior, and corneal refractive function. These advances are likely to drive greater clinical adoption of in vivo biomechanical analysis and to support more personalized medical and surgical decision-making.
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Affiliation(s)
- Jillian Chong
- Cleveland Clinic Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - William J Dupps
- Cleveland Clinic Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA; Dept. of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve Univ, Cleveland, OH, USA; Dept. of Biomedical Engineering, Lerner Research Institute and Case Western Reserve Univ, Cleveland, OH, USA.
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23
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Nair A, Singh M, Aglyamov S, Larin KV. Heartbeat optical coherence elastography: corneal biomechanics in vivo. JOURNAL OF BIOMEDICAL OPTICS 2021; 26:JBO-200338LR. [PMID: 33624461 PMCID: PMC7901857 DOI: 10.1117/1.jbo.26.2.020502] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 01/19/2021] [Indexed: 05/02/2023]
Abstract
SIGNIFICANCE Mechanical assessment of the cornea can provide important structural and functional information regarding its health. Current clinically available tools are limited in their efficacy at measuring corneal mechanical properties. Elastography allows for the direct estimation of mechanical properties of tissues in vivo but is generally performed using external excitation force. AIM To show that heartbeat optical coherence elastography (Hb-OCE) can be used to assess the mechanical properties of the cornea in vivo. APPROACH Hb-OCE was utilized to detect Hb-induced deformations in the rabbit cornea in vivo without the need for external excitation. Furthermore, we demonstrate how this technique can distinguish corneal stiffness between untreated (UT) and crosslinked (CXL) tissue. RESULTS Our results demonstrate that stiffness changes in the cornea can be detected using only the Hb-induced deformations in the cornea. Additionally, we demonstrate a statistically significant difference in strain between the UT and CXL corneas. CONCLUSIONS Hb-OCE may be an effective tool for assessing the mechanical properties of the cornea in vivo without the need for external excitation. This tool may be effective for clinical assessment of corneal mechanical properties because it only requires optical coherence tomography imaging and data processing.
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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 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,
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24
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Kling S, Torres-Netto EA, Spiru B, Sekundo W, Hafezi F. Quasi-Static Optical Coherence Elastography to Characterize Human Corneal Biomechanical Properties. Invest Ophthalmol Vis Sci 2021; 61:29. [PMID: 32539132 PMCID: PMC7415307 DOI: 10.1167/iovs.61.6.29] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Purpose Quasi-static optical coherence elastography (OCE) is an emerging technology to investigate corneal biomechanical behavior in situations similar to physiological stress conditions. Herein OCE was applied to evaluate previously inaccessible biomechanical characteristics of human corneal tissue and to study the role of Bowman's layer in corneal biomechanics. Methods Human corneal donor buttons (n = 23) were obtained and Descemet's membrane and endothelium were removed. In 11 corneas, Bowman's layer was ablated by a 20 µm stromal excimer laser ablation. Buttons were mounted on an artificial anterior chamber and subjected to a pressure modulation from 10 to 30 mm Hg, and back to 10 mm Hg, in steps of 1 mm Hg. At each step, a spectral-domain optical coherence tomography scan was obtained. Displacements were analyzed by optical flow tracking, and strain over the entire stromal depth was retrieved from the phase gradient of the complex interference signal. Results During pressure increase, corneal tissue moved upward (486–585 nm/mm Hg) but did not fully recover (Δ= 2.63 to 8.64 µm) after pressure decrease. Vertical corneal strain distribution was negative in the anterior and positive in the posterior cornea, indicating simultaneous corneal compression and expansion, respectively. Bowman's layer caused minor localized differences in corneal strain distribution. Conclusions Corneal strain distribution is more complex than previously assumed, with a fundamental difference in mechanical response between the anterior and posterior stroma. Clinically, OCE technology might be used to monitor the progression of corneal ectatic diseases and to determine the success of corneal cross-linking.
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25
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In vivo measurement of shear modulus of the human cornea using optical coherence elastography. Sci Rep 2020; 10:17366. [PMID: 33060714 PMCID: PMC7567833 DOI: 10.1038/s41598-020-74383-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Accepted: 06/05/2020] [Indexed: 01/01/2023] Open
Abstract
Corneal stiffness plays a critical role in shaping the cornea with respect to intraocular pressure and physical interventions. However, it remains difficult to measure the mechanical properties noninvasively. Here, we report the first measurement of shear modulus in human corneas in vivo using optical coherence elastography (OCE) based on surface elastic waves. In a pilot study of 12 healthy subjects aged between 25 and 67, the Rayleigh-wave speed was 7.86 ± 0.75 m/s, corresponding to a shear modulus of 72 ± 14 kPa. Our data reveal two unexpected trends: no correlation was found between the wave speed and IOP between 13–18 mmHg, and shear modulus decreases with age (− 0.32 ± 0.17 m/s per decade). We propose that shear stiffness is governed by the interfibrillar matrix, whereas tensile strength is dominated by collagen fibrils. Rayleigh-wave OCE may prove useful for clinical diagnosis, refractive surgeries, and treatment monitoring.
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26
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Wilson A, Jones J, Tyrer JR, Marshall J. An interferometric ex vivo study of corneal biomechanics under physiologically representative loading, highlighting the role of the limbus in pressure compensation. EYE AND VISION 2020; 7:43. [PMID: 32832574 PMCID: PMC7433364 DOI: 10.1186/s40662-020-00207-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 07/25/2020] [Indexed: 12/23/2022]
Abstract
Background The mechanical properties of the cornea are complex and regionally variable. This paper uses an original method to investigate the biomechanics of the cornea in response to hydrostatic loading over the typical physiological range of intra-ocular pressure (IOP) fluctuations thereby increasing understanding of clinically relevant corneal biomechanical properties and their contributions to the refractive properties of the cornea. Methods Displacement speckle pattern interferometry (DSPI) was used to measure the total surface displacement of 40 porcine and 6 human corneal-scleral specimens in response to pressure variations up to 1 mmHg from a baseline of 16.5 mmHg. All specimens were mounted in a modified artificial anterior chamber (AAC) and loaded hydrostatically. Areas of high strain in response to loading were identified by comparing the displacements across different regions. Results The nature of the response of the corneal surface to loading demonstrated high regional topographic variation. Mechanical properties were shown to be asymmetrical, and deformation of the limbal and pre-limbal regions dominated these responses respectively with over 90% (N-T) and 60% (S-I) of the total maximum displacement occurring in these regions indicating high-strain. In contrast, the curvature of the central cornea remained relatively unchanged merely translating in position. Conclusions The limbal and pre-limbal regions of the cornea appear to be fundamental to the absorption of small pressure fluctuations facilitating the curvature of the central cornea to remain relatively unchanged. The differential mechanical properties of this region could have important implications for the application of corneal surgery and corneal crosslinking, warranting further investigation.
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Affiliation(s)
- Abby Wilson
- Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, UK
| | - John Jones
- Laser Optical Engineering Ltd., Derbyshire, UK
| | - John R Tyrer
- Wolfson School of Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough, UK.,Laser Optical Engineering Ltd., Derbyshire, UK
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27
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Jin Z, Chen S, Dai Y, Bao C, Ye S, Zhou Y, Wang Y, Huang S, Wang Y, Shen M, Zhu D, Lu F. In vivo noninvasive measurement of spatially resolved corneal elasticity in human eyes using Lamb wave optical coherence elastography. JOURNAL OF BIOPHOTONICS 2020; 13:e202000104. [PMID: 32368840 DOI: 10.1002/jbio.202000104] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 04/24/2020] [Accepted: 04/29/2020] [Indexed: 05/23/2023]
Abstract
Current elastography techniques are limited in application to accurately assess spatially resolved corneal elasticity in vivo for human eyes. The air-puff optical coherence elastography (OCE) with an eye motion artifacts correction algorithm is developed to distinguish the in vivo cornea vibration from the eye motion and visualize the Lamb wave propagation clearly in healthy subjects. Based on the Lamb wave model, the phase velocity dispersion curve in the high-frequency is calculated to obtain spatially resolved corneal elasticity accurately with high repeatability. It is found that the corneal elasticity has regional variations and is correlated with intraocular pressure, which suggests that the method has the potential to provide noninvasive measurement of spatially resolved corneal elasticity in clinical practice.
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Affiliation(s)
- Zi Jin
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Sisi Chen
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Yingying Dai
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Chenhong Bao
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Shuling Ye
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Yuheng Zhou
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Yiyi Wang
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Shenghai Huang
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Yuanyuan Wang
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Meixiao Shen
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Dexi Zhu
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
| | - Fan Lu
- School of Ophthalmology and Optometry, Wenzhou Medical University, Zhejiang, China
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Preoperative, intraoperative, and postoperative assessment of corneal biomechanics in refractive surgery. Curr Opin Ophthalmol 2020; 31:234-240. [PMID: 32452876 DOI: 10.1097/icu.0000000000000663] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
PURPOSE OF REVIEW To review current and emerging methods and utilities of preoperative, intraoperative, and postoperative measurements of corneal biomechanics and their effects on refractive surgery decision-making. RECENT FINDINGS Several recent clinical and preclinical studies have demonstrated the utility of corneal biomechanical analysis in refractive surgery. These studies focus on both screening surgical candidates for keratoconic disease as well as intraoperative and postoperative monitoring. The measurement of spatially resolved biomechanics is beginning to be studied in humans. SUMMARY Clinically available screening methods combining corneal biomechanics with topographic and tomographic data provide increased utility when screening for keratoconic disorder. Spatially resolved measurement of corneal biomechanics holds great potential for preoperative, intraoperative, and postoperative evaluation of refractive surgery candidates as well as for more individualized procedures in the future.
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De Stefano VS, Ford MR, Seven I, Dupps WJ. Depth-Dependent Corneal Biomechanical Properties in Normal and Keratoconic Subjects by Optical Coherence Elastography. Transl Vis Sci Technol 2020; 9:4. [PMID: 32832211 PMCID: PMC7414661 DOI: 10.1167/tvst.9.7.4] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 04/07/2020] [Indexed: 12/15/2022] Open
Abstract
Purpose Compare depth-resolved biomechanical properties in normal and keratoconic corneas in live human subjects using optical coherence elastography (OCE). Methods In a prospective series of normal and keratoconus (KC) eyes, a corneal perturbation was applied by a custom swept-source OCE system using a transparent flat lens coupled to force transducers. Cross-correlation was applied to track frame-by-frame OCT speckle displacement. Regional displacements for the anterior and posterior stroma were plotted in force versus displacement (k) graphs. A spatial biomechanical property ratio (ka/kp ) was defined by dividing the maximum total displacement by the maximum force for the anterior (ka ) and posterior cornea (kp) and was compared between normal and KC groups with the Mann-Whitney U test. Area under the receiver operating characteristics curve (AUROC) for differentiating normal and KC eyes was calculated for ka/kp , kmax, and thinnest point of corneal thickness (TPCT). Results Thirty-six eyes were analyzed (21 eyes of 12 normal subjects and 15 KC eyes of 12 subjects). The ka/kp for the normal group was 1.135 ± 0.07 (mean ± standard deviation) and 1.02 ± 0.08 for the KC group (P < 0.001), indicating a relative deficit in anterior stromal stiffness in KC eyes. AUROC was 0.91 for ka /kp , 0.95 for kmax, and 1 for TPCT. Conclusions Significant differences in depth-dependent corneal biomechanical properties were observed between normal and KC subjects. Translational Relevance OCE was applied for the first time to human KC subjects and revealed alterations in the normal anterior-to-posterior stromal stiffness gradient, a novel and clinically accessible disease biomarker.
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Affiliation(s)
- Vinicius S De Stefano
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA.,Department of Ophthalmology and Visual Sciences, Federal University of Sao Paulo, Sao Paulo, Brazil
| | - Matthew R Ford
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Ibrahim Seven
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA
| | - William J Dupps
- Cole Eye Institute, Cleveland Clinic, Cleveland, OH, USA.,Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, USA.,Department of Ophthalmology, Cleveland Clinic Lerner College of Medicine of Case Western Reserve University, Cleveland, OH, USA
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31
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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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Li Y, Moon S, Chen JJ, Zhu Z, Chen Z. Ultrahigh-sensitive optical coherence elastography. LIGHT, SCIENCE & APPLICATIONS 2020; 9:58. [PMID: 32337022 PMCID: PMC7154028 DOI: 10.1038/s41377-020-0297-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 03/16/2020] [Accepted: 03/19/2020] [Indexed: 05/07/2023]
Abstract
The phase stability of an optical coherence elastography (OCE) system is the key determining factor for achieving a precise elasticity measurement, and it can be affected by the signal-to-noise ratio (SNR), timing jitters in the signal acquisition process, and fluctuations in the optical path difference (OPD) between the sample and reference arms. In this study, we developed an OCE system based on swept-source optical coherence tomography (SS-OCT) with a common-path configuration (SS-OCECP). Our system has a phase stability of 4.2 mrad without external stabilization or extensive post-processing, such as averaging. This phase stability allows us to detect a displacement as small as ~300 pm. A common-path interferometer was incorporated by integrating a 3-mm wedged window into the SS-OCT system to provide intrinsic compensation for polarization and dispersion mismatch, as well as to minimize phase fluctuations caused by the OPD variation. The wedged window generates two reference signals that produce two OCT images, allowing for averaging to improve the SNR. Furthermore, the electrical components are optimized to minimize the timing jitters and prevent edge collisions by adjusting the delays between the trigger, k-clock, and signal, utilizing a high-speed waveform digitizer, and incorporating a high-bandwidth balanced photodetector. We validated the SS-OCECP performance in a tissue-mimicking phantom and an in vivo rabbit model, and the results demonstrated a significantly improved phase stability compared to that of the conventional SS-OCE. To the best of our knowledge, we demonstrated the first SS-OCECP system, which possesses high-phase stability and can be utilized to significantly improve the sensitivity of elastography.
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Affiliation(s)
- Yan Li
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612 USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA 92617 USA
| | - Sucbei Moon
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612 USA
- Department of Physics, Kookmin University, Seoul, 02707 South Korea
| | - Jason J. Chen
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612 USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA 92617 USA
| | - Zhikai Zhu
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612 USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA 92617 USA
| | - Zhongping Chen
- Beckman Laser Institute, University of California, Irvine, Irvine, CA 92612 USA
- Department of Biomedical Engineering, University of California, Irvine, Irvine, CA 92617 USA
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Ambekar YS, Singh M, Zhang J, Nair A, Aglyamov SR, Scarcelli G, Larin KV. Multimodal quantitative optical elastography of the crystalline lens with optical coherence elastography and Brillouin microscopy. BIOMEDICAL OPTICS EXPRESS 2020; 11:2041-2051. [PMID: 32341865 PMCID: PMC7173892 DOI: 10.1364/boe.387361] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 02/27/2020] [Accepted: 03/05/2020] [Indexed: 05/03/2023]
Abstract
Assessing the biomechanical properties of the crystalline lens can provide crucial information for diagnosing disease and guiding precision therapeutic interventions. Existing noninvasive methods have been limited to global measurements. Here, we demonstrate the quantitative assessment of the elasticity of crystalline lens with a multimodal optical elastography technique, which combines dynamic wave-based optical coherence elastography (OCE) and Brillouin microscopy to overcome the drawbacks of individual modalities. OCE can provide direct measurements of tissue elasticity rapidly and quantitatively, but it is a challenge to image transparent samples such as the lens because this technique relies on backscattered light. On the other hand, Brillouin microscopy can map the longitudinal modulus with micro-scale resolution in transparent samples. However, the relationship between Brillouin-deduced modulus and Young's modulus is not straightforward and sample dependent. By combining these two techniques, we can calibrate Brillouin measurements with OCE, based on the same sample, allowing us to completely map the Young's modulus of the crystalline lens. The combined system was first validated with tissue-mimicking gelatin phantoms of varying elasticities (N = 9). The OCE data was used to calibrate the Brillouin shift measurements and subsequently map the Young's modulus of the phantoms. After validation, OCE and Brillouin measurements were performed on ex-vivo porcine lenses (N = 6), and the Young's modulus of the lenses was spatially mapped. The results show a strong correlation between Young's moduli measured by OCE and longitudinal moduli measured by Brillouin microscopy. The correlation coefficient R was 0.98 for the phantoms and 0.94 for the lenses, respectively. The mean Young's modulus of the anterior and posterior lens was 1.98 ± 0.74 kPa and 2.93 ± 1.13 kPa, respectively, and the Young's modulus of the lens nucleus was 11.90 ± 2.94 kPa. The results presented in this manuscript open a new way for truly quantitative biomechanical mapping of optically transparent (or low scattering) tissues in 3D.
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Affiliation(s)
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX 77030, USA
| | - Jitao Zhang
- Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, TX 77030, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX 77030, USA
| | - Giuliano Scarcelli
- Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX 77030, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
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Kling S, Khodadadi H, Goksel O. Optical Coherence Elastography-Based Corneal Strain Imaging During Low-Amplitude Intraocular Pressure Modulation. Front Bioeng Biotechnol 2020; 7:453. [PMID: 32083064 PMCID: PMC7004960 DOI: 10.3389/fbioe.2019.00453] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 12/18/2019] [Indexed: 11/15/2022] Open
Abstract
Purpose: Optical coherence elastography (OCE) is a promising technique for high-resolution strain imaging in ocular tissues. A major strain-inducing factor in the eye is intraocular pressure (IOP), with diurnal physiological fluctuations reaching up to 5 mmHg. We study herein low-amplitude IOP modulation to assess local corneal strain patterns. Methods:Ex vivo porcine eye globes were adjusted to an initial IOP of 15 mmHg and subsequently 25 mmHg. Corneal strain was induced by two subsequent pressure cycles, in which IOP was first increased and then decreased, each by a total of 5 mmHg. Two-dimensional optical coherence tomography (2D-OCT) B-scans were recorded after each loading step. Axial strain maps were obtained from magnitude and phase changes and supra-pixel displacements from cross-correlation. The strain detection sensitivity was evaluated in an isotropic material. Results: Deformations arising from a single 1-mmHg step could be resolved. The largest strain amplitudes (5.11·10−3) were observed in the posterior stroma at a low initial IOP. Strain amplitude was 1.34 times higher at 15 mmHg than at 25 mmHg (p = 0.003). Upon IOP increase, the anterior cornea was compressed, whereas the posterior cornea showed axial expansion. Both morphological images and strain maps were sensitive to postmortem time. Strains that are larger than 2.44·10−5 could be reliably measured. Conclusions: Low-amplitude IOP modulation, similar to diurnal physiological changes, induced measurable deformations in corneal tissue. Axial strain maps permit a localized comparison of the corneal biomechanical response. Small-strain OCE can likely be extended to other domains.
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Affiliation(s)
- Sabine Kling
- OPTIC Team, Computer-assisted Applications in Medicine Group, Computer Vision Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
| | - Hossein Khodadadi
- OPTIC Team, Computer-assisted Applications in Medicine Group, Computer Vision Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
| | - Orcun Goksel
- OPTIC Team, Computer-assisted Applications in Medicine Group, Computer Vision Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
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Grytz R, Krishnan K, Whitley R, Libertiaux V, Sigal IA, Girkin CA, Downs JC. A Mesh-Free Approach to Incorporate Complex Anisotropic and Heterogeneous Material Properties into Eye-Specific Finite Element Models. COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2020; 358:https://doi.org/10.1016/j.cma.2019.112654. [PMID: 32051652 PMCID: PMC7015153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Commercial finite element modeling packages do not have the tools necessary to effectively incorporate the complex anisotropic and heterogeneous material properties typical of the biological tissues of the eye. We propose a mesh-free approach to incorporate realistic material properties into finite element models of individual human eyes. The method is based on the idea that material parameters can be estimated or measured at so called control points, which are arbitrary and independent of the finite element mesh. The mesh-free approach approximates the heterogeneous material parameters at the Gauss points of each finite element while the boundary value problem is solved using the standard finite element method. The proposed method was applied to an eye-specific model a human posterior pole and optic nerve head. We demonstrate that the method can be used to effectively incorporate experimental measurements of the lamina cribrosa micro-structure into the eye-specific model. It was convenient to define characteristic material orientations at the anterior and posterior scleral surface based on the eye-specific geometry of each sclera. The mesh-free approach was effective in approximating these characteristic material directions with smooth transitions across the sclera. For the first time, the method enabled the incorporation of the complex collagen architecture of the peripapillary sclera into an eye-specific model including the recently discovered meridional fibers at the anterior surface and the depth dependent width of circumferential fibers around the scleral canal. The model results suggest that disregarding the meridional fiber region may lead to an underestimation of local strain concentrations in the retina. The proposed approach should simplify future studies that aim to investigate collagen remodeling in the sclera and optic nerve head or in other biological tissues with similar challenges.
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Affiliation(s)
- Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Kapil Krishnan
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Ryan Whitley
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Vincent Libertiaux
- Equine Clinic, Department of Companion Animals and Equids, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium
- FARAH, Research Center of the Faculty of Veterinary Medicine of Liège, Belgium
| | - Ian A. Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Christopher A. Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - J. Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
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Kling S. Optical coherence elastography by ambient pressure modulation for high-resolution strain mapping applied to patterned cross-linking. J R Soc Interface 2020; 17:20190786. [PMID: 31964268 PMCID: PMC7014812 DOI: 10.1098/rsif.2019.0786] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 12/12/2019] [Indexed: 11/12/2022] Open
Abstract
The purpose of this study was to develop a novel non-contact optical coherence elastography (OCE) approach to measure laterally and axially highly resolved corneal strain distribution at different stages of patterned corneal cross-linking (CXL). Freshly enucleated rat eyes were obtained and prepared for accelerated patterned CXL treatment with distinct ultraviolet (UV) patterns (central, peripheral, bow-tie irradiation). Each cornea was measured repeatedly, in three different conditions: (i) virgin, (ii) after epithelial debridement and 0.5% hypo-osmolar riboflavin instillation for 30 min, and (iii) after patterned CXL at 9 mW cm-2 for 10 min. For biomechanical assessment, the corneal deformation response to an ambient pressure variation of -2 mmHg was recorded by OCE. Strain maps were obtained from phase and magnitude changes in the complex optical coherence tomography signal. Virgin corneas presented negative strain (-2.7 ± 1.1‰) in the anterior cornea and positive strain (1.9 ± 1.3‰) in the posterior cornea. A pronounced shift towards positive strains in the anterior cornea (particularly in UV-irradiated regions) was observed after CXL. Patterned UV irradiation induced localized strain alterations closely matching the geometry of the irradiation pattern. This study demonstrates the possibility of non-contact OCE by ambient pressure modulation, which could substantially improve the early diagnosis of corneal degeneration, advance research in small-animal eyes and refine in vitro mechanical investigation.
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Affiliation(s)
- Sabine Kling
- O.P.T.I.C. Team, Computer-Assisted Applications in Medicine Group, Computer Vision Laboratory, Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
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37
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Liu X, Hubbi B, Zhou X. Spatial coordinate corrected motion tracking for optical coherence elastography. BIOMEDICAL OPTICS EXPRESS 2019; 10:6160-6171. [PMID: 31853392 PMCID: PMC6913417 DOI: 10.1364/boe.10.006160] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Revised: 11/03/2019] [Accepted: 11/04/2019] [Indexed: 05/28/2023]
Abstract
We investigate a spatial coordinate correction (SCC) method to track motion with high accuracy for optical coherence elastography (OCE). Through SCC, we refer the displacement field tracked by optical coherence tomography (OCT) in the loaded sample to individual material points defined in a fixed coordinate system. SCC allows OCE to perform spatially and temporally unambiguous tracking of displacement and enables accurate mechanical characterization of biological tissue for cancer diagnosis and tumor margin assessment. In this study, we validated the effectiveness of motion tracking based on SCC using experimental OCE data obtained from ex vivo human breast tissues.
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Affiliation(s)
- Xuan Liu
- Department of Electrical and Computer Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102, USA
| | - Basil Hubbi
- Department of Radiology, New Jersey Medical School, Newark, NJ 07103, USA
| | - Xianlian Zhou
- Department of Biomedical Engineering, New Jersey Institute of Technology, University Heights, Newark, NJ 07102, USA
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38
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Li Y, Chen J, Chen Z. Advances in Doppler optical coherence tomography and angiography. TRANSLATIONAL BIOPHOTONICS 2019; 1:e201900005. [PMID: 33005888 PMCID: PMC7523705 DOI: 10.1002/tbio.201900005] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 11/14/2019] [Indexed: 12/22/2022] Open
Abstract
Since the first demonstration of Doppler optical coherence tomography (OCT) in 1997, several functional extensions of Doppler OCT have been developed, including velocimetry, angiogram, and optical coherence elastography. These functional techniques have been widely used in research and clinical applications, particularly in ophthalmology. Here, we review the principles, representative methods, and applications of different Doppler OCT techniques, followed by discussion on the innovations, limitations, and future directions of each of these techniques.
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Affiliation(s)
- Yan Li
- Beckman Laser Institute, University of California, Irvine, California
- Department of Biomedical Engineering, University of California, Irvine, California
| | - Jason Chen
- Beckman Laser Institute, University of California, Irvine, California
- Department of Biomedical Engineering, University of California, Irvine, California
| | - Zhongping Chen
- Beckman Laser Institute, University of California, Irvine, California
- Department of Biomedical Engineering, University of California, Irvine, California
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Ramier A, Tavakol B, Yun SH. Measuring mechanical wave speed, dispersion, and viscoelastic modulus of the cornea using optical coherence elastography. OPTICS EXPRESS 2019; 27:16635-16649. [PMID: 31252887 PMCID: PMC6825608 DOI: 10.1364/oe.27.016635] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 04/14/2019] [Accepted: 04/16/2019] [Indexed: 05/22/2023]
Abstract
Acoustic wave velocity measurement based on optical coherence tomography (OCT) is a promising approach to assess the mechanical properties of biological tissues and soft materials. While studies to date have demonstrated proof of concept of different ways to excite and detect mechanical waves, the quantitative performance of this modality as mechanical measurement has been underdeveloped. Here, we investigate the frequency dependent measurement of the wave propagation in viscoelastic tissues, using a piezoelectric point-contact probe driven with various waveforms. We found that a frequency range of 2-10 kHz is a good window for corneal elastography, in which the lowest-order flexural waves can be identified in post processing. We tested our system on tissue-simulating phantoms and ex vivo porcine eyes, and demonstrate reproducibility and inter-sample variability. Using the Kelvin-Voigt model of viscoelasticity, we extracted the shear-elastic modulus and viscosity of the cornea and their correlation with the corneal thickness, curvature, and eyeball mass. Our results show that our method can be a quantitative, useful tool for the mechanical analysis of the cornea.
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Affiliation(s)
- Antoine Ramier
- Wellman Center for photomedicine and Harvard Medical School, Massachusetts General Hospital, 50 Blossom St., BAR-8, Boston, MA 02114,
USA
- Harvard-MIT division of Health Sciences and Technology, Cambridge, MA,
USA
| | - Behrouz Tavakol
- Wellman Center for photomedicine and Harvard Medical School, Massachusetts General Hospital, 50 Blossom St., BAR-8, Boston, MA 02114,
USA
| | - Seok-Hyun Yun
- Wellman Center for photomedicine and Harvard Medical School, Massachusetts General Hospital, 50 Blossom St., BAR-8, Boston, MA 02114,
USA
- Harvard-MIT division of Health Sciences and Technology, Cambridge, MA,
USA
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Dupps WJ, Santhiago MR. Structural relationships in post-refractive surgery ectasia: What have we learned? J Cataract Refract Surg 2019; 45:391-393. [PMID: 30947852 DOI: 10.1016/j.jcrs.2019.03.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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