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Salehi A, Balasubramanian M. Dense optic nerve head deformation estimated using CNN as a structural biomarker of glaucoma progression. Eye (Lond) 2023; 37:3819-3826. [PMID: 37330606 PMCID: PMC10697945 DOI: 10.1038/s41433-023-02623-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 05/03/2023] [Accepted: 06/02/2023] [Indexed: 06/19/2023] Open
Abstract
PURPOSE To present a new structural biomarker for detecting glaucoma progression based on structural transformation of the optic nerve head (ONH) region over time. METHODS Dense ONH deformation was estimated using deep learning methods namely DDCNet-Multires, FlowNet2, and FlowNetCorrelation, and legacy computational methods namely the topographic change analysis (TCA) and proper orthogonal decomposition (POD) methods. A candidate biomarker was estimated as the average magnitude of deformation of the ONH and evaluated using longitudinal confocal scans of 12 laser treated and 12 contralateral normal eyes of 12 primates from the LSU Experimental Glaucoma Study (LEGS); and 36 progressing eyes and 21 longitudinal normal eyes from the UCSD Diagnostic Innovations in Glaucoma Study (DIGS). Area under the ROC curve (AUC) was used to assess the diagnostic accuracy of the biomarker. RESULTS AUROC (95% CI) for LEGS were: 0.83 (0.79, 0.88) for DDCNet-Multires; 0.83 (0.78, 0.88) for FlowNet2; 0.83 (0.78, 0.88) for FlowNet-Correlation; 0.94 (0.91, 0.97) for POD; and 0.86 (0.82, 0.91) for TCA methods. For DIGS: 0.89 (0.80, 0.97) for DDCNet-Multires; 0.82 (0.71, 0.93) for FlowNet2; 0.93 (0.86, 0.99) for FlowNet-Correlation; 0.86 (0.76, 0.96) for POD; and 0.86 (0.77, 0.95) for TCA methods. Lower diagnostic accuracy of the learning-based methods for LEG study eyes were due to image alignment errors in confocal sequences. CONCLUSION Deep learning methods trained to estimate generic deformation were able to estimate ONH deformation from image sequences and provided a higher diagnostic accuracy. Our validation of the biomarker using ONH sequences from controlled experimental conditions confirms the diagnostic accuracy of the biomarkers observed in the clinical population. Performance can be further improved by fine-tuning these networks using ONH sequences.
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Affiliation(s)
- Ali Salehi
- Department of Electrical and Computer Engineering, The University of Memphis, Memphis, TN, 38152, USA
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Jones AD, Crossland SR, Nixon JE, Siddle HJ, Russell DA, Culmer PR. STrain Analysis and Mapping of the Plantar Surface (STAMPS): A novel technique of plantar load analysis during gait. Proc Inst Mech Eng H 2023; 237:841-854. [PMID: 37353979 DOI: 10.1177/09544119231181797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/25/2023]
Abstract
Diabetic foot ulceration is driven by peripheral neuropathy, resulting in abnormal foot biomechanics and elevated plantar load. Plantar load comprises normal pressure and tangential shear stress. Currently, there are no in-shoe devices measuring both components of plantar load. The STAMPS (STrain Analysis and Mapping of the Plantar Surface) system was developed to address this and utilises digital image correlation (DIC) to determine the strain sustained by a plastically deformable insole, providing an assessment of plantar load at the foot-surface interface during gait. STAMPS was developed as a multi-layered insole, comprising a deformable mid-layer, onto which a stochastic speckle pattern film is applied. A custom-built imaging platform is used to obtain high resolution pre- and post-walking images. Images are imported into commercially available DIC software (GOM Correlate, 2020) to obtain pointwise strain data. The strain and displacement data are exported and post-processed with custom analysis routines (MATLAB, Mathworks Inc.), to obtain the resultant global and regional peak strain (SMAG), antero-posterior strain (SAP) and medio-lateral strain (SML). To validate the core technique an experimental test process used a Universal Mechanical Tester (UMT) system (UMT TriboLab, Bruker) to apply controlled vertical and tangential load regimes to the proposed multi-layer insole. A pilot study was then conducted to assess the efficacy of using the STAMPS system to measure in-shoe plantar strain in three healthy participants. Each participant walked 10 steps on the STAMPS insole using a standardised shoe. They also walked 10 m in the same shoe using a plantar pressure measurement insole (Novel Pedar®) to record peak plantar pressure (PPP) as a gold-standard comparator. The results of the experimental validation tests show that with increased normal force, at a constant shear distance, SMAG increased in a linear fashion. Furthermore, they showed that with increased shear distance, at a constant force, SMAG increased. The results of the pilot study found participant 1 demonstrated greatest SMAG in the region toes 3-5 (15.31%). The highest mean SMAG for participant 2 was at the hallux (29.31%). Participant 3 exhibited highest strain in the regions of the first and second metatarsal heads (58.85% and 41.62% respectively). Increased PPP was strongly associated with increased SMAG with a Spearman's correlation coefficient 0.673 (p < 0.0001). This study has demonstrated the efficacy of a novel method to assess plantar load across the plantar surface of the foot. Experimental testing validated the sensitivity of the method to both normal pressure and tangential shear stress. This technique was successfully incorporated into the STAMPS insole to reliably measure and quantify the cumulative degree of strain sustained by a plastically deformable insole during a period of gait, which can be used to infer plantar loading patterns. Future work will explore how these measures relate to different pathologies, such as regions at risk of diabetic foot ulceration.
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Affiliation(s)
- Alexander D Jones
- Leeds Vascular Institute, Leeds Teaching Hospitals NHS Trust, Leeds, UK
- Leeds Institute of Clinical Trials Research, University of Leeds, Leeds, UK
| | - Sarah R Crossland
- Leeds School of Mechanical Engineering, University of Leeds, Leeds, UK
| | - Jane E Nixon
- Leeds Institute of Clinical Trials Research, University of Leeds, Leeds, UK
| | - Heidi J Siddle
- Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds, Leeds, UK
| | - David A Russell
- Leeds Vascular Institute, Leeds Teaching Hospitals NHS Trust, Leeds, UK
- Leeds Institute of Clinical Trials Research, University of Leeds, Leeds, UK
| | - Peter R Culmer
- Leeds School of Mechanical Engineering, University of Leeds, Leeds, UK
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Liou JJ, Drewry MD, Sweeney A, Brown BN, Vande Geest JP. Decellularizing the Porcine Optic Nerve Head: Toward a Model to Study the Mechanobiology of Glaucoma. Transl Vis Sci Technol 2020; 9:17. [PMID: 32855864 PMCID: PMC7422887 DOI: 10.1167/tvst.9.8.17] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Accepted: 04/07/2020] [Indexed: 12/17/2022] Open
Abstract
Purpose Studying the extracellular matrix (ECM) remodeling of the lamina cribrosa in vivo can be extremely challenging and costly. There exist very few options for studying optic nerve head (ONH) mechanobiology in vitro that are able to reproduce the complex anatomic and biomechanical environment of the ONH. Herein, we have developed a decellularization procedure that will enable more anatomically relevant and cost-efficient future studies of ECM remodeling of the ONH. Methods Porcine posterior poles were decellularized using a detergent and enzyme-based decellularization protocol. DNA quantification and histology were used to investigate the effectiveness of the protocol. We subsequently investigated the ability of a polyethylene glycol (PEG)-based hydrogel to restore the ONH's ability to hold pressure following decellularization. Anterior-posterior displacement of the decellularized and PEG treated ONH in a pressure bioreactor was used to evaluate the biomechanical response of the ONH. Results DNA quantification and histology confirmed decellularization using Triton X-100 at low concentration for 48 hours successfully reduced the cellular content of the tissue by 94.9% compared with native tissue while preserving the ECM microstructure and basal lamina of the matrix. Infiltrating the decellularized tissues with PEG 6000 and PEG 10,000 hydrogel restored their ability to hold pressure, producing displacements similar to those measured for the non-decellularized control samples. Conclusions Our decellularized ONH model is capable of producing scaffolds that are cell-free and maintain the native ECM microstructure. Translational Relevance This model represents a platform to study the mechanobiology in the ONH and potentially for glaucoma drug testing.
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Affiliation(s)
- Jr-Jiun Liou
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Michelle D Drewry
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Ashlinn Sweeney
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bryan N Brown
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA.,McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Jonathan P Vande Geest
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA.,McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, USA.,Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.,Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pittsburgh, PA, USA
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Bianco G, Bruno L, Girkin CA, Fazio MA. Full-field displacement measurement of corneoscleral shells by combining multi-camera speckle interferometry with 3D shape reconstruction. J Mech Behav Biomed Mater 2019; 103:103560. [PMID: 32090952 DOI: 10.1016/j.jmbbm.2019.103560] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 11/14/2019] [Accepted: 11/26/2019] [Indexed: 11/25/2022]
Abstract
Changes in the biomechanical properties of the connective tissue of the eye occur with age and underlie the development of several ocular diseases, such as glaucoma, myopia, and keratoconus. The biomechanical dynamics of ocular connective tissue are measured by ex vivo inflation testing, in which intraocular pressure (IOP) is varied and optical methods are used to produce maps of corneal and scleral displacement. Current optical methods are limited by acquisition rate, occlusions, poor spatial resolution, and insufficient 3D mapping. We developed an interferometric optical method integrates four-camera electronic speckle pattern interferometry (ESPI) and a novel three-dimensional (3D) shape reconstruction process to measure shape and full-field mechanical deformations of corneal and scleral shells during ex vivo inflation testing. Each camera provides accurate measurements of the laser beam phase related to deformations of the specimen surface; a multi-view stereovision method generates the shape of the specimen and a functional form that links every pixel of a given camera to 3D points on the specimen's visible surface. In this way, dynamic deformations of the specimen are localized, with quantification of the time-dependent 3D displacements of the specimen at nanometric accuracy. The ESPI-3D system is suitable for analyzing scleral deformation and morphological changes caused by time-varying IOP.
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Affiliation(s)
- Gianfranco Bianco
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA.
| | - Luigi Bruno
- Department of Biomedical Engineering, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA; Department of Mechanical, Energy and Management Engineering, University of Calabria, Via Bucci 44C, 87036, Arcavacata di Rende, CS, Italy.
| | - Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA.
| | - Massimo A Fazio
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA; Department of Biomedical Engineering, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA.
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5
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Du Z, Li R, Qian X, Lu G, Li Y, He Y, Qu Y, Jiang L, Chen Z, Humayun MS, Chen Z, Zhou Q. Quantitative confocal optical coherence elastography for evaluating biomechanics of optic nerve head using Lamb wave model. NEUROPHOTONICS 2019; 6:041112. [PMID: 31763352 PMCID: PMC6857697 DOI: 10.1117/1.nph.6.4.041112] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Accepted: 10/30/2019] [Indexed: 05/26/2023]
Abstract
The mechanosensitivity of the optic nerve head (ONH) plays a pivotal role in the pathogenesis of glaucoma. Characterizing elasticity of the ONH over changing physiological pressure may provide a better understanding of how changes in intraocular pressure (IOP) lead to changes in the mechanical environment of the ONH. Optical coherence elastography (OCE) is an emerging technique that can detect tissue biomechanics noninvasively with both high temporal and spatial resolution compared with conventional ultrasonic elastography. We describe a confocal OCE system in measuring ONH elasticity in vitro, utilizing a pressure inflation setup in which IOP is controlled precisely. We further utilize the Lamb wave model to fit the phase dispersion curve during data postprocessing. We present a reconstruction of Young's modulus of the ONH by combining our OCE system with a Lamb wave model for the first time. This approach enables the quantification of Young's modulus of the ONH, which can be fit using a piecewise polynomial to the corresponding IOP.
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Affiliation(s)
- Zhaodong Du
- The Affiliated Hospital of Qingdao University, Department of Ophthalmology, Qingdao, China
- University of Southern California, Roski Eye Institute, Los Angeles, California, United States
| | - Runze Li
- University of Southern California, Roski Eye Institute, Los Angeles, California, United States
- University of Southern California, Department of Biomedical Engineering, Los Angeles, California, United States
| | - Xuejun Qian
- University of Southern California, Roski Eye Institute, Los Angeles, California, United States
- University of Southern California, Department of Biomedical Engineering, Los Angeles, California, United States
| | - Gengxi Lu
- University of Southern California, Roski Eye Institute, Los Angeles, California, United States
- University of Southern California, Department of Biomedical Engineering, Los Angeles, California, United States
| | - Yan Li
- University of California Irvine, Beckman Laser Institute, Irvine, California, United States
- University of California Irvine, Department of Biomedical Engineering, Irvine, California, United States
| | - Youmin He
- University of California Irvine, Beckman Laser Institute, Irvine, California, United States
- University of California Irvine, Department of Biomedical Engineering, Irvine, California, United States
| | - Yueqiao Qu
- University of California Irvine, Beckman Laser Institute, Irvine, California, United States
- University of California Irvine, Department of Biomedical Engineering, Irvine, California, United States
| | - Laiming Jiang
- University of Southern California, Roski Eye Institute, Los Angeles, California, United States
| | - Zeyu Chen
- University of Southern California, Department of Biomedical Engineering, Los Angeles, California, United States
| | - Mark S. Humayun
- University of Southern California, Roski Eye Institute, Los Angeles, California, United States
| | - Zhongping Chen
- University of California Irvine, Beckman Laser Institute, Irvine, California, United States
- University of California Irvine, Department of Biomedical Engineering, Irvine, California, United States
| | - Qifa Zhou
- University of Southern California, Roski Eye Institute, Los Angeles, California, United States
- University of Southern California, Department of Biomedical Engineering, Los Angeles, California, United States
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Kollech HG, Ayyalasomayajula A, Behkam R, Tamimi E, Furdella K, Drewry M, Vande Geest JP. A Subdomain Method for Mapping the Heterogeneous Mechanical Properties of the Human Posterior Sclera. Front Bioeng Biotechnol 2019; 7:129. [PMID: 31214585 PMCID: PMC6554536 DOI: 10.3389/fbioe.2019.00129] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Accepted: 05/13/2019] [Indexed: 01/26/2023] Open
Abstract
Although strongly correlated with elevated intraocular pressure, primary open-angle glaucoma (POAG) occurs in normotensive eyes. Mechanical properties of the sclera around the optic nerve head (ONH) may play a role in this disparity. The purpose of this study is to present an automated inverse mechanics based approach to determine the distribution of heterogeneous mechanical properties of the human sclera as derived from its surface deformations arising from pressure inflation experiments. The scleral shell of a 78 year old European Descent male donor eye was utilized to demonstrate the method; the sclera was coated with a speckle pattern on the outer surface and was subjected to inflation pressures of 5, 15, 30, and 45 mmHg. The speckle pattern was imaged at each pressure, and a displacement field was calculated for each pressure step using a previously described sequential digital image correlation (S-DIC) technique. The fiber splay and fiber orientation of the sclera collagen were determined experimentally, and the thickness across the scleral globe was determined using micro CT images. The displacement field from the inflation test was used to calculate the strain and also used as an input for inverse mechanics to determine the heterogeneity of material properties. The scleral geometry was divided into subdomains using the first principal strain. The Holzapfel anisotropic material parameters of matrix and fiber stiffness were estimated within each individual subdomain using an inverse mechanics approach by minimizing the sum of the square of the residuals between the computational and experimental displacement fields. The mean and maximum error in displacement across all subdomains were 8.9 ± 3.0 μm and 13.2 μm, respectively. The full pressure-inflation forward mechanics experiment was done using subdomain-specific mechanical properties on the entire scleral surface. The proposed approach is effective in determining the distribution of heterogeneous mechanical properties of the human sclera in a user-independent manner. Our research group is currently utilizing this approach to better elucidate how scleral stiffness influences those at high risk for POAG.
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Affiliation(s)
- Hirut G Kollech
- Computational Modeling and Simulation Program, University of Pittsburgh, Pittsburgh, PA, United States
| | - Avinash Ayyalasomayajula
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ, United States
| | - Reza Behkam
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ehab Tamimi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Kenneth Furdella
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Michelle Drewry
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Jonathan P Vande Geest
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.,McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States.,Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pittsburgh, PA, United States
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7
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Hayes A, Easton K, Devanaboyina PT, Wu JP, Kirk TB, Lloyd D. A review of methods to measure tendon dimensions. J Orthop Surg Res 2019; 14:18. [PMID: 30636623 PMCID: PMC6330756 DOI: 10.1186/s13018-018-1056-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 12/27/2018] [Indexed: 12/16/2022] Open
Abstract
Tendons are soft tissues of the musculoskeletal system that are designed to facilitate joint movement. Tendons exhibit a wide range of mechanical properties matched to their functions and, as a result, have been of interest to researchers for many decades. Dimensions are an important aspect of tendon properties. Change in the dimensions of tissues is often seen as a sign of injury and degeneration, as it may suggest inflammation or general disorder of the tissue. Dimensions are also important for determining the mechanical properties and behaviours of materials, particularly the stress, strain, and elastic modulus. This makes the dimensions significant in the context of a mechanical study of degenerated tendons. Additionally, tendon dimensions are useful in planning harvesting for tendon transfer and joint reconstruction purposes. Historically, many methods have been used in an attempt to accurately measure the dimensions of soft tissue, since improper measurement can lead to large errors in the calculated properties. These methods can be categorised as destructive (by approximation), contact, and non-contact and can be considered in terms of in vivo and ex vivo.
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Affiliation(s)
- Alex Hayes
- Department of Mechanical Engineering, Curtin University of Technology, Perth, Western Australia, Australia. .,Medical Engineering and Physics, Royal Perth Hospital, Perth, Western Australia, Australia.
| | | | - Pavan Teja Devanaboyina
- Centre for Musculoskeletal Research, Menzies Health Institute Queensland, Griffith University, Gold Coast, Queensland, Australia
| | - Jian-Ping Wu
- Academy of Advanced Interdisciplinary Studies and the Department of Biomedical Engineering of Southern University of Science and Technology, No 1088, Xueyaun Rd, Xili, Nanshan District, Shenzhen City, 518055, Guangdong Province, China
| | - Thomas Brett Kirk
- Department of Mechanical Engineering, Curtin University of Technology, Perth, Western Australia, Australia.,Faculty of Science and Engineering, Curtin University of Technology, Perth, Western Australia, Australia
| | - David Lloyd
- Centre for Musculoskeletal Research, Menzies Health Institute Queensland, Griffith University, Gold Coast, Queensland, Australia
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8
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Yang B, Brazile B, Jan NJ, Hua Y, Wei J, Sigal IA. Structured polarized light microscopy for collagen fiber structure and orientation quantification in thick ocular tissues. JOURNAL OF BIOMEDICAL OPTICS 2018; 23:1-10. [PMID: 30277032 PMCID: PMC6210789 DOI: 10.1117/1.jbo.23.10.106001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 09/13/2018] [Indexed: 05/07/2023]
Abstract
Collagen is a major constituent of the eye and understanding its architecture and biomechanics is critical to preserve and restore vision. We, recently, demonstrated polarized light microscopy (PLM) as a powerful technique for measuring properties of the collagen fibers of the eye, such as spatial distribution and orientation. Our implementation of PLM, however, required sectioning the tissues for imaging using transmitted light. This is problematic because it limits analysis to thin sections. This is not only slow, but precludes study of dynamic events such as pressure-induced deformations, which are central to the role of collagen. We introduce structured polarized light microscopy (SPLM), an imaging technique that combines structured light illumination with PLM to allow imaging and measurement of collagen fiber properties in thick ocular tissues. Using pig and sheep eyes, we show that SPLM rejects diffuse background light effectively in thick tissues, significantly enhancing visualization of optic nerve head (ONH) structures, such as the lamina cribrosa, and improving the accuracy of the collagen fiber orientation measurements. Further, we demonstrate the integration of SPLM with an inflation device to enable direct visualization, deformation tracking, and quantification of collagen fibers in ONHs while under controlled pressure.
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Affiliation(s)
- Bin Yang
- University of Pittsburgh School of Medicine, Department of Ophthalmology, Pittsburgh, Pennsylvania, United States
| | - Bryn Brazile
- University of Pittsburgh School of Medicine, Department of Ophthalmology, Pittsburgh, Pennsylvania, United States
| | - Ning-Jiun Jan
- University of Pittsburgh School of Medicine, Department of Ophthalmology, Pittsburgh, Pennsylvania, United States
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, Pennsylvania, United States
| | - Yi Hua
- University of Pittsburgh School of Medicine, Department of Ophthalmology, Pittsburgh, Pennsylvania, United States
| | - Junchao Wei
- University of Pittsburgh School of Medicine, Department of Ophthalmology, Pittsburgh, Pennsylvania, United States
| | - Ian A. Sigal
- University of Pittsburgh School of Medicine, Department of Ophthalmology, Pittsburgh, Pennsylvania, United States
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, Pennsylvania, United States
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9
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Tamimi EA, Pyne JD, Muli DK, Axman KF, Howerton SJ, Davis MR, Girkin CA, Vande Geest JP. Racioethnic Differences in Human Posterior Scleral and Optic Nerve Stump Deformation. Invest Ophthalmol Vis Sci 2017; 58:4235-4246. [PMID: 28846773 PMCID: PMC5574446 DOI: 10.1167/iovs.17-22141] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Purpose The purpose of this study was to quantify the biomechanical response of human posterior ocular tissues from donors of various racioethnic groups to better understand how differences in these properties may play a role in the racioethnic health disparities known to exist in glaucoma. Methods Sequential digital image correlation (S-DIC) was used to measure the pressure-induced surface deformations of 23 normal human posterior poles from three racioethnic groups: African descent (AD), European descent (ED), and Hispanic ethnicity (HIS). Regional in-plane principal strains were compared across three zones: the optic nerve stump (ONS), the peripapillary (PP) sclera, and non-PP sclera. Results The PP scleral tensile strains were found to be lower for ED eyes compared with AD and HIS eyes at 15 mm Hg (P = 0.024 and 0.039, respectively). The mean compressive strains were significantly higher for AD eyes compared with ED eyes at 15 mm Hg (P = 0.018). We also found that the relationship between tensile strain and pressure was significant for those of ED and HIS eyes (P < 0.001 and P = 0.004, respectively), whereas it was not significant for those of AD (P = 0.392). Conclusions Our results suggest that, assuming glaucomatous nerve loss is caused by mechanical strains in the vicinity of the optic nerve head, the mechanism of increased glaucoma prevalence may be different in those of AD versus HIS. Our ONS strain analysis also suggested that it may be important to account for ONS geometry and material properties in future scleral biomechanical analysis.
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Affiliation(s)
- Ehab A Tamimi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Jeffrey D Pyne
- Department of Mechanical Engineering, University of California Berkeley, Berkeley, California, United States
| | - Dominic K Muli
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Katelyn F Axman
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Stephen J Howerton
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, Arizona, United States
| | - Matthew R Davis
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, Arizona, United States
| | - Christopher A Girkin
- Department of Ophthalmology, University of Alabama Birmingham, Birmingham, Alabama, United States
| | - Jonathan P Vande Geest
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pennsylvania, United States
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10
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Coudrillier B, Campbell IC, Read AT, Geraldes DM, Vo NT, Feola A, Mulvihill J, Albon J, Abel RL, Ethier CR. Effects of Peripapillary Scleral Stiffening on the Deformation of the Lamina Cribrosa. Invest Ophthalmol Vis Sci 2017; 57:2666-77. [PMID: 27183053 PMCID: PMC4874475 DOI: 10.1167/iovs.15-18193] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Purpose Scleral stiffening has been proposed as a treatment for glaucoma to protect the lamina cribrosa (LC) from excessive intraocular pressure–induced deformation. Here we experimentally evaluated the effects of moderate stiffening of the peripapillary sclera on the deformation of the LC. Methods An annular sponge, saturated with 1.25% glutaraldehyde, was applied to the external surface of the peripapillary sclera for 5 minutes to stiffen the sclera. Tissue deformation was quantified in two groups of porcine eyes, using digital image correlation (DIC) or computed tomography imaging and digital volume correlation (DVC). In group A (n = 14), eyes were subjected to inflation testing before and after scleral stiffening. Digital image correlation was used to measure scleral deformation and quantify the magnitude of scleral stiffening. In group B (n = 5), the optic nerve head region was imaged using synchrotron radiation phase-contrast microcomputed tomography (PC μCT) at an isotropic spatial resolution of 3.2 μm. Digital volume correlation was used to compute the full-field three-dimensional deformation within the LC and evaluate the effects of peripapillary scleral cross-linking on LC biomechanics. Results On average, scleral treatment with glutaraldehyde caused a 34 ± 14% stiffening of the peripapillary sclera measured at 17 mm Hg and a 47 ± 12% decrease in the maximum tensile strain in the LC measured at 15 mm Hg. The reduction in LC strains was not due to cross-linking of the LC. Conclusions Peripapillary scleral stiffening is effective at reducing the magnitude of biomechanical strains within the LC. Its potential and future utilization in glaucoma axonal neuroprotection requires further investigation.
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Affiliation(s)
- Baptiste Coudrillier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States
| | - Ian C Campbell
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States 2Atlanta VA Medical Center, Decatur, Georgia, United States
| | - A Thomas Read
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States
| | - Diogo M Geraldes
- Biomechanics Group, Department of Mechanical Engineering, Imperial College London, London, United Kingdom
| | - Nghia T Vo
- Diamond Light Source, Didcot, United Kingdom
| | - Andrew Feola
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States
| | - John Mulvihill
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States
| | - Julie Albon
- Optic Nerve Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom 6Cardiff Institute of Tissue Engineering and Repair, Cardiff University, Cardiff, Wales, United Kingdom
| | - Richard L Abel
- Department of Surgery and Cancer, Imperial College, London, United Kingdom
| | - C Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, United States 2Atlanta VA Medical Center, Decatur, Georgia, United States
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Palanca M, Tozzi G, Cristofolini L. The use of digital image correlation in the biomechanical area: a review. Int Biomech 2015. [DOI: 10.1080/23335432.2015.1117395] [Citation(s) in RCA: 92] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Affiliation(s)
- Marco Palanca
- School of Engineering and Architecture, University of Bologna, Bologna, Italy
| | - Gianluca Tozzi
- School of Engineering, University of Portsmouth, Portsmouth, UK
| | - Luca Cristofolini
- School of Engineering and Architecture, Department of Industrial Engineering, University of Bologna, Bologna, Italy
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Nguyen TD, Ethier CR. Biomechanical assessment in models of glaucomatous optic neuropathy. Exp Eye Res 2015; 141:125-38. [PMID: 26115620 PMCID: PMC4628840 DOI: 10.1016/j.exer.2015.05.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Revised: 05/20/2015] [Accepted: 05/31/2015] [Indexed: 01/26/2023]
Abstract
The biomechanical environment within the eye is of interest in both the regulation of intraocular pressure and the loss of retinal ganglion cell axons in glaucomatous optic neuropathy. Unfortunately, this environment is complex and difficult to determine. Here we provide a brief introduction to basic concepts of mechanics (stress, strain, constitutive relationships) as applied to the eye, and then describe a variety of experimental and computational approaches used to study ocular biomechanics. These include finite element modeling, direct experimental measurements of tissue displacements using optical and other techniques, direct experimental measurement of tissue microstructure, and combinations thereof. Thanks to notable technical and conceptual advances in all of these areas, we are slowly gaining a better understanding of how tissue biomechanical properties in both the anterior and posterior segments may influence the development of, and risk for, glaucomatous optic neuropathy. Although many challenging research questions remain unanswered, the potential of this body of work is exciting; projects underway include the coupling of clinical imaging with biomechanical modeling to create new diagnostic tools, development of IOP control strategies based on improved understanding the mechanobiology of the outflow tract, and attempts to develop novel biomechanically-based therapeutic strategies for preservation of vision in glaucoma.
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Affiliation(s)
- Thao D Nguyen
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA
| | - C Ross Ethier
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, USA; Department of Mechanical Engineering, Georgia Institute of Technology, USA; Institute of Biosciences and Bioengineering, Georgia Institute of Technology, USA; Department of Ophthalmology, Emory University, USA.
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Glaucoma-related Changes in the Mechanical Properties and Collagen Micro-architecture of the Human Sclera. PLoS One 2015; 10:e0131396. [PMID: 26161963 PMCID: PMC4498780 DOI: 10.1371/journal.pone.0131396] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Accepted: 06/01/2015] [Indexed: 12/13/2022] Open
Abstract
Objective The biomechanical behavior of the sclera determines the level of mechanical insult from intraocular pressure to the axons and tissues of the optic nerve head, as is of interest in glaucoma. In this study, we measure the collagen fiber structure and the strain response, and estimate the material properties of glaucomatous and normal human donor scleras. Methods Twenty-two posterior scleras from normal and diagnosed glaucoma donors were obtained from an eyebank. Optic nerve cross-sections were graded to determine the presence of axon loss. The specimens were subjected to pressure-controlled inflation testing. Full-field displacement maps were measured by digital image correlation (DIC) and spatially differentiated to compute surface strains. Maps of the collagen fiber structure across the posterior sclera of each inflated specimen were obtained using synchrotron wide-angle X-ray scattering (WAXS). Finite element (FE) models of the posterior scleras, incorporating a specimen-specific representation of the collagen structure, were constructed from the DIC-measured geometry. An inverse finite element analysis was developed to estimate the stiffness of the collagen fiber and inter-fiber matrix. Results The differences between glaucoma and non-glaucoma eyes were small in magnitude. Sectorial variations of degree of fiber alignment and peripapillary scleral strain significantly differed between normal and diagnosed glaucoma specimens. Meridional strains were on average larger in diagnosed glaucoma eyes compared with normal specimens. Non-glaucoma specimens had on average the lowest matrix and fiber stiffness, followed by undamaged glaucoma eyes, and damaged glaucoma eyes but the differences in stiffness were not significant. Conclusion The observed biomechanical and microstructural changes could be the result of tissue remodeling occuring in glaucoma and are likely to alter the mechanical environment of the optic nerve head and contribute to axonal damage.
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Murienne BJ, Jefferys JL, Quigley HA, Nguyen TD. The effects of glycosaminoglycan degradation on the mechanical behavior of the posterior porcine sclera. Acta Biomater 2015; 12:195-206. [PMID: 25448352 DOI: 10.1016/j.actbio.2014.10.033] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 08/28/2014] [Accepted: 10/23/2014] [Indexed: 10/24/2022]
Abstract
Pathological changes in scleral glycosaminoglycan (GAG) content and in scleral mechanical properties have been observed in eyes with glaucoma and myopia. The purpose of this study is to investigate the effect of GAG removal on the scleral mechanical properties to better understand the impact of GAG content variations in the pathophysiology of glaucoma and myopia. We measured how the removal of sulphated GAG (s-GAG) affected the hydration, thickness and mechanical properties of the posterior sclera in enucleated eyes of 6-9 month-old pigs. Measurements were made in 4 regions centered on the optic nerve head (ONH) and evaluated under 3 conditions: no treatment (control), after treatment in buffer solution alone, and after treatment in buffer containing chondroitinase ABC (ChABC) to remove s-GAGs. The specimens were mechanically tested by pressure-controlled inflation with full-field deformation mapping using digital image correlation (DIC). The mechanical outcomes described the tissue tensile and viscoelastic behavior. Treatment with buffer alone increased the hydration of the posterior sclera compared to controls, while s-GAG removal caused a further increase in hydration compared to buffer-treated scleras. Buffer-treatment significantly changed the scleral mechanical behavior compared to the control condition, in a manner consistent with an increase in hydration. Specifically, buffer-treatment led to an increase in low-pressure stiffness, hysteresis, and creep rate, and a decrease in high-pressure stiffness. ChABC-treatment on buffer-treated scleras had opposite mechanical effects than buffer-treatment on controls, leading to a decrease in low-pressure stiffness, hysteresis, and creep rate, and an increase in high-pressure stiffness and transition strain. Furthermore, s-GAG digestion dramatically reduced the differences in the mechanical behavior among the 4 quadrants surrounding the ONH as well as the differences between the circumferential and meridional responses compared to the buffer-treated condition. These findings demonstrate a significant effect of s-GAGs on both the stiffness and time-dependent behavior of the sclera. Alterations in s-GAG content may contribute to the altered creep and stiffness of the sclera of myopic and glaucoma eyes.
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Affiliation(s)
- Barbara J Murienne
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA.
| | - Joan L Jefferys
- Glaucoma Center of Excellence, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Harry A Quigley
- Glaucoma Center of Excellence, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Thao D Nguyen
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA
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