1
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Pitha I, Du L, Nguyen TD, Quigley H. IOP and glaucoma damage: The essential role of optic nerve head and retinal mechanosensors. Prog Retin Eye Res 2024; 99:101232. [PMID: 38110030 PMCID: PMC10960268 DOI: 10.1016/j.preteyeres.2023.101232] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Revised: 12/10/2023] [Accepted: 12/11/2023] [Indexed: 12/20/2023]
Abstract
There are many unanswered questions on the relation of intraocular pressure to glaucoma development and progression. IOP itself cannot be distilled to a single, unifying value, because IOP level varies over time, differs depending on ocular location, and can be affected by method of measurement. Ultimately, IOP level creates mechanical strain that affects axonal function at the optic nerve head which causes local extracellular matrix remodeling and retinal ganglion cell death - hallmarks of glaucoma and the cause of glaucomatous vision loss. Extracellular tissue strain at the ONH and lamina cribrosa is regionally variable and differs in magnitude and location between healthy and glaucomatous eyes. The ultimate targets of IOP-induced tissue strain in glaucoma are retinal ganglion cell axons at the optic nerve head and the cells that support axonal function (astrocytes, the neurovascular unit, microglia, and fibroblasts). These cells sense tissue strain through a series of signals that originate at the cell membrane and alter cytoskeletal organization, migration, differentiation, gene transcription, and proliferation. The proteins that translate mechanical stimuli into molecular signals act as band-pass filters - sensing some stimuli while ignoring others - and cellular responses to stimuli can differ based on cell type and differentiation state. Therefore, to fully understand the IOP signals that are relevant to glaucoma, it is necessary to understand the ultimate cellular targets of IOP-induced mechanical stimuli and their ability to sense, ignore, and translate these signals into cellular actions.
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Affiliation(s)
- Ian Pitha
- Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Center for Nanomedicine, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Glaucoma Center of Excellence, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Liya Du
- Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Thao D Nguyen
- Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, MD, USA
| | - Harry Quigley
- Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Glaucoma Center of Excellence, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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2
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Lee PY, Fryc G, Gnalian J, Wang B, Hua Y, Waxman S, Zhong F, Yang B, Sigal IA. Direct measurements of collagen fiber recruitment in the posterior pole of the eye. Acta Biomater 2024; 173:135-147. [PMID: 37967694 PMCID: PMC10843755 DOI: 10.1016/j.actbio.2023.11.013] [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: 04/15/2023] [Revised: 11/07/2023] [Accepted: 11/09/2023] [Indexed: 11/17/2023]
Abstract
Collagen is the main load-bearing component of the peripapillary sclera (PPS) and lamina cribrosa (LC) in the eye. Whilst it has been shown that uncrimping and recruitment of the PPS and LC collagen fibers underlies the macro-scale nonlinear stiffening of both tissues with increased intraocular pressure (IOP), the uncrimping and recruitment as a function of local stretch have not been directly measured. This knowledge is crucial to understanding their functions in bearing loads and maintaining tissue integrity. In this project we measured local stretch-induced collagen fiber bundle uncrimping and recruitment curves of the PPS and LC. Thin coronal samples of PPS and LC of sheep eyes were mounted and stretched biaxially quasi-statically using a custom system. At each step, we imaged the PPS and LC with instant polarized light microscopy and quantified pixel-level (1.5 μm/pixel) collagen fiber orientations. We used digital image correlation to measure the local stretch and quantified collagen crimp by the circular standard deviation of fiber orientations, or waviness. Local stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers than the LC at the low levels of stretch. At 10% stretch the curves crossed with 75% bundles recruited. The PPS had higher uncrimping rate and waviness remaining after recruitment than the LC: 0.9º vs. 0.6º and 3.1º vs. 2.7º. Altogether our findings support describing fiber recruitment of both PPS and LC with sigmoid curves, with the PPS recruiting faster and at lower stretch than the LC, consistent with a stiffer tissue. STATEMENT OF SIGNIFICANCE: Peripapillary sclera (PPS) and lamina cribrosa (LC) collagen recruitment behaviors are central to the nonlinear mechanical behavior of the posterior pole of the eye. How PPS and LC collagen fibers recruit under stretch is crucial to develop constitutive models of the tissues but remains unclear. We used image-based stretch testing to characterize PPS and LC collagen fiber bundle recruitment under local stretch. We found that fiber-level stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers at a low stretch, but at 10% bundle stretch the two curves crossed with 75% bundles recruited. We also found that PPS and LC fibers had different uncrimping rates and non-zero waviness's when recruited.
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Affiliation(s)
- Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Gosia Fryc
- Department of Chemistry, Dietrich School of Arts and Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - John Gnalian
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Biomedical Engineering, University of Mississippi, University, MS, USA; Department of Mechanical Engineering, University of Mississippi, University, MS, USA
| | - Susannah Waxman
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Fuqiang Zhong
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA, USA
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA.
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3
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Lee PY, Schilpp H, Naylor N, Watkins SC, Yang B, Sigal IA. Instant polarized light microscopy pi (IPOLπ) for quantitative imaging of collagen architecture and dynamics in ocular tissues. OPTICS AND LASERS IN ENGINEERING 2023; 166:107594. [PMID: 37193214 PMCID: PMC10168649 DOI: 10.1016/j.optlaseng.2023.107594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Collagen architecture determines the biomechanical environment in the eye, and thus characterizing collagen fiber organization and biomechanics is essential to fully understand eye physiology and pathology. We recently introduced instant polarized light microscopy (IPOL) that encodes optically information about fiber orientation and retardance through a color snapshot. Although IPOL allows imaging collagen at the full acquisition speed of the camera, with excellent spatial and angular resolutions, a limitation is that the orientation-encoding color is cyclic every 90 degrees (π/2 radians). In consequence, two orthogonal fibers have the same color and therefore the same orientation when quantified by color-angle mapping. In this study, we demonstrate IPOLπ, a new variation of IPOL, in which the orientation-encoding color is cyclic every 180 degrees (π radians). Herein we present the fundamentals of IPOLπ, including a framework based on a Mueller-matrix formalism to characterize how fiber orientation and retardance determine the color. The improved quantitative capability of IPOLπ enables further study of essential biomechanical properties of collagen in ocular tissues, such as fiber anisotropy and crimp. We present a series of experimental calibrations and quantitative procedures to visualize and quantify ocular collagen orientation and microstructure in the optic nerve head, a region in the back of the eye. There are four important strengths of IPOLπ compared to IPOL. First, IPOLπ can distinguish the orientations of orthogonal collagen fibers via colors, whereas IPOL cannot. Second, IPOLπ requires a lower exposure time than IPOL, thus allowing faster imaging speed. Third, IPOLπ allows visualizing non-birefringent tissues and backgrounds from tissue absorption, whereas both appear dark in IPOL images. Fourth, IPOLπ is cheaper and less sensitive to imperfectly collimated light than IPOL. Altogether, the high spatial, angular, and temporal resolutions of IPOLπ enable a deeper insight into ocular biomechanics and eye physiology and pathology.
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Affiliation(s)
- Po-Yi Lee
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Hannah Schilpp
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Nathan Naylor
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Simon C. Watkins
- Department of Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
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4
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Lee PY, Fryc G, Gnalian J, Hua Y, Waxman S, Zhong F, Yang B, Sigal IA. Direct measurements of collagen fiber recruitment in the posterior pole of the eye. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.07.539784. [PMID: 37215028 PMCID: PMC10197604 DOI: 10.1101/2023.05.07.539784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Collagen is the main load-bearing component of the peripapillary sclera (PPS) and lamina cribrosa (LC) in the eye. Whilst it has been shown that uncrimping and recruitment of the PPS and LC collagen fibers underlies the macro-scale nonlinear stiffening of both tissues with increased intraocular pressure (IOP), the uncrimping and recruitment as a function of local stretch have not been directly measured. This knowledge is crucial for the development of constitutive models associating micro and macro scales. In this project we measured local stretch-induced collagen fiber bundle uncrimping and recruitment curves of the PPS and LC. Thin coronal samples of PPS and LC of sheep eyes were mounted and stretched biaxially quasi-statically using a custom system. At each step, we imaged the PPS and LC with instant polarized light microscopy and quantified pixel-level (1.5 μm/pixel) collagen fiber orientations. We used digital image correlation to measure the local stretch and quantified collagen crimp by the circular standard deviation of fiber orientations, or waviness. Local stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers than the LC at the low levels of stretch. At 10% stretch the curves crossed with 75% bundles recruited. The PPS had higher uncrimping rate and waviness remaining after recruitment than the LC: 0.9° vs. 0.6° and 3.1° vs. 2.7°. Altogether our findings support describing fiber recruitment of both PPS and LC with sigmoid curves, with the PPS recruiting faster and at lower stretch than the LC, consistent with a stiffer tissue.
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Affiliation(s)
- Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Bioengineering, Swanson School of Engineering
| | - Gosia Fryc
- Department of Chemistry, Dietrich School of Arts and Sciences University of Pittsburgh, Pittsburgh, PA
| | - John Gnalian
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Biomedical Engineering, University of Mississippi, University, MS
- Department of Mechanical Engineering, University of Mississippi, University, MS
| | - Susannah Waxman
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Fuqiang Zhong
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Bioengineering, Swanson School of Engineering
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5
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Foong TY, Hua Y, Amini R, Sigal IA. Who bears the load? IOP-induced collagen fiber recruitment over the corneoscleral shell. Exp Eye Res 2023; 230:109446. [PMID: 36935071 PMCID: PMC10133210 DOI: 10.1016/j.exer.2023.109446] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2022] [Revised: 02/25/2023] [Accepted: 03/16/2023] [Indexed: 03/19/2023]
Abstract
Collagen is the main load-bearing component of cornea and sclera. When stretched, both of these tissues exhibit a behavior known as collagen fiber recruitment. In recruitment, as the tissues stretch the constitutive collagen fibers lose their natural waviness, progressively straightening. Recruited, straight, fibers bear substantially more mechanical load than non-recruited, wavy, fibers. As such, the process of recruitment underlies the well-established nonlinear macroscopic behavior of the corneoscleral shell. Recruitment has an interesting implication: when recruitment is incomplete, only a fraction of the collagen fibers is actually contributing to bear the loads, with the rest remaining "in reserve". In other words, at a given intraocular pressure (IOP), it is possible that not all the collagen fibers of the cornea and sclera are actually contributing to bear the loads. To the best of our knowledge, the fraction of corneoscleral shell fibers recruited and contributing to bear the load of IOP has not been reported. Our goal was to obtain regionally-resolved estimates of the fraction of corneoscleral collagen fibers recruited and in reserve. We developed a fiber-based microstructural constitutive model that could account for collagen fiber undulations or crimp via their tortuosity. We used experimentally-measured collagen fiber crimp tortuosity distributions in human eyes to derive region-specific nonlinear hyperelastic mechanical properties. We then built a three-dimensional axisymmetric model of the globe, assigning region-specific mechanical properties and regional anisotropy. The model was used to simulate the IOP-induced shell deformation. The model-predicted tissue stretch was then used to quantify collagen recruitment within each shell region. The calculations showed that, at low IOPs, collagen fibers in the posterior equator were recruited the fastest, such that at a physiologic IOP of 15 mmHg, over 90% of fibers were recruited, compared with only a third in the cornea and the peripapillary sclera. The differences in recruitment between regions, in turn, mean that at a physiologic IOP the posterior equator had a fiber reserve of only 10%, whereas the cornea and peripapillary sclera had two thirds. At an elevated IOP of 50 mmHg, collagen fibers in the limbus and the anterior/posterior equator were almost fully recruited, compared with 90% in the cornea and the posterior sclera, and 70% in the peripapillary sclera and the equator. That even at such an elevated IOP not all the fibers were recruited suggests that there are likely other conditions that challenge the corneoscleral tissues even more than IOP. The fraction of fibers recruited may have other potential implications. For example, fibers that are not bearing loads may be more susceptible to enzymatic digestion or remodeling. Similarly, it may be possible to control tissue stiffness through the fraction of recruited fibers without the need to add or remove collagen.
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Affiliation(s)
- Tian Yong Foong
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Biomedical Engineering, University of Mississippi, MS, United States; Department of Mechanical Engineering, University of Mississippi, MS, United States
| | - Rouzbeh Amini
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, United States; Department of Bioengineering, Northeastern University, Boston, MA, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, University of Pittsburgh Medical Center and University of Pittsburgh, Pittsburgh, PA, United States.
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6
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Lee PY, Schilpp H, Naylor N, Watkins SC, Yang B, Sigal IA. Instant polarized light microscopy pi (IPOLπ) for quantitative imaging of collagen architecture and dynamics in ocular tissues. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.29.526111. [PMID: 36778384 PMCID: PMC9915523 DOI: 10.1101/2023.01.29.526111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Collagen architecture determines the biomechanical environment in the eye, and thus characterizing collagen fiber organization and biomechanics is essential to fully understand eye physiology and pathology. We recently introduced instant polarized light microscopy (IPOL) that encodes optically information about fiber orientation and retardance through a color snapshot. Although IPOL allows imaging collagen at the full acquisition speed of the camera, with excellent spatial and angular resolutions, a limitation is that the orientation-encoding color is cyclic every 90 degrees (π/2 radians). In consequence, two orthogonal fibers have the same color and therefore the same orientation when quantified by color-angle mapping. In this study, we demonstrate IPOLπ, a new variation of IPOL, in which the orientation-encoding color is cyclic every 180 degrees (π radians). Herein we present the fundamentals of IPOLπ, including a framework based on a Mueller-matrix formalism to characterize how fiber orientation and retardance determine the color. The improved quantitative capability of IPOLπ enables further study of essential biomechanical properties of collagen in ocular tissues, such as fiber anisotropy and crimp. We present a series of experimental calibrations and quantitative procedures to visualize and quantify ocular collagen orientation and microstructure in the optic nerve head, a region in the back of the eye. There are four important strengths of IPOLπ compared to IPOL. First, IPOLπ can distinguish the orientations of orthogonal collagen fibers via colors, whereas IPOL cannot. Second, IPOLπ requires a lower exposure time than IPOL, thus allowing faster imaging speed. Third, IPOLπ allows visualizing non-birefringent tissues and backgrounds from tissue absorption, whereas both appear dark in IPOL images. Fourth, IPOLπ is cheaper and less sensitive to imperfectly collimated light than IPOL. Altogether, the high spatial, angular, and temporal resolutions of IPOLπ enable a deeper insight into ocular biomechanics and eye physiology and pathology.
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Affiliation(s)
- Po-Yi Lee
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Hannah Schilpp
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Nathan Naylor
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Simon C Watkins
- Department of Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA
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7
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Aging Effects on Optic Nerve Neurodegeneration. Int J Mol Sci 2023; 24:ijms24032573. [PMID: 36768896 PMCID: PMC9917079 DOI: 10.3390/ijms24032573] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 01/19/2023] [Accepted: 01/23/2023] [Indexed: 02/03/2023] Open
Abstract
Common risk factors for many ocular pathologies involve non-pathologic, age-related damage to the optic nerve. Understanding the mechanisms of age-related changes can facilitate targeted treatments for ocular pathologies that arise at any point in life. In this review, we examine these age-related, neurodegenerative changes in the optic nerve, contextualize these changes from the anatomic to the molecular level, and appreciate their relationship with ocular pathophysiology. From simple structural and mechanical changes at the optic nerve head (ONH), to epigenetic and biochemical alterations of tissue and the environment, multiple age-dependent mechanisms drive extracellular matrix (ECM) remodeling, retinal ganglion cell (RGC) loss, and lowered regenerative ability of respective axons. In conjunction, aging decreases the ability of myelin to preserve maximal conductivity, even with "successfully" regenerated axons. Glial cells, however, regeneratively overcompensate and result in a microenvironment that promotes RGC axonal death. Better elucidating optic nerve neurodegeneration remains of interest, specifically investigating human ECM, RGCs, axons, oligodendrocytes, and astrocytes; clarifying the exact processes of aged ocular connective tissue alterations and their ultrastructural impacts; and developing novel technologies and pharmacotherapies that target known genetic, biochemical, matrisome, and neuroinflammatory markers. Management models should account for age-related changes when addressing glaucoma, diabetic retinopathy, and other blinding diseases.
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8
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Wei J, Hua Y, Yang B, Wang B, Schmitt SE, Wang B, Lucy KA, Ishikawa H, Schuman JS, Smith MA, Wollstein G, Sigal IA. Comparing Acute IOP-Induced Lamina Cribrosa Deformations Premortem and Postmortem. Transl Vis Sci Technol 2022; 11:1. [DOI: 10.1167/tvst.11.12.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022] Open
Affiliation(s)
- Junchao Wei
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bin Yang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Engineering, Duquesne University, Pittsburgh, PA, USA
| | - Bo Wang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
- Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Samantha E. Schmitt
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Katie A. Lucy
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
| | - Hiroshi Ishikawa
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
- Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University, Portland, OR, USA
| | - Joel S. Schuman
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
- Department of Biomedical Engineering and Electrical and Computer Engineering, New York University Tandon School of Engineering, Brooklyn, NY, USA
- Neuroscience Institute, NYU Langone Health, New York, NY, USA
| | - Matthew A. Smith
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Gadi Wollstein
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
| | - Ian A. Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
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9
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Hua Y, Lu Y, Walker J, Lee PY, Tian Q, McDonald H, Pallares P, Ji F, Brazile BL, Yang B, Voorhees AP, Sigal IA. Eye-specific 3D modeling of factors influencing oxygen concentration in the lamina cribrosa. Exp Eye Res 2022; 220:109105. [PMID: 35568202 PMCID: PMC11007759 DOI: 10.1016/j.exer.2022.109105] [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: 12/21/2021] [Revised: 04/06/2022] [Accepted: 04/28/2022] [Indexed: 11/29/2022]
Abstract
Our goal was to identify the factors with the strongest influence on the minimum lamina cribrosa (LC) oxygen concentration as potentially indicative of conditions increasing hypoxia risk. Because direct measurement of LC hemodynamics and oxygenation is not yet possible, we developed 3D eye-specific LC vasculature models. The vasculature of a normal monkey eye was perfusion-labeled post-mortem. Serial cryosections through the optic nerve head were imaged using fluorescence and polarized light microscopy to visualize the vasculature and collagen, respectively. The vasculature within a 450 μm-thick region containing the LC - identified from the collagen, was segmented, skeletonized, and meshed for simulations. Using Monte Carlo sampling, 200 vascular network models were generated with varying vessel diameter, neural tissue oxygen consumption rate, inflow hematocrit, and blood pressures (arteriole, venule, anterior boundary, and posterior boundary). Factors were varied over ranges of baseline ±20% with uniform probability. For each model we first obtained the blood flow, and from this the neural tissue oxygen concentration. ANOVA was used to identify the factors with the strongest influence on the minimum (10th percentile) oxygen concentration in the LC. The three most influential factors were, in ranked order, vessel diameter, neural tissue oxygen consumption rate, and arteriole pressure. There was a strong interaction between vessel diameter and arteriole pressure whereby the impact of one factor was larger when the other factor was small. Our results show that, for the eye analyzed, conditions that reduce vessel diameter, such as vessel compression due to elevated intraocular pressure or gaze-induced tissue deformation, may particularly contribute to decreased LC oxygen concentration. More eyes must be analyzed before generalizing.
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Affiliation(s)
- Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States
| | - Yuankai Lu
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States
| | - Jason Walker
- Department of Biological Science, University of Pittsburgh, Pittsburgh, PA, United States
| | - Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Qi Tian
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Haiden McDonald
- Department of Biological Science, University of Pittsburgh, Pittsburgh, PA, United States
| | - Pedro Pallares
- Department of Biological Science, University of Pittsburgh, Pittsburgh, PA, United States
| | - Fengting Ji
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Bryn L Brazile
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States
| | - Bin Yang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA, United States
| | - Andrew P Voorhees
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.
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10
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Lee PY, Yang B, Hua Y, Waxman S, Zhu Z, Ji F, Sigal IA. Real-time imaging of optic nerve head collagen microstructure and biomechanics using instant polarized light microscopy. Exp Eye Res 2022; 217:108967. [PMID: 35114213 PMCID: PMC8957577 DOI: 10.1016/j.exer.2022.108967] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Revised: 11/04/2021] [Accepted: 01/25/2022] [Indexed: 01/09/2023]
Abstract
Current tools lack the temporal or spatial resolution necessary to image many important aspects of the architecture and dynamics of the optic nerve head (ONH). We evaluated the potential of instant polarized light microscopy (IPOL) to overcome these limitations by leveraging the ability to capture collagen fiber orientation and density in a single image. Coronal sections through the ONH of fresh normal sheep eyes were imaged using IPOL while they were stretched using custom uniaxial or biaxial micro-stretch devices. IPOL allows identifying ONH collagen architectural details, such as fiber interweaving and crimp, and has high temporal resolution, limited only by the frame rate of the camera. Local collagen fiber orientations and deformations were quantified using color analysis and image tracking techniques. We quantified stretch-induced collagen uncrimping of lamina cribrosa (LC) and peripapillary sclera (PPS), and changes in LC pore size (area) and shape (convexity and aspect ratio). The simultaneous high spatial and temporal resolutions of IPOL revealed complex ONH biomechanics: i) stretch-induced local deformation of the PPS was nonlinear and nonaffine. ii) under load the crimped collagen fibers in the PPS and LC straightened, without torsion and with only small rotations. iii) stretch-induced LC pore deformation was anisotropic and heterogeneous among pores. Overall, with stretch the pores were became larger, more convex, and more circular. We have demonstrated that IPOL reveals details of collagen morphology and mechanics under dynamic loading previously out of reach. IPOL can detect stretch-induced collagen uncrimping and other elements of the tissue nonlinear mechanical behavior. IPOL showed changes in pore morphology and collagen architecture that will help improve understanding of how LC tissue responds to load.
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Affiliation(s)
- Po-Yi Lee
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Bin Yang
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States; Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA, United States
| | - Yi Hua
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Susannah Waxman
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ziyi Zhu
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Fengting Ji
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States.
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11
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Voorhees AP, Hua Y, Brazile BL, Wang B, Waxman S, Schuman JS, Sigal IA. So-Called Lamina Cribrosa Defects May Mitigate IOP-Induced Neural Tissue Insult. Invest Ophthalmol Vis Sci 2021; 61:15. [PMID: 33165501 PMCID: PMC7671862 DOI: 10.1167/iovs.61.13.15] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Purpose The prevailing theory about the function of lamina cribrosa (LC) connective tissues is that they provide structural support to adjacent neural tissues. Missing connective tissues would compromise this support and therefore are regarded as “LC defects”, despite scarce actual evidence of their role. We examined how so-called LC defects alter IOP-related mechanical insult to the LC neural tissues. Methods We built numerical models incorporating LC microstructure from polarized light microscopy images. To simulate LC defects of varying sizes, individual beams were progressively removed. We then compared intraocular pressure (IOP)-induced neural tissue deformations between models with and without defects. To better understand the consequences of defect development, we also compared neural tissue deformations between models with partial and complete loss of a beam. Results The maximum stretch of neural tissues decreased non-monotonically with defect size. Maximum stretch in the model with the largest defect decreased by 40% in comparison to the model with no defects. Partial loss of a beam increased the maximum stretch of neural tissues in its adjacent pores by 162%, compared with 63% in the model with complete loss of a beam. Conclusions Missing LC connective tissues can mitigate IOP-induced neural tissue insult, suggesting that the role of the LC connective tissues is more complex than simply fortifying against IOP. The numerical models further predict that partial loss of a beam is biomechanically considerably worse than complete loss of a beam, perhaps explaining why defects have been reported clinically but partial beams have not.
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Affiliation(s)
- Andrew P Voorhees
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Bryn L Brazile
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, Sichuan, China
| | - Susannah Waxman
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Joel S Schuman
- Department of Ophthalmology, NYU Langone Health, New York University Grossman School of Medicine, New York, New York, United States.,Center for Neural Science, New York University, New York, New York, United States.,Department of Biomedical Engineering, New York University Tandon School of Engineering, Brooklyn, New York, United States.,Department of Physiology and Neuroscience, Neuroscience Institute, NYU Langone Health, New York University Grossman School of Medicine, New York, New York, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,McGowan Institute for Regenerative Medicine, University of Pittsburgh Medical Center and University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Louis J. Fox Center for Vision Restoration, University of Pittsburgh Medical Center and University of Pittsburgh, Pittsburgh, Pennsylvania, United States
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12
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Material properties and effect of preconditioning of human sclera, optic nerve, and optic nerve sheath. Biomech Model Mechanobiol 2021; 20:1353-1363. [PMID: 33877503 PMCID: PMC8298341 DOI: 10.1007/s10237-021-01448-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Accepted: 03/06/2021] [Indexed: 02/03/2023]
Abstract
The optic nerve (ON) is a recently recognized tractional load on the eye during larger horizontal eye rotations. In order to understand the mechanical behavior of the eye during adduction, it is necessary to characterize material properties of the sclera, ON, and in particular its sheath. We performed tensile loading of specimens taken from fresh postmortem human eyes to characterize the range of variation in their biomechanical properties and determine the effect of preconditioning. We fitted reduced polynomial hyperelastic models to represent the nonlinear tensile behavior of the anterior, equatorial, posterior, and peripapillary sclera, as well as the ON and its sheath. For comparison, we analyzed tangent moduli in low and high strain regions to represent stiffness. Scleral stiffness generally decreased from anterior to posterior ocular regions. The ON had the lowest tangent modulus, but was surrounded by a much stiffer sheath. The low-strain hyperelastic behaviors of adjacent anatomical regions of the ON, ON sheath, and posterior sclera were similar as appropriate to avoid discontinuities at their boundaries. Regional stiffnesses within individual eyes were moderately correlated, implying that mechanical properties in one region of an eye do not reliably reflect properties of another region of that eye, and that potentially pathological combinations could occur in an eye if regional properties are discrepant. Preconditioning modestly stiffened ocular tissues, except peripapillary sclera that softened. The nonlinear mechanical behavior of posterior ocular tissues permits their stresses to match closely at low strains, although progressively increasing strain causes particularly great stress in the peripapillary region.
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13
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Oikawa K, Teixeira LBC, Keikhosravi A, Eliceiri KW, McLellan GJ. Microstructure and resident cell-types of the feline optic nerve head resemble that of humans. Exp Eye Res 2020; 202:108315. [PMID: 33091431 DOI: 10.1016/j.exer.2020.108315] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 10/09/2020] [Accepted: 10/16/2020] [Indexed: 01/15/2023]
Abstract
The lamina cribrosa (LC) region of the optic nerve head (ONH) is considered a primary site for glaucomatous damage. In humans, biology of this region reflects complex interactions between retinal ganglion cell (RGC) axons and other resident ONH cell-types including astrocytes, lamina cribrosa cells, microglia and oligodendrocytes, as well as ONH microvasculature and collagenous LC beams. However, species differences in the microanatomy of this region could profoundly impact efforts to model glaucoma pathobiology in a research setting. In this study, we characterized resident cell-types, ECM composition and ultrastructure in relation to microanatomy of the ONH in adult domestic cats (Felis catus). Longitudinal and transverse cryosections of ONH tissues were immunolabeled with astrocyte, microglia/macrophage, oligodendrocyte, LC cell and vascular endothelial cell markers. Collagen fiber structure of the LC was visualized by second harmonic generation (SHG) with multiphoton microscopy. Fibrous astrocytes form glial fibrillary acidic protein (GFAP)-positive glial columns in the pre-laminar region, and cover the collagenous plates of the LC region in lamellae oriented perpendicular to the axons. GFAP-negative and alpha-smooth muscle actin-positive LC cells were identified in the feline ONH. IBA-1 positive immune cells and von Willebrand factor-positive blood vessel endothelial cells are also identifiable throughout the feline ONH. As in humans, myelination commences with a population of oligodendrocytes in the retro-laminar region of the feline ONH. Transmission electron microscopy confirmed the presence of capillaries and LC cells that extend thin processes in the core of the collagenous LC beams. In conclusion, the feline ONH closely recapitulates the complexity of the ONH of humans and non-human primates, with diverse ONH cell-types and a robust collagenous LC, within the beams of which, LC cells and capillaries reside. Thus, studies in a feline inherited glaucoma model have the potential to play a key role in enhancing our understanding of ONH cellular and molecular processes in glaucomatous optic neuropathy.
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Affiliation(s)
- Kazuya Oikawa
- Ophthalmology & Visual Sciences, University of Wisconsin-Madison, Madison, WI, USA; Surgical Sciences, University of Wisconsin-Madison, WI, USA; McPherson Eye Research Institute, Madison, WI, USA
| | - Leandro B C Teixeira
- McPherson Eye Research Institute, Madison, WI, USA; Pathobiological Sciences, University of Wisconsin-Madison, WI, USA
| | - Adib Keikhosravi
- Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Kevin W Eliceiri
- McPherson Eye Research Institute, Madison, WI, USA; Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, USA
| | - Gillian J McLellan
- Ophthalmology & Visual Sciences, University of Wisconsin-Madison, Madison, WI, USA; Surgical Sciences, University of Wisconsin-Madison, WI, USA; McPherson Eye Research Institute, Madison, WI, USA.
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14
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Grytz R, Yang H, Hua Y, Samuels BC, Sigal IA. Connective Tissue Remodeling in Myopia and its Potential Role in Increasing Risk of Glaucoma. CURRENT OPINION IN BIOMEDICAL ENGINEERING 2020; 15:40-50. [PMID: 32211567 DOI: 10.1016/j.cobme.2020.01.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Myopia and glaucoma are both increasing in prevalence and are linked by an unknown mechanism as many epidemiologic studies have identified moderate to high myopia as an independent risk factor for glaucoma. Myopia and glaucoma are both chronic conditions that lead to connective tissue remodeling within the sclera and optic nerve head. The mechanobiology underlying connective tissue remodeling differs substantially between both diseases, with different homeostatic control mechanisms. In this article, we discuss similarities and differences between connective tissue remodeling in myopia and glaucoma; selected multi-scale mechanisms that are thought to underlie connective tissue remodeling in both conditions; how asymmetric remodeling of the optic nerve head may predispose a myopic eye for pathological remodeling and glaucoma; and how neural tissue deformations may accumulate throughout both pathologies and increase the risk for mechanical insult of retinal ganglion cell axons.
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Affiliation(s)
- Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Hongli Yang
- Devers Eye Institute, Legacy Health System, Portland, Oregon, United States
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Brian C Samuels
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
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15
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Ling YTT, Shi R, Midgett DE, Jefferys JL, Quigley HA, Nguyen TD. Characterizing the Collagen Network Structure and Pressure-Induced Strains of the Human Lamina Cribrosa. Invest Ophthalmol Vis Sci 2019; 60:2406-2422. [PMID: 31157833 PMCID: PMC6545820 DOI: 10.1167/iovs.18-25863] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Purpose The purpose of this study was to measure the 2D collagen network structure of the human lamina cribrosa (LC), analyze for the correlations with age, region, and LC size, as well as the correlations with pressure-induced strains. Methods The posterior scleral cups of 10 enucleated human eyes with no known ocular disease were subjected to ex vivo inflation testing from 5 to 45 mm Hg. The optic nerve head was imaged by using second harmonic generation imaging (SHG) to identify the LC collagen structure at both pressures. Displacements and strains were calculated by using digital volume correlation of the SHG volumes. Nine structural features were measured by using a custom Matlab image analysis program, including the pore area fraction, node density, and beam connectivity, tortuosity, and anisotropy. Results All strain measures increased significantly with higher pore area fraction, and all but the radial-circumferential shear strain (Erθ) decreased with higher node density. The maximum principal strain (Emax) and maximum shear strain (Γmax) also increased with larger beam aspect ratio and tortuosity, respectively, and decreased with higher connectivity. The peripheral regions had lower node density and connectivity, and higher pore area fraction, tortuosity, and strains (except for Erθ) than the central regions. The peripheral nasal region had the lowest Emax, Γmax, radial strain, and pore area fraction. Conclusions Features of LC beam network microstructure that are indicative of greater collagen density and connectivity are associated with lower pressure-induced LC strain, potentially contributing to resistance to glaucomatous damage.
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Affiliation(s)
- Yik Tung Tracy Ling
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
| | - Ran Shi
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States.,Department of Materials Science and Engineering, Beijing Institute of Technology, Beijing, China
| | - Dan E Midgett
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
| | - Joan L Jefferys
- Wilmer Ophthalmological Institute, School of Medicine, The Johns Hopkins University, Baltimore, Maryland, United States
| | - Harry A Quigley
- Wilmer Ophthalmological Institute, School of Medicine, The Johns Hopkins University, Baltimore, Maryland, United States
| | - Thao D Nguyen
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
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