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Safa BN, Fraticelli Guzmán NS, Li G, Stamer WD, Feola AJ, Ethier CR. A Histomorphometric and Computational Investigation of the Stabilizing Role of Pectinate Ligaments in the Aqueous Outflow Pathway. J Biomech Eng 2024; 146:081011. [PMID: 38529724 DOI: 10.1115/1.4065164] [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: 12/01/2023] [Accepted: 03/22/2024] [Indexed: 03/27/2024]
Abstract
Murine models are commonly used to study glaucoma, the leading cause of irreversible blindness. Glaucoma is associated with elevated intra-ocular pressure (IOP), which is regulated by the tissues of the aqueous outflow pathway. In particular, pectinate ligaments (PLs) connect the iris and trabecular meshwork (TM) at the anterior chamber angle, with an unknown role in maintenance of the biomechanical stability of the aqueous outflow pathway, thus motivating this study. We conducted histomorphometric analysis and optical coherence tomography-based finite element (FE) modeling on three cohorts of C57BL/6 mice: "young" (2-6 months), "middle-aged" (11-16 months), and "elderly" (25-32 months). We evaluated the age-specific morphology of the outflow pathway tissues. Further, because of the known pressure-dependent Schlemm's canal (SC) narrowing, we assessed the dependence of the SC lumen area on varying IOPs in age-specific FE models over a physiological range of TM/PL stiffness values. We found age-dependent changes in morphology of outflow tissues; notably, the PLs were more developed in older mice compared to younger ones. In addition, FE modeling demonstrated that murine SC patency is highly dependent on the presence of PLs and that increased IOP caused SC collapse only with sufficiently low TM/PL stiffness values. Moreover, the elderly model showed more susceptibility to SC collapse compared to the younger models. In conclusion, our study elucidated the previously unexplored role of PLs in the aqueous outflow pathway, indicating their function in supporting TM and SC under elevated IOP.
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Affiliation(s)
- Babak N Safa
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA 30332
| | - Nina Sara Fraticelli Guzmán
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30318; Department of Ophthalmology, Emory University, Atlanta, GA 30332
- Georgia Institute of Technology
| | - Guorong Li
- Department of Ophthalmology, Duke University, Durham, NC 27705
- Duke University
| | - W Daniel Stamer
- Department of Ophthalmology, Duke University, Durham, NC 27705
- Duke University
| | - Andrew J Feola
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA 30332; Department of Ophthalmology, Emory University, Atlanta, GA 30322; Atlanta VA Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Healthcare System, Decatur, GA 30033
- Emory University
| | - C Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA 30332; George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30318; Department of Ophthalmology, Emory University, Atlanta, GA 30332
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Li G, van Batenburg-Sherwood J, Safa BN, Fraticelli Guzmán NS, Wilson A, Bahrani Fard MR, Choy K, de Ieso ML, Cui JS, Feola AJ, Weisz T, Kuhn M, Bowes Rickman C, Farsiu S, Ethier CR, Stamer WD. Aging and intraocular pressure homeostasis in mice. Aging Cell 2024:e14160. [PMID: 38566432 DOI: 10.1111/acel.14160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 03/09/2024] [Accepted: 03/14/2024] [Indexed: 04/04/2024] Open
Abstract
Age and elevated intraocular pressure (IOP) are the two primary risk factors for glaucoma, an optic neuropathy that is the leading cause of irreversible blindness. In most people, IOP is tightly regulated over a lifetime by the conventional outflow tissues. However, the mechanistic contributions of age to conventional outflow dysregulation, elevated IOP and glaucoma are unknown. To address this gap in knowledge, we studied how age affects the morphology, biomechanical properties and function of conventional outflow tissues in C57BL/6 mice, which have an outflow system similar to humans. As reported in humans, we observed that IOP in mice was maintained within a tight range over their lifespan. Remarkably, despite a constellation of age-related changes to the conventional outflow tissues that would be expected to hinder aqueous drainage and impair homeostatic function (decreased cellularity, increased pigment accumulation, increased cellular senescence and increased stiffness), outflow facility, a measure of conventional outflow tissue fluid conductivity, was stable with age. We conclude that the murine conventional outflow system has significant functional reserve in healthy eyes. However, these age-related changes, when combined with other underlying factors, such as genetic susceptibility, are expected to increase risk for ocular hypertension and glaucoma.
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Affiliation(s)
- Guorong Li
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | | | - Babak N Safa
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA
| | - Nina Sara Fraticelli Guzmán
- Department of Ophthalmology, Emory University, Atlanta, Georgia, USA
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
| | - Andrea Wilson
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - Mohammad Reza Bahrani Fard
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA
| | - Kevin Choy
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
| | - Michael L de Ieso
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - J Serena Cui
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - Andrew J Feola
- Department of Ophthalmology, Emory University, Atlanta, Georgia, USA
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
- Center for Visual and Neurocognitive Rehabilitation, Atlanta Virginia Medical Center, Decatur, Georgia, USA
| | - Tara Weisz
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - Megan Kuhn
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | | | - Sina Farsiu
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
| | - C Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA
- Department of Ophthalmology, Emory University, Atlanta, Georgia, USA
| | - W Daniel Stamer
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
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Safa BN, Guzmán NSF, Li G, Daniel Stamer W, Feola AJ, Ross Ethier C. A Histomorphometric and Computational Investigation of the Stabilizing Role of Pectinate Ligaments in the Aqueous Outflow Pathway. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.10.17.562754. [PMID: 37905127 PMCID: PMC10614930 DOI: 10.1101/2023.10.17.562754] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
Murine models are commonly used to study glaucoma, the leading cause of irreversible blindness. Glaucoma is associated with elevated intraocular pressure (IOP), which is regulated by the tissues of the aqueous outflow pathway. In particular, pectinate ligaments (PLs) connect the iris and trabecular meshwork (TM) at the anterior chamber angle, with an unknown role in maintenance of the biomechanical stability of the aqueous outflow pathway, thus motivating this study. We conducted histomorphometric analysis and optical coherence tomography-based finite element (FE) modeling on three cohorts of C57BL/6 mice: 'young' (2-6 months), 'middle-aged' (11-16 months), and 'elderly' (25-32 months). We evaluated the age-specific morphology of the outflow pathway tissues. Further, because of the known pressure-dependent Schlemm's canal (SC) narrowing, we assessed the dependence of the SC lumen area to varying IOPs in age-specific FE models over a physiological range of TM/PL stiffness values. We found age-dependent changes in morphology of outflow tissues; notably, the PLs were more developed in older mice compared to younger ones. In addition, FE modeling demonstrated that murine SC patency is highly dependent on the presence of PLs, and that increased IOP caused SC collapse only with sufficiently low TM/PL stiffness values. Moreover, the elderly model showed more susceptibility to SC collapse compared to the younger models. In conclusion, our study elucidated the previously unexplored role of PLs in the aqueous outflow pathway, indicating their function in supporting TM and SC under elevated IOP.
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Affiliation(s)
- Babak N. Safa
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA
| | - Nina Sara Fraticelli Guzmán
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
- Department of Ophthalmology, Emory University, Atlanta, GA, USA
| | - Guorong Li
- Department of Ophthalmology, Duke University, Durham, NC, USA
| | | | - Andrew J. Feola
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA
- Department of Ophthalmology, Emory University, Atlanta, GA, USA
- Atlanta VA Center for Visual and Neurocognitive Rehabilitation, Atlanta Veterans Affair Healthcare System, Decatur, GA, USA
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
- Department of Ophthalmology, Emory University, Atlanta, GA, USA
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Li G, van Batenburg-Sherwood J, Safa BN, Fraticelli Guzmán NS, Wilson A, Bahrani Fard MR, Choy K, De Ieso ML, Cui JS, Feola AJ, Weisz T, Kuhn M, Rickman CB, Farsiu S, Ethier CR, Stamer WD. Aging and intraocular pressure homeostasis in mice. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.17.562768. [PMID: 38106150 PMCID: PMC10723259 DOI: 10.1101/2023.10.17.562768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Age and elevated intraocular pressure (IOP) are the two primary risk factors for glaucoma, an optic neuropathy that is the leading cause of irreversible blindness. In most people, IOP is tightly regulated over a lifetime by the conventional outflow tissues. However, the mechanistic contributions of age to conventional outflow dysregulation, elevated IOP and glaucoma are unknown. To address this gap in knowledge, we studied how age affects the morphology, biomechanical properties and function of conventional outflow tissues in C57BL/6 mice, which have an outflow system similar to humans. As reported in humans, we observed that IOP in mice was maintained within a tight range over their lifespan. Remarkably, despite a constellation of age-related changes to the conventional outflow tissues that would be expected to hinder aqueous drainage and impair homeostatic function (decreased cellularity, increased pigment accumulation, increased cellular senescence and increased stiffness), outflow facility, a measure of conventional outflow tissue fluid conductivity, was stable with age. We conclude that the murine conventional outflow system has significant functional reserve in healthy eyes. However, these age-related changes, when combined with other underlying factors, such as genetic susceptibility, are expected to increase risk for ocular hypertension and glaucoma.
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Habibi M, Mobasseri S, Zare A, Souriaee V. Numerical simulation of drug delivery with therapeutic lens for the glaucoma treatment in the anterior eye chamber. BIOMEDICAL ENGINEERING ADVANCES 2022. [DOI: 10.1016/j.bea.2022.100032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
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Abstract
PURPOSE OF REVIEW Biomechanics is an important aspect of the complex family of diseases known as the glaucomas. Here, we review recent studies of biomechanics in glaucoma. RECENT FINDINGS Several tissues have direct and/or indirect biomechanical roles in various forms of glaucoma, including the trabecular meshwork, cornea, peripapillary sclera, optic nerve head/sheath, and iris. Multiple mechanosensory mechanisms and signaling pathways continue to be identified in both the trabecular meshwork and optic nerve head. Further, the recent literature describes a variety of approaches for investigating the role of tissue biomechanics as a risk factor for glaucoma, including pathological stiffening of the trabecular meshwork, peripapillary scleral structural changes, and remodeling of the optic nerve head. Finally, there have been advances in incorporating biomechanical information in glaucoma prognoses, including corneal biomechanical parameters and iridial mechanical properties in angle-closure glaucoma. SUMMARY Biomechanics remains an active aspect of glaucoma research, with activity in both basic science and clinical translation. However, the role of biomechanics in glaucoma remains incompletely understood. Therefore, further studies are indicated to identify novel therapeutic approaches that leverage biomechanics. Importantly, clinical translation of appropriate assays of tissue biomechanical properties in glaucoma is also needed.
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Affiliation(s)
- Babak N. Safa
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
| | - Cydney A. Wong
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
| | - Jungmin Ha
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
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Cai JC, Chen YL, Cao YH, Babenko A, Chen X. Numerical study of aqueous humor flow and iris deformation with pupillary block and the efficacy of laser peripheral iridotomy. Clin Biomech (Bristol, Avon) 2022; 92:105579. [PMID: 35085976 DOI: 10.1016/j.clinbiomech.2022.105579] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 11/29/2021] [Accepted: 01/13/2022] [Indexed: 02/07/2023]
Abstract
BACKGROUND Disclosing the mechanism of primary angle closure glaucoma with pupillary block is important to the diagnosis as well as treatments, such as the laser peripheral iridotomy. Comparing with abundant clinical researches, there have been fewer quantitative studies of the aqueous humor flows with synechia iris configurations, and the efficacy of laser peripheral iridotomy in treating glaucoma. METHODS Based on the mathematical models of aqueous humor flow and iris deformation, the flow fields were simulated by computational fluid dynamics with normal and synechia iris configurations (iris-lens gap of 30, 5 and 2 μm, respectively), and through one-way fluid-structure coupling technique the deformations of the iris under the flow field pressure were calculated by finite element analysis. The efficacy of glaucoma treatment with different orifice sizes was also investigated. FINDINGS Results show that the pressure difference between anterior and posterior chambers and iris deformation increase dramatically with the iris-lens gap distance less than 5 μm, and when further decreasing this gap may lead the iris touch the cornea causing angle closure glaucoma with noticeable iris bombé. Laser peripheral iridotomy simulation results show that iridotomy size of 0.2 mm can effectively decrease the pressure difference across the iris and relieve iris bombé. INTERPRETATION This is a biomechanical numerical study, and the results are reasonable compare to those of published works. It may shed additional light on the diagnosis and treatment of angle closure glaucoma with pupillary block.
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Affiliation(s)
- Jian-Cheng Cai
- College of Engineering, Zhejiang Normal University, Jinhua 321004, China.
| | - Yan-Ling Chen
- Department of Ophthalmology, Jinhua People's Hospital, Jinhua 321000, China
| | - Yue-Hong Cao
- Department of Ophthalmology, Jinhua People's Hospital, Jinhua 321000, China.
| | - Andrii Babenko
- College of Engineering, Zhejiang Normal University, Jinhua 321004, China
| | - Xi Chen
- College of Mathematics, Physics and Information Science and Engineering, Zhejiang Normal University, Jinhua 321004, China
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Panda SK, Tan RKY, Tun TA, Buist ML, Nongpiur M, Baskaran M, Aung T, Girard MJA. Changes in Iris Stiffness and Permeability in Primary Angle Closure Glaucoma. Invest Ophthalmol Vis Sci 2021; 62:29. [PMID: 34714323 PMCID: PMC8558521 DOI: 10.1167/iovs.62.13.29] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Purpose To evaluate the biomechanical properties of the iris by evaluating iris movement during pupil constriction and to compare such properties between healthy and primary angle-closure glaucoma (PACG) subjects. Methods A total of 140 subjects were recruited for this study. In a dark room, the anterior segments of one eye per subject were scanned using anterior segment optical coherence tomography imaging during induced pupil constriction with an external white light source of 1700 lux. Using a custom segmentation code, we automatically isolated the iris segments from the AS-OCT images, which were then discretized and transformed into a three-dimensional point cloud. For each iris, a finite element (FE) mesh was constructed from the point cloud, and an inverse FE simulation was performed to match the clinically observed iris constriction in the AS-OCT images. Through this optimization process, we were able to identify the elastic modulus and permeability of each iris. Results For all 140 subjects (95 healthy and 45 PACG of Indian/Chinese ethnicity; age 60.2 ± 8.7 for PACG subjects and 57.7 ± 10.1 for healthy subjects), the simulated deformation pattern of the iris during pupil constriction matched well with OCT images. We found that the iris stiffness was higher in PACG than in healthy controls (24.5 ± 8.4 kPa vs. 17.1 ± 6.6 kPa with 40 kPa of active stress specified in the sphincter region; P < 0.001), whereas iris permeability was lower (0.41 ± 0.2 mm2/kPa s vs. 0.55 ± 0.2 mm2/kPa s; p = 0.142). Conclusions This study suggests that the biomechanical properties of the iris in PACG are different from those in healthy controls. An improved understanding of the biomechanical behavior of the iris may have implications for the understanding and management of angle-closure glaucoma.
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Affiliation(s)
- Satish K Panda
- Ophthalmic Engineering & Innovation Laboratory (OEIL), Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.,Department of Biomedical Engineering, National University of Singapore, Singapore
| | - Royston K Y Tan
- Ophthalmic Engineering & Innovation Laboratory (OEIL), Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.,Department of Biomedical Engineering, National University of Singapore, Singapore
| | - Tin A Tun
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore
| | - Martin L Buist
- Department of Biomedical Engineering, National University of Singapore, Singapore
| | - Monisha Nongpiur
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore
| | - Mani Baskaran
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.,Sankara Nethralaya, Chennai, India
| | - Tin Aung
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.,Duke-NUS Medical School, Singapore.,Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Michaël J A Girard
- Ophthalmic Engineering & Innovation Laboratory (OEIL), Singapore Eye Research Institute, Singapore National Eye Centre, Singapore.,Duke-NUS Medical School, Singapore.,Institute of Molecular & Clinical Ophthalmology, Basel, Switzerland
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