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Alpogan O, Un Y, Tekcan H, Kose AO, Bolac R. Evaluation of Anterior Scleral Thickness and Angle Parameters in Eyes with Pseudoexfoliation Syndrome and Glaucoma. J Glaucoma 2024; 33:785-793. [PMID: 38771636 DOI: 10.1097/ijg.0000000000002438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2024] [Accepted: 05/11/2024] [Indexed: 05/23/2024]
Abstract
PRCIS The relationship between anterior scleral thickness (AST) and scleral spur (SS) length was disrupted in eyes with pseudoexfoliation (PX), and SS length was shorter in eyes with pseudoexfoliative glaucoma (PXG). OBJECTIVES To evaluate AST in eyes with PX and to examine the relationship between AST and Schlemm canal (SC), trabecular meshwork (TM), and SS. PATIENTS AND METHODS Thirty-eight patients with PX syndrome (PXS), 38 patients with PXG, and 38 healthy patients were included in the study. Using sweep source anterior segment optical coherence tomography, AST (0, 1, 2, and 3 mm from the SS), SC, and TM were visualized in the nasal and temporal areas, and measurements were compared between groups. The relationships between corneal thickness, TM, SS, SC, and AST were then evaluated. RESULTS In all groups, the AST, SC, and TM measurements were similar ( P > 0.05). In the PXG group, SS lengths in the temporal area were shorter than those in the control and PXS groups ( P = 0.012). There were significant correlations between TM length and AST in the PXG group ( P < 0.05). The SS length exhibited moderately positive correlations with SC length and mean TM thickness in the PXG ( P < 0.05). There was a significant relationship between AST0 and SS in healthy eyes ( P < 0.05), but not in other eyes. CONCLUSIONS The shorter SS length observed in eyes with PXG may be a sign of structural changes. In addition, disruption of the relationship between AST and SS may be an early sign of pathologic processes, especially in eyes with PXS, and may require closer follow-up of these eyes.
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Affiliation(s)
- Oksan Alpogan
- Department of Ophthalmology, Health Sciences University, Haydarpasa Numune Training and Research Hospital
| | - Yasemin Un
- Department of Ophthalmology, Beyoglu Eye Training and Research Hospital, Istanbul, Turkey
| | - Hatice Tekcan
- Department of Ophthalmology, Health Sciences University, Haydarpasa Numune Training and Research Hospital
| | - Alev Ozcelik Kose
- Department of Ophthalmology, Health Sciences University, Haydarpasa Numune Training and Research Hospital
| | - Ruveyde Bolac
- Department of Ophthalmology, Health Sciences University, Haydarpasa Numune Training and Research Hospital
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Lim S, Kim C, Jafari S, Park J, Garcia SS, Demer JL. Postmortem Digital Image Correlation and Finite Element Modeling Demonstrate Posterior Scleral Deformations during Optic Nerve Adduction Tethering. Bioengineering (Basel) 2024; 11:452. [PMID: 38790319 PMCID: PMC11117839 DOI: 10.3390/bioengineering11050452] [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: 03/04/2024] [Revised: 04/25/2024] [Accepted: 04/28/2024] [Indexed: 05/26/2024] Open
Abstract
Postmortem human eyes were subjected to optic nerve (ON) traction in adduction and elevated intraocular pressure (IOP) to investigate scleral surface deformations. We incrementally adducted 11 eyes (age 74.1 ± 9.3 years, standard deviation) from 26° to 32° under normal IOP, during imaging of the posterior globe, for analysis by three-dimensional digital image correlation (3D-DIC). In the same eyes, we performed uniaxial tensile testing in multiple regions of the sclera, ON, and ON sheath. Based on individual measurements, we analyzed eye-specific finite element models (FEMs) simulating adduction and IOP loading. Analysis of 3D-DIC showed that the nasal sclera up to 1 mm from the sheath border was significantly compressed during adduction. IOP elevation from 15 to 30 mmHg induced strains less than did adduction. Tensile testing demonstrated ON sheath stiffening above 3.4% strain, which was incorporated in FEMs of adduction tethering that was quantitatively consistent with changes in scleral deformation from 3D-DIC. Simulated IOP elevation to 30 mmHg did not induce scleral surface strains outside the ON sheath. ON tethering in incremental adduction from 26° to 32° compressed the nasal and stretched the temporal sclera adjacent to the ON sheath, more so than IOP elevation. The effect of ON tethering is influenced by strain stiffening of the ON sheath.
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Affiliation(s)
- Seongjin Lim
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Changzoo Kim
- Department of Ophthalmology, Kosin University, Busan 49267, Republic of Korea;
| | - Somaye Jafari
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Joseph Park
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Stephanie S. Garcia
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Joseph L. Demer
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
- Neuroscience Interdepartmental Program, University of California, Los Angeles, CA 90095, USA
- Department of Neurology, University of California, Los Angeles, CA 90095, USA
- Department of Bioengineering, University of California, Los Angeles, CA 90095, USA
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3
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Chuangsuwanich T, Tun TA, Braeu FA, Wang X, Chin ZY, Panda SK, Buist M, Milea D, Strouthidis N, Perera S, Nongpiur ME, Aung T, Girard MJA. Adduction induces large optic nerve head deformations in subjects with normal-tension glaucoma. Br J Ophthalmol 2024; 108:522-529. [PMID: 37011991 DOI: 10.1136/bjo-2022-322461] [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] [Received: 08/23/2022] [Accepted: 03/15/2023] [Indexed: 04/05/2023]
Abstract
PURPOSE To assess intraocular pressure (IOP)-induced and gaze-induced optic nerve head (ONH) strains in subjects with high-tension glaucoma (HTG) and normal-tension glaucoma (NTG). DESIGN Clinic-based cross-sectional study. METHODS The ONH from one eye of 228 subjects (114 subjects with HTG (pre-treatment IOP≥21 mm Hg) and 114 with NTG (pre-treatment IOP<21 mm Hg)) was imaged with optical coherence tomography (OCT) under the following conditions: (1) OCT primary gaze, (2) 20° adduction from OCT primary gaze, (3) 20° abduction from OCT primary gaze and (4) OCT primary gaze with acute IOP elevation (to approximately 33 mm Hg). We then performed digital volume correlation analysis to quantify IOP-induced and gaze-induced ONH tissue deformations and strains. RESULTS Across all subjects, adduction generated high effective strain (4.4%±2.3%) in the LC tissue with no significant difference (p>0.05) with those induced by IOP elevation (4.5%±2.4%); while abduction generated significantly lower (p=0.01) effective strain (3.1%±1.9%). The lamina cribrosa (LC) of HTG subjects exhibited significantly higher effective strain than those of NTG subjects under IOP elevation (HTG: 4.6%±1.7% vs NTG: 4.1%±1.5%, p<0.05). Conversely, the LC of NTG subjects exhibited significantly higher effective strain than those of HTG subjects under adduction (NTG: 4.9%±1.9% vs HTG: 4.0%±1.4%, p<0.05). CONCLUSION We found that NTG subjects experienced higher strains due to adduction than HTG subjects, while HTG subjects experienced higher strain due to IOP elevation than NTG subjects-and that these differences were most pronounced in the LC tissue.
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Affiliation(s)
- Thanadet Chuangsuwanich
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Tin A Tun
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Duke-NUS Medical School, Singapore
| | - Fabian A Braeu
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Singapore-MIT Alliance for Research and Technology, Singapore
| | - Xiaofei Wang
- Beijing Advanced Innovation Center for Biomedical Engineering, Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Biological Science and Medical Engineering, Beihang University, Beijing, China
| | - Zhi Yun Chin
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
| | - Satish K Panda
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Department of Biomedical Engineering, National University of Singapore, Singapore
| | - Martin Buist
- Department of Biomedical Engineering, National University of Singapore, Singapore
| | - Dan Milea
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Duke-NUS Medical School, Singapore
| | | | - Shamira Perera
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Duke-NUS Medical School, Singapore
| | - Monisha Esther Nongpiur
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Duke-NUS Medical School, Singapore
| | - Tin Aung
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Duke-NUS Medical School, Singapore
| | - Michael J A Girard
- Singapore Eye Research Institute, Singapore National Eye Center, Singapore
- Duke-NUS Medical School, Singapore
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van Koeverden AK, Afiat BC, Nguyen CT, Bui BV, Lee PY. Understanding how ageing impacts ganglion cell susceptibility to injury in glaucoma. Clin Exp Optom 2024; 107:147-155. [PMID: 37980904 DOI: 10.1080/08164622.2023.2279734] [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] [Received: 06/17/2023] [Accepted: 10/31/2023] [Indexed: 11/21/2023] Open
Abstract
Glaucoma is a leading cause of blindness worldwide, with a marked increase in prevalence with advancing age. Due to the multifactorial nature of glaucoma pathogenesis, dissecting how ageing impacts upon glaucoma risk requires analysis and synthesis of evidence from a vast literature. While there is a wealth of human clinical studies examining glaucoma pathogenesis and why older patients have increased risk, many aspects of the disease such as adaptations of retinal ganglion cells to stress, autophagy and the role of glial cells in glaucoma, require the use of animal models to study the complex cellular processes and interactions. Additionally, the accelerated nature of ageing in rodents facilitates the longitudinal study of changes that would not be feasible in human clinical studies. This review article examines evidence derived predominantly from rodent models on how the ageing process impacts upon various aspects of glaucoma pathology from the retinal ganglion cells themselves, to supporting cells and tissues such as glial cells, connective tissue and vasculature, in addition to oxidative stress and autophagy. An improved understanding of how ageing modifies these factors may lead to the development of different therapeutic strategies that target specific risk factors or processes involved in glaucoma.
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Affiliation(s)
- Anna K van Koeverden
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
| | - Brianna C Afiat
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
| | - Christine To Nguyen
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
| | - Bang V Bui
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
| | - Pei Ying Lee
- Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria, Australia
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5
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Qin Y, Liu T, Zhang Z, Xing S, Gong L, Ni Y. Scleral remodeling in early adulthood: the role of FGF-2. Sci Rep 2023; 13:20779. [PMID: 38012225 PMCID: PMC10682392 DOI: 10.1038/s41598-023-48264-5] [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: 09/03/2023] [Accepted: 11/24/2023] [Indexed: 11/29/2023] Open
Abstract
Emmetropization, a natural process of ocular elongation, is closely associated with scleral remodeling. The Fibroblast growth factor-2 (FGF-2) was reported involved in scleral remodeling in myopia models. Herein, we aimed to investigate the role of scleral fibroblast-to-myofibroblast differentiation and FGF-2 in scleral remodeling during maturation. Our findings revealed that the posterior scleral fibroblasts (SFs) from mature guinea pigs exhibit increased stiffness compared to those from young guinea pigs. Moreover, mature SFs displayed decreased cell proliferation but increased levels of α-SMA, matrix metalloproteinase 2 (MMP2), and collagen 1, when compared to young SFs. Additionally, the mRNA expression of scleral Fgf-2, Fgf receptor 1 (Fgfr1), Fgfr2, Fgfr3, and Fgfr4 was increased in mature SFs. Notably, exogenous FGF-2 showed increased cell proliferation and led to decreased expression of α-SMA, MMP2, and collagen 1 in mature SFs. Overall, our findings highlight the influence of maturation on SFs from posterior scleral shells, resulting in increased stiffness and the manifestation of fibroblast-to-myofibroblast differentiation during development. Exogenous FGF-2 increased cell proliferation and reversed the age-related fibroblast-to-myofibroblast differentiation, suggesting a potential role of FGF-2 in regulating scleral remodeling.
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Affiliation(s)
- Yingyan Qin
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, 54S Xianlie Road, Guangzhou, 510060, China
| | - Taixiang Liu
- Guizhou Ophthalmic Hospital, The Affiliated Hospital of Zunyi Medical University, Zunyi, 563003, China
| | - Zhaotian Zhang
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, 54S Xianlie Road, Guangzhou, 510060, China
| | - Shuwen Xing
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, 54S Xianlie Road, Guangzhou, 510060, China
| | - Li Gong
- Instrumental Analysis and Research Center, Sun Yat-Sen University, 135W Xingang Road, Guangzhou, 510275, China.
| | - Yao Ni
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, 54S Xianlie Road, Guangzhou, 510060, China.
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6
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Sayah DN, Mazzaferri J, Descovich D, Costantino S, Lesk MR. Ocular rigidity and neuroretinal damage in patients with vasospasticity: a pilot study. CANADIAN JOURNAL OF OPHTHALMOLOGY 2023; 58:338-345. [PMID: 35358484 DOI: 10.1016/j.jcjo.2022.02.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 02/08/2022] [Accepted: 02/12/2022] [Indexed: 11/22/2022]
Abstract
OBJECTIVE Evidence suggests that ocular blood flow dysregulation in patients with vasospasticity could occur in response to biomechanical stimuli, contributing to optic nerve head susceptibility in glaucoma. We evaluate the role of vasospasticity in the association between ocular rigidity (OR) and neuroretinal damage, hypothesizing that low OR correlates with greater glaucoma damage in patients with vasospasticity. DESIGN Cross-sectional study. PARTICIPANTS Patients with open-angle glaucoma (OAG), suspect discs, or no glaucoma. METHODS OR was measured using a noninvasive, validated method developed by our group. Retinal nerve fibre layer (RNFL) and ganglion cell complex thicknesses were acquired using spectral domain optical coherence tomography. Vasospasticity was assessed by a standardized questionnaire that was based on existing validated questionnaires and adapted to our requirements. Atherosclerosis was evaluated based on Broadway and Drance's (1998) cardiovascular disease score. Correlations between OR and structural parameters were assessed in patients with vasospasticity and those with atherosclerosis. RESULTS Of 118 patients with either OAG (n = 67), suspect discs (n = 26), or no glaucoma (n = 25) who were recruited consecutively, 10 were classified as having vasospasticity, and 37 as having atherosclerosis. In the vasospastic group, significant correlations were found between OR and the minimum ganglion cell complex thickness (rs = 0.681, p = 0.030), the average RNFL thickness (rs = 0.745, p = 0.013), and the RNFL in the temporal quadrant (rs = 0.772, p = 0.009), indicating more damage with lower OR. Similar trends were maintained when applying multiple testing correction; however, only the eighth RNFL clock hour corresponding to the inferior-temporal peripapillary region remained significantly correlated with OR in the vasospastic group (p = 0.015). In contrast, no correlation was found in the atherosclerotic group (p > 0.05). CONCLUSIONS The findings of the current pilot study indicate a trend for more neuronal structural damage in less-rigid eyes of patients with vasospasticity, meaning that OR may play a greater role in glaucoma in vasospastic patients than in patients with atherosclerosis. Although these results provide interesting insight into the pathophysiology of OAG, further investigation is needed to confirm our observations.
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Affiliation(s)
- Diane N Sayah
- Maisonneuve-Rosemont Hospital Research Centre, Montreal, QC; Department of Ophthalmology, Université de Montréal, Montreal, QC
| | | | | | - Santiago Costantino
- Maisonneuve-Rosemont Hospital Research Centre, Montreal, QC; Department of Ophthalmology, Université de Montréal, Montreal, QC; Centre Universitaire d'Ophtalmologie (CUO), Maisonneuve-Rosemont Hospital, CIUSSS-E, Montreal, QC
| | - Mark R Lesk
- Maisonneuve-Rosemont Hospital Research Centre, Montreal, QC; Department of Ophthalmology, Université de Montréal, Montreal, QC; Centre Universitaire d'Ophtalmologie (CUO), Maisonneuve-Rosemont Hospital, CIUSSS-E, Montreal, QC.
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7
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Brazuna R, Alonso RS, Salomão MQ, Fernandes BF, Ambrósio R. Ocular Biomechanics and Glaucoma. Vision (Basel) 2023; 7:vision7020036. [PMID: 37218954 DOI: 10.3390/vision7020036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 04/11/2023] [Accepted: 04/21/2023] [Indexed: 05/24/2023] Open
Abstract
Biomechanics is a branch of biophysics that deals with mechanics applied to biology. Corneal biomechanics have an important role in managing patients with glaucoma. While evidence suggests that patients with thin and stiffer corneas have a higher risk of developing glaucoma, it also influences the accurate measurement of intraocular pressure. We reviewed the pertinent literature to help increase our understanding of the biomechanics of the cornea and other ocular structures and how they can help optimize clinical and surgical treatments, taking into consideration individual variabilities, improve the diagnosis of suspected patients, and help monitor the response to treatment.
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Affiliation(s)
- Rodrigo Brazuna
- Department of Ophthalmology, Federal University of the State of Rio de Janeiro, Rio de Janeiro 22290-240, RJ, Brazil
| | - Ruiz S Alonso
- Department of Ophthalmology, Antonio Pedro University Hospital, Fluminense Federal University, Niterói 24033-900, RJ, Brazil
| | - Marcella Q Salomão
- Department of Ophthalmology, Federal University of São Paulo, São Paulo 04023-062, SP, Brazil
| | | | - Renato Ambrósio
- Department of Ophthalmology, Federal University of the State of Rio de Janeiro, Rio de Janeiro 22290-240, RJ, Brazil
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8
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Sayah DN, Lesk MR. Ocular Rigidity and Current Therapy. Curr Eye Res 2023; 48:105-113. [PMID: 35763027 DOI: 10.1080/02713683.2022.2093380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Purpose: Ocular rigidity (OR) is an important biomechanical parameter of the eye accounting for the material and geometrical properties of the corneoscleral shell.Methods: This study used a literature search to review the role of ocular rigidity and the application of potential therapies targeting this parameter in glaucoma and myopia.Conclusion: Biomechanical modeling and improved understanding of the biochemistry, and molecular arrangement of sclera and its constituents have yielded important insights. Recent developments, including that of a non-invasive and direct OR measurement method and improved ocular imaging techniques are helping to elucidate the role of OR in healthy and diseased eyes by facilitating large scale and longitudinal clinical studies. Improved understanding of OR at the initial stages of disease processes and its alterations with disease progression will undoubtedly propel research in the field. Furthermore, a better understanding of the determinants of OR is helping to refine novel therapeutic approaches which target and alter the biomechanical properties of the sclera in sight-threatening conditions such as glaucoma and myopia.
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Affiliation(s)
- Diane N Sayah
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Canada.,School of Optometry, Université de Montréal, Montreal, Canada
| | - Mark R Lesk
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Canada.,Department of Ophthalmology, Faculty of Medicine, Université de Montréal, Montreal, Canada.,Centre Universitaire d'ophtalmologie de l'Université de Montréal de l'Hôpital Maisonneuve-Rosemont, CIUSSS-E, Montreal, Canada
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9
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Lysyl oxidase-like 1 deficiency alters ultrastructural and biomechanical properties of the peripapillary sclera in mice. Matrix Biol Plus 2022; 16:100120. [PMID: 36060791 PMCID: PMC9436796 DOI: 10.1016/j.mbplus.2022.100120] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Accepted: 08/17/2022] [Indexed: 11/30/2022] Open
Abstract
Lysyl oxidate-like 1 knockout (Loxl1-/-) mice have decreased vision without elevated intraocular pressure. Loxl1-/- mice exhibit biometric changes of the anterior segment of the eye. Loxl1-/- mice have altered elastin and collagen structure in peripapillary sclera. Structural alternations of peripapillary sclera correlate with its increased stiffness in Loxl1-/- mice.
Lysyl oxidase-like 1 encoded by the LOXL1 gene is a member of the lysyl oxidase family of enzymes that are important in the maintenance of extracellular matrix (ECM)-rich tissue. LOXL1 is important for proper elastic fiber formation and mice lacking LOXL1 (Loxl1−/−) exhibit systemic elastic fiber disorders, such as pelvic organ prolapse, a phenotype associated with exfoliation syndrome (XFS) in humans. Patients with XFS have a significant risk of developing exfoliation glaucoma (XFG), a severe form of glaucoma, which is a neurodegenerative condition leading to irreversible blindness if not detected and treated in a timely fashion. Although Loxl1−/− mice have been used extensively to investigate mechanisms of pelvic organ prolapse, studies of eyes in those mice are limited and some showed inconsistent ocular phenotypes. In this study we demonstrate that Loxl1−/− mice have significant anterior segment biometric abnormalities which recapitulate some human XFS features. We then focused on the peripapillary sclera (PPS), a critical structure for maintaining optic nerve health. We discovered quantitative and qualitive changes in ultrastructure of PPS, such as reduced elastic fibers, enlarged collagen fibrils, and transformed collagen lamella organization detected by transmission electron microscopy (TEM). Importantly, these changes corelate with altered tissue biomechanics detected by Atomic Force Microscopy (AFM) of PPS in mice. Together, our results support a crucial role for LOXL1 in ocular tissue structure and biomechanics, and Loxl1−/− mice could be a valuable resource for understanding the role of scleral tissue biomechanics in ocular disease.
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10
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Ohn K, Noh YH, Moon JI, Jung Y. Measurement of corneal biomechanical properties in diabetes mellitus using the Corvis ST. Medicine (Baltimore) 2022; 101:e30248. [PMID: 36086751 PMCID: PMC10980441 DOI: 10.1097/md.0000000000030248] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 07/13/2022] [Indexed: 11/26/2022] Open
Abstract
We sought to assess changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with those among healthy controls using Corvis ST (CST). The study group included 209 eyes from healthy control subjects and 33 eyes from diabetic subjects, respectively. Following an ophthalmological examination, measurements with CST were taken. Additionally, hemoglobin A1c and blood glucose values were collected. Results were then compared to those of the control group after adjusting for potential confounding factors, including age-, intraocular pressure (IOP)-, central corneal thickness (CCT)-, spherical equivalent (SE)- and axial length (AL). After adjusting for potential confounding factors, including the age, IOP, CCT, SE, and AL, patients with DM presented significantly lower whole-eye movement (WEM) (ms) values than patients without DM (21.71 ± 0.84 vs. 22.15 ± 0.64 ms; P < .001). There was a significant and negative correlation between WEM (ms) and hemoglobin A1c in DM patients (r = -0.733; P = .001). In univariate and multivariate general linear mixed model (GLMM) analyses, IOP (P < .001 and P < .001, respectively) and the presence of DM (P = .001 and P < .001, respectively) significantly affected WEM (ms). In DM, significant changes in corneal biomechanical properties were detectable. The DM group showed significantly less deformable cornea and sclera than did the normal controls, even after adjusting for age, IOP, CCT, SE, and AL. These findings may cause misinterpretation of IOP measurements in diabetic patients. Therefore, the measurement of corneal biomechanics should be taken into consideration in clinical practice.
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Affiliation(s)
- Kyoung Ohn
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Young Ho Noh
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Jung Il Moon
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
| | - Younhea Jung
- Department of Ophthalmology, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
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11
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Finite Element Analysis of Cornea and Lid Wiper during Blink, with and without Contact Lens. J Ophthalmol 2022; 2022:7930334. [PMID: 35620413 PMCID: PMC9129998 DOI: 10.1155/2022/7930334] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2022] [Accepted: 04/26/2022] [Indexed: 11/18/2022] Open
Abstract
Ocular surface disorders such as Lid Wiper Epitheliopathy (LWE), Superior Epithelial Arcuate Lesion (SEAL), and contact lens-induced Limbal Stem Cell Deficiency (LSCD) as well as Superior Limbic Keratoconjunctivitis (SLK) affect one’s quality of life. Hence, it is imperative to investigate the underlying causes of these ocular surface disorders. During blink, the undersurface of the eyelid tends to interact with the cornea and the conjunctiva. The presence of a contact lens can add to the biomechanical frictional changes on these surfaces. To estimate these changes with and without a contact lens, a finite element model (FEM) of the eyelid wiper, eyeball, and contact lens was developed using COMSOL Multiphysics. Biomechanical properties such as von Mises stress (VMS) and displacement were calculated. Our study concluded that (a) maximum VMS was observed in the lid wiper in the absence of contact lens in the eye and (b) maximum VMS was observed in the superior 1.3 mm of the cornea in the presence of the contact lens in the eye. Thus, the development of friction-induced ocular surface disorders such as LWE, SLK, SEAL, and LSCD could be attributed to increased VMS. FEA is a useful simulation tool that helps us to understand the effect of blink on a normal eye with and without CL.
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12
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Baek J, Park HYL, Kim SA, Hong KE, Jeon SJ, Shin DY, Jung Y, Park CK. Parapapillary Choroidal Microvasculature Dropout in Branched Retinal Vein Occlusion and Glaucoma. Invest Ophthalmol Vis Sci 2022; 63:27. [PMID: 35348587 PMCID: PMC8976936 DOI: 10.1167/iovs.63.3.27] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose To investigate parapapillary choroidal microvasculature dropout (MvD) in branch retinal vein occlusion (BRVO) patients and compare them with open-angle glaucoma (OAG) patients using optical coherence tomography angiography (OCT-A). Methods In total, 85 eyes of BRVO patients and 85 eyes of OAG patients, matched by age, spherical equivalent, and baseline mean deviation (MD) of the visual field (VF), were assessed. MvD was defined as complete loss of microvasculature within the choroidal layer on OCT-A. Linear regression analysis was used to obtain the slope of the MD change of the VF. Results The presence of MvD on OCT-A was significantly more frequent in OAG eyes (63.1%) compared to BRVO eyes (31.8%). BRVO eyes with MvD showed worse baseline MD of the VF than BRVO eyes without MvD (−10.19 ± 8.50 and −7.77 ± 6.46 dB, respectively; P = 0.045). The presence of MvD was the only factor significantly associated with MD change of the VF in OAG eyes. Lower baseline average RNFL thickness, greater MvD angle, and lower macular superficial vessel density were significantly associated with MD change of the VF in BRVO eyes. Conclusions OCT-A of the parapapillary area showed choroidal microvasculature impairment in both BRVO and OAG patients. However, the frequency was higher in glaucoma patients with similar degrees of VF damage, which suggests that the glaucomatous process contributes to MvD development. The effect of MvD on VF change was different between BRVO and OAG, suggesting that the underlying pathogenesis may also be different.
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Affiliation(s)
- Jiwon Baek
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Bucheon St. Mary's Hospital, Gyeonggi-do, South Korea
| | - Hae-Young Lopilly Park
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Seoul St. Mary's Hospital, Seoul, South Korea
| | - Seong Ah Kim
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Seoul St. Mary's Hospital, Seoul, South Korea
| | - Kyung Euy Hong
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Seoul St. Mary's Hospital, Seoul, South Korea
| | - Soo Ji Jeon
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Bucheon St. Mary's Hospital, Gyeonggi-do, South Korea
| | - Da Young Shin
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Eunpyeong St. Mary's Hospital, Seoul, South Korea
| | - Younhea Jung
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Yeouido St. Mary's Hospital, Seoul, South Korea
| | - Chan Kee Park
- Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul, South Korea.,Seoul St. Mary's Hospital, Seoul, South Korea
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13
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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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14
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Yan X, Li M, Chen Z, Zhou X. The anterior scleral thickness in eyes with primary open-angle glaucoma. Graefes Arch Clin Exp Ophthalmol 2022; 260:1601-1610. [PMID: 35067770 PMCID: PMC9007782 DOI: 10.1007/s00417-021-05523-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 12/07/2021] [Accepted: 12/14/2021] [Indexed: 11/24/2022] Open
Abstract
Abstract
Purpose
To investigate the anterior scleral thickness (AST) and its associations with Schlemm’s canal (SC) area, trabecular meshwork (TM) thickness and length, and scleral spur (SS) length in healthy and primary open-angle glaucoma (POAG) groups.
Methods
Thirty-five eyes of 35 healthy subjects and 23 eyes of 23 patients with POAG were included. The AST, SC area, TM thickness and length, and SS length were measured using swept-source optical coherence tomography. AST was measured at 0 mm (AST0), 1 mm (AST1), 2 mm (AST2), and 3 mm (AST3) from SS. Associations between AST and SC area, TM thickness and length, and SS length were also estimated.
Results
AST0 (728.84 ± 99.33 vs. 657.39 ± 67.02 μm, p < 0.001), AST1 (537.79 ± 79.55 vs. 506.83 ± 57.37 μm, p = 0.038), AST3 (571.09 ± 79.15 vs. 532.13 ± 59.84 μm, p = 0.009), SC area (6304.26 ± 1238.72 vs. 4755.64 ± 1122.71 μm2, p < 0.001), TM thickness (107.21 ± 31.26 vs. 94.51 ± 24.18 μm, p = 0.035), TM length (736.20 ± 141.85 vs. 656.43 ± 127.03 μm, p = 0.004), and SS length (219.89 ± 50.29 vs. 174.54 ± 35.58 μm, p < 0.001) were significantly greater in healthy group than in POAG group. In addition, SC area, TM thickness, and SS length were significantly and positively associated with AST0 in the healthy group, whereas no similar associations were observed in the POAG group.
Conclusions
Compared with the healthy group, AST was significantly thinner in the POAG group, which also had smaller SC and TM dimensions. Moreover, the SC area, TM thickness, and SS length were significantly and positively associated with AST in the healthy group. Thus, AST might play an important role in maintaining TM and SC morphology and further in the pathogenesis of POAG.
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Affiliation(s)
- Xiaoqin Yan
- Department of Ophthalmology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
| | - Mu Li
- Department of Ophthalmology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430022, China
| | - Zhiqi Chen
- Department of Ophthalmology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China
| | - Xiongwu Zhou
- Department of Ophthalmology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China.
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15
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Kim J, Gardiner SK, Ramazzotti A, Karuppanan U, Bruno L, Girkin CA, Downs JC, Fazio MA. Strain by virtual extensometers and video-imaging optical coherence tomography as a repeatable metric for IOP-Induced optic nerve head deformations. Exp Eye Res 2021; 211:108724. [PMID: 34375590 PMCID: PMC8511063 DOI: 10.1016/j.exer.2021.108724] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 07/27/2021] [Accepted: 08/06/2021] [Indexed: 11/20/2022]
Abstract
PURPOSE To determine if in vivo strain response of the Optic Nerve Head (ONH) to IOP elevation visualized using Optical Coherence Tomography (OCT) video imaging and quantified using novel virtual extensometers was able to be provided repeatable measurements of tissue specific deformations. METHODS The ONHs of 5 eyes from 5 non-human primates (NHPs) were imaged by Spectralis OCT. A vertical and a horizontal B-scan of the ONH were continuously recorded for 60 s at 6 Hz (video imaging mode) during IOP elevation from 10 to 30 mmHg. Imaging was repeated over three imaging sessions. The 2D normal strain was computed by template-matching digital image correlation using virtual extensometers. ANOVA F-test (F) was used to compare inter-eye, inter-session, and inter-tissue variability for the prelaminar, Bruch's membrane opening (BMO), lamina cribrosa (LC) and choroidal regions (against variance the error term). F-test of the ratio between inter-eye to inter-session variability was used to test for strain repeatability across imaging sessions (FIS). RESULTS Variability of strain across imaging session (F = 0.7263, p = 0.4855) and scan orientation was not significant (F = 1.053, p = 0.3066). Inter session variability of strain was significantly lower than inter-eye variability (FIS = 22.63, p = 0.0428) and inter-tissue variability (FIS = 99.33 p = 0.00998). After IOP elevation, strain was highest in the choroid (-18.11%, p < 0.001), followed by prelaminar tissue (-11.0%, p < 0.001), LC (-3.79%, p < 0.001), and relative change in BMO diameter (-0.57%, p = 0.704). CONCLUSIONS Virtual extensometers applied to video-OCT were sensitive to the eye-specific and tissue-specific mechanical response of the ONH to IOP and were repeatable across imaging sessions.
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Affiliation(s)
- Jihee Kim
- Biomedical Engineering, University of Alabama at Birmingham, Birmingham, AL, USA
| | | | - Andrea Ramazzotti
- Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Udayakumar Karuppanan
- Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Luigi Bruno
- Department of Mechanical, Energy and Management Engineering, University of Calabria, Rende, CS, Italy
| | - Christopher A Girkin
- Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | - J Crawford Downs
- Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Massimo A Fazio
- Biomedical Engineering, University of Alabama at Birmingham, Birmingham, AL, USA; Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA; The Viterbi Family Department of Ophthalmology, UC San Diego, La Jolla, CA, USA.
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16
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Park SA, Komáromy AM. Biomechanics of the optic nerve head and sclera in canine glaucoma: A brief review. Vet Ophthalmol 2021; 24:316-325. [PMID: 34402566 DOI: 10.1111/vop.12923] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 06/04/2021] [Accepted: 07/25/2021] [Indexed: 01/17/2023]
Abstract
Glaucoma is a leading cause of irreversible blindness, a progressive optic neuropathy with retinal ganglion cell (RGC) death beginning in the optic nerve head (ONH). A primary risk factor for developing glaucoma is elevated intraocular pressure (IOP). Reducing IOP is the only treatment proven to be effective at delaying disease progression. Nevertheless, even when patients have their IOP reduced, the majority of them continue to lose vision. There are, in both humans and dogs, significant interindividual variabilities in susceptibilities to IOP-induced optic nerve damage. Vision loss progresses much more slowly in Beagles with open-angle glaucoma (OAG) caused by ADAMTS10 mutation. This can be attributed to the mutation-related altered ocular biomechanical properties. The principal site of optic nerve (ON) damage in glaucoma is the ONH. It is suggested that the biomechanical properties of the ONH and the surrounding peripapillary sclera (PPS) contribute to glaucoma development and progression. As far as the beneficial biomechanical properties of the ONH and PPS for a decreased susceptibility and slow progression of glaucoma, data are inconsistent and conflicting. Recent biomechanical studies on beagles with ADAMTS10 mutation demonstrated that the mutant dogs have mechanically weak posterior sclera. This weakness was associated with a reduced collagen density and a lower proportion of insoluble collagen. These changes, observed before glaucoma development, were considered intrinsic characteristics caused by the mutation rather than a secondary effect of IOP elevation. Further studies of ADAMTS10-OAG may elucidate the effects of altered biomechanical properties of ONH and PPS in determining the glaucoma progression.
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Affiliation(s)
- Shin Ae Park
- Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, Indiana, USA
| | - András M Komáromy
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA
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17
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Sayah DN, Mazzaferri J, Descovich D, Costantino S, Lesk MR. The Association Between Ocular Rigidity and Neuroretinal Damage in Glaucoma. Invest Ophthalmol Vis Sci 2021; 61:11. [PMID: 33151280 PMCID: PMC7671866 DOI: 10.1167/iovs.61.13.11] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose Ocular rigidity (OR) is an important biomechanical property, thought to be relevant in the pathophysiology of open-angle glaucoma (OAG). This study aims to evaluate the relationship between OR and neuroretinal damage caused by glaucoma. Methods One hundred eight subjects (22 with healthy eyes, 23 with suspect discs, and 63 with OAG) were included in this study. OR was measured using a noninvasive optical coherence tomography (OCT)-based method developed by our group. We also measured central corneal thickness (CCT), corneal hysteresis (CH), and corneal resistance factor (CRF). Pearson and partial correlations were performed to evaluate the relationship between OR and glaucomatous damage represented by ganglion cell complex (GCC), retinal nerve fiber layer (RNFL) thicknesses, and neuroretinal rim area. Results Significant positive correlations were found between OR and minimum GCC thickness (r = 0.325, P = 0.001), average GCC thickness (r = 0.320, P = 0.002), rim area (r = 0.344, P < 0.001), and RNFL thickness in the superior (r = 0.225, P = 0.023), and inferior (r = 0.281, P = 0.004) quadrants. These correlations were generally greater than those found for CCT, CH, and CRF. Furthermore, no correlation was found between OR and corneal biomechanical parameters. After adjusting for age, sex, and ethnicity, significant correlations were found between OR and minimum and average GCC thickness (r = 0.357, P = 0.001 and r = 0.344, P = 0.001, respectively), rim area (r = 0.327, P = 0.001), average RNFL thickness (r = 0.331, P = 0.001), and RNFL thickness in the superior (r = 0.296, P = 0.003) and inferior (r = 0.317, P = 0.001) quadrants. Conclusions In this study, we found a positive correlation between structural OCT-based parameters and OR, indicating more neuroretinal damage in eyes with lower OR. These findings could provide insight into the pathophysiology of OAG.
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Affiliation(s)
- Diane N Sayah
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Quebec, Canada.,Department of Ophthalmology, Faculty of Medicine, Université de Montréal, Montreal, Quebec, Canada
| | - Javier Mazzaferri
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Quebec, Canada
| | - Denise Descovich
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Quebec, Canada
| | - Santiago Costantino
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Quebec, Canada.,Department of Ophthalmology, Faculty of Medicine, Université de Montréal, Montreal, Quebec, Canada.,Centre Universitaire d'ophtalmologie de l'Université de Montréal de l'Hôpital Maisonneuve-Rosemont, CIUSSS-E, Montreal, Quebec, Canada
| | - Mark R Lesk
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Quebec, Canada.,Department of Ophthalmology, Faculty of Medicine, Université de Montréal, Montreal, Quebec, Canada.,Centre Universitaire d'ophtalmologie de l'Université de Montréal de l'Hôpital Maisonneuve-Rosemont, CIUSSS-E, Montreal, Quebec, Canada
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18
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Wu HJ, Kuchtey J, Kuchtey RW. Increased Susceptibility to Glaucomatous Damage in Microfibril Deficient Mice. Invest Ophthalmol Vis Sci 2021; 61:28. [PMID: 32797197 PMCID: PMC7441341 DOI: 10.1167/iovs.61.10.28] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Purpose To test whether mice with microfibril deficiency due to the Tsk mutation of fibrillin-1 (Fbn1Tsk/+) have increased susceptibility to pressure-induced retinal ganglion cell (RGC) degeneration. Methods Intraocular pressure (IOP) elevation was induced in Fbn1Tsk/+ and wild type (wt) mice by injecting microbeads into the anterior chamber. Mice were then followed up for four months, with IOP measurements every three to six days. Retinas were stained for Brn3a to determine RGC number. Optic nerve cross-sections were stained with p-phenylene diamine to determine nerve area, axon number, and caliber and thickness of the pia mater. Results Microbead injection induced significant IOP elevation that was significantly less for Fbn1Tsk/+ mice compared with wt. The optic nerves and optic nerve axons were larger, and the elastic fiber-rich pia mater was thinner in Fbn1Tsk/+ mice. Microbead injection resulted in reduced optic nerve size, thicker pia mater, and a slight decrease in axon size. Fbn1Tsk/+ mice had significantly greater loss of RGCs and optic nerve axons compared with wt (14.8% vs. 5.8%, P = 0.002, and 17.0% vs. 7.5%, P = 0.002, respectively). Conclusions Fbn1Tsk/+mice had altered optic nerve structure as indicated by larger optic nerves, larger optic nerve axons and thinner pia mater, consistent with our previous findings. Despite lower IOP elevation, Fbn1Tsk/+mice had greater loss of RGCs and optic nerve axons, suggesting increased susceptibility to IOP-induced optic nerve degeneration in microfibril-deficient mice.
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Affiliation(s)
- Hang-Jing Wu
- Vanderbilt Eye Institute, Vanderbilt University Medical Center, Nashville, Tennessee, United States
| | - John Kuchtey
- Vanderbilt Eye Institute, Vanderbilt University Medical Center, Nashville, Tennessee, United States
| | - Rachel W Kuchtey
- Vanderbilt Eye Institute, Vanderbilt University Medical Center, Nashville, Tennessee, United States.,Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States
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19
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Karimi A, Grytz R, Rahmati SM, Girkin CA, Downs JC. Analysis of the effects of finite element type within a 3D biomechanical model of a human optic nerve head and posterior pole. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2021; 198:105794. [PMID: 33099262 PMCID: PMC7722137 DOI: 10.1016/j.cmpb.2020.105794] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Accepted: 10/05/2020] [Indexed: 05/24/2023]
Abstract
BACKGROUND AND OBJECTIVE Biomechanical stresses and strains can be simulated in the optic nerve head (ONH) using the finite element (FE) method, and various element types have been used. This study aims to investigate the effects of element type on the resulting ONH stresses and strains. METHODS A single eye-specific model was constructed using 3D delineations of anatomic surfaces in a high-resolution, fluorescent, 3D reconstruction of a human posterior eye, then meshed using our simple meshing algorithm at various densities using 4- and 10-noded tetrahedral elements, as well as 8- and 20-noded hexahedral elements. A mesh-free approach was used to assign heterogeneous, anisotropic, hyperelastic material properties to the lamina cribrosa, sclera and pia. The models were subjected to elevated IOP of 45 mmHg after pre-stressing from 0 to 10 mmHg, and solved in the open-source FE package Calculix; results were then interpreted in relation to computational time and simulation accuracy, using the quadratic hexahedral model as the reference standard. RESULTS The 10-noded tetrahedral and 20R-noded hexahedral elements exhibited similar scleral canal and laminar deformations, as well as laminar and scleral stress and strain distributions; the quadratic tetrahedral models ran significantly faster than the quadratic hexahedral models. The linear tetrahedral and hexahedral elements were stiffer compared to the quadratic element types, yielding much lower stresses and strains in the lamina cribrosa. CONCLUSIONS Prior studies have shown that 20-noded hexahedral elements yield the most accurate results in complex models. Results show that 10-noded tetrahedral elements yield very similar results to 20-noded hexahedral elements and so they can be used interchangeably, with significantly lower computational time. Linear element types did not yield acceptable results.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | | | - Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States.
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20
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Unal O, Caglayan M, Kosekahya P, Yulek F, Taslipinar G. Evaluation of Optic Nerve Head Biomechanical Properties in Pseudoexfoliation Glaucoma with Real-time Elastography. Curr Med Imaging 2020; 15:637-644. [PMID: 32008511 DOI: 10.2174/1573405614666180621093908] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Revised: 05/17/2018] [Accepted: 05/28/2018] [Indexed: 12/12/2022]
Abstract
PURPOSE To investigate the biomechanical properties of the optic nerve head in patients with Pseudoexfoliation (PEX) glaucoma using Real-time Elastography (RTE) and to compare these results with those of Primary Open Angle Glaucoma (POAG) patients and healthy subjects. METHODS Twenty eyes of 20 PEX glaucoma patients (PEX group), 20 eyes of 20 POAG patients (POAG group), and 20 eyes of 20 healthy subjects (control group) were enrolled in this prospective study. The strain Ratios of Orbital Fat to Optic Nerve head (ROFON) and lateral rectus muscle to optic nerve head (RLRON) were determined. Comparisons were performed using Chi-square, Kruskal Wallis, Mann-Whitney U, and One-way ANOVA tests. RESULTS The strain ratios of orbital fat to optic nerve head were 2.34, 6.85 and 1.76 in PEX glaucoma, POAG, and control groups, respectively (p<0.001). The strain ratios of the lateral rectus muscle to the optic nerve head were 0.51, 0.82, and 0.55 in PEX glaucoma, POAG, and control groups, respectively (p=0.256). CONCLUSION The strain ratios of orbital fat to optic nerve head were different in PEX glaucoma patients than in POAG and control groups. RTE can provide biomechanical assessment of the optic nerve head in a non-invasive, quick, easily accessible, and user-friendly manner.
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Affiliation(s)
- Ozlem Unal
- Department of Radiology, Yildirim Beyazit University, Ataturk Research and Training Hospital, Ankara, Turkey
| | - Mehtap Caglayan
- Department of Ophthalmology, Yildirim Beyazit University, Ataturk Research and Training Hospital, Ankara, Turkey
| | - Pinar Kosekahya
- Ulucanlar Eye Research and Training Hospital, Ankara, Turkey
| | - Fatma Yulek
- Department of Ophthalmology, Yildirim Beyazit University, Ataturk Research and Training Hospital, Ankara, Turkey
| | - Guzin Taslipinar
- Department of Ophthalmology, Yildirim Beyazit University, Ataturk Research and Training Hospital, Ankara, Turkey
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21
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Chuangsuwanich T, Hung PT, Wang X, Liang LH, Schmetterer L, Boote C, Girard MJA. Morphometric, Hemodynamic, and Biomechanical Factors Influencing Blood Flow and Oxygen Concentration in the Human Lamina Cribrosa. Invest Ophthalmol Vis Sci 2020; 61:3. [PMID: 32271886 PMCID: PMC7401712 DOI: 10.1167/iovs.61.4.3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Purpose We developed a combined biomechanical and hemodynamic model of the human eye to estimate blood flow and oxygen concentration within the lamina cribrosa (LC) and rank the factors that influence LC oxygen concentration. Methods We generated 5000 finite-element eye models with detailed microcapillary networks of the LC and computed the oxygen concentration of the lamina retinal ganglion cell axons. For each model, we varied the intraocular pressure (IOP) from 10 mm Hg to 55 mm Hg in 5-mm Hg increments, the cerebrospinal fluid pressure (13 ± 2 mm Hg), cup depth (0.2 ± 0.1 mm), scleral stiffness (±20% of the mean values), LC stiffness (0.41 ± 0.2 MPa), LC radius (1.2 ± 0.12 mm), average LC pore size (5400 ± 2400 µm2), the microcapillary arrangement (radial, isotropic, or circumferential), and perfusion pressure (50 ± 9 mm Hg). Blood flow was assumed to originate from the LC periphery and drain via the central retinal vein. Finally, we performed linear regressions to rank the influence of each factor on the LC tissue oxygen concentration. Results LC radius and perfusion pressure were the most important factors in influencing the oxygen concentration of the LC. IOP was another important parameter, and eyes with higher IOP had higher compressive strain and slightly lower oxygen concentration. In general, superior–inferior regions of the LC had significantly lower oxygen concentration than the nasal–temporal regions, resulting in an hourglass pattern of oxygen deficiency. Conclusions To the best of our knowledge, this study is the first to implement a comprehensive hemodynamical model of the eye that accounts for the biomechanical forces and morphological parameters of the LC. The results provide further insight into the possible relationship of biomechanical and vascular pathways leading to ischemia-induced optic neuropathy.
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22
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Lazkani N, Butler J, Rickard MJA, Truitt S, Kawaguchi NK, DeWolf AJ, Van Zant CA, Villegas JP, Hassel AR, Park JJ, Jones CF. Development of a Nanofabricated Sensor for Monitoring Intraocular Pressure via Ocular Tissue Strain. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020; 2019:4363-4367. [PMID: 31946834 DOI: 10.1109/embc.2019.8857430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
As the number of individuals developing glaucoma is increasing, researchers and ophthalmologists are exploring new approaches to monitor intraocular pressure, which is a critical measurement for glaucoma detection. Current monitoring methods, such as implantable pressure sensors and wearable contact lenses with sensors, are being explored in eye research clinics. However, these systems currently lack in providing 24 hours data through a practical platform for large-scale use. This paper presents a novel method that provides constant measurements of the scleral strain, which is correlated with the change of intraocular pressure, using a nanofabricated discrete resistor array implant sensor. A preliminary bench-top test was performed using the sensor, and it showed that the nanofabricated 1.6 mm by 2.7 mm resistor array exhibits discrete sensing levels at increments of 41 ohms as a fixture needle traversed approximately half of the array. Though the nanosensor is in the prototype developing stage, it promises a new modality for constant, remote, and around the clock glaucoma monitoring.
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23
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Geraghty B, Abass A, Eliasy A, Jones SW, Rama P, Kassem W, Akhtar R, Elsheikh A. Inflation experiments and inverse finite element modelling of posterior human sclera. J Biomech 2019; 98:109438. [PMID: 31679759 DOI: 10.1016/j.jbiomech.2019.109438] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Revised: 10/16/2019] [Accepted: 10/17/2019] [Indexed: 11/30/2022]
Abstract
The complexity of inverse finite element modelling methods used in ocular biomechanics research has significantly increased in recent years in order to produce material parameters that capture microscale tissue behaviour. This study presents a more accessible method for researchers to optimise sclera material parameters for use in finite element studies where macroscale sclera displacements are required. Five human donor sclerae aged between 36 and 72 years were subjected to cycles of internal pressure up to 61 mmHg using a custom-built inflation rig. Displacements were measured using a laser beam and two cameras through a digital image correlation algorithm. Specimen-specific finite element models incorporating regional thickness variation and sclera surface topography were divided into six circumferential regions. An inverse finite element procedure was used to optimise Ogden material parameters for each region. The maximum root mean squared (RMS) error between the numerical and experimental displacements within individual specimens was 17.5 µm. The optimised material parameters indicate a gradual reduction in material stiffness (as measured by the tangent modulus) from the equator to the posterior region at low-stress levels up to 0.005 MPa. The variation in stiffness between adjacent regions became gradually less apparent and statistically insignificant at higher stresses. The study demonstrated how inflation testing combined with inverse modelling could be used to effectively characterise regional material properties capable of reproducing global sclera displacements. The material properties were found to vary between specimens, and it is expected that age could be a contributing factor behind this variation.
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Affiliation(s)
- Brendan Geraghty
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, L7 8TX, UK.
| | - Ahmed Abass
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Ashkan Eliasy
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Stephen W Jones
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Paolo Rama
- Ophthalmology Department, San Raffaelle Scientific Institute, Milan, Italy
| | - Wael Kassem
- Division of Construction Engineering, Umm Al-Qura University, College of Engineering at Al-Qunfudah, Al-Qunfudah 21912, Saudi Arabia
| | - Riaz Akhtar
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK; National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields, Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, UK; School of Biological Science and Biomedical Engineering, Beihang University, Beijing, China
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In vivo optic nerve head mechanical response to intraocular and cerebrospinal fluid pressure: imaging protocol and quantification method. Sci Rep 2018; 8:12639. [PMID: 30140057 PMCID: PMC6107503 DOI: 10.1038/s41598-018-31052-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 08/09/2018] [Indexed: 01/22/2023] Open
Abstract
This study presents a quantification method for the assessment of the optic nerve head (ONH) deformations of the living human eye under acute intraocular pressure (IOP) elevation and change of cerebrospinal fluid pressure (CSFP) with body position. One eye from a brain-dead organ donor with open-angle glaucoma was imaged by optical coherence tomography angiography during an acute IOP and CSFP elevation test. Volumetric 3D strain was computed by digital volume correlation. With increase in IOP the shear strain consistently increased in both sitting and supine position (p < 0.001). When CSFP was increased at constant IOP by changing body position, a global reduction in the ONH strain was observed (−0.14% p = 0.0264). Strain in the vasculature was significantly higher than in the structural tissue (+0.90%, p = 0.0002). Retinal nerve fiber layer (RNFL) thickness strongly associated (ρ = −0.847, p = 0.008) with strain in the peripapillary sclera (ppScl) but not in the retina (p = 0.433) and lamina (p = 0.611). These initial results show that: CSFP independently to IOP modulates strain in the human ONH; ppScl strains are greater than strains in lamina and retina; strain in the retinal vasculature was higher than in the structural tissue; In this glaucoma eye, higher ppScl strain associated with lower RNFL thickness.
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Schwaner SA, Kight AM, Perry RN, Pazos M, Yang H, Johnson EC, Morrison JC, Burgoyne CF, Ross Ethier C. A Methodology for Individual-Specific Modeling of Rat Optic Nerve Head Biomechanics in Glaucoma. J Biomech Eng 2018; 140:2679249. [PMID: 30003249 PMCID: PMC6056184 DOI: 10.1115/1.4039998] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2018] [Revised: 04/10/2018] [Indexed: 12/20/2022]
Abstract
Glaucoma is the leading cause of irreversible blindness and involves the death of retinal ganglion cells (RGCs). Although biomechanics likely contributes to axonal injury within the optic nerve head (ONH), leading to RGC death, the pathways by which this occurs are not well understood. While rat models of glaucoma are well-suited for mechanistic studies, the anatomy of the rat ONH is different from the human, and the resulting differences in biomechanics have not been characterized. The aim of this study is to describe a methodology for building individual-specific finite element (FE) models of rat ONHs. This method was used to build three rat ONH FE models and compute the biomechanical environment within these ONHs. Initial results show that rat ONH strains are larger and more asymmetric than those seen in human ONH modeling studies. This method provides a framework for building additional models of normotensive and glaucomatous rat ONHs. Comparing model strain patterns with patterns of cellular response seen in studies using rat glaucoma models will help us to learn more about the link between biomechanics and glaucomatous cell death, which in turn may drive the development of novel therapies for glaucoma.
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Affiliation(s)
- Stephen A. Schwaner
- George W. Woodruff School of Mechanical Engineering,
Georgia Institute of Technology,
315 Ferst Drive,
2306 IBB,
Atlanta, GA 30332
e-mail:
| | - Alison M. Kight
- Coulter Department of Biomedical Engineering,
Georgia Institute of Technology/Emory University,
Atlanta, GA 30332
e-mail:
| | - Robert N. Perry
- Coulter Department of Biomedical Engineering,
Georgia Institute of Technology/Emory University,
Atlanta, GA 30332
e-mail:
| | - Marta Pazos
- Institut Clínic d'Oftalmologia,
Hospital Clínic de Barcelona,
Barcelona 08036, Spain
e-mail:
| | - Hongli Yang
- Optic Nerve Head Research Laboratory,
Discoveries in Sight Research Laboratories,
Devers Eye Institute, Legacy Health System,
Portland, OR 97210
e-mail:
| | - Elaine C. Johnson
- The Kenneth C. Swan Ocular Neurobiology Laboratory,
Casey Eye Institute,
Oregon Health and Science University,
Portland, OR 97239
e-mail:
| | - John C. Morrison
- The Kenneth C. Swan Ocular Neurobiology Laboratory,
Casey Eye Institute,
Oregon Health and Science University,
Portland, OR 97239
e-mail:
| | - Claude F. Burgoyne
- Optic Nerve Head Research Laboratory,
Discoveries in Sight Research Laboratories,
Devers Eye Institute,
Legacy Health System,
Portland, OR 97210
e-mail:
| | - C. Ross Ethier
- Coulter Department of Biomedical Engineering,
Georgia Institute of Technology/Emory University,
Atlanta, GA 30332
e-mail:
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Park HYL, Kim JW, Park CK. Choroidal Microvasculature Dropout Is Associated with Progressive Retinal Nerve Fiber Layer Thinning in Glaucoma with Disc Hemorrhage. Ophthalmology 2018; 125:1003-1013. [DOI: 10.1016/j.ophtha.2018.01.016] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 01/09/2018] [Accepted: 01/10/2018] [Indexed: 10/17/2022] Open
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Rusovici R, Dalli D, Mitra K, Ganiban G, Grace M, Mazzocchi R, Calhoun M. Finite element modeling, validation, and parametric investigations of a retinal reattachment stent. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2017; 33. [PMID: 28349647 DOI: 10.1002/cnm.2885] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 02/06/2017] [Accepted: 03/22/2017] [Indexed: 06/06/2023]
Abstract
A new retinal reattachment surgical procedure is based on a stent that is deployed to press the retina back in place. An eye-stent finite element model studied the strain induced by the stent on retina. Finite element model simulations were performed for several stent geometric configurations (number of loops, wire diameter, and intraocular pressure). The finite element model was validated against experiment. Parametric studies demonstrated that stents could be successfully designed so that the maximum strain would be below permanent damage strain threshold of 2%.
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Affiliation(s)
- R Rusovici
- Mechanical and Aerospace Engineering, Florida Institute of Technology, 150 W. University Blvd., Melbourne, Florida, 32901, USA
| | - D Dalli
- Mechanical and Aerospace Engineering, Florida Institute of Technology, 150 W. University Blvd., Melbourne, Florida, 32901, USA
| | - K Mitra
- Mechanical and Aerospace Engineering, Florida Institute of Technology, 150 W. University Blvd., Melbourne, Florida, 32901, USA
| | - G Ganiban
- OptiStent Inc., Surgery, Rockledge, Florida, USA
| | - M Grace
- Department of Biological Sciences, Florida Institute of Technology, Melbourne, Florida, USA
| | - R Mazzocchi
- OptiStent Inc., Management, Rockledge, Florida, USA
| | - M Calhoun
- OptiStent Inc., R and D, 2700 Northeast 24th Street, Lighthouse Point, Florida, 33064, USA
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28
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Kosekahya P, Caglayan M, Unal O, Yuzbasioglu S, Koc M, Ucgul Atilgan C, Yulek F. Optic Nerve Head Elastometry in Both Eyes of Patients with Unilateral Non-arteritic Anterior Ischaemic Optic Neuropathy - May It Be a Novel Aspect of the Pathogenesis? Neuroophthalmology 2017; 42:222-228. [PMID: 30042792 DOI: 10.1080/01658107.2017.1397702] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 10/24/2017] [Accepted: 10/24/2017] [Indexed: 12/21/2022] Open
Abstract
In this prospective study, the biomechanical properties of optic nerve head (ONH) and cornea in both eyes of patients with non-arteritic anterior ischaemic optic neuropathy and healthy control eyes were investigated. ONH elastometry was measured with real-time elastography, and corneal elastometry was measured with ocular response analyser. Elastometry of cornea and ONH was lower in both eyes of patients with unilateral non-arteritic ischaemic optic neuropathy than in healthy control eyes. The role of these biomechanical differences in the pathogenesis of non-arteritic ischaemic optic neuropathy should be investigated further.
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Affiliation(s)
- Pinar Kosekahya
- Ulucanlar Eye Training and Research Hospital, Ankara, Turkey
| | - Mehtap Caglayan
- Department of Ophthalmology, Mardin State Hospital, Mardin, Turkey
| | - Ozlem Unal
- Department of Radiology, Ataturk Training and Research Hospital, Ankara, Turkey
| | - Sema Yuzbasioglu
- Department of Ophthalmology, Ataturk Training and Research Hospital, Ankara, Turkey
| | - Mustafa Koc
- Ulucanlar Eye Training and Research Hospital, Ankara, Turkey
| | | | - Fatma Yulek
- Department of Ophthalmology, Yildirim Beyazit University Ataturk Research and Training Hospital, Ankara, Turkey
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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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30
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Yang H, Reynaud J, Lockwood H, Williams G, Hardin C, Reyes L, Stowell C, Gardiner SK, Burgoyne CF. The connective tissue phenotype of glaucomatous cupping in the monkey eye - Clinical and research implications. Prog Retin Eye Res 2017; 59:1-52. [PMID: 28300644 PMCID: PMC5603293 DOI: 10.1016/j.preteyeres.2017.03.001] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 02/14/2017] [Accepted: 03/06/2017] [Indexed: 10/20/2022]
Abstract
In a series of previous publications we have proposed a framework for conceptualizing the optic nerve head (ONH) as a biomechanical structure. That framework proposes important roles for intraocular pressure (IOP), IOP-related stress and strain, cerebrospinal fluid pressure (CSFp), systemic and ocular determinants of blood flow, inflammation, auto-immunity, genetics, and other non-IOP related risk factors in the physiology of ONH aging and the pathophysiology of glaucomatous damage to the ONH. The present report summarizes 20 years of technique development and study results pertinent to the characterization of ONH connective tissue deformation and remodeling in the unilateral monkey experimental glaucoma (EG) model. In it we propose that the defining pathophysiology of a glaucomatous optic neuropathy involves deformation, remodeling, and mechanical failure of the ONH connective tissues. We view this as an active process, driven by astrocyte, microglial, fibroblast and oligodendrocyte mechanobiology. These cells, and the connective tissue phenomena they propagate, have primary and secondary effects on retinal ganglion cell (RGC) axon, laminar beam and retrolaminar capillary homeostasis that may initially be "protective" but eventually lead to RGC axonal injury, repair and/or cell death. The primary goal of this report is to summarize our 3D histomorphometric and optical coherence tomography (OCT)-based evidence for the early onset and progression of ONH connective tissue deformation and remodeling in monkey EG. A second goal is to explain the importance of including ONH connective tissue processes in characterizing the phenotype of a glaucomatous optic neuropathy in all species. A third goal is to summarize our current efforts to move from ONH morphology to the cell biology of connective tissue remodeling and axonal insult early in the disease. A final goal is to facilitate the translation of our findings and ideas into neuroprotective interventions that target these ONH phenomena for therapeutic effect.
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Affiliation(s)
- Hongli Yang
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Juan Reynaud
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Howard Lockwood
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Galen Williams
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Christy Hardin
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Luke Reyes
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Cheri Stowell
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Stuart K Gardiner
- Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States
| | - Claude F Burgoyne
- Devers Eye Institute, Optic Nerve Head Research Laboratory, Legacy Research Institute, Portland, OR, United States; Devers Eye Institute, Discoveries in Sight Research Laboratories, Legacy Research Institute, Portland, OR, United States.
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DAI PEISHAN, ZHAO YALI, SHENG HANWEI, LI LING, WU JING, HAN HAN. SIMULATING THE EFFECTS OF ELEVATED INTRAOCULAR PRESSURE ON OCULAR STRUCTURES USING A GLOBAL FINITE ELEMENT MODEL OF THE HUMAN EYE. J MECH MED BIOL 2017. [DOI: 10.1142/s0219519417500385] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Elevated intraocular pressure (IOP) may be the primary risk factor to the development of glaucoma. Finite element (FE) modeling is commonly considered as an effective method to quantitatively analyze pathogenesis of glaucoma. Recent researches focus on establishing partial human eye models. A refined global human eye model was developed using ANSYS software to investigate the correlation between IOP elevation and biomechanical responses. First, the pressure transferring process according to IOP elevation in the whole eye was analyzed to simulate the effects of IOP elevation on glaucoma. Then, the biomechanical responses of the anterior eye segment under various pressure differences between the anterior and posterior chambers (AC and PC) were analyzed to simulate posterior nonadhesion of iris and posterior synechia. This global eye model not only simulated the responses of elevated IOP on ocular structures, but also revealed the process of pressure transferring among each tissue from the anterior eye segment to the optic nerve head (ONH) region. The local mechanical characteristics of the ocular structures obtained from the global model agreed with previous findings. This global model may shed light on the studies of multifactorial glaucoma.
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Affiliation(s)
- PEISHAN DAI
- Department of Biomedical Engineering, School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, P. R. China
| | - YALI ZHAO
- Department of Biomedical Engineering, School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, P. R. China
| | - HANWEI SHENG
- Department of Biomedical Engineering, School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, P. R. China
| | - LING LI
- Department of Biomedical Engineering, School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, P. R. China
| | - JING WU
- Department of Biomedical Engineering, School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, P. R. China
| | - HAN HAN
- Department of Electrical and Computer Engineering, Faculty of Engineering, National University of Singapore, Singapore 117576, Singapore
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Jia X, Yu J, Liao SH, Duan XC. Biomechanics of the sclera and effects on intraocular pressure. Int J Ophthalmol 2016; 9:1824-1831. [PMID: 28003987 DOI: 10.18240/ijo.2016.12.21] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 08/03/2016] [Indexed: 11/23/2022] Open
Abstract
Accumulating evidence indicates that glaucoma is a multifactorial neurodegenerative disease characterized by the loss of retinal ganglion cells (RGC), resulting in gradual and progressive permanent loss of vision. Reducing intraocular pressure (IOP) remains the only proven method for preventing and delaying the progression of glaucomatous visual impairment. However, the specific role of IOP in optic nerve injury remains controversial, and little is known about the biomechanical mechanism by which elevated IOP leads to the loss of RGC. Published studies suggest that the biomechanical properties of the sclera and scleral lamina cribrosa determine the biomechanical changes of optic nerve head, and play an important role in the pathologic process of loss of RGC and optic nerve damage. This review focuses on the current understanding of biomechanics of sclera in glaucoma and provides an overview of the possible interactions between the sclera and IOP. Treatments and interventions aimed at the sclera are also discussed.
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Affiliation(s)
- Xu Jia
- Department of Ophthalmology, the Second Xiangya Hospital, Central South University, Changsha 410011, Hunan Province, China
| | - Juan Yu
- Department of Ophthalmology, the First Hospital of Hunan University of Chinese Medicine, Changsha 410011, Hunan Province, China
| | - Sheng-Hui Liao
- School of Information Science and Engineering, Central South University, Changsha 410011, Hunan Province, China
| | - Xuan-Chu Duan
- Department of Ophthalmology, the Second Xiangya Hospital, Central South University, Changsha 410011, Hunan Province, China
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DAI PEISHAN, HAN HAN, ZHAO YALI, FAN MIN. FINITE ELEMENT ANALYSIS OF THE MECHANICAL CHARACTERISTICS OF GLAUCOMA. J MECH MED BIOL 2016. [DOI: 10.1142/s0219519416500603] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Purpose: Construct a finite element model of the human eye to quantitatively analyze the mechanical characteristics of the human eye, especially the glaucoma damage process of the optic nerve head (ONH). Method: First, the geometry model of the human eye with nonuniform thickness was established based on a reasonable hypothesis and assumptions. Because the ONH is an important factor for glaucoma, we refine the structure of the ONH with lamina cribrosa. Then, mesh division was applied for finite element analysis. To simplify the complexity of the analysis, the materials of the model were assumed to be isotropic linear elastic materials, and physical properties such as Young’s modulus and Poisson’s ratio were set according to published literature. Next, proper constraints and loads were applied to the model and solved with a finite element method. Result: A finite element model of the human eye was created to simulate the mechanical characteristics of the eye structures under high intraocular pressure (IOP). The ONH depressed 1.057[Formula: see text]mm under 0.009[Formula: see text]MPa pressure to simulate high IOP. Conclusion: The constructed model is able to quantitatively simulate excavation of the optic disc and damage of the optic nerve. The result proved Houcheng Liang’s hypothesis about the ONH damage mechanism in glaucoma.
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Affiliation(s)
- PEISHAN DAI
- Department of Biomedical Engineering, School of Geosciences and Info-Physics, Central South University, Changsha 410083, P. R. China
| | - HAN HAN
- Department of Electrical and Computer Engineering, National University of Singapore, S117576, Singapore
| | - YALI ZHAO
- Department of Biomedical Engineering, School of Geosciences and Info-Physics, Central South University, Changsha 410083, P. R. China
| | - MIN FAN
- Department of Education and Law, Hunan Women’s University, Changsha 410004, P. R. China
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Qu J, Chen H, Zhu L, Ambalavanan N, Girkin CA, Murphy-Ullrich JE, Downs JC, Zhou Y. High-Magnitude and/or High-Frequency Mechanical Strain Promotes Peripapillary Scleral Myofibroblast Differentiation. Invest Ophthalmol Vis Sci 2016; 56:7821-30. [PMID: 26658503 DOI: 10.1167/iovs.15-17848] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
PURPOSE To determine the effects of altered mechanical strain on human peripapillary scleral (ppSc) fibroblast-to-myofibroblast differentiation. METHODS Eight human ppSc fibroblast cultures were isolated from three paired eyes and two unilateral eyes of five donors using an explant approach. Human ppSc fibroblast isolates were subjected to 1% and 4% cyclic strain at 0.05 to 5 Hz for 24 hours. Levels of α smooth muscle actin (αSMA) mRNA and protein were determined by real-time PCR and immunoblot. Incorporation of αSMA into actin stress fibers was evaluated by confocal immunofluorescent microscopy. Myofibroblast contractility was measured by fibroblast-populated three-dimensional collagen gel contraction assay and phosphorylation of myosin light chain (MLC20). RESULTS Human ppSc fibroblasts contained 6% to 47% fully differentiated myofibroblasts before strain application; 4% cyclic strain increased αSMA mRNA and protein expression in ppSc fibroblasts compared with 1% strain applied at 5 Hz, but not at lower frequencies. Seven of eight ppSc fibroblast isolates responded to high-magnitude and high-frequency strain with increased cellular contractility and increased MLC20 phosphorylation. In addition, increasing strain frequency promoted αSMA expression in ppSc fibroblasts under both 1% and 4% strain conditions. CONCLUSIONS High-magnitude and/or high-frequency mechanical strain promotes differentiation of human ppSc fibroblasts into contractile myofibroblasts, a fibroblast phenotypic change known to be key to tissue injury-repair responses. These findings suggest that the cellular constituent of ppSc may play an important role in the regulation of optic nerve head biomechanics in response to injurious IOP fluctuations.
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Affiliation(s)
- Jing Qu
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Huaping Chen
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Lanyan Zhu
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States 2The Second Xiangya Hospital, Central-South University, Changsha, Hunan, China
| | - Namasivayam Ambalavanan
- Department of Pediatrics, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Christopher A Girkin
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Joanne E Murphy-Ullrich
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States 5Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - J Crawford Downs
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States 6Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Yong Zhou
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States 4Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States 6Department of Biomedical Engineering, University of Alab
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Stockslager MA, Samuels BC, Allingham RR, Klesmith ZA, Schwaner SA, Forest CR, Ethier CR. System for Rapid, Precise Modulation of Intraocular Pressure, toward Minimally-Invasive In Vivo Measurement of Intracranial Pressure. PLoS One 2016; 11:e0147020. [PMID: 26771837 PMCID: PMC4714900 DOI: 10.1371/journal.pone.0147020] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 12/27/2015] [Indexed: 11/18/2022] Open
Abstract
Pathologic changes in intracranial pressure (ICP) are commonly observed in a variety of medical conditions, including traumatic brain injury, stroke, brain tumors, and glaucoma. However, current ICP measurement techniques are invasive, requiring a lumbar puncture or surgical insertion of a cannula into the cerebrospinal fluid (CSF)-filled ventricles of the brain. A potential alternative approach to ICP measurement leverages the unique anatomy of the central retinal vein, which is exposed to both intraocular pressure (IOP) and ICP as it travels inside the eye and through the optic nerve; manipulating IOP while observing changes in the natural pulsations of the central retinal vein could potentially provide an accurate, indirect measure of ICP. As a step toward implementing this technique, we describe the design, fabrication, and characterization of a system that is capable of manipulating IOP in vivo with <0.1 mmHg resolution and settling times less than 2 seconds. In vitro tests were carried out to characterize system performance. Then, as a proof of concept, we used the system to manipulate IOP in tree shrews (Tupaia belangeri) while video of the retinal vessels was recorded and the caliber of a selected vein was quantified. Modulating IOP using our system elicited a rapid change in the appearance of the retinal vein of interest: IOP was lowered from 10 to 3 mmHg, and retinal vein caliber sharply increased as IOP decreased from 7 to 5 mmHg. Another important feature of this technology is its capability to measure ocular compliance and outflow facility in vivo, as demonstrated in tree shrews. Collectively, these proof-of-concept demonstrations support the utility of this system to manipulate IOP for a variety of useful applications in ocular biomechanics, and provide a framework for further study of the mechanisms of retinal venous pulsation.
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Affiliation(s)
- Max A. Stockslager
- G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States of America
| | - Brian C. Samuels
- Department of Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States of America
| | - R. Rand Allingham
- Department of Ophthalmology, Duke University School of Medicine, Durham, NC, United States of America
| | - Zoe A. Klesmith
- G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States of America
| | - Stephen A. Schwaner
- G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States of America
| | - Craig R. Forest
- G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States of America
| | - C. Ross Ethier
- G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States of America
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States of America
- * E-mail:
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Buckhurst HD, Gilmartin B, Cubbidge RP, Logan NS. Measurement of Scleral Thickness in Humans Using Anterior Segment Optical Coherent Tomography. PLoS One 2015. [PMID: 26218188 PMCID: PMC4517791 DOI: 10.1371/journal.pone.0132902] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Anterior segment optical coherent tomography (AS-OCT, Visante; Zeiss) is used to examine meridional variation in anterior scleral thickness (AST) and its association with refractive error, ethnicity and gender. Scleral cross-sections of 74 individuals (28 males; 46 females; aged between 18-40 years (27.7±5.3)) were sampled twice in random order in 8 meridians: [superior (S), inferior (I), nasal (N), temporal (T), superior-temporal (ST), superior-nasal (SN), inferior-temporal (IT) and inferior-nasal (IN)]. AST was measured in 1mm anterior-to-posterior increments (designated the A-P distance) from the scleral spur (SS) over a 6mm distance. Axial length and refractive error were measured with a Zeiss IOLMaster biometer and an open-view binocular Shin-Nippon autorefractor. Intra- and inter-observer variability of AST was assessed for each of the 8 meridians. Mixed repeated measures ANOVAs tested meridional and A-P distance differences in AST with refractive error, gender and ethnicity. Only right eye data were analysed. AST (mean±SD) across all meridians and A-P distances was 725±46 μm. Meridian SN was the thinnest (662±57 μm) and I the thickest (806±60 μm). Significant differences were found between all meridians (p<0.001), except S:ST, IT:IN, IT:N and IN:N. Significant differences between A-P distances were found except between SS and 6 mm and between 2 and 4 mm. AST measurements at 1mm (682±48 μm) were the thinnest and at 6mm (818±49 μm) the thickest (p<0.001); a significant interaction occurred between meridians and A-P distances (p<0.001). AST was significantly greater (p<0.001) in male subjects but no significant differences were found between refractive error or ethnicity. Significant variations in AST occur with regard to meridian and distance from the SS and may have utility in selecting optimum sites for pharmaceutical or surgical intervention.
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Affiliation(s)
- Hetal D. Buckhurst
- Plymouth University, School of Health Professions, Peninsula Allied Health Centre, Derriford Road, Plymouth, United Kingdom
- * E-mail:
| | - Bernard Gilmartin
- Aston University, School of Life & Health Sciences, Birmingham, United Kingdom
| | - Robert P. Cubbidge
- Aston University, School of Life & Health Sciences, Birmingham, United Kingdom
| | - Nicola S Logan
- Aston University, School of Life & Health Sciences, Birmingham, United Kingdom
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Coudrillier B, Pijanka J, Jefferys J, Sorensen T, Quigley HA, Boote C, Nguyen TD. Effects of age and diabetes on scleral stiffness. J Biomech Eng 2015; 137:2196535. [PMID: 25751456 DOI: 10.1115/1.4029986] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2014] [Indexed: 02/05/2023]
Abstract
The effects of diabetes on the collagen structure and material properties of the sclera are unknown but may be important to elucidate whether diabetes is a risk factor for major ocular diseases such as glaucoma. This study provides a quantitative assessment of the changes in scleral stiffness and collagen fiber alignment associated with diabetes. Posterior scleral shells from five diabetic donors and seven non-diabetic donors were pressurized to 30 mm Hg. Three-dimensional surface displacements were calculated during inflation testing using digital image correlation (DIC). After testing, each specimen was subjected to wide-angle X-ray scattering (WAXS) measurements of its collagen organization. Specimen-specific finite element models of the posterior scleras were generated from the experimentally measured geometry. An inverse finite element analysis was developed to determine the material properties of the specimens, i.e., matrix and fiber stiffness, by matching DIC-measured and finite element predicted displacement fields. Effects of age and diabetes on the degree of fiber alignment, matrix and collagen fiber stiffness, and mechanical anisotropy were estimated using mixed effects models accounting for spatial autocorrelation. Older age was associated with a lower degree of fiber alignment and larger matrix stiffness for both diabetic and non-diabetic scleras. However, the age-related increase in matrix stiffness was 87% larger in diabetic specimens compared to non-diabetic controls and diabetic scleras had a significantly larger matrix stiffness (p = 0.01). Older age was associated with a nearly significant increase in collagen fiber stiffness for diabetic specimens only (p = 0.06), as well as a decrease in mechanical anisotropy for non-diabetic scleras only (p = 0.04). The interaction between age and diabetes was not significant for all outcomes. This study suggests that the age-related increase in scleral stiffness is accelerated in eyes with diabetes, which may have important implications in glaucoma.
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Argento A, Kim W, Rozsa FW, DeBolt KL, Zikanova S, Richards JR. Shear behavior of bovine scleral tissue. J Biomech Eng 2014; 136:1870708. [PMID: 24805965 DOI: 10.1115/1.4027615] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2013] [Accepted: 05/08/2014] [Indexed: 11/08/2022]
Abstract
Ocular tissue properties have been widely studied in tension and compression for humans and a variety of animals. However, direct shear testing of the tissues of the sclera appear to be absent from the literature even though modeling, analyses, and anatomical studies have indicated that shear may play a role in the etiology of primary open angle glaucoma (POAG). In this work, the mechanical behavior of bovine scleral tissue in shear has been studied in both out-of-plane and in-plane modes of deformation. Stress-strain and relaxation tests were conducted on tissue specimens at controlled temperature and hydration focusing on trends related to specimen location and orientation. There was generally found to be no significant effect of specimen orientation and angular location in the globe on shear stiffness in both modes. The in-plane response, which is the primary load carrying mode, was found to be substantially stiffer than the out-of-plane mode. Also, within the in-plane studies, tissue further from the optic nerve was stiffer than the near tissue. The viscosity coefficient of the tissue varied insignificantly with distance from the optic nerve, but overall was much higher in-plane than out-of-plane.
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Grytz R, Fazio MA, Libertiaux V, Bruno L, Gardiner S, Girkin CA, Downs JC. Age- and race-related differences in human scleral material properties. Invest Ophthalmol Vis Sci 2014; 55:8163-72. [PMID: 25389203 DOI: 10.1167/iovs.14-14029] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE We tested the hypothesis that there are age- and race-related differences in posterior scleral material properties, using eyes from human donors of European (20-90 years old, n = 40 eyes) and African (23-74 years old, n = 22 eyes) descent. METHODS Inflation tests on posterior scleral shells were performed while full-field, three-dimensional displacements were recorded using laser speckle interferometry. Scleral material properties were fit to each eye using a microstructure-based constitutive formulation that incorporates the collagen fibril crimp and the local anisotropic collagen architecture. The effects of age and race were estimated using Generalized Estimating Equations, while accounting for intradonor correlations. RESULTS The shear modulus significantly increased (P = 0.038) and collagen fibril crimp angle significantly decreased with age (P = 0.002). Donors of African descent exhibited a significantly higher shear modulus (P = 0.019) and showed evidence of a smaller collagen fibril crimp angle (P = 0.057) compared to donors of European descent. The in-plane strains in the peripapillary sclera were significantly lower with age (P < 0.015) and African ancestry (P < 0.015). CONCLUSIONS The age- and race-related differences in scleral material properties result in a loss of scleral compliance due to a higher shear stiffness and a lower level of stretch at which the collagen fibrils uncrimp. The loss of compliance should lead to larger high frequency IOP fluctuations and changes in the optic nerve head (ONH) biomechanical response in the elderly and in persons of African ancestry, and may contribute to the higher susceptibility to glaucoma in these at-risk populations.
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Affiliation(s)
- Rafael Grytz
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - Massimo A Fazio
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - Vincent Libertiaux
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - Luigi Bruno
- Mechanical Engineering, University of Calabria, Calabria, Italy
| | - Stuart Gardiner
- Discoveries in Sight Research Laboratories, Devers Eye Institute, Portland, Oregon, United States
| | - Christopher A Girkin
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - J Crawford Downs
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
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Fazio MA, Grytz R, Morris JS, Bruno L, Girkin CA, Downs JC. Human scleral structural stiffness increases more rapidly with age in donors of African descent compared to donors of European descent. Invest Ophthalmol Vis Sci 2014; 55:7189-98. [PMID: 25237162 PMCID: PMC4228862 DOI: 10.1167/iovs.14-14894] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Accepted: 09/08/2014] [Indexed: 11/24/2022] Open
Abstract
PURPOSE We tested the hypothesis that the variation of peripapillary scleral structural stiffness with age is different in donors of European (ED) and African (AD) descent. METHODS Posterior scleral shells from normal eyes from donors of European (n = 20 pairs; previously reported) and African (n = 9 pairs) descent aged 0 and 90 years old were inflation tested within 48 hours post mortem. Scleral shells were pressurized from 5 to 45 mm Hg and the full-field, 3-dimensional (3D) deformation of the outer surface was recorded at submicrometric accuracy using speckle interferometry (ESPI). Mean maximum principal (tensile) strain of the peripapillary and midperipheral regions surrounding the optic nerve head (ONH) were fit using a functional mixed effects model that accounts for intradonor variability, same-race correlation, and spatial autocorrelation to estimate the effect of race on the age-related changes in mechanical scleral strain. RESULTS Mechanical tensile strain significantly decreased with age in the peripapillary sclera in the African and European descent groups (P < 0.001), but the age-related stiffening was significantly greater in the African descent group (P < 0.05). Maximum principal strain in the peripapillary sclera was significantly higher than in the midperipheral sclera for both ethnic groups. CONCLUSIONS The sclera surrounding the ONH stiffens more rapidly with age in the African descent group compared to the European group. Stiffening of the peripapillary sclera with age may be related to the higher prevalence of glaucoma in the elderly and persons of African descent.
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Affiliation(s)
- Massimo A. Fazio
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Rafael Grytz
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Jeffrey S. Morris
- Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States
| | - Luigi Bruno
- Department of Mechanical Engineering, University of Calabria, Calabria, Italy
| | - Christopher A. Girkin
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - J. Crawford Downs
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States
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Lopilly Park HY, Lee NY, Choi JA, Park CK. Measurement of scleral thickness using swept-source optical coherence tomography in patients with open-angle glaucoma and myopia. Am J Ophthalmol 2014; 157:876-84. [PMID: 24412142 DOI: 10.1016/j.ajo.2014.01.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Revised: 01/02/2014] [Accepted: 01/04/2014] [Indexed: 10/25/2022]
Abstract
PURPOSE To use swept-source optical coherence tomography (OCT) to image the posterior sclera at the posterior pole and around the optic nerve head (ONH) and measure the subfoveal scleral thickness and laminar thickness to evaluate the relationship between the measured thicknesses and ocular parameters. DESIGN Prospective, cross-sectional design. METHODS The study included 103 patients with glaucoma and 43 controls with axial lengths more than 26 mm. Swept-source OCT images were obtained to capture the subfoveal and ONH regions. Subfoveal scleral thickness and laminar thickness were measured from obtained B-scan images. To verify the reproducibility of the measurement, intraclass correlation coefficients were calculated from selected B-scans. Scleral and laminar thicknesses in patients with normal-tension glaucoma (NTG) was compared with that in patients with primary open-angle glaucoma (POAG). A Pearson correlation was calculated to assess the relationships of scleral and laminar thicknesses with ocular parameters. RESULTS Posterior scleral thickness could be measured in 68.4% of patients, and laminar thickness could be measured in 88.6% by using swept-source OCT. Interobserver and intraobserver measurement reproducibility was moderate to excellent. The subfoveal scleral thickness was 670.84 ± 160.60 μm in the POAG group and 496.55 ± 115.20 μm in the NTG group; a significant difference between the groups was observed. Subfoveal scleral thickness (r = -0.677, P < 0.001) was negatively correlated with axial length only in patients with NTG, not in patients with POAG. CONCLUSIONS Swept-source OCT detected differences in the thicknesses of the posterior sclera between eyes with NTG and eyes with POAG. Subfoveal scleral thickness was negatively correlated with axial length only in eyes with NTG.
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Park HYL, Shin HY, Park CK. Imaging the posterior segment of the eye using swept-source optical coherence tomography in myopic glaucoma eyes: comparison with enhanced-depth imaging. Am J Ophthalmol 2014; 157:550-7. [PMID: 24239773 DOI: 10.1016/j.ajo.2013.11.008] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 11/06/2013] [Accepted: 11/07/2013] [Indexed: 02/05/2023]
Abstract
PURPOSE To compare the detection rates of identifying the posterior border of the sclera and lamina cribrosa and measurement reproducibility of scleral and laminar thicknesses using the enhanced depth imaging (EDI) of Heidelberg Spectralis optical coherence tomography (OCT) and swept-source OCT. DESIGN Cross-sectional design. METHODS Both EDI-OCT and swept-source OCT images were obtained in 32 myopic glaucoma patients. Subfoveal choroidal, subfoveal scleral, and central laminar thicknesses were measured from obtained B-scan images. Each measurement was performed at 3 locations by 2 masked observers. The detection rates and measurement reproducibility were evaluated from selected B-scans. RESULTS The posterior border of the sclera was visible in 10 eyes (31%) using EDI-OCT. This was improved to be visible in 17 eyes (53%) using swept-source OCT. According to the McNemar χ(2) test, the detection rate of the posterior border of the sclera was significantly different between EDI-OCT and swept-source OCT (P = 0.008). The detection rate of the posterior border of the lamina cribrosa was similar for the 2 devices. In highly myopic eyes, the detection rate of the posterior border of the sclera and lamina cribrosa was not statistically different between EDI-OCT and swept-source OCT. Intersystem ICCs was 0.769 (95% CI, 0.714-0.893) for subfoveal scleral thickness and 0.900 (95% CI, 0.887-0.917) for laminar thickness. The mean subfoveal scleral thickness was 464.32 ± 213.24 μm using EDI-OCT and 650.26 ± 222.30 μm using swept-source OCT. There was statistical difference in the measured subfoveal scleral thickness by the 2 devices (P = 0.018). CONCLUSIONS Compared with EDI-OCT, swept-source OCT had an advantage in imaging the posterior sclera. Imaging the lamina cribrosa was similar when using both devices.
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Campbell IC, Coudrillier B, Ross Ethier C. Biomechanics of the Posterior Eye: A Critical Role in Health and Disease. J Biomech Eng 2014; 136:021005. [DOI: 10.1115/1.4026286] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 12/19/2013] [Indexed: 01/16/2023]
Abstract
The posterior eye is a complex biomechanical structure. Delicate neural and vascular tissues of the retina, choroid, and optic nerve head that are critical for visual function are subjected to mechanical loading from intraocular pressure, intraocular and extraorbital muscles, and external forces on the eye. The surrounding sclera serves to counteract excessive deformation from these forces and thus to create a stable biomechanical environment for the ocular tissues. Additionally, the eye is a dynamic structure with connective tissue remodeling occurring as a result of aging and pathologies such as glaucoma and myopia. The material properties of these tissues and the distribution of stresses and strains in the posterior eye is an area of active research, relying on a combination of computational modeling, imaging, and biomechanical measurement approaches. Investigators are recognizing the increasing importance of the role of the collagen microstructure in these material properties and are undertaking microstructural measurements to drive microstructurally-informed models of ocular biomechanics. Here, we review notable findings and the consensus understanding on the biomechanics and microstructure of the posterior eye. Results from computational and numerical modeling studies and mechanical testing of ocular tissue are discussed. We conclude with some speculation as to future trends in this field.
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Affiliation(s)
- Ian C. Campbell
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
- Rehabilitation Research and Development Center of Excellence, Atlanta VA Medical Center, 1670 Clairmont Road, Decatur, GA 30032
| | - Baptiste Coudrillier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
- Rehabilitation Research and Development Center of Excellence, Atlanta VA Medical Center, 1670 Clairmont Road, Decatur, GA 30032
- Department of Ophthalmology, School of Medicine, Emory University, Atlanta, GA 30322
- Department of Bioengineering, Imperial College London, London SW7 2AZ, UK e-mail:
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Pallikaris IG, Dastiridou AI, Tsilimbaris MK, Karyotakis NG, Ginis HS. Ocular rigidity. EXPERT REVIEW OF OPHTHALMOLOGY 2014. [DOI: 10.1586/eop.10.30] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Huang W, Fan Q, Wang W, Zhou M, Laties AM, Zhang X. Collagen: a potential factor involved in the pathogenesis of glaucoma. Med Sci Monit Basic Res 2013; 19:237-40. [PMID: 24002298 PMCID: PMC3767582 DOI: 10.12659/msmbr.889061] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Numerous studies have been completed on glaucoma pathogenesis. However, the potential and controversial interaction between ocular biomechanical properties and the glaucomatous diseases process has received much more attention recently. Previous studies have found that collagen tissues gain mutation change in glaucoma patients. This study was conducted to determine the role of collagen in the biomechanics of glaucoma in humans. Its changes may be the result of mechanical modifications brought on by intraocular pressure (IOP) fluctuations. More importantly, biomechanics and genetic evidence indicate that the mutation of collagen may play a role in the process of glaucoma. Alteration of collagen in the outflow pathway may alter mechanical tissue characteristics and a concomitant increase of aqueous humor outflow resistance and elevation of IOP. The variations of collagen, leading to inter-individual differences in scleral and lamina cribrosa properties, result in different susceptibility of individuals to elevated IOP. Therefore, this study hypothesized that collagen mutations may be an original cause of glaucoma.
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Affiliation(s)
- Wenbin Huang
- Zhongshan Ophthalmic Center, State Key Laboratory of Ophthalmology, Sun Yat-sen University, PR China
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Fazio MA, Grytz R, Morris JS, Bruno L, Gardiner SK, Girkin CA, Downs JC. Age-related changes in human peripapillary scleral strain. Biomech Model Mechanobiol 2013; 13:551-63. [PMID: 23896936 DOI: 10.1007/s10237-013-0517-9] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Accepted: 07/17/2013] [Indexed: 11/27/2022]
Abstract
To test the hypothesis that mechanical strain in the posterior human sclera is altered with age, 20 pairs of normal eyes from human donors aged 20 to 90 years old were inflation tested within 48-h postmortem. The intact posterior scleral shells were pressurized from 5 to 45 mmHg, while the full-field three-dimensional displacements of the scleral surface were measured using laser speckle interferometry. The full strain tensor of the outer scleral surface was calculated directly from the displacement field. Mean maximum principal (tensile) strain was computed for eight circumferential sectors (45° wide) within the peripapillary and mid-peripheral regions surrounding the optic nerve head (ONH). To estimate the age-related changes in scleral strain, results were fit using a functional mixed effects model that accounts for intradonor variability and spatial autocorrelation. Mechanical tensile strain in the peripapillary sclera is significantly higher than the strain in the sclera farther away from the ONH. Overall, strains in the peripapillary sclera decrease significantly with age. Sectorially, peripapillary scleral tensile strains in the nasal sectors are significantly higher than the temporal sectors at younger ages, but the sectorial strain pattern reverses with age, and the temporal sectors exhibited the highest tensile strains in the elderly. Overall, peripapillary scleral structural stiffness increases significantly with age. The sectorial pattern of peripapillary scleral strain reverses with age, which may predispose adjacent regions of the lamina cribrosa to biomechanical insult. The pattern and age-related changes in sectorial peripapillary scleral strain closely match those seen in disk hemorrhages and neuroretinal rim area measurement change rates reported in previous studies of normal human subjects.
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Affiliation(s)
- Massimo A Fazio
- Department of Ophthalmology, Center for Ocular Biomechanics and Biotransport, University of Alabama at Birmingham, 1670 University Blvd., VH 390A, Birmingham, AL, 35294, USA
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Geraghty B, Jones SW, Rama P, Akhtar R, Elsheikh A. Age-related variations in the biomechanical properties of human sclera. J Mech Behav Biomed Mater 2012. [PMID: 23182387 DOI: 10.1016/j.jmbbm.2012.10.011] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This study examined age-related changes in biomechanical behaviour in the anterior, equatorial and posterior regions of the human sclera (white of the eye). Circumferential strip specimens were extracted from areas close to the limbus, equator and posterior pole in 45 donor scleras ranging in age between 51 and 84 years. The strips were subjected to cycles of uniaxial tension loading at a strain rate of 8% per minute while monitoring their load-deformation behaviour. All specimens demonstrated nonlinear behaviour with an initially low tangent modulus (a measure of material stiffness) increasing under higher stresses. The average ratios between the tangent modulus at a high stress of 1 MPa and that at a low stress of 0.05 MPa were 11.2±1.7, 12.0±1.7 and 12.4±1.5 for anterior, equatorial and posterior specimens, respectively. Stiffening was observed with age in all regions, but it was statistically significant only in the anterior region (P<0.01). Anterior specimens showed the largest stiffness growth with advancing age in both the initial, matrix regulated phase of behaviour (0.32 MPa/decade), and the final, collagen regulated phase (3.97 MPa/decade), followed by equatorial (0.27 and 2.15 MPa/decade) then posterior specimens (0.14 and 0.26 MPa/decade). The stress-strain behaviour of scleral tissue exhibits increasing stiffness with higher age. In addition to a regional variation of material stiffness, the rate of stiffness growth with age also varies between regions.
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Affiliation(s)
- Brendan Geraghty
- Division of Civil Engineering, University of Dundee, Nethergate, Dundee, Tayside DD1 4HN, UK
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48
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Fazio MA, Grytz R, Bruno L, Girard MJA, Gardiner S, Girkin CA, Downs JC. Regional variations in mechanical strain in the posterior human sclera. Invest Ophthalmol Vis Sci 2012; 53:5326-33. [PMID: 22700704 DOI: 10.1167/iovs.12-9668] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE The goal of this study was to establish sectorial and regional variability in the mechanical strain of peripapillary and mid-peripheral sclera in normal eyes from elderly human donors. METHODS Ten pairs of normal eyes from human donors aged 57 to 90 years old were mechanically inflation-tested within 48 hours post mortem. The intact posterior scleral shells were pressurized from 5 to 45 mm Hg while the full-field three-dimensional displacements of the scleral surface were measured using laser speckle interferometry. The displacement field was fit to continuous and differentiable analytical functions, from which the full strain tensor of the outer scleral surface was calculated. Mean maximum principal (tensile) strain was computed for eight circumferential sectors (45° wide) within the peripapillary and mid-peripheral regions surrounding the optic nerve head (ONH). RESULTS Overall, the peripapillary sclera exhibited significantly higher tensile strain (1.2%) than mid-peripheral sclera (0.95%) for a 40 mm Hg IOP elevation (P < 0.00001). In the peripapillary region, the inferotemporal sector exhibited the highest tensile strain (1.45%) while the superior sector had the lowest (1.19%; P < 0.00001). Mid-peripheral scleral strains were lower but exhibited a similar sectorial pattern. CONCLUSIONS Human posterior sclera exhibits complex regional mechanical behavior in response to acute IOP elevations from 5 to 45 mm Hg. Results indicate 1) the peripapillary sclera is subjected to significantly higher tensile strain than the adjacent mid-peripheral sclera, and 2) strains are significantly higher in the temporal and inferior quadrants of the peripapillary sclera, which may contribute to the increased prevalence of glaucomatous damage associated with these regions of the ONH.
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Affiliation(s)
- Massimo A Fazio
- Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, Oregon 97232, USA
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Pijanka JK, Coudrillier B, Ziegler K, Sorensen T, Meek KM, Nguyen TD, Quigley HA, Boote C. Quantitative mapping of collagen fiber orientation in non-glaucoma and glaucoma posterior human sclerae. Invest Ophthalmol Vis Sci 2012; 53:5258-70. [PMID: 22786908 DOI: 10.1167/iovs.12-9705] [Citation(s) in RCA: 110] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE The posterior sclera has a major biomechanical influence on the optic nerve head, and may therefore be important in glaucoma. Scleral material properties are influenced significantly by collagen fiber architecture. Here we quantitatively map fiber orientation in non-glaucoma and glaucoma posterior human sclerae. METHODS Wide-angle x-ray scattering quantified fiber orientation at 0.5-mm intervals across seven non-glaucoma post-mortem human sclerae, and five sclerae with glaucoma history and confirmed axon loss. Multiphoton microscopy provided semiquantitative depth-profiling in the peripapillary sclera. RESULTS Midposterior fiber orientation was either uniaxial (one preferred direction) or biaxial (two directions). The peripapillary sclera was characterized by a ring of fibers located mainly in the mid-/outer stromal depth and encompassing ∼50% of the total tissue thickness. Fiber anisotropy was 37% higher in the peripapillary sclera compared with midposterior, varied up to 4-fold with position around the scleral canal, and was consistently lowest in the superior-nasal quadrant. Mean fiber anisotropy was significantly lower in the superior-temporal (P < 0.01) and inferior-nasal (P < 0.05) peripapillary scleral quadrants in glaucoma compared with non-glaucoma eyes. CONCLUSIONS The collagen fiber architecture of the posterior human sclera is highly anisotropic and inhomogeneous. Regional differences in peripapillary fiber anisotropy between non-glaucoma and glaucoma eyes may represent adaptive changes in response to elevated IOP and/or glaucoma, or baseline structural properties that associate with predisposition to glaucomatous axon damage. Quantitative fiber orientation data will benefit numerical eye models aimed at predicting the sclera's influence on nerve head biomechanics, and thereby its possible role in glaucoma.
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Affiliation(s)
- Jacek K Pijanka
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
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Coudrillier B, Tian J, Alexander S, Myers KM, Quigley HA, Nguyen TD. Biomechanics of the human posterior sclera: age- and glaucoma-related changes measured using inflation testing. Invest Ophthalmol Vis Sci 2012; 53:1714-28. [PMID: 22395883 DOI: 10.1167/iovs.11-8009] [Citation(s) in RCA: 229] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
PURPOSE The objective of this study was to measure the biomechanical response of the human posterior sclera in vitro and to estimate the effects of age and glaucoma. METHODS Scleral specimens from 22 donors with no history of glaucoma and 11 donors with a history of glaucoma were excised 3 mm posterior to the equator and affixed to an inflation chamber. Optic nerve cross-sections were graded to determine the presence of axon loss. The time-dependent inflation response was measured in a series of pressure-controlled load-unload tests to 30 mm Hg and creep tests to 15 and 30 mm Hg. Circumferential and meridional strains were computed from the digital image correlation displacements, and midposterior stresses were determined from pressure and deformed geometry. RESULTS Among normal specimens, older age was predictive of a stiffer response and a thinner sclera. In the age group 75 to 93, diagnosed glaucoma eyes with axon damage were thicker than normal eyes. Both damaged and undamaged glaucoma eyes had a different strain response in the peripapillary sclera characterized by a stiffer meridional response. Undamaged glaucoma eyes had slower circumferential creep rates in the peripapillary sclera than normal eyes. Glaucoma eyes were not different from normal eyes in stresses and strains in the midposterior sclera. CONCLUSIONS The observed differences in the biomechanical response of normal and glaucoma sclera may represent baseline properties that contribute to axon damage, or may be characteristics that result from glaucomatous disease.
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Affiliation(s)
- Baptiste Coudrillier
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
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