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Lee PY, Fryc G, Gnalian J, Wang B, Hua Y, Waxman S, Zhong F, Yang B, Sigal IA. Direct measurements of collagen fiber recruitment in the posterior pole of the eye. Acta Biomater 2024; 173:135-147. [PMID: 37967694 PMCID: PMC10843755 DOI: 10.1016/j.actbio.2023.11.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Revised: 11/07/2023] [Accepted: 11/09/2023] [Indexed: 11/17/2023]
Abstract
Collagen is the main load-bearing component of the peripapillary sclera (PPS) and lamina cribrosa (LC) in the eye. Whilst it has been shown that uncrimping and recruitment of the PPS and LC collagen fibers underlies the macro-scale nonlinear stiffening of both tissues with increased intraocular pressure (IOP), the uncrimping and recruitment as a function of local stretch have not been directly measured. This knowledge is crucial to understanding their functions in bearing loads and maintaining tissue integrity. In this project we measured local stretch-induced collagen fiber bundle uncrimping and recruitment curves of the PPS and LC. Thin coronal samples of PPS and LC of sheep eyes were mounted and stretched biaxially quasi-statically using a custom system. At each step, we imaged the PPS and LC with instant polarized light microscopy and quantified pixel-level (1.5 μm/pixel) collagen fiber orientations. We used digital image correlation to measure the local stretch and quantified collagen crimp by the circular standard deviation of fiber orientations, or waviness. Local stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers than the LC at the low levels of stretch. At 10% stretch the curves crossed with 75% bundles recruited. The PPS had higher uncrimping rate and waviness remaining after recruitment than the LC: 0.9º vs. 0.6º and 3.1º vs. 2.7º. Altogether our findings support describing fiber recruitment of both PPS and LC with sigmoid curves, with the PPS recruiting faster and at lower stretch than the LC, consistent with a stiffer tissue. STATEMENT OF SIGNIFICANCE: Peripapillary sclera (PPS) and lamina cribrosa (LC) collagen recruitment behaviors are central to the nonlinear mechanical behavior of the posterior pole of the eye. How PPS and LC collagen fibers recruit under stretch is crucial to develop constitutive models of the tissues but remains unclear. We used image-based stretch testing to characterize PPS and LC collagen fiber bundle recruitment under local stretch. We found that fiber-level stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers at a low stretch, but at 10% bundle stretch the two curves crossed with 75% bundles recruited. We also found that PPS and LC fibers had different uncrimping rates and non-zero waviness's when recruited.
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Affiliation(s)
- Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Gosia Fryc
- Department of Chemistry, Dietrich School of Arts and Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - John Gnalian
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Biomedical Engineering, University of Mississippi, University, MS, USA; Department of Mechanical Engineering, University of Mississippi, University, MS, USA
| | - Susannah Waxman
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Fuqiang Zhong
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA, USA
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA.
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Bradford S, Luo S, Brown D, Juhasz T, Jester J. A review of the epithelial and stromal effects of corneal collagen crosslinking. Ocul Surf 2023; 30:150-159. [PMID: 37683969 PMCID: PMC10993773 DOI: 10.1016/j.jtos.2023.09.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 08/31/2023] [Accepted: 09/05/2023] [Indexed: 09/10/2023]
Abstract
Induced corneal collagen crosslinking and mechanical stiffening via ultraviolet-A photoactivation of riboflavin (UVA CXL) is now a common treatment for corneal ectasia and Keratoconus. Some effects of the procedure such as induced mechanical stiffening, corneal flattening, and cellular toxicity are well-known, but others remain more controversial. Authors report a variety of contradictory effects, and provide evidence based on individual results and observations. A full understanding of the effects of and mechanisms behind this procedure are essential to predicting its outcome. A growing interest in modifications to the standard UVA CXL protocol, such as transepithelial or accelerated UVA CXL, makes analyzing the literature as a whole more urgent. This review presents an analysis of both the agreed-upon and contradictory results reported and the various methods used to obtain them.
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Affiliation(s)
- Samantha Bradford
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA.
| | - Shangbang Luo
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Donald Brown
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - Tibor Juhasz
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
| | - James Jester
- Department of Ophthalmology and Biomedical Engineering, University of California, Irvine, Irvine, CA, USA
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Wang X, Elbahrawi RT, Abdukadir AM, Ali ZM, Chan V, Corridon PR. A proposed model of xeno-keratoplasty using 3D printing and decellularization. Front Pharmacol 2023; 14:1193606. [PMID: 37799970 PMCID: PMC10548234 DOI: 10.3389/fphar.2023.1193606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2023] [Accepted: 09/06/2023] [Indexed: 10/07/2023] Open
Abstract
Corneal opacity is a leading cause of vision impairment and suffering worldwide. Transplantation can effectively restore vision and reduce chronic discomfort. However, there is a considerable shortage of viable corneal graft tissues. Tissue engineering may address this issue by advancing xeno-keratoplasty as a viable alternative to conventional keratoplasty. In particular, livestock decellularization strategies offer the potential to generate bioartificial ocular prosthetics in sufficient supply to match existing and projected needs. To this end, we have examined the best practices and characterizations that have supported the current state-of-the-art driving preclinical and clinical applications. Identifying the challenges that delimit activities to supplement the donor corneal pool derived from acellular scaffolds allowed us to hypothesize a model for keratoprosthesis applications derived from livestock combining 3D printing and decellularization.
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Affiliation(s)
- Xinyu Wang
- Biomedical Engineering and Healthcare Engineering Innovation Center, Khalifa University, Abu Dhabi, United Arab Emirates
- Department of Immunology and Physiology, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates
| | - Rawdah Taha Elbahrawi
- Department of Immunology and Physiology, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates
| | - Azhar Mohamud Abdukadir
- Department of Immunology and Physiology, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates
| | - Zehara Mohammed Ali
- Department of Immunology and Physiology, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates
| | - Vincent Chan
- Biomedical Engineering and Healthcare Engineering Innovation Center, Khalifa University, Abu Dhabi, United Arab Emirates
| | - Peter R. Corridon
- Biomedical Engineering and Healthcare Engineering Innovation Center, Khalifa University, Abu Dhabi, United Arab Emirates
- Department of Immunology and Physiology, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates
- Center for Biotechnology, Khalifa University, Abu Dhabi, United Arab Emirates
- Hleathcare, Engineering and Innovation Center, Khalifa University, Abu Dhabi, United Arab Emirates
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Lee PY, Fryc G, Gnalian J, Hua Y, Waxman S, Zhong F, Yang B, Sigal IA. Direct measurements of collagen fiber recruitment in the posterior pole of the eye. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.07.539784. [PMID: 37215028 PMCID: PMC10197604 DOI: 10.1101/2023.05.07.539784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Collagen is the main load-bearing component of the peripapillary sclera (PPS) and lamina cribrosa (LC) in the eye. Whilst it has been shown that uncrimping and recruitment of the PPS and LC collagen fibers underlies the macro-scale nonlinear stiffening of both tissues with increased intraocular pressure (IOP), the uncrimping and recruitment as a function of local stretch have not been directly measured. This knowledge is crucial for the development of constitutive models associating micro and macro scales. In this project we measured local stretch-induced collagen fiber bundle uncrimping and recruitment curves of the PPS and LC. Thin coronal samples of PPS and LC of sheep eyes were mounted and stretched biaxially quasi-statically using a custom system. At each step, we imaged the PPS and LC with instant polarized light microscopy and quantified pixel-level (1.5 μm/pixel) collagen fiber orientations. We used digital image correlation to measure the local stretch and quantified collagen crimp by the circular standard deviation of fiber orientations, or waviness. Local stretch-recruitment curves of PPS and LC approximated sigmoid functions. PPS recruited more fibers than the LC at the low levels of stretch. At 10% stretch the curves crossed with 75% bundles recruited. The PPS had higher uncrimping rate and waviness remaining after recruitment than the LC: 0.9° vs. 0.6° and 3.1° vs. 2.7°. Altogether our findings support describing fiber recruitment of both PPS and LC with sigmoid curves, with the PPS recruiting faster and at lower stretch than the LC, consistent with a stiffer tissue.
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Affiliation(s)
- Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Bioengineering, Swanson School of Engineering
| | - Gosia Fryc
- Department of Chemistry, Dietrich School of Arts and Sciences University of Pittsburgh, Pittsburgh, PA
| | - John Gnalian
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Biomedical Engineering, University of Mississippi, University, MS
- Department of Mechanical Engineering, University of Mississippi, University, MS
| | - Susannah Waxman
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Fuqiang Zhong
- Department of Ophthalmology, University of Pittsburgh School of Medicine
| | - Bin Yang
- Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine
- Department of Bioengineering, Swanson School of Engineering
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Foong TY, Hua Y, Amini R, Sigal IA. Who bears the load? IOP-induced collagen fiber recruitment over the corneoscleral shell. Exp Eye Res 2023; 230:109446. [PMID: 36935071 PMCID: PMC10133210 DOI: 10.1016/j.exer.2023.109446] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2022] [Revised: 02/25/2023] [Accepted: 03/16/2023] [Indexed: 03/19/2023]
Abstract
Collagen is the main load-bearing component of cornea and sclera. When stretched, both of these tissues exhibit a behavior known as collagen fiber recruitment. In recruitment, as the tissues stretch the constitutive collagen fibers lose their natural waviness, progressively straightening. Recruited, straight, fibers bear substantially more mechanical load than non-recruited, wavy, fibers. As such, the process of recruitment underlies the well-established nonlinear macroscopic behavior of the corneoscleral shell. Recruitment has an interesting implication: when recruitment is incomplete, only a fraction of the collagen fibers is actually contributing to bear the loads, with the rest remaining "in reserve". In other words, at a given intraocular pressure (IOP), it is possible that not all the collagen fibers of the cornea and sclera are actually contributing to bear the loads. To the best of our knowledge, the fraction of corneoscleral shell fibers recruited and contributing to bear the load of IOP has not been reported. Our goal was to obtain regionally-resolved estimates of the fraction of corneoscleral collagen fibers recruited and in reserve. We developed a fiber-based microstructural constitutive model that could account for collagen fiber undulations or crimp via their tortuosity. We used experimentally-measured collagen fiber crimp tortuosity distributions in human eyes to derive region-specific nonlinear hyperelastic mechanical properties. We then built a three-dimensional axisymmetric model of the globe, assigning region-specific mechanical properties and regional anisotropy. The model was used to simulate the IOP-induced shell deformation. The model-predicted tissue stretch was then used to quantify collagen recruitment within each shell region. The calculations showed that, at low IOPs, collagen fibers in the posterior equator were recruited the fastest, such that at a physiologic IOP of 15 mmHg, over 90% of fibers were recruited, compared with only a third in the cornea and the peripapillary sclera. The differences in recruitment between regions, in turn, mean that at a physiologic IOP the posterior equator had a fiber reserve of only 10%, whereas the cornea and peripapillary sclera had two thirds. At an elevated IOP of 50 mmHg, collagen fibers in the limbus and the anterior/posterior equator were almost fully recruited, compared with 90% in the cornea and the posterior sclera, and 70% in the peripapillary sclera and the equator. That even at such an elevated IOP not all the fibers were recruited suggests that there are likely other conditions that challenge the corneoscleral tissues even more than IOP. The fraction of fibers recruited may have other potential implications. For example, fibers that are not bearing loads may be more susceptible to enzymatic digestion or remodeling. Similarly, it may be possible to control tissue stiffness through the fraction of recruited fibers without the need to add or remove collagen.
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Affiliation(s)
- Tian Yong Foong
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Biomedical Engineering, University of Mississippi, MS, United States; Department of Mechanical Engineering, University of Mississippi, MS, United States
| | - Rouzbeh Amini
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, United States; Department of Bioengineering, Northeastern University, Boston, MA, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, University of Pittsburgh Medical Center and University of Pittsburgh, Pittsburgh, PA, United States.
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Kirby MA, Regnault G, Pelivanov I, O'Donnell M, Wang RK, Shen TT. Noncontact Acoustic Micro-Tapping Optical Coherence Elastography for Quantification of Corneal Anisotropic Elasticity: In Vivo Rabbit Study. Transl Vis Sci Technol 2023; 12:15. [PMID: 36930138 PMCID: PMC10036949 DOI: 10.1167/tvst.12.3.15] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/18/2023] Open
Abstract
Purpose The purpose of this study was to demonstrate accurate measurement of corneal elastic moduli in vivo with noncontact and noninvasive optical coherence elastography. Methods Elastic properties (in-plane Young's modulus, E, and both in-plane, μ, and out-of-plane, G, shear moduli) of rabbit cornea were quantified in vivo using noncontact dynamic acoustic micro-tapping optical coherence elastography (AµT-OCE). The intraocular pressure (IOP)-dependence of measured mechanical properties was explored in extracted whole globes following in vivo measurement. A nearly incompressible transverse isotropic (NITI) model was used to reconstruct moduli from AµT-OCE data. Independently, cornea elastic moduli were also measured ex vivo with traditional, destructive mechanical tests (tensile extensometry and shear rheometry). Results Our study demonstrates strong anisotropy of corneal elasticity in rabbits. The in-plane Young's modulus, computed as E = 3μ, was in the range of 20 MPa to 44 MPa, whereas the out-of-plane shear modulus was in the range of 34 kPa to 261 kPa. Both pressure-dependent ex vivo OCE and destructive mechanical tests performed on the same samples within an hour of euthanasia strongly support the results of AµT-OCE measurements. Conclusions Noncontact AµT-OCE can noninvasively quantify cornea anisotropic elastic properties in vivo. Translational Relevance As optical coherence tomography (OCT) is broadly accepted in ophthalmology, these results suggest the potential for rapid translation of AµT-OCE into clinical practice. In addition, AµT-OCE can likely improve diagnostic criteria of ectatic corneal diseases, leading to early diagnosis, reduced complications, customized surgical treatment, and personalized biomechanical models of the eye.
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Affiliation(s)
- Mitchell A Kirby
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Gabriel Regnault
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Ivan Pelivanov
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Matthew O'Donnell
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Ruikang K Wang
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Department of Ophthalmology, University of Washington, Seattle, WA, USA
| | - Tueng T Shen
- School of Medicine, University of Washington, Seattle, WA, USA
- Department of Ophthalmology, University of Washington, Seattle, WA, USA
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Wang C, Shen M, Song Y, Chang L, Yang Y, Li Y, Liu T, Wang Y. Biaxial hyperelastic and anisotropic behaviors of the corneal anterior central stroma along the preferential fibril orientations. Part II: Quantitative computational analysis of mechanical response of stromal components. J Mech Behav Biomed Mater 2023; 142:105802. [PMID: 37043981 DOI: 10.1016/j.jmbbm.2023.105802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Revised: 03/20/2023] [Accepted: 03/23/2023] [Indexed: 03/30/2023]
Abstract
To study the hyperelastic and anisotropic behaviors of the central anterior stroma for patients with myopia, 40 corneal stromal specimens extracted after small incision lenticule extraction (SMILE) surgery were used in the biaxial extension test along two preferential fibril orientations. An improved collagen fibril crimping constitutive model with a specific physical meaning was proposed to analyze the hyperelasticity and anisotropy of the stroma. The effective elastic modulus of the two families of preferentially oriented collagen fibrils and the stiffness of the non-collagenous matrix along all three directions were compared according to the specific physical meaning of the parameters. Anisotropic behavior was found in the hyperelastic properties of the corneal anterior central stroma in the preferential fibril orientations. The stiffness of non-collagenous matrix is significantly larger in the optical axis direction than in the nasal-temporal (NT) and superior-inferior (SI) directions. Moreover, individual differences between males and females slightly impact on hyperelastic and anisotropic behaviors. The differences of these behaviors were significant in the comparison of the left and right eyes. These results have a guiding significance for the accurate design of surgical plans for refractive surgery according to a patient's condition and have a driving value for the further exploration of the biomechanical properties of the whole cornea.
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Biomechanics of keratoconus: Two numerical studies. PLoS One 2023; 18:e0278455. [PMID: 36730305 PMCID: PMC9894483 DOI: 10.1371/journal.pone.0278455] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Accepted: 11/16/2022] [Indexed: 02/03/2023] Open
Abstract
BACKGROUND The steep cornea in keratoconus can greatly impair eyesight. The etiology of keratoconus remains unclear but early injury that weakens the corneal stromal architecture has been implicated. To explore keratoconus mechanics, we conducted two numerical simulation studies. METHODS A finite-element model describing the five corneal layers and the heterogeneous mechanical behaviors of the ground substance and lamellar collagen-fiber architecture in the anterior and posterior stroma was developed using the Holzapfel-Gasser-Ogden constitutive model. The geometry was from a healthy subject. Its stroma was divided into anterior, middle, and posterior layers to assess the effect of changing regional mechanical parameters on corneal displacement and maximum principal stress under intraocular pressure. Specifically, the effect of softening an inferocentral corneal button, the collagen-based tissues throughout the whole cornea, or specific stromal layers in the button was examined. The effect of simply disorganizing the orthogonally-oriented posterior stromal fibers in the button was also assessed. The healthy cornea was also subjected to eye rubbing-like loading to identify the corneal layer(s) that experienced the most tensional stress. RESULTS Conical deformation and corneal thinning emerged when the corneal button or the mid-posterior stroma of the button underwent gradual softening or when the collagen fibers in the mid-posterior stroma of the button were dispersed. Softening the anterior layers of the button or the whole cornea did not evoke conical deformation. Button softening greatly increased and disrupted the stress on Bowman's membrane while mid-posterior stromal softening increased stress in the anterior layers. Eye rubbing profoundly stressed the deep posterior stroma while other layers were negligibly affected. DISCUSSION These observations suggest that keratoconus could be initiated, at least partly, by mechanical instability/damage in the mid-posterior stroma that then imposes stress on the anterior layers. This may explain why subclinical keratoconus is marked by posterior but not anterior elevation on videokeratoscopy.
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Kirby MA, Regnault G, Pelivanov I, O’Donnell M, Wang RK, Shen TT. Non-contact acoustic micro-tapping optical coherence elastography for quantification of corneal anisotropic elasticity: in vivo rabbit study. ARXIV 2023:2301.10652. [PMID: 36748003 PMCID: PMC9900963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
PURPOSE To demonstrate accurate measurement of corneal elastic moduli in vivo with non-contact and non-invasive optical coherence elastography. METHODS Elastic properties (in-plane Young's modulus E and both in-plane, u, and out-of-plane, G, shear moduli) of rabbit cornea were quantified in vivo using non-contact dynamic Acoustic micro-Tapping Optical Coherence Elastography (AuT-OCE). The IOP-dependence of measured mechanical properties was explored in extracted whole globes following in vivo measurement. A nearly-incompressible transverse isotropic (NITI) model was used to reconstruct moduli from AuT-OCE data. Independently, cornea elastic moduli were also measured ex vivo with traditional, destructive mechanical tests (tensile extensometry and shear rheometry). RESULTS Our study demonstrates strong anisotropy of corneal elasticity in rabbits. The in-plane Young's modulus, computer as E=3u, was in the range of 20-44 MPa, whereas the out-of-plane shear modulus was in the range of 34-261 kPa. Both pressure-dependent ex vivo OCE and destructive mechanical tests performed on the same samples within an hour of euthanasia strongly support the results of AuT-OCE measurements. CONCLUSIONS Non-contact AuT-OCE can non-invasively quantify cornea anisotropic elastic properties in vivo. TRANSLATIONAL RELEVANCE As OCT is broadly accepted in Ophthalmology, these results suggest the potential for rapid translation of AuT-OCE into clinical practice. In addition, AuT-OCE can likely improve diagnostic criteria of ectatic corneal diseases, leading to early diagnosis, reduced complications, customized surgical treatment, and personalized biomechanical models of the eye.
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Affiliation(s)
- Mitchell A. Kirby
- Department of Bioengineering, University of Washington, Seattle, Washington 98105, USA
| | - Gabriel Regnault
- Department of Bioengineering, University of Washington, Seattle, Washington 98105, USA
- Correspondence: Gabriel Regnault, Department of Bioengineering, University of Washington, Seattle, Washington 98105, USA
| | - Ivan Pelivanov
- Department of Bioengineering, University of Washington, Seattle, Washington 98105, USA
| | - Matthew O’Donnell
- Department of Bioengineering, University of Washington, Seattle, Washington 98105, USA
| | - Ruikang K. Wang
- Department of Bioengineering, University of Washington, Seattle, Washington 98105, USA
- Department of Ophthalmology, University of Washington, Seattle, Washington 98104, USA
| | - Tueng T. Shen
- School of Medicine, University of Washington, Seattle, Washington 98195, USA
- Department of Ophthalmology, University of Washington, Seattle, Washington 98104, USA
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Chang L, Zhang L, Cheng Z, Zhang N, Wang C, Wang Y, Liu W. Effectiveness of collagen cross-linking induced by two-photon absorption properties of a femtosecond laser in ex vivo human corneal stroma. BIOMEDICAL OPTICS EXPRESS 2022; 13:5067-5081. [PMID: 36187250 PMCID: PMC9484424 DOI: 10.1364/boe.468593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 08/20/2022] [Accepted: 08/22/2022] [Indexed: 06/16/2023]
Abstract
This study aimed to investigate the effectiveness of two-photon induced collagen cross-linking (CXL) using femtosecond lasers in human corneal stroma. An 800-nm femtosecond laser optical path for CXL was established. Corneal samples that received two-photon induced CXL and ultraviolet-A (UVA) CXL underwent uniaxial stretching experiments, proteolytic resistance assays and observation of collagen fiber structure changes. Two-photon induced CXL can achieve corneal stiffening effects comparable to UVA CXL and showed better advantages at low strains. The cornea after two-photon induced CXL exhibited high enzymatic resistance and tight collagen fiber arrangement. Two-photon induced CXL promises to be a new option for keratoconus.
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Affiliation(s)
- Le Chang
- Clinical College of Ophthalmology, Tianjin Medical University, No. 22 Meteorological Terrace Road, Heping District, Tianjin 300070, China
| | - Lin Zhang
- Clinical College of Ophthalmology, Tianjin Medical University, No. 22 Meteorological Terrace Road, Heping District, Tianjin 300070, China
- Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin Eye Institute, Nankai University Affiliated Eye Hospital, Nankai University, No. 4 Gansu Road, Heping District, Tianjin 300020, China
| | - Zhenzhou Cheng
- Institute of Modern Optics, Nankai University, No. 94 Weijin Road, Nankai District, Tianjin 300071, China
- Tianjin Key Laboratory of Micro-scale Optical Information Science and Technology, No. 94 Weijin Road, Nankai District, Tianjin 300071, China
| | - Nan Zhang
- Institute of Modern Optics, Nankai University, No. 94 Weijin Road, Nankai District, Tianjin 300071, China
- Tianjin Key Laboratory of Micro-scale Optical Information Science and Technology, No. 94 Weijin Road, Nankai District, Tianjin 300071, China
| | - Congzheng Wang
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, No. 92 Weijin Road, Nankai District, Tianjin 300072, China
| | - Yan Wang
- Clinical College of Ophthalmology, Tianjin Medical University, No. 22 Meteorological Terrace Road, Heping District, Tianjin 300070, China
- Tianjin Key Laboratory of Ophthalmology and Visual Science, Tianjin Eye Hospital, Tianjin Eye Institute, Nankai University Affiliated Eye Hospital, Nankai University, No. 4 Gansu Road, Heping District, Tianjin 300020, China
| | - Weiwei Liu
- Institute of Modern Optics, Nankai University, No. 94 Weijin Road, Nankai District, Tianjin 300071, China
- Tianjin Key Laboratory of Micro-scale Optical Information Science and Technology, No. 94 Weijin Road, Nankai District, Tianjin 300071, China
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11
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Karimi A, Rahmati SM, Razaghi R, Girkin CA, Crawford Downs J. Finite element modeling of the complex anisotropic mechanical behavior of the human sclera and pia mater. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2022; 215:106618. [PMID: 35026624 PMCID: PMC8847341 DOI: 10.1016/j.cmpb.2022.106618] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 12/31/2021] [Accepted: 01/01/2022] [Indexed: 06/14/2023]
Abstract
BACKGROUND AND OBJECTIVE Accurate finite element (FE) simulation of the optic nerve head (ONH) depends on accurate mechanical properties of the load-bearing tissues. The peripapillary sclera in the ONH exhibits a depth-dependent, anisotropic, heterogeneous collagen fiber distribution. This study proposes a novel cable-in-solid modeling approach that mimics heterogeneous anisotropic collagen fiber distribution, validates the approach against published experimental biaxial tensile tests of scleral patches, and demonstrates its effectiveness in a complex model of the posterior human eye and ONH. METHODS A computational pipeline was developed that defines control points in the sclera and pia mater, distributes the depth-dependent circumferential, radial, and isotropic cable elements in the sclera and pia in a pattern that mimics collagen fiber orientation, and couples the cable elements and solid matrix using a mesh-free penalty-based cable-in-solid algorithm. A parameter study was performed on a model of a human scleral patch subjected to biaxial deformation, and computational results were matched to published experimental data. The new approach was incorporated into a previously published eye-specific model to test the method; results were then interpreted in relation to the collagen fibers' (cable elements) role in the resultant ONH deformations, stresses, and strains. RESULTS Results show that the cable-in-solid approach can mimic the full range of scleral mechanical behavior measured experimentally. Disregarding the collagen fibers/cable elements in the posterior eye model resulted in ∼20-60% greater tensile and shear stresses and strains, and ∼30% larger posterior deformations in the lamina cribrosa and peripapillary sclera. CONCLUSIONS The cable-in-solid approach can easily be implemented into commercial FE packages to simulate the heterogeneous and anisotropic mechanical properties of collagenous biological tissues.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
| | | | - Reza Razaghi
- Research Department, Heel of Scene Ltd., Tokyo, Japan
| | - Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
| | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
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12
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Lee PY, Yang B, Hua Y, Waxman S, Zhu Z, Ji F, Sigal IA. Real-time imaging of optic nerve head collagen microstructure and biomechanics using instant polarized light microscopy. Exp Eye Res 2022; 217:108967. [PMID: 35114213 PMCID: PMC8957577 DOI: 10.1016/j.exer.2022.108967] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Revised: 11/04/2021] [Accepted: 01/25/2022] [Indexed: 01/09/2023]
Abstract
Current tools lack the temporal or spatial resolution necessary to image many important aspects of the architecture and dynamics of the optic nerve head (ONH). We evaluated the potential of instant polarized light microscopy (IPOL) to overcome these limitations by leveraging the ability to capture collagen fiber orientation and density in a single image. Coronal sections through the ONH of fresh normal sheep eyes were imaged using IPOL while they were stretched using custom uniaxial or biaxial micro-stretch devices. IPOL allows identifying ONH collagen architectural details, such as fiber interweaving and crimp, and has high temporal resolution, limited only by the frame rate of the camera. Local collagen fiber orientations and deformations were quantified using color analysis and image tracking techniques. We quantified stretch-induced collagen uncrimping of lamina cribrosa (LC) and peripapillary sclera (PPS), and changes in LC pore size (area) and shape (convexity and aspect ratio). The simultaneous high spatial and temporal resolutions of IPOL revealed complex ONH biomechanics: i) stretch-induced local deformation of the PPS was nonlinear and nonaffine. ii) under load the crimped collagen fibers in the PPS and LC straightened, without torsion and with only small rotations. iii) stretch-induced LC pore deformation was anisotropic and heterogeneous among pores. Overall, with stretch the pores were became larger, more convex, and more circular. We have demonstrated that IPOL reveals details of collagen morphology and mechanics under dynamic loading previously out of reach. IPOL can detect stretch-induced collagen uncrimping and other elements of the tissue nonlinear mechanical behavior. IPOL showed changes in pore morphology and collagen architecture that will help improve understanding of how LC tissue responds to load.
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Affiliation(s)
- Po-Yi Lee
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Bin Yang
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States; Department of Engineering, Rangos School of Health Sciences, Duquesne University, Pittsburgh, PA, United States
| | - Yi Hua
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Susannah Waxman
- Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ziyi Zhu
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Fengting Ji
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, United States; Department of Ophthalmology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States.
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13
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Raoux C, Schmeltz M, Bied M, Alnawaiseh M, Hansen U, Latour G, Schanne-Klein MC. Quantitative structural imaging of keratoconic corneas using polarization-resolved SHG microscopy. BIOMEDICAL OPTICS EXPRESS 2021; 12:4163-4178. [PMID: 34457406 PMCID: PMC8367248 DOI: 10.1364/boe.426145] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 04/29/2021] [Accepted: 05/22/2021] [Indexed: 05/20/2023]
Abstract
The human cornea is mainly composed of collagen fibrils aligned together within stacked lamellae. This lamellar structure can be affected in pathologies such as keratoconus, which is characterized by progressive corneal thinning and local steepening. In this study, we use polarization-resolved second harmonic generation (P-SHG) microscopy to characterize 8 control and 6 keratoconic human corneas. Automated processing of P-SHG images of transverse sections provides the collagen orientation in every pixel with sub-micrometer resolution. Series of P-SHG images recorded in the most anterior region of the stroma evidence sutural lamellae inclined at 22° ± 5° to the corneal surface, but show no significant difference between control and keratoconic corneas. In contrast, series of P-SHG images acquired along the full thickness of the stroma show a loss of order in the lamellar structure of keratoconic corneas, in agreement with their defective mechanical properties. This structural difference is analyzed quantitatively by computing the entropy and the orientation index of the collagen orientation distribution and significant differences are obtained along the full thickness of the stroma. This study shows that P-SHG is an effective tool for automatic quantitative analysis of structural defects of human corneas and should be applied to other collagen-rich tissues.
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Affiliation(s)
- Clothilde Raoux
- Laboratory for Optics and Biosciences, Ecole polytechnique, CNRS, INSERM, Institut Polytechnique de Paris, 91128 Palaiseau, France
- These authors contributed equally
| | - Margaux Schmeltz
- Laboratory for Optics and Biosciences, Ecole polytechnique, CNRS, INSERM, Institut Polytechnique de Paris, 91128 Palaiseau, France
- These authors contributed equally
| | - Marion Bied
- Laboratory for Optics and Biosciences, Ecole polytechnique, CNRS, INSERM, Institut Polytechnique de Paris, 91128 Palaiseau, France
| | - Maged Alnawaiseh
- Department of Ophthalmology, Hospital Fulda, University of Marburg, Campus Fulda, 36043 Fulda, Germany
| | - Uwe Hansen
- Institute for Musculoskeletal Medicine, University Hospital Münster, 48149 Münster, Germany
| | - Gaël Latour
- Laboratory for Optics and Biosciences, Ecole polytechnique, CNRS, INSERM, Institut Polytechnique de Paris, 91128 Palaiseau, France
- Université Paris-Saclay, 91190 Saint-Aubin, France
| | - Marie-Claire Schanne-Klein
- Laboratory for Optics and Biosciences, Ecole polytechnique, CNRS, INSERM, Institut Polytechnique de Paris, 91128 Palaiseau, France
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14
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Niemczyk M, Danielewska ME, Kostyszak MA, Lewandowski D, Iskander DR. The effect of intraocular pressure elevation and related ocular biometry changes on corneal OCT speckle distribution in porcine eyes. PLoS One 2021; 16:e0249213. [PMID: 33770135 PMCID: PMC7997020 DOI: 10.1371/journal.pone.0249213] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 03/14/2021] [Indexed: 11/21/2022] Open
Abstract
The aim of this study was to evaluate the influence of increase in intraocular pressure (IOP) and cooccurring changes in ocular biometry parameters on the corneal optical coherence tomography (OCT) speckle distribution in ex-vivo experiments on porcine intact eyes. Twenty-three eyeballs were used in the inflation test where IOP in the anterior chamber was precisely set from 10 mmHg to 40 mmHg in steps of 5 mmHg and where eye biometry was utilized (IOL Master 700). To assess the influence of the duration of the experiment on the OCT speckle statistics, the second experiment was performed with 10 eyeballs at the constant IOP of 15 mmHg. Based on the OCT scans of central cornea (Copernicus REVO), spatial maps of the scale parameter (a) and the shape parameter (v) of the gamma distribution speckle model were estimated. The means of both parameters for each spatial map were computed within the 2 mm of the central stroma. Both distributional parameters statistically significantly varied with IOP and time (one way repeated measures ANOVA, all p-values < 0.001). The a parameter revealed a faster statistically significant increase in IOP up to 25 mmHg, regardless of time. Central corneal thickness (CCT), the anterior chamber depth, and the mean equivalent spherical power varied significantly with IOP, whereas CCT and axial length changed statistically significantly with time. Statistically significant correlation was found between CCT and the a parameter, after removing IOP as a confounding factor (r = -0.576, p < 0.001). The parameters of the gamma distribution can be used not only for identifying IOP induced changes in the optical scattering within the corneal stroma, but also in corneal geometry. The approach of corneal speckle analysis could be potentially utilized for an indirect and noninvasive assessment of some properties of corneal stroma.
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Affiliation(s)
- Marcela Niemczyk
- Department of Biomedical Engineering, Wroclaw University of Science and Technology, Wroclaw, Poland
| | - Monika E. Danielewska
- Department of Biomedical Engineering, Wroclaw University of Science and Technology, Wroclaw, Poland
| | - Malgorzata A. Kostyszak
- Department of Biomedical Engineering, Wroclaw University of Science and Technology, Wroclaw, Poland
| | - Daniel Lewandowski
- Department of Mechanics, Materials and Biomedical Engineering, Wroclaw University of Science and Technology, Wroclaw, Poland
| | - D. Robert Iskander
- Department of Biomedical Engineering, Wroclaw University of Science and Technology, Wroclaw, Poland
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15
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Çağlayan M, Akyol L, Balcı MA, Öncül H, Alakuş MF, Dağ U. Evaluation of corneal safety in systemic lupus erythematosus patients undergoing long-term hydroxychloroquine treatment. Cutan Ocul Toxicol 2020; 40:21-25. [PMID: 33353410 DOI: 10.1080/15569527.2020.1861003] [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: 10/22/2022]
Abstract
PURPOSE The aim of this study was to examine the effects of long-term use of hydroxychloroquine (HQ) on the pachymetric, aberrometric, and densitometric values of the cornea and corneal endothelium in lupus patients. METHOD Twenty-two eyes (study group) of 22 patients using HQ for treatment of lupus and 25 eyes (control group) of 25 healthy individuals were included in this prospective study. A specular microscopy was used to measure corneal endothelial cell density (ECD), percentage of hexagonal cells (HEX%), coefficient of variation of the cell size (CV). Then, a Pentacam® HR corneal tomography system was used to measure central corneal thickness (CCT), corneal aberrometry values in 6-mm pupil diameters and corneal densitometry values in 6-mm corneal zones (0-2 mm and 2-6 mm). RESULTS While ECD was significantly lower in the study group than in the control group (p = 0.034), CCT was significantly higher in the study group (p = 0.032). The higher-order aberrations values and the anterior corneal densitometry values in the 0-2 mm and 2-6 mm corneal zones in the study group were found to be significantly higher than the control group (p = 0.021, p = 0.007 and p = 0.013). CONCLUSION Prolonged use of HQ may cause some changes in the cornea. In the follow-up of these cases, detailed examination of the cornea as well as the macula may be important for the protection of corneal health.
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Affiliation(s)
- Mehtap Çağlayan
- Ophthalmology Clinic, Gazi Yaşargil Diyarbakir Training and Research Hospital, University of Health Sciences, Diyarbakir, Turkey
| | - Lütfi Akyol
- Rheumatology Clinic, Gazi Yaşargil Diyarbakır Training and Research Hospital, University of Healthy Sciences, Diyarbakir, Turkey
| | - Mehmet Ali Balcı
- Rheumatology Clinic, Gazi Yaşargil Diyarbakır Training and Research Hospital, University of Healthy Sciences, Diyarbakir, Turkey
| | - Hasan Öncül
- Ophthalmology Clinic, Gazi Yaşargil Diyarbakir Training and Research Hospital, University of Health Sciences, Diyarbakir, Turkey
| | - Mehmet Fuat Alakuş
- Ophthalmology Clinic, Gazi Yaşargil Diyarbakir Training and Research Hospital, University of Health Sciences, Diyarbakir, Turkey
| | - Umut Dağ
- Ophthalmology Clinic, Gazi Yaşargil Diyarbakir Training and Research Hospital, University of Health Sciences, Diyarbakir, Turkey
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16
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McLean JP, Fang S, Gallos G, Myers KM, Hendon CP. Three-dimensional collagen fiber mapping and tractography of human uterine tissue using OCT. BIOMEDICAL OPTICS EXPRESS 2020; 11:5518-5541. [PMID: 33149968 PMCID: PMC7587264 DOI: 10.1364/boe.397041] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 07/23/2020] [Accepted: 07/30/2020] [Indexed: 05/10/2023]
Abstract
Automatic quantification and visualization of 3-D collagen fiber architecture using Optical Coherence Tomography (OCT) has previously relied on polarization information and/or prior knowledge of tissue-specific fiber architecture. This study explores image processing, enhancement, segmentation, and detection algorithms to map 3-D collagen fiber architecture from OCT images alone. 3-D fiber mapping, histogram analysis, and 3-D tractography revealed fiber groupings and macro-organization previously unseen in uterine tissue samples. We applied our method on centimeter-scale mosaic OCT volumes of uterine tissue blocks from pregnant and non-pregnant specimens revealing a complex, patient-specific network of fibrous collagen and myocyte bundles.
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Affiliation(s)
- James P. McLean
- Department of Electrical Engineering, Columbia University, New York, NY 10027, USA
| | - Shuyang Fang
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - George Gallos
- Department of Anesthesiology, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Kristin M. Myers
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Christine P. Hendon
- Department of Electrical Engineering, Columbia University, New York, NY 10027, USA
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17
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Espana EM, Birk DE. Composition, structure and function of the corneal stroma. Exp Eye Res 2020; 198:108137. [PMID: 32663498 PMCID: PMC7508887 DOI: 10.1016/j.exer.2020.108137] [Citation(s) in RCA: 92] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 06/29/2020] [Accepted: 06/30/2020] [Indexed: 12/13/2022]
Abstract
No other tissue in the body depends more on the composition and organization of the extracellular matrix (ECM) for normal structure and function than the corneal stroma. The precise arrangement and orientation of collagen fibrils, lamellae and keratocytes that occurs during development and is needed in adults to maintain stromal function is dependent on the regulated interaction of multiple ECM components that contribute to attain the unique properties of the cornea: transparency, shape, mechanical strength, and avascularity. This review summarizes the contribution of different ECM components, their structure, regulation and function in modulating the properties of the corneal stroma. Fibril forming collagens (I, III, V), fibril associated collagens with interrupted triple helices (XII and XIV), network forming collagens (IV, VI and VIII) as well as small leucine-rich proteoglycans (SLRP) expressed in the stroma: decorin, biglycan, lumican, keratocan, and fibromodulin are some of the ECM components reviewed in this manuscript. There are spatial and temporal differences in the expression of these ECM components, as well as interactions among them that contribute to stromal function. Unique regions within the stroma like Bowman's layer and Descemet's layer are discussed. To define the complexity of corneal stroma composition and structure as well as the relationship to function is a daunting task. Our knowledge is expanding, and we expect that this review provides a comprehensive overview of current knowledge, definition of gaps and suggests future research directions.
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Affiliation(s)
- Edgar M Espana
- Department of Molecular Pharmacology and Physiology, USA; Cornea, External Disease and Refractive Surgery, Department of Ophthalmology, University of South Florida, Morsani College of Medicine, Tampa, FL, USA
| | - David E Birk
- Department of Molecular Pharmacology and Physiology, USA.
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18
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Dogan AS, Gurda C, Caliskan S, Onder E, Kaymaz F, Bilgic E. Effects of Topical Ozone Application on Outcomes after Accelerated Corneal Collagen Cross-linking: An Experimental Study. J Ophthalmic Vis Res 2020; 15:289-298. [PMID: 32864059 PMCID: PMC7431725 DOI: 10.18502/jovr.v15i3.7447] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 04/03/2020] [Indexed: 11/24/2022] Open
Abstract
Purpose Ozone is a trioxygen molecule that spontaneously degrades into oxygen and oxygen free radicals. This study was designed to assess the effects of topical ozone application on outcomes after corneal collagen cross-linking (CXL). Methods Enucleated fresh cadaver yearling sheep eyes (n = 28) were divided into five groups: control (C, n = 6), sham (S, n = 6), ozone only (Z, n = 6), CXL only (X, n = 5), and Ozone + CXL (ZX, n = 5). In all groups, except C, the epithelial layer was removed. In group Z, 20 μg/mL liquid ozone was topically applied. In group X, CXL was performed in the accelerated pulse mode. In group ZX, both CXL and ozone were applied. Post-interventional oxygen levels were determined and corneal confocal microscopy and optical coherence tomography were performed. Corneas were evaluated using light and electron microscopy. Results Pre-interventional central corneal thickness (CCT) was highest in the control group and considerably similar in the remaining groups (P = 0.006). Pre- and post-interventional CCT were significantly different in the ozonated groups (Z and ZX) (P = 0.028; P = 0.043). Demarcation line depths were similar in groups Z, X, and ZX (P = 0.343). Increased stromal tissue reflectivity was observed in groups Z, X, and ZX. Oxygen levels were higher in the ozonated groups (Z and ZX) (P = 0.006), and caspase activity was higher in the CXL groups (X and ZX) (P = 0.028) as compared to the other groups. Group ZX showed tighter, more regular, and parallel fibrils. Conclusion Ozone increases corneal stromal oxygenation which can probably augment the effect of CXL. Future studies should investigate the safety and feasibility of ozone application during CXL.
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Affiliation(s)
- Aysun Sanal Dogan
- Department of Ophthalmology, Saglik Bilimleri University, Diskapi Yildirim Beyazit Training and Research Hospital, Ankara, Turkey
| | - Canan Gurda
- Department of Ophthalmology, Saglik Bilimleri University, Diskapi Yildirim Beyazit Training and Research Hospital, Ankara, Turkey
| | - Sinan Caliskan
- Department of Ophthalmology, Saglik Bilimleri University, Diskapi Yildirim Beyazit Training and Research Hospital, Ankara, Turkey
| | - Evrim Onder
- Department of Pathology, Saglik Bilimleri University, Diskapi Yildirim Beyazit Training and Research Hospital, Ankara, Turkey
| | - Figen Kaymaz
- Department of Histology and Embryology, Hacettepe University, School of Medicine, Ankara, Turkey
| | - Elif Bilgic
- Department of Histology and Embryology, Hacettepe University, School of Medicine, Ankara, Turkey
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19
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Pitre JJ, Kirby MA, Li DS, Shen TT, Wang RK, O'Donnell M, Pelivanov I. Nearly-incompressible transverse isotropy (NITI) of cornea elasticity: model and experiments with acoustic micro-tapping OCE. Sci Rep 2020; 10:12983. [PMID: 32737363 PMCID: PMC7395720 DOI: 10.1038/s41598-020-69909-9] [Citation(s) in RCA: 53] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Accepted: 07/21/2020] [Indexed: 12/28/2022] Open
Abstract
The cornea provides the largest refractive power for the human visual system. Its stiffness, along with intraocular pressure (IOP), are linked to several pathologies, including keratoconus and glaucoma. Although mechanical tests can quantify corneal elasticity ex vivo, they cannot be used clinically. Dynamic optical coherence elastography (OCE), which launches and tracks shear waves to estimate stiffness, provides an attractive non-contact probe of corneal elasticity. To date, however, OCE studies report corneal moduli around tens of kPa, orders-of-magnitude less than those (few MPa) obtained by tensile/inflation testing. This large discrepancy impedes OCE's clinical adoption. Based on corneal microstructure, we introduce and fully characterize a nearly-incompressible transversely isotropic (NITI) model depicting corneal biomechanics. We show that the cornea must be described by at least two shear moduli, contrary to current single-modulus models, decoupling tensile and shear responses. We measure both as a function of IOP in ex vivo porcine cornea, obtaining values consistent with both tensile and shear tests. At pressures above 30 mmHg, the model begins to fail, consistent with non-linear changes in cornea at high IOP.
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Affiliation(s)
- John J Pitre
- Department of Bioengineering, University of Washington, Seattle, WA, USA.
| | - Mitchell A Kirby
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - David S Li
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Department of Chemical Engineering, University of Washington, Seattle, WA, USA
| | - Tueng T Shen
- Department of Ophthalmology, University of Washington, Seattle, WA, USA
| | - Ruikang K Wang
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Department of Ophthalmology, University of Washington, Seattle, WA, USA
| | - Matthew O'Donnell
- Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Ivan Pelivanov
- Department of Bioengineering, University of Washington, Seattle, WA, USA
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20
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Li H, Liu T, Mu B, Zhao X, Xue C, Shen M, Jhanji V, Wang Y. Biomechanical effect of ultraviolet-A-riboflavin cross-linking on simulated human corneal stroma model and its correlation with changes in corneal stromal microstructure. Exp Eye Res 2020; 197:108109. [PMID: 32565111 DOI: 10.1016/j.exer.2020.108109] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 05/11/2020] [Accepted: 06/02/2020] [Indexed: 12/28/2022]
Abstract
In this study, we established an experimental human corneal stroma model of simulated cornea tissue composed of thin anterior cornea strips layers obtained from small incision lenticular extraction (SMILE) surgery. We investigated the biomechanical effect of ultraviolet-A- riboflavin cross-linking at different depths of corneal stroma model and correlated it with stromal microstructural changes examined by transmission electron microscopy (TEM). Corneal strips were harvested from fresh human corneal lenticules obtained after SMILE surgery. Experimental models (n = 34) were established by superimposing the corneal lenticule strips until their thickness reached close to 500 μm. Corneal cross-linking (CXL) was performed subsequently using standard or accelerated protocol. Elasticity and viscosity were quantified using stress-strain extensometer. TEM was used to visualize the collagen fiber diameter and interfibrillar spacing. The relative change in Young's modulus (rel. ΔE) decreased nonlinearly with increasing stromal depth both in the standard and accelerated groups. Compared to the sham controls, the rel. ΔE in standard and accelerated CXL groups increased significantly in the anterior 400 μm and 275 μm depth, respectively. Also, the relative change in stress (rel. ΔS) was significantly lower after standard and accelerated CXL compared to sham controls. Depth analysis showed similar results for the elastic effect. TEM images showed a small, non-significant increase in fibril diameter. The interfibrillar spacing decreased significantly after standard and accelerated CXL in the anterior-mid stromal region. We noted that the increase of corneal stiffness correlated with decrease in interfibrillar spacing after CXL. The stiffening effect was depth dependent. The effect of accelerated CXL was less in the deep corneal stromal regions compared to standard CXL.
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Affiliation(s)
- Hongxun Li
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China; Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Tianjin Eye Hospital Tianjin, China
| | - Taiwei Liu
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, China
| | - Bokun Mu
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China; Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Tianjin Eye Hospital Tianjin, China
| | - Xinheng Zhao
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China; Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Tianjin Eye Hospital Tianjin, China
| | - Chao Xue
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China
| | - Min Shen
- Department of Mechanics, School of Mechanical Engineering, Tianjin University, Tianjin, China
| | - Vishal Jhanji
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Yan Wang
- Clinical College of Ophthalmology, Tianjin Medical University, Tianjin, China; Tianjin Key Lab of Ophthalmology and Visual Science, Tianjin Eye Institute, Tianjin Eye Hospital Tianjin, China.
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21
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Rodriguez-Pozo JA, Ramos-Lopez JF, Gonzalez-Gallardo MC, Campos F, Sanchez-Porras D, Oyonarte S, Oruezabal RI, Campos A, Martin-Piedra MA, Alaminos M. Evaluation of myopic cornea lenticules. A histochemical and clinical correlation. Exp Eye Res 2020; 196:108066. [PMID: 32439395 DOI: 10.1016/j.exer.2020.108066] [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: 09/01/2019] [Revised: 03/31/2020] [Accepted: 05/10/2020] [Indexed: 10/24/2022]
Abstract
In this work, we have analyzed the main clinical and corneal histological parameters that may be associated to the spherical equivalent (SE), age and gender of individuals with myopic refractive errors. For this purpose, 108 cornea stroma lenticules were obtained from patients subjected to ReLEx-SMILE myopia correction. Histological analyses were carried out and histochemistry and immunohistochemistry were used to quantify key histological components of the cornea stroma, including mature collagen fibers, reticular and elastic fibers, glycoproteins, proteoglycans, type-V collagen and several crystallins. Clinical and histological data were analyzed to determine their association with SE, age and gender. Results showed a significant correlation between the age range of the patients and the expression of crystallins CRY-α-A, CRY-λ1 and type-V collagen and between CRY-λ1 and corneal thickness, spherical diopters (D) and SE, although correlation between CRY-λ1 and SE was non-significant when age was controlled. Comparison of cases with low myopia and high/moderate myopia found statistical differences for D and lenticule thickness and diameter. The binary logistic regression analysis allowed us to construct a model using two clinical parameters (D and lenticule thickness). Parameters showing significant correlation with the age were the corneal radius, keratometry reading (K), OZ, CRY-α-A and type-V collagen, whereas SE, lenticule thickness, OZ, CRY-λ1 and type-V collagen showed statistically significant differences between the youngest and the oldest patients. A binary logistic regression analysis model was generated including 3 variables (D, cornea radius and OZ). No gender differences were found. The specific clinical and histological modifications found to be associated to the SE and age could be useful for a better understanding of the mechanisms involved in the genesis or progression of myopia and could establish the basement for future therapeutic options.
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Affiliation(s)
- J A Rodriguez-Pozo
- Tissue Engineering Group, Department of Histology, University of Granada, Spain
| | - J F Ramos-Lopez
- University Hospital Virgen de las Nieves, Granada, Spain; Instituto Oftalmológico de Granada, Spain
| | - M C Gonzalez-Gallardo
- Tissue Engineering Group, Department of Histology, University of Granada, Spain; Instituto de Investigación Biosanitaria ibs.GRANADA, Spain; University Hospital San Cecilio, Granada, Spain
| | - F Campos
- Tissue Engineering Group, Department of Histology, University of Granada, Spain; Instituto de Investigación Biosanitaria ibs.GRANADA, Spain
| | - D Sanchez-Porras
- Tissue Engineering Group, Department of Histology, University of Granada, Spain
| | - S Oyonarte
- Tissue Engineering Group, Department of Histology, University of Granada, Spain; Instituto de Investigación Biosanitaria ibs.GRANADA, Spain; Blood and Tissue Bank of Granada, Spain
| | - R I Oruezabal
- Andalusian Network for the design and translation of Advanced Therapies, Sevilla, Spain
| | - A Campos
- Tissue Engineering Group, Department of Histology, University of Granada, Spain; Instituto de Investigación Biosanitaria ibs.GRANADA, Spain
| | - M A Martin-Piedra
- Tissue Engineering Group, Department of Histology, University of Granada, Spain; Instituto de Investigación Biosanitaria ibs.GRANADA, Spain.
| | - M Alaminos
- Tissue Engineering Group, Department of Histology, University of Granada, Spain; Instituto de Investigación Biosanitaria ibs.GRANADA, Spain
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22
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Characterization of hyperelastic mechanical properties for youth corneal anterior central stroma based on collagen fibril crimping constitutive model. J Mech Behav Biomed Mater 2020; 103:103575. [DOI: 10.1016/j.jmbbm.2019.103575] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2019] [Revised: 11/03/2019] [Accepted: 11/29/2019] [Indexed: 11/19/2022]
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23
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Grytz R, Krishnan K, Whitley R, Libertiaux V, Sigal IA, Girkin CA, Downs JC. A Mesh-Free Approach to Incorporate Complex Anisotropic and Heterogeneous Material Properties into Eye-Specific Finite Element Models. COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2020; 358:https://doi.org/10.1016/j.cma.2019.112654. [PMID: 32051652 PMCID: PMC7015153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Commercial finite element modeling packages do not have the tools necessary to effectively incorporate the complex anisotropic and heterogeneous material properties typical of the biological tissues of the eye. We propose a mesh-free approach to incorporate realistic material properties into finite element models of individual human eyes. The method is based on the idea that material parameters can be estimated or measured at so called control points, which are arbitrary and independent of the finite element mesh. The mesh-free approach approximates the heterogeneous material parameters at the Gauss points of each finite element while the boundary value problem is solved using the standard finite element method. The proposed method was applied to an eye-specific model a human posterior pole and optic nerve head. We demonstrate that the method can be used to effectively incorporate experimental measurements of the lamina cribrosa micro-structure into the eye-specific model. It was convenient to define characteristic material orientations at the anterior and posterior scleral surface based on the eye-specific geometry of each sclera. The mesh-free approach was effective in approximating these characteristic material directions with smooth transitions across the sclera. For the first time, the method enabled the incorporation of the complex collagen architecture of the peripapillary sclera into an eye-specific model including the recently discovered meridional fibers at the anterior surface and the depth dependent width of circumferential fibers around the scleral canal. The model results suggest that disregarding the meridional fiber region may lead to an underestimation of local strain concentrations in the retina. The proposed approach should simplify future studies that aim to investigate collagen remodeling in the sclera and optic nerve head or in other biological tissues with similar challenges.
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Affiliation(s)
- Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Kapil Krishnan
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Ryan Whitley
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Vincent Libertiaux
- Equine Clinic, Department of Companion Animals and Equids, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium
- FARAH, Research Center of the Faculty of Veterinary Medicine of Liège, Belgium
| | - Ian A. Sigal
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Christopher A. Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - J. Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, Alabama, United States
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24
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Lee SL, Chen YF, Dong CY. Second harmonic generation imaging reveals asymmetry in the rotational helicity of collagen lamellae in chicken corneas. BIOMEDICAL OPTICS EXPRESS 2019; 10:5223-5234. [PMID: 31646043 PMCID: PMC6788602 DOI: 10.1364/boe.10.005223] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 09/04/2019] [Accepted: 09/05/2019] [Indexed: 05/03/2023]
Abstract
High tensile strength and optical clarity are unique properties of the cornea. These features are dictated by the three-dimensional architecture of corneal lamellae. Therefore, understanding the microscopic details of the cornea's structural organization may contribute to the development of artificial cornea for the treatment of corneal diseases. In this study, the combination of forward second harmonic generation (SHG) microcopy and fast Fourier-transform based image analysis was used to characterize the depth-dependent superstructure of chicken corneal stroma. Our results show that from the surface, adjacent lamellae of anterior chicken cornea lamella rotate in a counterclockwise direction, and the same rotational helicity is observed in left and right corneas. Furthermore, the overall average rotational pitch of lamellae is 0.92 ± 0.11 degree/µm which persists for 176 ± 14 µm in the anterior stroma. As depth further increased, the rate of lamellar rotation decreases. Upon reaching posterior stroma, lamellar orientation remains constant. Throughout the stroma, collagen lamellae in chicken rotate a total of 169 ± 21 degrees. The lack of lamellar rotation in posterior stroma suggests that packing efficiency cannot be used to explain the helicity of depth-dependent rotation of anterior stroma. In addition, although the right cornea has a higher rotational pitch (0.95 ± 11 vs 0.90 ± 10 degrees/µm) and thinner anterior stroma (173 ± 13 vs 179 ± 14 µm) than the left cornea, the two effects cancel each other out and result in similar total angular rotation of anterior stroma (161 ± 23 and 165 degrees ± 21). Finally, our observation of a total angular rotation of 169 ± 21 degrees shows that within experimental error, chicken cornea lamellae rotate around 180 degrees or half of a complete turn. Additional studies are needed to arrive at an explanation of chicken superstructure in three dimensions.
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Affiliation(s)
- Sheng-Lin Lee
- Department of Physics, National Taiwan University, Taipei 106, Taiwan, China
| | - Yang-Fang Chen
- Department of Physics, National Taiwan University, Taipei 106, Taiwan, China
| | - Chen-Yuan Dong
- Department of Physics, National Taiwan University, Taipei 106, Taiwan, China
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25
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Ávila FJ, Artal P, Bueno JM. Quantitative Discrimination of Healthy and Diseased Corneas With Second Harmonic Generation Microscopy. Transl Vis Sci Technol 2019; 8:51. [PMID: 31293806 PMCID: PMC6601709 DOI: 10.1167/tvst.8.3.51] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Accepted: 04/30/2019] [Indexed: 12/20/2022] Open
Abstract
Purpose To analyze the spatial organization of pathological corneas with second harmonic generation (SHG) imaging and to provide a proof of concept to objectively distinguish these from the healthy corneas. Methods A custom-built SHG microscope was used to image the anterior stroma of ex vivo corneas, both control and affected by some representative pathologies. The structure tensor (ST) was employed as a metric to explore and quantify the alterations in the spatial distribution of the collagen lamellae. Results The collagen arrangement differed between healthy and pathological samples. The former showed a regular distribution and a low structural dispersion (SD < 40°) within the stroma with a well-defined dominant orientation. This regular arrangement drastically turns into a disorganized pattern in pathological corneas (SD > 40°). Conclusions The combination of SHG imaging and the ST allows obtaining quantitative information to differentiate the stromal collagen organization in healthy and diseased corneas. This approach represents a feasible and powerful technique with potential applications in clinical corneal diagnoses. Translational Relevance The ST applied to SHG microscopy images of the corneal stroma provides an experimental objective score to differentiate control from pathological or damaged corneas. Future implementations of this technique in clinical environments might might be a promising tool in Ophthalmology, not only to diagnose and monitor corneal diseases, but also to follow-up surgical outcome.
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Affiliation(s)
- Francisco J Ávila
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain
| | - Pablo Artal
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain
| | - Juan M Bueno
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain
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26
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Mobaraki M, Abbasi R, Omidian Vandchali S, Ghaffari M, Moztarzadeh F, Mozafari M. Corneal Repair and Regeneration: Current Concepts and Future Directions. Front Bioeng Biotechnol 2019; 7:135. [PMID: 31245365 PMCID: PMC6579817 DOI: 10.3389/fbioe.2019.00135] [Citation(s) in RCA: 84] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Accepted: 05/20/2019] [Indexed: 12/13/2022] Open
Abstract
The cornea is a unique tissue and the most powerful focusing element of the eye, known as a window to the eye. Infectious or non-infectious diseases might cause severe visual impairments that need medical intervention to restore patients' vision. The most prominent characteristics of the cornea are its mechanical strength and transparency, which are indeed the most important criteria considerations when reconstructing the injured cornea. Corneal strength comes from about 200 collagen lamellae which criss-cross the cornea in different directions and comprise nearly 90% of the thickness of the cornea. Regarding corneal transparency, the specific characteristics of the cornea include its immune and angiogenic privilege besides its limbus zone. On the other hand, angiogenic privilege involves several active cascades in which anti-angiogenic factors are produced to compensate for the enhanced production of proangiogenic factors after wound healing. Limbus of the cornea forms a border between the corneal and conjunctival epithelium, and its limbal stem cells (LSCs) are essential in maintenance and repair of the adult cornea through its support of corneal epithelial tissue repair and regeneration. As a result, the main factors which threaten the corneal clarity are inflammatory reactions, neovascularization, and limbal deficiency. In fact, the influx of inflammatory cells causes scar formation and destruction of the limbus zone. Current studies about wound healing treatment focus on corneal characteristics such as the immune response, angiogenesis, and cell signaling. In this review, studied topics related to wound healing and new approaches in cornea regeneration, which are mostly related to the criteria mentioned above, will be discussed.
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Affiliation(s)
- Mohammadmahdi Mobaraki
- Biomaterials Group, Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran
| | - Reza Abbasi
- Biomaterials Group, Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran
| | - Sajjad Omidian Vandchali
- Biomaterials Group, Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran
| | - Maryam Ghaffari
- Biomaterials Group, Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran
| | - Fathollah Moztarzadeh
- Biomaterials Group, Department of Biomedical Engineering, Amirkabir University of Technology, Tehran, Iran
| | - Masoud Mozafari
- Department of Tissue Engineering and Regenerative Medicine, Faculty of Advanced Technologies in Medicine, Iran University of Medical Sciences, Tehran, Iran
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27
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Pijanka JK, Markov PP, Midgett D, Paterson NG, White N, Blain EJ, Nguyen TD, Quigley HA, Boote C. Quantification of collagen fiber structure using second harmonic generation imaging and two-dimensional discrete Fourier transform analysis: Application to the human optic nerve head. JOURNAL OF BIOPHOTONICS 2019; 12:e201800376. [PMID: 30578592 PMCID: PMC6506269 DOI: 10.1002/jbio.201800376] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Revised: 12/13/2018] [Accepted: 12/19/2018] [Indexed: 05/17/2023]
Abstract
Second harmonic generation (SHG) microscopy is widely used to image collagen fiber microarchitecture due to its high spatial resolution, optical sectioning capabilities and relatively nondestructive sample preparation. Quantification of SHG images requires sensitive methods to capture fiber alignment. This article presents a two-dimensional discrete Fourier transform (DFT)-based method for collagen fiber structure analysis from SHG images. The method includes integrated periodicity plus smooth image decomposition for correction of DFT edge discontinuity artefact, avoiding the loss of peripheral image data encountered with more commonly used windowing methods. Outputted parameters are as follows: the collagen fiber orientation distribution, aligned collagen content and the degree of collagen fiber dispersion along the principal orientation. We demonstrate its application to determine collagen microstructure in the human optic nerve head, showing its capability to accurately capture characteristic structural features including radial fiber alignment in the innermost layers of the bounding sclera and a circumferential collagen ring in the mid-stromal tissue. Higher spatial resolution rendering of individual lamina cribrosa beams within the nerve head is also demonstrated. Validation of the method is provided in the form of correlative results from wide-angle X-ray scattering and application of the presented method to other fibrous tissues.
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Affiliation(s)
- Jacek K. Pijanka
- Structural Biophysics Group, School of Optometry and
Vision Sciences, Cardiff University, CF24 4HQ, Cardiff, UK
| | - Petar P. Markov
- Structural Biophysics Group, School of Optometry and
Vision Sciences, Cardiff University, CF24 4HQ, Cardiff, UK
| | - Dan Midgett
- Department of Mechanical Engineering, The Johns Hopkins
University, Baltimore, MD 21218, USA
- Department of Materials Science, The Johns Hopkins
University, Baltimore, MD 21218, USA
| | - Neil G. Paterson
- Diamond Light Source, Harwell Science and Innovation
Campus, Harwell, UK
| | - Nick White
- Vivat Scientia Bioimaging Labs, School of Optometry and
Visual Sciences, Cardiff University, CF24 4HQ, Cardiff, UK
| | - Emma J. Blain
- Arthritis Research UK Biomechanics and Bioengineering
Centre, Cardiff University, CF10 3AX, Cardiff, UK
| | - Thao D. Nguyen
- Department of Mechanical Engineering, The Johns Hopkins
University, Baltimore, MD 21218, USA
- Department of Materials Science, The Johns Hopkins
University, Baltimore, MD 21218, USA
| | - Harry A. Quigley
- Wilmer Ophthalmological Institute, School of Medicine, The
Johns Hopkins University, Baltimore, MD 21287, USA
| | - Craig Boote
- Structural Biophysics Group, School of Optometry and
Vision Sciences, Cardiff University, CF24 4HQ, Cardiff, UK
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28
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Sorushanova A, Delgado LM, Wu Z, Shologu N, Kshirsagar A, Raghunath R, Mullen AM, Bayon Y, Pandit A, Raghunath M, Zeugolis DI. The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1801651. [PMID: 30126066 DOI: 10.1002/adma.201801651] [Citation(s) in RCA: 476] [Impact Index Per Article: 95.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Revised: 06/03/2018] [Indexed: 05/20/2023]
Abstract
Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.
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Affiliation(s)
- Anna Sorushanova
- Regenerative, Modular and Developmental Engineering Laboratory (REMODEL), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Luis M Delgado
- Regenerative, Modular and Developmental Engineering Laboratory (REMODEL), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Zhuning Wu
- Regenerative, Modular and Developmental Engineering Laboratory (REMODEL), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Naledi Shologu
- Regenerative, Modular and Developmental Engineering Laboratory (REMODEL), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Aniket Kshirsagar
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Rufus Raghunath
- Centre for Cell Biology and Tissue Engineering, Competence Centre Tissue Engineering for Drug Development (TEDD), Department Life Sciences and Facility Management, Institute for Chemistry and Biotechnology (ICBT), Zürich University of Applied Sciences, Wädenswil, Switzerland
| | | | - Yves Bayon
- Sofradim Production-A Medtronic Company, Trevoux, France
| | - Abhay Pandit
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
| | - Michael Raghunath
- Centre for Cell Biology and Tissue Engineering, Competence Centre Tissue Engineering for Drug Development (TEDD), Department Life Sciences and Facility Management, Institute for Chemistry and Biotechnology (ICBT), Zürich University of Applied Sciences, Wädenswil, Switzerland
| | - Dimitrios I Zeugolis
- Regenerative, Modular and Developmental Engineering Laboratory (REMODEL), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
- Science Foundation Ireland (SFI) Centre for Research in Medical Devices (CÚRAM), Biomedical Sciences Building, National University of Ireland Galway (NUI Galway), Galway, Ireland
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29
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Bradford SM, Mikula ER, Juhasz T, Brown DJ, Jester JV. Collagen fiber crimping following in vivo UVA-induced corneal crosslinking. Exp Eye Res 2018; 177:173-180. [PMID: 30118656 PMCID: PMC6911705 DOI: 10.1016/j.exer.2018.08.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 08/03/2018] [Accepted: 08/13/2018] [Indexed: 02/03/2023]
Abstract
The purpose of this study was to measure collagen fiber crimping (CFC) using nonlinear optical imaging of second harmonic generated (SHG) signals to determine the effects of UVA-riboflavin induced corneal collagen crosslinking (UVA CXL) on collagen structure. Two groups, four rabbits each, were treated in the right eye with standard UVA CXL. In vivo confocal microscopy was performed at 1, 2, and 4 weeks after treatment for the first group and up to three months for the second group to measure epithelial/stromal thickness and corneal haze during recovery. Rabbits were sacrificed at one and three months, respectively, and their corneas fixed under pressure. Regions of crosslinking were identified by the presence of collagen autofluorescence (CAF) and then collagen structure was imaged using SHG microscopy. The degree of CFC was determined by measuring the percentage difference between the length of the collagen fiber and the linear distance traveled. CFC was measured in the central anterior and posterior CXL region, the peripheral non-crosslinked region in the same cornea, and the central cornea of the non-crosslinked contralateral eye. No change in corneal thickness was detected after one month, however the stromal thickness surpassed its original baseline thickness at three months by 25.9 μm. Corneal haze peaked at one month and then began to clear. Increased CAF was detected in all CXL corneas, localized to the anterior stroma and extending to 42.4 ± 3.4% and 47.7 ± 7.6% of the corneal thickness at one and three months. There was a significant (P < 0.05) reduction in CFC in the CAF region in all eyes averaging 1.007 ± 0.006 and 1.009 ± 0.005 in one and three month samples compared to 1.017 ± 0.04 and 1.016 ± 0.06 for controls. These results indicate that there is a significant reduction in collagen crimping following UVA CXL of approximately 1%. One possible explanation for this loss of crimping could be shortening of the collagen fibers over the CXL region.
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Affiliation(s)
- Samantha M Bradford
- Biomedical Engineering, University of California, Irvine, Irvine, CA, United States.
| | - Eric R Mikula
- Ophthalmology, University of California, Irvine, Irvine, CA, United States.
| | - Tibor Juhasz
- Biomedical Engineering, University of California, Irvine, Irvine, CA, United States; Ophthalmology, University of California, Irvine, Irvine, CA, United States.
| | - Donald J Brown
- Ophthalmology, University of California, Irvine, Irvine, CA, United States.
| | - James V Jester
- Biomedical Engineering, University of California, Irvine, Irvine, CA, United States; Ophthalmology, University of California, Irvine, Irvine, CA, United States.
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30
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Microwave treatment of the cornea leads to localised disruption of the extracellular matrix. Sci Rep 2018; 8:13742. [PMID: 30213993 PMCID: PMC6137159 DOI: 10.1038/s41598-018-32110-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Accepted: 08/31/2018] [Indexed: 11/11/2022] Open
Abstract
Microwave keratoplasty is a thermo-refractive surgical procedure that can correct myopia (short-sightedness) and pathologic corneal steepening by using microwave energy to cause localised shrinkage around an annulus of the cornea leading to its flattening and vision correction. The effects on the corneal extracellular matrix, however, have not yet been evaluated, thus the current study to assess post-procedure ultrastructural changes in an in-vivo rabbit model. To achieve this a series of small-angle x-ray scattering (SAXS) experiments were carried out across whole transects of treated and untreated rabbit corneas at 0.25 mm intervals, which indicated no significant change in collagen intra-fibrillar parameters (i.e. collagen fibril diameter or axial D-period), whereas inter-fibrillar measures (i.e. fibril spacing and the degree of spatial order) were markedly altered in microwave-treated regions of the cornea. These structural matrix alterations in microwave-treated corneas have predicted implications for corneal biomechanical strength and tissue transparency, and, we contend, potentially render microwave-treated corneas resistant to surgical stabilization using corneal cross-linking procedures currently employed to combat refractive error caused by corneal steepening.
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31
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Evolution of the vertebrate corneal stroma. Prog Retin Eye Res 2018; 64:65-76. [DOI: 10.1016/j.preteyeres.2018.01.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 01/12/2018] [Accepted: 01/15/2018] [Indexed: 12/14/2022]
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32
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Jan NJ, Brazile BL, Hu D, Grube G, Wallace J, Gogola A, Sigal IA. Crimp around the globe; patterns of collagen crimp across the corneoscleral shell. Exp Eye Res 2018; 172:159-170. [PMID: 29660327 DOI: 10.1016/j.exer.2018.04.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 04/05/2018] [Accepted: 04/09/2018] [Indexed: 12/20/2022]
Abstract
Our goal was to systematically quantify the collagen crimp morphology around the corneoscleral shell, and test the hypothesis that collagen crimp is not uniform over the globe. Axial longitudinal cryosections (30 μm) of three sheep eyes, fixed at 0 mmHg IOP, were imaged using polarized light microscopy to quantify the local collagen in 8 regions: two corneal (central and peripheral) and six scleral (limbus, anterior-equatorial, equatorial, posterior-equatorial, posterior and peripapillary). Collagen crimp period (length of one wave), tortuosity (path length divided by end-to-end length), waviness (SD of orientation), amplitude (half the peak to trough distance), and conformity (width of contiguous similarly oriented bundles) were measured in each region. Measurements were obtained on 8216 collagen fiber bundles. When pooling measurements across the whole eye globe, the median crimp values were: 23.9 μm period, 13.2 μm conformity, 0.63 μm amplitude, 1.006 tortuosity, and 12.7° waviness. However, all parameters varied significantly across the globe. Median bundle periods in the central cornea, limbus, and peripapillary sclera (PPS) were 14.1 μm, 29.5 μm, and 22.9 μm, respectively. Median conformities were 20.8 μm, 14.5 μm, and 15.1 μm, respectively. Median tortuosities were 1.005, 1.007, and 1.007, respectively. Median waviness' were 11.4°, 13.2°, and 13.2°, respectively. Median amplitudes were 0.35 μm, 0.87 μm, and 0.65 μm, respectively. All parameters varied significantly across the globe. All regions differed significantly from one another on at least one parameter. Regions with small periods had large conformities, and bundles with high tortuosity had high waviness and amplitude. Waviness, tortuosity, and amplitude, associated with nonlinear biomechanical behavior, exhibited "double hump" distributions, whereas period and conformity, representing tissue organization, were substantially different between sclera and cornea. Though the biomechanical implications and origin of the patterns observed remain unclear, our findings of well-defined patterns of collagen crimp across the corneoscleral shell, consistent between eyes, support the existence of mechanisms that regulate collagen characteristics at the regional or smaller levels. These results are experimental data necessary for more realistic models of ocular biomechanics and remodeling.
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Affiliation(s)
- Ning-Jiun Jan
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Bryn L Brazile
- Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Danielle Hu
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Garrett Grube
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA
| | - Jacob Wallace
- Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Alexandra Gogola
- Department of Ophthalmology, University of Pittsburgh School of Medicine, USA
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, USA; Department of Ophthalmology, University of Pittsburgh School of Medicine, USA; McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, USA; The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA, USA.
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Anderson EW, Dwarakanathan S, Haddadin R. Experimental use of an extracellular matrix graft in pterygium surgery. Digit J Ophthalmol 2018; 23:15-17. [PMID: 29403336 DOI: 10.5693/djo.02.2017.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A 40-year-old man presented with a primary pterygium of the right eye and underwent pterygium excision using mitomycin C and placement of an extracellular matrix (ECM) adjuvant. As an adjuvant in pterygium surgery, ECM serves as a scaffold while promoting the growth of normal conjunctiva. Perioperatively, the ECM graft was found to be easily manipulated on the surgical field. It attached to the scleral bed with fibrin glue without complication. Postoperatively, there was no inflammation or local tissue reaction to the porcine ECM graft. At the most recent follow-up examination, 6 months postoperatively, there were no signs of recurrence of the pterygium past the limbus. This is the first report describing the use of ECM as an adjuvant to pterygium excision.
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Affiliation(s)
- Erik W Anderson
- Wake Forest Baptist Medical Center, Winston Salem, North Carolina
| | | | - Ramez Haddadin
- John H. Stroger, Jr. Hospital of Cook County, Chicago Illinois
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Zyablitskaya M, Munteanu EL, Nagasaki T, Paik DC. Second Harmonic Generation Signals in Rabbit Sclera As a Tool for Evaluation of Therapeutic Tissue Cross-linking (TXL) for Myopia. J Vis Exp 2018. [PMID: 29364259 DOI: 10.3791/56385] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Methods to strengthen tissue by introducing chemical bonds (non-enzymatic cross-linking) into structural proteins (fibrillar collagens) for therapy include photochemical cross-linking and tissue cross-linking (TXL) methods. Such methods for inducing mechanical tissue property changes are being employed to the cornea in corneal thinning (mechanically weakened) disorders such as keratoconus as well as the sclera in progressive myopia, where thinning and weakening of the posterior sclera occurs and likely contributes to axial elongation. The primary target proteins for such tissue strengthening are fibrillar collagens which constitute the great majority of dry weight proteins in the cornea and sclera. Fortuitously, fibrillar collagens are the main source of second harmonic generation signals in the tissue extracellular space. Therefore, modifications of the collagen proteins, such as those induced through cross-linking therapies, could potentially be detected and quantitated through the use of second harmonic generation microscopy (SHGM). Monitoring SHGM signals through the use of a laser scanning microscopy system coupled with an infrared excitation light source is an exciting modern imaging method that is enjoying widespread usage in the biomedical sciences. Thus, the present study was undertaken in order to evaluate the use of SHGM microscopy as a means to measure induced cross-linking effects in ex vivo rabbit sclera, following an injection of a chemical cross-linking agent into the sub-Tenon's space (sT), an injection approach that is standard practice for causing ocular anesthesia during ophthalmologic clinical procedures. The chemical cross-linking agent, sodium hydroxymethylglycinate (SMG), is from a class of cosmetic preservatives known as formaldehyde releasing agents (FARs). Scleral changes following reaction with SMG resulted in increases in SHG signals and correlated with shifts in thermal denaturation temperature, a standard method for evaluating induced tissue cross-linking effects.
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Affiliation(s)
- Mariya Zyablitskaya
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons
| | - E Laura Munteanu
- Confocal and Specialized Microscopy Shared Resource, Herbert Irving Comprehensive Cancer Center, Columbia University
| | - Takayuki Nagasaki
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons
| | - David C Paik
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons;
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Seoudi RS, Mechler A. Design Principles of Peptide Based Self-Assembled Nanomaterials. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1030:51-94. [DOI: 10.1007/978-3-319-66095-0_4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Jan NJ, Gomez C, Moed S, Voorhees AP, Schuman JS, Bilonick RA, Sigal IA. Microstructural Crimp of the Lamina Cribrosa and Peripapillary Sclera Collagen Fibers. Invest Ophthalmol Vis Sci 2017; 58:3378-3388. [PMID: 28687851 PMCID: PMC5501496 DOI: 10.1167/iovs.17-21811] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Purpose Although collagen microstructural crimp is a major determinant of ocular biomechanics, no direct measurements of optic nerve head (ONH) crimp have been reported. Our goal was to characterize the crimp period of the lamina cribrosa (LC) and peripapillary sclera (PPS) at low and normal IOPs. Methods ONHs from 11 sheep eyes were fixed at 10-, 5-, or 0-mm Hg IOP and crimp periods measured manually from coronal cryosections imaged with polarized light microscopy (PLM). Using linear mixed-effect models, we characterized the LC and PPS periods, and how they varied with distance from the scleral canal edge. Results A total of 17,374 manual collagen crimp period measurements were obtained with high repeatability (1.9 μm) and reproducibility (4.7 μm). The periods were smaller (P < 0.001) and less variable in the LC than in the PPS: average (SD) of 13.8 (3.1) μm in the LC, and 31.0 (10.4) μm in the PPS. LC crimp period did not vary with distance from the scleral canal wall (P > 0.1). PPS period increased with the square root of the distance to the canal (P < 0.0001). Conclusions Small, uniform crimp periods within the sheep LC and immediately adjacent PPS may indicate that these tissues are setup to prevent large or heterogeneous deformations that insult the neural tissues within the canal. An increasing more variable period with distance from the canal provides a smooth transition of mechanical properties that minimizes stress and strain concentrations.
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Affiliation(s)
- Ning-Jiun Jan
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pennsylvania, United States 2Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States 3McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania, United States 4The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Celeste Gomez
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pennsylvania, United States
| | - Saundria Moed
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pennsylvania, United States
| | - Andrew P Voorhees
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States 3McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania, United States 4The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Joel S Schuman
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States 3McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania, United States 4The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, Pennsylvania, United States 5NYU Langone Eye Center, New York University, New York, New York, United States
| | - Richard A Bilonick
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Ian A Sigal
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pennsylvania, United States 2Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States 3McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania, United States 4The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, Pennsylvania, United States
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Jan NJ, Lathrop K, Sigal IA. Collagen Architecture of the Posterior Pole: High-Resolution Wide Field of View Visualization and Analysis Using Polarized Light Microscopy. Invest Ophthalmol Vis Sci 2017; 58:735-744. [PMID: 28146238 PMCID: PMC5295768 DOI: 10.1167/iovs.16-20772] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose The purpose of this study was to leverage polarized light microscopy (PLM) to visualize the collagen fiber architecture of posterior pole and optic nerve head with micrometer-scale resolution and to identify and quantify major organizational components. Methods Eight sheep posterior poles were cryosectioned and imaged using PLM. Collagen fiber orientation was determined by using custom scripts, and the resulting orientation maps were inspected and quantified to identify major structural elements and tested for differences in mean fiber orientation and anisotropy, using linear mixed effect models. Results Images revealed an intricate organization of collagen fibers in the posterior pole. In the lamina cribrosa, interweaving fibers formed large knots and wrapped around nerve fiber pores, with beam insertions into the scleral canal wall that were either narrow and straight or wide. In the peripapillary sclera, three significantly different (P < 0.0001) components were identified: fibers oriented circumferentially proximal to the canal, radially in the innermost sclera, and unaligned with interweaving fibers. The radial fibers were between 60 and 180 μm thick, extending at least 3 mm from the canal. Conclusions PLM revealed structural aspects of the lamina cribrosa and sclera that may have important biomechanical roles but that were previously unreported or not characterized quantitatively. In the lamina cribrosa, these roles included wide and narrow beam insertions and details of collagen fibers interweaving and wrapping around the pores. In the sclera, we described regions of circumferential, radial, and unaligned “random” fibers. Although there is consensus that circumferential fibers protect neural tissues by resisting canal expansion, the role of the radial fibers remains unclear.
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Affiliation(s)
- Ning-Jiun Jan
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States 2Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Kira Lathrop
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States 2Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States 2Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
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Zyablitskaya M, Takaoka A, Munteanu EL, Nagasaki T, Trokel SL, Paik DC. Evaluation of Therapeutic Tissue Crosslinking (TXL) for Myopia Using Second Harmonic Generation Signal Microscopy in Rabbit Sclera. Invest Ophthalmol Vis Sci 2017; 58:21-29. [PMID: 28055099 PMCID: PMC5225996 DOI: 10.1167/iovs.16-20241] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Purpose Second harmonic generation signals (SHG) are emitted preferentially from collagenous tissue structures and have been used to evaluate photochemically-induced (CXL) crosslinking changes in the cornea. Since therapeutic tissue crosslinking (TXL) using sodium hydroxymethylglycinate (SMG) of the sclera is a potential treatment for high myopia, we explored the use of SHG microscopy to evaluate the effects. Methods Single sub-Tenon's (sT) injections (400 μL) using SMG (40-400 mM) were made at the equatorial 12 o'clock position of the right eye of cadaveric rabbit heads (n = 16 pairs). After 3.5 hours, confocal microscopy (CM) was performed using 860 nm two-photon excitation and 400 to 450 nm emission. Pixel density and fiber bundle "waviness" analyses were performed on the images. Crosslinking effects were confirmed using thermal denaturation (Tm) temperature. Comparison experiments with riboflavin photochemical crosslinking were done. Results Therapeutic tissue crosslinking localization studies indicated that crosslinking changes occurred at the site of injection and in adjacent sectors. Second harmonic generation signals revealed large fibrous collagenous bundled structures that displayed various degrees of waviness. Histogram analysis showed a nearly 6-fold signal increase in 400 mM SMG over 40 mM. This corresponded to a ΔTm = 13°C for 400 mM versus ΔTm = 4°C for 40 mM. Waviness analysis indicated increased fiber straightening as a result of SMG CXL. Conclusions Second harmonic generation signal intensity and fiber bundle waviness is altered by scleral tissue crosslinking using SMG. These changes provide insights into the macromolecular changes that are induced by therapeutic crosslinking technology and may provide a method to evaluate connective tissue protein changes induced by scleral crosslinking therapies.
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Affiliation(s)
- Mariya Zyablitskaya
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons, New York, New York, United States
| | - Anna Takaoka
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons, New York, New York, United States
| | - Emilia L Munteanu
- Confocal and Specialized Microscopy Shared Resource, Herbert Irving Comprehensive Cancer Center, Columbia University, New York, New York, United States
| | - Takayuki Nagasaki
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons, New York, New York, United States
| | - Stephen L Trokel
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons, New York, New York, United States
| | - David C Paik
- Department of Ophthalmology, Columbia University College of Physicians and Surgeons, New York, New York, United States
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Anayol MA, Bostancı B, Şekeroğlu MA, Şimşek M, Günaydın S, Yılmazbaş P. Assessment of Corneal Densitometry in Rheumatoid Arthritis Patients. Turk J Ophthalmol 2017. [PMID: 28630785 PMCID: PMC5468523 DOI: 10.4274/tjo.89577] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Objectives: To evaluate corneal densitometry and anterior segment parameters of rheumatoid arthritis (RA) patients and compare these results with those of age-matched healthy control subjects. Materials and Methods: Anterior segment parameters and corneal densitometry of patients with RA and healthy control subjects were assessed by Scheimpflug corneal topography. For densitometry analysis, the 12-mm diameter area of the cornea was subdivided into four concentric radial zones and anterior, central, and posterior layers based on corneal depth. Right eyes of subjects were used for statistical analysis. Results: Twenty-three consecutive patients with RA and 22 healthy control subjects were included in the study. There was no significant difference with regard to age (p=0.487) or gender (p=0.514). When anterior segment parameters of both groups were compared, no significant difference was found (p>0.05). Total corneal densitometry values were statistically higher in the RA group (p=0.030). In addition, when subdivisions of the cornea were evaluated, higher densitometry values were found in the RA group in 0-2 and 2-6 mm radial zones both in the anterior and total depth (p=0.001, p=0.003 for the 0-2 mm zone and p=0.002, p=0.009 for the 2-6 mm zone). Corneal densitometry measurement was not correlated with central corneal thickness or simulated keratometry value in RA patients or healthy control subjects. Conclusion: The corneal densitometry values were higher in RA patients when compared to healthy control subjects, even if they had clinically clear corneas. Corneal densitometry as an objective measure of corneal clarity warrants further studies in order to ascertain its clinical relevance in RA patients.
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Affiliation(s)
| | - Başak Bostancı
- Keçiören Dünyagöz Hospital, Ophthalmology Clinic, Ankara, Turkey
| | - Mehmet Ali Şekeroğlu
- Ulucanlar Eye Training and Research Hospital, Ophthalmology Clinic, Ankara, Turkey
| | - Mert Şimşek
- Ulucanlar Eye Training and Research Hospital, Ophthalmology Clinic, Ankara, Turkey
| | | | - Pelin Yılmazbaş
- Ulucanlar Eye Training and Research Hospital, Ophthalmology Clinic, Ankara, Turkey
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Robertson DM, Rogers NA, Petroll WM, Zhu M. Second harmonic generation imaging of corneal stroma after infection by Pseudomonas aeruginosa. Sci Rep 2017; 7:46116. [PMID: 28397809 PMCID: PMC5387403 DOI: 10.1038/srep46116] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 03/08/2017] [Indexed: 02/05/2023] Open
Abstract
Pseudomonas aeruginosa is a pathogenic gram-negative organism that has the ability to cause blinding corneal infections following trauma and during contact lens wear. In this study, we investigated the directional movement and orientation of an invasive corneal isolate of P. aeruginosa in the corneal stroma during infection of ex vivo and in vivo rabbit corneas using multiphoton fluorescence and second harmonic generation (SHG) imaging. Ex vivo, rabbit corneas were subject to three partial thickness wounds prior to inoculation. In vivo, New Zealand white rabbits were fit with P. aeruginosa laden contact lenses in the absence of a penetrating wound. At all time points tested, infiltration of the corneal stroma by P. aeruginosa revealed a high degree of alignment between the bacteria and collagen lamellae ex vivo (p < 0.001). In vivo, P. aeruginosa traveled throughout the stroma in discrete regions or bands. Within each region, the bacteria showed good alignment with collagen lamellae (P = 0.002). Interestingly, in both the in vitro and in vivo models, P. aeruginosa did not appear to cross the corneal limbus. Taken together, our findings suggest that P. aeruginosa exploits the precise spacing of collagen lamellae in the central cornea to facilitate spread throughout the stroma.
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Affiliation(s)
- Danielle M Robertson
- Department of Ophthalmology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Nathan A Rogers
- Department of Ophthalmology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - W Matthew Petroll
- Department of Ophthalmology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Meifang Zhu
- Department of Ophthalmology, The University of Texas Southwestern Medical Center, Dallas, TX, USA
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Su L, Huang L, Xu Y, Zhang C, Song Z. Quantitative Analysis of Collagen Produced by Rabbit Keratocytes using Second Harmonic Generation Microscopy. Curr Eye Res 2016; 42:195-200. [PMID: 27399973 DOI: 10.1080/02713683.2016.1180398] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Li Su
- Department of Ophthalmology, Shanghai General Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, People’s Republic of China
| | - Li Huang
- Department of Ophthalmology, Shanghai General Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, People’s Republic of China
| | - Yupeng Xu
- Department of Ophthalmology, Shanghai General Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, People’s Republic of China
| | - Cheng Zhang
- Department of Ophthalmology, Shanghai General Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, People’s Republic of China
| | - Zhengyu Song
- Department of Ophthalmology, Shanghai General Hospital, School of Medicine, Shanghai Jiaotong University, Shanghai, People’s Republic of China
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Benoit A, Latour G, Marie-Claire SK, Allain JM. Simultaneous microstructural and mechanical characterization of human corneas at increasing pressure. J Mech Behav Biomed Mater 2015; 60:93-105. [PMID: 26773650 DOI: 10.1016/j.jmbbm.2015.12.031] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Revised: 09/23/2015] [Accepted: 12/22/2015] [Indexed: 11/24/2022]
Abstract
The cornea, through its shape, is the main contributor to the eye׳s focusing power. Pathological alterations of the cornea strongly affect the eye power. To improve treatments, complex biomechanical models have been developed based on the architecture and mechanical properties of the collagen network in the stroma, the main layer of the cornea. However, direct investigations of the structure of the stroma, as well as its link to the mechanical response, remained limited. We propose here an original set up, associating nonlinear optical imaging and mechanical testing. By using polarization resolved Second Harmonic signals, we simultaneously quantified micrometer (orientation of the collagen lamellae) and nanometer (local disorder within lamellae) scale corneal organization. We showed that the organization of the lamellae changes along the stroma thickness. Then, we measured simultaneously the deformation on the epithelial side of the cornea and the reorientation of the collagen lamellae for increasing intraocular pressure levels, from physiological ones to pathological ones. We showed that the observed deformation is not correlated to initial orientation, but to the reorganization of the lamellae in the stroma. Our results, by providing a direct multi-scale observation, will be useful for the development of more accurate biomechanical models.
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Affiliation(s)
- Aurélie Benoit
- LMS, École polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France
| | - Gaël Latour
- LOB, École polytechnique, CNRS, Inserm U1128, Université Paris-Saclay, 91128 Palaiseau cedex, France; IMNC, Univ. Paris-Sud, Univ. Paris-Diderot, CNRS, Université Paris-Saclay, 91405 Orsay cedex, France
| | | | - Jean-Marc Allain
- LMS, École polytechnique, CNRS, Université Paris-Saclay, 91128 Palaiseau, France.
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Jan NJ, Grimm JL, Tran H, Lathrop KL, Wollstein G, Bilonick RA, Ishikawa H, Kagemann L, Schuman JS, Sigal IA. Polarization microscopy for characterizing fiber orientation of ocular tissues. BIOMEDICAL OPTICS EXPRESS 2015; 6:4705-18. [PMID: 26713188 PMCID: PMC4679248 DOI: 10.1364/boe.6.004705] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 10/01/2015] [Accepted: 10/30/2015] [Indexed: 05/03/2023]
Abstract
Characterizing the collagen fiber orientation and organization in the eye is necessary for a complete understanding of ocular biomechanics. In this study, we assess the performance of polarized light microscopy to determine collagen fiber orientation of ocular tissues. Our results demonstrate that the method provides objective, accurate, repeatable and robust data on fiber orientation with µm-scale resolution over a broad, cm-scale, field of view, unaffected by formalin fixation, without requiring tissue dehydration, labeling or staining. Together, this shows that polarized light microscopy is a powerful method for studying collagen architecture in the eye, with applications ranging from normal physiology and aging, to pathology and transplantation.
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Affiliation(s)
- Ning-Jiun Jan
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
| | - Jonathan L. Grimm
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
| | - Huong Tran
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
| | - Kira L. Lathrop
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
| | - Gadi Wollstein
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
| | - Richard A. Bilonick
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
| | - Hiroshi Ishikawa
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
| | - Larry Kagemann
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
| | - Joel S. Schuman
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
| | - Ian A. Sigal
- Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- UPMC Eye Center, Eye and Ear Institute, Ophthalmology and Visual Science Research Center, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania,
USA
- McGowan Institute for Regenerative Medicine, University of Pittsburgh School of Medicine and University of Pittsburgh, Pittsburgh, Pennsylvania,
USA
- The Louis J. Fox Center for Vision Restoration of UPMC and the University of Pittsburgh, Pittsburgh, PA,
USA
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Biophysical chemistry of the ageing eye lens. Biophys Rev 2015; 7:353-368. [PMID: 28510099 DOI: 10.1007/s12551-015-0176-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 06/23/2015] [Indexed: 12/24/2022] Open
Abstract
This review examines both recent and historical literature related to the biophysical chemistry of the proteins in the ageing eye, with a particular focus on cataract development. The lens is a vital component of the eye, acting as an optical focusing device to form clear images on the retina. The lens maintains the necessary high transparency and refractive index by expressing crystallin proteins in high concentration and eliminating all large cellular structures that may cause light scattering. This has the consequence of eliminating lens fibre cell metabolism and results in mature lens fibre cells having no mechanism for protein expression and a complete absence of protein recycling or turnover. As a result, the crystallins are some of the oldest proteins in the human body. Lack of protein repair or recycling means the lens tends to accumulate damage with age in the form of protein post-translational modifications. The crystallins can be subject to a wide range of age-related changes, including isomerisation, deamidation and racemisation. Many of these modification are highly correlated with cataract formation and represent a biochemical mechanism for age-related blindness.
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