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Villegas L, Zvietcovich F, Marcos S, Birkenfeld JS. Revealing regional variations in scleral shear modulus in a rabbit eye model using multi-directional ultrasound optical coherence elastography. Sci Rep 2024; 14:21010. [PMID: 39251655 PMCID: PMC11384758 DOI: 10.1038/s41598-024-71343-0] [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: 03/17/2024] [Accepted: 08/27/2024] [Indexed: 09/11/2024] Open
Abstract
The mechanical properties of the sclera play a critical role in supporting the ocular structure and maintaining its shape. However, non-invasive measurements to quantify scleral biomechanics remain challenging. Recently introduced multi-directional optical coherence elastography (OCE) combined with an air-coupled ultrasound transducer for excitation of elastic surface waves was used to estimate phase speed and shear modulus in ex vivo rabbit globes (n = 7). The scleral phase speed (12.1 ± 3.2 m/s) was directional-dependent and higher than for corneal tissue (5.9 ± 1.4 m/s). In the tested locations, the sclera proved to be more anisotropic than the cornea by a factor of 11 in the maximum of modified planar anisotropy coefficient. The scleral shear moduli, estimated using a modified Rayleigh-Lamb wave model, showed significantly higher values in the circumferential direction (65.4 ± 31.9 kPa) than in meridional (22.5 ± 7.2 kPa); and in the anterior zone (27.3 ± 9.3 kPa) than in the posterior zone (17.8 ± 7.4 kPa). The multi-directional scanning approach allowed both quantification and radial mapping of estimated parameters within a single measurement. The results indicate that multi-directional OCE provides a valuable non-invasive assessment of scleral tissue properties that may be useful in the development of improved ocular models, the evaluation of potential myopia treatment strategies, and disease characterization and monitoring.
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Affiliation(s)
- Lupe Villegas
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
| | - Fernando Zvietcovich
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain
- Department of Engineering, Pontificia Universidad Católica del Peru, Lima, Peru
| | - Susana Marcos
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain
- The Center for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, Rochester, NY, USA
| | - Judith S Birkenfeld
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Spain
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Bianco G, Girkin CA, Samuels BC, Fazio MA, Grytz R. Biomechanical changes of tree shrew posterior sclera during experimental myopia, after retrobulbar vehicle injections, and crosslinking using genipin. Sci Rep 2024; 14:20667. [PMID: 39237593 PMCID: PMC11377427 DOI: 10.1038/s41598-024-71276-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2024] [Accepted: 08/26/2024] [Indexed: 09/07/2024] Open
Abstract
Myopia is a common ocular condition characterized by biomechanical weakening revealed by increasing creep rate, cyclic softening scleral thinning, change of collagen fibril crimping, and excessive elongation of the posterior sclera resulting in blurred vision. Animal studies support scleral crosslinking as a potential treatment for myopia control by strengthening the weakened sclera and slowing scleral expansion. While multiple studies investigated aspects of the biomechanical weakening and strengthening effects in myopia and after scleral crosslinking, a comprehensive analysis of the underlying mechanical changes including the effect of vehicle injections is still missing. The purpose of this study was to provide a comprehensive analysis of biomechanical changes by scleral inflation testing in experimental myopia, after retrobulbar vehicle injections and scleral crosslinking using genipin in tree shrews. Our results suggest that biomechanical weakening in myopia involves an increased creep rate and higher strain levels at which collagen fibers uncrimp. Both weakening effects were reduced after scleral crosslinking using genipin at doses that were effective in slowing myopia progression. Vehicle injections increased mechanical hysteresis and had a small but significant effect on slowing myopia progression. Also, our results support scleral crosslinking as a potential treatment modality that can prevent or counteract scleral weakening effects in myopia. Furthermore, vehicle solutions may cause independent biomechanical effects, which should be considered when developing and evaluating scleral crosslinking procedures.
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Affiliation(s)
- Gianfranco Bianco
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
| | - Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
| | - Brian C Samuels
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
| | - Massimo A Fazio
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
| | - Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, 35294, USA
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De La Hoz A, Villegas L, Marcos S, Birkenfeld JS. A simple computational model for scleral stiffness assessments via air-puff deformation OCT. Front Bioeng Biotechnol 2024; 12:1426060. [PMID: 39144479 PMCID: PMC11323745 DOI: 10.3389/fbioe.2024.1426060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2024] [Accepted: 07/16/2024] [Indexed: 08/16/2024] Open
Abstract
Introduction: The mechanical properties of the sclera are related to its structural function, and changes to these properties are believed to contribute to pathologies such as myopia. Air-puff deformation imaging is a tool that uses an imaging system coupled with an air-puff excitation source to induce and measure deformation in a tissue in vivo. Typically used for the study of the cornea's mechanical properties and IOP, this tool has been proposed as a method to evaluate scleral stiffness. Methods: In this work, we present a computational model of the rabbit eye to assess scleral deformation under air-puff. Parametric studies were conducted to evaluate the effects of material properties, intraocular pressure, and other parameters on the deformation response. Output from the model was also compared to experimental measurements of air-puff deformation in rabbit eyes under varying IOP. Results: Central deformation response was found to be most influenced by material properties of the sclera (at site of air-puff and posterior), thickness, and IOP, whereas deformation profile was most influenced by material properties. Experimental and simulated IOP dependence were found to be similar (RMSE = 0.13 mm). Discussion: Scleral APDI could be a useful tool for quick in vivo assessment of scleral stiffness.
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Affiliation(s)
- Andres De La Hoz
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Lupe Villegas
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Susana Marcos
- Center for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, Rochester, NY, United States
| | - Judith S. Birkenfeld
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
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Hannay V, Czerpak C, Quigley HA, Nguyen TD. A Noninvasive Clinical Method to Measure in Vivo Mechanical Strains of the Lamina Cribrosa by OCT. OPHTHALMOLOGY SCIENCE 2024; 4:100473. [PMID: 38560276 PMCID: PMC10973664 DOI: 10.1016/j.xops.2024.100473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Revised: 01/04/2024] [Accepted: 01/12/2024] [Indexed: 04/04/2024]
Abstract
Objective To measure mechanical strain of the lamina cribrosa (LC) after intraocular pressure (IOP) change produced 1 week after a change in glaucoma medication. Design Cohort study. Participants Adult glaucoma patients (23 eyes, 15 patients) prescribed a change in IOP-lowering medication. Intervention Noninvasive OCT imaging of the eye. Main Outcome Measures Deformation calculated by digital volume correlation of OCT scans of the LC before and after IOP lowering by medication. Results Among 23 eyes, 17 eyes of 12 persons had IOP lowering ≥ 3 mmHg (reduced IOP group) with tensile anterior-posterior Ezz strain = 1.0% ± 1.1% (P = 0.003) and compressive radial strain (Err) = -0.3% ± 0.5% (P = 0.012; random effects models accounting inclusion of both eyes in some persons). Maximum in-plane principal (tensile) strain and maximum shear strain in the reduced-IOP group were as follows: Emax = 1.7% ± 1.0% and Γmax = 1.4% ± 0.7%, respectively (both P < 0.0001 vs. zero). Reduced-IOP group strains Emax and Γmax were significantly larger with greater % IOP decrease (P < 0.0001 and P < 0.0001, respectively). The compliances of the Ezz, Emax, and Γmax strain responses, defined as strain normalized by the IOP decrease, were larger with more abnormal perimetric mean deviation or visual field index values (all P ≤ 0.02). Strains were unrelated to age (all P ≥ 0.088). In reduced-IOP eyes, mean LC anterior border posterior movement was only 2.05 μm posteriorly (P = 0.052) and not related to % IOP change (P = 0.94, random effects models). Only Err was significantly related to anterior lamina depth change, becoming more negative with greater posterior LC border change (P = 0.015). Conclusions Lamina cribrosa mechanical strains can be effectively measured by changes in eye drop medication using OCT and are related to degree of visual function loss in glaucoma. Financial Disclosures Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
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Affiliation(s)
- Vanessa Hannay
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland
| | - Cameron Czerpak
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland
| | - Harry A. Quigley
- Department of Ophthalmology, Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Thao D. Nguyen
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland
- Department of Ophthalmology, Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland
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Siddharth A, Bhandari A, Singh SS, Udai AD. Effect of twisting of intravitreal injections on ocular bio-mechanics: a novel insight to ocular surgery. Biomech Model Mechanobiol 2024; 23:1013-1030. [PMID: 38361086 DOI: 10.1007/s10237-024-01819-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 01/02/2024] [Indexed: 02/17/2024]
Abstract
Although intravitreal (IVT) injections provide several advantages in treating posterior segment eye diseases, several associated challenges remain. The current study uses the finite element method (FEM) to highlight the effect of IVT needle rotation along the insertion axis on the reaction forces and deformation inside the eye. A comparison of the reaction forces at the eye's key locations has been made with and without rotation. In addition, a sensitivity analysis of various parameters, such as the needle's angular speed, insertion location, angle, gauge, shape, and intraocular pressure (IOP), has been carried out to delineate the individual parameter's effect on reaction forces during rotation. Results demonstrate that twisting the needle significantly reduces the reaction forces at the penetration location and throughout the needle travel length, resulting in quicker penetration. Moreover, ocular biomechanics are influenced by needle insertion location, angle, shape, size, and IOP. The reaction forces incurred by the patient may be reduced by using a bevel needle of the higher gauge when inserted close to the normal of the local scleral surface toward the orra serrata within the Pars Plana region. Results obtained from the current study can deepen the understanding of the twisting needle's interaction with the ocular tissue.
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Affiliation(s)
- Ashish Siddharth
- Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, 826004, India
| | - Ajay Bhandari
- Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, 826004, India.
| | - Sarthak S Singh
- Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, 826004, India
| | - Arun Dayal Udai
- Department of Mechanical Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad, 826004, India.
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Lim S, Kim C, Jafari S, Park J, Garcia SS, Demer JL. Postmortem Digital Image Correlation and Finite Element Modeling Demonstrate Posterior Scleral Deformations during Optic Nerve Adduction Tethering. Bioengineering (Basel) 2024; 11:452. [PMID: 38790319 PMCID: PMC11117839 DOI: 10.3390/bioengineering11050452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 04/25/2024] [Accepted: 04/28/2024] [Indexed: 05/26/2024] Open
Abstract
Postmortem human eyes were subjected to optic nerve (ON) traction in adduction and elevated intraocular pressure (IOP) to investigate scleral surface deformations. We incrementally adducted 11 eyes (age 74.1 ± 9.3 years, standard deviation) from 26° to 32° under normal IOP, during imaging of the posterior globe, for analysis by three-dimensional digital image correlation (3D-DIC). In the same eyes, we performed uniaxial tensile testing in multiple regions of the sclera, ON, and ON sheath. Based on individual measurements, we analyzed eye-specific finite element models (FEMs) simulating adduction and IOP loading. Analysis of 3D-DIC showed that the nasal sclera up to 1 mm from the sheath border was significantly compressed during adduction. IOP elevation from 15 to 30 mmHg induced strains less than did adduction. Tensile testing demonstrated ON sheath stiffening above 3.4% strain, which was incorporated in FEMs of adduction tethering that was quantitatively consistent with changes in scleral deformation from 3D-DIC. Simulated IOP elevation to 30 mmHg did not induce scleral surface strains outside the ON sheath. ON tethering in incremental adduction from 26° to 32° compressed the nasal and stretched the temporal sclera adjacent to the ON sheath, more so than IOP elevation. The effect of ON tethering is influenced by strain stiffening of the ON sheath.
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Affiliation(s)
- Seongjin Lim
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Changzoo Kim
- Department of Ophthalmology, Kosin University, Busan 49267, Republic of Korea;
| | - Somaye Jafari
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Joseph Park
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Stephanie S. Garcia
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
| | - Joseph L. Demer
- Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA; (S.L.); (S.J.); (J.P.); (S.S.G.)
- Neuroscience Interdepartmental Program, University of California, Los Angeles, CA 90095, USA
- Department of Neurology, University of California, Los Angeles, CA 90095, USA
- Department of Bioengineering, University of California, Los Angeles, CA 90095, USA
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7
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Luo J, Zhang Y, Ai S, Shi G, Han X, Wang Y, Zhao Y, Yang H, Li Y, He X. Two-dimensional elastic distribution imaging of the sclera using acoustic radiation force optical coherence elastography. JOURNAL OF BIOPHOTONICS 2024; 17:e202300368. [PMID: 38010344 DOI: 10.1002/jbio.202300368] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Revised: 10/23/2023] [Accepted: 11/15/2023] [Indexed: 11/29/2023]
Abstract
The scleral elasticity is closely related with many ocular diseases, but the relevant research is still insufficient. Here, we utilized optical coherence elastography to carefully study biomechanical properties of the sclera at different positions and under different intraocular pressures. Meanwhile, elastic wave velocity and Young's modulus of each position were obtained using a phase velocity algorithm. Accordingly, the two-dimensional elasticity distribution image was achieved by mapping the Young's modulus values to the corresponding structure based on the relationship between the position and its Young's modulus. Therefore, elastic information in regions-of-interest can be read and compared directly from the scleral structure, indicating that our method may be a very useful tool to evaluate the elasticity of sclera and provide intuitive and reliable proof for diagnosis and research.
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Affiliation(s)
- Jiahui Luo
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province and Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang, PR China
| | - Yubao Zhang
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province and Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang, PR China
| | - Sizhu Ai
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province and Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang, PR China
| | - Gang Shi
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province and Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang, PR China
| | - Xiao Han
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province and Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang, PR China
| | - Yidi Wang
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province and Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang, PR China
| | - Yanzhi Zhao
- Eye Center, Second Affiliated Hospital of Nanchang University, Nanchang, PR China
| | - Hongwei Yang
- Eye Center, Second Affiliated Hospital of Nanchang University, Nanchang, PR China
| | - Yingjie Li
- Department of Ophthalmology, Nanchang First Hospital, Nanchang, PR China
| | - Xingdao He
- Key Laboratory of Opto-Electronic Information Science and Technology of Jiangxi Province and Jiangxi Engineering Laboratory for Optoelectronics Testing Technology, Nanchang Hangkong University, Nanchang, PR China
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Braeu FA, Chuangsuwanich T, Tun TA, Perera S, Husain R, Thiery AH, Aung T, Barbastathis G, Girard MJA. AI-based clinical assessment of optic nerve head robustness superseding biomechanical testing. Br J Ophthalmol 2024; 108:223-231. [PMID: 36627175 DOI: 10.1136/bjo-2022-322374] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Accepted: 12/22/2022] [Indexed: 01/11/2023]
Abstract
BACKGROUND/AIMS To use artificial intelligence (AI) to: (1) exploit biomechanical knowledge of the optic nerve head (ONH) from a relatively large population; (2) assess ONH robustness (ie, sensitivity of the ONH to changes in intraocular pressure (IOP)) from a single optical coherence tomography (OCT) volume scan of the ONH without the need for biomechanical testing and (3) identify what critical three-dimensional (3D) structural features dictate ONH robustness. METHODS 316 subjects had their ONHs imaged with OCT before and after acute IOP elevation through ophthalmo-dynamometry. IOP-induced lamina cribrosa (LC) deformations were then mapped in 3D and used to classify ONHs. Those with an average effective LC strain superior to 4% were considered fragile, while those with a strain inferior to 4% robust. Learning from these data, we compared three AI algorithms to predict ONH robustness strictly from a baseline (undeformed) OCT volume: (1) a random forest classifier; (2) an autoencoder and (3) a dynamic graph convolutional neural network (DGCNN). The latter algorithm also allowed us to identify what critical 3D structural features make a given ONH robust. RESULTS All three methods were able to predict ONH robustness from a single OCT volume scan alone and without the need to perform biomechanical testing. The DGCNN (area under the curve (AUC): 0.76±0.08) outperformed the autoencoder (AUC: 0.72±0.09) and the random forest classifier (AUC: 0.69±0.05). Interestingly, to assess ONH robustness, the DGCNN mainly used information from the scleral canal and the LC insertion sites. CONCLUSIONS We propose an AI-driven approach that can assess the robustness of a given ONH solely from a single OCT volume scan of the ONH, and without the need to perform biomechanical testing. Longitudinal studies should establish whether ONH robustness could help us identify fast visual field loss progressors. PRECIS Using geometric deep learning, we can assess optic nerve head robustness (ie, sensitivity to a change in IOP) from a standard OCT scan that might help to identify fast visual field loss progressors.
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Affiliation(s)
- Fabian A Braeu
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Singapore-MIT Alliance for Research and Technology, Singapore
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore
| | - Thanadet Chuangsuwanich
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore
| | - Tin A Tun
- Singapore Eye Research Institute, Singapore
- Singapore National Eye Centre, Singapore
| | - Shamira Perera
- Singapore Eye Research Institute, Singapore
- Singapore National Eye Centre, Singapore
| | - Rahat Husain
- Singapore Eye Research Institute, Singapore
- Singapore National Eye Centre, Singapore
| | - Alexandre H Thiery
- Statistics and Applied Probability, National University of Singapore, Singapore
| | - Tin Aung
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Singapore Eye Research Institute, Singapore
- Singapore National Eye Centre, Singapore
- Duke-NUS Graduate Medical School, Singapore
| | - George Barbastathis
- Singapore-MIT Alliance for Research and Technology, Singapore
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Michaël J A Girard
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore
- Duke-NUS Graduate Medical School, Singapore
- Institute for Molecular and Clinical Ophthalmology, Basel, Switzerland
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Lyons LJ, Kazemi A, Bakri SJ, Barkmeier AJ, Iezzi R, Olsen TW, Hodge DO, Sit AJ. The Effect of Scleral Buckle Surgery on Tonographic Outflow Facility, Positional Intraocular Pressure, and Ocular Biomechanics. Ophthalmol Glaucoma 2024; 7:1-7. [PMID: 37482122 DOI: 10.1016/j.ogla.2023.07.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 06/15/2023] [Accepted: 07/17/2023] [Indexed: 07/25/2023]
Abstract
PURPOSE To investigate the in vivo effect of scleral buckle surgery on ocular biomechanics and aqueous humor dynamics. DESIGN Prospective observational cross-sectional study. PARTICIPANTS Nine patients with unilateral 360 degree encircling scleral buckles without vitrectomy for rhegmatogenous retinal detachments, between 3 and 39 months postoperative. METHODS All measurements were performed in both eyes of all participants. Intraocular pressure (IOP) was measured in the seated and supine positions using pneumatonometry. Outflow facility was measured using 2-minute weighted pneumatonography. Ocular rigidity coefficient was determined from the Friedenwald equations based on the difference in IOP with and without a weighted tonometer tip. The percentage change in IOP upon transitioning from seated to supine was calculated. Measurements for buckled and nonbuckled eyes were compared using paired Student t test of means. MAIN OUTCOME MEASURES Sitting and supine IOP and percentage difference between the 2 positions; outflow facility; ocular rigidity coefficient. RESULTS Seated IOP was similar between buckled and nonbuckled eyes (16.1 ± 2.5 vs. 16.7 ± 2.7 mmHg; P = 0.5) whereas supine IOP was lower in buckled eyes compared with nonbuckled eyes (18.7 ± 2.6 vs. 21.3 ± 2.5 mmHg; P = 0.008). The percentage increase in IOP upon change in body position from seated to supine was greater in nonbuckled eyes (17.4 ± 9.4% vs. 27.6 ± 9.5%; P = 0.005). Ocular rigidity coefficient was lower in buckled (9.9 × 10-3 ± 1.4 × 10-3 μL-1) vs. nonbuckled eyes (14.4 × 10-3 ± 3.1 × 10-3 μL-1; P = 0.006). Outflow facility was not significantly different in buckled and nonbuckled eyes. CONCLUSIONS Scleral buckling decreases ocular rigidity but does not affect outflow facility. This change in ocular biomechanics likely results in the attenuated IOP change from seated to supine position. Decreased ocular rigidity may also reduce IOP fluctuations and potentially reduce the risk for glaucoma progression. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
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Affiliation(s)
- Lance J Lyons
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota
| | - Arash Kazemi
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota
| | - Sophie J Bakri
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota
| | | | - Raymond Iezzi
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota
| | - Timothy W Olsen
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota
| | - David O Hodge
- Department of Quantitative Health Sciences, Mayo Clinic, Jacksonville, Florida
| | - Arthur J Sit
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota.
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10
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Girkin CA, Garner MA, Gardiner SK, Clark ME, Hubbard M, Karuppanan U, Bianco G, Bruno L, Fazio MA. Displacement of the Lamina Cribrosa With Acute Intraocular Pressure Increase in Brain-Dead Organ Donors. Invest Ophthalmol Vis Sci 2023; 64:19. [PMID: 38099735 PMCID: PMC10729839 DOI: 10.1167/iovs.64.15.19] [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: 05/30/2023] [Accepted: 11/21/2023] [Indexed: 12/18/2023] Open
Abstract
Purpose To examine deformations of the optic nerve head (ONH) deep tissues in response to acute elevation of intraocular pressure (IOP). Methods Research-consented brain-dead organ donors underwent imaging by spectral domain optical coherence tomography (OCT). OCT imaging was repeated while the eye was sequentially maintained at manometric pressures of 10, 30, and 50 mm Hg. Radial scans of the ONH were automatically segmented by deep learning and quantified in three dimensions by a custom algorithm. Change in lamina cribrosa (LC) depth and choroidal thickness was correlated with IOP and age by linear mixed-effect models. LC depth was computed against commonly utilized reference planes. Results Twenty-six eyes from 20 brain-dead organ donors (age range, 22-62 years; median age, 43 years) were imaged and quantified. LC depth measured against a reference plane based on Bruch's membrane (BM), BM opening, and an anterior sclera canal opening plane showed both a reduction and an increase in LC depth with IOP elevation. LC depth universally increased in depth when measured against a sclera reference plane. Choroidal (-0.5222 µm/mm Hg, P < 0.001) and retinal nerve fiber layer thickness (-0.0717 µm/mm Hg, P < 0.001) significantly thinned with increasing IOP. The magnitude of LC depth change with IOP was significantly smaller with increasing age (P < 0.03 for all reference planes). Conclusions LC depth changes with IOP reduce with age and are significantly affected by the reference plane of choice, which highlights a need for standardizing LC metrics to properly follow progressive remodeling of the loadbearing tissues of the ONH by OCT imaging and for the definition of a reference database.
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Affiliation(s)
- Christopher A. Girkin
- Department of Ophthalmology, University of Alabama at Birmingham/Callahan Eye Hospital, Birmingham, Alabama, United States
| | - Mary A. Garner
- Department of Neuroscience, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | | | - Mark E. Clark
- Department of Ophthalmology, University of Alabama at Birmingham/Callahan Eye Hospital, Birmingham, Alabama, United States
| | | | - Udayakumar Karuppanan
- Department of Ophthalmology, University of Alabama at Birmingham/Callahan Eye Hospital, Birmingham, Alabama, United States
| | - Gianfranco Bianco
- Department of Ophthalmology, University of Alabama at Birmingham/Callahan Eye Hospital, Birmingham, Alabama, United States
| | - Luigi Bruno
- Department of Mechanical, Energy and Management Engineering, University of Calabria, Rende, Italy
| | - Massimo A. Fazio
- Department of Ophthalmology, University of Alabama at Birmingham/Callahan Eye Hospital, Birmingham, Alabama, United States
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Ji F, Quinn M, Hua Y, Lee PY, Sigal IA. 2D or not 2D? Mapping the in-depth inclination of the collagen fibers of the corneoscleral shell. Exp Eye Res 2023; 237:109701. [PMID: 37898229 PMCID: PMC10872428 DOI: 10.1016/j.exer.2023.109701] [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: 06/26/2023] [Revised: 10/16/2023] [Accepted: 10/26/2023] [Indexed: 10/30/2023]
Abstract
The collagen fibers of the corneoscleral shell play a central role in the eye mechanical behavior. Although it is well-known that these fibers form a complex three-dimensional interwoven structure, biomechanical and microstructural studies often assume that the fibers are aligned in-plane with the tissues. This is convenient as it removes the out-of-plane components and allows focusing on the 2D maps of in-plane fiber organization that are often quite complex. The simplification, however, risks missing potentially important aspects of the tissue architecture and mechanics. In the cornea, for instance, fibers with high in-depth inclination have been shown to be mechanically important. Outside the cornea, the in-depth fiber orientations have not been characterized, preventing a deeper understanding of their potential roles. Our goal was to characterize in-depth collagen fiber organization over the whole corneoscleral shell. Seven sheep whole-globe axial sections from eyes fixed at an IOP of 50 mmHg were imaged using polarized light microscopy to measure collagen fiber orientations and density. In-depth fiber orientation distributions and anisotropy (degree of fiber alignment) accounting for fiber density were quantified over the whole sclera and in 15 regions: central cornea, peripheral cornea, limbus, anterior equator, equator, posterior equator, posterior sclera and peripapillary sclera on both nasal and temporal sides. Orientation distributions were fitted using a combination of a uniform distribution and a sum of π-periodic von Mises distributions, each with three parameters: primary orientation μ, fiber concentration factor k, and weighting factor a. To study the features of fibers that are not in-plane, i.e., fiber inclination, we quantified the percentage of inclined fibers and the range of inclination angles (half width at half maximum of inclination angle distribution). Our measurements showed that the fibers were not uniformly in-plane but exhibited instead a wide range of in-depth orientations, with fibers significantly more aligned in-plane in the anterior parts of the globe. We found that fitting the orientation distributions required between one and three π-periodic von Mises distributions with different primary orientations and fiber concentration factors. Regions of the posterior globe, particularly on the temporal side, had a larger percentage of inclined fibers and a larger range of inclination angles than anterior and equatorial regions. Variations of orientation distributions and anisotropies may imply varying out-of-plane tissue mechanical properties around the eye globe. Out-of-plane fibers could indicate fiber interweaving, not necessarily long, inclined fibers. Effects of small-scale fiber undulations, or crimp, were minimized by using tissues from eyes at high IOPs. These fiber features also play a role in tissue stiffness and stability and are therefore also important experimental information.
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Affiliation(s)
- Fengting Ji
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Marissa Quinn
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering and Department of Mechanical Engineering, University of Mississippi, University, MS, USA
| | - Po-Yi Lee
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.
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Hannay V, Czerpak CA, Quigley HA, Nguyen TD. A noninvasive clinical method to measure in vivo mechanical strains of the lamina cribrosa by optical coherence tomography. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.08.14.23294082. [PMID: 37645852 PMCID: PMC10462204 DOI: 10.1101/2023.08.14.23294082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
Objective To measure mechanical strain of the lamina cribrosa (LC) after intraocular pressure (IOP) change produced one week after a change in glaucoma medication. Design Cohort study. Participants Adult glaucoma patients (23 eyes, 15 patients) prescribed a change in IOP-lowering medication. Intervention Non-invasive optical coherence tomography (OCT) imaging of the eye. Main Outcomes Deformation calculated by digital volume correlation of OCT scans of the LC before and after IOP lowering by medication. Results Among 23 eyes, 17 eyes of 12 persons had IOP lowering ≥ 3 mmHg (reduced IOP group) with tensile anterior-posterior E zz strain = 1.0% ± 1.1% (p = 0.003) and compressive radial strain ( E rr ) = -0.3% ± 0.5% (p=0.012; random effects models accounting inclusion of both eyes in some persons). Maximum in-plane principal (tensile) strain and maximum shear strain in the reduced IOP group were: E max = 1.7% ± 1.0% and Γ max = 1.4% ± 0.7%, respectively (both p<0.0001 versus zero). Reduced IOP group strains E max and Γ max were significantly larger with greater %IOP decrease (<0.0001, <0.0001). The compliance of the E zz , E max , and Γ max strain response, defined as strain normalized by the IOP decrease, were larger with more abnormal perimetric mean deviation or visual field index values (all p≥0.02). Strains were unrelated to age (all p≥0.088). In reduced IOP eyes, mean LC anterior border posterior movement was only 2.05 μm posteriorly (p=0.052) and not related to % IOP change (p=0.94, random effects models). Only E rr was significantly related to ALD change, becoming more negative with greater posterior LC border change (p=0.015). Conclusion LC mechanical strains can be effectively measured by changes in eye drop medication using OCT and are related to degree of visual function loss in glaucoma. Trial Registration ClinicalTrials.gov Identifier: NCT03267849.
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13
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Chuangsuwanich T, Tun TA, Braeu FA, Yeoh CHY, Chong RS, Wang X, Aung T, Hoang QV, Girard MJA. How Myopia and Glaucoma Influence the Biomechanical Susceptibility of the Optic Nerve Head. Invest Ophthalmol Vis Sci 2023; 64:12. [PMID: 37552032 PMCID: PMC10411647 DOI: 10.1167/iovs.64.11.12] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Accepted: 07/06/2023] [Indexed: 08/09/2023] Open
Abstract
PURPOSE The purpose of this study was to assess optic nerve head (ONH) deformations following acute intraocular pressure (IOP) elevations and horizontal eye movements in control eyes, highly myopic (HM) eyes, HM eyes with glaucoma (HMG), and eyes with pathologic myopia (PM) alone or PM with staphyloma (PM + S). METHODS We studied 282 eyes, comprising of 99 controls (between +2.75 and -2.75 diopters), 51 HM (< -5 diopters), 35 HMG, 21 PM, and 75 PM + S eyes. For each eye, we imaged the ONH using spectral-domain optical coherence tomography (OCT) under the following conditions: (1) primary gaze, (2) 20 degrees adduction, (3) 20 degrees abduction, and (4) primary gaze with acute IOP elevation (to ∼35 mm Hg) achieved through ophthalmodynamometry. We then computed IOP- and gaze-induced ONH displacements and effective strains. Effective strains were compared across groups. RESULTS Under IOP elevation, we found that HM eyes exhibited significantly lower strains (3.9 ± 2.4%) than PM eyes (6.9 ± 5.0%, P < 0.001), HMG eyes (4.7 ± 1.8%, P = 0.04), and PM + S eyes (7.0 ± 5.2%, P < 0.001). Under adduction, we found that HM eyes exhibited significantly lower strains (4.8% ± 2.7%) than PM + S eyes (6.0 ± 3.1%, P = 0.02). We also found that eyes with higher axial length were associated with higher strains. CONCLUSIONS Our study revealed that eyes with HMG experienced significantly greater strains under IOP compared to eyes with HM. Furthermore, eyes with PM + S had the highest strains on the ONH of all groups.
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Affiliation(s)
- Thanadet Chuangsuwanich
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Centre, Singapore
| | - Tin A. Tun
- Eye-ACP, Duke-NUS Medical School, Singapore, Singapore
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore
| | - Fabian A. Braeu
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Centre, Singapore
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore
| | - Clarice H. Y. Yeoh
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
| | - Rachel S. Chong
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore
| | - Xiaofei Wang
- Laboratory for Biomechanics and Mechanobiology of Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, School of Engineering Medicine, Beihang University, Beijing, China
| | - Tin Aung
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Eye-ACP, Duke-NUS Medical School, Singapore, Singapore
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore
| | - Quan V. Hoang
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Eye-ACP, Duke-NUS Medical School, Singapore, Singapore
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Singapore
- Department of Ophthalmology, Columbia University, New York, New York, United States
| | - Michaël J. A. Girard
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Centre, Singapore
- Eye-ACP, Duke-NUS Medical School, Singapore, Singapore
- Institute for Molecular and Clinical Ophthalmology, Basel, Switzerland
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14
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Ji F, Bansal M, Wang B, Hua Y, Islam MR, Matuschke F, Axer M, Sigal IA. A direct fiber approach to model sclera collagen architecture and biomechanics. Exp Eye Res 2023; 232:109510. [PMID: 37207867 PMCID: PMC10330555 DOI: 10.1016/j.exer.2023.109510] [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: 11/15/2022] [Revised: 04/16/2023] [Accepted: 05/15/2023] [Indexed: 05/21/2023]
Abstract
Sclera collagen fiber microstructure and mechanical behavior are central to eye physiology and pathology. They are also complex, and are therefore often studied using modeling. Most models of sclera, however, have been built within a conventional continuum framework. In this framework, collagen fibers are incorporated as statistical distributions of fiber characteristics such as the orientation of a family of fibers. The conventional continuum approach, while proven successful for describing the macroscale behavior of the sclera, does not account for the sclera fibers are long, interwoven and interact with one another. Hence, by not considering these potentially crucial characteristics, the conventional approach has only a limited ability to capture and describe sclera structure and mechanics at smaller, fiber-level, scales. Recent advances in the tools for characterizing sclera microarchitecture and mechanics bring to the forefront the need to develop more advanced modeling techniques that can incorporate and take advantage of the newly available highly detailed information. Our goal was to create a new computational modeling approach that can represent the sclera fibrous microstructure more accurately than with the conventional continuum approach, while still capturing its macroscale behavior. In this manuscript we introduce the new modeling approach, that we call direct fiber modeling, in which the collagen architecture is built explicitly by long, continuous, interwoven fibers. The fibers are embedded in a continuum matrix representing the non-fibrous tissue components. We demonstrate the approach by doing direct fiber modeling of a rectangular patch of posterior sclera. The model integrated fiber orientations obtained by polarized light microscopy from coronal and sagittal cryosections of pig and sheep. The fibers were modeled using a Mooney-Rivlin model, and the matrix using a Neo-Hookean model. The fiber parameters were determined by inversely matching experimental equi-biaxial tensile data from the literature. After reconstruction, the direct fiber model orientations agreed well with the microscopy data both in the coronal plane (adjusted R2 = 0.8234) and in the sagittal plane (adjusted R2 = 0.8495) of the sclera. With the estimated fiber properties (C10 = 5746.9 MPa; C01 = -5002.6 MPa, matrix shear modulus 200 kPa), the model's stress-strain curves simultaneously fit the experimental data in radial and circumferential directions (adjusted R2's 0.9971 and 0.9508, respectively). The estimated fiber elastic modulus at 2.16% strain was 5.45 GPa, in reasonable agreement with the literature. During stretch, the model exhibited stresses and strains at sub-fiber level, with interactions among individual fibers which are not accounted for by the conventional continuum methods. Our results demonstrate that direct fiber models can simultaneously describe the macroscale mechanics and microarchitecture of the sclera, and therefore that the approach can provide unique insight into tissue behavior questions inaccessible with continuum approaches.
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Affiliation(s)
- Fengting Ji
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
| | - Manik Bansal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Mohammad R Islam
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Felix Matuschke
- Institute of Neuroscience and Medicine (INM-1), Forschungszentrum Jülich GmbH, Jülich, Germany
| | - Markus Axer
- Institute of Neuroscience and Medicine (INM-1), Forschungszentrum Jülich GmbH, Jülich, Germany
| | - Ian A Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.
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15
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Kwok S, Ma Y, Pan X, Liu J. Three-Dimensional Ultrasound Elastography Detects Age-Related Increase in Anterior Peripapillary Sclera and Optic Nerve Head Compression During IOP Elevation. Invest Ophthalmol Vis Sci 2023; 64:16. [PMID: 37289169 PMCID: PMC10257341 DOI: 10.1167/iovs.64.7.16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 05/18/2023] [Indexed: 06/09/2023] Open
Abstract
Purpose High-frequency ultrasound elastography offers a tool to resolve the complex and heterogeneous deformation through the full thickness of the optic nerve head (ONH) and peripapillary sclera (PPS). Using this tool, we quantified the three-dimensional deformation of the ONH and PPS in human donor eyes and evaluated age-associated changes. Methods The ONH and PPS in 15 human donor globes were imaged with a 50-MHz ultrasound probe while increasing intraocular pressure (IOP) from 15 to 30 mm Hg. Tissue displacements were obtained using correlation-based ultrasound speckle tracking. Three-dimensional spherical strains (radial, circumferential, meridional, and respective shear strains) were calculated for the ONH and PPS volumes segmented from three-dimensional ultrasound images. Age-related trends of different strains in each region of interest were explored. Results The dominant form of IOP-induced deformation in the ONH and PPS was radial compression. High-magnitude localized out-of-plane shear strains were also observed in both regions. Most strains were concentrated in the anterior one-half of the ONH and PPS. The magnitude of radial and volumetric strains increased with age in the anterior ONH and anterior PPS, indicating greater radial compression and volume loss during IOP elevation in older age. Conclusions The age-associated increase of radial compression, the predominant form of IOP-induced deformation in anterior ONH and PPS, may underlie age-associated glaucoma risk. High-frequency ultrasound elastography offers a useful tool to quantify all types of deformation comprehensively in all regions of ONH and PPS, which may improve our understanding of the biomechanical factors contributing to glaucoma risk.
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Affiliation(s)
- Sunny Kwok
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
| | - Yanhui Ma
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
- Department of Ophthalmology and Visual Sciences, The Ohio State University, Columbus, Ohio, United States
| | - Xueliang Pan
- Department of Biomedical Informatics, The Ohio State University, Columbus, Ohio, United States
| | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
- Department of Ophthalmology and Visual Sciences, The Ohio State University, Columbus, Ohio, United States
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16
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Hoerig C, Hoang QV, Aichele J, Catheline S, Mamou J. High-frequency ultrasound point-of-care device to quantify myopia-induced microstructural changes in the anterior sclera. Ophthalmic Physiol Opt 2023; 43:544-557. [PMID: 36943177 PMCID: PMC10183215 DOI: 10.1111/opo.13122] [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: 10/15/2022] [Revised: 02/06/2023] [Accepted: 02/28/2023] [Indexed: 03/23/2023]
Abstract
PURPOSE To develop a point-of-care (POC) device using high-frequency ultrasound (US) for evaluating microstructural changes in the anterior sclera associated with myopia. METHODS The proposed POC device must satisfy four primary requirements for effective clinical use: the measurement component is handheld; the software must be simple and provide real-time feedback; patient safety and health data security requirements set forth by relevant governing bodies must be satisfied and the measurement data must have sufficient signal-to-noise ratio (SNR) and repeatability. Radiofrequency (RF) echo data acquired by the POC device will be processed using our quantitative US methods to characterise tissue microstructure and biomechanical properties. RESULTS All stated requirements have been met in the developed POC device. The high-frequency transducer is housed in a custom, 3D-printed, pen-like holder that allows for easy measurements of the anterior sclera. Custom software provides a simple interface for data acquisition, real-time data display and secure data storage. Exposimetry measurements of the US pressure field indicate device compliance with United States Food and Drug Administration limits for ophthalmic US. In vivo measurements on a volunteer suggest the RF data SNR and acquisition consistency are suitable for quantitative analysis. CONCLUSIONS A fully functioning POC device using high-frequency US has been created for evaluating the microstructure of the anterior sclera. Planned studies using the POC device to scan the eyes of myopia patients will help clarify how the anterior sclera microstructure may be affected by myopia. If effective, this portable, inexpensive and user-friendly system could be an important part of routine eye examinations.
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Affiliation(s)
- Cameron Hoerig
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA
| | - Quan V. Hoang
- Singapore Eye Research Institute, Singapore National Eye Centre, Duke-NUS, Singapore
- Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, New York, USA
| | - Johannes Aichele
- Department of Earth Sciences, Institute of Geophysics, Swiss Federal Institute of Technology, Zurich, Switzerland
| | - Stefan Catheline
- Univ Lyon, Université Lyon 1, Centre Léon Bérard, INSERM, LabTAU, F-69003, Lyon, France
| | - Jonathan Mamou
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA
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17
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Sit AJ, Chen TC, Takusagawa HL, Rosdahl JA, Hoguet A, Chopra V, Richter GM, Ou Y, Kim SJ, WuDunn D. Corneal Hysteresis for the Diagnosis of Glaucoma and Assessment of Progression Risk: A Report by the American Academy of Ophthalmology. Ophthalmology 2023; 130:433-442. [PMID: 36529572 DOI: 10.1016/j.ophtha.2022.11.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 11/03/2022] [Accepted: 11/08/2022] [Indexed: 12/23/2022] Open
Abstract
PURPOSE To review the current published literature on the utility of corneal hysteresis (CH) to assist the clinician in the diagnosis of glaucoma or in the assessment of risk for disease progression in existing glaucoma patients. METHODS Searches of the peer-reviewed literature in the PubMed database were performed through July 2022. The abstracts of 423 identified articles were examined to exclude reviews and non-English articles. After inclusion and exclusion criteria were applied, 19 articles were selected, and the panel methodologist rated them for level of evidence. Eight articles were rated level I, and 5 articles were rated level II. The 6 articles rated level III were excluded. RESULTS Corneal hysteresis is lower in patients with primary open-angle glaucoma, primary angle-closure glaucoma, pseudoexfoliative glaucoma, and pseudoexfoliation syndrome compared with normal subjects. Interpretation of low CH in patients with high intraocular pressure (IOP) or on topical hypotensive medications is complicated by the influence of these parameters on CH measurements. However, CH is also lower in treatment-naïve, normal-tension glaucoma patients compared with normal subjects who have a similar IOP. In addition, lower CH is associated with an increased risk of progression of glaucoma based on visual fields or structural markers in open-angle glaucoma patients, including those with apparently well-controlled IOP. CONCLUSIONS Corneal hysteresis is lower in glaucoma patients compared with normal subjects, and lower CH is associated with an increased risk of disease progression. However, a causal relationship remains to be demonstrated. Nevertheless, measurement of CH complements current structural and functional assessments in determining disease risk in glaucoma suspects and patients. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found after the references.
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Affiliation(s)
- Arthur J Sit
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota.
| | - Teresa C Chen
- Department of Ophthalmology, Harvard Medical School, Massachusetts Eye & Ear, Glaucoma Service, Boston, Massachusetts
| | - Hana L Takusagawa
- VA Eugene Healthcare Center, Eugene, Oregon; Casey Eye Institute, Oregon Health & Sciences University, Portland, Oregon
| | - Jullia A Rosdahl
- Department of Ophthalmology, Duke University School of Medicine, Durham, North Carolina
| | - Ambika Hoguet
- Ophthalmic Consultants of Boston, Boston, Massachusetts
| | | | - Grace M Richter
- Department of Ophthalmology, Southern California Permanente Medical Group, Kaiser Permanente Los Angeles Medical Center, Los Angeles, California; USC Roski Eye Institute Keck Medicine of University of Southern California Los Angeles, Los Angeles, California
| | - Yvonne Ou
- Department of Ophthalmology, UCSF Medical Center, San Francisco, California
| | - Stephen J Kim
- Department of Ophthalmology, Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Darrell WuDunn
- University of Florida College of Medicine, Jacksonville, Department of Ophthalmology, Jacksonville, Florida
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18
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Towler J, Consejo A, Zhou D, Romano V, Levis H, Boote C, Elsheikh A, Geraghty B, Abass A. Typical localised element-specific finite element anterior eye model. Heliyon 2023; 9:e13944. [PMID: 37101628 PMCID: PMC10123217 DOI: 10.1016/j.heliyon.2023.e13944] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 11/19/2022] [Accepted: 02/15/2023] [Indexed: 03/07/2023] Open
Abstract
Purpose The study presents an averaged anterior eye geometry model combined with a localised material model that is straightforward, appropriate and amenable for implementation in finite element (FE) modelling. Methods Both right and left eye profile data of 118 subjects (63 females and 55 males) aged 22-67 years (38.5 ± 7.6) were used to build an averaged geometry model. Parametric representation of the averaged geometry model was achieved through two polynomials dividing the eye into three smoothly connected volumes. This study utilised the collagen microstructure x-ray data of 6 ex-vivo healthy human eyes, 3 right eyes and 3 left eyes in pairs from 3 donors, 1 male and 2 females aged between 60 and 80 years, to build a localised element-specific material model for the eye. Results Fitting the cornea and the posterior sclera sections to a 5th-order Zernike polynomial resulted in 21 coefficients. The averaged anterior eye geometry model recorded a limbus tangent angle of 37° at a radius of 6.6 mm from the corneal apex. In terms of material models, the difference between the stresses generated in the inflation simulation up to 15 mmHg in the ring-segmented material model and localised element-specific material model were significantly different (p < 0.001) with the ring-segmented material model recording average Von-Mises stress 0.0168 ± 0.0046 MPa and the localised element-specific material model recording average Von-Mises stress 0.0144 ± 0.0025 MPa. Conclusions The study illustrates an averaged geometry model of the anterior human eye that is easy to generate through two parametric equations. This model is combined with a localised material model that can be used either parametrically through a Zernike fitted polynomial or non-parametrically as a function of the azimuth angle and the elevation angle of the eye globe. Both averaged geometry and localised material models were built in a way that makes them easy to implement in FE analysis without additional computation cost compared to the limbal discontinuity so-called idealised eye geometry model or ring-segmented material model.
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Affiliation(s)
- Joseph Towler
- Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, UK
| | | | - Dong Zhou
- Department of Civil Engineering and Industrial Design, School of Engineering, University of Liverpool, Liverpool, UK
| | - Vito Romano
- Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, UK
- Department of Medical and Surgical Specialities, Radiological Sciences, And Public Health, Ophthalmology Clinic, University of Brescia, Italy
| | - Hannah Levis
- Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, UK
| | - Craig Boote
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, UK
| | - Ahmed Elsheikh
- Department of Civil Engineering and Industrial Design, School of Engineering, University of Liverpool, Liverpool, UK
- Beijing Advanced Innovation Centre for Biomedical Engineering, Beihang University, Beijing, China
- NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, UK
| | - Brendan Geraghty
- Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, UK
| | - Ahmed Abass
- Department of Mechanical, Materials and Aerospace Engineering, School of Engineering, University of Liverpool, Liverpool, UK
- Department of Production Engineering and Mechanical Design, Faculty of Engineering, Port Said University, Egypt
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19
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Safa BN, Bleeker A, Berdahl JP, Ethier CR. The Effects of Negative Periocular Pressure on Biomechanics of the Optic Nerve Head and Cornea: A Computational Modeling Study. Transl Vis Sci Technol 2023; 12:5. [PMID: 36745441 PMCID: PMC9910383 DOI: 10.1167/tvst.12.2.5] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Purpose The purpose of this study was to evaluate the effects of negative periocular pressure (NPP), and concomitant intraocular pressure (IOP) lowering, on the biomechanics of the optic nerve head (ONH) and cornea. Methods We developed a validated finite element (FE) model of the eye to compute tissue biomechanical strains induced in response to NPP delivered using the Multi-Pressure Dial (MPD) system. The model was informed by clinical measurements of IOP lowering and was based on published tissue properties. We also conducted sensitivity analyses by changing pressure loads and tissue properties. Results Application of -7.9 mmHg NPP decreased strain magnitudes in the ONH by c. 50% whereas increasing corneal strain magnitudes by c. 25%. Comparatively, a similar increase in corneal strain was predicted to occur due to an increase in IOP of 4 mmHg. Sensitivity studies indicated that NPP lowers strain in the ONH by reducing IOP and that these effects persisted over a range of tissue stiffnesses and spatial distributions of NPP. Conclusions NPP is predicted to considerably decrease ONH strain magnitudes. It also increases corneal strain but to an extent expected to be clinically insignificant. Thus, using NPP to lower IOP and hence decrease ONH mechanical strain is likely biomechanically beneficial for patients with glaucoma. Translational Relevance This study provides the first description of how NPP affects ONH biomechanics and explains the underlying mechanism of ONH strain reduction. It complements current empirical knowledge about the MPD system and guides future studies of NPP as a treatment for glaucoma.
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Affiliation(s)
- Babak N. Safa
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA
| | - Adam Bleeker
- Dean McGee Eye Institute Department of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
| | - John P. Berdahl
- Equinox Ophthalmic, Newport Beach, CA, USA,Vance Thompson Vision, Sioux Falls, SD, USA
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA
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20
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Chuangsuwanich T, Tun TA, Braeu FA, Wang X, Chin ZY, Panda SK, Buist M, Strouthidis N, Perera S, Nongpiur M, Aung T, Girard MJA. Differing Associations between Optic Nerve Head Strains and Visual Field Loss in Patients with Normal- and High-Tension Glaucoma. Ophthalmology 2023; 130:99-110. [PMID: 35964710 DOI: 10.1016/j.ophtha.2022.08.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 07/13/2022] [Accepted: 08/04/2022] [Indexed: 01/06/2023] Open
Abstract
PURPOSE To study the associations between optic nerve head (ONH) strains under intraocular pressure (IOP) elevation with retinal sensitivity in patients with glaucoma. DESIGN Clinic-based cross-sectional study. PARTICIPANTS Two hundred twenty-nine patients with primary open-angle glaucoma (subdivided into 115 patients with high-tension glaucoma [HTG] and 114 patients with normal-tension glaucoma [NTG]). METHODS For 1 eye of each patient, we imaged the ONH using spectral-domain OCT under the following conditions: (1) primary gaze and (2) primary gaze with acute IOP elevation (to approximately 35 mmHg) achieved through ophthalmodynamometry. A 3-dimensional strain-mapping algorithm was applied to quantify IOP-induced ONH tissue strain (i.e., deformation) in each ONH. Strains in the prelaminar tissue (PLT), the retina, the choroid, the sclera, and the lamina cribrosa (LC) were associated (using linear regression) with measures of retinal sensitivity from the 24-2 Humphrey visual field test (Carl Zeiss Meditec). This was performed globally, then locally according to a previously published regionalization scheme. MAIN OUTCOME MEASURES Associations between ONH strains and values of retinal sensitivity from visual field testing. RESULTS For patients with HTG, we found (1) significant negative linear associations between ONH strains and retinal sensitivity (P < 0.001; on average, a 1% increase in ONH strains corresponded to a decrease in retinal sensitivity of 1.1 decibels [dB]), (2) that high-strain regions colocalized with anatomically mapped regions of high visual field loss, and (3) that the strongest negative associations were observed in the superior region and in the PLT. In contrast, for patients with NTG, no significant associations between strains and retinal sensitivity were observed except in the superotemporal region of the LC. CONCLUSIONS We found significant negative associations between IOP-induced ONH strains and retinal sensitivity in a relatively large glaucoma cohort. Specifically, patients with HTG who experienced higher ONH strains were more likely to exhibit lower retinal sensitivities. Interestingly, this trend in general was less pronounced in patients with NTG, which could suggest a distinct pathophysiologic relationship between the two glaucoma subtypes.
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Affiliation(s)
- Thanadet Chuangsuwanich
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Center, Singapore, Republic of Singapore; Department of Biomedical Engineering, National University of Singapore, Singapore, Republic of Singapore.
| | - Tin A Tun
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore; Duke-NUS Medical School, Singapore, Republic of Singapore
| | - Fabian A Braeu
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Center, Singapore, Republic of Singapore; Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore
| | - Xiaofei Wang
- Laboratory for Biomechanics and Mechanobiology of Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, School of Engineering Medicine, Beihang University, Beijing, China
| | - Zhi Yun Chin
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Center, Singapore, Republic of Singapore; Department of Biomedical Engineering, National University of Singapore, Singapore, Republic of Singapore
| | - Satish Kumar Panda
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Center, Singapore, Republic of Singapore; Department of Biomedical Engineering, National University of Singapore, Singapore, Republic of Singapore
| | - Martin Buist
- Department of Biomedical Engineering, National University of Singapore, Singapore, Republic of Singapore
| | - Nicholas Strouthidis
- National Institute of Health Research, Biomedical Sciences Centre, Moorfields Eye Hospital and UCL Institute of Ophthalmology, London, United Kingdom
| | - Shamira Perera
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore
| | - Monisha Nongpiur
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore; Duke-NUS Medical School, Singapore, Republic of Singapore
| | - Tin Aung
- Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore; Duke-NUS Medical School, Singapore, Republic of Singapore
| | - Michaël J A Girard
- Ophthalmic Engineering & Innovation Laboratory, Singapore Eye Research Institute, Singapore National Eye Center, Singapore, Republic of Singapore; Duke-NUS Medical School, Singapore, Republic of Singapore; Institute for Molecular and Clinical Ophthalmology, Basel, Switzerland.
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21
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Wei J, Hua Y, Yang B, Wang B, Schmitt SE, Wang B, Lucy KA, Ishikawa H, Schuman JS, Smith MA, Wollstein G, Sigal IA. Comparing Acute IOP-Induced Lamina Cribrosa Deformations Premortem and Postmortem. Transl Vis Sci Technol 2022; 11:1. [DOI: 10.1167/tvst.11.12.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022] Open
Affiliation(s)
- Junchao Wei
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Yi Hua
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bin Yang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Engineering, Duquesne University, Pittsburgh, PA, USA
| | - Bo Wang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
- Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Samantha E. Schmitt
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Bingrui Wang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
| | - Katie A. Lucy
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
| | - Hiroshi Ishikawa
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
- Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University, Portland, OR, USA
| | - Joel S. Schuman
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
- Department of Biomedical Engineering and Electrical and Computer Engineering, New York University Tandon School of Engineering, Brooklyn, NY, USA
- Neuroscience Institute, NYU Langone Health, New York, NY, USA
| | - Matthew A. Smith
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA
- Neuroscience Institute, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Gadi Wollstein
- Department of Ophthalmology, NYU Langone Health, NYU Grossman School of Medicine, New York, NY, USA
| | - Ian A. Sigal
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA
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22
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Numerical simulation of viscoelastic fluid–structure interaction benchmarks and their application to the human eye. SN APPLIED SCIENCES 2022. [DOI: 10.1007/s42452-022-05185-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022] Open
Abstract
AbstractWe present a numerical solution method for time-dependent viscoelastic fluid–structure interaction employing the arbitrary Lagrangian Eulerian framework. The derived monolithic variational formulation is discretized in time using the shifted Crank–Nicolson scheme and in space using the finite element method. For the linearisation we employ Newton’s method with exact Jacobians. The viscoelastic fluid is modelled either using the Oldroyd-B or a Burgers-type model. The elastic structures are non-linear hyperelastic materials. We validate the implementation on benchmark problems and numerically analyse the convergence for global mesh refinement and adaptive mesh refinement using the dual-weighted residual method. Furthermore we numerically analyse the influence of the viscoelasticity of the fluid on typical goal functionals like the drag, the lift and the displacement. The derived numerical solution method is applied to ophthalmology where we analyse the interaction of the viscoelastic vitreous with its surrounding elastic structures.
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23
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Arthur P, Muok L, Nathani A, Zeng EZ, Sun L, Li Y, Singh M. Bioengineering Human Pluripotent Stem Cell-Derived Retinal Organoids and Optic Vesicle-Containing Brain Organoids for Ocular Diseases. Cells 2022; 11:3429. [PMID: 36359825 PMCID: PMC9653705 DOI: 10.3390/cells11213429] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 10/13/2022] [Accepted: 10/23/2022] [Indexed: 08/24/2023] Open
Abstract
Retinal organoids are three-dimensional (3D) structures derived from human pluripotent stem cells (hPSCs) that mimic the retina's spatial and temporal differentiation, making them useful as in vitro retinal development models. Retinal organoids can be assembled with brain organoids, the 3D self-assembled aggregates derived from hPSCs containing different cell types and cytoarchitectures that resemble the human embryonic brain. Recent studies have shown the development of optic cups in brain organoids. The cellular components of a developing optic vesicle-containing organoids include primitive corneal epithelial and lens-like cells, retinal pigment epithelia, retinal progenitor cells, axon-like projections, and electrically active neuronal networks. The importance of retinal organoids in ocular diseases such as age-related macular degeneration, Stargardt disease, retinitis pigmentosa, and diabetic retinopathy are described in this review. This review highlights current developments in retinal organoid techniques, and their applications in ocular conditions such as disease modeling, gene therapy, drug screening and development. In addition, recent advancements in utilizing extracellular vesicles secreted by retinal organoids for ocular disease treatments are summarized.
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Affiliation(s)
- Peggy Arthur
- College of Pharmacy and Pharmaceutical Sciences, Florida A&M University, Tallahassee, FL 32307, USA
| | - Laureana Muok
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, FL 32306, USA
| | - Aakash Nathani
- College of Pharmacy and Pharmaceutical Sciences, Florida A&M University, Tallahassee, FL 32307, USA
| | - Eric Z. Zeng
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, FL 32306, USA
| | - Li Sun
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, FL 32306, USA
- Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL 32306, USA
| | - Yan Li
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, FL 32306, USA
| | - Mandip Singh
- College of Pharmacy and Pharmaceutical Sciences, Florida A&M University, Tallahassee, FL 32307, USA
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24
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Markert JE, Turner DC, Jasien JV, Nyankerh CNA, Samuels BC, Downs JC. Ocular Pulse Amplitude Correlates With Ocular Rigidity at Native IOP Despite the Variability in Intraocular Pulse Volume With Each Heartbeat. Transl Vis Sci Technol 2022; 11:6. [PMID: 36074454 PMCID: PMC9469039 DOI: 10.1167/tvst.11.9.6] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose The purpose of this study was to assess ocular coat mechanical behavior using controlled ocular microvolumetric injections (MVI) of 15 µL of balanced salt solution (BSS) infused over 1 second into the anterior chamber (AC) via a syringe pump. Methods Intraocular pressure (IOP) was continuously recorded at 200 Hz with a validated implantable IOP telemetry system in 7 eyes of 7 male rhesus macaques (nonhuman primates [NHPs]) during 5 MVIs in a series at native (3 trials), 15 and 20 mm Hg baseline IOPs, repeated in 2 to 5 sessions at least 2 weeks apart. Ocular rigidity coefficients (K) and ocular pulse volume (PV) were calculated for each trial. Data were averaged across sessions within eyes; PV was analyzed with a three-level nested ANOVA, and parameter relationships were analyzed with Pearson Correlation and linear regression. Results After MVI at native baseline IOP of 10.4 ± 1.6 mm Hg, IOP increased by 9.1 ± 2.8 mm Hg (∆IOP) at a 9.6 ± 2.7 mm Hg/s slope, ocular pulse amplitude (OPA) was 0.70 ± 0.13 mm Hg on average; the average K was 0.042 ± 0.010 µL-1 and average PV was 1.16 ± 0.43 µL. PV varied significantly between trials, days, and eyes (P ≤ 0.05). OPA was significantly correlated with K at native IOP: Pearson coefficients ranged from 0.71 to 0.83 (P ≤ 0.05) and R2 ranged from 0.50 to 0.69 (P ≤ 0.05) during the first trial. Conclusions The MVI-driven ∆IOP and slope can be used to assess ocular coat mechanical behavior and measure ocular rigidity. Translational Relevance Importantly, OPA at native IOP is correlated with ocular rigidity despite the significant variability in PV between heartbeats.
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Affiliation(s)
- John E Markert
- Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Daniel C Turner
- Vision Science Graduate Program, School of Optometry, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jessica V Jasien
- Vision Science Graduate Program, School of Optometry, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Cyril N A Nyankerh
- Vision Science Graduate Program, School of Optometry, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Brian C Samuels
- Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
| | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
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25
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Prior C, Panter J, Kusumaatmaja H. A minimal model of elastic instabilities in biological filament bundles. JOURNAL OF THE ROYAL SOCIETY, INTERFACE 2022; 19:20220287. [PMID: 36128703 PMCID: PMC9490347 DOI: 10.1098/rsif.2022.0287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
We present a model of a system of elastic fibres which exhibits complex, coupled, nonlinear deformations via a connecting elastic spring network. This model can capture physically observed deformations such as global buckling, pinching and internal collapse. We explore the transitions between these deformation modes numerically, using an energy minimization approach, highlighting how supported environments, or stiff outer sheath structures, favour internal structural collapse over global deformation. We then derive a novel analytic buckling criterion for the internal collapse of the system, a mode of structural collapse pertinent in many biological filament bundles such as the optic nerve bundle and microtubule bundles involved in cell abscission.
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Affiliation(s)
- Chris Prior
- Department of Mathematical Sciences, Durham University, Durham DH1 3LE, UK
| | - Jack Panter
- Department of Physics, Durham University, Durham DH1 3LE, UK
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26
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Tringides CM, Mooney DJ. Materials for Implantable Surface Electrode Arrays: Current Status and Future Directions. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2107207. [PMID: 34716730 DOI: 10.1002/adma.202107207] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Revised: 10/26/2021] [Indexed: 06/13/2023]
Abstract
Surface electrode arrays are mainly fabricated from rigid or elastic materials, and precisely manipulated ductile metal films, which offer limited stretchability. However, the living tissues to which they are applied are nonlinear viscoelastic materials, which can undergo significant mechanical deformation in dynamic biological environments. Further, the same arrays and compositions are often repurposed for vastly different tissues rather than optimizing the materials and mechanical properties of the implant for the target application. By first characterizing the desired biological environment, and then designing a technology for a particular organ, surface electrode arrays may be more conformable, and offer better interfaces to tissues while causing less damage. Here, the various materials used in each component of a surface electrode array are first reviewed, and then electrically active implants in three specific biological systems, the nervous system, the muscular system, and skin, are described. Finally, the fabrication of next-generation surface arrays that overcome current limitations is discussed.
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Affiliation(s)
- Christina M Tringides
- Harvard Program in Biophysics, Harvard University, Cambridge, MA, 02138, USA
- Harvard-MIT Division in Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA
| | - David J Mooney
- Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA, 02138, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA
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27
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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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28
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Ni L, Riesterer J, Wang H, Berry L, Blackburn K, Chuang J, Kim W, Xu G, Moroi SE, Argento A. Method for the biomechanical analysis of aqueous veins and perilimbal sclera by three-dimensional photoacoustic imaging and strain field calculation. Sci Rep 2021; 11:22108. [PMID: 34764362 PMCID: PMC8585983 DOI: 10.1038/s41598-021-01458-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 10/12/2021] [Indexed: 11/09/2022] Open
Abstract
A method motivated by the eye's aqueous veins is described for the imaging and strain calculation within soft biological tissues. A challenge to the investigation of the biomechanics of the aqueous vein-perilimbal sclera tissue complex is resolution of tissue deformations as a function of intraocular pressure and the subsequent calculation of strain (a normalized measure of deformation). The method involves perfusion of the eye with a contrast agent during conduction of non-invasive, optical resolution photoacoustic microscopy. This imaging technique permits three-dimensional displacement measurements of tracked points on the inner walls of the veins which are used in a finite element model to determine the corresponding strains. The methods are validated against two standard strain measurement methods. Representative porcine globe perfusion experiments are presented that demonstrate the power of the method to determine complex strain fields in the veins dependent on intraocular pressure as well as vein anatomy. In these cases, veins are observed to move radially outward during increases in intraocular pressure and to possess significant spatial strain variation, possibly influenced by their branching patterns. To the authors' knowledge, these are the only such quantitative, data driven, calculations of the aqueous vein strains available in the open literature.
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Affiliation(s)
- Linyu Ni
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA
| | - John Riesterer
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA
| | - Huaizhou Wang
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA.,Currently at Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Layla Berry
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA
| | - Kara Blackburn
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Jonathan Chuang
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Wonsuk Kim
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA
| | - Guan Xu
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA
| | - Sayoko E Moroi
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, MI, 48105, USA.,Department of Ophthalmology and Visual Sciences, Havener Eye Institute, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Alan Argento
- Department of Mechanical Engineering, University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI, 48128, USA.
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29
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Bronte-Ciriza D, Birkenfeld JS, de la Hoz A, Curatolo A, Germann JA, Villegas L, Varea A, Martínez-Enríquez E, Marcos S. Estimation of scleral mechanical properties from air-puff optical coherence tomography. BIOMEDICAL OPTICS EXPRESS 2021; 12:6341-6359. [PMID: 34745741 PMCID: PMC8548012 DOI: 10.1364/boe.437981] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 08/15/2021] [Accepted: 08/15/2021] [Indexed: 05/11/2023]
Abstract
We introduce a method to estimate the biomechanical properties of the porcine sclera in intact eye globes ex vivo, using optical coherence tomography that is coupled with an air-puff excitation source, and inverse optimization techniques based on finite element modeling. Air-puff induced tissue deformation was determined at seven different locations on the ocular globe, and the maximum apex deformation, the deformation velocity, and the arc-length during deformation were quantified. In the sclera, the experimental maximum deformation amplitude and the corresponding arc length were dependent on the location of air-puff excitation. The normalized temporal deformation profile of the sclera was distinct from that in the cornea, but similar in all tested scleral locations, suggesting that this profile is independent of variations in scleral thickness. Inverse optimization techniques showed that the estimated scleral elastic modulus ranged from 1.84 ± 0.30 MPa (equatorial inferior) to 6.04 ± 2.11 MPa (equatorial temporal). The use of scleral air-puff imaging holds promise for non-invasively investigating the structural changes in the sclera associated with myopia and glaucoma, and for monitoring potential modulation of scleral stiffness in disease or treatment.
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Affiliation(s)
- David Bronte-Ciriza
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- CNR - IPCF, Istituto per i Processi Chimico-Fisici, Messina, Italy
- Co-first authors
| | - Judith S Birkenfeld
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- Co-first authors
| | - Andrés de la Hoz
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Andrea Curatolo
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- International Centre for Translational Eye Research, Warsaw, Poland
- Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland
| | - James A Germann
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Lupe Villegas
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Alejandra Varea
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Eduardo Martínez-Enríquez
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Susana Marcos
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- Center for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, NY 14642, USA
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30
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Schwaner SA, Perry RN, Kight AM, Winder E, Yang H, Morrison JC, Burgoyne CF, Ross Ethier C. Individual-Specific Modeling of Rat Optic Nerve Head Biomechanics in Glaucoma. J Biomech Eng 2021; 143:041004. [PMID: 33210142 PMCID: PMC7871999 DOI: 10.1115/1.4049157] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 11/11/2020] [Indexed: 02/04/2023]
Abstract
Glaucoma is the second leading cause of blindness worldwide and is characterized by the death of retinal ganglion cells (RGCs), the cells that send vision information to the brain. Their axons exit the eye at the optic nerve head (ONH), the main site of damage in glaucoma. The importance of biomechanics in glaucoma is indicated by the fact that elevated intraocular pressure (IOP) is a causative risk factor for the disease. However, exactly how biomechanical insult leads to RGC death is not understood. Although rat models are widely used to study glaucoma, their ONH biomechanics have not been characterized in depth. Therefore, we aimed to do so through finite element (FE) modeling. Utilizing our previously described method, we constructed and analyzed ONH models with individual-specific geometry in which the sclera was modeled as a matrix reinforced with collagen fibers. We developed eight sets of scleral material parameters based on results from our previous inverse FE study and used them to simulate the effects of elevated IOP in eight model variants of each of seven rat ONHs. Within the optic nerve, highest strains were seen inferiorly, a pattern that was consistent across model geometries and model variants. In addition, changing the collagen fiber direction to be circumferential within the peripapillary sclera resulted in more pronounced decreases in strain than changing scleral stiffness. The results from this study can be used to interpret data from rat glaucoma studies to learn more about how biomechanics affects RGC pathogenesis in glaucoma.
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Affiliation(s)
- Stephen A. Schwaner
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332
| | - Robert N. Perry
- Department of Biomedical Engineering, University of Virginia, Charlottesville, VA 22904
| | - Alison M. Kight
- Department of Bioengineering, Stanford University, Stanford, CA 94305
| | - Emily Winder
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA 30332
| | - Hongli Yang
- Optic Nerve Head Research Laboratory, Discoveries in Sight Research Laboratories, Devers Eye Institute, Legacy Health System, Portland, OR 97210
| | - John C. Morrison
- The Kenneth C. Swan Ocular Neurobiology Laboratory, Casey Eye Institute, Oregon Health and Science University, Portland, OR 97239
| | - Claude F. Burgoyne
- Optic Nerve Head Research Laboratory, Discoveries in Sight Research Laboratories, Devers Eye Institute, Legacy Health System, Portland, OR 97210
| | - C. Ross Ethier
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA 30332
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Fazio MA, Gardiner SK, Bruno L, Hubbard M, Bianco G, Karuppanan U, Kim J, El Hamdaoui M, Grytz R, Downs JC, Girkin CA. Histologic validation of optical coherence tomography-based three-dimensional morphometric measurements of the human optic nerve head: Methodology and preliminary results. Exp Eye Res 2021; 205:108475. [PMID: 33516762 PMCID: PMC8044038 DOI: 10.1016/j.exer.2021.108475] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 01/12/2021] [Accepted: 01/22/2021] [Indexed: 11/16/2022]
Abstract
PURPOSE To compare the three-dimensional (3D) morphology of the deep load-bearing structures of the human optic nerve head (ONH) as revealed in vivo by spectral domain optical coherence tomography (SDOCT) with ex vivo quantitative 3D histology. METHODS SDOCT imaging of the ONH was performed in six eyes from three brain-dead organ donors on life-support equipment awaiting organ procurement (in vivo conditions). Following organ procurement (ex vivo conditions), the eyes were enucleated and underwent a pars plana vitrectomy followed by pressurization to physiologic IOP and immersion fixation. Ex vivo ONH morphology was obtained from high-fidelity episcopic fluorescent 3D reconstruction. Morphologic parameters of the observed ONH canal geometry and peripapillary choroid, as well as the shape, visibility and depth of the lamina cribrosa were compared between ex vivo and in vivo measurements using custom software to align, scale, and manually delineate the different regions of the ONH. RESULTS There was significant correspondence between in vivo and ex vivo measurements of the depth and shape of the lamina cribrosa, along with the size and shape of Bruch's membrane opening (BMO) and anterior scleral canal opening (ASCO). Weaker correspondence was observed for choroidal thickness; as expected, a thinner choroid was seen ex vivo due to loss of blood volume upon enucleation (-79.9%, p < 0.001). In addition, the lamina was shallower (-32.3%, p = 0.0019) and BMO was smaller ex vivo (-3.38%, p = 0.026), suggesting post mortem shrinkage of the fixed tissue. On average, while highly variable, only 31% of the anterior laminar surface was visible in vivo with SDOCT (p < 0.001). CONCLUSIONS Morphologic parameters by SDOCT imaging of the deep ONH showed promising correspondence to histology metrics. Small but significant shrinkage artifact, along with large effects of exsanguination of the choroid, was seen in the ex vivo reconstructions of fixed tissues that may impact the quantification of ex vivo histoarchitecture, and this should be considered when developing models and biomarkers based on ex vivo imaging of fixed tissue. Lack of visibly of most of the lamina surface in SDOCT images is an important limitation to metrics and biomarkers based on in vivo images of the ONH deep tissues.
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Affiliation(s)
- Massimo A Fazio
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States; Department of Biomedical Engineering, The University of Alabama at Birmingham, Birmingham, AL, United States; The Viterbi Family Department of Ophthalmology, University of California, San Diego, San Diego, CA, United States.
| | - Stuart K Gardiner
- Devers Eye Institute, Discoveries in Sight, Legacy Health, Portland, OR, United States
| | - Luigi Bruno
- Department of Mechanical, Energy and Management Engineering, University of Calabria, Rende, CS, Italy
| | - Meredith Hubbard
- Department of Neurobiology, The University of Alabama at Birmingham, Birmingham, AL, United States
| | - Gianfranco Bianco
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Udayakumar Karuppanan
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Jihee Kim
- Department of Biomedical Engineering, The University of Alabama at Birmingham, Birmingham, AL, United States
| | - Mustapha El Hamdaoui
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
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Sater SH, Sass AM, Rohr JJ, Marshall-Goebel K, Ploutz-Snyder RJ, Ethier CR, Stenger MB, Kramer LA, Martin BA, Macias BR. Automated MRI-based quantification of posterior ocular globe flattening and recovery after long-duration spaceflight. Eye (Lond) 2021; 35:1869-1878. [PMID: 33514895 PMCID: PMC8225832 DOI: 10.1038/s41433-021-01408-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Revised: 01/13/2021] [Accepted: 01/14/2021] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND/OBJECTIVES Spaceflight associated neuro-ocular syndrome (SANS), a health risk related to long-duration spaceflight, is hypothesized to result from a headward fluid shift that occurs with the loss of hydrostatic pressure gradients in weightlessness. Shifts in the vascular and cerebrospinal fluid compartments alter the mechanical forces at the posterior eye and lead to flattening of the posterior ocular globe. The goal of the present study was to develop a method to quantify globe flattening observed by magnetic resonance imaging after spaceflight. SUBJECTS/METHODS Volumetric displacement of the posterior globe was quantified in 10 astronauts at 5 time points after spaceflight missions of ~6 months. RESULTS Mean globe volumetric displacement was 9.88 mm3 (95% CI 4.56-15.19 mm3, p < 0.001) on the first day of assessment after the mission (R[return]+ 1 day); 9.00 mm3 (95% CI 3.73-14.27 mm3, p = 0.001) at R + 30 days; 6.53 mm3 (95% CI 1.24-11.83 mm3, p < 0.05) at R + 90 days; 4.45 mm3 (95% CI -0.96 to 9.86 mm3, p = 0.12) at R + 180 days; and 7.21 mm3 (95% CI 1.82-12.60 mm3, p < 0.01) at R + 360 days. CONCLUSIONS There was a consistent inward displacement of the globe at the optic nerve, which had only partially resolved 1 year after landing. More pronounced globe flattening has been observed in previous studies of astronauts; however, those observations lacked quantitative measures and were subjective in nature. The novel automated method described here allows for detailed quantification of structural changes in the posterior globe that may lead to an improved understanding of SANS.
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Affiliation(s)
- Stuart H Sater
- Alcyone Therapeutics Inc., Lowell, MA, USA.,Neurophysiological Imaging and Modeling Laboratory, University of Idaho, Moscow, ID, USA
| | - Austin M Sass
- Neurophysiological Imaging and Modeling Laboratory, University of Idaho, Moscow, ID, USA
| | - Jesse J Rohr
- Neurophysiological Imaging and Modeling Laboratory, University of Idaho, Moscow, ID, USA
| | | | - Robert J Ploutz-Snyder
- Applied Biostatistics Laboratory, School of Nursing, University of Michigan, Ann Arbor, MI, USA
| | - C Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Michael B Stenger
- Cardiovascular and Vision Laboratory, Johnson Space Center, National Aeronautics and Space Administration, Houston, TX, USA
| | - Larry A Kramer
- Department of Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, TX, USA
| | - Bryn A Martin
- Alcyone Therapeutics Inc., Lowell, MA, USA. .,Neurophysiological Imaging and Modeling Laboratory, University of Idaho, Moscow, ID, USA.
| | - Brandon R Macias
- Cardiovascular and Vision Laboratory, Johnson Space Center, National Aeronautics and Space Administration, Houston, TX, USA
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Zvietcovich F, Nair A, Singh M, Aglyamov SR, Twa MD, Larin KV. Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus. Invest Ophthalmol Vis Sci 2020; 61:7. [PMID: 33141893 PMCID: PMC7645208 DOI: 10.1167/iovs.61.13.7] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Purpose Currently, the biomechanical properties of the corneo-scleral limbus when the eye-globe deforms are largely unknown. The purpose of this study is to evaluate changes in elasticity of the cornea, sclera, and limbus when subjected to different intraocular pressures (IOP) using wave-based optical coherence elastography (OCE). Special attention was given to the elasticity changes of the limbal region with respect to the elasticity variations in the neighboring corneal and scleral regions. Methods Continuous harmonic elastic waves (800 Hz) were mechanically induced in the sclera near the corneo-sclera limbus of in situ porcine eye-globes (n = 8). Wave propagation was imaged using a phase-sensitive optical coherence tomography system (PhS-OCT). The eyes were subjected to five different IOP-levels (10, 15, 20, 30, and 40 mm Hg), and spatially distributed propagation velocities were calculated along corneal, limbal, and scleral regions. Finite element analysis (FEA) of the same regions under the same excitation conditions were conducted for further validation of results. Results FEA demonstrated that the stiffness of the heterogeneous cornea-limbus-sclera transition can be characterized by phase velocity measurements of the elastic waves produced at 800 Hz in the anterior eye. Experimental results revealed that the wave speed in the limbus (cL = 6.5 m/s) is between the cornea (cc = 2.9 m/s) and sclera (cs = 10.0 m/s) at a physiological IOP level (15 mm Hg) and rapidly increases as the IOP level is increased, even surpassing the wave speed in the sclera. Finally, the change in elastic wave speed in the limbus (ΔcL∼18.5 m/s) was greater than in the cornea (Δcc ∼12.6 m/s) and sclera (Δcs∼8.1 m/s) for the same change in IOP. Conclusions We demonstrated that wave-based OCE can be utilized to assess limbus biomechanical properties. Moreover, experimental evidence showed that the corneo-scleral limbus is highly nonlinear compared to the cornea and sclera when the eye-globe is deformed by an increase of IOP. This may suggest that the limbus has enough structural flexibility to stabilize anterior eye shape during IOP changes.
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Affiliation(s)
- Fernando Zvietcovich
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Salavat R Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, Texas, United States
| | - Michael D Twa
- College of Optometry, University of Houston, Houston, Texas, United States
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
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Wang B, Hua Y, Brazile BL, Yang B, Sigal IA. Collagen fiber interweaving is central to sclera stiffness. Acta Biomater 2020; 113:429-437. [PMID: 32585309 DOI: 10.1016/j.actbio.2020.06.026] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 06/01/2020] [Accepted: 06/15/2020] [Indexed: 12/27/2022]
Abstract
The mechanical properties of the microstructural components of sclera are central to eye physiology and pathology. Because these parameters are extremely difficult to measure directly, they are often estimated using inverse-modeling matching deformations of macroscopic samples measured experimentally. Although studies of sclera microstructure show collagen fiber interweaving, current models do not account for this interweaving or the resulting fiber-fiber interactions, which might affect parameter estimates. Our goal was to test the hypothesis that constitutive parameters estimated using inverse modeling differ if models account for fiber interweaving and interactions. We developed models with non-interweaving or interweaving fibers over a wide range of volume fractions (36-91%). For each model, we estimated fiber stiffness using inverse modeling matching biaxial experimental data of human sclera. We found that interweaving increased the estimated fiber stiffness. When the collagen volume fraction was 64% or less, the stiffness of interweaving fibers was about 1.25 times that of non-interweaving fibers. For higher volume fractions, the ratio increased substantially, reaching 1.88 for a collagen volume fraction of 91%. Simulating a model (interweaving/non-interweaving) using the fiber stiffness estimated from the other model produced substantially different behavior, far from that observed experimentally. These results show that estimating microstructural component mechanical properties is highly sensitive to the assumed interwoven/non-interwoven architecture. Moreover, the results suggest that interweaving plays an important role in determining the structural stiffness of sclera, and potentially of other soft tissues in which the collagen fibers interweave. STATEMENT OF SIGNIFICANCE: The collagen fibers of sclera are interwoven, but numerical models do not account for this interweaving or the resulting fiber-fiber interactions. To determine if interweaving matters, we examined the differences in the constitutive model parameters estimated using inverse modeling between models with interweaving and non-interweaving fibers. We found that the estimated stiffness of the interweaving fibers was up to 1.88 times that of non-interweaving fibers, and that the estimate increased with collagen volume fraction. Our results suggest that fiber interweaving is a fundamental characteristic of connective tissues, additional to anisotropy, density and orientation. Better characterization of interweaving, and of its mechanical effects is likely central to understanding microstructure and biomechanics of sclera and other soft tissues.
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Role of radially aligned scleral collagen fibers in optic nerve head biomechanics. Exp Eye Res 2020; 199:108188. [PMID: 32805265 DOI: 10.1016/j.exer.2020.108188] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 07/22/2020] [Accepted: 08/06/2020] [Indexed: 01/04/2023]
Abstract
Collagen fibers organized circumferentially around the canal in the peripapillary sclera are thought to provide biomechanical support to the sensitive tissues within the optic nerve head (ONH). Recent studies have demonstrated the existence of a family of fibers in the innermost sclera organized radially from the scleral canal. Our goal was to determine the role of these radial fibers in the sensitivity of scleral canal biomechanics to acute increases in intraocular pressure (IOP). Following the same general approach of previous parametric sensitivity studies, we created nonlinear generic finite element models of a posterior pole with various combinations of radial and circumferential fibers at an IOP of 0 mmHg. We then simulated the effects of normal and elevated IOP levels (15 and 30 mmHg). We monitored four IOP-induced geometric changes: peripapillary sclera stretch, scleral canal displacement, lamina cribrosa displacement, and scleral canal expansion. In addition, we examined the radial (maximum tension) and through-thickness (maximum compression) strains within the ONH tissues. Our models predicted that: 1) radial fibers reduced the posterior displacement of the lamina, especially at elevated IOP; 2) radial fibers reduced IOP-induced radial strain within the peripapillary sclera and retinal tissue; and 3) a combination of radial and circumferential fibers maintained strains within the ONH at a level similar to those conferred by circumferential fibers alone. In conclusion, radial fibers provide support for the posterior globe, additional to that provided by circumferential fibers. Most importantly, a combination of both fiber families can better protect ONH tissues from excessive IOP-induced deformation than either alone.
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Di Michele F, Tatone A, Romano MR, Repetto R. A mechanical model of posterior vitreous detachment and generation of vitreoretinal tractions. Biomech Model Mechanobiol 2020; 19:2627-2641. [DOI: 10.1007/s10237-020-01360-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Accepted: 06/19/2020] [Indexed: 01/21/2023]
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37
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Satekenova E, Ko MWL, Kim JR. Investigation of the Optic Nerve Head Morphology Influence to the Optic Nerve Head Biomechanics - Patient Specific Model. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020; 2019:5370-5373. [PMID: 31947069 DOI: 10.1109/embc.2019.8856743] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Glaucoma is associated with damage and death of optic nerve fibers within the Lamina Cribrosa (LC) region of the Optic Nerve Head. The pathogenesis of the disease is unclear, and the anterior LC surface morphology of different individuals can be one of the possible contributor of glaucoma development and progression. The current study evaluates the relationship between the LC surface curvature and distribution of shear stresses on the LC surface. The patient-specific reconstructed ocular model was developed and analyzed in a finite element analysis software. In addition, the effect of elastic modulus of both sclera and LC on the shear stress was examined. Results showed that there is a correlation between the shear stress distribution and the curvature of the anterior LC surface. This finding highlights the potential significance of the LC morphology on the distribution of LC shear stress and require further investigation.
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38
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Schwaner SA, Hannon BG, Feola AJ, Ethier CR. Biomechanical properties of the rat sclera obtained with inverse finite element modeling. Biomech Model Mechanobiol 2020; 19:2195-2212. [PMID: 32361821 DOI: 10.1007/s10237-020-01333-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 04/18/2020] [Indexed: 11/26/2022]
Abstract
It is widely accepted that biomechanics plays an important role in glaucoma pathophysiology, but the mechanisms involved are largely unknown. Rats are a common animal model of glaucoma, and finite element models are being developed to provide much-needed insight into the biomechanical environment of the posterior rat eye. However, material properties of rat ocular tissues, including the sclera, are currently unknown. Since the sclera plays a major role in posterior ocular biomechanics, our goal was to use inverse finite element modeling to extract rat scleral material properties. We first used digital image correlation to measure scleral surface displacement during whole-globe inflation testing. We modeled the sclera as a nonlinear material with embedded collagen fibers and then fit modeled displacements to experimental data using a differential evolution algorithm. Subject-specific models were constructed in which 3 parameters described the stiffness of the ground substance and collagen fibers in the posterior eye, and 16 parameters defined the primary orientation and alignment of fibers within eight scleral sub-regions. We successfully extracted scleral material properties for eight rat eyes. Model displacements recreated general patterns of the experimental displacements but did not always match local patterns. The fiber directions and fiber concentration parameters were highly variable, but on average, fibers were aligned circumferentially and were more aligned in the peripapillary sclera than in the peripheral sclera. The material properties determined here will be used to inform future finite element models of the rat posterior eye with the goal of elucidating the role of biomechanics in glaucoma pathophysiology.
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Affiliation(s)
- Stephen A Schwaner
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 315 Ferst Drive, 2116 IBB, Atlanta, GA, 30332, USA
| | - Bailey G Hannon
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 315 Ferst Drive, 2116 IBB, Atlanta, GA, 30332, USA
| | - Andrew J Feola
- Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Healthcare System, Atlanta, GA, USA
| | - C Ross Ethier
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 315 Ferst Drive, 2116 IBB, Atlanta, GA, 30332, USA.
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, 315 Ferst Drive, 2306 IBB, Atlanta, GA, 30332, USA.
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Ma Y, Pavlatos E, Clayson K, Kwok S, Pan X, Liu J. Three-Dimensional Inflation Response of Porcine Optic Nerve Head Using High-Frequency Ultrasound Elastography. J Biomech Eng 2020; 142:051013. [PMID: 31750882 PMCID: PMC7104765 DOI: 10.1115/1.4045503] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Revised: 10/30/2019] [Indexed: 12/29/2022]
Abstract
Characterization of the biomechanical behavior of the optic nerve head (ONH) in response to intraocular pressure (IOP) elevation is important for understanding glaucoma susceptibility. In this study, we aimed to develop and validate a three-dimensional (3D) ultrasound elastographic technique to obtain mapping and visualization of the 3D distributive displacements and strains of the ONH and surrounding peripapillary tissue (PPT) during whole globe inflation from 15 to 30 mmHg. 3D scans of the posterior eye around the ONH were acquired through full tissue thickness with a high-frequency ultrasound system (50 MHz). A 3D cross-correlation-based speckle-tracking algorithm was used to compute tissue displacements at ∼30,000 kernels distributed within the region of interest (ROI), and the components of the strain tensors were calculated at each kernel by using least square estimation of the displacement gradients. The accuracy of displacement calculation was evaluated using simulated rigid-body translation on ultrasound radiofrequency (RF) data obtained from a porcine posterior eye. The accuracy of strain calculation was evaluated using finite element (FE) models. Three porcine eyes were tested showing that ONH deformation was heterogeneous with localized high strains. Substantial radial (i.e., through-thickness) compression was observed in the anterior ONH and out-of-plane (i.e., perpendicular to the surface of the shell) shear was shown to concentrate in the vicinity of ONH/PPT border. These preliminary results demonstrated the feasibility of this technique to achieve comprehensive 3D evaluation of the mechanical responses of the posterior eye, which may provide mechanistic insights into the regional susceptibility in glaucoma.
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Affiliation(s)
- Yanhui Ma
- Department of Biomedical Engineering, Ohio State
University, 1080 Carmack Road,
Columbus, OH 43210
e-mail:
| | - Elias Pavlatos
- Department of Biomedical Engineering, Ohio State
University, 1080 Carmack Road,
Columbus, OH 43210
e-mail:
| | - Keyton Clayson
- Department of Biomedical Engineering, Ohio State
University, 1080 Carmack Road,
Columbus, OH 43210
e-mail:
| | - Sunny Kwok
- Department of Biomedical Engineering, Ohio State
University, 1080 Carmack Road,
Columbus, OH 43210
e-mail:
| | - Xueliang Pan
- Department of Biomedical Informatics, Ohio State
University, 1800 Cannon Drive,
Columbus, OH 43210
e-mail:
| | - Jun Liu
- Department of Biomedical Engineering, Ohio State
University, 1080 Carmack Road,
Columbus, OH 43210
e-mail:
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Zhang L, Beotra MR, Baskaran M, Tun TA, Wang X, Perera SA, Strouthidis NG, Aung T, Boote C, Girard MJA. In Vivo Measurements of Prelamina and Lamina Cribrosa Biomechanical Properties in Humans. Invest Ophthalmol Vis Sci 2020; 61:27. [PMID: 32186670 PMCID: PMC7401475 DOI: 10.1167/iovs.61.3.27] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose To develop and use a custom virtual fields method (VFM) to assess the biomechanical properties of human prelamina and lamina cribrosa (LC) in vivo. Methods Clinical data of 20 healthy, 20 ocular hypertensive (OHT), 20 primary open-angle glaucoma, and 16 primary angle-closure glaucoma eyes were analyzed. For each eye, the intraocular pressure (IOP) and optical coherence tomography (OCT) images of the optic nerve head (ONH) were acquired at the normal state and after acute IOP elevation. The IOP-induced deformation of the ONH was obtained from the OCT volumes using a three-dimensional tracking algorithm and fed into the VFM to extract the biomechanical properties of the prelamina and the LC in vivo. Statistical measurements and P values from the Mann-Whitney-Wilcoxon tests were reported. Results The average shear moduli of the prelamina and the LC were 64.2 ± 36.1 kPa and 73.1 ± 46.9 kPa, respectively. The shear moduli of the prelamina of healthy subjects were significantly lower than those of the OHT subjects. Comparisons between healthy and glaucoma subjects could not be made robustly due to a small sample size. Conclusions We have developed a methodology to assess the biomechanical properties of human ONH tissues in vivo and provide preliminary comparisons in healthy and OHT subjects. Our proposed methodology may be of interest for glaucoma management.
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Jett SV, Hudson LT, Baumwart R, Bohnstedt BN, Mir A, Burkhart HM, Holzapfel GA, Wu Y, Lee CH. Integration of polarized spatial frequency domain imaging (pSFDI) with a biaxial mechanical testing system for quantification of load-dependent collagen architecture in soft collagenous tissues. Acta Biomater 2020; 102:149-168. [PMID: 31734412 PMCID: PMC8101699 DOI: 10.1016/j.actbio.2019.11.028] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Revised: 11/11/2019] [Accepted: 11/12/2019] [Indexed: 12/30/2022]
Abstract
Collagen fiber networks provide the structural strength of tissues, such as tendons, skin and arteries. Quantifying the fiber architecture in response to mechanical loads is essential towards a better understanding of the tissue-level mechanical behaviors, especially in assessing disease-driven functional changes. To enable novel investigations into these load-dependent fiber structures, a polarized spatial frequency domain imaging (pSFDI) device was developed and, for the first time, integrated with a biaxial mechanical testing system. The integrated instrument is capable of a wide-field quantification of the fiber orientation and the degree of optical anisotropy (DOA), representing the local degree of fiber alignment. The opto-mechanical instrument''s performance was assessed through uniaxial loading on tendon tissues with known collagen fiber microstructures. Our results revealed that the bulk fiber orientation angle of the tendon tissue changed minimally with loading (median ± 0.5*IQR of 52.7° ± 3.3° and 51.9° ± 3.3° under 0 and 3% longitudinal strains, respectively), whereas on a micro-scale, the fibers became better aligned with the direction of loading: the DOA (mean ± SD) increased from 0.149 ± 0.032 to 0.198 ± 0.056 under 0 and 3% longitudinal strains, respectively, p < 0.001. The integrated instrument was further applied to study two representative mitral valve anterior leaflet (MVAL) tissues subjected to various biaxial loads. The fiber orientations within these representative MVAL tissue specimens demonstrated noticeable heterogeneity, with the local fiber orientations dependent upon the sample, the spatial and transmural locations, and the applied loading. Our results also showed that fibers were generally better aligned under equibiaxial (DOA = 0.089 ± 0.036) and circumferentially-dominant loading (DOA = 0.086 ± 0.037) than under the radially-dominant loading (DOA = 0.077 ± 0.034), indicating circumferential predisposition. These novel findings exemplify a deeper understanding of the load-dependent collagen fiber microstructures obtained through the use of the integrated opto-mechanical instrument. STATEMENT OF SIGNIFICANCE: In this study, a novel quantitative opto-mechanical system was developed by combining a polarized Spatial Frequency Domain Imaging (pSFDI) device with a biaxial mechanical tester. The integrated system was used to quantify the load-dependent collagen fiber microstructures in representative tendon and mitral valve anterior leaflet (MVAL) tissues. Our results revealed that MVAL's fiber architectures exhibited load-dependent spatial and transmural heterogeneities, suggesting further microstructural complexity than previously reported in heart valve tissues. These novel findings were possible through the system's ability to, for the first time, capture the load-dependent collagen architecture in the mitral valve anterior leaflet tissue over a wide field of view (e.g., 10 × 10 mm for the MVAL tissue specimens). Such capabilities afford unique future opportunities to improve patient outcomes through concurrent mechanical and microstructural assessments of healthy and diseased tissues in conditions such as heart valve regurgitation and calcification.
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Affiliation(s)
- Samuel V Jett
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, Affiliated Faculty Member, Institute for Biomedical Engineering, Science, and Technology, The University of Oklahoma, 865 Asp Ave., Felgar Hall Rm. 219C, Norman, OK 73019-3609, United States
| | - Luke T Hudson
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, Affiliated Faculty Member, Institute for Biomedical Engineering, Science, and Technology, The University of Oklahoma, 865 Asp Ave., Felgar Hall Rm. 219C, Norman, OK 73019-3609, United States
| | - Ryan Baumwart
- Center for Veterinary Health Sciences, Oklahoma State University, 2065 W. Farm Rd., Stillwater, OK 74078, United States
| | - Bradley N Bohnstedt
- Department of Neurosurgery, The University of Oklahoma Health Sciences Center, 1000 N Lincoln Blvd #400, Oklahoma City, OK 73104, United States
| | - Arshid Mir
- Division of Pediatric Cardiology, Department of Pediatrics, The University of Oklahoma Health Sciences Center, 1200 Children's Ave., Suite 2F, Oklahoma City, OK 73104, United States
| | - Harold M Burkhart
- Division of Cardiothoracic Surgery, Department of Surgery, The University of Oklahoma Health Sciences Center, 800 Stanton L. Young Blvd. Suite 9000, Oklahoma City, OK 73104, United States
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2 8010 Graz, Austria; Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway
| | - Yi Wu
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, Affiliated Faculty Member, Institute for Biomedical Engineering, Science, and Technology, The University of Oklahoma, 865 Asp Ave., Felgar Hall Rm. 219C, Norman, OK 73019-3609, United States
| | - Chung-Hao Lee
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, Affiliated Faculty Member, Institute for Biomedical Engineering, Science, and Technology, The University of Oklahoma, 865 Asp Ave., Felgar Hall Rm. 219C, Norman, OK 73019-3609, United States; Institute for Biomedical Engineering, Science and Technology, The University of Oklahoma, 202 West Boyd St., Norman, OK 73019, United States.
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42
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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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43
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Bianco G, Bruno L, Girkin CA, Fazio MA. Full-field displacement measurement of corneoscleral shells by combining multi-camera speckle interferometry with 3D shape reconstruction. J Mech Behav Biomed Mater 2019; 103:103560. [PMID: 32090952 DOI: 10.1016/j.jmbbm.2019.103560] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 11/14/2019] [Accepted: 11/26/2019] [Indexed: 11/25/2022]
Abstract
Changes in the biomechanical properties of the connective tissue of the eye occur with age and underlie the development of several ocular diseases, such as glaucoma, myopia, and keratoconus. The biomechanical dynamics of ocular connective tissue are measured by ex vivo inflation testing, in which intraocular pressure (IOP) is varied and optical methods are used to produce maps of corneal and scleral displacement. Current optical methods are limited by acquisition rate, occlusions, poor spatial resolution, and insufficient 3D mapping. We developed an interferometric optical method integrates four-camera electronic speckle pattern interferometry (ESPI) and a novel three-dimensional (3D) shape reconstruction process to measure shape and full-field mechanical deformations of corneal and scleral shells during ex vivo inflation testing. Each camera provides accurate measurements of the laser beam phase related to deformations of the specimen surface; a multi-view stereovision method generates the shape of the specimen and a functional form that links every pixel of a given camera to 3D points on the specimen's visible surface. In this way, dynamic deformations of the specimen are localized, with quantification of the time-dependent 3D displacements of the specimen at nanometric accuracy. The ESPI-3D system is suitable for analyzing scleral deformation and morphological changes caused by time-varying IOP.
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Affiliation(s)
- Gianfranco Bianco
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA.
| | - Luigi Bruno
- Department of Biomedical Engineering, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA; Department of Mechanical, Energy and Management Engineering, University of Calabria, Via Bucci 44C, 87036, Arcavacata di Rende, CS, Italy.
| | - Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA.
| | - Massimo A Fazio
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA; Department of Biomedical Engineering, University of Alabama at Birmingham, 1670, University Blvd - 35294, Birmingham, AL, USA.
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44
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Sherwood JM, Boazak EM, Feola AJ, Parker K, Ethier CR, Overby DR. Measurement of Ocular Compliance Using iPerfusion. Front Bioeng Biotechnol 2019; 7:276. [PMID: 31709244 PMCID: PMC6823226 DOI: 10.3389/fbioe.2019.00276] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 10/01/2019] [Indexed: 11/25/2022] Open
Abstract
The pressure-volume relationship of the eye is determined by the biomechanical properties of the corneoscleral shell and is classically characterised by Friedenwald's coefficient of ocular rigidity or, alternatively, by the ocular compliance (OC), defined as dV/dP. OC is important in any situation where the volume (V) or pressure (P) of the eye is perturbed, as occurs during several physiological and pathological processes. However, accurately measuring OC is challenging, particularly in rodents. We measured OC in 24 untreated enucleated eyes from 12 C57BL/6 mice using the iPerfusion system to apply controlled pressure steps, whilst measuring the time-varying flow rate into the eye. Pressure and flow data were analysed by a “Discrete Volume” (integrating the flow trace) and “Step Response” method (fitting an analytical solution to the pressure trace). OC evaluated at 13 mmHg was similar between the two methods (Step Response, 41 [37, 46] vs. Discrete Volume, 42 [37, 48] nl/mmHg; mean [95% CI]), although the Step Response Method yielded tighter confidence bounds on individual eyes. OC was tightly correlated between contralateral eyes (R2 = 0.75, p = 0.0003). Following treatment with the cross-linking agent genipin, OC decreased by 40 [33, 47]% (p = 0.0001; N = 6, Step Response Method). Measuring OC provides a powerful tool to assess corneoscleral biomechanics in mice and other species.
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Affiliation(s)
- Joseph M Sherwood
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - Elizabeth M Boazak
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States
| | - Andrew J Feola
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States.,Atlanta VA Medical Center, Atlanta, GA, United States
| | - Kim Parker
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - C Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States.,George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States
| | - Darryl R Overby
- Department of Bioengineering, Imperial College London, London, United Kingdom
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45
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Geraghty B, Abass A, Eliasy A, Jones SW, Rama P, Kassem W, Akhtar R, Elsheikh A. Inflation experiments and inverse finite element modelling of posterior human sclera. J Biomech 2019; 98:109438. [PMID: 31679759 DOI: 10.1016/j.jbiomech.2019.109438] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Revised: 10/16/2019] [Accepted: 10/17/2019] [Indexed: 11/30/2022]
Abstract
The complexity of inverse finite element modelling methods used in ocular biomechanics research has significantly increased in recent years in order to produce material parameters that capture microscale tissue behaviour. This study presents a more accessible method for researchers to optimise sclera material parameters for use in finite element studies where macroscale sclera displacements are required. Five human donor sclerae aged between 36 and 72 years were subjected to cycles of internal pressure up to 61 mmHg using a custom-built inflation rig. Displacements were measured using a laser beam and two cameras through a digital image correlation algorithm. Specimen-specific finite element models incorporating regional thickness variation and sclera surface topography were divided into six circumferential regions. An inverse finite element procedure was used to optimise Ogden material parameters for each region. The maximum root mean squared (RMS) error between the numerical and experimental displacements within individual specimens was 17.5 µm. The optimised material parameters indicate a gradual reduction in material stiffness (as measured by the tangent modulus) from the equator to the posterior region at low-stress levels up to 0.005 MPa. The variation in stiffness between adjacent regions became gradually less apparent and statistically insignificant at higher stresses. The study demonstrated how inflation testing combined with inverse modelling could be used to effectively characterise regional material properties capable of reproducing global sclera displacements. The material properties were found to vary between specimens, and it is expected that age could be a contributing factor behind this variation.
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Affiliation(s)
- Brendan Geraghty
- Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, University of Liverpool, L7 8TX, UK.
| | - Ahmed Abass
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Ashkan Eliasy
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Stephen W Jones
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Paolo Rama
- Ophthalmology Department, San Raffaelle Scientific Institute, Milan, Italy
| | - Wael Kassem
- Division of Construction Engineering, Umm Al-Qura University, College of Engineering at Al-Qunfudah, Al-Qunfudah 21912, Saudi Arabia
| | - Riaz Akhtar
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool L69 3GH, UK; National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields, Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, UK; School of Biological Science and Biomedical Engineering, Beihang University, Beijing, China
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46
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Kollech HG, Ayyalasomayajula A, Behkam R, Tamimi E, Furdella K, Drewry M, Vande Geest JP. A Subdomain Method for Mapping the Heterogeneous Mechanical Properties of the Human Posterior Sclera. Front Bioeng Biotechnol 2019; 7:129. [PMID: 31214585 PMCID: PMC6554536 DOI: 10.3389/fbioe.2019.00129] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Accepted: 05/13/2019] [Indexed: 01/26/2023] Open
Abstract
Although strongly correlated with elevated intraocular pressure, primary open-angle glaucoma (POAG) occurs in normotensive eyes. Mechanical properties of the sclera around the optic nerve head (ONH) may play a role in this disparity. The purpose of this study is to present an automated inverse mechanics based approach to determine the distribution of heterogeneous mechanical properties of the human sclera as derived from its surface deformations arising from pressure inflation experiments. The scleral shell of a 78 year old European Descent male donor eye was utilized to demonstrate the method; the sclera was coated with a speckle pattern on the outer surface and was subjected to inflation pressures of 5, 15, 30, and 45 mmHg. The speckle pattern was imaged at each pressure, and a displacement field was calculated for each pressure step using a previously described sequential digital image correlation (S-DIC) technique. The fiber splay and fiber orientation of the sclera collagen were determined experimentally, and the thickness across the scleral globe was determined using micro CT images. The displacement field from the inflation test was used to calculate the strain and also used as an input for inverse mechanics to determine the heterogeneity of material properties. The scleral geometry was divided into subdomains using the first principal strain. The Holzapfel anisotropic material parameters of matrix and fiber stiffness were estimated within each individual subdomain using an inverse mechanics approach by minimizing the sum of the square of the residuals between the computational and experimental displacement fields. The mean and maximum error in displacement across all subdomains were 8.9 ± 3.0 μm and 13.2 μm, respectively. The full pressure-inflation forward mechanics experiment was done using subdomain-specific mechanical properties on the entire scleral surface. The proposed approach is effective in determining the distribution of heterogeneous mechanical properties of the human sclera in a user-independent manner. Our research group is currently utilizing this approach to better elucidate how scleral stiffness influences those at high risk for POAG.
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Affiliation(s)
- Hirut G Kollech
- Computational Modeling and Simulation Program, University of Pittsburgh, Pittsburgh, PA, United States
| | - Avinash Ayyalasomayajula
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ, United States
| | - Reza Behkam
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ehab Tamimi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Kenneth Furdella
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Michelle Drewry
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States
| | - Jonathan P Vande Geest
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.,McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, United States.,Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pittsburgh, PA, United States
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47
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Kim YW, Lee DH, Lim HB, Oh BL, Kim YK, Girard MJA, Mari JM, Park KH, Jeoung JW. Age-Dependent Variation of Lamina Cribrosa Displacement During the Standardized Valsalva Maneuver. Sci Rep 2019; 9:6645. [PMID: 31040379 PMCID: PMC6491605 DOI: 10.1038/s41598-019-43206-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 04/17/2019] [Indexed: 01/17/2023] Open
Abstract
Based on biomechanical theory, lamina cribrosa (LC) displacement, the key component of progressive glaucomatous change, is presumed to be dependent on intraocular pressure (IOP) as well as tissue stiffness of LC. In the performance of the Valsalva maneuver, both IOP and cerebrospinal fluid pressure can increase. The present study investigated the age-dependent variation of LC displacement during the standardized Valsalva maneuver in healthy subjects. Sixty-three (63) eyes (age range: 20-76 years) were prospectively underwent IOP measurement and Cirrus HD-OCT optic disc scans before and during the standardized Valsalva maneuver. During the standardized Valsalva maneuver, the IOP significantly increased from 13.2 ± 2.9 mmHg to 18.6 ± 5.2 mmHg (P < 0.001). The maximal LC depth significantly decreased in the younger age groups (age: 20 s to 40 s) but not in the older age groups (age: over 50). The BMO distance did not change significantly. Younger age (P = 0.009), a smaller increase of IOP during the Valsalva maneuver (P = 0.002), and greater baseline maximal LC depth (P = 0.013) were associated with more anterior displacement of the LC during the standardized Valsalva maneuver. Taken together, age as well as translaminar pressure dynamics seems to play a crucial role in LC biomechanics.
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Affiliation(s)
- Yong Woo Kim
- Department of Ophthalmology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.,Department of Ophthalmology, Armed Forces Capital Hospital, Seongnam, Korea
| | - Dong Hyun Lee
- Department of Ophthalmology, Armed Forces Capital Hospital, Seongnam, Korea
| | - Hyung Bin Lim
- Department of Ophthalmology, Armed Forces Capital Hospital, Seongnam, Korea
| | - Baek-Lok Oh
- Department of Ophthalmology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.,Department of Ophthalmology, Armed Forces Capital Hospital, Seongnam, Korea
| | - Young Kook Kim
- Department of Ophthalmology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea
| | - Michael J A Girard
- Department of Biomedical Engineering, National University of Singapore, Singapore, Singapore.,Singapore Eye Research Institute, Singapore, Singapore
| | | | - Ki Ho Park
- Department of Ophthalmology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea
| | - Jin Wook Jeoung
- Department of Ophthalmology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea.
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48
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Smith DW, Lee CJ, Morgan W, Gardiner BS. Estimating three-dimensional outflow and pressure gradients within the human eye. PLoS One 2019; 14:e0214961. [PMID: 30964894 PMCID: PMC6456205 DOI: 10.1371/journal.pone.0214961] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 03/23/2019] [Indexed: 12/22/2022] Open
Abstract
In this paper we set the previously reported pressure-dependent, ordinary differential equation outflow model by Smith and Gardiner for the human eye, into a new three-dimensional (3D) porous media outflow model of the eye, and calibrate model parameters using data reported in the literature. Assuming normal outflow through anterior pathways, we test the ability of 3D flow model to predict the pressure elevation with a silicone oil tamponade. Then assuming outflow across the retinal pigment epithelium is normal, we test the ability of the 3D model to predict the pressure elevation in Schwartz-Matsuo syndrome. For the first time we find the flow model can successfully model both conditions, which helps to build confidence in the validity and accuracy of the 3D pressure-dependent outflow model proposed here. We employ this flow model to estimate the translaminar pressure gradient within the optic nerve head of a normal eye in both the upright and supine postures, and during the day and at night. Based on a ratio of estimated and measured pressure gradients, we define a factor of safety against acute interruption of axonal transport at the laminar cribrosa. Using a completely independent method, based on the behaviour of dynein molecular motors, we compute the factor of safety against stalling the dynein molecule motors, and so compromising retrograde axonal transport. We show these two independent methods for estimating factors of safety agree reasonably well and appear to be consistent. Taken together, the new 3D pressure-dependent outflow model proves itself to capable of providing a useful modeling platform for analyzing eye behaviour in a variety of physiological and clinically useful contexts, including IOP elevation in Schwartz-Matsuo syndrome and with silicone oil tamponade, and potentially for risk assessment for optic glaucomatous neuropathy.
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Affiliation(s)
- David W. Smith
- Faculty of Engineering and Mathematical Sciences, The University of Western Australia, Perth, Australia
- * E-mail:
| | - Chang-Joon Lee
- Faculty of Engineering and Mathematical Sciences, The University of Western Australia, Perth, Australia
- College of Science, Health, Engineering and Education, Murdoch University, Murdoch, Western Australia, Australia
| | - William Morgan
- Lions Eye Institute, The University of Western Australia, Perth, Australia
| | - Bruce S. Gardiner
- College of Science, Health, Engineering and Education, Murdoch University, Murdoch, Western Australia, Australia
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49
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Zhou D, Eliasy A, Abass A, Markov P, Whitford C, Boote C, Movchan A, Movchan N, Elsheikh A. Analysis of X-ray scattering microstructure data for implementation in numerical simulations of ocular biomechanical behaviour. PLoS One 2019; 14:e0214770. [PMID: 30934028 PMCID: PMC6443175 DOI: 10.1371/journal.pone.0214770] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Accepted: 03/19/2019] [Indexed: 11/18/2022] Open
Abstract
This study aimed to analyse microstructure data on the density and orientation of collagen fibrils in whole eye globes and to propose an effective method for the preparation of data for use in numerical simulations of the eye’s biomechanical performance. Wide-angle X-ray scattering was applied to seven healthy ex-vivo human eyes. Each eye was dissected into an anterior and a posterior cup, and radial incisions were used to flatten the tissue before microstructure characterisation. A method was developed to use the microstructure data obtained for the dissected tissue to build realistic 3D maps of fibril density and orientation covering the whole eye globe. At the central cornea, 61.5±2.3% of fibrils were aligned within 45° sectors surrounding the two orthogonal directions. In contrast, more than one-third of the total fibril content was concentrated along the circumferential direction at the limbus (37.0±2.4%) and around the optic nerve head (34.8±2.1%). The insertion locations of the four recti muscles exhibited a preference in the meridional direction near the equator (38.6±3.9%). There was also a significant difference in fibril density between the limbus and other regions (ratio = 1.91±0.45, p <0.01 at the central cornea and ratio = 0.80±0.21, p <0.01 at the posterior pole). Characterisation of collagen fibril density and orientation across the whole ocular surface has been possible but required the use of a technique that involved tissue dissection and hence caused tissue damage. The method presented in this paper aimed to minimise the effect of dissection on the quality of obtained data and was successful in identifying fibril distribution trends that were compatible with earlier studies, which concentrated on localised areas of the ocular globe.
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Affiliation(s)
- Dong Zhou
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- * E-mail:
| | - Ashkan Eliasy
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Ahmed Abass
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Petar Markov
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | | | - Craig Boote
- School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom
| | - Alexander Movchan
- Department of Mathematical Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Natalia Movchan
- Department of Mathematical Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- National Institute for Health Research Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital National Health Service Foundation Trust and University College London Institute of Ophthalmology, London, United Kingdom
- School of Biological Science and Biomedical Engineering, Beihang University, Beijing, China
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50
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Levy AM, Fazio MA, Grytz R. Experimental myopia increases and scleral crosslinking using genipin inhibits cyclic softening in the tree shrew sclera. Ophthalmic Physiol Opt 2019; 38:246-256. [PMID: 29691925 DOI: 10.1111/opo.12454] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Accepted: 03/15/2018] [Indexed: 11/30/2022]
Abstract
PURPOSE Myopia progression is thought to involve biomechanical weakening of the sclera, which leads to irreversible deformations and axial elongation of the eye. Scleral crosslinking has been proposed as a potential treatment option for myopia control by strengthening the mechanically weakened sclera. The biomechanical mechanism by which the sclera weakens during myopia and strengthens after crosslinking is not fully understood. Here, we assess the effect of lens-induced myopia and exogenous crosslinking using genipin on the inelastic mechanical properties of the tree shrew sclera measured by cyclic tensile tests. METHODS Cyclic tensile tests were performed on 2-mm wide scleral strips at physiological loading conditions (50 cycles, 0-3.3 g, 30 s cycle-1 ). Two scleral strips were obtained from each eye of juvenile tree shrews exposed to two different visual conditions: normal and 4 days of monocular -5 D lens wear to accelerate scleral remodelling and induce myopia. Scleral strips were mechanically tested at three alternative conditions: immediately after enucleation; after incubation in phosphate buffered saline (PBS) for 24 h at 37°C; and after incubation for 24 h in PBS supplemented with genipin at a low cytotoxicity concentration (0.25 mm). Cyclic softening was defined as the incremental strain increase from one cycle to the next. RESULTS -5D lens treatment significantly increased the cyclic softening response of the sclera when compared to contralateral control eyes (0.10% ± 0.029%, mean ± standard error, P = 0.037). Exogenous crosslinking of the lens treated sclera significantly decreased the cyclic softening response (-0.12% ± 0.014%, P = 2.2 × 10-5 ). Contrary to all other groups, the genipin-cross-linked tissue did not exhibit cyclic softening significantly different from zero within the 50-cycle test. CONCLUSIONS Results indicated that cyclic tensile loading leads to an inelastic, cyclic softening of the juvenile tree shrew sclera. The softening rate increased during lens-induced myopia and was diminished after genipin crosslinking. This finding suggests that axial elongation in myopia may involve a biomechanical weakening mechanism that increased the cyclic softening response of the sclera, which was inhibited by scleral crosslinking using genipin.
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Affiliation(s)
- Alexander M Levy
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, USA
| | - Massimo A Fazio
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, USA.,Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, USA
| | - Rafael Grytz
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, USA
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