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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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2
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Raphtis VA, Sharma D, Wang S, Kim JY, Jacobson AL, Harman CD, Komáromy AM. Ocular pulse amplitude (OPA) in canine ADAMTS10-open-angle glaucoma ( ADAMTS10-OAG). Front Bioeng Biotechnol 2023; 11:1242166. [PMID: 38130820 PMCID: PMC10733518 DOI: 10.3389/fbioe.2023.1242166] [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: 06/18/2023] [Accepted: 11/27/2023] [Indexed: 12/23/2023] Open
Abstract
Introduction: The role of ocular rigidity and biomechanics remains incompletely understood in glaucoma, including assessing an individual's sensitivity to intraocular pressure (IOP). In this regard, the clinical assessment of ocular biomechanics represents an important need. The purpose of this study was to determine a possible relationship between the G661R missense mutation in the ADAMTS10 gene and the ocular pulse amplitude (OPA), the difference between diastolic and systolic intraocular pressure (IOP), in a well-established canine model of open-angle glaucoma (OAG). Methods: Animals studied included 39 ADAMTS10-mutant dogs with different stages of OAG and 14 unaffected control male and female dogs between 6 months and 12 years (median: 3.2 years). Dogs were sedated intravenously with butorphanol tartrate and midazolam HCl, and their IOPs were measured with the Icare® Tonovet rebound tonometer. The Reichert Model 30™ Pneumotonometer was used to measure OPA. Central corneal thickness (CCT) was measured via Accutome® PachPen, and A-scan biometry was assessed with DGH Technology Scanmate. All outcome measures of left and right eyes were averaged for each dog. Data analysis was conducted with ANOVA, ANCOVA, and regression models. Results: ADAMTS10-OAG-affected dogs displayed a greater IOP of 23.0 ± 7.0 mmHg (mean ± SD) compared to 15.3 ± 3.6 mmHg in normal dogs (p < 0.0001). Mutant dogs had a significantly lower OPA of 4.1 ± 2.0 mmHg compared to 6.5 ± 2.8 mmHg of normal dogs (p < 0.01). There was no significant age effect, but OPA was correlated with IOP in ADAMTS10-mutant dogs. Conclusion: The lower OPA in ADAMTS10-mutant dogs corresponds to the previously documented weaker and biochemically distinct posterior sclera, but a direct relationship remains to be confirmed. The OPA may be a valuable clinical tool to assess ocular stiffness and an individual's susceptibility to IOP elevation.
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Affiliation(s)
- Vanessa A. Raphtis
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI, United States
| | - Dhruv Sharma
- Center for Statistical Training and Consulting, Michigan State University, East Lansing, MI, United States
| | - Sichao Wang
- Center for Statistical Training and Consulting, Michigan State University, East Lansing, MI, United States
| | - Jae Y. Kim
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI, United States
| | - Amanda L. Jacobson
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI, United States
| | - Christine D. Harman
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI, United States
| | - András M. Komáromy
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI, United States
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Gao C, Mu G, Zhao H, Zheng J, Feng Q, Wu Y, Li Y, Huang X, Sun W. Intraocular pressure effect of intravitreal conbercept injection for retinopathy of prematurity. Front Pharmacol 2023; 14:1165356. [PMID: 37324456 PMCID: PMC10266213 DOI: 10.3389/fphar.2023.1165356] [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: 02/14/2023] [Accepted: 05/10/2023] [Indexed: 06/17/2023] Open
Abstract
Purpose: Intravitreal injection of conbercept (IVC) is a novel anti-vascular endothelial growth factor (anti-VEGF) treatment for retinopathy of prematurity (ROP). This study aimed to assess the intraocular pressure (IOP) effect of IVC. Methods: All IVC surgeries were performed in the Department of Ophthalmology, Guangdong Women and Children Hospital, from January 2021 to May 2021. In this study, 30 eyes of 15 infants who received intravitreal injections of conbercept at a dose of 0.25 mg/0.025 mL were included. The IOP of all participants was measured prior to administering the injection and subsequently at 2 min, 1 h, 1 day, and 1 week thereafter. Results: We included 30 eyes (10 boys and 5 girls) with ROP. For the male group, the mean birth weight, mean gestational age at birth, and the mean time of postmenstrual age (PMA) at IVC treatment were 1,174.0 ± 446.0 g, 28.4 ± 3.0 weeks, and 37.1 ± 1.6 weeks, respectively; for the female group, they were 1,108 ± 285.5 g, 28.2 ± 2.5 weeks, and 36.8 ± 2.1 weeks, respectively. For the male group, the IOP at baseline, 2 min, 1 h, 1 day, and 1 week after IVC were 12.4 ± 1.5 mmHg, 49.0 ± 3.1 mmHg, 26.3 ± 2.5 mmHg, 13.4 ± 2.2 mmHg, and 11.6 ± 1.7 mmHg, respectively; for the female group, they were 10.7 ± 2.0 mmHg, 47.3 ± 3.2 mmHg, 26.4 ± 3.2 mmHg, 10.7 ± 1.8 mmHg, and 10.2 ± 1.8 mmHg, respectively. In both groups, the IOP immediately (2 min) after the operation was significantly higher than that at any other time point (p < 0.01). IOP values returned to the preoperative baseline level on the first day after surgery, with no significant difference compared with that before injection (p > 0.05). IOP continued to be maintained at the preoperative baseline level on the first week after surgery, with no significant difference compared with that before surgery (p > 0.05). Conclusion: Infants with ROP who received IVC experienced a sharp increase in the IOP immediately after injection, which decreased to below 30 mmHg after 1 h and maintain that level for 1 week or longer.
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Affiliation(s)
- Caifeng Gao
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
| | - Ge Mu
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
| | - Huanhuan Zhao
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
| | - Jiao Zheng
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
| | - Qingyang Feng
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
| | - Yining Wu
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
| | - Yinan Li
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
- Department of Anesthesiology, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
| | - Xuelin Huang
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
| | - Wei Sun
- Department of Ophthalmology, Guangdong Women and Children Hospital, Guangzhou, China
- Department of Ophthalmology, Guangdong Eye Institute, Guangdong Provincial People’s Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, Guangzhou, China
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Brazuna R, Alonso RS, Salomão MQ, Fernandes BF, Ambrósio R. Ocular Biomechanics and Glaucoma. Vision (Basel) 2023; 7:vision7020036. [PMID: 37218954 DOI: 10.3390/vision7020036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 04/11/2023] [Accepted: 04/21/2023] [Indexed: 05/24/2023] Open
Abstract
Biomechanics is a branch of biophysics that deals with mechanics applied to biology. Corneal biomechanics have an important role in managing patients with glaucoma. While evidence suggests that patients with thin and stiffer corneas have a higher risk of developing glaucoma, it also influences the accurate measurement of intraocular pressure. We reviewed the pertinent literature to help increase our understanding of the biomechanics of the cornea and other ocular structures and how they can help optimize clinical and surgical treatments, taking into consideration individual variabilities, improve the diagnosis of suspected patients, and help monitor the response to treatment.
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Affiliation(s)
- Rodrigo Brazuna
- Department of Ophthalmology, Federal University of the State of Rio de Janeiro, Rio de Janeiro 22290-240, RJ, Brazil
| | - Ruiz S Alonso
- Department of Ophthalmology, Antonio Pedro University Hospital, Fluminense Federal University, Niterói 24033-900, RJ, Brazil
| | - Marcella Q Salomão
- Department of Ophthalmology, Federal University of São Paulo, São Paulo 04023-062, SP, Brazil
| | | | - Renato Ambrósio
- Department of Ophthalmology, Federal University of the State of Rio de Janeiro, Rio de Janeiro 22290-240, RJ, Brazil
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5
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Sayah DN, Lesk MR. Ocular Rigidity and Current Therapy. Curr Eye Res 2023; 48:105-113. [PMID: 35763027 DOI: 10.1080/02713683.2022.2093380] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Purpose: Ocular rigidity (OR) is an important biomechanical parameter of the eye accounting for the material and geometrical properties of the corneoscleral shell.Methods: This study used a literature search to review the role of ocular rigidity and the application of potential therapies targeting this parameter in glaucoma and myopia.Conclusion: Biomechanical modeling and improved understanding of the biochemistry, and molecular arrangement of sclera and its constituents have yielded important insights. Recent developments, including that of a non-invasive and direct OR measurement method and improved ocular imaging techniques are helping to elucidate the role of OR in healthy and diseased eyes by facilitating large scale and longitudinal clinical studies. Improved understanding of OR at the initial stages of disease processes and its alterations with disease progression will undoubtedly propel research in the field. Furthermore, a better understanding of the determinants of OR is helping to refine novel therapeutic approaches which target and alter the biomechanical properties of the sclera in sight-threatening conditions such as glaucoma and myopia.
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Affiliation(s)
- Diane N Sayah
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Canada.,School of Optometry, Université de Montréal, Montreal, Canada
| | - Mark R Lesk
- Maisonneuve-Rosemont Hospital Research Center, Montreal, Canada.,Department of Ophthalmology, Faculty of Medicine, Université de Montréal, Montreal, Canada.,Centre Universitaire d'ophtalmologie de l'Université de Montréal de l'Hôpital Maisonneuve-Rosemont, CIUSSS-E, Montreal, Canada
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6
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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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7
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Abstract
PURPOSE OF REVIEW Biomechanics is an important aspect of the complex family of diseases known as the glaucomas. Here, we review recent studies of biomechanics in glaucoma. RECENT FINDINGS Several tissues have direct and/or indirect biomechanical roles in various forms of glaucoma, including the trabecular meshwork, cornea, peripapillary sclera, optic nerve head/sheath, and iris. Multiple mechanosensory mechanisms and signaling pathways continue to be identified in both the trabecular meshwork and optic nerve head. Further, the recent literature describes a variety of approaches for investigating the role of tissue biomechanics as a risk factor for glaucoma, including pathological stiffening of the trabecular meshwork, peripapillary scleral structural changes, and remodeling of the optic nerve head. Finally, there have been advances in incorporating biomechanical information in glaucoma prognoses, including corneal biomechanical parameters and iridial mechanical properties in angle-closure glaucoma. SUMMARY Biomechanics remains an active aspect of glaucoma research, with activity in both basic science and clinical translation. However, the role of biomechanics in glaucoma remains incompletely understood. Therefore, further studies are indicated to identify novel therapeutic approaches that leverage biomechanics. Importantly, clinical translation of appropriate assays of tissue biomechanical properties in glaucoma is also needed.
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Affiliation(s)
- Babak N. Safa
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
| | - Cydney A. Wong
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
| | - Jungmin Ha
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta GA, USA
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8
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Park SA, Komáromy AM. Biomechanics of the optic nerve head and sclera in canine glaucoma: A brief review. Vet Ophthalmol 2021; 24:316-325. [PMID: 34402566 DOI: 10.1111/vop.12923] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 06/04/2021] [Accepted: 07/25/2021] [Indexed: 01/17/2023]
Abstract
Glaucoma is a leading cause of irreversible blindness, a progressive optic neuropathy with retinal ganglion cell (RGC) death beginning in the optic nerve head (ONH). A primary risk factor for developing glaucoma is elevated intraocular pressure (IOP). Reducing IOP is the only treatment proven to be effective at delaying disease progression. Nevertheless, even when patients have their IOP reduced, the majority of them continue to lose vision. There are, in both humans and dogs, significant interindividual variabilities in susceptibilities to IOP-induced optic nerve damage. Vision loss progresses much more slowly in Beagles with open-angle glaucoma (OAG) caused by ADAMTS10 mutation. This can be attributed to the mutation-related altered ocular biomechanical properties. The principal site of optic nerve (ON) damage in glaucoma is the ONH. It is suggested that the biomechanical properties of the ONH and the surrounding peripapillary sclera (PPS) contribute to glaucoma development and progression. As far as the beneficial biomechanical properties of the ONH and PPS for a decreased susceptibility and slow progression of glaucoma, data are inconsistent and conflicting. Recent biomechanical studies on beagles with ADAMTS10 mutation demonstrated that the mutant dogs have mechanically weak posterior sclera. This weakness was associated with a reduced collagen density and a lower proportion of insoluble collagen. These changes, observed before glaucoma development, were considered intrinsic characteristics caused by the mutation rather than a secondary effect of IOP elevation. Further studies of ADAMTS10-OAG may elucidate the effects of altered biomechanical properties of ONH and PPS in determining the glaucoma progression.
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Affiliation(s)
- Shin Ae Park
- Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, Indiana, USA
| | - András M Komáromy
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA
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9
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Lazkani N, Butler J, Rickard MJA, Truitt S, Kawaguchi NK, DeWolf AJ, Van Zant CA, Villegas JP, Hassel AR, Park JJ, Jones CF. Development of a Nanofabricated Sensor for Monitoring Intraocular Pressure via Ocular Tissue Strain. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020; 2019:4363-4367. [PMID: 31946834 DOI: 10.1109/embc.2019.8857430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
As the number of individuals developing glaucoma is increasing, researchers and ophthalmologists are exploring new approaches to monitor intraocular pressure, which is a critical measurement for glaucoma detection. Current monitoring methods, such as implantable pressure sensors and wearable contact lenses with sensors, are being explored in eye research clinics. However, these systems currently lack in providing 24 hours data through a practical platform for large-scale use. This paper presents a novel method that provides constant measurements of the scleral strain, which is correlated with the change of intraocular pressure, using a nanofabricated discrete resistor array implant sensor. A preliminary bench-top test was performed using the sensor, and it showed that the nanofabricated 1.6 mm by 2.7 mm resistor array exhibits discrete sensing levels at increments of 41 ohms as a fixture needle traversed approximately half of the array. Though the nanosensor is in the prototype developing stage, it promises a new modality for constant, remote, and around the clock glaucoma monitoring.
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10
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Sayah DN, Szigiato AA, Mazzaferri J, Descovich D, Duval R, Rezende FA, Costantino S, Lesk MR. Correlation of ocular rigidity with intraocular pressure spike after intravitreal injection of bevacizumab in exudative retinal disease. Br J Ophthalmol 2020; 105:392-396. [PMID: 32345604 DOI: 10.1136/bjophthalmol-2019-315595] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 04/03/2020] [Accepted: 04/07/2020] [Indexed: 11/04/2022]
Abstract
BACKGROUND/AIMS To evaluate the non-invasive measurement of ocular rigidity (OR), an important biomechanical property of the eye, as a predictor of intraocular pressure (IOP) elevation after anti-vascular endothelial growth factor (anti-VEGF) intravitreal injection (IVI). METHODS Subjects requiring IVI of anti-VEGF for a pre-existing retinal condition were enrolled in this prospective cross-sectional study. OR was assessed in 18 eyes of 18 participants by measurement of pulsatile choroidal volume change using video-rate optical coherence tomography, and pulsatile IOP change using dynamic contour tonometry. IOP was measured using Tono-Pen XL before and immediately following the injection and was correlated with OR. RESULTS The average increase in IOP following IVI was 19±9 mm Hg, with a range of 7-33 mm Hg. The Spearman correlation coefficient between OR and IOP elevation following IVI was 0.796 (p<0.001), showing higher IOP elevation in more rigid eyes. A regression line was also calculated to predict the IOP spike based on the OR coefficient, such that IOP spike=664.17 mm Hg·µL×OR + 4.59 mm Hg. CONCLUSION This study shows a strong positive correlation between OR and acute IOP elevation following IVI. These findings indicate that the non-invasive measurement of OR could be an effective tool in identifying patients at risk of IOP spikes following IVI.
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Affiliation(s)
- Diane N Sayah
- Ophthalmology, Maisonneuve-Rosemont Hospital Research Centre, Montreal, Quebec, Canada.,Ophthalmology, University of Montreal, Montreal, Quebec, Canada
| | | | - Javier Mazzaferri
- Ophthalmology, Maisonneuve-Rosemont Hospital Research Centre, Montreal, Quebec, Canada
| | - Denise Descovich
- Ophthalmology, Maisonneuve-Rosemont Hospital Research Centre, Montreal, Quebec, Canada
| | - Renaud Duval
- Ophthalmology, Maisonneuve-Rosemont Hospital Research Centre, Montreal, Quebec, Canada.,Ophthalmology, University of Montreal, Montreal, Quebec, Canada
| | - Flavio A Rezende
- Ophthalmology, Maisonneuve-Rosemont Hospital Research Centre, Montreal, Quebec, Canada.,Ophthalmology, University of Montreal, Montreal, Quebec, Canada
| | - Santiago Costantino
- Ophthalmology, Maisonneuve-Rosemont Hospital Research Centre, Montreal, Quebec, Canada.,Ophthalmology, University of Montreal, Montreal, Quebec, Canada
| | - Mark R Lesk
- Ophthalmology, Maisonneuve-Rosemont Hospital Research Centre, Montreal, Quebec, Canada .,Ophthalmology, University of Montreal, Montreal, Quebec, Canada
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11
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Corneal pulsation and biomechanics during induced ocular pulse. An ex-vivo pilot study. PLoS One 2020; 15:e0228920. [PMID: 32053692 PMCID: PMC7018024 DOI: 10.1371/journal.pone.0228920] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 01/15/2020] [Indexed: 01/16/2023] Open
Abstract
The purpose of this study was to ascertain the relationships between the amplitude of the corneal pulse (CP) signal and the parameters of corneal biomechanics during ex-vivo intraocular pressure (IOP) elevation experiments on porcine eyes with artificially induced ocular pulse cycles. Two experiments were carried out using porcine eyes. In the first one, a selected eye globe was subjected to three IOP levels (15, 30 and 45 mmHg), where changes in physical ocular pulse amplitude were controlled by infusion/withdrawal volumes (ΔV). In the second experiment, six eyes were subjected to IOP from 15 mmHg to 45 mmHg in steps of 5 mmHg with a constant ΔV, where corneal deformation parameters were measured using Corvis ST. In both experiments, at each IOP, the CP and IOP signals were acquired synchronically using a non-contact ultrasonic distance sensor and a pressure transmitter, respectively. Based on the amplitudes of the CP and IOP signals ocular pulse based corneal rigidity index (OPCRI) was calculated. Results indicate positive correlations between ΔV and the physical ocular pulse amplitude, and between ΔV and the corneal pulse amplitude (both p < 0.001). OPCRI was found to increase with elevated IOP. Furthermore, IOP statistically significantly differentiated changes in OPCRI, the amplitudes of CP and IOP signals and in most of the corneal deformation parameters (p < 0.05). The partial correlation analysis, with IOP as a control variable, revealed a significant correlation between the length of the flattened cornea during the first applanation (A1L) and the corneal pulse amplitude (p = 0.002), and between A1L and OPCRI (p = 0.003). In conclusion, this study proved that natural corneal pulsations, detected with a non-contact ultrasonic technique, reflect pressure-volume dynamics and can potentially be utilized to assess stiffness of the cornea. The proposed new rigidity index could be a simple approach to estimating corneal rigidity.
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12
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Tram NK, Jiang P, Jacobs KM, Ruzga MN, Allen MG, Prieto RP, Carus SA, Reilly MA, Swindle-Reilly KE. Accommodative tissues influence the shape of the cornea and potentially drive corneal morphogenesis. J Biomech 2020; 100:109582. [PMID: 31902607 DOI: 10.1016/j.jbiomech.2019.109582] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 10/26/2019] [Accepted: 12/10/2019] [Indexed: 11/27/2022]
Abstract
This study investigates whether the presence of accommodative tissues biomechanically influences the shape of the cornea and potentially drives corneal morphogenesis during embryonic ocular development. Porcine eyes were subjected to an internal pressure simulating intraocular pressure. Ocular geometry was evaluated using a corneal topographer and digital cameras before and after dissection of the accommodative tissues. A computational model of the porcine eye was constructed and loaded by an internal pressure representing intraocular pressure. Eye shape was evaluated in models with and without the ciliary body. The porcine model was generalized to the human model, simplified model, or embryonic model with different ocular tissue shapes, sizes, and stiffnesses. Experimental data showed that, even in the six-month-old pig eye, the average corneal radius of curvature increased after the removal of accommodative tissues compared to sham controls (p = 0.002). Computational results agreed with the experimental data and further suggested that the change in corneal radius is greater when the tissue stiffness is low and the intraocular pressure is high, regardless of the geometry and size of the eye components. Using a combined in vitro and in silico approach, this study explores the biomechanical influence of the accommodative tissues and related loads on the cornea and offers additional factors that might influence the shape of the cornea.
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Affiliation(s)
- Nguyen K Tram
- Department of Biomedical Engineering, The Ohio State University, United States
| | - Pengfei Jiang
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, United States
| | - Kane M Jacobs
- William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, United States
| | - Marissa N Ruzga
- Department of Biomedical Engineering, The Ohio State University, United States
| | - Mallory G Allen
- Department of Biomedical Engineering, The Ohio State University, United States
| | - Ryan P Prieto
- Department of Biomedical Engineering, The Ohio State University, United States
| | - Sophie A Carus
- Department of Biomedical Engineering, The Ohio State University, United States
| | - Matthew A Reilly
- Department of Biomedical Engineering, The Ohio State University, United States; Department of Ophthalmology and Visual Science, The Ohio State University, United States
| | - Katelyn E Swindle-Reilly
- Department of Biomedical Engineering, The Ohio State University, United States; William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, United States; Department of Ophthalmology and Visual Science, The Ohio State University, United States.
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Jasien JV, Turner DC, Girkin CA, Downs JC. Cyclic Pattern of Intraocular Pressure (IOP) and Transient IOP Fluctuations in Nonhuman Primates Measured with Continuous Wireless Telemetry. Curr Eye Res 2019; 44:1244-1252. [PMID: 31170817 PMCID: PMC6829065 DOI: 10.1080/02713683.2019.1629594] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 05/04/2019] [Accepted: 06/04/2019] [Indexed: 01/26/2023]
Abstract
Purpose: Most studies on intraocular pressure (IOP) to monitor IOP "fluctuations" in glaucoma patients have been performed with snapshot tonometry techniques that obtain IOP measurements at single time points weeks to months apart. However, IOP telemetry has shown that IOP varies from second-to-second due to blinks, saccades, and systolic vascular filling. The purpose of this study was to characterize the cyclic pattern of baseline IOP and transient IOP fluctuations in 3 nonhuman primates (NHPs).Methods: Bilateral IOP was measured using a proven implantable telemetry system and recorded 500 times per second, 24 hours a day, up to 451 continuous days in 3 male rhesus macaques aged 4 to 5 years old. The IOP transducers were calibrated every two weeks via anterior chamber cannulation manometry and all data were continuously corrected for signal drift via software, filtered for signal noise and dropout, and peaks and troughs were quantified and counted using a finite impulse response filter; waking hours were defined as 6:00-18:00 hours based on room light cycle.Results: Fourier transform analyses of baseline IOP and the hourly mean frequency of transient IOP fluctuations > 0.6 mmHg, 0.6-5 mmHg and > 5 mmHg above baseline during waking hours exhibited an approximate 16- to 91-day cyclic pattern in all NHPs. There were no measured environmental or experimental factors associated with this cyclical pattern.Conclusions: While the importance of the cyclic pattern identified in IOP and its fluctuations is unknown at this time, it is plausible that this pattern is relevant to both homeostasis and pathophysiology of the ONH, corneoscleral shell, and aqueous outflow pathways.
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Affiliation(s)
- Jessica V. Jasien
- Vision Science Graduate Program, School of Optometry, University of Alabama at Birmingham
| | - Daniel C. Turner
- Vision Science Graduate Program, School of Optometry, University of Alabama at Birmingham
| | - Christopher A. Girkin
- Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham
| | - J. Crawford Downs
- Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham
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14
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Boote C, Sigal IA, Grytz R, Hua Y, Nguyen TD, Girard MJA. Scleral structure and biomechanics. Prog Retin Eye Res 2019; 74:100773. [PMID: 31412277 DOI: 10.1016/j.preteyeres.2019.100773] [Citation(s) in RCA: 144] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Revised: 08/07/2019] [Accepted: 08/08/2019] [Indexed: 12/18/2022]
Abstract
As the eye's main load-bearing connective tissue, the sclera is centrally important to vision. In addition to cooperatively maintaining refractive status with the cornea, the sclera must also provide stable mechanical support to vulnerable internal ocular structures such as the retina and optic nerve head. Moreover, it must achieve this under complex, dynamic loading conditions imposed by eye movements and fluid pressures. Recent years have seen significant advances in our knowledge of scleral biomechanics, its modulation with ageing and disease, and their relationship to the hierarchical structure of the collagen-rich scleral extracellular matrix (ECM) and its resident cells. This review focuses on notable recent structural and biomechanical studies, setting their findings in the context of the wider scleral literature. It reviews recent progress in the development of scattering and bioimaging methods to resolve scleral ECM structure at multiple scales. In vivo and ex vivo experimental methods to characterise scleral biomechanics are explored, along with computational techniques that combine structural and biomechanical data to simulate ocular behaviour and extract tissue material properties. Studies into alterations of scleral structure and biomechanics in myopia and glaucoma are presented, and their results reconciled with associated findings on changes in the ageing eye. Finally, new developments in scleral surgery and emerging minimally invasive therapies are highlighted that could offer new hope in the fight against escalating scleral-related vision disorder worldwide.
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Affiliation(s)
- Craig Boote
- Structural Biophysics Research Group, School of Optometry & Vision Sciences, Cardiff University, UK; Ophthalmic Engineering & Innovation Laboratory (OEIL), Department of Biomedical Engineering, National University of Singapore, Singapore; Newcastle Research & Innovation Institute Singapore (NewRIIS), Singapore.
| | - Ian A Sigal
- Laboratory of Ocular Biomechanics, Department of Ophthalmology, University of Pittsburgh, USA
| | - Rafael Grytz
- Department of Ophthalmology & Visual Sciences, University of Alabama at Birmingham, USA
| | - Yi Hua
- Laboratory of Ocular Biomechanics, Department of Ophthalmology, University of Pittsburgh, USA
| | - Thao D Nguyen
- Department of Mechanical Engineering, Johns Hopkins University, USA
| | - Michael J A Girard
- Ophthalmic Engineering & Innovation Laboratory (OEIL), Department of Biomedical Engineering, National University of Singapore, Singapore; Singapore Eye Research Institute (SERI), Singapore National Eye Centre, Singapore
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15
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Acute and chronic optic nerve head biomechanics and intraocular pressure changes in patients receiving multiple intravitreal injections of anti-VEGF. Graefes Arch Clin Exp Ophthalmol 2019; 257:2221-2231. [DOI: 10.1007/s00417-019-04354-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 04/30/2019] [Accepted: 05/06/2019] [Indexed: 01/24/2023] Open
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16
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Chung J, Park IK, Choi S, Shin JH. Semi-automatic Measurement of Ocular Volume from Facial Computed Tomography and Correlation with Axial Length. JOURNAL OF THE KOREAN OPHTHALMOLOGICAL SOCIETY 2019. [DOI: 10.3341/jkos.2019.60.3.210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Junkyu Chung
- Department of Ophthalmology, Kyung Hee University Hospital at Gangdong, Kyung Hee University School of Medicine, Seoul, Korea
| | - In Ki Park
- Department of Ophthalmology, Kyung Hee University Medical Center, Kyung Hee University School of Medicine, Seoul, Korea
| | - Samjin Choi
- Department of Bioengineering, Kyung Hee University School of Medicine, Seoul, Korea
| | - Jae-Ho Shin
- Department of Ophthalmology, Kyung Hee University Hospital at Gangdong, Kyung Hee University School of Medicine, Seoul, Korea
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17
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Markert JE, Jasien JV, Turner DC, Huisingh C, Girkin CA, Downs JC. IOP, IOP Transient Impulse, Ocular Perfusion Pressure, and Mean Arterial Pressure Relationships in Nonhuman Primates Instrumented With Telemetry. Invest Ophthalmol Vis Sci 2018; 59:4496-4505. [PMID: 30208417 PMCID: PMC6133237 DOI: 10.1167/iovs.18-23802] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Purpose To characterize relationships between intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP), IOP transient impulse, and IOP baseline impulse using continuous telemetry in nonhuman primates. Methods We used our validated implantable telemetry system to wirelessly record bilateral IOP and arterial BP at 500 Hz in 7 eyes of 4 male rhesus macaques, aged 4 to 5 years. IOP, MAP, OPP, IOP transient impulse, and IOP baseline impulse were averaged into 1-hour periods over 20 days for each NHP. IOP transient impulse was defined as the portion of total IOP due to transient IOP fluctuations <0.5 seconds duration alone and IOP baseline impulse as the remaining area under the IOP versus time curve. OPP was defined as arterial BP-IOP (calculated continuously), and MAP was the hourly average of the continuous BP curve. Relationships between the variables were analyzed for each 24-hour period using either multivariate linear regression or Spearman Correlation Coefficients as appropriate. Results Over twenty 24-hour periods, IOP transient impulse and OPP showed significant positive relationship in all eyes, which was driven largely by the data during waking hours. There was no significant relationship between IOP and MAP, IOP transient impulse and MAP, or IOP baseline impulse and IOP transient impulse. Conclusions There are significant positive relationships between the frequency and/or size of transient IOP fluctuations (IOP transient impulse) and OPP. A possible explanation of this finding is that higher OPP, as well as a greater number of blinks and saccades (the primary sources of IOP transients), are associated with increased activity.
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Affiliation(s)
- John E Markert
- Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Jessica V Jasien
- Vision Science Graduate Program, School of Optometry, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Daniel C Turner
- Vision Science Graduate Program, School of Optometry, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Carrie Huisingh
- Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Christopher A Girkin
- Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
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18
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Zhao D, Nguyen CTO, He Z, Wong VHY, van Koeverden AK, Vingrys AJ, Bui BV. Age-related changes in the response of retinal structure, function and blood flow to pressure modification in rats. Sci Rep 2018; 8:2947. [PMID: 29440700 PMCID: PMC5811482 DOI: 10.1038/s41598-018-21203-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 01/29/2018] [Indexed: 12/11/2022] Open
Abstract
Age-related changes to the balance between the pressure inside the eye (intraocular pressure, IOP) and the pressure inside the brain (intracranial pressure, ICP) can modify the risk of glaucoma. In this study, we consider whether the optic nerve in older rat eyes is more susceptible to acute IOP and ICP modification. We systematically manipulate both ICP and IOP and quantify their effects on ganglion cell function (electroretinography, ERG), optic nerve structure (optical coherence tomography, OCT) and retinal blood flow (Doppler OCT). We show that ganglion cell function in older eyes was more susceptible to a higher optic nerve pressure difference (ONPD = IOP - ICP). This age-related susceptibility could not be explained by poorer blood flow with elevated ONPD. Rather, as ONPD increased the retinal nerve fibre layer showed greater compression, and the retinal surface showed less deformation in older eyes. Our data suggest that age-related changes to connective tissues in and around the rat optic nerve make it less flexible, which may result in greater strain on ganglion cell axons. This may account for greater functional susceptibility to higher optic nerve pressure differences in older rat eyes. Further studies in a species with a well-developed lamina cribrosa are needed to determine the clinical importance of these observations.
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Affiliation(s)
- Da Zhao
- Department of Optometry and Vision Sciences, University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Christine T O Nguyen
- Department of Optometry and Vision Sciences, University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Zheng He
- Department of Optometry and Vision Sciences, University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Vickie H Y Wong
- Department of Optometry and Vision Sciences, University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Anna K van Koeverden
- Department of Optometry and Vision Sciences, University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Algis J Vingrys
- Department of Optometry and Vision Sciences, University of Melbourne, Parkville, 3010, Victoria, Australia
| | - Bang V Bui
- Department of Optometry and Vision Sciences, University of Melbourne, Parkville, 3010, Victoria, Australia.
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19
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Zhou B, Sit AJ, Zhang X. Noninvasive measurement of wave speed of porcine cornea in ex vivo porcine eyes for various intraocular pressures. ULTRASONICS 2017; 81:86-92. [PMID: 28618301 PMCID: PMC5541902 DOI: 10.1016/j.ultras.2017.06.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Revised: 05/30/2017] [Accepted: 06/05/2017] [Indexed: 05/16/2023]
Abstract
The objective of this study was to extend an ultrasound surface wave elastography (USWE) technique for noninvasive measurement of ocular tissue elastic properties. In particular, we aim to establish the relationship between the wave speed of cornea and the intraocular pressure (IOP). Normal ranges of IOP are between 12 and 22mmHg. Ex vivo porcine eye balls were used in this research. The porcine eye ball was supported by the gelatin phantom in a testing container. Some water was pour into the container for the ultrasound measurement. A local harmonic vibration was generated on the side of the eye ball. An ultrasound probe was used to measure the wave propagation in the cornea noninvasively. A 25 gauge butterfly needle was inserted into the vitreous humor of the eye ball under the ultrasound imaging guidance. The needle was connected to a syringe. The IOP was obtained by the water height difference between the water level in the syringe and the water level in the testing container. The IOP was adjusted between 5mmHg and 30mmHg with a 5mmHg interval. The wave speed was measured at each IOP for three frequencies of 100, 150 and 200Hz. Finite element method (FEM) was used to simulate the wave propagation in the corneal according to our experimental setup. A linear viscoelastic FEM model was used to compare the experimental data. Both the experiments and the FEM analyses showed that the wave speed of cornea increased with IOP.
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Affiliation(s)
- Boran Zhou
- Department of Radiology, Mayo Clinic, USA
| | | | - Xiaoming Zhang
- Department of Radiology, Mayo Clinic, USA; Department of Biomedical Engineering and Physiology, Mayo Clinic, USA.
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20
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Tamimi EA, Pyne JD, Muli DK, Axman KF, Howerton SJ, Davis MR, Girkin CA, Vande Geest JP. Racioethnic Differences in Human Posterior Scleral and Optic Nerve Stump Deformation. Invest Ophthalmol Vis Sci 2017; 58:4235-4246. [PMID: 28846773 PMCID: PMC5574446 DOI: 10.1167/iovs.17-22141] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Purpose The purpose of this study was to quantify the biomechanical response of human posterior ocular tissues from donors of various racioethnic groups to better understand how differences in these properties may play a role in the racioethnic health disparities known to exist in glaucoma. Methods Sequential digital image correlation (S-DIC) was used to measure the pressure-induced surface deformations of 23 normal human posterior poles from three racioethnic groups: African descent (AD), European descent (ED), and Hispanic ethnicity (HIS). Regional in-plane principal strains were compared across three zones: the optic nerve stump (ONS), the peripapillary (PP) sclera, and non-PP sclera. Results The PP scleral tensile strains were found to be lower for ED eyes compared with AD and HIS eyes at 15 mm Hg (P = 0.024 and 0.039, respectively). The mean compressive strains were significantly higher for AD eyes compared with ED eyes at 15 mm Hg (P = 0.018). We also found that the relationship between tensile strain and pressure was significant for those of ED and HIS eyes (P < 0.001 and P = 0.004, respectively), whereas it was not significant for those of AD (P = 0.392). Conclusions Our results suggest that, assuming glaucomatous nerve loss is caused by mechanical strains in the vicinity of the optic nerve head, the mechanism of increased glaucoma prevalence may be different in those of AD versus HIS. Our ONS strain analysis also suggested that it may be important to account for ONS geometry and material properties in future scleral biomechanical analysis.
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Affiliation(s)
- Ehab A Tamimi
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Jeffrey D Pyne
- Department of Mechanical Engineering, University of California Berkeley, Berkeley, California, United States
| | - Dominic K Muli
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Katelyn F Axman
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Stephen J Howerton
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, Arizona, United States
| | - Matthew R Davis
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, Arizona, United States
| | - Christopher A Girkin
- Department of Ophthalmology, University of Alabama Birmingham, Birmingham, Alabama, United States
| | - Jonathan P Vande Geest
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States.,Louis J. Fox Center for Vision Restoration, University of Pittsburgh, Pennsylvania, United States
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21
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Clayson K, Pan X, Pavlatos E, Short R, Morris H, Hart RT, Liu J. Corneoscleral stiffening increases IOP spike magnitudes during rapid microvolumetric change in the eye. Exp Eye Res 2017; 165:29-34. [PMID: 28864177 DOI: 10.1016/j.exer.2017.08.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 07/17/2017] [Accepted: 08/23/2017] [Indexed: 12/16/2022]
Abstract
Factors governing the steady-state IOP have been extensively studied; however, the dynamic aspects of IOP are less understood. Clinical studies have suggested that intraocular pressure (IOP) fluctuation may be associated with glaucoma risk. This study aims to investigate how stiffening of corneoscleral biomechanical properties affects IOP spikes induced by rapid microvolumetric change. Porcine eyes (n = 25 in total) were subjected to volumetric infusions before and after external treatment of a circular area (11 mm diameter) in either the central cornea or posterior sclera. The treated area in the control group was immersed in phosphate-buffered saline (PBS) for 40 min, while the treated area of the chemical crosslinking group was immersed in 4% glutaraldehyde/PBS for 40 min. A subset of the sham-treated eyes was also subjected to volumetric infusions at a raised steady-state IOP. The magnitude of IOP spikes increased after localized chemical crosslinking of either the cornea (27.5% increase, p < 0.001) or the sclera (14.3% increase, p < 0.001) with corneal crosslinking having a stronger effect than scleral crosslinking (p = 0.018). We also observed that raising the steady-state IOP from 15 to 25 mmHg resulted in marked increase in IOP spike magnitudes by 63.9% (p < 0.001). These results suggested that an increased corneoscleral stiffness could significantly increase IOP spike magnitudes at the same volumetric change. Corneal stiffness appeared to have a strong impact on the IOP spike magnitude and may play a major role in regulating rapid volume-pressure dynamics. An increase in steady-state IOP also resulted in larger IOP fluctuations due to the increased "apparent" stiffness of the ocular shell, suggesting a potential interaction between the magnitude of IOP and its fluctuations. Corneoscleral properties may represent additional pathways for understanding and managing glaucoma risk and warrant future investigation.
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Affiliation(s)
- Keyton Clayson
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA; Biophysics Interdisciplinary Program, Ohio State University, Columbus, OH, USA
| | - Xueliang Pan
- Center for Biostatistics, Ohio State University, Columbus, OH, USA
| | - Elias Pavlatos
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA
| | - Ryan Short
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA
| | - Hugh Morris
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA
| | - Richard T Hart
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA
| | - Jun Liu
- Department of Biomedical Engineering, Ohio State University, Columbus, OH, USA; Biophysics Interdisciplinary Program, Ohio State University, Columbus, OH, USA; Department of Ophthalmology and Visual Science, Ohio State University, Columbus, OH, USA.
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22
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Rogala MM, Danielewska ME, Antończyk A, Kiełbowicz Z, Rogowska ME, Kozuń M, Detyna J, Iskander DR. In-vivo corneal pulsation in relation to in-vivo intraocular pressure and corneal biomechanics assessed in-vitro. An animal pilot study. Exp Eye Res 2017; 162:27-36. [PMID: 28689748 DOI: 10.1016/j.exer.2017.07.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Revised: 06/30/2017] [Accepted: 07/05/2017] [Indexed: 01/27/2023]
Abstract
The aim was to ascertain whether the characteristics of the corneal pulse (CP) measured in-vivo in a rabbit eye change after short-term artificial increase of intraocular pressure (IOP) and whether they correlate with corneal biomechanics assessed in-vitro. Eight New Zealand white rabbits were included in this study and were anesthetized. In-vivo experiments included simultaneous measurements of the CP signal, registered with a non-contact method, IOP, intra-arterial blood pressure, and blood pulse (BPL), at the baseline and short-term elevated IOP. Afterwards, thickness of post-mortem corneas was determined and then uniaxial tensile tests were conducted leading to estimates of their Young's modulus (E). At the baseline IOP, backward stepwise regression analyses were performed in which successively the ocular biomechanical, biometric and cardiovascular predictors were separately taken into account. Results of the analysis revealed that the 3rd CP harmonic can be statistically significantly predicted by E and central corneal thickness (Models: R2 = 0.662, p < 0.005 and R2 = 0.832, p < 0.001 for the signal amplitude and power, respectively). The 1st CP harmonic can be statistically significantly predicted by the amplitude and power of the 1st BPL harmonic (Models: R2 = 0.534, p = 0.015 and R2 = 0.509, p < 0.018, respectively). For elevated IOP, non-parametric analysis indicated significant differences for the power of the 1st CP harmonic (Kruskal-Wallis test; p = 0.031) and for the mean, systolic and diastolic blood pressures (p = 0.025, p = 0.019, p = 0.033, respectively). In conclusion, for the first time, the association between parameters of the CP signal in-vivo and corneal biomechanics in-vitro was confirmed. In particular, spectral analysis revealed that higher amplitude and power of the 3rd CP harmonic indicates higher corneal stiffness, while the 1st CP harmonic correlates positively with the corresponding harmonic of the BPL signal.
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Affiliation(s)
- Maja M Rogala
- Wroclaw University of Science and Technology, Department of Mechanics, Materials Science and Engineering, Faculty of Mechanical Engineering, ul. Smoluchowskiego 25, 50-370 Wroclaw, Poland.
| | - Monika E Danielewska
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
| | - Agnieszka Antończyk
- Wroclaw University of Environmental and Life Sciences, Department of Surgery, Faculty of Veterinary Medicine, pl. Grunwaldzki 51, 50-366 Wroclaw, Poland.
| | - Zdzisław Kiełbowicz
- Wroclaw University of Environmental and Life Sciences, Department of Surgery, Faculty of Veterinary Medicine, pl. Grunwaldzki 51, 50-366 Wroclaw, Poland.
| | - Marta E Rogowska
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
| | - Marta Kozuń
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Mechatronics and Theory of Mechanisms, Faculty of Mechanical Engineering, ul. Lukasiewicza 7/9, 50-371 Wroclaw, Poland.
| | - Jerzy Detyna
- Wroclaw University of Science and Technology, Department of Mechanics, Materials Science and Engineering, Faculty of Mechanical Engineering, ul. Smoluchowskiego 25, 50-370 Wroclaw, Poland.
| | - D Robert Iskander
- Wroclaw University of Science and Technology, Department of Biomedical Engineering, Faculty of Fundamental Problems of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland.
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Abstract
PURPOSE OF REVIEW This article presents, summarizes, and interprets the most recent advances in the study and understanding of the lamina cribrosa in glaucoma, in the context of previous work. RECENT FINDINGS The lamina is an active living structure that responds to strain by changing morphology at the micro-scale and macro-scale in glaucoma. Changes in lamina cribrosa morphology in glaucoma include posteriorization of the laminar insertion into the sclera, increased cupping or depth of the lamina cribrosa, and the development of focal lamina cribrosa defects. These lamina cribrosa changes are associated with disk hemorrhages and visual field damage, and are detectable with clinical imaging techniques such as optical coherence tomography. Glaucomatous changes in the lamina cribrosa are thought to be driven by cellular processes mediated by focal cyclical mechanical strain. Strain is eye specific and mediated by intraocular pressure, cerebrospinal fluid pressure, scleral and lamina cribrosa morphology, and structural stiffness; deleterious lamina cribrosa strains can occur at all levels of mean intraocular pressure. SUMMARY Laminar morphology is ever changing in health and disease, and recent studies have identified several promising morphological changes that are indicative of glaucoma susceptibility, onset, and progression.
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Precise measurement of scleral radius using anterior eye profilometry. Cont Lens Anterior Eye 2016; 40:47-52. [PMID: 27863894 DOI: 10.1016/j.clae.2016.11.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2016] [Revised: 10/14/2016] [Accepted: 11/08/2016] [Indexed: 11/23/2022]
Abstract
PURPOSE To develop a new and precise methodology to measure the scleral radius based on anterior eye surface. METHODS Eye Surface Profiler (ESP, Eaglet-Eye, Netherlands) was used to acquire the anterior eye surface of 23 emmetropic subjects aged 28.1±6.6years (mean±standard deviation) ranging from 20 to 45. Scleral radius was obtained based on the approximation of the topographical scleral data to a sphere using least squares fitting and considering the axial length as a reference point. To better understand the role of scleral radius in ocular biometry, measurements of corneal radius, central corneal thickness, anterior chamber depth and white-to-white corneal diameter were acquired with IOLMaster 700 (Carl Zeiss Meditec AG, Jena, Germany). RESULTS The estimated scleral radius (11.2±0.3mm) was shown to be highly precise with a coefficient of variation of 0.4%. A statistically significant correlation between axial length and scleral radius (R2=0.957, p<0.001) was observed. Moreover, corneal radius (R2=0.420, p<0.001), anterior chamber depth (R2=0.141, p=0.039) and white-to-white corneal diameter (R2=0.146, p=0.036) have also shown statistically significant correlations with the scleral radius. Lastly, no correlation was observed comparing scleral radius to the central corneal thickness (R2=0.047, p=0.161). CONCLUSIONS Three-dimensional topography of anterior eye acquired with Eye Surface Profiler together with a given estimate of the axial length, can be used to calculate the scleral radius with high precision.
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Pavlatos E, Perez BC, Morris HJ, Chen H, Palko JR, Pan X, Weber PA, Hart RT, Liu J. Three-Dimensional Strains in Human Posterior Sclera Using Ultrasound Speckle Tracking. J Biomech Eng 2016; 138:021015. [PMID: 26632258 DOI: 10.1115/1.4032124] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Indexed: 02/02/2023]
Abstract
Intraocular pressure (IOP) induced strains in the peripapillary sclera may play a role in glaucoma progression. Using inflation testing and ultrasound speckle tracking, the 3D strains in the peripapillary sclera were measured in nine human donor globes. Our results showed that the peripapillary sclera experienced through-thickness compression and meridional stretch during inflation, while minimal circumferential dilation was observed when IOP was increased from 10 to 19 mmHg. The maximum shear was primarily oriented in the through-thickness, meridional cross sections and had a magnitude slightly larger than the first principal strain. The tissue volume had minimal overall change, confirming near-incompressibility of the sclera. Substantial strain heterogeneity was present in the peripapillary region, with local high strain areas likely corresponding to structural heterogeneity caused by traversing blood vessels. These 3D strain characteristics provide new insights into the biomechanical responses of the peripapillary sclera during physiological increases of IOP. Future studies are needed to confirm these findings and investigate the role of these biomechanical characteristics in ocular diseases.
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Palko JR, Morris HJ, Pan X, Harman CD, Koehl KL, Gelatt KN, Plummer CE, Komáromy AM, Liu J. Influence of Age on Ocular Biomechanical Properties in a Canine Glaucoma Model with ADAMTS10 Mutation. PLoS One 2016; 11:e0156466. [PMID: 27271467 PMCID: PMC4894564 DOI: 10.1371/journal.pone.0156466] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 05/13/2016] [Indexed: 11/29/2022] Open
Abstract
Soft tissue often displays marked age-associated stiffening. This study aims to investigate how age affects scleral biomechanical properties in a canine glaucoma model with ADAMTS10 mutation, whose extracellular matrix is concomitantly influenced by the mutation and an increased mechanical load from an early age. Biomechanical data was acquired from ADAMTS10-mutant dogs (n = 10, 21 to 131 months) and normal dogs (n = 5, 69 to 113 months). Infusion testing was first performed in the whole globes to measure ocular rigidity. After infusion experiments, the corneas were immediately trephined to prepare scleral shells that were mounted on a pressurization chamber to measure strains in the posterior sclera using an inflation testing protocol. Dynamic viscoelastic mechanical testing was then performed on dissected posterior scleral strips and the data were combined with those reported earlier by our group from the same animal model (Palko et al, IOVS 2013). The association between age and scleral biomechanical properties was evaluated using multivariate linear regression. The relationships between scleral properties and the mean and last measured intraocular pressure (IOP) were also evaluated. Our results showed that age was positively associated with complex modulus (p<0.001) and negatively associated with loss tangent (p<0.001) in both the affected and the normal groups, suggesting an increased stiffness and decreased mechanical damping with age. The regression slopes were not different between the groups, although the complex modulus was significantly lower in the affected group (p = 0.041). The posterior circumferential tangential strain was negatively correlated with complex modulus (R = -0.744, p = 0.006) showing consistent mechanical evaluation between the testing methods. Normalized ocular rigidity was negatively correlated with the last IOP in the affected group (p = 0.003). Despite a mutation that affects the extracellular matrix and a chronic IOP elevation in the affected dogs, age-associated scleral stiffening and loss of mechanical damping were still prominent and had a similar rate of change as in the normal dogs.
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Affiliation(s)
- Joel R. Palko
- Department of Biomedical Engineering, Ohio State University, Columbus, Ohio, United States of America
- Department of Ophthalmology, Washington University, St. Louis, Missouri, United States of America
| | - Hugh J. Morris
- Department of Biomedical Engineering, Ohio State University, Columbus, Ohio, United States of America
| | - Xueliang Pan
- Center for Biostatistics, Ohio State University, Columbus, OH, United States of America
| | - Christine D. Harman
- Department of Small Animal Clinical Sciences, Michigan State University, Lansing, Michigan, United States of America
| | - Kristin L. Koehl
- Department of Small Animal Clinical Sciences, Michigan State University, Lansing, Michigan, United States of America
| | - Kirk N. Gelatt
- Department of Small Animal Clinical Sciences, University of Florida, Gainesville, Florida, United States of America
| | - Caryn E. Plummer
- Department of Small Animal Clinical Sciences, University of Florida, Gainesville, Florida, United States of America
| | - András M. Komáromy
- Department of Small Animal Clinical Sciences, Michigan State University, Lansing, Michigan, United States of America
- Department of Small Animal Clinical Sciences, University of Florida, Gainesville, Florida, United States of America
- Department of Clinical Studies, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail: (JL); (AMK)
| | - Jun Liu
- Department of Biomedical Engineering, Ohio State University, Columbus, Ohio, United States of America
- Department of Ophthalmology, Ohio State University, Columbus, Ohio, United States of America
- * E-mail: (JL); (AMK)
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Characterization of the mechanical behavior of the optic nerve sheath and its role in spaceflight-induced ophthalmic changes. Biomech Model Mechanobiol 2016; 16:33-43. [PMID: 27236645 DOI: 10.1007/s10237-016-0800-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Accepted: 05/17/2016] [Indexed: 12/14/2022]
Abstract
Visual impairment and intracranial pressure (VIIP) syndrome is characterized by a number of permanent ophthalmic changes, including loss of visual function. It occurs in some astronauts during long-duration spaceflight missions. Thus, understanding the pathophysiology of VIIP is currently a major priority in space medicine research. It is hypothesized that maladaptive remodeling of the optic nerve sheath (ONS), in response to microgravity-induced elevations in intracranial pressure (ICP), contributes to VIIP. However, little is known about ONS biomechanics. In this study, we developed a custom mechanical testing system that allowed for unconfined lengthening, twisting, and circumferential distension of the porcine ONS during inflation and axial loading. Data were fit to a four-fiber family constitutive equation to extract material and structural parameters. Inflation testing showed a characteristic "cross-over point" in the pressure-diameter curves under different axial loads in all samples that were tested; the cross-over pressure was [Formula: see text] mmHg ([Formula: see text]). Large sample-to-sample variations were observed in the circumferential strain, while only modest variations were observed in the circumferential stress. Multiphoton microscopy revealed that the collagen fibers of the ONS were primarily oriented axially when the tissue was loaded. The existence of this cross-over behavior is expected to be neuroprotective, as it would avoid optic nerve compression during routine changes in gaze angle, so long as ICP was within the normal range. Including these observations into computational models of VIIP will help provide insight into the pathophysiology of VIIP and could help identify risk factors and potential interventions.
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Qu J, Chen H, Zhu L, Ambalavanan N, Girkin CA, Murphy-Ullrich JE, Downs JC, Zhou Y. High-Magnitude and/or High-Frequency Mechanical Strain Promotes Peripapillary Scleral Myofibroblast Differentiation. Invest Ophthalmol Vis Sci 2016; 56:7821-30. [PMID: 26658503 DOI: 10.1167/iovs.15-17848] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
PURPOSE To determine the effects of altered mechanical strain on human peripapillary scleral (ppSc) fibroblast-to-myofibroblast differentiation. METHODS Eight human ppSc fibroblast cultures were isolated from three paired eyes and two unilateral eyes of five donors using an explant approach. Human ppSc fibroblast isolates were subjected to 1% and 4% cyclic strain at 0.05 to 5 Hz for 24 hours. Levels of α smooth muscle actin (αSMA) mRNA and protein were determined by real-time PCR and immunoblot. Incorporation of αSMA into actin stress fibers was evaluated by confocal immunofluorescent microscopy. Myofibroblast contractility was measured by fibroblast-populated three-dimensional collagen gel contraction assay and phosphorylation of myosin light chain (MLC20). RESULTS Human ppSc fibroblasts contained 6% to 47% fully differentiated myofibroblasts before strain application; 4% cyclic strain increased αSMA mRNA and protein expression in ppSc fibroblasts compared with 1% strain applied at 5 Hz, but not at lower frequencies. Seven of eight ppSc fibroblast isolates responded to high-magnitude and high-frequency strain with increased cellular contractility and increased MLC20 phosphorylation. In addition, increasing strain frequency promoted αSMA expression in ppSc fibroblasts under both 1% and 4% strain conditions. CONCLUSIONS High-magnitude and/or high-frequency mechanical strain promotes differentiation of human ppSc fibroblasts into contractile myofibroblasts, a fibroblast phenotypic change known to be key to tissue injury-repair responses. These findings suggest that the cellular constituent of ppSc may play an important role in the regulation of optic nerve head biomechanics in response to injurious IOP fluctuations.
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Affiliation(s)
- Jing Qu
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Huaping Chen
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Lanyan Zhu
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States 2The Second Xiangya Hospital, Central-South University, Changsha, Hunan, China
| | - Namasivayam Ambalavanan
- Department of Pediatrics, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Christopher A Girkin
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Joanne E Murphy-Ullrich
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States 5Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - J Crawford Downs
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States 6Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Yong Zhou
- Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama, United States 4Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama, United States 6Department of Biomedical Engineering, University of Alab
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Nguyen TD, Ethier CR. Biomechanical assessment in models of glaucomatous optic neuropathy. Exp Eye Res 2015; 141:125-38. [PMID: 26115620 PMCID: PMC4628840 DOI: 10.1016/j.exer.2015.05.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Revised: 05/20/2015] [Accepted: 05/31/2015] [Indexed: 01/26/2023]
Abstract
The biomechanical environment within the eye is of interest in both the regulation of intraocular pressure and the loss of retinal ganglion cell axons in glaucomatous optic neuropathy. Unfortunately, this environment is complex and difficult to determine. Here we provide a brief introduction to basic concepts of mechanics (stress, strain, constitutive relationships) as applied to the eye, and then describe a variety of experimental and computational approaches used to study ocular biomechanics. These include finite element modeling, direct experimental measurements of tissue displacements using optical and other techniques, direct experimental measurement of tissue microstructure, and combinations thereof. Thanks to notable technical and conceptual advances in all of these areas, we are slowly gaining a better understanding of how tissue biomechanical properties in both the anterior and posterior segments may influence the development of, and risk for, glaucomatous optic neuropathy. Although many challenging research questions remain unanswered, the potential of this body of work is exciting; projects underway include the coupling of clinical imaging with biomechanical modeling to create new diagnostic tools, development of IOP control strategies based on improved understanding the mechanobiology of the outflow tract, and attempts to develop novel biomechanically-based therapeutic strategies for preservation of vision in glaucoma.
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Affiliation(s)
- Thao D Nguyen
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, USA
| | - C Ross Ethier
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, USA; Department of Mechanical Engineering, Georgia Institute of Technology, USA; Institute of Biosciences and Bioengineering, Georgia Institute of Technology, USA; Department of Ophthalmology, Emory University, USA.
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Mapping 3D Strains with Ultrasound Speckle Tracking: Method Validation and Initial Results in Porcine Scleral Inflation. Ann Biomed Eng 2015; 44:2302-12. [PMID: 26563101 DOI: 10.1007/s10439-015-1506-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Accepted: 11/05/2015] [Indexed: 10/22/2022]
Abstract
This study aimed to develop and validate a high frequency ultrasound method for measuring distributive, 3D strains in the sclera during elevations of intraocular pressure. A 3D cross-correlation based speckle-tracking algorithm was implemented to compute the 3D displacement vector and strain tensor at each tracking point. Simulated ultrasound radiofrequency data from a sclera-like structure at undeformed and deformed states with known strains were used to evaluate the accuracy and signal-to-noise ratio (SNR) of strain estimation. An experimental high frequency ultrasound (55 MHz) system was built to acquire 3D scans of porcine eyes inflated from 15 to 17 and then 19 mmHg. Simulations confirmed good strain estimation accuracy and SNR (e.g., the axial strains had less than 4.5% error with SNRs greater than 16.5 for strains from 0.005 to 0.05). Experimental data in porcine eyes showed increasing tensile, compressive, and shear strains in the posterior sclera during inflation, with a volume ratio close to one suggesting near-incompressibility. This study established the feasibility of using high frequency ultrasound speckle tracking for measuring 3D tissue strains and its potential to characterize physiological deformations in the posterior eye.
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Abstract
This review is focused on continuous IOP monitoring using telemetry systems in the nonhuman primate (NHP), presented in the context that IOP fluctuations at various timescales may be involved in glaucoma pathogenesis and progression. We use glaucoma as the primary framework to discuss how the dynamic nature of IOP might change with age, racial heritage, and disease in the context of glaucoma susceptibility and progression. We focus on the limited work that has been published in IOP telemetry in NHPs, as well as the emerging data and approaches. We review the ongoing efforts to measure continuous IOP, and the strengths, weaknesses and general pitfalls of the various approaches.
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Affiliation(s)
- J Crawford Downs
- Department of Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, AL, USA.
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Glaucoma-related Changes in the Mechanical Properties and Collagen Micro-architecture of the Human Sclera. PLoS One 2015; 10:e0131396. [PMID: 26161963 PMCID: PMC4498780 DOI: 10.1371/journal.pone.0131396] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Accepted: 06/01/2015] [Indexed: 12/13/2022] Open
Abstract
Objective The biomechanical behavior of the sclera determines the level of mechanical insult from intraocular pressure to the axons and tissues of the optic nerve head, as is of interest in glaucoma. In this study, we measure the collagen fiber structure and the strain response, and estimate the material properties of glaucomatous and normal human donor scleras. Methods Twenty-two posterior scleras from normal and diagnosed glaucoma donors were obtained from an eyebank. Optic nerve cross-sections were graded to determine the presence of axon loss. The specimens were subjected to pressure-controlled inflation testing. Full-field displacement maps were measured by digital image correlation (DIC) and spatially differentiated to compute surface strains. Maps of the collagen fiber structure across the posterior sclera of each inflated specimen were obtained using synchrotron wide-angle X-ray scattering (WAXS). Finite element (FE) models of the posterior scleras, incorporating a specimen-specific representation of the collagen structure, were constructed from the DIC-measured geometry. An inverse finite element analysis was developed to estimate the stiffness of the collagen fiber and inter-fiber matrix. Results The differences between glaucoma and non-glaucoma eyes were small in magnitude. Sectorial variations of degree of fiber alignment and peripapillary scleral strain significantly differed between normal and diagnosed glaucoma specimens. Meridional strains were on average larger in diagnosed glaucoma eyes compared with normal specimens. Non-glaucoma specimens had on average the lowest matrix and fiber stiffness, followed by undamaged glaucoma eyes, and damaged glaucoma eyes but the differences in stiffness were not significant. Conclusion The observed biomechanical and microstructural changes could be the result of tissue remodeling occuring in glaucoma and are likely to alter the mechanical environment of the optic nerve head and contribute to axonal damage.
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Downs JC. Optic nerve head biomechanics in aging and disease. Exp Eye Res 2015; 133:19-29. [PMID: 25819451 DOI: 10.1016/j.exer.2015.02.011] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Revised: 12/31/2014] [Accepted: 02/12/2015] [Indexed: 11/28/2022]
Abstract
This nontechnical review is focused upon educating the reader on optic nerve head biomechanics in both aging and disease along two main themes: what is known about how mechanical forces and the resulting deformations are distributed in the posterior pole and ONH (biomechanics) and what is known about how the living system responds to those deformations (mechanobiology). We focus on how ONH responds to IOP elevations as a structural system, insofar as the acute mechanical response of the lamina cribrosa is confounded with the responses of the peripapillary sclera, prelaminar neural tissues, and retrolaminar optic nerve. We discuss the biomechanical basis for IOP-driven changes in connective tissues, blood flow, and cellular responses. We use glaucoma as the primary framework to present the important aspects of ONH biomechanics in aging and disease, as ONH biomechanics, aging, and the posterior pole extracellular matrix (ECM) are thought to be centrally involved in glaucoma susceptibility, onset and progression.
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Affiliation(s)
- J Crawford Downs
- Department of Ophthalmology, University of Alabama at Birmingham School of Medicine, 1670 University Blvd., VH 390A, Birmingham, AL 35294, USA.
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Pijanka JK, Spang MT, Sorensen T, Liu J, Nguyen TD, Quigley HA, Boote C. Depth-dependent changes in collagen organization in the human peripapillary sclera. PLoS One 2015; 10:e0118648. [PMID: 25714753 PMCID: PMC4340934 DOI: 10.1371/journal.pone.0118648] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 01/08/2015] [Indexed: 11/18/2022] Open
Abstract
PURPOSE The collagen structure of the human peripapillary sclera plays a significant role in determining optic nerve head (ONH) biomechanics, and is therefore of interest in the study of glaucoma. The aim of the current work was to map the anisotropic collagen structure of the normal human peripapillary sclera as a function of tissue depth. METHODS Wide-angle x-ray scattering was used to quantify collagen fibril orientation at 0.5 mm intervals across six 150 μm-thick serial sections through the peripapillary sclera of eight normal European-derived human eyes. Two structural parameters were measured: 1) the relative number of fibrils preferentially aligned at a given angle within the tissue plane, 2) the degree of collagen alignment (anisotropy). RESULTS The inner-most one-third of the peripapillary scleral stroma (nearest to the choroid) was characterised by collagen fibrils either randomly arranged or preferentially aligned radially with respect to the ONH. In contrast, the outer two-thirds of the tissue was dominated by a circumferential arrangement of collagen encircling the ONH. In all tissue regions the degree of collagen anisotropy peaked in the mid-stroma and progressively decreased towards the tissue surfaces, with the largest depth variations occurring in the inferior-nasal quadrant, and the smallest occurring in the superior-nasal quadrant. CONCLUSIONS Significant, region-specific variations in collagen structure are present in the human peripapillary sclera as a function of depth. In normal eyes, the circumferential collagen fibril architecture is most prominent in the outer two-thirds of the stroma, possibly as a mechanical adaption to more effectively support the lamina cribrosa at the level of its insertion into the scleral canal wall.
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Affiliation(s)
- Jacek K. Pijanka
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, United Kingdom
| | - Martin T. Spang
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, United Kingdom
| | | | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States of America
| | - Thao D. Nguyen
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Harry A. Quigley
- Glaucoma Center of Excellence, Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Craig Boote
- Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, United Kingdom
- * E-mail:
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Coudrillier B, Pijanka J, Jefferys J, Sorensen T, Quigley HA, Boote C, Nguyen TD. Collagen structure and mechanical properties of the human sclera: analysis for the effects of age. J Biomech Eng 2015; 137:041006. [PMID: 25531905 DOI: 10.1115/1.4029430] [Citation(s) in RCA: 88] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Indexed: 11/08/2022]
Abstract
The objective of this study was to measure the collagen fiber structure and estimate the material properties of 7 human donor scleras, from age 53 to 91. The specimens were subjected to inflation testing, and the full-field displacement maps were measured by digital image correlation. After testing, the collagen fiber structure was mapped using wide-angle X-ray scattering. A specimen-specific inverse finite element method was applied to calculate the material properties of the collagen fibers and interfiber matrix by minimizing the difference between the experimental displacements and model predictions. Age effects on the fiber structure and material properties were estimated using multivariate models accounting for spatial autocorrelation. Older age was associated with a larger matrix stiffness (p = 0.001), a lower degree of fiber alignment in the peripapillary sclera (p = 0.01), and a lower mechanical anisotropy in the peripapillary sclera (p = 0.03).
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Grytz R, Fazio MA, Libertiaux V, Bruno L, Gardiner S, Girkin CA, Downs JC. Age- and race-related differences in human scleral material properties. Invest Ophthalmol Vis Sci 2014; 55:8163-72. [PMID: 25389203 DOI: 10.1167/iovs.14-14029] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE We tested the hypothesis that there are age- and race-related differences in posterior scleral material properties, using eyes from human donors of European (20-90 years old, n = 40 eyes) and African (23-74 years old, n = 22 eyes) descent. METHODS Inflation tests on posterior scleral shells were performed while full-field, three-dimensional displacements were recorded using laser speckle interferometry. Scleral material properties were fit to each eye using a microstructure-based constitutive formulation that incorporates the collagen fibril crimp and the local anisotropic collagen architecture. The effects of age and race were estimated using Generalized Estimating Equations, while accounting for intradonor correlations. RESULTS The shear modulus significantly increased (P = 0.038) and collagen fibril crimp angle significantly decreased with age (P = 0.002). Donors of African descent exhibited a significantly higher shear modulus (P = 0.019) and showed evidence of a smaller collagen fibril crimp angle (P = 0.057) compared to donors of European descent. The in-plane strains in the peripapillary sclera were significantly lower with age (P < 0.015) and African ancestry (P < 0.015). CONCLUSIONS The age- and race-related differences in scleral material properties result in a loss of scleral compliance due to a higher shear stiffness and a lower level of stretch at which the collagen fibrils uncrimp. The loss of compliance should lead to larger high frequency IOP fluctuations and changes in the optic nerve head (ONH) biomechanical response in the elderly and in persons of African ancestry, and may contribute to the higher susceptibility to glaucoma in these at-risk populations.
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Affiliation(s)
- Rafael Grytz
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - Massimo A Fazio
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - Vincent Libertiaux
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - Luigi Bruno
- Mechanical Engineering, University of Calabria, Calabria, Italy
| | - Stuart Gardiner
- Discoveries in Sight Research Laboratories, Devers Eye Institute, Portland, Oregon, United States
| | - Christopher A Girkin
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
| | - J Crawford Downs
- Ophthalmology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, United States
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Causin P, Guidoboni G, Harris A, Prada D, Sacco R, Terragni S. A poroelastic model for the perfusion of the lamina cribrosa in the optic nerve head. Math Biosci 2014; 257:33-41. [DOI: 10.1016/j.mbs.2014.08.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Revised: 07/31/2014] [Accepted: 08/03/2014] [Indexed: 10/24/2022]
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Abstract
BACKGROUND/AIMS To determine which biometric parameters provide optimum predictive power for ocular volume. METHODS Sixty-seven adult subjects were scanned with a Siemens 3-T MRI scanner. Mean spherical error (MSE) (D) was measured with a Shin-Nippon autorefractor and a Zeiss IOLMaster used to measure (mm) axial length (AL), anterior chamber depth (ACD) and corneal radius (CR). Total ocular volume (TOV) was calculated from T2-weighted MRIs (voxel size 1.0 mm(3)) using an automatic voxel counting and shading algorithm. Each MR slice was subsequently edited manually in the axial, sagittal and coronal plane, the latter enabling location of the posterior pole of the crystalline lens and partitioning of TOV into anterior (AV) and posterior volume (PV) regions. RESULTS Mean values (±SD) for MSE (D), AL (mm), ACD (mm) and CR (mm) were -2.62±3.83, 24.51±1.47, 3.55±0.34 and 7.75±0.28, respectively. Mean values (±SD) for TOV, AV and PV (mm(3)) were 8168.21±1141.86, 1099.40±139.24 and 7068.82±1134.05, respectively. TOV showed significant correlation with MSE, AL, PV (all p<0.001), CR (p=0.043) and ACD (p=0.024). Bar CR, the correlations were shown to be wholly attributable to variation in PV. Multiple linear regression indicated that the combination of AL and CR provided optimum R(2) values of 79.4% for TOV. CONCLUSION Clinically useful estimations of ocular volume can be obtained from measurement of AL and CR.
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Affiliation(s)
- Manbir Nagra
- School of Life & Health Sciences, Aston University, Birmingham, UK
| | | | - Nicola S Logan
- School of Life & Health Sciences, Aston University, Birmingham, UK
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Campbell IC, Coudrillier B, Ross Ethier C. Biomechanics of the Posterior Eye: A Critical Role in Health and Disease. J Biomech Eng 2014; 136:021005. [DOI: 10.1115/1.4026286] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 12/19/2013] [Indexed: 01/16/2023]
Abstract
The posterior eye is a complex biomechanical structure. Delicate neural and vascular tissues of the retina, choroid, and optic nerve head that are critical for visual function are subjected to mechanical loading from intraocular pressure, intraocular and extraorbital muscles, and external forces on the eye. The surrounding sclera serves to counteract excessive deformation from these forces and thus to create a stable biomechanical environment for the ocular tissues. Additionally, the eye is a dynamic structure with connective tissue remodeling occurring as a result of aging and pathologies such as glaucoma and myopia. The material properties of these tissues and the distribution of stresses and strains in the posterior eye is an area of active research, relying on a combination of computational modeling, imaging, and biomechanical measurement approaches. Investigators are recognizing the increasing importance of the role of the collagen microstructure in these material properties and are undertaking microstructural measurements to drive microstructurally-informed models of ocular biomechanics. Here, we review notable findings and the consensus understanding on the biomechanics and microstructure of the posterior eye. Results from computational and numerical modeling studies and mechanical testing of ocular tissue are discussed. We conclude with some speculation as to future trends in this field.
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Affiliation(s)
- Ian C. Campbell
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
- Rehabilitation Research and Development Center of Excellence, Atlanta VA Medical Center, 1670 Clairmont Road, Decatur, GA 30032
| | - Baptiste Coudrillier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332
- Rehabilitation Research and Development Center of Excellence, Atlanta VA Medical Center, 1670 Clairmont Road, Decatur, GA 30032
- Department of Ophthalmology, School of Medicine, Emory University, Atlanta, GA 30322
- Department of Bioengineering, Imperial College London, London SW7 2AZ, UK e-mail:
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Perez BC, Morris HJ, Hart RT, Liu J. Finite element modeling of the viscoelastic responses of the eye during microvolumetric changes. ACTA ACUST UNITED AC 2013; 6:29-37. [PMID: 24672621 PMCID: PMC3963399 DOI: 10.4236/jbise.2013.612a005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
A linear viscoelastic finite element model was built to investigate factors that influenced the intraocular pressure (IOP) elevations due to micro-volumetric changes in the eye at three different rates. The viscoelastic properties of the cornea and the sclera, including the instantaneous modulus, equilibrium modulus, and relaxation time constants, parametrically varied to examine their effects on IOP elevations at different rates of volumetric changes. The simulated responses were in good agreement with the previously reported experimental results obtained from porcine globes, showing the general trend of higher IOP elevations at faster rates. The simulations showed that all viscoelastic properties influenced the profile of the dynamic IOP due to volumetric changes, and the relative significance of a specific parameter was highly dependent on the rate of change.
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Affiliation(s)
- Benjamin Cruz Perez
- Department of Biomedical Engineering, The Ohio State University, Columbus, USA
| | - Hugh J Morris
- Department of Biomedical Engineering, The Ohio State University, Columbus, USA
| | - Richard T Hart
- Department of Biomedical Engineering, The Ohio State University, Columbus, USA
| | - Jun Liu
- Department of Biomedical Engineering, The Ohio State University, Columbus, USA ; Department of Ophthalmology, The Ohio State University, Columbus, USA
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