1
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Li G, van Batenburg-Sherwood J, Safa BN, Fraticelli Guzmán NS, Wilson A, Bahrani Fard MR, Choy K, de Ieso ML, Cui JS, Feola AJ, Weisz T, Kuhn M, Bowes Rickman C, Farsiu S, Ethier CR, Stamer WD. Aging and intraocular pressure homeostasis in mice. Aging Cell 2024:e14160. [PMID: 38566432 DOI: 10.1111/acel.14160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 03/09/2024] [Accepted: 03/14/2024] [Indexed: 04/04/2024] Open
Abstract
Age and elevated intraocular pressure (IOP) are the two primary risk factors for glaucoma, an optic neuropathy that is the leading cause of irreversible blindness. In most people, IOP is tightly regulated over a lifetime by the conventional outflow tissues. However, the mechanistic contributions of age to conventional outflow dysregulation, elevated IOP and glaucoma are unknown. To address this gap in knowledge, we studied how age affects the morphology, biomechanical properties and function of conventional outflow tissues in C57BL/6 mice, which have an outflow system similar to humans. As reported in humans, we observed that IOP in mice was maintained within a tight range over their lifespan. Remarkably, despite a constellation of age-related changes to the conventional outflow tissues that would be expected to hinder aqueous drainage and impair homeostatic function (decreased cellularity, increased pigment accumulation, increased cellular senescence and increased stiffness), outflow facility, a measure of conventional outflow tissue fluid conductivity, was stable with age. We conclude that the murine conventional outflow system has significant functional reserve in healthy eyes. However, these age-related changes, when combined with other underlying factors, such as genetic susceptibility, are expected to increase risk for ocular hypertension and glaucoma.
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Affiliation(s)
- Guorong Li
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | | | - Babak N Safa
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA
| | - Nina Sara Fraticelli Guzmán
- Department of Ophthalmology, Emory University, Atlanta, Georgia, USA
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA
| | - Andrea Wilson
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - Mohammad Reza Bahrani Fard
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA
| | - Kevin Choy
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
| | - Michael L de Ieso
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - J Serena Cui
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - Andrew J Feola
- Department of Ophthalmology, Emory University, Atlanta, Georgia, USA
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
- Center for Visual and Neurocognitive Rehabilitation, Atlanta Virginia Medical Center, Decatur, Georgia, USA
| | - Tara Weisz
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | - Megan Kuhn
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
| | | | - Sina Farsiu
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
| | - C Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA
- Department of Ophthalmology, Emory University, Atlanta, Georgia, USA
| | - W Daniel Stamer
- Department of Ophthalmology, Duke University, Durham, North Carolina, USA
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA
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2
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Tambroni N, Tomassetti G, Lombardi S, Repetto R. A mechanical model of ocular bulb vibrations and implications for acoustic tonometry. PLoS One 2024; 19:e0294825. [PMID: 38236823 PMCID: PMC10796012 DOI: 10.1371/journal.pone.0294825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Accepted: 12/13/2023] [Indexed: 01/22/2024] Open
Abstract
In this study, we propose a comprehensive mechanical model of ocular bulb vibrations and discuss its implications for acoustic tonometry. The model describes the eye wall as a spherical, pre-stressed elastic shell containing a viscoelastic material and accounts for the interaction between the elastic corneoscleral shell and the viscoelastic vitreous humor. We investigate the natural frequencies of the system and the corresponding vibration modes, expanding the solution in terms of scalar and vector spherical harmonics. From a quantitative point of view, our findings reveal that the eyebulb vibration frequencies significantly depend on IOP. This dependency has two origins: "geometric" stiffening, due to an increase of the pre-stress, and "material" stiffening, due to the nonlinearity of the stress-strain curve of the sclera. The model shows that the second effect is by far dominant. We also find that the oscillation frequencies depend on ocular rigidity, but this dependency is important only at relatively large values of IOP. Thus close to physiological conditions, IOP is the main determinant of ocular vibration frequencies. The vitreous rheological properties are found to mostly influence vibration damping. This study contributes to the understanding of the mechanical behavior of the eye under dynamic conditions and thus has implications for non-contact intraocular pressure measurement techniques, such as acoustic tonometry. The model can also be relevant for other ocular pathological conditions, such as traumatic retinal detachment, which are believed to be influenced by the dynamic behavior of the eye.
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Affiliation(s)
- Nicoletta Tambroni
- Department of Civil, Chemical and Enivironmental Engineering, University of Genoa, Genoa, Italy
| | - Giuseppe Tomassetti
- Department of Industrial, Electronic, and Mechanical Engineering, Roma Tre University, Rome, Italy
| | | | - Rodolfo Repetto
- Department of Civil, Chemical and Enivironmental Engineering, University of Genoa, Genoa, Italy
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3
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Döbeli L, Haack C, Heim H. Modeling the compliance of the human eye with elastic membranes based on a bionic approach. BIOMED ENG-BIOMED TE 2023; 68:599-606. [PMID: 37279245 DOI: 10.1515/bmt-2023-0079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2022] [Accepted: 05/15/2023] [Indexed: 06/08/2023]
Abstract
OBJECTIVES Together with the corneoscleral shell the intraocular pressure maintains the shape of the human eyeball and thus ensures both mechanical and optical integrity, whereby the relationship between the intraocular volume and pressure is described by the so-called ocular compliance. The compliance of the human eye is of significance in situations where a variation of the intraocular volume leads to a change in pressure or vice versa, as this is the case in many clinical settings. In order to provide a framework and set-up for experimental investigations and testing this paper presents a bionic inspired approach to simulate the ocular compliance by using elastomeric membranes - based on physiological behaviour. METHODS For parameter studies and for validation, the numerical analysis with hyperelastic material models shows good agreement with reported compliance curves. In addition, the compliance curves of six different elastomeric membranes have been measured. RESULTS The results show that the characteristics of the compliance curve of the human eye can be modeled within a 5 % range using the proposed elastomeric membranes. CONCLUSIONS A set-up for experimental investigations is presented that allows the simulation of the compliance curve of the human eye without simplifications in terms of shape, geometry, and deformation behaviour.
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Affiliation(s)
- Lionardo Döbeli
- Institute of Mechanical Engineering and Energy Technology, Lucerne University of Applied Sciences and Arts, Horw, Switzerland
| | - Carsten Haack
- Institute of Mechanical Engineering and Energy Technology, Lucerne University of Applied Sciences and Arts, Horw, Switzerland
| | - Heiko Heim
- Oertli Instrumente AG, Berneck, Switzerland
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4
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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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5
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Li G, van Batenburg-Sherwood J, Safa BN, Fraticelli Guzmán NS, Wilson A, Bahrani Fard MR, Choy K, De Ieso ML, Cui JS, Feola AJ, Weisz T, Kuhn M, Rickman CB, Farsiu S, Ethier CR, Stamer WD. Aging and intraocular pressure homeostasis in mice. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.17.562768. [PMID: 38106150 PMCID: PMC10723259 DOI: 10.1101/2023.10.17.562768] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Age and elevated intraocular pressure (IOP) are the two primary risk factors for glaucoma, an optic neuropathy that is the leading cause of irreversible blindness. In most people, IOP is tightly regulated over a lifetime by the conventional outflow tissues. However, the mechanistic contributions of age to conventional outflow dysregulation, elevated IOP and glaucoma are unknown. To address this gap in knowledge, we studied how age affects the morphology, biomechanical properties and function of conventional outflow tissues in C57BL/6 mice, which have an outflow system similar to humans. As reported in humans, we observed that IOP in mice was maintained within a tight range over their lifespan. Remarkably, despite a constellation of age-related changes to the conventional outflow tissues that would be expected to hinder aqueous drainage and impair homeostatic function (decreased cellularity, increased pigment accumulation, increased cellular senescence and increased stiffness), outflow facility, a measure of conventional outflow tissue fluid conductivity, was stable with age. We conclude that the murine conventional outflow system has significant functional reserve in healthy eyes. However, these age-related changes, when combined with other underlying factors, such as genetic susceptibility, are expected to increase risk for ocular hypertension and glaucoma.
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6
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Mohamed Y, Passaglia CL. Simulation of gravity- and pump-driven perfusion techniques for measuring outflow facility of ex vivo and in vivo eyes. PLoS One 2023; 18:e0294607. [PMID: 37988400 PMCID: PMC10662726 DOI: 10.1371/journal.pone.0294607] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 11/03/2023] [Indexed: 11/23/2023] Open
Abstract
Aqueous humor dynamics are commonly assessed by infusing fluid into the eye and measuring intraocular pressure (IOP). From the pressure-flow relationship, conventional outflow facility is estimated to study glaucomatous processes that lower facility or identify therapeutics that enhance facility in hopes of restoring healthy IOP levels. The relative merits and limitations of constant flow (CF), gravity-driven constant pressure (CPg), and pump-driven constant pressure (CPp) infusion techniques were explored via simulations of a lumped parameter viscoelastic model of the eye. Model parameter values were based on published perfusion system properties and outflow facility data from rodents. Step increases in pressure or flow were simulated without and with IOP noise recorded from enucleated eyes, anesthetized animals, and conscious animals. Steady-state response levels were determined using published window and ratio criteria. Model simulations show that all perfusion techniques estimate facility accurately and that ocular fluid dynamics set a hard limit on how fast measurements can be taken. This limit can be approached with CPg and CPp systems by increasing their gain but not with CF systems, which invariably take longest to settle. Facility experiment duration is further lengthened by inclusion of IOP noise, and data filtering is needed for steady-state detection with in vivo noise. The ratio criterion was particularly affected because noise in the flow data is amplified by the higher gain of CPg and CPp systems. A recursive regression method is introduced, which can ignore large transient IOP fluctuations that interfere with steady-state detection by fitting incoming data to the viscoelastic eye model. The fitting method greatly speeds up data collection without loss of accuracy, which could enable outflow facility measurements in conscious animals. The model may be generalized to study response dynamics to fluid infusion in other viscoelastic compartments of the body and model insights extended to optimize experiment design.
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Affiliation(s)
- Youssef Mohamed
- Department of Medical Engineering, University of South Florida, Tampa, FL, United States of America
| | - Christopher L. Passaglia
- Department of Medical Engineering, University of South Florida, Tampa, FL, United States of America
- Department of Ophthalmology, University of South Florida, Tampa, FL, United States of America
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7
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Strohmaier CA, McDonnell FS, Zhang X, Wanderer D, Stamer WD, Weinreb RN, Huang AS. Differences in Outflow Facility Between Angiographically Identified High- Versus Low-Flow Regions of the Conventional Outflow Pathways in Porcine Eyes. Invest Ophthalmol Vis Sci 2023; 64:29. [PMID: 36939719 PMCID: PMC10043501 DOI: 10.1167/iovs.64.3.29] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/21/2023] Open
Abstract
Purpose To investigate differences in outflow facility between angiographically determined high- and low-flow segments of the conventional outflow pathway in porcine eyes. Methods Porcine anterior segments (n = 14) were mounted in a perfusion chamber and perfused using Dulbecco's phosphate buffered solution with glucose. Fluorescein angiography was performed to determine high- and low-flow regions of the conventional outflow pathways. The trabecular meshwork (TM) was occluded using cyanoacrylate glue, except for residual 5-mm TM areas that were either high or low flow at baseline, designating these eyes as "residual high-flow" or "residual low-flow" eyes. Subsequently, outflow was quantitatively reassessed and compared between residual high-flow and residual low-flow eyes followed by indocyanine green angiography. Results Fluorescein aqueous angiography demonstrated high-flow and low-flow regions. Baseline outflow facilities were 0.320 ± 0.08 and 0.328 ± 0.10 µL/min/mmHg (P = 0.676) in residual high-flow and residual low-flow eyes before TM occlusion, respectively. After partial trabecular meshwork occlusion, outflow facility decreased to 0.209 ± 0.07 µL/min/mmHg (-32.66% ± 19.53%) and 0.114 ± 0.08 µL/min/mmHg (-66.57% ± 23.08%) in residual high- and low-flow eyes (P = 0.035), respectively. There was a significant difference in the resulting IOP increase (P = 0.034). Conclusions Angiographically determined high- and low-flow regions in the conventional outflow pathways differ in their segmental outflow facility; thus, there is an uneven distribution of local outflow facility across different parts of the TM.
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Affiliation(s)
- Clemens A Strohmaier
- Department of Ophthalmology and Optometry, Kepler University Hospital, Johannes Kepler University, Linz, Austria
- Hamilton Glaucoma Center, The Viterbi Family Department of Ophthalmology, Shiley Eye Institute, University of California, San Diego, California, United States
| | - Fiona S McDonnell
- Department of Ophthalmology, Duke University, Durham, North Carolina, United States
| | - Xiaowei Zhang
- Hamilton Glaucoma Center, The Viterbi Family Department of Ophthalmology, Shiley Eye Institute, University of California, San Diego, California, United States
| | - Daniel Wanderer
- Hamilton Glaucoma Center, The Viterbi Family Department of Ophthalmology, Shiley Eye Institute, University of California, San Diego, California, United States
| | - W Daniel Stamer
- Department of Ophthalmology, Duke University, Durham, North Carolina, United States
- Department of Biomedical Engineering, Duke University, Durham, North Carolina, United States
| | - Robert N Weinreb
- Hamilton Glaucoma Center, The Viterbi Family Department of Ophthalmology, Shiley Eye Institute, University of California, San Diego, California, United States
| | - Alex S Huang
- Hamilton Glaucoma Center, The Viterbi Family Department of Ophthalmology, Shiley Eye Institute, University of California, San Diego, California, United States
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8
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Douglass A, Dattilo M, Feola AJ. Evidence for Menopause as a Sex-Specific Risk Factor for Glaucoma. Cell Mol Neurobiol 2023; 43:79-97. [PMID: 34981287 PMCID: PMC9250947 DOI: 10.1007/s10571-021-01179-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 12/03/2021] [Indexed: 01/07/2023]
Abstract
Glaucoma is a leading cause of irreversible blindness worldwide and is characterized by progressive loss of visual function and retinal ganglion cells (RGC). Current epidemiological, clinical, and basic science evidence suggest that estrogen plays a role in the aging of the optic nerve. Menopause, a major biological life event affecting all women, coincides with a decrease in circulating sex hormones, such as estrogen. While 59% of the glaucomatous population are females, sex is not considered a risk factor for developing glaucoma. In this review, we explore whether menopause is a sex-specific risk factor for glaucoma. First, we investigate how menopause is defined as a sex-specific risk factor for other pathologies, including cardiovascular disease, osteoarthritis, and bone health. Next, we discuss clinical evidence that highlights the potential role of menopause in glaucoma. We also highlight preclinical studies that demonstrate larger vision and RGC loss following surgical menopause and how estrogen is protective in models of RGC injury. Lastly, we explore how surgical menopause and estrogen signaling are related to risk factors associated with developing glaucoma (e.g., intraocular pressure, aqueous outflow resistance, and ocular biomechanics). We hypothesize that menopause potentially sets the stage to develop glaucoma and therefore is a sex-specific risk factor for this disease.
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Affiliation(s)
- Amber Douglass
- grid.484294.7Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Healthcare System, Decatur, GA USA
| | - Michael Dattilo
- grid.189967.80000 0001 0941 6502Department of Ophthalmology, Emory Eye Center, Emory University School of Medicine, B2503, Clinic B Building, 1365B Clifton Road NE, Atlanta, GA 30322 USA ,grid.414026.50000 0004 0419 4084Department of Ophthalmology, Atlanta Veterans Affairs Medical Center, Atlanta, GA USA ,grid.213917.f0000 0001 2097 4943Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA USA
| | - Andrew J. Feola
- grid.484294.7Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Healthcare System, Decatur, GA USA ,grid.189967.80000 0001 0941 6502Department of Ophthalmology, Emory Eye Center, Emory University School of Medicine, B2503, Clinic B Building, 1365B Clifton Road NE, Atlanta, GA 30322 USA ,grid.213917.f0000 0001 2097 4943Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA USA
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9
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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: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose 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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10
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Yarishkin O, Phuong TTT, Vazquez-Chona F, Bertrand J, van Battenburg-Sherwood J, Redmon SN, Rudzitis CN, Lakk M, Baumann JM, Freichel M, Hwang EM, Overby D, Križaj D. Emergent Temporal Signaling in Human Trabecular Meshwork Cells: Role of TRPV4-TRPM4 Interactions. Front Immunol 2022; 13:805076. [PMID: 35432302 PMCID: PMC9008486 DOI: 10.3389/fimmu.2022.805076] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Accepted: 03/02/2022] [Indexed: 11/26/2022] Open
Abstract
Trabecular meshwork (TM) cells are phagocytic cells that employ mechanotransduction to actively regulate intraocular pressure. Similar to macrophages, they express scavenger receptors and participate in antigen presentation within the immunosuppressive milieu of the anterior eye. Changes in pressure deform and compress the TM, altering their control of aqueous humor outflow but it is not known whether transducer activation shapes temporal signaling. The present study combines electrophysiology, histochemistry and functional imaging with gene silencing and heterologous expression to gain insight into Ca2+ signaling downstream from TRPV4 (Transient Receptor Potential Vanilloid 4), a stretch-activated polymodal cation channel. Human TM cells respond to the TRPV4 agonist GSK1016790A with fluctuations in intracellular Ca2+ concentration ([Ca2+]i) and an increase in [Na+]i. [Ca2+]i oscillations coincided with monovalent cation current that was suppressed by BAPTA, Ruthenium Red and the TRPM4 (Transient Receptor Potential Melastatin 4) channel inhibitor 9-phenanthrol. TM cells expressed TRPM4 mRNA, protein at the expected 130-150 kDa and showed punctate TRPM4 immunoreactivity at the membrane surface. Genetic silencing of TRPM4 antagonized TRPV4-evoked oscillatory signaling whereas TRPV4 and TRPM4 co-expression in HEK-293 cells reconstituted the oscillations. Membrane potential recordings suggested that TRPM4-dependent oscillations require release of Ca2+ from internal stores. 9-phenanthrol did not affect the outflow facility in mouse eyes and eyes from animals lacking TRPM4 had normal intraocular pressure. Collectively, our results show that TRPV4 activity initiates dynamic calcium signaling in TM cells by stimulating TRPM4 channels and intracellular Ca2+ release. It is possible that TRPV4-TRPM4 interactions downstream from the tensile and compressive impact of intraocular pressure contribute to homeostatic regulation and pathological remodeling within the conventional outflow pathway.
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Affiliation(s)
- Oleg Yarishkin
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States
| | - Tam T T Phuong
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States
| | - Felix Vazquez-Chona
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States
| | - Jacques Bertrand
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | | | - Sarah N Redmon
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States
| | - Christopher N Rudzitis
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States.,Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, United States
| | - Monika Lakk
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States
| | - Jackson M Baumann
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States.,Department of Bioengineering, University of Utah, Salt Lake City, United States
| | - Marc Freichel
- Institute of Pharmacology, Heidelberg University, Heidelberg, Germany
| | - Eun-Mi Hwang
- Center for Functional Connectomics, Korea Institute of Science and Technology (KIST), Seoul, South Korea
| | - Darryl Overby
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - David Križaj
- Department of Ophthalmology and Visual Sciences, University of Utah School of Medicine, Salt Lake City, United States.,Interdepartmental Program in Neuroscience, University of Utah, Salt Lake City, United States.,Department of Bioengineering, University of Utah, Salt Lake City, United States.,Department of Neurobiology, University of Utah, Salt Lake City, United States
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11
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Ma Y, Moroi SE, Roberts CJ. Non-invasive Clinical Measurement of Ocular Rigidity and Comparison to Biomechanical and Morphological Parameters in Glaucomatous and Healthy Subjects. Front Med (Lausanne) 2021; 8:701997. [PMID: 34291068 PMCID: PMC8287026 DOI: 10.3389/fmed.2021.701997] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Accepted: 06/07/2021] [Indexed: 11/13/2022] Open
Abstract
Purpose: To assess ocular rigidity using dynamic optical coherence tomography (OCT) videos in glaucomatous and healthy subjects, and to evaluate how ocular rigidity correlates with biomechanical and morphological characteristics of the human eye. Methods: Ocular rigidity was calculated using Friedenwald's empirical equation which estimates the change in intraocular pressure (IOP) produced by volumetric changes of the eye due to choroidal pulsations with each heartbeat. High-speed OCT video was utilized to non-invasively measure changes in choroidal volume through time-series analysis. A control-case study design was based on 23 healthy controls and 6 glaucoma cases. Multiple diagnostic modalities were performed during the same visit including Spectralis OCT for nerve head video, Pascal Dynamic Contour Tonometry for IOP and ocular pulse amplitude (OPA) measurement, Corvis ST for measuring dynamic biomechanical response, and Pentacam for morphological characterization. Results: Combining glaucoma and healthy cohorts (n = 29), there were negative correlations between ocular rigidity and axial length (Pearson R = −0.53, p = 0.003), and between ocular rigidity and anterior chamber volume (R = −0.64, p = 0.0002). There was a stronger positive correlation of ocular rigidity and scleral stiffness (i.e., stiffness parameter at the highest concavity [SP-HC]) (R = 0.62, p = 0.0005) compared to ocular rigidity and corneal stiffness (i.e., stiffness parameter at the first applanation [SP-A1]) (R = 0.41, p = 0.033). In addition, there was a positive correlation between ocular rigidity and the static pressure-volume ratio (P/V ratio) (R = 0.72, p < 0.0001). Conclusions: Ocular rigidity was non-invasively assessed using OCT video and OPA in a clinic setting. The significant correlation of ocular rigidity with biomechanical parameters, SP-HC and P/V ratio, demonstrated the validity of the ocular rigidity measurement. Ocular rigidity is driven to a greater extent by scleral stiffness than corneal stiffness. These in vivo methods offer an important approach to investigate the role of ocular biomechanics in glaucoma.
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Affiliation(s)
- Yanhui Ma
- Department of Ophthalmology and Visual Sciences, The Ohio State University Wexner Medical Center, Columbus, OH, United States
| | - Sayoko E Moroi
- Department of Ophthalmology and Visual Sciences, The Ohio State University Wexner Medical Center, Columbus, OH, United States
| | - Cynthia J Roberts
- Department of Ophthalmology and Visual Sciences, The Ohio State University Wexner Medical Center, Columbus, OH, United States.,Department of Biomedical Engineering, The Ohio State University, Columbus, OH, United States
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12
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Madekurozwa M, Stamer WD, Reina-Torres E, Sherwood JM, Overby DR. The ocular pulse decreases aqueous humor outflow resistance by stimulating nitric oxide production. Am J Physiol Cell Physiol 2021; 320:C652-C665. [PMID: 33439773 PMCID: PMC8260357 DOI: 10.1152/ajpcell.00473.2020] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Revised: 12/21/2020] [Accepted: 01/12/2021] [Indexed: 11/22/2022]
Abstract
Intraocular pressure (IOP) is not static, but rather oscillates by 2-3 mmHg because of cardiac pulsations in ocular blood volume known as the ocular pulse. The ocular pulse induces pulsatile shear stress in Schlemm's canal (SC). We hypothesize that the ocular pulse modulates outflow facility by stimulating shear-induced nitric oxide (NO) production by SC cells. We confirmed that living mice exhibit an ocular pulse with a peak-to-peak (pk-pk) amplitude of 0.5 mmHg under anesthesia. Using iPerfusion, we measured outflow facility (flow/pressure) during alternating periods of steady or pulsatile IOP in both eyes of 16 cadaveric C57BL/6J mice (13-14 weeks). Eyes were retained in situ, with an applied mean pressure of 8 mmHg and 1.0 mmHg pk-pk pressure amplitude at 10 Hz to mimic the murine heart rate. One eye of each cadaver was perfused with 100 µM L-NAME to inhibit NO synthase, whereas the contralateral eye was perfused with vehicle. During the pulsatile period in the vehicle-treated eye, outflow facility increased by 16 [12, 20] % (P < 0.001) relative to the facility measured during the preceding and subsequent steady periods. This effect was partly inhibited by L-NAME, where pressure pulsations increased outflow facility by 8% [4, 12] (P < 0.001). Thus, the ocular pulse causes an immediate increase in outflow facility in mice, with roughly one-half of the facility increase attributable to NO production. These studies reveal a dynamic component to outflow function that responds instantly to the ocular pulse and may be important for outflow regulation and IOP homeostasis.
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Affiliation(s)
- Michael Madekurozwa
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - W Daniel Stamer
- Department of Ophthalmology, Duke University, Durham, North Carolina
| | - Ester Reina-Torres
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - Joseph M Sherwood
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - Darryl R Overby
- Department of Bioengineering, Imperial College London, London, United Kingdom
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13
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Boazak EM, King R, Wang J, Chu CM, Toporek AM, Sherwood JM, Overby DR, Geisert EE, Ethier CR. Smarce1 and Tensin 4 Are Putative Modulators of Corneoscleral Stiffness. Front Bioeng Biotechnol 2021; 9:596154. [PMID: 33634081 PMCID: PMC7902041 DOI: 10.3389/fbioe.2021.596154] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 01/14/2021] [Indexed: 11/13/2022] Open
Abstract
The biomechanical properties of the cornea and sclera are important in the onset and progression of multiple ocular pathologies and vary substantially between individuals, yet the source of this variation remains unknown. Here we identify genes putatively regulating corneoscleral biomechanical tissue properties by conducting high-fidelity ocular compliance measurements across the BXD recombinant inbred mouse set and performing quantitative trait analysis. We find seven cis-eQTLs and non-synonymous SNPs associating with ocular compliance, and show by RT-qPCR and immunolabeling that only two of the candidate genes, Smarce1 and Tns4, showed significant expression in corneal and scleral tissues. Both have mechanistic potential to influence the development and/or regulation of tissue material properties. This work motivates further study of Smarce1 and Tns4 for their role(s) in ocular pathology involving the corneoscleral envelope as well as the development of novel mouse models of ocular pathophysiology, such as myopia and glaucoma.
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Affiliation(s)
- Elizabeth M Boazak
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA, United States
| | - Rebecca King
- Department of Ophthalmology, Emory University, Atlanta, GA, United States
| | - Jiaxing Wang
- Department of Ophthalmology, Emory University, Atlanta, GA, United States
| | - Cassandra M Chu
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA, United States
| | - Aaron M Toporek
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA, United States
| | - Joseph M Sherwood
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - Darryl R Overby
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - Eldon E Geisert
- Department of Ophthalmology, Emory University, Atlanta, GA, United States
| | - C Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA, United States.,George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States
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14
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Zhu W, Hou F, Fang J, Bahrani Fard MR, Liu Y, Ren S, Wu S, Qi Y, Sui S, Read AT, Sherwood JM, Zou W, Yu H, Zhang J, Overby DR, Wang N, Ethier CR, Wang K. The role of Piezo1 in conventional aqueous humor outflow dynamics. iScience 2021; 24:102042. [PMID: 33532718 PMCID: PMC7829208 DOI: 10.1016/j.isci.2021.102042] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 12/16/2020] [Accepted: 01/05/2021] [Indexed: 12/16/2022] Open
Abstract
Controlling intraocular pressure (IOP) remains the mainstay of glaucoma therapy. The trabecular meshwork (TM), the key tissue responsible for aqueous humor (AH) outflow and IOP maintenance, is very sensitive to mechanical forces. However, it is not understood whether Piezo channels, very sensitive mechanosensors, functionally influence AH outflow. Here, we characterize the role of Piezo1 in conventional AH outflow. Immunostaining and western blot analysis showed that Piezo1 is widely expressed by TM. Patch-clamp recordings in TM cells confirmed the activation of Piezo1-derived mechanosensitive currents. Importantly, the antagonist GsMTx4 for mechanosensitive channels significantly decreased steady-state facility, yet activation of Piezo1 by the specific agonist Yoda1 did not lead to a facility change. Furthermore, GsMTx4, but not Yoda1, caused a significant increase in ocular compliance, a measure of the eye's transient response to IOP perturbation. Our findings demonstrate a potential role for Piezo1 in conventional outflow, likely under pathological and rapid transient conditions. Piezo1 is functionally expressed in the TM, the most important tissue controlling IOP Suppression of mechanosensitive channel leads to a significant decrease in facility Our data suggest a role for Piezo in pathological situations and rapid IOP transients
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Affiliation(s)
- Wei Zhu
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China.,Beijing Advanced Innovation Center for Big Data-Based Precision Medicine, Beihang University & Capital Medical University, Beijing 100730, China
| | - Fei Hou
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China.,Department of Pharmacy, Affiliated Hospital of Qingdao University, Qingdao 266003, China
| | - Jingwang Fang
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China
| | - Mohammad Reza Bahrani Fard
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta 30332, GA, USA
| | - Yani Liu
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China
| | - Shouyan Ren
- Department of Pharmacy, Affiliated Hospital of Qingdao University, Qingdao 266003, China
| | - Shen Wu
- Beijing Institute of Ophthalmology, Beijing Tongren Hospital Eye Center, Beijing 100730 China
| | - Yunkun Qi
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China
| | - Shangru Sui
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China
| | - A Thomas Read
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta 30332, GA, USA
| | | | - Wei Zou
- School of Mechatronic Engineering, Jiangsu Normal University, Xuzhou 221116, China
| | - Hongxia Yu
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China
| | - Jingxue Zhang
- Beijing Institute of Ophthalmology, Beijing Tongren Hospital Eye Center, Beijing 100730 China
| | - Darryl R Overby
- Department of Bioengineering, Imperial College London, London, UK
| | - Ningli Wang
- Beijing Institute of Ophthalmology, Beijing Tongren Hospital Eye Center, Beijing 100730 China
| | - C Ross Ethier
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta 30332, GA, USA.,Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, 30332, GA, United States
| | - KeWei Wang
- Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao University Medical College, 38 Dengzhou Road, Qingdao 266021, Shandong, China.,Institute of Innovative Drugs, Qingdao University, 38 Dengzhou Road, Qingdao 266021, Shandong, China
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15
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Feola AJ, Sherwood JM, Pardue MT, Overby DR, Ethier CR. Age and Menopause Effects on Ocular Compliance and Aqueous Outflow. Invest Ophthalmol Vis Sci 2020; 61:16. [PMID: 32407519 PMCID: PMC7405619 DOI: 10.1167/iovs.61.5.16] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose Glaucoma is the second leading cause of blindness worldwide. Recent work suggests that estrogen and the timing of menopause play a role in modulating the risk of developing glaucoma. Menopause is known to cause modest changes in intraocular pressure; yet, whether this change is mediated through the outflow pathway remains unknown. Menopause also affects tissue biomechanical properties throughout the body; however, the impact of menopause on ocular biomechanical properties is not well characterized. Methods Here, we simultaneously assessed the impact of menopause on aqueous outflow facility and ocular compliance, as a measure of corneoscleral shell biomechanics. We used young (3-4 months old) and middle-aged (9-10 months old) Brown Norway rats. Menopause was induced by ovariectomy (OVX), and control animals underwent sham surgery, resulting in the following groups: young sham (n = 5), young OVX (n = 6), middle-aged sham (n = 5), and middle-aged OVX (n = 5). Eight weeks postoperatively, we measured outflow facility and ocular compliance. Results Menopause resulted in a 34% decrease in outflow facility and a 19% increase in ocular compliance (P = 0.011) in OVX animals compared with sham controls (P = 0.019). Conclusions These observations reveal that menopause affects several key physiological factors known to be associated with glaucoma, suggesting that menopause may contribute to an increased risk of glaucoma in women.
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16
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Li G, Schmitt H, Johnson WM, Lee C, Navarro I, Cui J, Fleming T, Gomez-Caraballo M, Elliott MH, Sherwood JM, Hauser MA, Farsiu S, Ethier CR, Stamer WD. Integral role for lysyl oxidase-like-1 in conventional outflow tissue function and behavior. FASEB J 2020; 34:10762-10777. [PMID: 32623782 DOI: 10.1096/fj.202000702rr] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 06/02/2020] [Accepted: 06/03/2020] [Indexed: 12/15/2022]
Abstract
Lysyl oxidase-like-1 (LOXL1), a vital crosslinking enzyme in elastin fiber maintenance, is essential for the stability and strength of elastic vessels and tissues. Variants in the LOXL1 locus associate with a dramatic increase in risk of exfoliation syndrome (XFS), a systemic fibrillopathy, which often presents with ocular hypertension and exfoliation glaucoma (XFG). We examined the role of LOXL1 in conventional outflow function, the prime regulator of intraocular pressure (IOP). Using Loxl1-/- , Loxl1+/- , and Loxl1+/+ mice, we observed an inverse relationship between LOXL1 expression and IOP, which worsened with age. Elevated IOP in Loxl1-/- mice was associated with a larger globe, decreased ocular compliance, increased outflow facility, extracellular matrix (ECM) abnormalities, and dilated intrascleral veins, yet, no dilation of arteries or capillaries. Interestingly, in living Loxl1-/- mouse eyes, Schlemm's canal (SC) was less susceptible to collapse when challenged with acute elevations in IOP, suggesting elevated episcleral venous pressure (EVP). Thus, LOXL1 expression is required for normal IOP control, while ablation results in altered ECM repair/homeostasis and conventional outflow physiology. Dilation of SC and distal veins, but not arteries, is consistent with key structural and functional roles for elastin in low-pressure vessels subjected to cyclical mechanical stress.
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Affiliation(s)
- Guorong Li
- Department of Ophthalmology, Duke University, Durham, NC, USA
| | - Heather Schmitt
- Department of Ophthalmology, Duke University, Durham, NC, USA
| | | | - Chanyoung Lee
- Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA
| | - Iris Navarro
- Department of Ophthalmology, Duke University, Durham, NC, USA
| | - Jenny Cui
- East Chapel Hill School, Chapel Hill, NC, USA
| | - Todd Fleming
- Department of Ophthalmology, Duke University, Durham, NC, USA
| | | | - Michael H Elliott
- Department of Ophthalmology and Physiology, University of Oklahoma Health, Oklahoma City, OK, USA
| | | | - Michael A Hauser
- Department of Ophthalmology, Duke University, Durham, NC, USA.,Molecular Physiology Institute, Duke University, Durham, NC, USA
| | - Sina Farsiu
- Department of Ophthalmology, Duke University, Durham, NC, USA.,Department of Biomedical Engineering, Duke University, Durham, NC, USA
| | - C Ross Ethier
- Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, GA, USA
| | - W Daniel Stamer
- Department of Ophthalmology, Duke University, Durham, NC, USA.,Department of Biomedical Engineering, Duke University, Durham, NC, USA
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