FIGURE 2 - uploaded by Ehab A Tamimi
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Microscope image of full optic nerve cross section used for semiautomated axon counting. Dark sections indicate bundles of axons separated by lighter connective tissue. Scale bar denotes 500 lm.
Source publication
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...
Context in source publication
Context 1
... method used individually imaged 603 magnifications with autofocus capabilities and a 15% overlap. A complete montage of an axon cross section is shown in Figure 2. Semiautomated axon counts were executed using image processing techniques in MatLab and methodology adapted from literature. ...
Citations
... The strain response of the ONH to IOP change has been characterized in postmortem human eyes [14][15][16] and more recently directly in patient eyes [17][18][19]. Cell-scale studies of ONH astrocyte responses to mechanical loading have been limited to two-dimensional cell culture [20][21][22][23] and more recently threedimensional cell culture methods have been proposed [24]. ...
The deformation of the mouse astrocytic lamina (AL) and adjacent peripapillary sclera (PPS) was measured in response to elevated intraocular pressure. We subjected explanted mouse eyes to inflation testing, comparing control eyes to those 3 days and 6 weeks after induction of ocular hypertension (OHT) via ocular microbead injection. Laser scanning microscopy was used with second harmonic generation to image the collagenous PPS and two-photon fluorescence to image transgenic fluorescent astrocytes in the AL. Digital volume correlation was applied to calculate strains in the PPS and AL. The specimen-averaged strains were biaxial in the AL and PPS, with greater strain overall in the x- than y- direction in the AL and greater strain in the θ- than the r -direction in the PPS. Strains increased after 3-day OHT, with greater strain overall in the 3-day AL than control AL, and greater circumferential strain in the 3-day PPS than control PPS. In the 6-week OHT eyes, AL and PPS strains were similar overall to controls. This experimental glaucoma model demonstrated a dynamic change in the mechanical behaviour of the AL and PPS over time at the site of neuronal injury and remodelling in glaucoma.
... Flattened tissues were clamped inside a customized pressurization chamber connecting to a pressure transducer and a syringe filled with 1X PBS. Three-dimensional (3D) images from an anterior viewpoint were taken using two-photon microscopy at 5 mm Hg and again at 15 mm Hg. 20,21 These pressures were chosen because the normal pressure in control pig eyes is reported 15.2 ± 2.1 mm Hg 22 and the LC showed the greatest displacement at these pressures in our previous study. 20,21,23 With this setup, we imaged the microstructural organization and mechanical response of the LC using an excitation wavelength of 780 nm, collecting collagen (collection 377/50 nm) and elastin (collection 460/80 nm) simultaneously. ...
... Three-dimensional (3D) images from an anterior viewpoint were taken using two-photon microscopy at 5 mm Hg and again at 15 mm Hg. 20,21 These pressures were chosen because the normal pressure in control pig eyes is reported 15.2 ± 2.1 mm Hg 22 and the LC showed the greatest displacement at these pressures in our previous study. 20,21,23 With this setup, we imaged the microstructural organization and mechanical response of the LC using an excitation wavelength of 780 nm, collecting collagen (collection 377/50 nm) and elastin (collection 460/80 nm) simultaneously. Image datasets from sequential levels of pressure at 5 and 15 mm Hg were de-noised, processed to measure anterior-posterior displacement of the LC, and normalized to the displacement of the same eye before decellularization. ...
Purpose: Studying the extracellular matrix (ECM) remodeling of the lamina cribrosa in vivo can be extremely challenging and costly. There exist very few options for studying optic nerve head (ONH) mechanobiology in vitro that are able to reproduce the complex anatomic and biomechanical environment of the ONH. Herein, we have developed a decellularization procedure that will enable more anatomically relevant and cost-efficient future studies of ECM remodeling of the ONH.
Methods: Porcine posterior poles were decellularized using a detergent and enzyme-based decellularization protocol. DNA quantification and histology were used to investigate the effectiveness of the protocol. We subsequently investigated the ability of a polyethylene glycol (PEG)-based hydrogel to restore the ONH’s ability to hold pressure following decellularization. Anterior-posterior displacement of the decellularized and PEG treated ONH in a pressure bioreactor was used to evaluate the biomechanical response of the ONH.
Results: DNA quantification and histology confirmed decellularization using Triton X-100 at low concentration for 48 hours successfully reduced the cellular content of the tissue by 94.9% compared with native tissue while preserving the ECM microstructure and basal lamina of the matrix. Infiltrating the decellularized tissues with PEG 6000 and PEG 10,000 hydrogel restored their ability to hold pressure, producing displacements similar to those measured for the non-decellularized control samples.
Conclusions: Our decellularized ONH model is capable of producing scaffolds that are cell-free and maintain the native ECM microstructure.
Translational Relevance: This model represents a platform to study the mechanobiology in the ONH and potentially for glaucoma drug testing.
... 60 In our studies, we found that the relationship between tensile strain and pressure was significant for eyes of Hispanic patients, whereas it was not significant for those of African patients, suggesting the mechanism of increased prevalence may be different between these two populations. 61 When we compared the peak shear strain in the superior quadrant of the LC, the numbers were higher in those of European descent than in those of African descent and Hispanic ethnicity. 62 The regional strain heterogeneity was detected in the LCs of African and Hispanic donors while it was absent in those of European donors. ...
Primary open-angle glaucoma is a neurodegenerative disease that affects 60 million people globally; however, the specific mechanisms that govern the initiation and progression of disease are currently unclear. In this book chapter, we describe the structure and function of the optic nerve head, review how mechanical stimuli and mechanical properties affect the development of the disease, and provide a discussion of future directions.
... The S-DIC approach was used to track the position of speckles in each sweep at each pressure state. The 3D point cloud from each of the four sweeps for a given pressure were then combined to assemble the scleral and ONH geometry (Tamimi et al., 2017). The ONH was removed and the cross-sections of the points on the sclera at different segments were created in the sagittal view. ...
... E was used to calculate first principal strains for each element. Additional details of the approach can be found in (Pyne et al., 2014;Tamimi et al., 2017). The intermediary pressure set measurements (15 and 30 mmHg) were utilized for the Finite element simulation and optimization. ...
Although strongly correlated with elevated intraocular pressure, primary open-angle glaucoma (POAG) occurs in normotensive eyes. Mechanical properties of the sclera around the optic nerve head (ONH) may play a role in this disparity. The purpose of this study is to present an automated inverse mechanics based approach to determine the distribution of heterogeneous mechanical properties of the human sclera as derived from its surface deformations arising from pressure inflation experiments. The scleral shell of a 78 year old European Descent male donor eye was utilized to demonstrate the method; the sclera was coated with a speckle pattern on the outer surface and was subjected to inflation pressures of 5, 15, 30, and 45 mmHg. The speckle pattern was imaged at each pressure, and a displacement field was calculated for each pressure step using a previously described sequential digital image correlation (S-DIC) technique. The fiber splay and fiber orientation of the sclera collagen were determined experimentally, and the thickness across the scleral globe was determined using micro CT images. The displacement field from the inflation test was used to calculate the strain and also used as an input for inverse mechanics to determine the heterogeneity of material properties. The scleral geometry was divided into subdomains using the first principal strain. The Holzapfel anisotropic material parameters of matrix and fiber stiffness were estimated within each individual subdomain using an inverse mechanics approach by minimizing the sum of the square of the residuals between the computational and experimental displacement fields. The mean and maximum error in displacement across all subdomains were 8.9 ± 3.0 μm and 13.2 μm, respectively. The full pressure-inflation forward mechanics experiment was done using subdomain-specific mechanical properties on the entire scleral surface. The proposed approach is effective in determining the distribution of heterogeneous mechanical properties of the human sclera in a user-independent manner. Our research group is currently utilizing this approach to better elucidate how scleral stiffness influences those at high risk for POAG.
... Although we did not find any differences in porosity across racioethnic groups, the variation in LC thickness, laminar beam orientation/thickness, collagen fibril crimp/splay, and peripapillary scleral strain are other prominent potential factors which may contribute the increased regional strain gradient in the HE and AD groups from one region to another region as compared to ED group. For instance, Tamimi et al. showed that the mean of the first principal strain in the peripapillary sclera is higher in the HE and AD groups compared to the ED group at 15 mmHg and that these differences are regionally dependent [63]. This work and that of Fazio et al. have also shown that strains in the peripapillary sclera of AD groups are reduced in comparison to ED as IOP increases [64]. ...
Glaucoma is the second leading cause of irreversible blindness in the world with a higher prevalence in those of African Descent (AD) and Hispanic Ethnicity (HE) than in those of European Descent (ED). The objective of this study was to investigate the pressure dependent biomechanical response of the lamina cribrosa (LC) in normal human donor tissues from these racioethnic backgrounds. Pressure inflation tests were performed on 24 human LCs (n = 9 AD, n = 6 ED, and n = 9 HE) capturing the second harmonic generation (SHG) signal of collagen at 5, 15, 30, and 45 mmHg from an anterior view. A non-rigid image registration technique was utilized to determine the 3D displacement field in each LC from which 3D Green strains were calculated. The peak shear strain in the superior quadrant of the LC in those of ED was significantly higher than in those of AD and HE (p-value = 0.005 & 0.034, respectively) where ED = 0.017 [IQR = 0.012–0.027], AD = 0.0002 [IQR = −0.001–0.007], HE = 0.0016 [IQR = −0.002–0.012]). There were also significant differences in the regional strain heterogeneity in those of AD and HE that were absent in those of ED. This work represents, to our knowledge, the first ex-vivo study identifying significant differences in the biomechanical response of the LC in populations at increased risk of glaucoma. Future work will be necessary to assess if and how these differences play a role in predisposing those of Hispanic Ethnicity and African Descent to the onset and/or progression of primary open angle glaucoma. Statement of significance: Glaucoma is the second leading cause of irreversible blindness in the world and occurs more frequently in those of African Descent and Hispanic Ethnicity than in those of European Descent. To date, there has been no ex-vivo study quantifying differences in the biomechanical response of the non-glaucomatous lamina cribrosa (LC) across these racioethnic backgrounds. In this work we report, for the first time, differences in the pressure dependent biomechanical response of LC across different racioethnic groups as quantified using nonlinear optical microscopy. This study lays the foundation for future work investigating if and how these differences may play a role in predisposing those at increased risk to the onset and/or progression of primary open angle glaucoma.
Purpose
To investigate the differences in the dimensions of the anterior ocular segment, and specifically in conjunctival-Tenon’s capsule thickness (CTT), anterior scleral thickness (AST) and ciliary muscle thickness (CMT), between Caucasian and Hispanic subjects using swept-source optical coherence tomography (SS-OCT).
Methods
Cross-sectional study including 53 Hispanic and 60 Caucasian healthy participants, matched by age, sex and refractive error, who underwent a complete ophthalmological examination. CTT, AST and CMT were manually measured in the temporal and nasal quadrants at 0, 1, 2 and 3 mm from the scleral spur using SS-OCT.
Results
Mean age and refractive error were 38.7 ± 12.3 years and −1.05 ± 2.6 diopters, and 41.8 ± 11.7 years and −0.50 ± 2.6 diopters for the Hispanic and Caucasians, respectively (p = 0.165 and p = 0.244). The CTT was increased in the temporal quadrant in the Hispanic group in the three studied regions (CTT1, CTT2 and CTT3; being the means 223.0 ± 68.4, 215.3 ± 66.4 and 203.8 ± 67.1 µm versus 190.8 ± 51.0, 189.4 ± 53.2 and 187.4 ± 55.3 µm respectively; p < 0.001). Larger AST values were observed in the temporal quadrant in the Hispanic group (AST2: 559.8 ± 80.8 µm and AST3: 591.6 ± 83.0 µm) compared to the Caucasian group (520.7 ± 50.1 and 558.9 ± 54.7 respectively; p ≤ 0.022). No differences were observed in the nasal quadrant for CTT, AST1 and AST3 (p ≥ 0.076). No differences emerged in the CM dimensions (p ≥ 0.055).
Conclusion
CTT and AST measurements were thicker in the temporal quadrant of Hispanic patients compared to Caucasians. This could have implications for the pathogenesis of different ocular diseases.
Little is known about the myopic characteristics of lamina cribrosa (LC) curvature. As such, we investigated nasal and temporal LC curvatures in myopia. In this retrospective, cross-sectional study, 144 myopic eyes (refraction < − 2D) and 88 non-myopic eyes (refraction > − 0.5D) underwent swept-source optical coherence tomography scanning of the LC. The anterior border of LC curvature was delineated with 17 points and interpolated with the “cardinal spline” curve-fitting method. The average curvature indices of the temporal and nasal sides were presented as the temporal and nasal curvatures. Myopic eyes had a mean refraction of − 6.7 ± 2.8D, while for non-myopic eyes, the value was 0.3 ± 1.0D. Nasal LC curvature was visible in 54 myopia (37.5%) and 42 non-myopia (47.7%) cases (P = 0.126), and temporal LC curvature was visible in 142 myopia (98.6%) and 68 non-myopia (77.3%) cases (P = 0.001). The nasal LC curvature was significantly larger in myopia than in non-myopia (P < 0.001). Contrastingly, the temporal LC curvature was significantly smaller in myopia than in non-myopia (P < 0.001). Axial length was associated with larger nasal LC curvature, smaller temporal LC curvature, and larger nasal–temporal LC curvature difference (all P’s < 0.05). In myopic relative to non-myopic eyes, LC curvature was decreased temporally and increased nasally.
Purpose:
To investigate the change of border tissue configuration during axial elongation in childhood.
Methods:
Fifty-four subjects (108 eyes; age range, 29.3-132.5 months) who had undergone a series of swept-source optical coherence tomography scans at intervals of 6 months or longer were classified into stable axial length (AXL) eyes (n = 55; AXL change of ≤0.36 mm) and elongating AXL eyes (n = 53; AXL change of >0.36 mm). The angle between the Bruch's membrane opening (BMO) reference plane and the border tissue of Elschnig was defined as the border tissue angle (BTA). The border tissue angle, BMO distance (BMOD) and minimum rim width (MRW) were measured in the temporal and nasal regions.
Results:
During 15.6 ± 7.2 months of follow-up, the AXL significantly increased from 22.8 ± 1.3 mm to 23.3 ± 1.4 mm (P < 0.001). Changes of border tissue angle and AXL showed a significant correlation only in the temporal region of elongating AXL eyes (r = -0.409; P = 0.002), but not in stable AXL eyes. Both BMOD and nasal MRW significantly increased from 1482.5 ± 153.0 to 1506.1 ± 154.6 µm and from 310.6 ± 83.2 to 324.6 ± 95.6 µm, respectively (all Ps < 0.001). The changes of BMOD and nasal MRW showed a significant positive correlation with changes of AXL in elongating AXL eyes but not in stable AXL eyes.
Conclusions:
During the axial elongation in childhood, temporal border tissue configuration change, BMO enlargement, and nasal peripapillary tissue elevation showed a significant correlation with changes in the AXL.
Purpose:
The aim of this paper is to concisely summarize what is currently known about open-angle glaucoma (OAG) among persons of Latin American descent (LAD) in the United States for the purpose of improving individualized care and highlighting areas requiring further study.
Materials and methods:
Review of relevant literature was performed through PubMed and Google Scholar from October 1978 through November 11, 2019.
Results:
As the Latin American population grows within the United States, it is predicted that by 2050, men of LAD will make up the largest demographic group with OAG. Persons of LAD experience a greater increase in OAG prevalence per decade of life compared to persons of African descent and may have unique risk factors. In particular, those with African ancestry and hypertension are at greater risk of elevated intraocular pressure (IOP). Maximum IOP, variability in IOP and diabetes are also important considerations. Unique anatomic and physiological characteristics such as scleral tensile strain, longer axial length, thin corneas, and corneal hysteresis may play a role in this populations' unique risk for the development and progression of OAG.
Conclusions:
OAG represents a growing concern among persons of LAD in the United States; however, information on specific risk factors in this population currently remains limited. Studies should be designed to investigate the LAD population and their respective structural, vascular, and social risk factors for the development and progression of OAG to assist clinicians in improving outcomes for this growing population.
