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Racioethnic differences in the biomechanical response of the lamina cribrosa.

ABSTRACT: 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.

SUBMITTER: Behkam R

PROVIDER: S-EPMC6440866 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Racioethnic differences in the biomechanical response of the lamina cribrosa.

Behkam Reza R Kollech Hirut G HG Jana Anirban A Hill Amy A Danford Forest F Howerton Stephen S Ram Sundaresh S Rodríguez Jeffrey J JJ Utzinger Urs U Girkin Christopher A CA Vande Geest Jonathan P JP

Acta biomaterialia 20190220

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 ...[more]

PMID: 30797107

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Project description:The objective of this study was to measure the pressure-induced deformation response of the human lamina cribrosa (LC) and analyze for variations with age and anatomical region. The posterior scleral cup of 8 eyes from 6 human donors was mounted onto a custom inflation chamber. A laser-scanning microscope was used for second harmonic generation (SHG) imaging of the collagen structure in the posterior volume of the LC at pressures from 5mmHg to 45mmHg. The SHG volumes were analyzed by the Fast-Fourier Iterative Digital Volume Correlation (DVC) algorithm for the three dimensional (3D) displacement field. The components of the Green-Lagrange strain tensor and the in-plane principal and maximum shear strains were evaluated from the DVC displacement field for the central and peripheral regions of the LC and the nasal, temporal, inferior, and superior quadrants surrounding the central retinal artery and vein. Among the major findings were that older age was associated with lower strains, the maximum shear strain was larger in the peripheral than central region, and the maximum principal strain was lower in the nasal quadrant. The elliptical shape of the LC was also predictive of the biaxial strain ratio. Age-related and structure-related variations in the pressure-induced strains of the LC may contribute to the susceptibility and severity of optic nerve damage in glaucoma, and regional variations may explain the progression of axonal damage and tissue remodeling observed in the LC in glaucoma.Glaucoma causes vision loss through progressive damage of the retinal ganglion axons at the lamina cribrosa (LC), the connective tissue structure that supports the axons as they leave the eye. Mechanical characterization of the LC is challenging because of the complex 3D shape and inaccessibility of the tissue. We present a new method using digital volume correlation to map the 3D displacement and strain fields in the LC under inflation. We report for the first time significant regional variations in the strains that are consistent with the pattern of optic nerve damage in early glaucoma. Thus regional strain variations may be predictive of the progression of axonal damage in glaucoma.

Project description:This study investigated the inflation response of the lamina cribrosa (LC) and adjacent peripapillary sclera (PPS) in post-mortem human eyes with no history of glaucoma. The posterior sclera of 13 human eyes from 7 donors was subjected to controlled pressurization between 5-45 mmHg. A laser-scanning microscope (LSM) was used to image the second harmonic generation (SHG) response of collagen and the two-photon fluorescent (TPF) response of elastin within the volume of the LC and PPS at each pressure. Image volumes were analyzed using digital volume correlation (DVC) to calculate the three-dimensional (3D) deformation field between pressures. The LC exhibited larger radial strain, Err, and maximum principal strain, Emax, (p < 0.0001) and greater posterior displacement (p=0.0007) compared to the PPS between 5-45 mmHg, but had similar average circumferential strain, Eθθ, and maximum shear strain, Γmax. The Emax and Γmax were highest near the LC-PPS interface and lowest in the nasal quadrant of both tissues. Larger LC area was associated with smaller Emax in the peripheral LC and larger Emax in the central LC (p ≤ 0.01). The Emax, Γmax, and Eθθ in the inner PPS increased with increasing strain in adjacent LC regions (p ≤ 0.001). Smaller strains in the PPS were associated with a larger difference in the posterior displacement between the PPS and central LC (p < 0.0001 for Emax and Err), indicating that a stiffer pressure-strain response of the PPS is associated with greater posterior bowing of the LC. STATEMENT OF SIGNIFICANCE: Glaucoma causes vision loss through progressive damage of the retinal ganglion axons at the lamina cribrosa (LC), a connective tissue structure that supports the axons as they pass through the eye wall. It is hypothesized that strains caused by intraocular pressure may initiate this damage and that these strains are modulated by the combined deformation of the LC and adjacent peripapillary sclera (PPS). In this study we present a method to measure the pressure-induced 3D displacement and strain field in the LC and PPS simultaneously. Regional strain variation in the LC and PPS was investigated and compared and strains were analyzed for associations with age, LC area, LC strain magnitude, and LC posterior motion relative to the PPS.

Dataset Information

Racioethnic differences in the biomechanical response of the lamina cribrosa.

Publications

Racioethnic differences in the biomechanical response of the lamina cribrosa.

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