Age related compliance of the lamina cribrosa in human eyes

The Role of αvβ3 Integrin in Lamina Cribrosa Cell Mechanotransduction in Glaucoma

Purpose: Glaucoma, one of the leading causes of irreversible blindness, is a common progressive optic neuropathy characterised by visual field defects and structural changes to the optic nerve head (ONH). There is extracellular matrix (ECM) accumulation and fibrosis of the lamina cribrosa (LC) in the ONH, and consequently increased tissue stiffness of the LC connective tissue. Integrins are cell surface proteins that provide the key molecular link connecting cells to the ECM and serve as bidirectional sensors transmitting signals between cells and their environment to promote cell adhesion, proliferation, and remodelling of the ECM. Here, we investigated the expression of αVβ3 integrin in glaucoma LC cell, and its effect on stiffness-induced ECM gene transcription and cellular proliferation rate in normal (NLC) and glaucoma (GLC) LC cells, by down-regulating αVβ3 integrin expression using cilengitide (a known potent αVβ3 and αVβ5 inhibitor) and β3 integrin siRNA knockdown. Methods: GLC cells were compared to age-matched controls NLC to determine differential expression levels of αVβ3 integrin, ECM genes (Col1A1, α-SMA, fibronectin, vitronectin), and proliferation rates. The effects of αVβ3 integrin blockade (with cilengitide) and silencing (with a pool of four predesigned αVβ3 integrin siRNAs) on ECM gene expression and proliferation rates were evaluated using both reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blotting in the human NLC cells cultured on soft (4 kPa) and stiff (100 kPa) substrate and in GLC cells grown on standard plastic plates. Results: αVβ3 integrin gene and protein expression were enhanced (p < 0.05) in GLC cells as compared to NLC. Both cilengitide and siRNA significantly reduced αVβ3 expression in GLC. When NLC were grown in the stiff substrate, cilengitide and siRNA also significantly reduced the increased expression in αVβ3, ECM components, and proliferation rate. Conclusions: Here, we provide evidence of cilengitide- and siRNA-mediated silencing of αVβ3 integrin expression, and inhibition of ECM synthesis in LC cells. Therefore, αVβ3 integrin may be a promising target for the development of novel anti-fibrotic therapies for treating the LC cupping of the ONH in glaucoma.

Association between corneal hysteresis and glaucoma in a Japanese population: the Hisayama Study

AIMS

To investigate the association between corneal hysteresis and the presence of glaucoma and its subtypes in a general Japanese population.

METHODS

We analysed the data of 2338 Japanese community-dwellers aged ≥40 years (1059 men, 1279 women) who underwent an eye examination in 2018 as part of the population-based, cross-sectional Hisayama Study. Participants were divided into quartile levels of corneal hysteresis, which had been measured with an ocular response analyzer. Glaucoma was defined based on the International Society of Geographical and Epidemiological Ophthalmology criteria. We conducted a logistic regression analysis to determine the ORs and their 95% CIs for the presence of outcomes according to the corneal hysteresis quartiles.

RESULTS

Glaucoma was diagnosed in 154 participants: primary open-angle glaucoma (POAG), n=115; primary angle-closure glaucoma, n=17; exfoliation glaucoma, n=21 and secondary glaucoma without exfoliation glaucoma, n=1. After adjustment for confounders, the OR for prevalent glaucoma was significantly increased in the participants in the first corneal-hysteresis quartile compared with those in the fourth quartile (OR: 1.80; 95% CI: 1.03 to 3.17). Regarding glaucoma subtypes, the first-quartile participants had significantly greater likelihoods of the presence of POAG (OR: 1.63; 95% CI: 1.02 to 2.61) and exfoliation glaucoma (OR: 6.49; 95% CI: 1.44 to 29.30) compared with those in the third and fourth quartiles after adjustment for potential confounders.

CONCLUSIONS

These results demonstrated a significant inverse association between corneal hysteresis and the likelihood of glaucoma, suggesting that the measurement of corneal hysteresis would provide useful information for elucidating the aetiology of glaucoma.

The Temporal Relation Between Rates of Retinal Nerve Fiber Layer and Minimum Rim Width Changes in Glaucoma

Purpose

This study aims to determine whether OCT-derived rates of change in minimum rim width (MRW) are associated with and can potentially predict corresponding alterations in retinal nerve fiber layer thickness (RNFLT) in people with glaucoma.

Methods

The rates of change between six-monthly visits were taken from 568 eyes of 278 participants in the P3 Study. Structural equation models (SEM) assessed whether one parameter was predicted by the concurrent or previous rate of the other parameter, after adjusting for its own rate in the previous time interval. Root mean square error of approximation (RMSEA, with 90% confidence intervals [CI]), Tucker Lewis index (TLI) and the comparative fit index (CFI) assessed goodness of fit.

Results

Models without a time lag provided a better fit for the data (RMSEA = 0.101 [CI, 0.089, 0.113]), compared to a model featuring a time lag in RNFLT (RMSEA = 0.114 [CI, 0.102, 0.126]) or MRW (RMSEA = 0.114 [CI, 0.102, 0.127]). The SEMs indicated that rates for both MRW and RNFLT were predicted by their own rate in the previous time interval and by the other measure's change in the concurrent time interval (P > 0.001 for all). No evidence of a clinically significant time lag for either parameter was determined.

Conclusions

MRW and RNFLT exhibit concurrent changes over time in patients with glaucoma, with no clinically significant time lag determined.

Translational Relevance

RNFLT may be more useful than MRW in early glaucoma assessment because of its previously reported lower variability and reduced sensitivity to intraocular pressure changes.

Glaucoma: from pathogenic mechanisms to retinal glial cell response to damage

Glaucoma is a neurodegenerative disease of the retina characterized by the irreversible loss of retinal ganglion cells (RGCs) leading to visual loss. Degeneration of RGCs and loss of their axons, as well as damage and remodeling of the lamina cribrosa are the main events in the pathogenesis of glaucoma. Different molecular pathways are involved in RGC death, which are triggered and exacerbated as a consequence of a number of risk factors such as elevated intraocular pressure (IOP), age, ocular biomechanics, or low ocular perfusion pressure. Increased IOP is one of the most important risk factors associated with this pathology and the only one for which treatment is currently available, nevertheless, on many cases the progression of the disease continues, despite IOP control. Thus, the IOP elevation is not the only trigger of glaucomatous damage, showing the evidence that other factors can induce RGCs death in this pathology, would be involved in the advance of glaucomatous neurodegeneration. The underlying mechanisms driving the neurodegenerative process in glaucoma include ischemia/hypoxia, mitochondrial dysfunction, oxidative stress and neuroinflammation. In glaucoma, like as other neurodegenerative disorders, the immune system is involved and immunoregulation is conducted mainly by glial cells, microglia, astrocytes, and Müller cells. The increase in IOP produces the activation of glial cells in the retinal tissue. Chronic activation of glial cells in glaucoma may provoke a proinflammatory state at the retinal level inducing blood retinal barrier disruption and RGCs death. The modulation of the immune response in glaucoma as well as the activation of glial cells constitute an interesting new approach in the treatment of glaucoma.

Phenotypic expressions of the optic disc in primary open-angle glaucoma

BACKGROUND

Which phenotypes are we able to recognize in the optic nerve of patients with primary open angle glaucoma?

METHODS

Retrospective interventional case series. 885 eyes from 885 patients at an outpatient tertiary care centre who met specified criteria for POAG were included. Disc photographs were classified by three glaucoma specialists into the following phenotypes according to their predominant characteristics: (1) concentric rim thinning, (2) focal rim thinning, (3) acquired pit of the optic nerve (APON), (4) tilted, (5) extensive peripapillary atrophy (PPA), and (6) broad rim thinning. Demographic, medical, and ocular data were collected. Kruskal-Wallis was used as a non-parametric test and pairwise comparison was performed by using Wilcoxon rank sum test corrected.

RESULTS

Phenotypic distribution was as follows: 398(45%) focal thinning, 153(18%) concentric thinning, 153(17%) broad thinning, 109(12%) tilted, 47(5%) extensive PPA and 25(3%) APON. Phenotypic traits of interest included a higher proportion of female patients with the focal thinning phenotype (p = 0.015); myopia (p = 0.000), Asian race (OR: 8.8, p = 0.000), and younger age (p = 0.000) were associated with the tilted phenotype; the concentric thinning patients had thicker RNFL (p = 0.000), higher MD (p = 0.008) and lower PSD (p = 0.043) than broad thinning, despite no difference in disc sizes (p = 0.849). The focal thinning group had a localized VF pattern with high PSD compared to concentric thinning (p = 0.005).

CONCLUSION

We report six phenotypic classifications of POAG patients with demographic and ocular differences between phenotypes. Future refinement of phenotypes should allow enhanced identification of genetic associations and improved individualization of patient care.

[Biomechanics of the lamina cribrosa: A determining factor in glaucomatous neuropathy. A review of the literature]

Glaucoma is a chronic optic neuropathy characterized by progressive sclero-laminar remodeling. The main factor at the origin of these deformations is the intraocular pressure (IOP), the effect of which varies according to the biomechanical properties of the individual lamina cribrosa (LC). In this environment, the LC represents a malleable zone of weakness within a rigid corneoscleral shell. It is a dynamic structure whose movements play a key role in the pathogenesis of glaucoma: displacing it posteriorly, in addition to contributing to the characteristic appearance of glaucomatous cupping, would increase constriction on the nerve fibers and the laminar capillaries. Often incorrectly considered permanent in adults, these deformations have a certain degree of reversibility, which is currently better characterized thanks to progress in imaging techniques. The occurrence of anterior displacement and laminar thickening following a reduction in IOP could thus constitute a good prognostic factor by reducing mechanical stress on this region. These changes would tend to reduce laminar pore tortuosity and shear forces, which are probably key mechanisms of axonal loss in glaucoma.

The Curvature, Collagen Network Structure, and Their Relationship to the Pressure-Induced Strain Response of the Human Lamina Cribrosa in Normal and Glaucoma Eyes

The lamina cribrosa (LC) is a connective tissue in the optic nerve head (ONH). The objective of this study was to measure the curvature and collagen microstructure of the human LC, compare the effects of glaucoma and glaucoma optic nerve damage, and investigate the relationship between the structure and pressure-induced strain response of the LC in glaucoma eyes. Previously, the posterior scleral cups of 10 normal eyes and 16 diagnosed glaucoma eyes were subjected to inflation testing with second harmonic generation (SHG) imaging of the LC and digital volume correlation (DVC) to calculate the strain field. In this study, we applied a custom microstructural analysis algorithm to the maximum intensity projection of SHG images to measure features of the LC beam and pore network. We also estimated the LC curvatures from the anterior surface of the DVC-correlated LC volume. Results showed that the LC in glaucoma eyes had larger curvatures p≤0.03), a smaller average pore area (p = 0.001), greater beam tortuosity (p < 0.0001), and more isotropic beam structure (p = 0.01) than in normal eyes. The difference measured between glaucoma and normal eyes may indicate remodeling of the LC with glaucoma or baseline differences that contribute to the development of glaucomatous axonal damage.

Three-Dimensional Ultrasound Elastography Detects Age-Related Increase in Anterior Peripapillary Sclera and Optic Nerve Head Compression During IOP Elevation

Purpose

High-frequency ultrasound elastography offers a tool to resolve the complex and heterogeneous deformation through the full thickness of the optic nerve head (ONH) and peripapillary sclera (PPS). Using this tool, we quantified the three-dimensional deformation of the ONH and PPS in human donor eyes and evaluated age-associated changes.

Methods

The ONH and PPS in 15 human donor globes were imaged with a 50-MHz ultrasound probe while increasing intraocular pressure (IOP) from 15 to 30 mm Hg. Tissue displacements were obtained using correlation-based ultrasound speckle tracking. Three-dimensional spherical strains (radial, circumferential, meridional, and respective shear strains) were calculated for the ONH and PPS volumes segmented from three-dimensional ultrasound images. Age-related trends of different strains in each region of interest were explored.

Results

The dominant form of IOP-induced deformation in the ONH and PPS was radial compression. High-magnitude localized out-of-plane shear strains were also observed in both regions. Most strains were concentrated in the anterior one-half of the ONH and PPS. The magnitude of radial and volumetric strains increased with age in the anterior ONH and anterior PPS, indicating greater radial compression and volume loss during IOP elevation in older age.

Conclusions

The age-associated increase of radial compression, the predominant form of IOP-induced deformation in anterior ONH and PPS, may underlie age-associated glaucoma risk. High-frequency ultrasound elastography offers a useful tool to quantify all types of deformation comprehensively in all regions of ONH and PPS, which may improve our understanding of the biomechanical factors contributing to glaucoma risk.

Evaluation of Retinal Vascular and Structural Alterations in Pediatric Idiopathic Intracranial Hypertension Patients without Papilledema

PURPOSE

The aim of this study was to evaluate retinal structural and microvascular alterations using optical coherence tomography-angiography (OCTA) in pediatric idiopathic intracranial hypertension (IIH) patients with regressed papilledema.

METHODS

This study included 40 eyes of 21 IIH patients and 69 eyes of 36 healthy controls. Radial peripapillary capillary (RPC) vessel density and peripapillary retinal nerve fiber layer (RNFL) thickness were evaluated by XR Avanti AngioVue OCTA (Optovue, Fremont, CA, USA). The data were obtained from measurement zones that are automatically divided into two equal hemispheres (superior and inferior) and eight quadrants (superior-temporal, superior-nasal, inferior-temporal, inferior-nasal, nasal-superior, nasal-inferior, temporal-superior, temporal-inferior). Initial cerebrospinal fluid (CSF) pressure, grade of papilledema, and duration of follow-up were recorded.

RESULTS

There were significant differences in RPC vessel densities and RNFL thicknesses between the study groups (p ˃ 0.05). Significantly higher RPC vessel density measurements were observed in the patient group for the whole image, peripapillary, inferior-hemi, and whole nasal quadrants (p < 0.05). Except for the temporal-superior, temporal-inferior, inferior-temporal, and superior-temporal quadrants, the RNFL in all regions was significantly thicker in the IIH group than in the control group (p ˂ 0.001).

CONCLUSIONS

RNFL thickness and RPC vessel density were significantly different between the IIH patient and control groups, suggesting that retinal microvascular and subclinical structural changes that were potentially secondary to CSF pressure can persist after the resolution of papilledema. However, our results should be confirmed by further longitudinal studies investigating the progress of these alterations to determine their effects on peripapillary tissues.

Glaucoma - 'A Stiff Eye in a Stiff Body'

Glaucoma is a progressive, age-related optic neuropathy, whereby the prevalence increases sharply over the age of 60 and is associated with increased systemic tissue stiffness. On a molecular basis, this is associated with increased deposition of collagen and loss of elastin structure, resulting in aberrant biomechanical compliance and reduced tissue elasticity. Increased tissue stiffness is a known driver of myofibroblast activation and persistence, especially in chronic cellular injuries via mechanotransduction pathways mediated by integrins and focal adhesion kinases. Evidence from histological and imaging studies plus force measurements of glaucomatous eyes show that several ocular tissues are stiffer than normal, healthy age-matched controls including the trabecular meshwork, Schlemm's canal, cornea, sclera and the lamina cribrosa. This is associated with increased extracellular matrix deposition and fibrosis. This review reports on the evidence to support the concept that glaucoma represents 'a stiff eye in a stiff body' and addresses potential mechanisms to attenuate this.

Aging Effects on Optic Nerve Neurodegeneration

Common risk factors for many ocular pathologies involve non-pathologic, age-related damage to the optic nerve. Understanding the mechanisms of age-related changes can facilitate targeted treatments for ocular pathologies that arise at any point in life. In this review, we examine these age-related, neurodegenerative changes in the optic nerve, contextualize these changes from the anatomic to the molecular level, and appreciate their relationship with ocular pathophysiology. From simple structural and mechanical changes at the optic nerve head (ONH), to epigenetic and biochemical alterations of tissue and the environment, multiple age-dependent mechanisms drive extracellular matrix (ECM) remodeling, retinal ganglion cell (RGC) loss, and lowered regenerative ability of respective axons. In conjunction, aging decreases the ability of myelin to preserve maximal conductivity, even with "successfully" regenerated axons. Glial cells, however, regeneratively overcompensate and result in a microenvironment that promotes RGC axonal death. Better elucidating optic nerve neurodegeneration remains of interest, specifically investigating human ECM, RGCs, axons, oligodendrocytes, and astrocytes; clarifying the exact processes of aged ocular connective tissue alterations and their ultrastructural impacts; and developing novel technologies and pharmacotherapies that target known genetic, biochemical, matrisome, and neuroinflammatory markers. Management models should account for age-related changes when addressing glaucoma, diabetic retinopathy, and other blinding diseases.

Association between Optic Nerve Sheath Diameter and Lamina Cribrosa Morphology in Normal-Tension Glaucoma

(1) Background: To compare optic nerve sheath diameter (ONSD) in normal-tension glaucoma (NTG) and healthy eyes and to investigate the association between ONSD and lamina cribrosa (LC) morphology. (2) Methods: This cross-sectional study included 69 NTG eyes and 69 healthy eyes matched for age, axial length, and intraocular pressure. The LC curvature index (LCCI) was measured from horizontal Cirrus HD-OCT B-scan images from five uniformly divided positions vertically of the optic nerve. The average LCCI was defined as the mean of the measurements at these five locations. ONSD was measured as the width of the optic nerve sheath at the site perpendicular 3 mm behind the posterior globe. LCCI and ONSD were compared in eyes with NTG and healthy eyes. The clinical factors that could affect LCCI were analyzed. (3) Results: NTG eyes had significantly smaller mean ONSD (4.55 ± 0.69 mm vs. 4.97 ± 0.58 mm, p < 0.001) and larger average LCCI (11.61 ± 1.43 vs. 7.58 ± 0.90, p < 0.001) than matched healthy control eyes. LCCI was significantly correlated with smaller ONSD, higher intraocular pressure, thinner global retinal nerve fiber thickness, and worse visual field loss in all subjects (all Ps ≤ 0.022). (4) Conclusions: NTG eyes had smaller ONSD and greater LCCI than healthy control eyes. In addition, a negative correlation was observed between ONSD and LCCI. These findings suggest that cerebrospinal fluid pressure, which ONSD indirectly predicts, may affect LC configuration. Changes in the retrolaminar compartment may play a role in glaucoma pathogenesis.

Effects of Myopia and Glaucoma on the Neural Canal and Lamina Cribrosa Using Optical Coherence Tomography

PRCIS

Glaucoma was associated with axial bowing and rotation of Bruchs membrane opening (BMO) and anterior laminar insertion (ALI), skewed neural canal, and deeper anterior lamina cribrosa surface (ALCS). Longer axial length was associated with wider, longer, and more skewed neural canal and flatter ALCS.

PURPOSE

Investigate the effects of myopia and glaucoma in the prelaminar neural canal and anterior lamina cribrosa using 1060-nm swept-source optical coherence tomography.

PATIENTS

19 control (38 eyes) and 38 glaucomatous subjects (63 eyes).

MATERIALS AND METHODS

Participants were imaged with swept-source optical coherence tomography, and the images were analyzed for the BMO and ALI dimensions, prelaminar neural canal dimensions, and ALCS depth.

RESULTS

Glaucomatous eyes had more bowed and nasally rotated BMO and ALI, more horizontally skewed prelaminar neural canal, and deeper ALCS than the control eyes. Increased axial length was associated with a wider, longer, and more horizontally skewed neural canal and a decrease in the ALCS depth and curvature.

CONCLUSION

Our findings suggest that glaucomatous posterior bowing or cupping of lamina cribrosa can be significantly confounded by the myopic expansion of the neural canal. This may be related to higher glaucoma risk associated with myopia from decreased compliance and increased susceptibility to IOP-related damage of LC being pulled taut.

Patterns of Optical Coherence Tomography Imaging in Preperimetric Open Angle Glaucoma: A Comparative Study With Young-Age-Onset and Old-Age-Onset Eyes

PRCIS

Optic coherence tomography imaging in preperimetric open angle glaucoma (OAG) differed between young-age-onset and old-age-onset eyes. Inferior and superior quadrants were thinner in young and old-age-onset eyes, respectively. Understanding the specific patterns of early glaucomatous damage based on age-at-onset may improve glaucoma diagnosis and monitoring.

PURPOSE

To investigate the patterns of retinal nerve fiber layer (RNFL) and macular ganglion cell-inner plexiform layer (GCIPL) thinning in preperimetric OAG by optical coherence tomography based on age at onset ("young-age onset (<40 y)" vs. "old-age onset (≥40 y)".

MATERIALS AND METHODS

The RNFL and GCIPL deviation images were acquired by Cirrus HD-optical coherence tomography, and overlaid, thus converted to a "deviation frequency map", respectively. The topographic thinning patterns and parameters of RNFL and GCIPL thickness measurements were compared.

RESULTS

A total of 194 eyes of 194 patients with preperimetric OAG and 97 eyes of 97 age-matched normal subjects were analyzed. Young-age-onset eyes of preperimetric OAG mainly had RNFL defects inferotemporally (264-296 degrees) with GCIPL defects in the inferior region (213-357 degrees). Old-age-onset preperimetric OAG eyes had RNFL defects inferotemporally (266-294°) and superotemporally (33-67 degrees), with GCIPL defects in the inferior and superior regions (206-360 degrees, 0-22 degrees). The inferior quadrant of RNFL and GCIPL thicknesses were significantly thinner in young-age-onset eyes compared with old-age-onset eyes ( P =0.012, 0.016), while the superior quadrant of those were significantly thinner in the old-age-onset eyes ( P =0.003, 0.005).

CONCLUSION

Young-age-onset and old-age-onset eyes of preperimetric OAG present different specific patterns of RNFL and GCIPL thinning.

Measurement of corneal biomechanical properties in diabetes mellitus using the Corvis ST

We sought to assess changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with those among healthy controls using Corvis ST (CST). The study group included 209 eyes from healthy control subjects and 33 eyes from diabetic subjects, respectively. Following an ophthalmological examination, measurements with CST were taken. Additionally, hemoglobin A1c and blood glucose values were collected. Results were then compared to those of the control group after adjusting for potential confounding factors, including age-, intraocular pressure (IOP)-, central corneal thickness (CCT)-, spherical equivalent (SE)- and axial length (AL). After adjusting for potential confounding factors, including the age, IOP, CCT, SE, and AL, patients with DM presented significantly lower whole-eye movement (WEM) (ms) values than patients without DM (21.71 ± 0.84 vs. 22.15 ± 0.64 ms; P < .001). There was a significant and negative correlation between WEM (ms) and hemoglobin A1c in DM patients (r = -0.733; P = .001). In univariate and multivariate general linear mixed model (GLMM) analyses, IOP (P < .001 and P < .001, respectively) and the presence of DM (P = .001 and P < .001, respectively) significantly affected WEM (ms). In DM, significant changes in corneal biomechanical properties were detectable. The DM group showed significantly less deformable cornea and sclera than did the normal controls, even after adjusting for age, IOP, CCT, SE, and AL. These findings may cause misinterpretation of IOP measurements in diabetic patients. Therefore, the measurement of corneal biomechanics should be taken into consideration in clinical practice.

Corneal Hysteresis, Intraocular Pressure, and Progression of Glaucoma: Time for a “Hyst-Oric” Change in Clinical Practice?

It is known that as people age their tissues become less compliant and the ocular structures are no different. Corneal Hysteresis (CH) is a surrogate marker for ocular compliance. Low hysteresis values are associated with optic nerve damage and visual field loss, the structural and functional components of glaucomatous optic neuropathy. Presently, a range of parameters are measured to monitor and stratify glaucoma, including intraocular pressure (IOP), central corneal thickness (CCT), optical coherence tomography (OCT) scans of the retinal nerve fibre layer (RNFL) and the ganglion cell layer (GCL), and subjective measurement such as visual fields. The purpose of this review is to summarise the current evidence that CH values area risk factor for the development of glaucoma and are a marker for its progression. The authors will explain what precisely CH is, how it can be measured, and the influence that medication and surgery can have on its value. CH is likely to play an integral role in glaucoma care and could potentially be incorporated synergistically with IOP, CCT, and visual field testing to establish risk stratification modelling and progression algorithms in glaucoma management in the future.

Matrix Mechanotransduction via Yes-Associated Protein in Human Lamina Cribrosa Cells in Glaucoma

Purpose

Extracellular matrix stiffening is characteristic of both aging and glaucoma, and acts as a promoter and perpetuator of pathological fibrotic remodeling. Here, we investigate the role of a mechanosensitive transcriptional coactivator, Yes-associated protein (YAP), a downstream effector of multiple signaling pathways, in lamina cribrosa (LC) cell activation to a profibrotic, glaucomatous state.

Methods

LC cells isolated from glaucomatous human donor eyes (GLC; n = 3) were compared to LC cells from age-matched nonglaucomatous controls (NLC; n = 3) to determine differential YAP expression, protein levels, and proliferation rates. NLC cells were then cultured on soft (4 kPa), and stiff (100 kPa), collagen-1 coated polyacrylamide hydrogel substrates. Quantitative real-time RT-PCR, immunoblotting, and immunofluorescence microscopy were used to measure the expression, activity, and subcellular location of YAP and its downstream targets, respectively. Proliferation rates were examined in NLC and GLC cells by methyl thiazolyl tetrazolium salt assays, across a range of incrementally increased substrate stiffness. Endpoints were examined in the presence or absence of a YAP inhibitor, verteporfin (2 µM).

Results

GLC cells show significantly (P < 0.05) increased YAP gene expression and total-YAP protein compared to NLC cells, with significantly increased proliferation. YAP regulation is mechanosensitive, because NLC cells cultured on pathomimetic, stiff substrates (100 kPa) show significantly upregulated YAP gene and protein expression, increased YAP phosphorylation at tyrosine 357, reduced YAP phosphorylation at serine 127, increased nuclear pooling, and increased transcriptional target, connective tissue growth factor. Accordingly, myofibroblastic markers, α-smooth muscle actin (α-SMA) and collagen type I, alpha 1 (Col1A1) are increased. Proliferation rates are elevated on 50 kPa substrates and tissue culture plastic. Verteporfin treatment significantly inhibits YAP-mediated cellular activation and proliferation despite a stiffened microenvironment.

Conclusions

These data demonstrate how YAP plays a pivotal role in LC cells adopting a profibrotic and proliferative phenotype in response to the stiffened LC present in aging and glaucoma. YAP provides an attractive and novel therapeutic target, and its inhibition via verteporfin warrants further clinical investigation.

Age and intraocular pressure in murine experimental glaucoma

Age and intraocular pressure (IOP) are the two most important risk factors for the development and progression of open-angle glaucoma. While IOP is commonly considered in models of experimental glaucoma (EG), most studies use juvenile or adult animals and seldom older animals which are representative of the human disease. This paper provides a concise review of how retinal ganglion cell (RGC) loss, the hallmark of glaucoma, can be evaluated in EG with a special emphasis on serial in vivo imaging, a parallel approach used in clinical practice. It appraises the suitability of EG models for the purpose of in vivo imaging and argues for the use of models that provide a sustained elevation of IOP, without compromise of the ocular media. In a study with parallel cohorts of adult (3-month-old, equivalent to 20 human years) and old (2-year-old, equivalent to 70 human years) mice, we compare the effects of elevated IOP on serial ganglion cell complex thickness and individual RGC dendritic morphology changes obtained in vivo. We also evaluate how age modulates the impact of elevated IOP on RGC somal and axonal density in histological analysis as well the density of melanopsin RGCs. We discuss the challenges of using old animals and emphasize the potential of single RGC imaging for understanding the pathobiology of RGC loss and evaluating new therapeutic avenues.

Rates of Retinal Nerve Fiber Layer Thinning in Distinct Glaucomatous Optic Disc Phenotypes in Early Glaucoma

PURPOSE

To compare spectral-domain optical coherence tomography (SDOCT) measured circumpapillary retinal nerve fiber layer (cpRNFL) among 4 glaucomatous optic disc phenotypes in early glaucoma.

DESIGN

Clinical cohort study METHODS: In this study, 218 early glaucoma eyes that had at least 3 years of follow-up and a minimum of 4 SDOCT scans were recruited. The optic discs were classified into 4 types based on appearance: 76 generalized cup enlargement (GE), 53 focal ischemic (FI), 22 myopic glaucomatous (MY), and 67 senile sclerotic (SS). A linear mixed effects model was used to compare the rates of global and regional cpRNFL thinning among optic disc phenotypes.

RESULTS

After adjusting for confounders, the SS group (mean [95% CI]: -1.01 [-1.30, -0.73] µm/y) had the fastest mean rate of global cpRNFL thinning followed by FI (-0.77 [-0.97, -0.57] µm/y), MY (0.59 [-0.81, -0.36] µm/y), and GE (-0.58 [-0.75, -0.40] µm/y) at P < .001. The inferior temporal sector had the fastest rate of cpRNFL thinning among the regional measurements except for the MY group (-0.68 [-1.10, -0.26] µm/y, P = .002). In the multivariable analysis, GE (P = .002) and MY (P = .010) phenotypes were associated with significantly slower global rates of cpRNFL thinning compared with the SS phenotype.

CONCLUSIONS

Rates of cpRNFL thinning were different among the 4 glaucomatous optic disc phenotypes. Those patients with early glaucoma with SS phenotype have the fastest cpRNFL thinning. These patients may benefit from more frequent monitoring and the need to advance therapy if cpRNFL thinning is detected.

The lysophosphatidic acid axis in fibrosis: Implications for glaucoma

Glaucoma is a common progressive optic neuropathy that results in visual field defects and can lead to irreversible blindness. The pathophysiology of glaucoma involves dysregulated extracellular matrix remodelling in both the trabecular meshwork in the anterior chamber and in the lamina cribrosa of the optic nerve head. Fibrosis in these regions leads to raised intraocular pressure and retinal ganglion cell degeneration, respectively. Lysophosphatidic acid (LPA) is a bioactive lipid mediator which acts via six G-protein coupled receptors on the cell surface to activate intracellular pathways that promote cell proliferation, transcription and survival. LPA signalling has been implicated in both normal wound healing and pathological fibrosis. LPA enhances fibroblast proliferation, migration and contraction, and induces expression of pro-fibrotic mediators such as connective tissue growth factor. The LPA axis plays a major role in diseases such as idiopathic pulmonary fibrosis, where it has been identified as an important pharmacological target. In glaucoma, LPA is present in high levels in the aqueous humour, and its signalling has been found to increase resistance to aqueous humour outflow through altered trabecular meshwork cellular contraction and extracellular matrix deposition. LPA signalling may, therefore, also represent an attractive target for treatment of glaucoma. In this review we wish to describe the role of LPA and its related proteins in tissue fibrosis and glaucoma.

Abnormal corneal properties in osteogenesis imperfecta and glaucoma: a case series

Objective

We aimed to carry out ocular examination and genetic studies in a family in which some members are affected with osteogenesis imperfecta (OI) and primary open-angle glaucoma (POAG). We compared the corneal properties of affected and unaffected members (ie, cases and controls).

Methods

Eight family members from two generations, both affected and unaffected, were examined. Corneal hysteresis (CH), intraocular pressure (IOP) measured with Goldmann applanation tonometer, central corneal thickness (CCT) and cornea-corrected IOP (IOPcc) were recorded. Blood samples were obtained from seven family members, both affected and unaffected, and tested for a panel of genes associated with OI.

Results

Family members affected with OI (n=6) had a heterozygous splice site mutation in intron 26 of the COL1A1 gene. The family members affected with OI had reduced CCT (476.5±24.6 µm) and CH (7.9 ±1.4 mmHg) compared with the unaffected controls (CCT, 575.8±10.8 µm; CH, 12.3±0.8 mmHg). Two of the six patients affected with OI had a glaucoma diagnosis and were on topical therapy and under regular clinical review.

Conclusions

Patients affected with OI have a significant risk of developing POAG due to the effects of abnormal collagen on various ocular structures. Two of these effects which place them at risk are reduced CCT and CH. They should be screened and monitored for glaucoma from a young age, and the examination should include corneal biomechanical measurements and CCT to identify those most at risk. IOPcc may be a more accurate way to monitor IOP in the presence of abnormal corneal properties.

Cell-Matrix Interactions in the Eye: From Cornea to Choroid

The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.

Glaucoma and neuroinflammation: An overview

Glaucoma is an optic neuropathy characterized by well-defined optic disc morphological changes (i.e., cup enlargement, neuroretinal border thinning, and notching, papillary vessel modifications) consequent to retinal ganglion cell loss, axonal degeneration, and lamina cribrosa remodeling. These modifications tend to be progressive and are the main cause of functional damage in glaucoma. Despite the latest findings about the pathophysiology of the disease, the exact trigger mechanisms and the mechanism of degeneration of retinal ganglion cells and their axons have not been completely elucidated. Neuroinflammation may play a role in both the development and the progression of the disease as a result of its effects on retinal environment and retinal ganglion cells. We summarize the latest findings about neuroinflammation in glaucoma and examine the connection between risk factors, neuroinflammation, and retinal ganglion cell degeneration.

Oxidative Stress and the Role of NADPH Oxidase in Glaucoma

Glaucoma is characterised by loss of retinal ganglion cells, and their axons and many pathophysiological processes are postulated to be involved. It is increasingly understood that not one pathway underlies glaucoma aetiology, but rather they occur as a continuum that ultimately results in the apoptosis of retinal ganglion cells. Oxidative stress is recognised as an important mechanism of cell death in many neurodegenerative diseases, including glaucoma. NADPH oxidase (NOX) are enzymes that are widely expressed in vascular and non-vascular cells, and they are unique in that they primarily produce reactive oxygen species (ROS). There is mounting evidence that NOX are an important source of ROS and oxidative stress in glaucoma and other retinal diseases. This review aims to provide a perspective on the complex role of oxidative stress in glaucoma, in particular how NOX expression may influence glaucoma pathogenesis as illustrated by different experimental models of glaucoma and highlights potential therapeutic targets that may offer a novel treatment option to glaucoma patients.

Optic Nerve Head Changes in Patients with Optic Neuritis Secondary to Multiple Sclerosis: A Comparison of the Affected and Fellow Healthy Eyes

OBJECTIVE

To evaluate the thickness of lamina cribrosa (LC) in patients with multiple sclerosis (MS) using optical coherence tomography (OCT) and the effect of optic neuritis (ON) attack on these measurements during the remission period.

METHODS

The study included 20 cases diagnosed with relapsing-remitting MS with a history of ON attacks affecting one eye and in remission of MS and ON attacks for at least three months, and 28 randomly selected eyes of age- and sex-matched healthy controls. In the MS group, the eyes affected by ON attack were assigned as Group 1 (MS+ON), their fellow unaffected eyes as Group 2 (MS-ON), and healthy control eyes as Group 3. The LC, peripapillary retinal nerve fiber layer (ppRNFL), and subfoveal choroidal thickness measurements were made by using OCT in all cases, and results were compared between the groups.

RESULTS

The mean LC thickness in MS+ON and MS-ON groups was significantly lower than the control group (p<0.001). There was no significant difference between MS+ON and MS-ON groups in terms of mean LC thickness (p=0.073). The mean ppRNFL in the MS+ON and MS-ON groups was statistically significantly lower than the control group (p=0.003, p=0.035, respectively).

CONCLUSIONS

It is noteworthy that LC is significantly affected in eyes with MS who have not had a history of ON attack. Evaluation of the LC measurements can be important for early detection of optic nerve damage in patients with MS.

Age-dependent changes in visual sensitivity induced by moving fixation points in adduction and abduction using imo perimetry

Visual field (VF) testing has usually been performed with the central gaze as a fixed point. Recent publications indicated optic nerve head deformations induced by optic nerve traction force can promote the progression of optic neuropathies, including glaucoma. We generated a new static test protocol that adds 6° adduction and abduction to gaze position (fixation points) movement. The aim of this study was to investigate both whether quantifying VF sensitivities at lateral horizontal gaze positions is feasible and whether horizontal gaze positions change sensitivities differently in subjects of different ages. Healthy adult eyes from 29 younger (≤ 45 years) and 28 elderly (> 45 years) eyes were examined in this cross-sectional study. After VF testing with central gaze as a fixation point using 24 plus (1) imo static perimetry, subjects underwent VF testing with 6° adduction and 6° abduction as fixation points. The average mean sensitivities with central gaze, adduction, and abduction were 29.9 ± 1.0, 29.9 ± 1.3, and 30.0 ± 1.2 decibels (dB) in younger subjects and 27.7 ± 1.2, 27.5 ± 1.7, and 28.1 ± 1.3 dB in elderly subjects, respectively. Visual sensitivity in young healthy subjects was similar among the three fixation points, whereas visual sensitivity in elderly healthy subjects was significantly better with abduction as a fixation point than with central gaze and adduction (both p < 0.05). We expect this test protocol to contribute to our understanding of visual function during horizontal eye gaze movement in various eye diseases.

IOP-induced regional displacements in the optic nerve head and correlation with peripapillary sclera thickness

Mechanical insult induced by intraocular pressure (IOP) is likely a driving force in the disease process of glaucoma. This study aimed to evaluate regional displacements in human optic nerve head (ONH) and peripapillary tissue (PPT) in response to acute IOP elevations, and their correlations with morphological characteristics of the posterior eye. Cross-sectional (2D) images of the ONH and PPT in 14 globes of 14 human donors were acquired with high-frequency ultrasound during whole globe inflation from 5 to 30 mm Hg. High-frequency ultrasound has a spatial resolution of tens of micrometers and is capable of imaging through the ONH and PPT thickness. Tissue displacements were calculated using a correlation-based speckle tracking algorithm for a dense matrix of kernels covering the 2D imaging plane. The ONH was manually segmented in the ultrasound B-mode images acquired at 5 mmHg based on echogenicity. The lamina cribrosa (LC) boundaries were visible in eight of the fourteen eyes and the LC region was segmented using a semi-automated superpixel-based method. The ONH had larger radial displacement than the PPT in all tested eyes and the difference increased with increasing IOP. A significant negative correlation was found between ONH-PPT displacement difference and PPT thickness (p < 0.05), while no significant correlations were found between ONH-PPT displacement difference and other morphological parameters including PPT radius of curvature, scleral canal size, LC thickness and anterior LC surface depth. Within the ONH, the radial displacement decreased in the region anterior to and across LC but not in the region posterior to LC. Finite element models using simplified geometry and material properties confirmed the role of LC in reducing the overall ONH radial displacements, but did not predict the displacement gradient change observed experimentally. These results suggested that a thinner PPT may be associated with a larger relative posterior motion of the ONH with respect to the surrounding PPT and the LC may play a major role in preventing excessive posterior displacement of ONH during acute IOP elevations.

Effect of Changing Heart Rate on the Ocular Pulse and Dynamic Biomechanical Behavior of the Optic Nerve Head

Purpose

To study the effect of changing heart rate on the ocular pulse and the dynamic biomechanical behavior of the optic nerve head (ONH) using a comprehensive mathematical model.

Methods

In a finite element model of a healthy eye, a biphasic choroid consisted of a solid phase with connective tissues and a fluid phase with blood, and the lamina cribrosa (LC) was viscoelastic as characterized by a stress-relaxation test. We applied arterial pressures at 18 ocular entry sites (posterior ciliary arteries), and venous pressures at four exit sites (vortex veins). In the model, the heart rate was varied from 60 to 120 bpm (increment: 20 bpm). We assessed the ocular pulse amplitude (OPA), pulse volume, ONH deformations, and the dynamic modulus of the LC at different heart rates.

Results

With an increasing heart rate, the OPA decreased by 0.04 mm Hg for every 10 bpm increase in heart rate. The ocular pulse volume decreased linearly by 0.13 µL for every 10 bpm increase in heart rate. The storage modulus and the loss modulus of the LC increased by 0.014 and 0.04 MPa, respectively, for every 10 bpm increase in heart rate.

Conclusions

In our model, the OPA, pulse volume, and ONH deformations decreased with an increasing heart rate, whereas the LC became stiffer. The effects of blood pressure/heart rate changes on ONH stiffening may be of interest for glaucoma pathology.

The role of lamina cribrosa tissue stiffness and fibrosis as fundamental biomechanical drivers of pathological glaucoma cupping

The primary biomechanical driver of pathological glaucomatous cupping remains unknown. Finite element modeling indicates that stress and strain play key roles. In this article, primarily a review, we utilize known biomechanical data and currently unpublished results from our lab to propose a three-stage, tissue stiffness-based model to explain glaucomatous cupping occurring at variable levels of translaminar pressure (TLP). In stage 1, a short-term increase in TLP gradient induces a transient increase in lamina cribrosa (LC) strain. Beyond a critical level of strain, the tissue stiffness rises steeply provoking cellular responses via integrin-mediated mechanotransduction. This early mechanoprotective cellular contraction reduces strain, which reduces tissue stiffness by return of the posteriorly deflected LC to baseline. In stage 2 a prolonged period of TLP increase elicits extracellular matrix (ECM) production leading to fibrosis, increasing baseline tissue stiffness and strain and diminishing the contractile ability/ability to return to the baseline LC position. This is supported by our three-dimensional collagen contraction assays, which show significantly reduced capacity to contract in glaucoma compared with normal LC cells. Second, 15% cyclic strain in LC cells over 24 h elicits a typical increase in ECM profibrotic genes in normal LC cells but a highly blunted response in glaucoma LC cells. Stage 3 is characterized by persistent fibrosis causing further stiffening and inducing a feed-forward ECM production cycle. Repeated cycles of increased strain and stiffness with profibrotic ECM deposition prevent optic nerve head (ONH) recoil from the new deflected position. This incremental maladaptive modeling leads to pathological ONH cupping.

Corneal Stiffness and Collagen Cross-Linking Proteins in Glaucoma: Potential for Novel Therapeutic Strategy

Biomechanical properties of the cornea have recently emerged as clinically useful in risk assessment of diagnosing glaucoma and predicting disease progression. Corneal hysteresis (CH) is a dynamic tool, which measures viscoelasticity of the cornea. It represents the overall deformability of the cornea, and reduces significantly with age. Low CH has also been associated with optic nerve damage and progression of visual field loss in glaucoma. The extracellular matrix (ECM) constituents of the cornea, trabecular meshwork (TM), sclera, and lamina cribrosa (LC) are similar, as they are predominantly made of fibrillar collagen. This suggests that biomechanical changes in the cornea may also reflect optic nerve compliance in glaucomatous optic neuropathy, and in the known increase of TM tissue stiffness in glaucoma. Increased collagen cross-linking contributes to tissue stiffening throughout the body, which is observed in normal aging and occurs at an accelerated rate in systemic conditions such as fibrotic and cardiovascular diseases, cancer, and glaucoma. We reviewed 3 ECM cross-linking proteins that may have a potential role in the disease process of increased tissue stiffness in glaucoma, including lysyl oxidase (LOX)/lysyl oxidase-like 1 (LOXL1), tissue transglutaminase (TG2), and advanced glycation end products. We also report elevated messenger RNA (mRNA) levels of LOX and TG2 in glaucoma LC cells to support our proposed theory that increased levels of cross-linking proteins in glaucoma play a role in LC tissue stiffness. We highlight areas of research that are needed to better understand the role of cross-linking in glaucoma pathogenesis, leading potentially to a novel therapeutic strategy.

Bilaminar Mechanics of the Human Optic Nerve Sheath

PURPOSE/AIM

The adult human optic nerve (ON) sheath has recently been recognized to be bilaminar, consisting of inner layer (IL) and outer layer (OL). Since the ON and sheath exert tension on the globe in large angle adduction as these structures transmit reaction force of the medial rectus muscle to the globe, this study investigated the laminar biomechanics of the human ON sheath.

MATERIALS AND METHODS

Biomechanical characterization was performed in ON sheath specimens from 12 pairs of fresh, post-mortem adult eyes. Some ON sheath specimens were tested completely, while others were separated into IL and OL. Uniaxial tensile loading under physiological temperature and humidity was used to characterize a linear approximation as Young's modulus, and hyperelastic non-linear behavior using the formulation of Ogden. Micro-indentation was performed by imposing small compressive deformations with small, hard spheres. Specimens of the same sheaths were paraffin embedded, sectioned at 10 micron thickness, and stained with van Gieson's stain for anatomical correlation.

RESULTS

Mean (± standard error of the mean, SEM) tensile Young's modulus of the inner sheath at 19.8 ± 1.6 MPa significantly exceeded that for OL at 9.7 ± 1.2 MPa; the whole sheath showed intermediate modulus of 15.4 ± 1.1 MPa. Under compression, the inner sheath was stiffer (7.9 ± 0.5 vs 5.2 ± 0.5 kPa) and more viscous (150.8 ± 10.6 vs 75.6 ± 6 kPa s) than outer sheath. The inner sheath had denser elastin fibers than outer sheath, correlating with greater stiffness.

CONCLUSIONS

We conclude that maximum tensile stiffness occurs in the elastin-rich ON sheath IL that inserts near the lamina cribrosa where tension in the sheath exerted during adduction tethering may be concentrated adjacent the ON head.

Three-Dimensional Inflation Response of Porcine Optic Nerve Head Using High-Frequency Ultrasound Elastography

Characterization of the biomechanical behavior of the optic nerve head (ONH) in response to intraocular pressure (IOP) elevation is important for understanding glaucoma susceptibility. In this study, we aimed to develop and validate a three-dimensional (3D) ultrasound elastographic technique to obtain mapping and visualization of the 3D distributive displacements and strains of the ONH and surrounding peripapillary tissue (PPT) during whole globe inflation from 15 to 30 mmHg. 3D scans of the posterior eye around the ONH were acquired through full tissue thickness with a high-frequency ultrasound system (50 MHz). A 3D cross-correlation-based speckle-tracking algorithm was used to compute tissue displacements at ∼30,000 kernels distributed within the region of interest (ROI), and the components of the strain tensors were calculated at each kernel by using least square estimation of the displacement gradients. The accuracy of displacement calculation was evaluated using simulated rigid-body translation on ultrasound radiofrequency (RF) data obtained from a porcine posterior eye. The accuracy of strain calculation was evaluated using finite element (FE) models. Three porcine eyes were tested showing that ONH deformation was heterogeneous with localized high strains. Substantial radial (i.e., through-thickness) compression was observed in the anterior ONH and out-of-plane (i.e., perpendicular to the surface of the shell) shear was shown to concentrate in the vicinity of ONH/PPT border. These preliminary results demonstrated the feasibility of this technique to achieve comprehensive 3D evaluation of the mechanical responses of the posterior eye, which may provide mechanistic insights into the regional susceptibility in glaucoma.

Corneal biomechanical responses detected using corvis st in primary open angle glaucoma and normal tension glaucoma

Structural differences have been reported between primary open angle glaucoma (POAG) and normal tension glaucoma (NTG), and biomechanical differences between POAG and NTG may account for why NTG patients are more vulnerable to lower intraocular pressure (IOP). This study compared the biomechanical properties of POAG and NTG patients using the Corvis scheimpflug technology (ST) non-contact Scheimpflug-based tonometer, and determined the factors associated with these properties.In this retrospective cross-sectional study, 46 eyes with POAG, 54 eyes with NTG, and 61 control eyes were included. A non-contact Scheimpflug-based tonometer was used to examine and compare the corneal biomechanical responses in the POAG, NTG, and normal groups. We used univariate and multivariate regression analyses to determine the factors associated with the deformation amplitude in each group.Baseline characteristics, including age, IOP, spherical equivalent, keratometry, axial length, and central corneal thickness, were similar among the 3 groups. Severity of glaucoma, as measured by mean deviation, was similar between POAG and NTG groups. Applanation 1 velocity and deformation amplitude were significantly smaller in POAG (0.13 ± 0.02 and 1.06 ± 0.14, respectively) than NTG (0.14 ± 0.01 and 1.13 ± 0.11, respectively) and normal groups (0.14 ± 0.02 and 1.13 ± 0.10, respectively). Radius of curvature was significantly larger in the POAG group compared to the normal group. In normal controls, IOP and keratometry were significant factors related to deformation amplitude. In POAG eyes, IOP was a statistically significant predictor of deformation amplitude. In NTG eyes, however, IOP , keratometry, and axial length were statistically significant predictors of deformation amplitude.POAG eyes showed less deformable corneas compared to NTG and normal controls. IOP was significantly correlated with deformation amplitude in all groups. However, axial length was positively correlated with deformation amplitude only in NTG eyes. Characterization of the differences in biomechanical properties between POAG and NTG may contribute to a better understanding of the underlying pathophysiologies associated with these diseases.

Differences of megalopapilla and normal sized disk with age-an optical coherence tomography analysis

PURPOSE

To compare the optic disks of children and adults with megalopapilla using optical coherence tomography (OCT).

SUBJECTS AND METHODS

We conducted a case-control study of subjects with megalopapilla and normal sized disks seen between February 2013 and July 2015 at the Hospital da Luz, Lisbon. All subjects and controls were imaged with spectral domain OCT, and optic nerve head (ONH) parameters were evaluated. The main outcome measures were rim area, cup:disk ratio, and cup volume.

RESULTS

A total of 168 eyes of 168 subjects were included: 78 with megalopapilla (39 children/39 adults) and 90 (45/45) with normal sized disks. For the same ONH area, children had a higher rim area (P = 0.000), a smaller cup:disk ratio (P = 0.001), and a smaller cup volume (P = 0.001) than adults. For the same age group, megalopapilla had a larger cup:disk ratio (P = 0.000) and a larger cup volume (P = 0.000) than normal-sized disks.

CONCLUSIONS

In this study cohort, compared to adults with the same disk size, children (with megalopapilla or normal-sized disks) had a larger rim area and smaller cup. These findings suggest that enlargement of the cup of the optic disk and reduction of the rim area can occur through life.

Connective Tissue Remodeling in Myopia and its Potential Role in Increasing Risk of Glaucoma

Myopia and glaucoma are both increasing in prevalence and are linked by an unknown mechanism as many epidemiologic studies have identified moderate to high myopia as an independent risk factor for glaucoma. Myopia and glaucoma are both chronic conditions that lead to connective tissue remodeling within the sclera and optic nerve head. The mechanobiology underlying connective tissue remodeling differs substantially between both diseases, with different homeostatic control mechanisms. In this article, we discuss similarities and differences between connective tissue remodeling in myopia and glaucoma; selected multi-scale mechanisms that are thought to underlie connective tissue remodeling in both conditions; how asymmetric remodeling of the optic nerve head may predispose a myopic eye for pathological remodeling and glaucoma; and how neural tissue deformations may accumulate throughout both pathologies and increase the risk for mechanical insult of retinal ganglion cell axons.

Compression of the Choroid by Horizontal Duction

Purpose

The optic nerve becomes tethered in adduction in most people, which deforms the disc. We investigated the effect of horizontal ocular duction and subject age on choroidal volume at the macular side of the optic disc.

Methods

In 25 younger (18-33 years) and 15 older (50-73 years) normal subjects, the disc and the peripapillary choroid were imaged with optical coherence tomography (OCT) in central gaze and 35° adduction and abduction. The choroid temporal to the optic disc underlying the region between the Bruch's membrane opening and fovea was segmented into regions that were multiples of the disc radius for determination of local choroidal thickness. Regional volume changes from central gaze were determined in adduction and abduction.

Results

In adduction, regional choroidal volume decreased by 42.4 ± 3.4 nanoliters (nL) (standard error of the mean) in younger (P < 0.0001) and 6.2 ± 2.6 nL in older (P < 0.02) subjects. Relative volume reduction in adduction was 7.5% ± 0.6% in younger (P < 0.001) and 1.3% ± 0.6% in older (P < 0.02) subjects. Volume reduction was greatest near the disc and significant up to three disc radii from it in younger and 1 radius in older subjects but was insignificant in abduction.

Conclusions

Horizontal duction compresses the temporal peripapillary choroid, more in adduction than in abduction and more in younger than older subjects. This reflects duction-related peripapillary tissue deformation probably related, at least in part, to optic nerve tethering in adduction.

Age-dependent Deformation of the Optic Nerve Head and Peripapillary Retina by Horizontal Duction

PURPOSE

To study effects of age and horizontal duction on deformation of the optic nerve head (ONH) and peripapillary retina (PPR), as reflected by displacement of vascular landmarks, to explore the influence of adduction tethering.

DESIGN

Cross-sectional study.

METHODS

Setting: University.

STUDY POPULATION

Single eyes of 20 healthy young adults (average age 23.9 ± 3.9 [SD] years) were compared to 20 older subjects (average age 61.4 ± 9.3 years). Observational Procedure: The disc and PPR were imaged by scanning laser ophthalmoscopy in central gaze and at 35 degrees abduction and adduction.

MAIN OUTCOME MEASURE

Deformations of the disc and adjacent PPR were measured by comparing positions of epipapillary and epiretinal blood vessels.

RESULTS

Vessels within the ONH of younger subjects shifted temporally during adduction and nasally during abduction. Displacement of the nasal hemi-disc in adduction was greater at 38.5 ± 1.7 μm (standard error of mean) than the temporal half at 4.1 ± 2.1 μm (P < .001). PPR within 1 radius of the disc margin underwent 7.6 ± 1.6 μm average temporal displacement in adduction in young subjects. In abduction, the young temporal hemi-disc shifted 4.4 ± 0.6 μm nasally without significant displacement in the nasal half. Older subjects' ONH showed less temporal shift and less displacement in the PPR within 1 disc radius (P < .0001) in adduction; the nasal hemi-disc shifted 24.5 ± 1.3 μm compared with 4.4 ± 2.1 μm in the temporal half. There were no significant deformations of the disc during abduction by older subjects.

CONCLUSION

Large horizontal duction, particularly adduction, deforms the disc and peripapillary vasculature. This deformation, which is larger in younger than older subjects, may be due to optic nerve tethering in adduction.

Unraveling the Enigma of Nonarteritic Anterior Ischemic Optic Neuropathy

Non-arteritic anterior ischemic optic neuropathy (NAON) is the second most common optic neuropathy in adults. Despite extensive study, the etiology of NAION is not definitively known. The best evidence suggests that NAION is caused by an infarction in the region of the optic nerve head (ONH), which is perfused by paraoptic short posterior ciliary arteries (sPCAs) and their branches. To examine the gaps in knowledge that defies our understanding of NAION, a historical review was performed both of anatomical investigations of the ONH and its relevant blood vessels and the evolution of clinical understanding of NAION. Notably, almost all of the in vitro vascular research was performed prior our current understanding of NAION, which has largely precluded a hypothesis-based laboratory approach to study the etiological conundrum of NAION. More recent investigative techniques, like fluorescein angiography, have provided valuable insight into vascular physiology, but such light-based techniques have not been able to image blood vessels located within or behind the dense connective tissue of the sclera and laminar cribrosa, sites that are likely culpable in NAION. The lingering gaps in knowledge clarify investigative paths that might be taken to uncover the pathogenesis of NAION and possibly glaucoma, the most common optic neuropathy for which evidence of a vascular pathology also exists.

High-risk retinoblastoma based on age at primary enucleation: a study of 616 eyes

PURPOSE

To study the high-risk histopathology features of retinoblastoma based on age at primary enucleation.

METHODS

Retrospective study of 616 patients.

RESULTS

The mean age at presentation and primary enucleation for retinoblastoma was 34 months (median, 28 months; range, <1-455 months). Of these cases, 128 (21%) were aged ≤1 year, 149 (24%) were in the age group of 1-2 years, 117 (19%) in 2-3 years, 104 (17%) in 3-4 years, and 118 (19%) were >4 years of age at the time of enucleation. Bilateral retinoblastoma (34%; p < 0.0001) and buphthalmos (20%; p < 0.0001) were more common in children ≤1 year of age. Anterior chamber pseudohypopyon (15%; p < 0.0001) and vitreous seeds (53%; p < 0.0001) were more common in children aged >4 years. Based on 8th edition American Joint Committee on Cancer staging system, pT3 was less common in children ≤1 year of age (13%; p < 0.001). Based on histopathology, 38% patients had high-risk features including 24% children aged ≤1 year, 42% in the age group of 1-2 years, 34% in 2-3 years age group, 45% in 3-4 years age group, and 48% patients were >4 years of age. Post-laminar optic nerve infiltration (6%; p = 0.02) and massive choroidal infiltration (9%; p = 0.04) was least common in children ≤1 year of age. Over a mean follow-up period of 52 months (median, 36 months; range, <1-218 months), systemic metastasis and death occurred in 9% patients despite adjuvant systemic chemotherapy.

CONCLUSION

The predominant high-risk histopathology feature of retinoblastoma varies with age at primary enucleation.

Cyclic Pattern of Intraocular Pressure (IOP) and Transient IOP Fluctuations in Nonhuman Primates Measured with Continuous Wireless Telemetry

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.

Quantitative confocal optical coherence elastography for evaluating biomechanics of optic nerve head using Lamb wave model

The mechanosensitivity of the optic nerve head (ONH) plays a pivotal role in the pathogenesis of glaucoma. Characterizing elasticity of the ONH over changing physiological pressure may provide a better understanding of how changes in intraocular pressure (IOP) lead to changes in the mechanical environment of the ONH. Optical coherence elastography (OCE) is an emerging technique that can detect tissue biomechanics noninvasively with both high temporal and spatial resolution compared with conventional ultrasonic elastography. We describe a confocal OCE system in measuring ONH elasticity in vitro, utilizing a pressure inflation setup in which IOP is controlled precisely. We further utilize the Lamb wave model to fit the phase dispersion curve during data postprocessing. We present a reconstruction of Young's modulus of the ONH by combining our OCE system with a Lamb wave model for the first time. This approach enables the quantification of Young's modulus of the ONH, which can be fit using a piecewise polynomial to the corresponding IOP.

Mechanical Deformation of Human Optic Nerve Head and Peripapillary Tissue in Response to Acute IOP Elevation

Purpose

To measure the deformation of the human optic nerve head (ONH) and peripapillary tissue (PPT) in response to acute intraocular pressure (IOP) elevation.

Methods

The ONH and PPT of 14 human donor globes were imaged with high-frequency ultrasonography during inflation testing from 5 to 30 mm Hg. A correlation-based speckle tracking algorithm was used to compute tissue displacements, and the through-thickness, in-plane, and shear strains were calculated by using least-squares strain estimation methods. The ONH and PPT were segmented along the anterior-posterior direction and the nasal-temporal direction. Regional displacements and strains were analyzed and compared.

Results

The ONH displaced more posteriorly than the PPT in response to an acute IOP increase. Scleral canal expansion was minimal but correlated with ONH posterior displacement at all IOP levels. Through-thickness compression was concentrated in the anterior of both the ONH and the PPT. Shear was concentrated in the vicinity of the canal with higher shear in the peripheral ONH than the central ONH and higher shear in the PPT near the scleral canal than that further away from the canal.

Conclusions

High-resolution ultrasound speckle tracking showed a displacement mismatch between the ONH and the PPT, larger compressive strains in the direction of IOP loading in the anterior ONH and PPT, and higher shear strains in the periphery of ONH in response to acute IOP elevation in the human eye. These findings delineate the deformation patterns within and around the ONH and may help understand IOP-associated optic nerve damage.

Evaluation of lamina cribrosa thickness in patients diagnosed with central retinal vein occlusion

PURPOSE

To evaluate the thickness of lamina cribrosa (LC) in both eyes of patients with unilateral central retinal vein occlusion (CRVO) and to compare with eyes of age-matched healthy control subjects.

METHODS

This prospective case-control study included a total of 38 patients with unilateral CRVO and 42 healthy control subjects. The LC thickness was measured at the center of the optic disc using an enhanced depth imaging with the spectral domain optical coherence tomography in both eyes of patients with unilateral CRVO and eyes of healthy control subjects. The LC thickness of CRVO patients was evaluated one month after dexamethasone intravitreal implant (Ozurdex) injection.

RESULTS

The mean LC thickness in affected eyes of patients with CRVO was significantly thinner than that of the healthy eyes (204.4 ± 8.8 and 228.0 ± 7.1 μm, p < 0.001, respectively). Also, the unaffected fellow eyes had significantly thinner LC compared with eyes of healthy subjects (205.3 ± 9.3 and 228.0 ± 7.1 μm, p < 0.001, respectively). There was no statistically significant difference in the thickness of LC between the affected and unaffected fellow eyes (p = 0.669).

CONCLUSIONS

The LC thickness in both eyes of CRVO patients was thinner than that of the healthy eyes. This finding suggests that thin LC may contribute to the development of CRVO as an ocular risk factor in addition to systemic factors.

Menopause exacerbates visual dysfunction in experimental glaucoma

Glaucoma is the leading cause of irreversible blindness worldwide. Recently, estrogen deficiencies caused by early menopause, alterations in estrogen signaling via mutations in estrogen receptors, and polymorphisms along estrogen metabolic pathways have all been linked to an increased risk of developing glaucoma. Here, we examined how menopause and age impact visual function and retinal structure in an experimental model of glaucoma. Young (3-4 months) and aged (9-10 months) female Brown Norway rats were divided into pre- and post-menopausal cohorts by surgically inducing menopause via ovariectomy (OVX). After six weeks, ocular hypertension (OHT) was induced unilaterally for a period of eight weeks. Four cohorts were successfully followed to eight weeks: young sham (n = 8), young OVX (n = 9), aged sham (n = 10), and aged OVX (n = 11) animals. Intraocular pressure (IOP) was monitored weekly in all groups. Prior to inducing OHT (baseline) and at four and eight weeks after inducing OHT, we assessed visual acuity via the optomotor response (OMR) and retinal structure using optical coherence tomography (OCT). OHT decreased the OMR in all cohorts. We found that spatial frequency thresholds decreased by 54% in OVX animals after OHT compared to sham animals after OHT, regardless of age (p < 0.001). We also found thinning of the retinal nerve fiber layer (RNFL) and loss of total retinal thickness after induction of OHT. Aged animals had more thinning of the RNFL and loss of total retinal thickness compared to young animals (p < 0.001). Overall, OHT caused significant changes in visual function and retinal structure. Observing that OVX in young and aged animals further decreased spatial frequency thresholds after OHT suggests that an estrogen deficiency may intensify visual impairment after OHT.

Modeling the Mechanical Parameters of Glaucoma

Glaucoma is a major eye disease characterized by a progressive loss of retinal ganglion cells (RGCs). Biomechanical forces as a result of hydrostatic pressure and strain play a role in this disease. Decreasing intraocular pressure is the only available therapy so far, but is not always effective and does not prevent blindness in many cases. There is a need for drugs that protect RGCs from dying in glaucoma; to develop these, we need valid glaucoma and drug screening models. Since in vivo models are unsuitable for screening purposes, we focus on in vitro and ex vivo models in this review. Many groups have studied pressure and strain model systems to mimic glaucoma, to investigate the molecular and cellular events leading to mechanically induced RGC death. Therefore, the focus of this review is on the different mechanical model systems used to mimic the biomechanical forces in glaucoma. Most models use either cell or tissue strain, or fluid- or gas-controlled hydrostatic pressure application and apply it to the relevant cell types such as trabecular meshwork cells, optic nerve head astrocytes, and RGCs, but also to entire eyes. New model systems are warranted to study concepts and test experimental compounds for the development of new drugs to protect vision in glaucoma patients. Impact Statement The outcome of currently developed models to investigate mechanically induced retinal ganglion cell death by applying different mechanical strains varies widely. This suggests that a robust glaucoma model has not been developed yet. However, a comprehensive overview of current developments is not available. In this review, we have therefore assessed what has been done before and summarized the available knowledge in the field, which can be used to develop improved models for glaucoma research.

Age-Dependent Variation of Lamina Cribrosa Displacement During the Standardized Valsalva Maneuver

Based on biomechanical theory, lamina cribrosa (LC) displacement, the key component of progressive glaucomatous change, is presumed to be dependent on intraocular pressure (IOP) as well as tissue stiffness of LC. In the performance of the Valsalva maneuver, both IOP and cerebrospinal fluid pressure can increase. The present study investigated the age-dependent variation of LC displacement during the standardized Valsalva maneuver in healthy subjects. Sixty-three (63) eyes (age range: 20-76 years) were prospectively underwent IOP measurement and Cirrus HD-OCT optic disc scans before and during the standardized Valsalva maneuver. During the standardized Valsalva maneuver, the IOP significantly increased from 13.2 ± 2.9 mmHg to 18.6 ± 5.2 mmHg (P < 0.001). The maximal LC depth significantly decreased in the younger age groups (age: 20 s to 40 s) but not in the older age groups (age: over 50). The BMO distance did not change significantly. Younger age (P = 0.009), a smaller increase of IOP during the Valsalva maneuver (P = 0.002), and greater baseline maximal LC depth (P = 0.013) were associated with more anterior displacement of the LC during the standardized Valsalva maneuver. Taken together, age as well as translaminar pressure dynamics seems to play a crucial role in LC biomechanics.

Optic nerve head damage relation to intracranial pressure and corneal properties of eye in glaucoma risk assessment

This work presents results from numerical simulations of optic nerve head's (ONH) biomechanical behavior during exposure to elevated intraocular (IOP) and/or intracranial pressure (ICP) for ocular hypertension conditions. At the same time, a range of geometric and material properties of the eye structure and their interrelation with elevated IOP and ICP values are investigated. These simulations are performed on a generic model of the eye, which allows parametrical modification of geometric and material properties. Our main interest is in measuring ONH's potential damage in ocular hypertension due to intracranial pressure. Simulation results indicate a significant role of ICP in post-laminar neural tissue failure and a possible role of central corneal thickness (CCT) and scleral modulus in clinical assessment and treatment of patients with ocular hypertension (OHT). Specifically, CCT was found to affect ONH at early stages of damage in ocular hypertension conditions, and high scleral modulus seems to result in reduced shear failure in lamina cribrosa in a similar OHT state. These findings suggest that CCT could be a risk factor for glaucoma in OHT patients at initial stage along with cornea stiffness. Graphical abstract Graphical abstract.

Ultrastructural Morphology of the Optic Nerve Head in Aged and Glaucomatous Mice

Purpose

To study age- and intraocular pressure–induced changes in the glial lamina of the murine optic nerve on the ultrastructural level.

Methods

Naïve C57bl/6 mice at various ages spanning the time between early adulthood (3 months) and senescence (30 months) were used in this study. In addition, the intraocular pressure (IOP) was increased in a group of young mice by injection of microbeads into the anterior chamber. The unmyelinated segments of the optic nerve containing the glial lamina were prepared for transmission electron microscopy and imaged at high resolution.

Results

Axon packing density decreased slightly with age. Aging nerves contained higher numbers of enlarged and degenerating axons. Mean axonal diameter and in particular the variance of axonal diameter correlated well with age. Axonal mitochondria also showed age-dependent signs of pathology. The mean diameter of axonal mitochondria increased, and aged axons often contained profiles of mitochondria with very few or no cristae. Astrocytic mitochondria remained normal even in very old nerves. Changes to axons and axonal mitochondria in young glaucomatous nerves were comparable with those of 18- to 30-month-old naïve mice. In addition to axons and mitochondria, aged and glaucomatous nerves showed thickening of the blood vessel basement membranes and increased deposition of basement membrane collagen.

Conclusions

On the ultrastructural level, the effects of age and elevated IOP are quite similar. One month of elevated IOP seems to have as strongly detrimental effects on the nerve as at least 18 months of normal aging.

Seeing the Hidden Lamina: Effects of Exsanguination on the Optic Nerve Head

Purpose

To introduce an experimental approach for direct comparison of the primate optic nerve head (ONH) before and after death by exsanguination.

Method

The ONHs of four eyes from three monkeys were imaged with spectral-domain optical coherence tomography (OCT) before and after exsanguination under controlled IOP. ONH structures, including the Bruch membrane (BM), BM opening, inner limiting membrane (ILM), and anterior lamina cribrosa (ALC) were delineated on 18 virtual radial sections per OCT scan. Thirteen parameters were analyzed: scleral canal at BM opening (area, planarity, and aspect ratio), ILM depth, BM depth; ALC (depth, shape index, and curvedness), and ALC visibility (globally, superior, inferior, nasal, and temporal quadrants).

Results

All four ALC quadrants had a statistically significant improvement in visibility after exsanguination (overall P < 0.001). ALC visibility increased by 35% globally and by 36%, 37%, 14%, and 4% in the superior, inferior, nasal, and temporal quadrants, respectively. ALC increased 4.1%, 1.9%, and 0.1% in curvedness, shape index, and depth, respectively. Scleral canals increased 7.2%, 25.2%, and 1.1% in area, planarity, and aspect ratio, respectively. ILM and BM depths averaged -7.5% and -55.2% decreases in depth, respectively. Most, but not all, changes were beyond the repeatability range.

Conclusions

Exsanguination allows for improved lamina characterization, especially in regions typically blocked by shadowing in OCT. The results also demonstrate changes in ONH morphology due to the loss of blood pressure. Future research will be needed to determine whether there are differences in ONH biomechanics before and after exsanguination and what those differences would imply.