Aqueous humor outflow: dynamics and disease

Aqueous humor as eye lymph: A crossroad between venous and lymphatic system

Aqueous humor (AQH) is a transparent fluid with characteristics similar to those of the interstitial fluid, which fills the eyeball posterior and anterior chambers and circulates in them from the sites of production to those of drainage. The AQH volume and pressure homeostasis is essential for the trophism of the ocular avascular tissues and their normal structure and function. Different AQH outflow pathways exist, including a main pathway, quite well defined anatomically and referred to as the conventional pathway, and some accessory pathways, more recently described and still not fully morphofunctionally understood, generically referred to as unconventional pathways. The conventional pathway is based on the existence of a series of conduits starting with the trabecular meshwork and Schlemm's Canal and continuing with a system of intrascleral and episcleral venules, which are tributaries to veins of the anterior segment of the eyeball. The unconventional pathways are mainly represented by the uveoscleral pathway, in which AQH flows through clefts, interstitial conduits located in the ciliary body and sclera, and then merges into the aforementioned intrascleral and episcleral venules. A further unconventional pathway, the lymphatic pathway, has been supported by the demonstration of lymphatic microvessels in the limbal sclera and, possibly, in the uvea (ciliary body, choroid) as well as by the ocular glymphatic channels, present in the neural retina and optic nerve. It follows that AQH may be drained from the eyeball through blood vessels (TM-SC pathway, US pathway) or lymphatic vessels (lymphatic pathway), and the different pathways may integrate or compensate for each other, optimizing the AQH drainage. The present review aims to define the state-of-the-art concerning the structural organization and the functional anatomy of all the AQH outflow pathways. Particular attention is paid to examining the regulatory mechanisms active in each of them. The new data on the anatomy and physiology of AQH outflow pathways is the key to understanding the pathophysiology of AQH outflow disorders and could open the way for novel approaches to their treatment.

Lipid mediators in glaucoma: Unraveling their diverse roles and untapped therapeutic potential

Glaucoma is a complex neurodegenerative disease characterized by optic nerve damage and visual field loss, and remains a leading cause of irreversible blindness. Elevated intraocular pressure (IOP) is a critical risk factor that requires effective management. Emerging research underscores dual roles of bioactive lipid mediators in both IOP regulation, and the modulation of neurodegeneration and neuroinflammation in glaucoma. Bioactive lipids, encompassing eicosanoids, specialized pro-resolving mediators (SPMs), sphingolipids, and endocannabinoids, have emerged as crucial players in these processes, orchestrating inflammation and diverse effects on aqueous humor dynamics and tissue remodeling. Perturbations in these lipid mediators contribute to retinal ganglion cell loss, vascular dysfunction, oxidative stress, and neuroinflammation. Glaucoma management primarily targets IOP reduction via pharmacological agents and surgical interventions, with prostaglandin analogues at the forefront. Intriguingly, additional lipid mediators offer promise in attenuating inflammation and providing neuroprotection. Here we explore these pathways to shed light on their intricate roles, and to unveil novel therapeutic avenues for glaucoma management.

Low expression of TGF-β2 and matrilin2 in human aqueous humour with acute primary angle closure

Primary angle-closure glaucoma (PACG) is the leading cause of irreversible blindness in the world. Angle closure induced by pupil block and secondary iris synechia is the fundamental pathology of the PACG. The molecular mechanisms of angle closure have not yet been clearly illustrated. This study was designed to investigate the protein difference in the aqueous humour and explore new biomarker of the PACG. Aqueous humour (AH) was collected from patients with acute primary angle closure (APAC) and cataract (n = 10 in APAC group) and patients with cataract only (n = 10 in control group). Samples were pooled and measured using label-free proteome technology. Then, the differentially expressed proteins (DEPs) were verified by ELISA using independent AH samples (n = 20 each group). More than 400 proteins were revealed in both groups through proteomics. Comparing the two groups, there were 91DEPs. These proteins participate in biological activities such as inflammation, fibrosis, nerve growth and degeneration and metabolism. We found that the expression of transforming growth factor-β2 and matrilin2 was downregulated in the APAC group. The two proteins are related to inflammation and extracellular matrix formation, which might be involved in angle closure. This study characterized DEPs in AH of the APAC and found a downregulated protein matrilin2.

Proteomic analysis of aqueous humor reveals novel regulators of diabetic macular edema

Diabetic macular edema (DME) is the most common cause of blindness in patients with diabetic retinopathy. To investigate the proteomic profiles of the aqueous humor (AH) of individuals with diabetic macular edema (DME), AH samples were collected from patients with non-diabetes mellitus (NDM), DM, nonproliferative diabetic retinopathy (NPDR), and DME. We performed comparative proteomic analyses using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and bioinformatics analyses. We identified 425 proteins in these AH samples, of which 113 showed changes in expression in DME compared with NDM, 95 showed changes in expression in DME vs. DM, and 84 showed changes in expression in DME compared with NPDR. The bioinformatics analysis suggested that DME is closely associated with platelet degranulation, oxidative stress-related pathway, and vascular-related pathways. Upregulation of haptoglobin (HP) and downregulation of fibrillin 1 (FBN1) were validated by ELISA. Receiver operating characteristic (ROC) analysis showed that HP and FBN1 could distinguish DME from NPDR with areas under the curve of 0.987 (p = 0.00608) and 0.791 (p = 0.00629), respectively. The findings provide potential clues for further analysis of the molecular mechanisms and the development of new treatments for DME. HP and FBN1 may be potential key proteins and therapeutic targets in human DME. The proteomics dataset generated has been deposited to the ProteomeXchange/iProX Consortium with Identifier: PXD033404/IPX0004353001.

Biologically Driven In Vivo Occlusion Design Provides a Reliable Experimental Glaucoma Model

Fluid flow transport through the trabecular meshwork tissues is a major regulator of intraocular pressure (IOP) modulation in healthy and glaucomatous individuals. Microbead occlusion models of ocular hypertension regulate aqueous humor drainage to induce high IOP to allow for in vivo study of pressure-related glaucomatous pathology. However, the reliability and application of current injectable microbeads are hindered by inadequate design of the beads-tissue interfaces to maintain a stable IOP elevation over the long term. Considering the graded, porous architecture and fluid transport of the trabecular meshwork, we developed a tailored, injectable "viscobeads" technique, which induced a sustained elevation of IOP for at least 8 weeks. These composite viscobeads contain a non-degradable polystyrene (PS) core for structural support and a biodegradable polylactic-co-glycolic acid (PLGA) viscoelastic surface. This approach enhances the obstruction of aqueous humor drainage through heterogeneous sizes of trabecular meshwork fenestrations and reliably modulates the magnitude and duration of ocular hypertension. In a mouse model, a single viscobeads injection resulted in sustained IOP elevation (average 21.4±1.39 mm Hg), leading to a 34% retinal ganglion cell (RGC) loss by 56 days. In an earlier stage of glaucoma progression, we conducted non-invasive electroretinography (ERG) recording and revealed glaucomatous progression by analyzing high-frequency oscillatory potentials. To further explore the application of the viscobeads glaucoma models, we assayed a series of genes through adeno-associated virus (AAV)-mediated screening in mice and assessed the impact of genetic manipulation on RGC survivals. CRISPR mediated disruption of the genes, PTEN, ATF3 and CHOP enhanced RGC survival while LIN 28 disruption negatively impacted RGC survival. This biologically driven viscobeads design provides an accessible approach to investigate chronic intraocular hypertension and glaucoma-like neurodegeneration and ultimately tenders the opportunity to evaluate genetic and pharmacological therapeutics.

Identification and validation of key biomarkers and potential therapeutic targets for primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a prevalent cause of blindness worldwide, resulting in degeneration of retinal ganglion cells and permanent damage to the optic nerve. However, the underlying pathogenetic mechanisms of POAG are currently indistinct, and there has been no effective nonsurgical treatment regimen. The objective of this study is to identify novel biomarkers and potential therapeutic targets for POAG. The mRNA expression microarray datasets GSE27276 and GSE138125, as well as the single-cell high-throughput RNA sequencing (scRNA-seq) dataset GSE148371 were utilized to screen POAG-related differentially expressed genes (DEGs). Functional enrichment analyses, protein-protein interaction (PPI) analysis, and weighted gene co-expression network analysis (WGCNA) of the DEGs were performed. Subsequently, the hub genes were validated at a single-cell level, where trabecular cells were annotated, and the mRNA expression levels of target genes in different cell clusters were analyzed. Immunofluorescence and quantitative real-time PCR (qPCR) were performed for further validation. DEGs analysis identified 43 downregulated and 32 upregulated genes in POAG, which were mainly enriched in immune-related pathways, oxidative stress, and endoplasmic reticulum (ER) stress. PPI networks showed that FN1 and DUSP1 were the central hub nodes, while GPX3 and VAV3 were screened out as hub genes through WGCNA and subsequently validated by qPCR. Finally, FN1, GPX3, and VAV3 were determined to be pivotal core genes via single-cell validation. The relevant biomarkers involved in the pathogenesis of POAG, may serve as potential therapeutic targets. Further studies are necessary to unveil the mechanisms underlying the expression variations of these genes in POAG.

Smart Contact Lenses as Wearable Ophthalmic Devices for Disease Monitoring and Health Management

The eye contains a complex network of physiological information and biomarkers for monitoring disease and managing health, and ocular devices can be used to effectively perform point-of-care diagnosis and disease management. This comprehensive review describes the target biomarkers and various diseases, including ophthalmic diseases, metabolic diseases, and neurological diseases, based on the physiological and anatomical background of the eye. This review also includes the recent technologies utilized in eye-wearable medical devices and the latest trends in wearable ophthalmic devices, specifically smart contact lenses for the purpose of disease management. After introducing other ocular devices such as the retinal prosthesis, we further discuss the current challenges and potential possibilities of smart contact lenses.

Ciliary body size in chronic angle-closure glaucoma

To examine the size of the ciliary body stroma (CBS) in dependence of the morphology of the anterior chamber angle in enucleated human eyes, we histomorphometrically examined human enucleated eyes. The study included 107 eyes (with a mean axial length of 25.1 ± 2.8 mm (range 21.0-36.0 mm). The anterior chamber angle was open in 68 eyes and it was closed and endothelialized in 39 eyes. The maximal CBS width (541 ± 210 µm versus 59 ± 179 µm; P < 0.001) and the minimal CBS width (214 ± 107 µm versus 17 ± 55 µm; P < 0.001) and maximal ciliary muscle height (593 ± 557 µm versus 293 ± 111 µm; P = 0.001) were significantly smaller in the angle-closure group than in the open-angle group. Maximal CBS width increased with presence of an open anterior chamber angle (beta: 0.82; B: 517; 95% CI 435, 599; P < 0.001) and longer axial length (beta: 0.17; B: 18.2; 95% CI 4.2, 32.2; P = 0.01). Minimal CBS width increased with the presence of an open anterior chamber angle (beta: 0.48; B: 131; 95% CI 80.4, 181; P < 0.001) and a larger maximal ciliary muscle height (beta: 0.33; B: 0.28; 95% CI 0.12, 0.44; P = 0.001). Maximal ciliary muscle height correlated with the maximal CBS height (beta: 0.35; B: 0.53; 95% CI 0.25, 0.81; P < 0.001). The findings suggest that the CBS size is markedly smaller in eyes with a chronically closed endothelialized anterior chamber angle than in eyes with open angles. The tightening of the angle in eyes with angle-closure may prevent the access of aqueous humor not only to the trabecular meshwork but also to the ciliary body and may reduce the uveoscleral or uveovortex outflow pathway.

Watching intense movies increase IOP of primary open angle glaucoma patients: A prospective study

PURPOSE

To investigate intraocular pressure (IOP) changes while viewing smartphone movies under artificial intelligence (AI) monitoring.

METHODS

In all, 48 subjects were recruited from the glaucoma clinic of Xianyou maternal and child health hospital from January 2018 to March 2020. The research consisted of three parts. In part 1, movies rated by the Motion Picture Association of America (MPAA) were viewed via smartphones of various screen sizes under AI supervision for 90minutes, at a distance of 40cm. IOP and biological parameters including anterior chamber angle, Schlemm's canal (SC) cross-sectional area, heart rate, systolic and diastolic blood pressures (SBP and DBP) were measured and analyzed. In part 2, blue-blocking glasses (BB glasses) were worn to repeat the above experiments. In part 3, the efficacy of AI in decreasing attention loss was analyzed. In addition, results were analyzed to determine whether interval breaks, prompted by AI, prevented IOP from rising.

RESULTS

In part 1, the mean IOP of primary open angle glaucoma (POAG) subjects' right eyes significantly increased by 4.828 and 4.974mmHg after watching R and NC-17 movies, respectively. In their left eyes, it increased by 2.876 and 5.767 after watching R and NC-17 movies, respectively. The maximum IOP difference was also increased by 4.782 and 4.510 on right and left eyes, respectively, after viewing NC-17 movies on a 6.1-inch screen. Furthermore, the SC became narrower, whereas heart rate, DBP and SBP increased in the POAG group. In addition, maximum IOP difference was significantly correlated with SC cross-sectional area, DBP and SBP in the POAG group. In part 2, symptom scores were improved by BB glasses; however, IOP was not decreased. In part 3, attention loss was significantly decreased by AI monitoring. On the contrary, AI also prevented IOP from rising via promoting interval rest.

CONCLUSION

Watching adult movies (NC-17) can significantly increase the IOP of POAG patients. AI can prevent IOP from rising by promoting interval rest when viewing NC-17 movies.

Novel discovery of a lymphatic bridge connecting Schlemm's canal to limbal and conjunctival lymphatic pathway

PURPOSE

Schlemm's canal (SC) is a critical structure regulating aqueous humor (AH) drainage and intraocular pressure (IOP). It is known that in the conventional outflow pathway, AH flows from SC to episcleral veins. We recently reported a high-resolution three-dimensional (3D) imaging technology for intact eyeballs, SC and ocular surface. Using this advanced technology, we herein report the discovery of a new structure, termed lymphatic bridge, that directly connects SC to the limbal and conjunctival lymphatic pathway. Further investigation on this novel outflow pathway may provide new mechanisms and therapeutic approaches for glaucoma.

METHODS

As reported previously, intact eyeballs were harvested from Prox-1-GFP (green fluorescent protein) mice and processed by a tissue clearing technique with CLARITY. Samples were immunolabeled with specific antibodies for CD31 (pan-endothelial marker) and LYVE-1 (lymphatic vessel endothelial hyaluronan receptor-1) and imaged by light-sheet fluorescent microscopy. The limbal areas were examined to locate connecting channels between SC and limbal and conjunctival lymphatic vessels. Moreover, in vivo anterior chamber dye injection was performed with Texas Red dextran for functional analysis on AH outflow.

RESULTS

A novel lymphatic bridge structure that expressed both Prox-1 and LYVE-1 was discovered between the SC and limbal lymphatic vessels connected with conjunctival lymphatic pathway. Results from the anterior chamber dye injection also confirmed AH drainage into the conjunctival lymphatic outflow pathway.

CONCLUSIONS

This study provides the first evidence on the direct connection between SC and conjunctival lymphatic pathway. This new pathway is distinctive from the traditional episcleral vein pathway and merits further investigation.

Morphological and biomechanical analyses of the human healthy and glaucomatous aqueous outflow pathway: Imaging-to-modeling

BACKGROUND AND OBJECTIVE

Intraocular pressure (IOP) is maintained via a dynamic balance between the production of aqueous humor and its drainage through the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway. Primary open angle glaucoma (POAG) is often associated with IOP elevation that occurs due to an abnormally high outflow resistance across the outflow pathway. Outflow tissues are viscoelastic and actively interact with aqueous humor dynamics through a two-way fluid-structure interaction coupling. While glaucoma affects the morphology and stiffness of the outflow tissues, their biomechanics and hydrodynamics in glaucoma eyes remain largely unknown. This research aims to develop an image-to-model method allowing the biomechanics and hydrodynamics of the conventional aqueous outflow pathway to be studied.

METHODS

We used a combination of X-ray computed tomography and scanning electron microscopy to reconstruct high-fidelity, eye-specific, 3D microstructural finite element models of the healthy and glaucoma outflow tissues in cellularized and decellularized conditions. The viscoelastic TM/JCT/SC complex finite element models with embedded viscoelastic beam elements were subjected to a physiological IOP load boundary; the stresses/strains and the flow state were calculated using fluid-structure interaction and computational fluid dynamics.

RESULTS

Based on the resultant hydrodynamics parameters across the outflow pathway, the primary site of outflow resistance in healthy eyes was in the JCT and immediate vicinity of the SC inner wall, while the majority of the outflow resistance in the glaucoma eyes occurred in the TM. The TM and JCT in the glaucoma eyes showed 1.32-fold and 1.13-fold larger beam thickness and smaller trabecular space size (2.24-fold and 1.50-fold) compared to the healthy eyes.

CONCLUSIONS

Characterizing the accurate morphology of the outflow tissues may significantly contribute to constructing more accurate, robust, and reliable models, that can eventually help to better understand the dynamic IOP regulation, hydrodynamics of the aqueous humor, and outflow resistance dynamic in the human eyes. This model demonstrates proof of concept for determining changes to outflow resistance in healthy and glaucomatous tissues and thus may be utilized in larger cohorts of donor tissues where disease specificity, race, age, and gender of the eye donors may be accounted for.

Dexamethasone Modulates the Dynamics of Wnt Signaling in Human Trabecular Meshwork Cells

Trabecular meshwork (TM) tissue is highly specialized, and its structural integrity is crucial for maintaining homeostatic intraocular pressure (IOP). The administration of glucocorticoids, such as dexamethasone (DEX), can perturb the TM structure and significantly increase IOP in susceptible individuals, resulting in ocular diseases such as steroid-induced glaucoma, a form of open-angle glaucoma. Although the exact mechanism involved in steroid-induced glaucoma remains elusive, increasing evidence suggests that DEX may act through various signaling cascades in TM cells. Despite uncertainty surrounding the specific process by which steroid-induced glaucoma occurs, there is growing evidence to indicate that DEX can impact multiple signaling pathways within TM cells. In this study, we examined the impact of DEX treatment on the Wnt signaling pathway in TM cells, given that Wnt signaling has been reported to play a crucial role in regulating extracellular matrix (ECM) levels in the TM. To further elucidate the role of Wnt signaling in the glaucomatous phenotype, we examined mRNA expression patterns between Wnt signaling markers AXIN2 and sFRP1 and DEX-mediated induction of myocilin (MYOC) mRNA and protein levels over 10 days in DEX-treated primary TM cells. We observed a sequential pattern of peak expression between AXIN2, sFRP1, and MYOC. Based on the study, we propose that sFRP1 upregulation could be a result of a negative feedback mechanism generated by stressed TM cells to suppress abnormal Wnt signaling activities.

Acoustic radiation force optical coherence elastography: A preliminary study on biomechanical properties of trabecular meshwork

Evaluating biomechanical properties of trabecular meshwork (TM) is of great significance for understanding the mechanism of aqueous humor circulation and its relationship to some eye diseases such as glaucoma; however, there is almost no relevant study due to the lack of clinical measurement tool. In this paper, an acoustic radiation force optical coherence elastography (ARF-OCE) system is developed with the advantages of noninvasive detection, high resolution, high sensitivity, and high-speed imaging, by which elastic modulus of the porcine and human TMs is accurately quantified. As the first OCE imaging of TM, our study demonstrates that ARF-OCE may be an effective approach to advance the research of diseases related to aqueous humor circulation.

Extracellular vesicles as a new horizon in the diagnosis and treatment of inflammatory eye diseases: A narrative review of the literature

Extracellular vesicles include exosomes, microvesicles, and apoptotic bodies. Their cargos contain a diverse variety of lipids, proteins, and nucleic acids that are involved in both normal physiology and pathology of the ocular system. Thus, studying extracellular vesicles may lead to a more comprehensive understanding of the pathogenesis, diagnosis, and even potential treatments for various diseases. The roles of extracellular vesicles in inflammatory eye disorders have been widely investigated in recent years. The term “inflammatory eye diseases” refers to a variety of eye conditions such as inflammation-related diseases, degenerative conditions with remarkable inflammatory components, neuropathy, and tumors. This study presents an overview of extracellular vesicles’ and exosomes’ pathogenic, diagnostic, and therapeutic values in inflammatory eye diseases, as well as existing and potential challenges.

Anatomical and physiological considerations in scleral lens wear: Intraocular pressure

Intraocular pressure (IOP) is maintained through complex and interrelated systems which control aqueous production and drainage, and it has been suggested that scleral lens (SL) wear may disrupt these vital homeostatic processes. This review provides an overview of anatomical and physiological processes that control IOP, identifies potential effects of SLs on these regulatory mechanisms, and examines studies that have attempted to quantify the effect of SLs on IOP. Lack of access to the cornea during SL wear makes accurate assessment of IOP challenging; therefore, a range of different assessment techniques and instruments have been employed to quantify IOP during and following SL wear. Some studies have evaluated IOP using standard techniques prior to lens application and following lens removal, or through a large central fenestration. Other studies have utilised instruments that facilitate assessment of IOP on the peripheral cornea or conjunctiva overlying the sclera (e.g. Schiotz, transpalpebral, and pneumatonometry). Two studies have recently evaluated changes in optic nerve structure during SL wear. Conflicting results have been reported on this topic, much of which examines changes in IOP in healthy subjects over limited periods of time. Currently, only a few studies have reported on long-term effects of SL wear on IOP in habitual SL wearers (after lens removal). Future research in this area must not only consider the fact that ocular conditions treated with SLs may potentially alter corneal biomechanical properties which can influence IOP, but also that these properties may be further altered by SL wear. Monitoring other risk factors for glaucoma (permanent alterations in optic nerve physiology, visual field defects) could provide a more comprehensive assessment of potentially increased risk of glaucomatous optic neuropathy due to SL wear. Ongoing clinical assessment of optic nerve structure and function is advisable in patients at risk for glaucoma who require SLs.

The Influence of Near Vision Tasks on Intraocular Pressure in Normal Subjects and Glaucoma Patients

Purpose

To investigate the effect of static accommodative tasks on intraocular pressure (IOP) of glaucomatous and normal eyes.

Methods

Four groups of subjects categorized as primary open-angle glaucoma (POAG), primary angle-closure suspects (PACS), normal age-matched controls, and normal young adults (NYA; age < 40 years) were enrolled. The baseline IOPs were measured after the subjects were looking at a distant target for 15 min. Static accommodation was obtained by execution of near vision tasks (reading at 33 cm in daylight [300 lux] for 60 min). IOPs were measured at 15, 30, 45, and 60 min intervals while accommodating and then measured again after 15 min of relaxing accommodation while looking at a distant target.

Results

One-hundred and eighteen eyes of 98 subjects were recruited. The study groups consisted of the following categories: 25 POAG (46 eyes), 24 PACS (47 eyes), 25 matched controls (50 eyes), and 24 NYA (48 eyes). Within all groups, the mean IOP decreased throughout the accommodation period at all time points. Maximum IOP reduction after accommodation was detected at the 30-min time among the POAG subjects, at the 45-min time in the PACS and matched control groups, and at 15 min after the relaxation of accommodation in the NYA group. IOP reduction levels showed no statistically significant difference among POAG, PACS, and the normal matched groups in their response to accommodation. However, NYA had significantly lower IOP and greater IOP reduction after the resting period (relaxation of accommodation).

Conclusion

Static accommodative tasks can significantly reduce IOP in normal, POAG, and PACS individuals. Encouraging glaucoma patients to practice periodical near vision tasks could be viewed as an adjunctive measure for glaucoma management.

Viscoelastic Biomechanical Properties of the Conventional Aqueous Outflow Pathway Tissues in Healthy and Glaucoma Human Eyes

Background: Although the tissues comprising the ocular conventional outflow pathway have shown strong viscoelastic mechanical response to aqueous humor pressure dynamics, the viscoelastic mechanical properties of the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm’s canal (SC) inner wall are largely unknown. Methods: A quadrant of the anterior segment from two human donor eyes at low- and high-flow (LF and HF) outflow regions was pressurized and imaged using optical coherence tomography (OCT). A finite element (FE) model of the TM, the adjacent JCT, and the SC inner wall was constructed and viscoelastic beam elements were distributed in the extracellular matrix (ECM) of the TM and JCT to represent anisotropic collagen. An inverse FE-optimization algorithm was used to calculate the viscoelastic properties of the ECM/beam elements such that the TM/JCT/SC model and OCT imaging data best matched over time. Results: The ECM of the glaucoma tissues showed significantly larger time-dependent shear moduli compared to the heathy tissues. Significantly larger shear moduli were also observed in the LF regions of both the healthy and glaucoma eyes compared to the HF regions. Conclusions: The outflow tissues in both glaucoma eyes and HF regions are stiffer and less able to respond to dynamic IOP.

Anti-glaucoma medications lowered decorin and altered profibrotic proteins in human tenon's fibroblasts

Long term exposure to anti-glaucoma medications (AGMs) leads to an increase in extracellular matrix (ECM) accumulation in primary glaucoma patients. This study aims to evaluate the effect of topical AGMs in primary human tenon's fibroblasts (HTFs) and analyze the expression of profibrotic and anti-fibrotic proteins. Primary HTFs were cultured from patients undergoing cataract (control) and trabeculectomy. The different types of AGMs in single/multiple combinations (BB, PG, AA, CAI, CH, combinations of 3- PG + AA + CAI, 4A- BB + PG + AA + CAI, 4B- BB + PG + CAI + CH and 5- BB + PG + AA + CAI + CH) on chronic exposure were tested for cell viability using MTT assay and morphological alterations. Profibrotic proteins mainly SPARC, LOXL2, COL1A1 and anti-fibrotic DCN were analyzed in treated HTFs using q-PCR and ELISA. Sirius red staining and collagen gel contraction (CGC) assay were performed to assess collagen synthesis and the contractility of HTFs, respectively. Except for AA and CH, the other AGMs at a higher concentration were found to decrease the cell viability of HTFs. The morphology of HTFs were altered on exposure to BB, CH and AA; Profibrotic proteins i.e., SPARC, LOXL2 and COL1A1 were significantly increased (p < 0.05) on exposure to a combination of AGMs with TGF-β1, whereas the anti-fibrotic DCN expression was significantly lowered (p < 0.05) in single/multiple AGM exposure. Sirius red staining showed increased collagen synthesis with combinations of AGMs with TGF-β1. Meanwhile, HTFs showed increased collagen gel contraction with TGF-β1, CAI and CH. This study reveals that altered profibrotic proteins, with significantly lowered DCN on chronic exposure of AGMs in HTFs.

Geometric Model and Numerical Study of Aqueous Humor Hydrodynamics in the Human Eye

The flow of aqueous humor (AH) in the human eye plays a key role in the process of transporting nutrients to the intraocular tissues and maintaining normal intraocular pressure. The pathogenesis of many ophthalmic diseases is also closely related to the flow of AH. Therefore, it is of great significance to study the mechanism of AH dynamics in the human eye. In this paper, we used image processing technology to denoise and segment the anterior segment optical coherence tomography (AS-OCT) images and established a geometric model based on the human eye. At the same time, a model of AH dynamics in the human eye based on the lattice Boltzmann (LB) method was proposed. Then, we simulated the AH flow in the human eye with different morphological structures and different physical properties and analyzed the factors that affect the AH flow, including the shape of anterior chamber (AC), the crypts of iris, the indentation of cornea, the permeability of trabecular meshwork (TM), the secretion rate of AH, and the viscosity of AH. The results showed that the changes in eye tissue morphological structures and physical properties would affect the flow of AH. For example, the maximum velocity of AH flow decreases with the increases in cornea deformation. When the distance of cornea indentation changes from 0.3 mm to 0.5 mm, the maximum velocity of AH reduces by 17%. In the asymmetrical AC, the AH will form two different vortices. In the crypts of the iris, we found that the AH flow forms small vortices, a phenomenon that has not been reported in other papers. In addition, we found that the intraocular pressure (IOP) decreases with the increase of the TM permeability and increases with the increase of the AH secretion rate, and it is not sensitive to changes in the viscosity of AH.

Pathogenesis of glaucoma: Extracellular matrix dysfunction in the trabecular meshwork-A review

The trabecular meshwork regulates aqueous humour outflow from the anterior chamber of the eye. It does this by establishing a tunable outflow resistance, defined by the interplay between cells and their extracellular matrix (ECM) milieu, and the molecular interactions between ECM proteins. During normal tissue homeostasis, the ECM is remodelled and trabecular cell behaviour is modified, permitting increased aqueous fluid outflow to maintain intraocular pressure (IOP) within a relatively narrow physiological pressure. Dysfunction in the normal homeostatic process leads to increased outflow resistance and elevated IOP, which is a primary risk factor for glaucoma. This review delineates some of the changes in the ECM that lead to gross as well as some more subtle changes in the structure and function of the ECM, and their impact on trabecular cell behaviour. These changes are discussed in the context of outflow resistance and glaucoma.

Application of an organotypic ocular perfusion model to assess intravitreal drug distribution in human and animal eyes

Intravitreal (ITV) drug delivery is a new cornerstone for retinal therapeutics. Yet, predicting the disposition of formulations in the human eye remains a major translational hurdle. A prominent, but poorly understood, issue in pre-clinical ITV toxicity studies is unintended particle movements to the anterior chamber (AC). These particles can accumulate in the AC to dangerously raise intraocular pressure. Yet, anatomical differences, and the inability to obtain equivalent human data, make investigating this issue extremely challenging. We have developed an organotypic perfusion strategy to re-establish intraocular fluid flow, while maintaining homeostatic pressure and pH. Here, we used this approach with suitably sized microbeads to profile anterior and posterior ITV particle movements in live versus perfused porcine eyes, and in human donor eyes. Small-molecule suspensions were then tested with the system after exhibiting differing behaviours in vivo. Aggregate particle size is supported as an important determinant of particle movements in the human eye, and we note these data are consistent with a poroelastic model of bidirectional vitreous transport. Together, this approach uses ocular fluid dynamics to permit, to our knowledge, the first direct comparisons between particle behaviours from human ITV injections and animal models, with potential to speed pre-clinical development of retinal therapeutics.

Characterizing the metabolic profile of dexamethasone treated human trabecular meshwork cells

The trabecular meshwork (TM) is the leading site of aqueous humor outflow in the eye and plays a critical role in maintaining normal intraocular pressure. When the TM fails to maintain normal intraocular pressure, glaucoma may develop. Mitochondrial damage has previously been found in glaucomatous TM cells; however, the precise metabolic activity of glaucomatous TM cells has yet to be quantitatively assessed. Using dexamethasone (Dex) treated primary human TM cells to model glaucomatous TM cells, we measure the respiratory and glycolytic activity of Dex-treated TM cells with an extracellular flux assay. We found that Dex-treated TM cells had quantifiably altered metabolic profiles, including increased spare respiratory capacity and ATP production rate from oxidative phosphorylation. Therefore, we propose that reversing or preventing these metabolic changes may represent an avenue for future research.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Report: The effects of topical pleurotus tuberregium (PT) aqueous extract on intraocular pressure in monkeys

PURPOSE

In earlier experiments in Nigeria, aqueous extract of Pleurotus tuber-regium (PT) had been shown to lower intra ocular pressure (IOP) in a feline model. The aim of the current study was to determine whether PT had the same or a similar IOP-lowering effect in ocularly normal non-human primates.

METHODS

Four monkeys were treated twice daily for 4 days with 2 x 20 μl drops of 50 mg/ml PT (pH = 4.3). The monkeys were sedated with 5-10 mg/kg ketamine HCl IM. PT was administered to the right eye and BSS to the left eye. Baseline IOP was measured just prior to beginning treatment, and on day 5 before treatment and then hourly for 3 hours, beginning 1 hour after treatment. SLEs were performed at baseline and on day 5 pre- and 3 hours post-treatment.

RESULTS

There was no significant difference between IOP in treated vs control eyes in the protocol. There were no adverse effects or toxicity as seen by SLE.

CONCLUSIONS

The inability of the extract to lower IOP in monkeys, in contrast to ocular hypertensive cats in an earlier study, could be due to species differences or duration of treatment. Since no adverse effects were observed in the monkeys, further studies with varying durations and dosages are recommended.

Pharmacological Profile and Ocular Hypotensive Effects of Cromakalim Prodrug 1, a Novel ATP-Sensitive Potassium Channel Opener, in Normotensive Dogs and Nonhuman Primates

Purpose: To evaluate pharmacokinetic parameters and ocular hypotensive effects of cromakalim prodrug 1 (CKLP1) in normotensive large animal models. Methods: Optimal CKLP1 concentration was determined by dose response and utilized in short- (5-8 days) and long-term (60 days) evaluation in hound dogs (n = 5) and African Green Monkeys (n = 5). Blood pressure was recorded 3-5 times per week with a tail cuff. Concentrations of CKLP1 and the parent compound levcromakalim were assessed in hound dog plasma and select tissues by LC-MS/MS after bilateral ocular treatment with CKLP1 for 8 days. Pharmacokinetic parameters were calculated from days 1, 4, and 8 data. After necropsy, histology was assessed in 43 tissue samples from each animal. Results: In hound dogs and African Green monkeys, 10 mM CKLP1 (optimal concentration) significantly lowered intraocular pressure (IOP) by 18.9% ± 1.1% and 16.7% ± 6.7%, respectively, compared with control eyes (P < 0.05). During treatment, no significant change in systolic or diastolic blood pressure was observed in either species (P > 0.1). Average values for half-life of CKLP1 was 295.3 ± 140.4 min, Cmax, 10.5 ± 1.6 ng/mL, and area under the concentration vs. time curve (AUClast) 5261.4 ± 918.9 ng·min/mL. For levcromakalim, average values of half-life were 96.2 ± 27 min, Cmax 1.2 ± 0.2 ng/mL, and AUClast 281.2 ± 110.8 ng·min/mL. No significant pathology was identified. Conclusions: CKLP1 lowered IOP in hound dogs and African green monkeys with no effect on systemic blood pressure. Ocular topical treatment of CKLP1 showed excellent tolerability even after extended treatment periods.

IOP and Optic Nerve Head Morphology during Scleral Lens Wear

SIGNIFICANCE

Scleral lenses (SLs) are increasing in scope, and understanding their ocular health impact is imperative. The unique fit of an SL raises concern that the landing zone causes compression of conjunctival tissue that can lead to resistance of aqueous humor outflow and increased intraocular pressure (IOP).

PURPOSE

This study aimed to assess changes in optic nerve head morphology as an indirect assessment of IOP and evaluate other IOP assessment methods during SL wear.

METHODS

Twenty-six healthy adults wore SL on one randomly selected eye for 6 hours, whereas the fellow eye served as a control. Global minimum rim width (optical coherence tomography) and IOP (Icare, Diaton) were measured at baseline, 2 and 6 hours after SL application, and again after SL removal. Central corneal thickness, anterior chamber depth, and fluid reservoir depth were monitored.

RESULTS

Minimum rim width thinning was observed in the test (-8 μm; 95% confidence interval [CI], -11 to -6 μm) and control (-6 μm; 95% CI, -9 to -3 μm) eyes after 6 hours of SL wear (P < .01), although the magnitude of thinning was not significantly greater in the lens-wearing eyes (P = .09). Mean IOP (Icare) significantly increased +2 mmHg (95% CI, +1 to +3 mmHg) in the test eyes (P = .002), with no change in the control eyes. Mean IOP changes with Diaton were +0.3 mmHg (95% CI, -0.9 to +3.2 mmHg) in the test eyes and +0.4 mmHg (95% CI, -0.8 to +1.7 mmHg) in the control eyes. However, Diaton tonometry showed poor within-subject variation and poor correlation with Icare. No clinically significant changes were observed in central corneal thickness or anterior chamber depth.

CONCLUSIONS

This study suggests that SLs have a minimal effect on IOP homeostasis in the normal eye during SL wear and an insignificant impact on the optic nerve head morphology in healthy adult eyes.

Trabecular meshwork's collagen network formation is inhibited by non-pigmented ciliary epithelium-derived extracellular vesicles

The present research aims to determine whether the application of non‐pigmented ciliary epithelium cells derived extracellular vesicles to human trabecular meshwork cells affects the formation and secretion of collagen type I to the extracellular matrix formation. Following the extraction of non‐pigmented ciliary epithelium derived extracellular vesicles by a precipitation method, their size and concentration were determined using tunable resistive pulse sensing technology. Extracellular vesicles were incubated with trabecular meshwork cells for 3 days. Morphological changes of collagen type I in the extracellular matrix of trabecular meshwork cells were visualized using confocal microscopy and scanning electron microscopy. A Sirius Red assay was used to determine the total amount of collagen. Finally, collagen type I expression levels in the extracellular matrix of trabecular meshwork cells were quantified by cell western analysis. We found that non‐pigmented ciliary epithelium extracellular vesicles were very effective at preventing collagen fibres formation by the trabecular meshwork cells, and their secretion to the extracellular matrix was significantly reduced (P < .001). Morphological changes in the extracellular matrix of trabecular meshwork cells were observed. Our study indicates that non‐pigmented ciliary epithelium extracellular vesicles can be used to control collagen type I fibrillogenesis in trabecular meshwork cells. These fibrils net‐like structure is responsible for remodelling the extracellular matrix. Moreover, we suggest that targeting collagen type I fibril assembly may be a viable treatment for primary open‐angle glaucoma abnormal matrix deposition of the extracellular matrix.

Crosstalk between MicroRNA and Oxidative Stress in Primary Open-Angle Glaucoma

Reactive oxygen species (ROS) plays a key role in the pathogenesis of primary open-angle glaucoma (POAG), a chronic neurodegenerative disease that damages the trabecular meshwork (TM) cells, inducing apoptosis of the retinal ganglion cells (RGC), deteriorating the optic nerve head, and leading to blindness. Aqueous humor (AH) outflow resistance and intraocular pressure (IOP) elevation contribute to disease progression. Nevertheless, despite the existence of pharmacological and surgical treatments, there is room for the development of additional treatment approaches. The following review is aimed at investigating the role of different microRNAs (miRNAs) in the expression of genes and proteins involved in the regulation of inflammatory and degenerative processes, focusing on the delicate balance of synthesis and deposition of extracellular matrix (ECM) regulated by chronic oxidative stress in POAG related tissues. The neutralizing activity of a couple of miRNAs was described, suggesting effective downregulation of pro-inflammatory and pro-fibrotic signaling pathways, including nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), transforming growth factor-beta 2 (TGF-β2), Wnt/β-Catenin, and PI3K/AKT. In addition, with regards to the elevated IOP in many POAG patients due to increased outflow resistance, Collagen type I degradation was stimulated by some miRNAs and prevented ECM deposition in TM cells. Mitochondrial dysfunction as a consequence of oxidative stress was suppressed following exposure to different miRNAs. In contrast, increased oxidative damage by inhibiting the mTOR signaling pathway was described as part of the action of selected miRNAs. Summarizing, specific miRNAs may be promising therapeutic targets for lowering or preventing oxidative stress injury in POAG patients.

Non-pigmented ciliary epithelium derived extracellular vesicles uptake mechanism by the trabecular meshwork

Consistent with increasing findings, extracellular vesicles (EVs), consider as a major constituents of the aqueous humor, have a role as signaling mediators in glaucoma. Following secretion, EVs hold immense promise for utilization as bio-therapeutics and drug delivery vehicles due to their nature as biological nanoparticles that facilitate intercellular molecular transport. Yet, the specific pathway utilizing for transferring signals by EVs in the ocular drainage system is not fully understood. Hence, the objective of this study was to examine internalization mechanisms by which Non-Pigmented Ciliary Epithelium (NPCE)-derived EVs deliver their signals to the Trabecular Meshwork (TM) cells. EVs were isolated and size and concentration were determined. Internalization study of treated EVs with Proteinase-K to achieve removal of surface membrane proteins on EVs was conducted. Energy dependent uptake mechanism was examined under various temperatures. Using uptake inhibitors endocytosis, phagocytosis, and Wnt-TGFβ2 signaling were investigated. TM cells exposed to NPCE EVs demonstrate a significant decrease in the levels of two proteins in two Wnt-TGFb2 signaling proteins levels: p-GSK3β and β-catenin. A significant decrease in the uptake by TM cells of Proteinase-K-treated EVs was found, followed by attenuation of the Wnt-TGFβ2 proteins expression. Energy dependent uptake revealed a significant decrease in EVs internalization. The exposure of TM cells to endocytosis uptake inhibitors abolished the decrease of the Wnt-TGFβ2 proteins levels. Exposure to phagocytosis uptake inhibitor resulted in a partial inhibition of NPCE EVs effect in TM cells. The attenuation of proteins expression levels following uptake inhibitors treatment or EVs membrane proteins removal indicates that Wnt-TGFβ2 signaling in TM cells is mediated through NPCE EVs surface proteins in an active manner that involves endocytosis-dependent routes.

A Surrogate Matrix-Based Approach Toward Multiplexed Quantitation of an sGC Stimulator and cGMP in Ocular Tissue and Plasma

A liquid chromatography-tandem mass spectrometry assay was developed and qualified for the multiplexed quantitation of a small molecule stimulator of soluble guanylate cyclase (sGC) and its target engagement biomarker, 3',5'-cyclic guanosine monophosphate (cGMP), in ocular tissues and plasma from a single surrogate matrix calibration curve. A surrogate matrix approach was used in this assay due to the limited quantities of blank ocular matrices in a discovery research setting. After optimization, the assay showed high accuracy, precision, and recovery as well as parallelism between the surrogate matrix and the biological matrices (rabbit plasma, vitreous, and retina-choroid). This assay provided pharmacokinetic and target engagement data after intravitreal administration of the sGC stimulator. The nitric oxide-sGC-cGMP pathway is a potential target to address glaucoma. Increasing sGC-mediated production of cGMP could improve aqueous humor outflow and ocular blood flow. The sGC stimulator showed dose-dependent exposure in rabbit vitreous, retina-choroid, and plasma. The cGMP exhibited a delayed yet sustained increase in vitreous humor but not retina-choroid. Multiplexed measurement of both pharmacokinetic and target engagement analytes reduced animal usage and provided improved context for interpreting PK and PD relationships.

CNS axonal degeneration and transport deficits at the optic nerve head precede structural and functional loss of retinal ganglion cells in a mouse model of glaucoma

BACKGROUND

Glaucoma is a leading neurodegenerative disease affecting over 70 million individuals worldwide. Early pathological events of axonal degeneration and retinopathy in response to elevated intraocular pressure (IOP) are limited and not well-defined due to the lack of appropriate animal models that faithfully replicate all the phenotypes of primary open angle glaucoma (POAG), the most common form of glaucoma. Glucocorticoid (GC)-induced ocular hypertension (OHT) and its associated iatrogenic open-angle glaucoma share many features with POAG. Here, we characterized a novel mouse model of GC-induced OHT for glaucomatous neurodegeneration and further explored early pathological events of axonal degeneration in response to elevated IOP.

METHODS

C57BL/6 J mice were periocularly injected with either vehicle or the potent GC, dexamethasone 21-acetate (Dex) once a week for 10 weeks. Glaucoma phenotypes including IOP, outflow facility, structural and functional loss of retinal ganglion cells (RGCs), optic nerve (ON) degeneration, gliosis, and anterograde axonal transport deficits were examined at various stages of OHT.

RESULTS

Prolonged treatment with Dex leads to glaucoma in mice similar to POAG patients including IOP elevation due to reduced outflow facility and dysfunction of trabecular meshwork, progressive ON degeneration and structural and functional loss of RGCs. Lowering of IOP rescued Dex-induced ON degeneration and RGC loss, suggesting that glaucomatous neurodegeneration is IOP dependent. Also, Dex-induced neurodegeneration was associated with activation of astrocytes, axonal transport deficits, ON demyelination, mitochondrial accumulation and immune cell infiltration in the optic nerve head (ONH) region. Our studies further show that ON degeneration precedes structural and functional loss of RGCs in Dex-treated mice. Axonal damage and transport deficits initiate at the ONH and progress toward the distal end of ON and target regions in the brain (i.e. superior colliculus). Most of anterograde transport was preserved during initial stages of axonal degeneration (30% loss) and complete transport deficits were only observed at the ONH during later stages of severe axonal degeneration (50% loss).

CONCLUSIONS

These findings indicate that ON degeneration and transport deficits at the ONH precede RGC structural and functional loss and provide a new potential therapeutic window for rescuing neuronal loss and restoring health of damaged axons in glaucoma.

Rho-kinase (ROCK) Inhibitors - A Neuroprotective Therapeutic Paradigm with a Focus on Ocular Utility

BACKGROUND

Glaucoma is a progressive optic neuropathy causing visual impairment and Retinal Ganglionic Cells (RGCs) death gradually posing a need for neuroprotective strategies to minimize the loss of RGCs and visual field. It is recognized as a multifactorial disease, Intraocular Pressure (IOP) being the foremost risk factor. ROCK inhibitors have been probed for various possible indications, such as myocardial ischemia, hypertension, kidney diseases. Their role in neuroprotection and neuronal regeneration has been suggested to be of value in the treatment of neurological diseases, like spinal-cord injury, Alzheimer's disease and multiple sclerosis but recently Rho-associated Kinase inhibitors have been recognized as potential antiglaucoma agents.

EVIDENCE SYNTHESIS

Rho-Kinase is a serine/threonine kinase with a kinase domain which is constitutively active and is involved in the regulation of smooth muscle contraction and stress fibre formation. Two isoforms of Rho-Kinase, ROCK-I (ROCK β) and ROCK-II (ROCK α) have been identified. ROCK II plays a pathophysiological role in glaucoma and hence the inhibitors of ROCK may be beneficial to ameliorate the vision loss. These inhibitors decrease the intraocular pressure in the glaucomatous eye by increasing the aqueous humour outflow through the trabecular meshwork pathway. They also act as anti-scarring agents and hence prevent post-operative scarring after the glaucoma filtration surgery. Their major role involves axon regeneration by increasing the optic nerve blood flow which may be useful in treating the damaged optic neurons. These drugs act directly on the neurons in the central visual pathway, interrupting the RGC apoptosis and therefore serve as a novel pharmacological approach for glaucoma neuroprotection.

CONCLUSION

Based on the results of high-throughput screening, several Rho kinase inhibitors have been designed and developed comprising of diverse scaffolds exhibiting Rho kinase inhibitory activity from micromolar to subnanomolar ranges. This diversity in the scaffolds with inhibitory potential against the kinase and their SAR development will be intricated in the present review. Ripasudil is the only Rho kinase inhibitor marketed to date for the treatment of glaucoma. Another ROCK inhibitor AR-13324 has recently passed the clinical trials whereas AMA0076, K115, PG324, Y39983 and RKI-983 are still under trials. In view of this, a detailed and updated account of ROCK II inhibitors as the next generation therapeutic agents for glaucoma will be discussed in this review.

Differential DNA methylation patterns in human Schlemm's canal endothelial cells with glaucoma

Purpose

Schlemm's canal (SC) endothelial cells derived from donors with or without glaucoma showed different mechanical properties and gene expression. As an important contributor to the regulation of intraocular pressure (IOP) and pathogenesis of primary open-angle glaucoma (POAG), the heritable key epigenetic changes, methylation may play an important role in the physiologic function of SC cells. This study aims to identify differentially methylated CpG sites (DMSs) in primary cultures of human SC cells with or without glaucoma.

Methods

We examined the methylation pattern of seven strains of primary human cells (two glaucoma and five normal SC cell samples), which were isolated and characterized using established protocols. DNA methylation was profiled using Illumina Human Methylation 450 BeadChip. Raw data were extracted and exported using Illumina GenomeStudio software. After quantile normalization, DNA methylation data were analyzed using R package RnBeads in Bioconductor. DMSs were filtered with p ≤ 1E-5, methylation change ≥ 0.1, and false discovery rate ≤ 0.05. The closest genes and the location of each CpG site were annotated using R package FDb.InfiniumMethylation.hg19. Gene Ontology and pathway analysis was performed using WebGestalt. Selected DMSs were validated using the Zymo qMethyl kit.

Results

We used five non-glaucoma and two glaucomatous SC cell samples to profile genome-wide DNA methylation using Illumina Infinium Methylation BeadChips. Principle component analysis showed the separation between the glaucoma and control samples. After quality control and differential analysis, we identified 298 highly significant DMSs (p ≤ 1E-5). Among them, 221 DMSs were within 1 kb of a nearby gene. Gene Ontology analysis demonstrated significant enrichment in positive regulation of cell migration, negative regulation of endothelial cell proliferation, and stress fiber and actin filament bundles. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed enrichment in cell adhesion and gap junctions. Several glaucoma-related genes were identified, including TGFBR3, THBS1, PITX2, DAXX, TBX3, TNXB, ANGPT1, and PLEKHA7. We also examined differentially methylated regions (DMRs) near these CpG sites and identified significant DMRs in TBX3, TNXB1, DAXX, and PITX2.

Conclusions

This study represents the first genome-wide DNA methylation profiling in cultured human primary SC cells. The DMSs were enriched in the pathways related to outflow resistance. Several DMRs were validated in glaucoma-associated genes, further suggesting the role of DNA methylation in glaucoma development. This study could provide comprehensive understanding of DNA methylation in glaucoma and its effect on aqueous humor outflow.

Pharmacological and pharmacokinetic profile of the novel ocular hypotensive prodrug CKLP1 in Dutch-belted pigmented rabbits

Elevated intraocular pressure is the only treatable risk factor for glaucoma, an eye disease that is the leading cause of irreversible blindness worldwide. We have identified cromakalim prodrug 1 (CKLP1), a novel water-soluble ATP-sensitive potassium channel opener, as a new ocular hypotensive agent. To evaluate the pharmacokinetic and safety profile of CKLP1 and its parent compound levcromakalim, Dutch-belted pigmented rabbits were treated intravenously (0.25 mg/kg) or topically (10 mM; 4.1 mg/ml) with CKLP1. Body fluids (blood, aqueous and vitreous humor) were collected at multiple time points and evaluated for the presence of CKLP1 and levcromakalim using a liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) based assay. Histology of tissues isolated from Dutch-belted pigmented rabbits treated once daily for 90 days was evaluated in a masked manner by a certified veterinary pathologist. The estimated plasma parameters following intravenous administration of 0.25 mg/kg of CKLP1 showed CKLP1 had a terminal half-life of 61.8 ± 55.2 min, Tmax of 19.8 ± 23.0 min and Cmax of 1968.5 ± 831.0 ng/ml. Levcromakalim had a plasma terminal half-life of 85.0 ± 37.0 min, Tmax of 61.0 ± 32.0 min and Cmax of 10.6 ± 1.2 ng/ml. Topical CKLP1 treatment in the eye showed low levels (<0.3 ng/mL) of levcromakalim in aqueous and vitreous humor, and trace amounts of CKLP1 and levcromakalim in the plasma. No observable histological changes were noted in selected tissues that were examined following topical application of CKLP1 for 90 consecutive days. These results suggest that CKPL1 is converted to levcromakalim in the eye and likely to some extent in the systemic circulation.

In Vivo Imaging of Schlemm's Canal and Limbal Vascular Network in Mouse Using Visible-Light OCT

Purpose

To validate the ability of visible-light optical coherence tomography (vis-OCT) in imaging the full Schlemm's canal (SC) and its surrounding limbal vascular network in mice in vivo through a compound circumlimbal scan.

Methods

We developed an anterior segment vis-OCT system and a compound circumlimbal scanning method, which montages eight rotated raster scans. We calibrated the circumlimbal scan geometry using a three-dimensional printed phantom eyeball before imaging wild-type C57BL/6J mice. We measured SC size by segmenting SC cross sections from vis-OCT B-scan images and imaged the limbal microvascular network using vis-OCT angiography (vis-OCTA). To introduce changes in SC size, we used a manometer to adjust the intraocular pressure (IOP) to different levels. To create additional optical scattering contrast to enhance SC imaging, we surgically increased the episcleral venous pressure (EVP) and caused blood reflux into SC.

Results

Using the compound circumlimbal scan, our anterior segment vis-OCT noninvasively imaged the full SC and limbal microvascular network in mouse for the first time. We observed an average 123% increase in SC volume when we decreased the IOP by 10 mm Hg from the baseline IOP of 7 to 10 mm Hg and an average 72% decrease in SC volume when the IOP level was elevated by 10 mm Hg from the baseline IOP. We also observed location-dependent SC size responses to IOP changes. Blood reflux caused by increased EVP enabled vis-OCTA to directly visualize SC, which matched well with the segmented SC.

Conclusions

Vis-OCT and vis-OCTA can accurately image the entire SC and limbal microvascular network in vivo using the compound circumlimbal scan. Vis-OCT is also able to quantitatively measure SC responses to changing IOP levels.

Episcleral Venous Fluid Wave in the Living Human Eye Adjacent to Microinvasive Glaucoma Surgery (MIGS) Supports Laboratory Research: Outflow is Limited Circumferentially, Conserved Distally, and Favored Inferonasally

PURPOSE

The purpose of this study was to describe downstream patterns of outflow with the episcleral venous fluid wave (EVFW) in the living human eye adjacent to microinvasive glaucoma surgery (MIGS) and determine if the EVFW supports existing ex-vivo laboratory outflow research.

DESIGN

Retrospective, noncomparative case series.

PATIENTS

A total of 10 eyes of 10 patients who underwent phaco-Trabectome and 10 eyes of 10 patients who underwent phaco-iStent consecutively at Glaucoma Associates of Texas for cataract and uncontrolled glaucoma who demonstrated an episcleral wave.

METHODS

The EVFW was visualized and recorded during irrigation and aspiration. To describe the hydrodynamic properties of the fluid wave, its degrees, extent, and characteristics were measured with a protractor in Photoshop.

RESULTS

The incised Trabectome arc produced adjacent episcleral blanching of 134±11 degrees (range, 112 to 150 degrees) with an additional 54 degrees of marginal recruitment (41 degrees inferonasal plus 13 degrees superonasal) adjacent to the ends of the Trabectome incision. The mean episcleral blanch for the iStent was 51±19 degrees (range, 19 to 90 degrees), comprised of 29 degrees inferonasal plus 22 degrees superonasal.

CONCLUSIONS

Downstream episcleral flow in the living human eye adjacent to the iStent is variable and mainly confined to 2 clock hours indicating a lack of significant circumferential flow in glaucomatous eyes. Flow distal to the Trabectome site encompasses the Trabectome incisional arc with an additional 2 clock hours of lateral fluid wave favoring the inferonasal over superonasal quadrant 3 to 1. These in-vivo findings made visible with MIGS, corroborate recent in-vivo and long-standing ex-vivo laboratory research that outflow is largely segmented, favored inferonasally and conserved distally.

Study on the effectiveness and safety of Foldable Capsular Vitreous Body implantation

Background

Foldable capsular vitreous body (FCVB) was designed to treat severe retinal detachment. The aim of this study was to evaluate the efficacy and safety of the implantation of foldable capsular vitreous body in 1-year follow-up.

Methods

A retrospective analysis was conducted for 20 patients with severe ocular trauma or silicone oil (SO) dependent eyes underwent vitrectomy and FCVB implantation in a 1-year follow-up. All treated eyes were peformed clinical examinations involved the visual acuity (VA) examination, Goldmann applanation tonometer, noncontact specular microscopy, fundus photography, B-Scan examination and optical coherence tomography (OCT). The groups were compared with t-test and the McNemar - Bowker test.

Results

In 1-year follow-up, 20 eyes were evaluated in the study. FCVB well supported the vitreous retina in all treated eyes, and 6 treated eyes achieved retinal reattachment 12 months after FCVB implantation. There were no significant differences in VA before and after FCVB implantation (P = 1.000). In addition, the postoperative IOP markedly elevated from the preoperative IOP of 12.90 ± 7.06 mmHg to 15.15 ± 3.36 mmHg (P = 0.000017). The intraocular pressure (IOP) of 10 eyes maintained at a normal level after surgeries. The other 10 eyes showed slightly lower IOP within the acceptable level. Though two patients developed keratopathy and ocular inflammation respectively, other treated eyes were symmetric with fellow eyes showing satisfactory appearance. Moreover, there was no SO emulsification or leakage happened in the observation.

Conclusions

FCVB implantation was an effective and safe treatment in the eyes with severe retinal detachment.

Wearing Swimming Goggles Reduces Central Corneal Thickness and Anterior Chamber Angle, and Increases Intraocular Pressure

Purpose/Aim: To assess the changes in anterior eye segment biometrics and intraocular pressure during and after wearing swimming goggles.Materials and methods: Anterior segment biometry and intraocular pressure were assessed in 20 healthy young adults (22.2 ± 4.7 years) during the wearing of a drilled swimming goggle. The central corneal thickness, anterior chamber depth, anterior chamber volume, and anterior chamber angle, using the Pentacam rotating Scheimpflug camera (Oculus Optikgerate GmbH, Wetzlar, Germany), and intraocular pressure, using a rebound tonometer, were obtained before, at 2, 3.5, and 5 min of wearing swimming goggle, just after removal, as well as after 5 min of recovery.Results: During swimming goggles wear, there was a significant corneal thinning (54.8 ± 41.1 µm, p < .001, ƞ_p² = 0.532), iridocorneal angle reduction (2.6 ± 2.6 degrees, p < .001, ƞ_p² = 0.241) and intraocular pressure elevation (4.0 ± 1.9 mmHg, p < .001, ƞ_p² = 0.530). These changes returned to baseline values immediately after swimming goggle removal (corrected p-value <0.05 in all cases). No significant effects of swimming goggles use were observed for anterior chamber depth and anterior chamber volume.Conclusions: Wearing swimming goggles leads to acute corneal thinning, iridocorneal angle reduction, and intraocular pressure elevation. These findings may be of special relevance for individuals with corneal ectasias, as well as for individuals at high risk of glaucoma onset or progression.

Evaluation of anterior segment parameters with two anterior segment optical coherence tomography systems: Visante and Casia, in primary angle closure disease

Purpose:

To determine the comparability of anterior chamber biometric measurements in primary angle closure disease (PACD) patients using two commercially available anterior segment optical coherence tomography machines (ASOCT): Visante and Casia.

Methods:

This was a cross-sectional observational study, which included clinically, diagnosed cases of PACD. Anterior segment biometric measurements were done using Casia and Visante ASOCT. Parameters studied were central corneal thickness (CCT), anterior chamber depth (ACD), nasal (N) and temporal (T) angle opening distance at 500 μm (AOD500) and 750 μm (AOD750), and N and T trabecular iris space area at 500 μm (TISA500) and 750 μm (TISA750).

Results:

Total 36 PACD patients (72 eyes) with average age of 59.48 ± 7.95 years were recruited, out of which 25 were females (69.44%) and 11 males (30.56%). The mean measurements of CCT, ACD, AOD500, and TISA on Casia and Visante machines were 522.5 ± 34.75 μm and 539.55 ± 29.56 μm (P = 0.00); ACD- 2.144 ± 0.38 mm and 2.133 ± 0.39 mm (P = 0.487); AOD500-0.27 ± 0.16 μm and 0.21 ± 0.10 μm (P = 0.04); and TISA500-0.100 ± 0.07 μm and 0.063 ± 0.03 μm (P = 0.00), respectively. A statistically significant difference was noted in CCT, N and T AOD, and TISA. A good corelation for ACD and CCT (ACD = 0.9816 and CCT = 0.772) only were noted between the two machines. The Bland-Altman plot analysis of different parameters between two machines has revealed good agreement of measurement of ACD and CCT but poor agreement for rest of the parameters.

Conclusion:

It is advisable not use the two machines interchangeably because of the wide limits of agreement and poor correlation of angle measurement values of Casia and Visante ASOCT.

Review of rodent hypertensive glaucoma models

Glaucoma is a neurodegenerative disease characterized by the progressive loss of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is a primary risk factor for the development and progression of glaucoma. Rodent models of glaucoma have greatly improved our understanding of the pathophysiology of glaucoma and served as a useful tool to investigate neuroprotective agents. An ideal glaucoma animal model should be easy to induce, reproducible, biologically plausible and predictable. Of the available animal models of glaucoma, rodents are commonly studied because they have a relatively short life span and can be genetically altered. A successful hypertensive glaucoma model should induce structural glaucomatous changes: including loss of retinal nerve fibres, retinal ganglion cells and optic-disc cupping along with IOP elevation. The level and duration of IOP elevation should be titratable depending on the targeted glaucomatous damage. This review summarizes the outcomes of induced rodent hypertensive glaucoma models including intracameral injection of microbeads, laser photocoagulation, episcleral vein cauterization, injection of hypertonic saline and hyaluronic acid. We aim to provide a detailed overview of each of the models with a focus on parameters that defines a successful glaucoma model. The induced IOP elevation and duration of elevation varied among the different models and strain of rodent; nonetheless, they all achieved a sustainable raised IOP with corresponding RGC loss. The limitations of each model are discussed.

Translational Preclinical Pharmacologic Disease Models for Ophthalmic Drug Development

Preclinical models of human diseases are critical to our understanding of disease etiology, pathology, and progression and enable the development of effective treatments. An ideal model of human disease should capture anatomical features and pathophysiological mechanisms, mimic the progression pattern, and should be amenable to evaluating translational endpoints and treatment approaches. Preclinical animal models have been developed for a variety of human ophthalmological diseases to mirror disease mechanisms, location of the affected region in the eye and severity. These models offer clues to aid in our fundamental understanding of disease pathogenesis and enable progression of new therapies to clinical development by providing an opportunity to gain proof of concept (POC). Here, we review preclinical animal models associated with development of new therapies for diseases of the ocular surface, glaucoma, presbyopia, and retinal diseases, including diabetic retinopathy and age-related macular degeneration (AMD). We have focused on summarizing the models critical to new drug development and described the translational features of the models that contributed to our understanding of disease pathogenesis and establishment of preclinical POC.

Anterior Chamber Flare as an Objective and Quantitative Noninvasive Method for Oculopathy in Transthyretin V30M Amyloidosis Patients

Purpose

Assess the aqueous humor flare in transthyretin V30M amyloidosis patients (ATTRV30M).

Materials and Methods

This is a retrospective, cross-sectional, noninterventional comparative study including 28 ATTRV30M patients with a unilateral scalloped iris. For comparative analysis, the fellow eye, the nonscalloped iris eye, from each patient was used as control. All patients underwent aqueous humor flare meter and intraocular pressure (IOP) measurements.

Results

Mean aqueous humor flare was significantly higher in the eyes with the scalloped iris than the control group with the nonscalloped iris (14.1 ± 2.2 versus 6.5 ± 0.9 pc/ms, respectively). No significant differences in IOP were found in the scalloped iris eyes than those in the nonscalloped iris control group (17.1 ± 0.8 versus 16.8 ± 0.7 mmHg, respectively). No significant correlation was not found between the flare and the IOP value within groups.

Conclusions

In this study, aqueous humor flare values in the scalloped iris eyes may be a valid marker for controlling the stage of the oculopathy in ATTRV30M patients.

Dynamic Changes in Schlemm Canal and Iridocorneal Angle Morphology During Accommodation in Children With Healthy Eyes: A Cross-Sectional Cohort Study

Purpose

The purpose of this study was to explore changes in Schlemm canal (SC), trabecular meshwork (TM), and iridocorneal angle (ICA) morphology during accommodative effort in children and young adults.

Methods

We acquired anterior segment optical coherence tomography images (AS-OCT) of the ICA and ciliary muscle (CM) of both eyes of 50 children age 4 to 16 years with healthy eyes, at two levels of accommodation: 2.5 and 15 diopters (D). Semiautomated nasal ICA measurements were as follows: angle opening distance at 500/750 μm (AOD-500, -750), trabecular iris space area at 500/750 μm (TISA-500, -750), and trabecular iris angle at 500/750 μm (TIA-500, -750). Manual measurements were as follows: anteroposterior and radial SC diameter (SC-APD, SC-RD), cross-sectional area of SC (SC-CSA) and TM height (TMH), TM length (TML), and TM density (TMD). CM width was measured at 1, 2, and 3 mm from the scleral spur (CM-1, CM-2, CM-3). For each parameter, a three-level random-effects model was fitted to estimate differences between the two levels of accommodation.

Results

With accommodative effort, SC diameters and CSA increase significantly, as do TM length and iridocorneal angle parameters. With increasing age, SC dimensions reduce. Angle parameters are smaller in eyes with greater spherical equivalent (hypermetropia).

Conclusions

AS-OCT can be used to visualize dynamic morphologic changes in outflow structures with physiologic accommodation. The increase in SC dimensions with accommodative effort may contribute to the regulation of IOP in children.

Uteroglobin and FLRG concentrations in aqueous humor are associated with age in primary open angle glaucoma patients

Background

The pathophysiological changes occurring in the trabecular meshwork in primary open angle glaucoma are poorly understood, but are thought to include increased extracellular matrix deposition, trabecular meshwork cell apoptosis, inflammation, trabecular meshwork calcification and altered protein composition of the aqueous humor. Although many proteins are present in aqueous humor, relatively few have been studied extensively, and their potential roles in primary open angle glaucoma are unknown.

Methods

Analyte concentrations in aqueous humor from 19 primary open angle glaucoma and 18 cataract patients were measured using a multiplex immunoassay. Fisher’s exact test was used to assess statistical significance between groups, and correlations of analyte concentrations with age, intraocular pressure, pattern standard deviation, mean deviation, cup-to-disc ratio and disease duration since commencing treatment were tested by Spearman’s method.

Results

CHI3L1, FLRG, HGF, MIF, P-selectin and Uteroglobin were detected in more than 50% of samples of one or both patient groups, some of which have not previously been quantified in aqueous humor. In the glaucoma but not the cataract group, significant correlations were determined with age for Uteroglobin/SCGB1A1 (r_s = 0.805, p < 0.0001) and FLRG (r_s = 0.706, p = 0.0007). Furthermore, HGF correlated significantly with disease duration (r_s = − 0.723, p = 0.0007). There were no differences in analyte concentrations between groups, and no other significant associations with clinical descriptors that passed correction for multiple testing.

Conclusions

The correlations of uteroglobin and FLRG with age in primary open angle glaucoma but not cataract may suggest a heightened requirement for anti-inflammatory (uteroglobin) or anti-calcification (FLRG) activity in the ageing glaucomatous trabecular meshwork.

Electronic supplementary material

The online version of this article (10.1186/s12886-018-0723-4) contains supplementary material, which is available to authorized users.

Blockade of KCa3.1: A novel target to treat TGF-β1 induced conjunctival fibrosis

Postoperative conjunctival fibrosis is common in patients after glaucoma filtration surgery. The calcium activated potassium (KCa3.1) channel has been shown to inhibit fibrosis in many non-ocular tissues. However, its potential in treating ocular fibrosis remains unknown. We tested the anti-fibrotic potential of TRAM34, a selective blocker of KCa3.1 channel, in treating conjunctival fibrosis. Primary human conjunctival fibroblast (HCF) cultures derived from donor tissues. Myofibroblasts causing conjunctival fibrosis were generated by growing HCFs in the presence of TGFβ1 for 72 h. KCa3.1 mRNA and protein expression in HCF was examined with PCR and western blot. The anti-fibrotic potential of TRAM34 was examined by measuring fibrotic gene expression with quantitative PCR (qPCR), immunofluorescence, and western blotting in HCFs in ± TGFβ1 (5 ng/ml) and TRAM34 (0-25 μM). The cytotoxicity of Tram34 was analyzed with trypan blue assay and its role in Smad signaling was studied with immunofluorescence. Expression of KCa3.1 mRNA and protein was detected in HCFs and TGFβ1 treatment to HCFs significantly increased expression of KCa3.1. TRAM34 treatment attenuated transcription of fibrotic markers, αSMA (p < .001), fibronectin (p < .05), collagen I (p < .001) and collagen IV (p < .001) in TGFβ1-induced HCFs. Further, TRAM34 significantly inhibited TGFβ1-stimulated αSMA protein expression (p < .01) and nuclear translocation of fibrotic Smad2/3 in HCFs and showed no significant cytotoxicity (p < .05). The KCa3.1 potassium channel plays a significant role in the prevention of conjunctival fibrosis and TRAM34 has potential to control post surgical bleb fibrosis in patients. In vivo studies are warranted.

Effect of Cromakalim Prodrug 1 (CKLP1) on Aqueous Humor Dynamics and Feasibility of Combination Therapy With Existing Ocular Hypotensive Agents

Purpose

Cromakalim prodrug 1 (CKLP1) is a water-soluble ATP-sensitive potassium channel opener that has shown ocular hypotensive properties in ex vivo and in vivo experimental models. To determine its mechanism of action, we assessed the effect of CKLP1 on aqueous humor dynamics and in combination therapy with existing ocular hypotensive agents.

Methods

Outflow facility was assessed in C57BL/6 mice by ex vivo eye perfusions and by in vivo constant flow infusion following CKLP1 treatment. Human anterior segments with no trabecular meshwork were evaluated for effect on pressure following CKLP1 treatment. CKLP1 alone and in combination with latanoprost, timolol, and Rho kinase inhibitor Y27632 were evaluated for effect on intraocular pressure in C57BL/6 mice and Dutch-belted pigmented rabbits.

Results

CKLP1 lowered episcleral venous pressure (control: 8.9 ± 0.1 mm Hg versus treated: 6.2 ± 0.1 mm Hg, P < 0.0001) but had no detectable effect on outflow facility, aqueous humor flow rate, or uveoscleral outflow. Treatment with CKLP1 in human anterior segments without the trabecular meshwork resulted in a 50% ± 9% decrease in pressure, suggesting an effect on the distal portion of the conventional outflow pathway. CKLP1 worked additively with latanoprost, timolol, and Y27632 to lower IOP, presumably owing to combined effects on different aspects of aqueous humor dynamics.

Conclusions

CKLP1 lowered intraocular pressure by reducing episcleral venous pressure and lowering distal outflow resistance in the conventional outflow pathway. Owing to this unique mechanism of action, CKLP1 works in an additive manner to lower intraocular pressure with latanoprost, timolol, and Rho kinase inhibitor Y27632.

Inhibition of Rho Kinase Induces Antioxidative Molecules and Suppresses Reactive Oxidative Species in Trabecular Meshwork Cells

Purpose

To investigate the effect of rho kinase inhibitors on oxidative stress in trabecular meshwork (TM) cells.

Methods

TM cells were isolated from the eyes of cynomolgus monkeys. Y-27632 and menadione were used to inhibit rho kinase and induce production of reactive oxygen species (ROS), respectively. The cynomolgus monkey array and 12,613 probes were used in DNA microarray analysis, and the affected genes were categorized using gene ontology analysis. The mRNA levels of the target genes were confirmed by real-time RT-PCR. Intracellular oxidative stress was detected using a fluorescent reagent sensitive to ROS. Cell viability was assessed by the WST-8 assay.

Results

Gene ontology analysis revealed upregulation of genes involved in antioxidant activity, and upregulation of catalase was confirmed by real-time RT-PCR after 30 min treatment with Y-27632. Production of ROS was increased by menadione, and the effect was partly suppressed by pretreatment with Y-27632. At a lower dose of menadione, Y-27632 stimulated TM cells and significantly increased their viability following menadione treatment compared to control cells.

Conclusion

Using microarray analysis, Y-27632 was shown to upregulate antioxidative genes including catalase and partially reduce ROS production and cell death by oxidative stress caused by menadione.

Roles of exosomes in the normal and diseased eye

Exosomes are nanometer-sized vesicles that are released by cells in a controlled fashion and mediate a plethora of extra- and intercellular activities. Some key functions of exosomes include cell-cell communication, immune modulation, extracellular matrix turnover, stem cell division/differentiation, neovascularization and cellular waste removal. While much is known about their role in cancer, exosome function in the many specialized tissues of the eye is just beginning to undergo rigorous study. Here we review current knowledge of exosome function in the visual system in the context of larger bodies of data from other fields, in both health and disease. Additionally, we discuss recent advances in the exosome field including use of exosomes as a therapeutic vehicle, exosomes as a source of biomarkers for disease, plus current standards for isolation and validation of exosome populations. Finally, we use this foundational information about exosomes in the eye as a platform to identify areas of opportunity for future research studies.