How many aqueous humor outflow pathways are there?

Development of Cell Culture Platforms for Study of Trabecular Meshwork Cells and Glaucoma Development

BACKGROUND

Various cell culture platforms that could display native environmental cue-mimicking stimuli were developed, and effects of environmental cues on cell behaviors were studied with the cell culture platforms. Likewise, various cell culture platforms mimicking native trabecular meshwork (TM) composed of juxtacanalicular, corneoscleral and uveal meshwork located in internal scleral sulcus were used to study effects of environmental cues and/or drug treatments on TM cells and glaucoma development. Glaucoma is a disease that could cause blindness, and cause of glaucoma is not clearly identified yet. It appears that aqueous humor (AH) outflow resistance increased by damages on pathway of AH outflow can elevate intraocular pressure (IOP). These overall possibly contribute to development of glaucoma.

METHODS

For the study of glaucoma, static and dynamic cell culture platforms were developed. Particularly, the dynamic platforms exploiting AH outflow-mimicking perfusion or increased IOP-mimicking increased pressure were used to study how perfusion or increased pressure could affect TM cells. Overall, potential mechanisms of glaucoma development, TM structures and compositions, TM cell culture platform types and researches on TM cells and glaucoma development with the platforms were described in this review.

RESULTS AND CONCLUSION

This will be useful to improve researches on TM cells and develop enhanced therapies targeting glaucoma.

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.

BCLA CLEAR presbyopia: Mechanism and optics

With over a billion adults worldwide currently affected, presbyopia remains a ubiquitous, global problem. Despite over a century of study, the precise mechanism of ocular accommodation and presbyopia progression remains a topic of debate. Accordingly, this narrative review outlines the lenticular and extralenticular components of accommodation together with the impact of age on the accommodative apparatus, neural control of accommodation, models of accommodation, the impact of presbyopia on retinal image quality, and both historic and contemporary theories of presbyopia.

Clinical Results of the MINIject Implant for Suprachoroidal Drainage

Objective: This retrospective study evaluated the safety and efficacy of the new minimally invasive MINIject implant placed in the suprachoroidal space. The aim was to assess its impact on intraocular pressure (IOP) reduction and complication rate. Methods: 18 eyes from 18 patients with insufficiently controlled glaucoma received the implant using topical medications. Outcomes were changes in IOP, change in IOP medication, need for other glaucoma surgery, and rate of adverse events. Results: IOP reduced by 15% (p < 0.05) following MINIject implantation. IOP medication decreased from 3 to 1 agent (p < 0.05). Four patients (22%) required other glaucoma surgery while we did not observe any clinically relevant adverse event. Conclusions: This retrospective study indicates that MINIject implants may be a safe and effective means of reducing IOP together with a reduction in IOP medications in most patients. Larger prospective studies with longer follow-ups are necessary to confirm our results, though.

Chemical Insights into Topical Agents in Intraocular Pressure Management: From Glaucoma Etiopathology to Therapeutic Approaches

Glaucoma encompasses a group of optic neuropathies characterized by complex and often elusive etiopathology, involvihttng neurodegeneration of the optic nerve in conjunction with abnormal intraocular pressure (IOP). Currently, there is no cure for glaucoma, and treatment strategies primarily aim to halt disease progression by managing IOP. This review delves into the etiopathology, diagnostic methods, and treatment approaches for glaucoma, with a special focus on IOP management. We discuss a range of active pharmaceutical ingredients used in glaucoma therapy, emphasizing their chemical structure, pharmacological action, therapeutic effectiveness, and safety/tolerability profiles. Notably, most of these therapeutic agents are administered as topical formulations, a critical aspect considering patient compliance and drug delivery efficiency. The classes of glaucoma therapeutics covered in this review include prostaglandin analogs, beta blockers, alpha agonists, carbonic anhydrase inhibitors, Rho kinase inhibitors, and miotic (cholinergic) agents. This comprehensive overview highlights the importance of topical administration in glaucoma treatment, offering insights into the current state and future directions of pharmacological management in glaucoma.

The Anti-Inflammatory and Antioxidant Properties of Acebuche Oil Exert a Retinoprotective Effect in a Murine Model of High-Tension Glaucoma

Glaucoma is characterized by cupping of the optic disc, apoptotic degeneration of retinal ganglion cells (RGCs) and their axons, and thinning of the retinal nerve fiber layer, with patchy loss of vision. Elevated intraocular pressure (IOP) is a major risk factor for hypertensive glaucoma and the only modifiable one. There is a need to find novel compounds that counteract other risk factors contributing to RGC degeneration. The oil derived from the wild olive tree (Olea europaea var. sylvestris), also called Acebuche (ACE), shows powerful anti-inflammatory, antioxidant and retinoprotective effects. We evaluated whether ACE oil could counteract glaucoma-related detrimental effects. To this aim, we fed mice either a regular or an ACE oil-enriched diet and then induced IOP elevation through intraocular injection of methylcellulose. An ACE oil-enriched diet suppressed glaucoma-dependent retinal glia reactivity and inflammation. The redox status of the glaucomatous retinas was restored to a control-like situation, and ischemia was alleviated by an ACE oil-enriched diet. Notably, retinal apoptosis was suppressed in the glaucomatous animals fed ACE oil. Furthermore, as shown by electroretinogram analyses, RGC electrophysiological functions were almost completely preserved by the ACE oil-enriched diet. These ameliorative effects were IOP-independent and might depend on ACE oil's peculiar composition. Although additional studies are needed, nutritional supplementation with ACE oil might represent an adjuvant in the management of glaucoma.

Evaluation of the nutraceutical Palmitoylethanolamide in reducing intraocular pressure (IOP) in patients with glaucoma or ocular hypertension: a systematic review and meta-analysis

Intraocular pressure (IOP) positively correlates with both normal and high-tension glaucoma. To date, IOP targeting remains the validated pharmacological approach in counteracting glaucoma progression as well as in halting vision loss. Among the different adjuvant compounds, evidence highlighted the potential effectiveness of Palmitoylethanolamide (PEA), an endogenous fatty acid amide. Thus, a systematic review of the literature was conducted, thoroughly evaluating PEA treatment regimen in decreasing IOP in patients with eye disorders. We checked for articles across the scientific databases Pubmed (MEDLINE), Embase (OVID), and Web of Science from the inception to 30 August 2023, and a total of 828 articles were recovered. Six of these studies (199 patients) were included in the systematic review after the study selection process, and three studies for meta-analysia. Overall, PEA showed significant efficacy in reducing IOP in patients, this encourages its clinical use in glaucoma as well as across different forms of eye disorders.

Serine to proline mutation at position 341 of MYOC impairs trabecular meshwork function by causing autophagy deregulation

Glaucoma is a highly heritable disease, and myocilin was the first identified causal and most common pathogenic gene in glaucoma. Serine-to-proline mutation at position 341 of myocilin (MYOCS341P) is associated with severe glaucoma phenotypes in a five-generation primary open-angle glaucoma family. However, the underlying mechanisms are underexplored. Herein, we established the MYOCS341P transgenic mouse model and characterized the glaucoma phenotypes. Further, we systematically explored the functional differences between wild-type and MYOCS341P through immunoprecipitation, mass spectrometry, and RNA-seq analyses. We found that MYOCS341P transgenic mice exhibit glaucoma phenotypes, characterized by reduced aqueous humor outflow, elevated intraocular pressure, decreased trabecular meshwork (TM) cell number, narrowed Schlemm's canal, retinal ganglion cell loss, and visual impairment. Mechanistically, the secretion of dysfunctional MYOCS341P accumulated in the endoplasmic reticulum (ER), inducing ER stress and dysregulation of autophagy, thereby promoting TM cell death. We describe an effective transgenic model for mechanistic studies and the screening of therapeutic targets. Our data generated from high-throughput analyses help elucidate the mechanism underlying mutant MYOC-related glaucoma.

Integrating genetic regulation and single-cell expression with GWAS prioritizes causal genes and cell types for glaucoma

Primary open-angle glaucoma (POAG), characterized by retinal ganglion cell death, is a leading cause of irreversible blindness worldwide. However, its molecular and cellular causes are not well understood. Elevated intraocular pressure (IOP) is a major risk factor, but many patients have normal IOP. Colocalization and Mendelian randomization analysis of >240 POAG and IOP genome-wide association study (GWAS) loci and overlapping expression and splicing quantitative trait loci (e/sQTLs) in 49 GTEx tissues and retina prioritizes causal genes for 60% of loci. These genes are enriched in pathways implicated in extracellular matrix organization, cell adhesion, and vascular development. Analysis of single-nucleus RNA-seq of glaucoma-relevant eye tissues reveals that the POAG and IOP colocalizing genes and genome-wide associations are enriched in specific cell types in the aqueous outflow pathways, retina, optic nerve head, peripapillary sclera, and choroid. This study nominates IOP-dependent and independent regulatory mechanisms, genes, and cell types that may contribute to POAG pathogenesis.

Microfluidics in the eye: a review of glaucoma implants from an engineering perspective

Glaucoma is a progressive optic neuropathy in the eye, which is a leading cause of irreversible blindness worldwide and currently affects over 70 million individuals. Clinically, intraocular pressure (IOP) reduction is the only proven treatment to halt the progression of glaucoma. Microfluidic devices such as glaucoma drainage devices (GDDs) and minimally invasive glaucoma surgery (MIGS) devices are routinely used by ophthalmologists to manage elevated IOP, by creating an artificial pathway for the over-accumulated aqueous humor (AH) in a glaucomatous eye, when the natural pathways are severely blocked. Herein, a detailed modelling and analysis of both the natural microfluidic pathways of the AH in the eye and artificial microfluidic pathways formed additionally by the various glaucoma implants are conducted to provide an insight into the causes of the IOP abnormality and the improvement schemes of current implant designs. The mechanisms of representative glaucoma implants have been critically reviewed from the perspective of microfluidics, and we have categorized the current implants into four groups according to the targeted drainage sites of the AH, namely Schlemm's canal, suprachoroidal space, subconjunctival space, and ocular surface. In addition, we propose to divide the development and evolution of glaucoma implant designs into three technological waves, which include microtube (1st), microvalve (2nd) and microsystem (3rd). With the emerging trends of minimal invasiveness and artificial intelligence in the development of medical implants, we envision that a comprehensive glaucoma treatment microsystem is on the horizon, which is featured with active and wireless control of IOP, real-time continuous monitoring of IOP and aqueous rate, etc. The current review could potentially cast light on the unmatched needs, challenges, and future directions of the microfluidic structural and functional designs of glaucoma implants, which would enable an enhanced safety profile, reduced complications, increased efficacy of lowering IOP and reduced IOP fluctuations, closed-loop and on-demand control of IOP, etc.

Glaucoma as a Tauopathy-Is It the Missing Piece in the Glaucoma Puzzle?

Glaucoma is a chronic neurodegenerative disorder affecting the visual system which can result in vision loss and blindness. The pathogenetic mechanisms underlying glaucomatous optic neuropathy are ultimately enigmatic, prompting ongoing investigations into its potential shared pathogenesis with other neurodegenerative neurological disorders. Tauopathies represent a subclass of neurodegenerative diseases characterized by the abnormal deposition of tau protein within the brain and consequent microtubule destabilization. The extended spectrum of tauopathies includes conditions such as frontotemporal dementias, progressive supranuclear palsy, chronic traumatic encephalopathy, and Alzheimer's disease. Notably, recent decades have witnessed emerging documentation of tau inclusion among glaucoma patients, providing substantiation that this ocular disease may similarly manifest features of tauopathies. These studies found that: (i) aggregated tau inclusions are present in the somatodendritic compartment of RGCs in glaucoma patients; (ii) the etiology of the disease may affect tau splicing, phosphorylation, oligomerization, and subcellular localization; and (iii) short interfering RNA against tau, administered intraocularly, significantly decreased retinal tau accumulation and enhanced RGC somas and axon survival, demonstrating a crucial role for tau modifications in ocular hypertension-induced neuronal injury. Here, we examine the most recent evidence surrounding the interplay between tau protein dysregulation and glaucomatous neurodegeneration. We explore the novel perspective of glaucoma as a tau-associated disorder and open avenues for cross-disciplinary collaboration and new treatment strategies.

Inhibition of TGF-β2-Induced Trabecular Meshwork Fibrosis by Pirfenidone

Purpose

Trabecular meshwork (TM) fibrosis is a crucial pathophysiological process in the development of primary open-angle glaucoma. Pirfenidone (PFD) is a new, broad-spectrum antifibrotic agent approved for the treatment of idiopathic pulmonary fibrosis. This study investigated the inhibitory effect of PFD on TM fibrosis and evaluated its efficacy in lowering intraocular pressure (IOP).

Methods

Human TM cells were isolated, cultured, and characterized. Cell Counting Kit-8 was used to evaluate the proliferation and toxicity of different concentrations of PFD on normal or fibrotic TM cells. TM cells were treated with transforming growth factor beta-2 (TGF-β2) in the absence or presence of PFD. Western blotting and immunofluorescence analyses were used to analyze changes in the TM cell cytoskeleton and extracellular matrix (ECM) proteins, including alpha-smooth muscle actin (α-SMA), F-actin, collagen IV (COL IV), and fibronectin (FN). An ocular hypertension (OHT) mouse model was induced with Ad-TGF-β2C226/228S and then treated with PFD or latanoprost (LT) eye drops to confirm the efficacy of PFD in lowering IOP.

Results

PFD inhibited the proliferation of fibrotic TM cells in a dose-dependent manner and inhibited TGF-β2-induced overexpression of α-SMA, COL IV, and FN in TM cells. PFD stabilized F-actin. In vivo, PFD eye drops reduced the IOP of the OHT models and showed no significant difference compared with LT eye drops.

Conclusions

PFD inhibited TGF-β2-induced TM cell fibrosis by rearranging the disordered cytoskeleton and decreasing ECM deposition, thereby enhancing the aqueous outflow from the TM outflow pathway and lowering IOP, which provides a potential new approach to treating glaucoma.

Translational Relevance

Our work with pirfenidone provides a new approach to treat glaucoma.

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.

The role of conventional and unconventional adaptive routes in lowering of intraocular pressure: Theoretical model and simulation

In this article, we propose a theoretical model leveraging the analogy between fluid and electric variables to investigate the relation among aqueous humor (AH) circulation and drainage and intraocular pressure (IOP), the principal established risk factor of severe neuropathologies of the optic nerve such as glaucoma. IOP is the steady-state result of the balance among AH secretion (AHs), circulation (AHc), and drainage (AHd). AHs are modeled as a given volumetric flow rate electrically corresponding to an input current source. AHc is modeled by the series of two linear hydraulic conductances (HCs) representing the posterior and anterior chambers. AHd is modeled by the parallel of three HCs: a linear HC for the conventional adaptive route (ConvAR), a nonlinear HC for the hydraulic component of the unconventional adaptive route (UncAR), and a nonlinear HC for the drug-dependent component of the UncAR. The proposed model is implemented in a computational virtual laboratory to study the value attained by the IOP under physiological and pathological conditions. Simulation results (i) confirm the conjecture that the UncAR acts as a relief valve under pathological conditions, (ii) indicate that the drug-dependent AR is the major opponent to IOP increase in the case of elevated trabecular meshwork resistance, and (iii) support the use of the model as a quantitative tool to complement in vivo studies and help design and optimize medications for ocular diseases.

Evidence for Menopause as a Sex-Specific Risk Factor for Glaucoma

Glaucoma is a leading cause of irreversible blindness worldwide and is characterized by progressive loss of visual function and retinal ganglion cells (RGC). Current epidemiological, clinical, and basic science evidence suggest that estrogen plays a role in the aging of the optic nerve. Menopause, a major biological life event affecting all women, coincides with a decrease in circulating sex hormones, such as estrogen. While 59% of the glaucomatous population are females, sex is not considered a risk factor for developing glaucoma. In this review, we explore whether menopause is a sex-specific risk factor for glaucoma. First, we investigate how menopause is defined as a sex-specific risk factor for other pathologies, including cardiovascular disease, osteoarthritis, and bone health. Next, we discuss clinical evidence that highlights the potential role of menopause in glaucoma. We also highlight preclinical studies that demonstrate larger vision and RGC loss following surgical menopause and how estrogen is protective in models of RGC injury. Lastly, we explore how surgical menopause and estrogen signaling are related to risk factors associated with developing glaucoma (e.g., intraocular pressure, aqueous outflow resistance, and ocular biomechanics). We hypothesize that menopause potentially sets the stage to develop glaucoma and therefore is a sex-specific risk factor for this disease.

Rapid Pathogen Identification in Aqueous Humor Samples by Combining Fc-MBL@Fe3O4 Enrichment and Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry Profiling

Prompt clinical diagnosis and antimicrobial therapy are key to managing infective endophthalmitis. The small volume of aqueous humor, low bacterial counts, and empirical medication by physicians make existing diagnostic methods time-consuming and imprecise. Here, we investigated the feasibility of combining Fc-containing mannose-binding lectin-coated Fe₃O₄ (Fc-MBL@Fe₃O₄) enrichment with matrix-assisted laser desorption-ionization time of flight mass spectrometry (MALDI-TOF MS) profiling to identify pathogens in aqueous humor. Aqueous humor aspirated from freshly enucleated porcine eyes was treated with different inocula of Staphylococcus aureus, Staphylococcus epidermidis, and Klebsiella pneumoniae. We performed identification directly in aqueous humor samples and after short-term culture of micro-LB broth. Aqueous humor endophthalmitis samples were enriched with Fc-MBL@Fe₃O₄ and analyzed using MALDI-TOF MS. The identification time and minimum bacterial concentration required for identification were determined. The enrichment efficiency of Fc-MBL@Fe₃O₄ for different bacteria was greater than (87.5 ± 5.0)%. The objects of direct identification include live bacteria and bacteria treated with antibiotics, which can be completed within 1.5 h. The minimum number of bacteria needed for positive identification was 2.20 × 10⁶ CFU. For micro-LB broth culture, the identification of bacteria can be completed within 6.5 to 9.5 h for aqueous humor samples with an initial bacterial count of tens to hundreds. IMPORTANCE Fc-MBL@Fe₃O₄ capture not only live bacteria in aqueous humor but also bacteria inactivated by antibiotics. Fc-MBL@Fe₃O₄ combined with micro-LB broth culture significantly reduced the turnaround time (TAT) by more than half a day by shortening the time required for bacterial identification. Our findings demonstrate that combining Fc-MBL@Fe₃O₄ enrichment with MALDI-TOF MS identification is a fast, sensitive, and efficient analytical method with great potential for identifying pathogens in aqueous humor samples.

First Evidence Indicates the Physiology- and Axial-Myopia-Dependent Profiles of Steroid Hormones in Aqueous Humor

The quantitative level of steroid hormones (SHs) in some body fluids have been accepted for clinical diagnosis, whereas their distribution in aqueous humor (AH) is unknown yet. Herein, a profiling study was conducted with a total of 171 AH and 107 plasma samples using liquid chromatography coupled with tandem mass spectrometry (LC MS/MS). For the first time, six kinds of SHs in AH were quantitatively estimated, and their abundances were ranked at cortisol (F), corticosterone (COR), androstenedione (A2), and 11-deoxycortisol (11DOC). The corresponding abundance of all SHs in AH was significantly lower than those in plasma, while there was a lack of a proportional relationship with the abundance of plasma SHs. Dehydroepiandrosterone sulfate, the most abundant plasma SH, was undetectable in AH, implying that the blood-aqueous barrier might specifically block its transferral. Axial myopia generally results from many factors throughout the entire eye from tissues and molecules; furthermore, the correlation of AH SHs and axial myopia was assessed to look for their indication in such myopia. The panel with five kinds of AH SHs (F, COR, CORT, ALD and A2) was functional as a discriminator for axial myopia and control. The abundance of SHs, therefore, has a specific distribution in AH and can potentially contribute to axial myopia.

The Effect of Latanoprost on Choroidal Vascularity Index in Glaucoma and Ocular Hypertension

PRCIS

The choroidal vascularity index (CVI) is a new marker for the choroid. The decrease in CVI following latanoprost use can provide a better understanding of the pathogenesis of the posterior segment side effects of latanoprost such as cystoid macular edema and central serous choroidopathy.

PURPOSE

The purpose of this paper is to evaluate the changes in the CVI, total choroidal area (TCA), stromal area (SA), luminal area (LA), and choroidal thickness (CT) following latanoprost therapy in patients with primary open angle glaucoma and ocular hypertension.

MATERIALS AND METHODS

Patients with newly diagnosed primary open angle glaucoma or ocular hypertension who had never received antiglaucoma therapy were included. Each patient received latanoprost 0.005% once daily. Enhanced depth imaging mode of spectral-domain optical coherence tomography scans was taken before the start of latanoprost therapy and in the first and third months. Subfoveal CT, CVI, TCA, LA, and SA for the submacular area, and 4 quadrants of the peripapillary area were calculated from the scans.

RESULTS

A total of 36 eyes of 18 patients were analyzed. Subfoveal CT increased significantly ( P =0.007). Mean TCA ( P =0.008) and SA ( P <0.001) in the first and third months were higher than baseline in the submacular regions. Mean CVI was lower in the first and third months ( P <0.001). There was an increase in the mean TCA and SA in the peripapillary temporal ( P =0.001 and 0.028) and inferior ( P =0.002 and <0.001) quadrants and a decrease in mean CVI in the temporal ( P =0.027) and inferior ( P =0.003) peripapillary quadrants. A negative correlation was found between the rate of decrease in intraocular pressure and the macular region CVI.

CONCLUSIONS

Following latanoprost use for several months, the CVI was significantly decreased in newly treated patients with glaucoma or ocular hypertension, among other changes to the choroid. These findings may contribute to a better understanding of the effects of prostaglandins on the posterior segment of the eye.

Epigallocatechin-3-Gallate Protects Trabecular Meshwork Cells from Endoplasmic Reticulum Stress

Primary open-angle glaucoma (POAG) is the most common form of glaucoma, for which elevated intraocular pressure (IOP) is a major risk factor. IOP is mainly regulated by dynamic balance of aqueous humor (AH) production and outflow via the conventional trabecular meshwork/Schlemm's canal (TM/SC) pathway. Dysfunctions of TM cells due to endoplasmic reticulum (ER) stress have been demonstrated to increase the resistance of AH outflow, resulting in IOP elevation. Epigallocatechin-3-gallate (EGCG), the most abundant polyphenolic component in green tea, has been shown to alleviate ER stress in several diseases while its potential roles in alleviating ER stress in TM cells have not been determined. In this study, we investigate the mitigation of tunicamycin-induced ER stress in TM cells by EGCG. MTT assay was used to measure the cell viability of human TM (HTM) cells and primary porcine TM (PTM) cells. ER stress levels in both HTM cells and primary PTM cells were detected by quantitative real-time PCR. The primary PTM cells isolated from porcine TM tissues were characterized by immunostaining. We found that 40 μM and 80 μM EGCG pretreatment substantially promoted HTM cell survival under 3 μM tunicamycin-induced ER stress. Pretreatment of 40 μM EGCG markedly reduced the expression of ER stress markers ATF4, HSPA5, and DDIT3, evoked by 3 μM tunicamycin in HTM cells. Furthermore, 40 μM EGCG pretreatment significantly decreased the expressions of ATF4, HSPA5, and DDIT3 at the mRNA level induced by 3 μM tunicamycin and improved cell viability in primary PTM cells. Our results show that EGCG is capable of protecting TM cells from ER stress. EGCG provides a promising therapeutic option for POAG treatment.

Suprachoroidal injection of polyzwitterion hydrogel for treating glaucoma

Glaucoma is the primary cause of irreversible blindness worldwide. The current treatments are primarily based on drug usage or surgical operation to reduce intraocular pressure (IOP). However, it is expensive and requires patients to insist on taking the medicine for a long time. The suprachoroidal space (SCS) is the space between the choroid and the sclera, which forms part of the uveovortex pathway in the circulation of aqueous humor. So far, it is still challenging to realize the injection of hydrogels into the SCS with long-term duration. In this work, an in situ-forming polyzwitterionic polycarboxybetaine hydrogel is designed and injected to expand SCS to increase the drainage of aqueous humor from the eye via the uveovortex pathway, thus reducing IOP for at least 6 weeks, while commercial hyaluronic acid hydrogel can only last for about 4 weeks. The clinical ophthalmological safety assessment examination shows that the treatment of polyzwitterion hydrogel is well-tolerated that leads to minimal inflammatory reaction, and histopathology assessment demonstrates that the SCS is expanded after injection of the hydrogel. Further analysis of ultrasound biomicroscopy reveals that there is a strong correlation between IOP reduction and SCS expansion. In short, the polyzwitterion hydrogel developed in this work can prolong the period of IOP reduction by expanding SCS, thus treating ocular hypertension and glaucoma without resorting to drugs or regular surgery.

Clinical pharmacology and pharmacogenetics of prostaglandin analogues in glaucoma

Glaucoma is the main cause of irreversible visual loss worldwide, and comprises a group of progressive, age-related, and chronic optic neuropathies. Prostaglandin analogs are considered a first-line treatment in the management of glaucoma and have the best efficacy in reducing intraocular pressure. When comparing these therapeutic agents between them, long-term therapy with 0.03% bimatoprost is the most effective followed by treatment with 0.005% latanoprost and 0.004% travoprost. The prevalence of adverse events is lower for latanoprost than for other prostaglandin analogs. However, some patients do not respond to the treatment with prostaglandin analogs (non-responders). Intraocular pressure-lowering efficacy differs significantly between individuals partly owing to genetic factors. Rs1045642 in ABCB1, rs4241366 in SLCO2A1, rs9503012 in GMDS, rs10306114 in PTGS1, rs11568658 in MRP4, rs10786455 and rs6686438 in PTGFR were reported to be positive with the response to prostaglandin analogs in patients with glaucoma. A negative association was found between single nucleotide polymorphisms of PTGFR (rs11578155 and rs6672484) and the response to prostaglandin analogs in patients with glaucoma. The current review is an analysis of the information relevant to prostaglandin analog treatments based on previous literatures. It describes in detail the clinical pharmacology and pharmacogenetics of drugs belonging to this therapeutical class to provide a sound pharmacological basis for their proper use in ophthalmological clinical practice.

Cooperation of Angiopoietin-2 and Angiopoietin-4 in Schlemm's Canal Maintenance

Purpose

Defects in the iridocorneal angle tissues, including the trabecular meshwork (TM) and Schlemm's canal (SC), impair aqueous humor flow and increase the intraocular pressure (IOP), eventually resulting in glaucoma. Activation of endothelial tyrosine kinase receptor Tie2 by angiopoietin-1 (Angpt1) has been demonstrated to be essential for SC formation, but roles of the other two Tie2 ligands, Angpt2 and Angpt4, have been controversial or not yet characterized, respectively.

Methods

Angpt4 expression was investigated using genetic cell fate mapping and reporter mice. Congenital deletion of Angpt2 and Angpt4 and tamoxifen-inducible deletion of Angpt1 in mice were used to study the effects of Angpt4 deletion alone and in combination with the other angiopoietins. SC morphology was examined with immunofluorescent staining. IOP measurements, electron microscopy, and histologic evaluation were used to study glaucomatous changes.

Results

Angpt4 was postnatally expressed in the TM. While Angpt4 deletion alone did not affect SC and Angpt4 deletion did not aggravate Angpt1 deletion phenotype, absence of Angpt4 combined with Angpt2 deletion had detrimental effects on SC morphology in adult mice. Consequently, Angpt2^−/−;Angpt4^−/− mice displayed glaucomatous changes in the eye. Mice with Angpt2 deletion alone showed only moderate SC defects, but Angpt2 was necessary for proper limbal vasculature development. Mechanistically, analysis of Tie2 phosphorylation suggested that Angpt2 and Angpt4 cooperate as agonistic Tie2 ligands in maintaining SC integrity.

Conclusions

Our results indicated an additive effect of Angpt4 in SC maintenance and Tie2 activation and a spatiotemporally regulated interplay between the angiopoietins in the mouse iridocorneal angle.

Transgene expression of Stanniocalcin-1 provides sustained intraocular pressure reduction by increasing outflow facility

Glaucoma is the leading cause of irreversible blindness worldwide. Therapies for glaucoma are directed toward reducing intraocular pressure (IOP), the leading risk factor and only reliable therapeutic target via topical medications or with procedural intervention including laser or surgery. Though topical therapeutics are typically first line, less than 50% of patients take drops as prescribed. Sustained release technologies that decrease IOP for extended periods of time are being examined for clinical use. We recently identified Stanniocalcin-1, a naturally occurring hormone, as an IOP-lowering agent. Here, we show that a single injection into the anterior chamber of mice with an adeno-associated viral vector containing the transgene of stanniocalcin-1 results in diffuse and sustained expression of the protein and produces IOP reduction for up to 6 months. As the treatment effect begins to wane, IOP-lowering can be rescued with a repeat injection. Aqueous humor dynamic studies revealed an increase in outflow facility as the mechanism of action. This first-in-class therapeutic approach has the potential to improve care and reduce the rates of vision loss in the 80 million people worldwide currently affected by glaucoma.

Ocular Autonomic Nervous System: An Update from Anatomy to Physiological Functions

The autonomic nervous system (ANS) confers neural control of the entire body, mainly through the sympathetic and parasympathetic nerves. Several studies have observed that the physiological functions of the eye (pupil size, lens accommodation, ocular circulation, and intraocular pressure regulation) are precisely regulated by the ANS. Almost all parts of the eye have autonomic innervation for the regulation of local homeostasis through synergy and antagonism. With the advent of new research methods, novel anatomical characteristics and numerous physiological processes have been elucidated. Herein, we summarize the anatomical and physiological functions of the ANS in the eye within the context of its intrinsic connections. This review provides novel insights into ocular studies.

Visualization of Anterior Chamber Angle Structures With Scattering- and Polarization-Sensitive Anterior Segment Optical Coherence Tomography

Purpose

The purpose of this study was to compare three optical coherence tomography (OCT) modalities in the observation of anterior chamber angle structures; trabecular meshwork (TM), Schlemm's canal (SC), and band of extracanalicular limbal lamina (BELL).

Methods

Three OCT modalities were used: (1) 2 × 2 Jones-matrix scattering OCT (S-OCT) representing conventional intensity OCT, (2) polarization-diverse S-OCT that was calculated as summation of all elements of the Jones-matrix to eliminate the influence of artifacts caused by sample birefringence, and (3) polarization-sensitive OCT (PS-OCT) to assess depth-resolved phase retardation.

Results

In a total of 97 eyes of 55 subjects, nasal and temporal angles were scanned. The detection rate of TM and BELL was significantly different among modalities; highest with PS-OCT (95.1% and 99.2%), followed by 2 × 2 Jones-matrix S-OCT (71.1% and 88.7%) and polarization-diverse S-OCT (33.2% and 25.0%), indicating the influence of artifacts on 2 × 2 Jones-matrix S-OCT measurements. SC was visible with 2 × 2 Jones-matrix S-OCT, polarization-diverse S-OCT, and PS-OCT in 14.2%, 14.9%, and 0.3% of images, respectively. The intergrader agreement as evaluated with the prevalence-adjusted bias-adjusted κ value was higher with PS-OCT than with other S-OCTs.

Conclusions

Visibility of anterior chamber angle structures was assessed with three OCT modalities. For TM and BELL that are rich in collagen fibers, PS-OCT provides significantly better visibility than S-OCT without the influence of artifacts arising from polarization or birefringence. Visualization of SC was more difficult with any OCT modalities.

Translational Relevance

PS-OCT is a useful tool to investigate the anterior chamber angle structures which are difficult to observe with conventional OCT.

Inhibition of the cysteinyl leukotriene pathways increases survival of RGCs and reduces microglial activation in ocular hypertension

Glaucoma is the second leading cause of blindness worldwide. This multifactorial, neurodegenerative group of diseases is characterized by the progressive loss of retinal ganglion cells (RGCs) and their axons, leading to irreversible visual impairment and blindness. There is a huge unmet and urging need for the development of new and translatable strategies and treatment options to prevent this progressive loss of RGC. Accumulating evidence points towards a critical role of neuroinflammation, in particular microglial cells, in the pathogenesis of glaucoma. Leukotrienes are mediators of neuroinflammation and are involved in many neurodegenerative diseases. Therefore, we tested the leukotriene receptors CysLT1R/GPR17-selective antagonist Montelukast (MTK) for its efficacy to modulate the reactive state of microglia in order to ameliorate RGCs loss in experimental glaucoma. Ocular hypertension (OHT) was induced unilaterally by injection of 8 μm magnetic microbead (MB) into the anterior chamber of female Brown Norway rats. The contralateral, untreated eye served as control. Successful induction of OHT was verified by daily IOP measurement using a TonoLab rebound tonometer. Simultaneously to OHT induction, one group received daily MTK treatment and the control group vehicle solution by oral gavage. Animals were sacrificed 13-15 days after MB injection. Retina and optic nerves (ON) of OHT and contralateral eyes were analyzed by immunofluorescence with specific markers for RGCs (Brn3a), microglial cells/macrophages (Iba1 and CD68), and cysteinyl leukotriene pathway receptors (CysLT1R and GPR17). Protein labeling was documented by confocal microscopy and analyzed with ImageJ plugins. Further, mRNA expression of genes of the inflammatory and leukotriene pathway was analyzed in retinal tissue. MTK treatment resulted in a short-term IOP reduction at day 2, which dissipated by day 5 of OHT induction in MTK treated animals. Furthermore, MTK treatment resulted in a decreased activation of Iba1⁺ microglial cells in the retina and ON, and in a significantly increased RGC survival in OHT eyes. Within the retina, GPR17 and CysLT1R expression was demonstrated in single RCGs and in microglial cells respectively. Further, increased mRNA expression of pro-inflammatory genes was detected in OHT induced retinas. In the ON, OHT induction increased the number of GPR17⁺ cells, showing a trend of reduction following MTK treatment. This study shows for the first time a significantly increased RGC survival in an acute OHT model following treatment with the leukotriene receptor antagonist MTK. These results strongly suggest a neuroprotective effect of MTK and a potential new therapeutic strategy for glaucoma treatment.

Measures of disease activity in glaucoma

Glaucoma is the leading cause of irreversible blindness globally which significantly affects the quality of life and has a substantial economic impact. Effective detective methods are necessary to identify glaucoma as early as possible. Regular eye examinations are important for detecting the disease early and preventing deterioration of vision and quality of life. Current methods of measuring disease activity are powerful in describing the functional and structural changes in glaucomatous eyes. However, there is still a need for a novel tool to detect glaucoma earlier and more accurately. Tear fluid biomarker analysis and new imaging technology provide novel surrogate endpoints of glaucoma. Artificial intelligence is a post-diagnostic tool that can analyse ophthalmic test results. A detail review of currently used clinical tests in glaucoma include intraocular pressure test, visual field test and optical coherence tomography are presented. The advanced technologies for glaucoma measurement which can identify specific disease characteristics, as well as the mechanism, performance and future perspectives of these devices are highlighted. Applications of AI in diagnosis and prediction in glaucoma are mentioned. With the development in imaging tools, sensor technologies and artificial intelligence, diagnostic evaluation of glaucoma must assess more variables to facilitate earlier diagnosis and management in the future.

Effects of topical low-dose preservative-free hydrocortisone on intraocular pressure in patients affected by ocular surface disease with and without glaucoma

PURPOSE

This study aims to investigate the safety and efficacy of short-term treatment for ocular surface disease (OSD) with topical low-dose (1,005 mg) preservative-free hydrocortisone in one hundred patients with and without glaucoma.

METHODS

This was an open label non-randomized clinical trial. Patients with OSD with and without primary open-angle glaucoma (POAG) received topical low-dose (1,005 mg) preservative-free hydrocortisone twice daily in each eye for 2 weeks. All patients underwent a complete ophthalmological examination at baseline (T0) and at 1 (T1) and 2 (T2) weeks post-treatment. At each visit, the intraocular pressure (IOP) and the ocular surface disease index (OSDI) questionnaire scores were recorded; the Schirmer test was performed only at T0 and T2.

RESULTS

The OSDI score significantly decreased in both the POAG and no-POAG groups (both p < 0.0001) after hydrocortisone treatment, with no difference between the two groups (p = 0.72). There were no significant differences in IOP and Schirmer test results between T0 and T2 in both treatment groups (p = 0.68 and p = 0.83, respectively).

CONCLUSIONS

Topical low-dose (1,005 mg) preservative-free hydrocortisone is safe and effective for improving OSD symptoms both in patients with and without POAG.

TRIAL REGISTRATION

The trial was registered at clinicaltrials.gov under NCT04536129 on 01/09/2020 ("retrospectively registered").

GLIS1 regulates trabecular meshwork function and intraocular pressure and is associated with glaucoma in humans

Chronically elevated intraocular pressure (IOP) is the major risk factor of primary open-angle glaucoma, a leading cause of blindness. Dysfunction of the trabecular meshwork (TM), which controls the outflow of aqueous humor (AqH) from the anterior chamber, is the major cause of elevated IOP. Here, we demonstrate that mice deficient in the Krüppel-like zinc finger transcriptional factor GLI-similar-1 (GLIS1) develop chronically elevated IOP. Magnetic resonance imaging and histopathological analysis reveal that deficiency in GLIS1 expression induces progressive degeneration of the TM, leading to inefficient AqH drainage from the anterior chamber and elevated IOP. Transcriptome and cistrome analyses identified several glaucoma- and extracellular matrix-associated genes as direct transcriptional targets of GLIS1. We also identified a significant association between GLIS1 variant rs941125 and glaucoma in humans (P = 4.73 × 10-6), further supporting a role for GLIS1 into glaucoma etiology. Our study identifies GLIS1 as a critical regulator of TM function and maintenance, AqH dynamics, and IOP.

Lymphatics in Eye Fluid Homeostasis: Minor Contributors or Significant Actors?

Lymphatic vessels exert major effects on the maintenance of interstitial fluid homeostasis, immune cell trafficking, lipid absorption, tumor progression and metastasis. Recently, novel functional roles for the lymphatic vasculature have emerged, which can be associated with pathological situations. Among them, lymphatics have been proposed to participate in eye aqueous humor drainage, with potential consequences on intraocular pressure, a main risk factor for progression of glaucoma disease. In this review, after the description of eye fluid dynamics, we provide an update on the data concerning the distribution of ocular lymphatics. Particular attention is given to the results of investigations allowing the three dimensional visualization of the ocular surface vasculature, and to the molecular mechanisms that have been characterized to regulate ocular lymphatic vessel development. The studies concerning the potential role of lymphatics in aqueous humor outflow are reported and discussed. We also considered the novel studies mentioning the existence of an ocular glymphatic system which may have, in connection with lymphatics, important repercussions in retinal clearance and in diseases affecting the eye posterior segment. Some remaining unsolved questions and new directions to explore are proposed to improve the knowledge about both lymphatic and glymphatic system interactions with eye fluid homeostasis.

[Rho kinase inhibitors as new local therapy option in primary open angle glaucoma]

BACKGROUND

In 2014 in Japan and 2017 in the USA, the Rho-kinase inhibitors were approved as a new antiglaucomatous substance group and will now be launched in Europe.

OBJECTIVE

On this occasion the current state of knowledge on Rho-kinase inhibitors is presented.

METHODS

In intensive search in PubMed the relevant experimental and clinical literature on the Rho-kinase inhibitors ripasudil and netarsudil and the combination of netarsudil and latanoprost were selected and compiled for this review.

RESULTS

The intraocular pressure lowering efficacy of ripasudil and netarsudil is in the range of the beta blocker timolol and the prostaglandin analogue latanoprost. In the fixed combination netarsudil/latanoprost the intraocular pressure reduction is greater than that of the single components and reaches a target pressure of below 15 mm Hg in 32%. Conjunctival hyperemia with 53-65% is the most common local side effect. Systemic side effects are very rare and so far there are no contraindications.

CONCLUSION

The Rho-kinase inhibitors are an interesting new introduction for glaucoma therapy, as each new pressure-lowering therapy represents an additional chance to reach the individually defined target pressure level in a glaucoma patient with local therapy; however, many of the pleiotropic effects associated with Rho-kinase inhibitors have so far only been found experimentally and will require clinical confirmation in the future.

Neuroinflammation in Primary Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is the second leading cause of irreversible blindness worldwide. Increasing evidence suggests oxidative damage and immune response defects are key factors contributing to glaucoma onset. Indeed, both the failure of the trabecular meshwork tissue in the conventional outflow pathway and the neuroinflammation process, which drives the neurodegeneration, seem to be linked to the age-related over-production of free radicals (i.e., mitochondrial dysfunction) and to oxidative stress-linked immunostimulatory signaling. Several previous studies have described a wide range of oxidative stress-related makers which are found in glaucomatous patients, including low levels of antioxidant defences, dysfunction/activation of glial cells, the activation of the NF-κB pathway and the up-regulation of pro-inflammatory cytokines, and so on. However, the intraocular pressure is still currently the only risk factor modifiable by medication or glaucoma surgery. This present review aims to summarize the multiple cellular processes, which promote different risk factors in glaucoma including aging, oxidative stress, trabecular meshwork defects, glial activation response, neurodegenerative insults, and the altered regulation of immune response.

Minimally Invasive Surgery in Mild-to-Moderate Glaucoma Patients in Italy: Is It Time to Change?

Medical therapy is the first treatment choice for most patients with glaucoma; however, in a relevant proportion of patients, intraocular pressure (IOP) reduction is achieved with multi-therapy and/or high therapeutic doses. Conventional surgery is the standard alternative to medical therapy when this is not effective or not tolerated. Recently, selective laser trabeculoplasty (SLT) has been advocated as first-line therapy, and "minimally invasive glaucoma surgery" (MIGS) has been developed as safer and less traumatic surgical intervention for patients with glaucoma. Schlemm's canal surgery has emerged as one of the approaches with the most favorable risk-benefit profile for glaucoma patients in need of cataract surgery. However, despite the promising results, use of MIGS in Italy has been extremely low. We aimed to investigate the reasons of the lower-than-expected use of Schlemm's canal-based MIGS devices in Italy, share our perspective on their potential place in therapy, and give practical suggestions to improve the management of glaucoma patients.

Conjunctival thickness as a predictive imaging biomarker for the glaucoma filtration surgery outcome: An optical coherence tomography study

IMPORTANCE

To analyse the preoperative conjunctival thickness in glaucomatous patients undergoing filtration surgery (FS), using optical coherence tomography (OCT).

BACKGROUND

The conjunctival status represents one of the most critical determinants of the FS outcome.

DESIGN

Retrospective study.

PARTICIPANTS

Sixty-seven patients candidate to FS for uncontrolled glaucoma were enrolled.

METHODS

OCT was performed at the superior bulbar conjunctiva before FS, and at bleb site at the last follow-up (LF-up) after surgery.

MAIN OUTCOME MEASURES

Preoperative full, epithelial, and stromal conjunctival thickness (FCT, CET, CST) and reflectivity (CR), and LF-up bleb-wall thickness (BT), reflectivity (BR) and intraocular pressure (IOP), were the major outcomes. The relations between preoperative parameters and LF-up-IOP, BT and BR were calculated.

RESULTS

FS was completely successful in 23 patients (group 1), successful with medications in 22 (group 2), and failed in 22 (group 3). FCT, CET and CST were lower, whereas CR higher, in group 3 compared to groups 1 and 2 (P < .05); BT was lower (P < .001), whereas BR higher (P < .05) in group 3 compared to group 1. FCT and CST were predictors of FS outcome with lower thickness associated with increased odds of failure (odds ratio 0.922, P = .08; 0.941, P = .025). LF-up-IOP inversely correlated with FCT and CST (r = -0.447, P = .003; r = -0.408, P = .007), whereas positively correlated with CR (r = 0.789, P < .001).

CONCLUSIONS AND RELEVANCE

Preoperative conjunctival thickness and reflectivity show significant correlations with the FS outcome, both in terms of IOP and bleb-wall features. Therefore, they may be proposed as predictive imaging biomarkers to estimate the risk of filtration failure.

Cell atlas of aqueous humor outflow pathways in eyes of humans and four model species provides insight into glaucoma pathogenesis

Increased intraocular pressure (IOP) represents a major risk factor for glaucoma, a prevalent eye disease characterized by death of retinal ganglion cells; lowering IOP is the only proven treatment strategy to delay disease progression. The main determinant of IOP is the equilibrium between production and drainage of aqueous humor, with compromised drainage generally viewed as the primary contributor to dangerous IOP elevations. Drainage occurs through two pathways in the anterior segment of the eye called conventional and uveoscleral. To gain insights into the cell types that comprise these pathways, we used high-throughput single-cell RNA sequencing (scRNAseq). From ∼24,000 single-cell transcriptomes, we identified 19 cell types with molecular markers for each and used histological methods to localize each type. We then performed similar analyses on four organisms used for experimental studies of IOP dynamics and glaucoma: cynomolgus macaque (Macaca fascicularis), rhesus macaque (Macaca mulatta), pig (Sus scrofa), and mouse (Mus musculus). Many human cell types had counterparts in these models, but differences in cell types and gene expression were evident. Finally, we identified the cell types that express genes implicated in glaucoma in all five species. Together, our results provide foundations for investigating the pathogenesis of glaucoma and for using model systems to assess mechanisms and potential interventions.