Aqueous Humor Outflow Research Articles

Aqueous Humor Angiography.

Aqueous humor angiography, or aqueous angiography, is an anterior segment imaging technique capable of visualizing the conventional/trabecular aqueous humor outflow pathways. As a translational technique, it is applicable for in vivo imaging in living subjects and ex vivo imaging using whole-globe preparations or anterior segment perfusion setups. Excellent spatial and temporal resolution has enabled insights into the segmental distribution of aqueous humor outflow in physiological conditions as well as after trabecular bypass surgery. In this chapter, we thoroughly describe aqueous humor angiography in various experimental setups. The necessary materials for different settings and their application for in vivo and ex vivo experiments as well as notes on dye choice, dye sequences, and special considerations on performing aqueous humor angiography during surgery are presented.

Evaluation of Cross-Linked Actin Networks (CLANs) in Human Trabecular Meshwork Cells and Tissues.

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of glaucoma, the leading cause of irreversible vision loss and blindness. An overall increase in resistance to aqueous humor outflow causes sustained elevation in IOP. Glaucomatous insults in the aqueous humor outflow pathway, including the trabecular meshwork (TM), precede such chronic physiological changes in IOP. These insults include ultrastructural changes with excessive extracellular matrix deposition and actin cytoskeletal reorganization that leads to pathological stiffening of the ocular tissues. One of the most common cytoskeletal changes associated with TM tissue stiffness in glaucoma is the increased prevalence of cross-linked actin networks (CLANs) in cells of the trabecular meshwork (TM) and lamina cribrosa (LC). In glaucomatous cells, rearrangement of linear actin stress fibers leads to formation of polygonal arrays within the cytoplasm, resembling a geodesic dome-like structure, that we identified as CLANs. In addition to increased amounts of CLANs in POAG TM cells and tissues, we also discovered that glucocorticoid (GC) and TGFβ2 signaling pathways associated with the development of ocular hypertension (OHT) and glaucoma also induced CLANs in the TM. Despite a clear association, we are yet to completely understand the mechanisms involved in CLAN formation and their direct relevance to disease pathology. In this chapter, we will describe methods to identify and characterize CLANs using fluorescent microscopy in primary TM cell cultures, ex vivo perfusion cultured human anterior segments, and in situ in human donor eyes.

Time-Lapse Live-Cell Imaging Using Fluorescent Protein Sensors in Outflow Pathway Cells Under Fluid Flow Conditions.

The role of shear stress in regulating aqueous humor (AH) outflow and intraocular pressure (IOP) in the trabecular meshwork (TM) and Schlemm's canal (SC) of the eye is an emerging field. Shear stress has been shown to activate mechanosensitive ion channels in TM cells and induce nitric oxide production in SC cells, which can affect outflow resistance and lower IOP. Live-cell imaging using fluorescent protein sensors has provided real-time data to investigate the physiological relationship between fluid flow and shear stress in the outflow pathway cells. The successful application of time-lapse live-cell imaging in primary cultured cells has led to the identification of key cellular and molecular mechanisms involved in regulating AH outflow and IOP, including the role of autophagy and primary cilia as mechanosensors. This chapter presents a detailed protocol for conducting time-lapse live-cell imaging under fluid flow conditions in the outflow pathway cells.

Protocol for the Extraction and Characterization of Trabecular Meshwork Cell Cytoskeleton Fraction.

Among various cellular attributes modulating aqueous humor (AH) outflow through the trabecular pathway and eventually intraocular pressure, the involvement of actomyosin regulated cellular contraction and relaxation, cell-extracellular matrix adhesion and cell-cell junctions, and mechanotransduction are well recognized. Although various biological and pharmacological agent-modulated AH outflows were associated with altered actin cytoskeletal organization and cell adhesive interactions of trabecular meshwork (TM) cells, these changes were analyzed largely with a biased approach to examine the specific proteins, but there were very few efforts in examining them with hypothesis-free unbiased approach in their native state. Therefore, in this chapter, we describe a protocol tailored to characterize the cytoskeleton of TM cells. This simple protocol can be applied to identifying the differentially regulated TM cell cytoskeleton proteins under any given treatment condition in conjunction with quantitative proteomic analysis.

Effectiveness and biocompatibility of a novel Schlemm’s canal microstent for glaucoma management

To evaluate the effectiveness and biocompatibility of Wistend, a novel Schlemm’s canal (SC) microstent made of Nitinol designed to improve aqueous humor outflow. New Zealand white (NZW) rabbits were divided into blank, sham-operated and Wistend groups. ICare® Tonovet Plus®, swept-source optical coherence tomography (SS-OCT), slit lamp biomicroscopy, retinal camera and scanning electron microscopy (SEM) were used for preoperative and postoperative observations. Hematoxylin and Eosin (H&E) tissue staining was adopted for biocompatibility. A significant difference in intraocular pressure (IOP) between the Wistend group and the control groups was observed during the six-month follow-up. SS-OCT identified arc line internal reflections within the SC in the anterior chamber angle. Conjunctival congestion and edema gradually diminished in the early stages. No corneal vascularization, no anterior chamber inflammatory response and no significant tissue reactions were noted in any groups. SEM showed the Wistend’s windows and orifices remained clear, encircled by minimal incidental ocular tissue and free from blockage. Histopathological examination revealed no discernible differences between the Wistend-implanted and sham-operated eyes. These in vivo studies demonstrate the effectiveness and biocompatibility of the microstent. Our findings suggest a promising potential for Wistend in significantly reducing IOP and effectively facilitating the outflow of aqueous humor.

Green-Light-Triggered and Self-Calibrated Cascade Release of Nitric Oxide and Carbon Monoxide for Synergistic Glaucoma Therapy.

Glaucoma is an optic degenerative neuropathy that is driven by a vicious cycle of oxidative stress and mechanical stress. Current clinical treatments aim exclusively at alleviating mechanical stress by reducing the intraocular pressure (IOP). With the unattended oxidative stress, recurrence and deterioration of mechanical stress are inevitable. Nitric oxide (NO) and carbon monoxide (CO) are endogenous gaseous signaling molecules for vasodilation and anti-inflammation, respectively. Mounting evidence suggests an intricate interplay between NO and CO to mediate their biological roles, like how it takes two to dance a waltz. This leads to the concept of "gas waltz therapy" for glaucoma, in which NO is released to reduce IOP and stoichiometric CO is coreleased to suppress oxidative stress. CND570 is the first phototriggered cascade NO/CO donor, to the best of our knowledge. Notably, the release of NO/CO is accompanied by the concomitant release of a rhodamine dye whose bright fluorescence is harnessed as a convenient calibration mechanism of the gas release profile. CND570 exhibits excellent transcorneal permeability and reaches the target aqueous humor outflow pathway. Further, green-light irradiation triggers release of CO and NO in the eye tissue of glaucoma mice. NO and CO could promote the upregulation of soluble guanylate cyclase (sGC) in both in vitro and in vivo models. Notably, CND570 treatment significantly reduces the oxidative stress associated with glaucoma. NO/CO-based gas waltz therapy is a promising new avenue for glaucoma treatment.

Corticosteroids and glaucoma: How do treatments trigger ocular nerve damage? - A systematic literature review

Corticosteroids are steroid hormone derivatives produced by the adrenal glands. Corticosteroids in the health sector have been widely utilized as anti-inflammatory agents because of their strong and rapid effects. This study aimed to identify the impact of long-term corticosteroid use on eye damage. This study uses a systematic literature review, which is guided by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) to the article screening process. The data of this study, in the form of demographic variables, route of administration, steroid type, comorbidities, and patient risk factors, were descriptively analyzed. As a result, 15 of the 22 articles were selected for analysis. Chronic corticosteroid administration may precipitate optic neuropathy, manifesting as glaucoma, which is characterized by progressive structural degeneration of retinal ganglion cells (RGCs) and concomitant visual function deterioration. The locus of primary pathological insult in glaucomatous conditions is the optic nerve head, specifically at the optic disc. This anatomical site is notable for the abrupt 90-degree angular deviation of RGC axons as they transition from the retinal nerve fiber layer to their trajectory within the optic nerve proper. The use of corticosteroids can damage ocular nerve tissue through an increase in intraocular pressure (IOP) beyond 21 mmHg. This increase in IOP is due to changes in the microstructure of the trabeculum webbing, resulting in increased obstruction to the outflow of aqueous humor.

Delayed onset Spontaneous Hyphema after OMNI® Surgical System

Minimally invasive glaucoma surgery (MIGS) offers options for glaucoma treatment that have generally improved safety profiles compared with filtering surgery. MIGS vary in design and procedure, but all angle-based MIGS function by bypassing or removing aqueous humor outflow resistance at the level of the trabecular meshwork. This can lower intraocular pressure but also remove the blood-aqueous barrier. Most studies of MIGS report on relatively short-term safety, but awareness of potential long-term complications is critical for optimal patient management. This case report describes a patient with recurrent and refractory delayed onset spontaneous hyphema after OMNI procedure. To the best of our knowledge, this is the first case report describing this complication of the OMNI surgical system.

Low Intraocular Pressure Induces Fibrotic Changes in the Trabecular Meshwork and Schlemm's Canal of Sprague Dawley Rats.

Continuous artificial aqueous humor drainage in the eyes of patients with glaucoma undergoing trabeculectomy likely exerts abnormal shear stress. However, it remains unknown how changes in intraocular pressure (IOP) can affect aqueous humor outflow (AHO). Here, we induced and maintained low intraocular pressure (L-IOP) in healthy Sprague Dawley (SD) rats by puncturing their eyes using a tube (200-µm diameter) for 2 weeks. After the rats were euthanized, their eyes were removed, fixed, embedded, stained, and scanned to analyze the physiological and pathological changes in the trabecular meshwork (TM) and Schlemm's canal (SC). We measured SC parameters using ImageJ software and assessed the expression of various markers related to flow shear stress (KLF4), fibrosis (TGF-β1, TGF-β2, α-SMA, pSmad1/5, pSmad2/3, and fibronectin), cytoskeleton (integrin β1 and F-actin), diastolic function (nitric oxide synthase and endothelial nitric oxide synthase [eNOS]), apoptosis (cleaved caspase-3), and proliferation (Ki-67) using immunofluorescence or immunohistochemistry. L-IOP eyes showed a larger SC area, higher eNOS expression, and lower KLF4 and F-actin expression in the TM and SC (both P < 0.05) than control eyes. The aqueous humor of L-IOP eyes had a higher abundance of fibrotic proteins and apoptotic cells than that of control eyes, with significantly higher TGF-β1, α-SMA, fibronectin, and cleaved caspase-3 expression (all P < 0.05). In conclusion, a persistence of L-IOP for 2 weeks may contribute to fibrosis in the TM and SC and might be detrimental to conventional AHO in SD rat eyes. Clinicians should consider that aberrant shear force induced by aqueous humor fluctuation may damage AHO outflow channel when treating patients.

Schlemm's canal-selective Tie2/TEK knockdown induces sustained ocular hypertension in adult mice

Deficient Angiopoietin-Tie2 signaling is linked to ocular hypertension in glaucoma. Receptor Tie2/TEK expression and signaling at Schlemm's canal (SC) is indispensable for canal integrity and homeostatic regulation of aqueous humor outflow (AHO) and intraocular pressure (IOP), as validated by conditional deletion of Tie2, its ligands (Angpt1, Angpt2 and Angpt3/4) or regulators (Tie1 and PTPRB/VE-PTP). However, these Tie2/TEK knockouts and conditional knockouts are global or endothelial, preventing separation of systemic and ocular vascular defects that impact retinal or renal integrity. To develop a more targeted model of ocular hypertension induced by selective knockdown of Tie2/TEK expressed in SC, we combined the use of viral vectors to target the canal, and two distinct gene-editing strategies to disrupt the Tie2 gene. Adeno-associated virus (AAV2) is known to transduce rodent SC when delivered into the anterior chamber by intracameral injection. First, delivery of Cre recombinase via AAV2.Cre into R26tdTomato/+ reporter mice confirmed preferential and stable transduction in SC endothelium. Next, to disrupt Tie2 expression in SC, we injected AAV2.Cre into homozygous floxed Tie2 (Tie2FL/FL) mice. This led to attenuated Tie2 protein expression along the SC inner wall, decreased SC area and reduced trabecular meshwork (TM) cellularity. Functionally, IOP was significantly and steadily elevated, whereas AHO facility was reduced. In contrast, hemizygous Tie2FL/+ mice responded to AAV2.Cre with inconsistent and low IOP elevation, corroborating the dose-dependency of ocular hypertension on Tie2 expression/activation. In a second model using CRISPR/SaCas9 genome editing, wild-type C57BL/6 J mice injected with AAV2.saCas9-sgTie2 showed similar selective SC transduction and comparable IOP elevation in course and magnitude to that induced by AAV2.Cre in Tie2FL/FL mice. Together, our findings, demonstrate that selective Tie2 knockdown in SC is a targeted strategy that reliably induces chronic ocular hypertension and reproduces glaucomatous damage to the conventional outflow pathway, providing novel models of SC-Tie2 signaling loss valuable for preclinical studies.

Neuroprotective Actions of Hydrogen Sulfide-Releasing Compounds in Isolated Bovine Retinae

Background: We have evidence that hydrogen sulfide (H2S)-releasing compounds can reduce intraocular pressure in normotensive and glaucomatous rabbits by increasing the aqueous humor (AH) outflow through the trabecular meshwork. Since H2S has been reported to possess neuroprotective actions, the prevention of retinal ganglion cell loss is an important strategy in the pharmacotherapy of glaucoma. Consequently, the present study aimed to investigate the neuroprotective actions of H2S-releasing compounds against hydrogen peroxide (H2O2)-induced oxidative stress in an isolated bovine retina. Materials and Methods: The isolated neural retinae were pretreated with a substrate for H2S biosynthesis called L-cysteine, with the fast H2S-releasing compound sodium hydrosulfide, and with a mitochondrial-targeting H2S-releasing compound, AP123, for thirty minutes before a 30-min oxidative insult with H2O2 (100 µM). Lipid peroxidation was assessed via an enzyme immunoassay by measuring the stable oxidative stress marker, 8-epi PGF2α (8-isoprostane), levels in the retinal tissues. To determine the role of endogenous H2S, studies were performed using the following biosynthesis enzyme inhibitors: aminooxyacetic acid (AOAA, 30 µM); a cystathione-β-synthase/cystathionine-γ-lyase (CBS/CSE) inhibitor, α–ketobutyric acid (KBA, 1 mM); and a 3-mercaptopyruvate-s-sulfurtransferase (3-MST) inhibitor, in the absence and presence of H2S-releasing compounds. Results: Exposure of the isolated retinas to H2O2 produced a time-dependent (10–40 min) and concentration-dependent (30–300 µM) increase in the 8-isoprostane levels when compared to the untreated tissues. L-cysteine (10 nM–1 µM) and NaHS (30 –100 µM) significantly (p &lt; 0.001; n = 12) prevented H2O2-induced oxidative damage in a concentration-dependent manner. Furthermore, AP123 (100 nM–1 µM) attenuated oxidative H2O2 damage resulted in an approximated 60% reduction in 8-isoprostane levels compared to the tissues treated with H2O2 alone. While AOAA (30 µM) and KBA (1 mM) did not affect the L-cysteine evoked attenuation of H2O2-induced oxidative stress, KBA reversed the antioxidant responses caused by AP123. Conclusions: In conclusion, various forms of H2S-releasing compounds and the substrate, L-cysteine, can prevent H2O2-induced lipid peroxidation in an isolated bovine retina.

Robotic Visible-Light Optical Coherence Tomography Visualizes Segmental Schlemm's Canal Anatomy and Segmental Pilocarpine Response.

To use robotic visible-light OCT (vis-OCT) to study circumferential segmental Schlemm's canal (SC) anatomy in mice after topical pilocarpine administration. Anterior segment imaging was performed using a vis-OCT sample arm attached to a 6-degree-of-freedom robotic arm to maintain normal (perpendicular) laser illumination aimed at SC around the limbus. Sixteen mice were studied for repeatability testing and to study aqueous humor outflow (AHO) pathway response to topical drug. Pharmaceutical-grade pilocarpine (1%; n = 5) or control artificial tears (n = 9) were given, and vis-OCT imaging was performed before and 15 minutes after drug application. After SC segmentation, SC areas and volumes were measured circumferentially in control- and drug-treated eyes. Circumferential vis-OCT provided high-resolution imaging of the anterior segment and AHO pathways, including SC. Segmental SC anatomy was visualized with the average cross-sectional area greatest temporal (3971 ± 328 µm 2 ) and the least nasal (2727 ± 218 µm 2 ; p = 0.018). After pilocarpine administration, the iris became flatter, and SC became larger (pilocarpine: 26.8 ± 5.0% vs. control: 8.9 ± 4.6% volume increase; p = 0.030). However, the pilocarpine alteration was segmental as well, with a greater increase observed superior (pilocarpine: 31.6 ± 8.9% vs. control: 1.8 ± 5.7% volume increase; p = 0.023) and nasal (pilocarpine: 41.1 ± 15.3% vs. control: 13.9 ± 4.5% volume increase; p = 0.045). High-resolution circumferential non-invasive imaging using AS-OCT of AHO pathways is possible in living animals with robotic control. Segmental SC anatomy was seen at baseline and was consistent with the known segmental nature of trabecular AHO. Segmental SC anatomical response to a muscarinic agonist was seen as well. Segmental glaucoma drug response around the circumference of AHO pathways is a novel observation that may explain the variable patient response to glaucoma treatments.

Roles of Prostaglandins and Hydrogen Sulfide in an Outflow Model of the Porcine Ocular Anterior Segment Ex Vivo

Background: Hydrogen sulfide (H2S)-releasing compounds can reduce intraocular pressure in normotensive rabbits by increasing aqueous humor (AH) outflow through the trabecular meshwork. In the present study, we investigated the contribution of endogenous H2S and the role of intramurally generated prostaglandins in the observed increase in AH outflow facility in an ex vivo porcine ocular anterior segment model. Material and Methods: Porcine ocular anterior segment explants were perfused with Dulbecco’s Modified Eagle’s Medium maintained at 37 °C and gassed with 5% CO2 and 95% air under an elevated pressure of 15 mmHg for four hours. Perfusates from the anterior segment explants were collected and immediately assayed for their H2S and prostaglandin E2 content. Results: Elevating perfusion pressure from 7.35 to 15 mm Hg significantly (p &lt; 0.001) increased H2S concentration in the perfusate from 0.4 ± 0.1 to 67.6 ± 3.6 nM/µg protein. In the presence of an inhibitor of cystathionine ß-synthase/cystathionine γ-lyase, aminooxyacetic acid (AOAA, 30 µM), or an inhibitor of 3-mercaptopyruvate sulfurtransferase, α-ketobutyric acid (KBA, 1 mM), the effects of elevated pressure on H2S levels in the perfusate was significant (p &lt; 0.001). Furthermore, flurbiprofen (30 µM) and indomethacin (10 µM) attenuated the elevated pressure-induced increase in H2S levels in the perfusate. Interestingly, elevating perfusion pressure had no significant effect on PGE2 concentrations in the perfusate. While the inhibition of H2S biosynthesis by AOAA or KBA did not affect PGE2 levels in perfusate, flurbiprofen (30 µM) caused a significant (p &lt; 0.05) decrease in the concentration of PGE2 under conditions of elevated perfusion pressure. Conclusions: We conclude that the elevated perfusion pressure-induced increase in H2S concentrations depends upon the endogenous biosynthesis of H2S and intramurally produced prostaglandins in the porcine anterior segment explants. While the concentration of PGE2 in the perfusate under elevated perfusion pressure was unaffected by pretreatment with inhibitors of H2S biosynthesis, it was reduced in the presence of an inhibitor of cyclooxygenase.

Role for NLRP3 inflammasome-mediated, Caspase1-dependent response in glaucomatous trabecular meshwork cell death and regulation of aqueous humor outflow

PurposeAcute ocular hypertension (AOH) is the defining feature of acute glaucoma. The mechanical stress and excessive production of reactive oxygen species (ROS) during episodes can directly or indirectly damage the trabecular meshwork (TM). Despite its significance, a clear understanding of its pathogenesis and an effective therapeutic target remain lacking in acute glaucoma. In the present study, we explored the potential molecular mechanisms underlying TM cell death following oxidative damage and AOH. The use of NAC/VX-765 as a potential pharmaceutical intervention for reducing intraocular pressure (IOP) was discussed. MethodsThe levels of NLRP3 and caspase-1 were compared between normal and glaucomatous TM samples. An in vitro oxidative damage model and an AOH rat model were used to investigate the potential molecular mechanism behind TM cell death. The ROS scavenger N-acetyl-L-cysteine (NAC) and caspase-1 inhibitor VX-765 were used to counteract TM damage. ResultsElevated levels of NLRP3 and caspase-1 were observed in patients with acute glaucoma. H2O2 exposure decreased the viability of human trabecular meshwork (HTM) cells and increased intracellular ROS levels. Both Gene and protein expressions of NLRP3, caspase-1, GSDMD-N, and IL-1β were notably upregulated in H2O2-induced HTM cells and the rodent AOH model. Both NAC and VX-765 demonstrated protective effects against TM injury by inhibiting pyroptosis. The IOP-lowering effects of NAC and VX-765 persisted for 7 days. ConclusionsOur findings indicate that the classical pyroptosis pathway, NLRP3/caspase-1/IL-1β, plays a key role in acute glaucomatous TM injury. Targeting pyroptosis provides novel therapeutic avenues for treating AOH-induced irreversible TM injury. This provides not only a promising therapeutic target for glaucoma but also introduces a new approach to intervention.

Secondary Glaucoma Following Corneal Transplantation: A Comprehensive Review of Pathophysiology and Therapeutic Approaches.

Corneal transplantation is a critical surgical procedure aimed at restoring vision in patients with corneal blindness or severe damage. This review focuses on secondary glaucoma, a significant postoperative complication, with the primary objective of providing a comprehensive analysis of its pathophysiology, risk factors, diagnostic challenges, and therapeutic approaches. Unlike other reviews, this work emphasizes the interplay between inflammatory responses, corticosteroid use, and structural changes in the eye that lead to elevated intraocular pressure (IOP) after transplantation. A comprehensive review of the literature was conducted, including studies on postcorneal transplantation glaucoma, to highlight both clinical outcomes and the efficacy of current management strategies. Key findings indicate that medical treatments, such as prostaglandin analogs and beta-blockers, are effective for IOP control in the early stages, while surgical interventions, like trabeculectomy, are often necessary for more advanced cases. Diagnostic challenges, such as the difficulty of accurate IOP measurement posttransplant, are underscored, along with the importance of advanced imaging techniques for the early detection of optic nerve damage. The pathophysiology of secondary glaucoma involves a complex interaction of postsurgical inflammation, steroid-induced complications, and anatomical changes that hinder aqueous humor outflow. Diagnosis requires a combination of tonometry, gonioscopy, and imaging technologies. Management strategies range from pharmacological treatments to surgical options, with a critical focus on balancing IOP control and minimizing risks to graft survival. Clinically, these findings highlight the need for proactive and tailored management of IOP in corneal transplant patients to preserve both graft function and long-term visual outcomes. Future research should focus on improving diagnostic accuracy, developing less invasive surgical techniques, and exploring personalized medicine approaches, including genetic profiling and targeted therapies.

In Vivo Models of Steroid-Induced Intraocular Hypertension

Corticosteroids are widely utilized for their anti-inflammatory and immunosuppressive properties but often lead to ocular complications, including ocular hypertension. If untreated, ocular hypertension can progress to optic nerve atrophy and eventually result in steroid-induced glaucoma, which poses a risk of irreversible visual damage. Approximately 40% of individuals experience increased intraocular pressure after steroid use, and around 6% develop glaucoma. Although steroid-induced glaucoma is usually temporary and reversible if the treatment duration is under a year, prolonged exposure can cause permanent vision impairment. The pathogenesis of steroid-induced glaucoma is suggested to arise from increased outflow resistance of aqueous humor, primarily due to decreased expression of matrix metalloproteinases. This deficiency promotes the deposition of extracellular matrix and the dysfunction of trabecular meshwork cells. Additionally, modifications in the actin cytoskeleton increase the stiffness and alter the morphology of trabecular meshwork, further impeding aqueous humor outflow. Molecular changes, such as elevated expression of the MYOC gene, have also been implicated in restricting aqueous outflow. Various animal models, including rats, mice, primates, rabbits, cattle, sheep, cats, and dogs, have been developed to study steroid-induced glaucoma. These models exhibit pathological, pathophysiological, and molecular similarities to human disease, making them valuable for research. This review aims to summarize common animal models of steroid-induced ocular hypertension, discussing their advantages and limitations. The goal is to help researchers select appropriate models for future studies, thereby advancing the understanding of disease mechanisms and developing preventive strategies.

Visualization of the Postoperative Position of the Hydrus® Microstent Using Automatic 360° Gonioscopy.

Introduction: Glaucoma, one leading cause of irreversible vision loss worldwide, is primarily caused by elevated intraocular pressure (IOP). Recently, minimally invasive glaucoma surgeries (MIGSs) have become popular due to their shorter surgical times, tissue-sparing nature, and faster recovery. One such MIGS, the Hydrus® nickel-titanium alloy Microstent, helps lower IOP by improving aqueous humor outflow. The NIDEK GS-1 automated 360° gonioscope provides advanced imaging of the chamber angle for evaluation and documentation. The aim of this study was to test automated 360° gonioscopy for the detection of postoperative positional variations after Hydrus® Microstent implantation. This study is the largest to date to evaluate post-op positioning of the Hydrus® Microstent using the NIDEK GS-1. Materials and Methods: This study analyzed postoperative outcomes and stent location in eyes diagnosed with mild to moderate glaucoma that underwent Hydrus® Microstent implantation with or without phacoemulsification. Patients with prior IOP-lowering surgery or vitrectomy were excluded. Analyses of the postoperative Hydrus® Microstent position were based on the evaluation of automated 360° gonioscopy images. Results: Twenty-three eyes were included in the study, and all showed a reduction in IOP and a decrease in antiglaucomatous drop use postoperatively. Postoperative gonoscopic images showed variations in implant position. In all cases, the proximal inlet was clearly visible in the anterior chamber. The degree of protrusion into the anterior chamber was variable. The distal tip of the stent was visible behind the trabecular meshwork in Schlemm's canal in five cases, in the anterior chamber in one case, and not visible in seven cases. In no case did postoperative alterations in the position of the implant lead to explantation. Conclusions: This study demonstrated that the Hydrus® Microstent can effectively lower IOP even in the presence of postoperative positional variations. Automated 360° gonioscopy was found to be a useful tool to verify and document the postoperative position of the implant. Positional changes did not require device explantation in any of the cases evaluated.

Changes in anterior segment after short-term scleral lens wear in healthy Chinese population

PurposeTo evaluate the impact of short-term scleral lens (SL) wear on anterior chamber (AC) dimension and central corneal thickness (CCT) in healthy Chinese people. MethodsThis is a prospective, daily wear study. Eligible participants were dispensed SLs to correct refractive errors. Anterior segment (AS) parameters were measured by AS optical coherence tomography (AS-OCT) before, during, and after 2 and 4 hours of lens wear. Repeated-measures analysis of variance (ANOVA) was used to analyze the changes in AS parameters over time. ResultsTwelve subjects (10 females and 2 males) with a mean age of 25.3 ± 3.8 years (ranging from 21 to 34 years) were recruited. The AC parameters, including anterior chamber depth (ACD) from the endothelium (endo-ACD), angle opening distance at 500 μm (AOD500), and trabecular-iris space area at 500 μm (TISA500), significantly decreased after wearing SLs for 4 hours (P<0.05). CCT increased by 12 μm (2.29 %) after wearing SLs for 4 hours (P=0.013). ConclusionThis study suggests that SL wear has a significant impact on AS dimensions in patients with healthy corneas in the short term with SL in situ, but tend to recover quickly after SL removal. Further research is needed to determine whether the change in AS dimensions during SL wear affects aqueous humor (AH) outflow and causes changes in intraocular pressure (IOP).

The S341P mutant MYOC renders the trabecular meshwork sensitive to cyclic mechanical stretch

The trabecular meshwork (TM) plays an essential role in the circulation of aqueous humor by sensing mechanical stretch. The balance between the outflow and inflow of aqueous humor is critical in regulating intraocular pressure (IOP). A dysfunctional TM leads to resistance to the outflow of aqueous humor, resulting in an elevated IOP, a major risk factor for glaucoma. It is widely accepted that mutant myocilin (MYOC) can cause damage to the TM. However, few studies have investigated how TM cells carrying mutant MYOC respond to cyclic mechanical stretch (CMS) and whether these cells are more sensitive to CMS under this genetic background. In this study, we applied mechanical stretch to TM cells using the Flexcell system to mimic physiological stress. In addition, we performed genome-wide transcriptome analysis and oxidized lipidomics to systematically compare the gene expression and oxylipin profiles of non-stretched control human primary TM cells, human primary TM cells under CMS (TM-CMS), and human primary TM cells overexpressing MYOCS341P under CMS (S341P-CMS). We found that TM cells that overexpressed MYOCS341P were more sensitive to mechanical stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that downregulated genes were most enriched in oxidative phosphorylation, indicating mitochondria dysfunction and the likelihood of oxidative stress. Oxidized lipidomics analysis revealed significant changes in oxylipin profiles between the S341P-CMS and TM-CMS groups. Through further genome-wide transcriptomic analysis, we identified several genes that may be involved in the sensitivity of TM cells that overexpressed MYOCS341P to mechanical stress, including SARM1, AHNAK2, NT5C, and SOX8. The importance of these genes was validated by quantitative real-time PCR. Collectively, our findings indicate that mitochondrial dysfunction may contribute to the damage that occurs to TM cells with a MYOCS341P background under mechanical stretch.

Engineered sensor actuator modulator as aqueous humor outflow actuator for gene therapy of primary open-angle glaucoma

Glaucoma, a blinding eye disease with optic neuropathy, is usually associated with elevated intraocular pressure (IOP). The currently available pharmacological and surgical treatments for glaucoma have significant limitations and side effects, which include systemic reactions to medications, patient non-compliance, eye infections, surgical device failure, and damage to the eye. Here, we present Sensor-Actuator-Modulator (SAM), an engineered double mutant version of the bacterial stretch-activated mechanosensitive channel of large conductance (MscL) that directly senses tension in the membrane lipid bilayer of cells and in response, transiently opens its large nonspecific pore to release cytoplasmic fluid. The heterologously expressed mechanosensitive SAM channel acts as a tension-activated pressure release valve in trabeculocytes. In the trabecular meshwork (TM), SAM is activated by membrane stretch caused by elevated IOP. We have identified several SAM variants that are activated at physiologically relevant pressures. Using this barogenetic technology, we have demonstrated that SAM is functional in cultured TM cells, and successfully transduced in vivo in TM cells by use of AAV2/8. Further, it is effective in enhancing aqueous humor outflow facility leading to lowering the IOP in a mouse model of ocular hypertension.