Aqueous Humor Flow Research Articles

Human Anterior Segment Perfusion Organ Culture.

The human anterior segment perfusion organ culture is an ex vivo model system for studying the human conventional outflow pathway with reference to pressure regulation. In this model, anterior segments dissected from human donor eyes can be fixed to a modified petri dish and perfused with media along with various study agents at the physiological flow rate of 2.5μL/min. The model mimics the one-way flow of aqueous humor in human eyes and can be used to evaluate the effects of various drugs on eye pressure in real time. Using this model, cells and tissues of the anterior segment can be maintained for up to 28days, enabling histological and molecular evaluations.

A Mini-Review on Gene Therapy in Glaucoma and Future Directions

Glaucoma is a group of optic neuropathies characterized by the degeneration of retinal ganglion cells and the loss of their axons in the optic nerve. The only approved therapies for the treatment of glaucoma are topical medications and surgical procedures aimed at lowering intraocular pressure. Gene therapy involves the insertion, removal, or modification of genetic material within cells to repair or compensate for the loss of a gene’s function. It describes a process or technology that enables the genetic modification of cells to produce a therapeutic effect. However, changing the genetic material alone does not extend the duration of overexpression of proteins that combat disease, nor does it facilitate the production of new proteins for this purpose. We reviewed the literature concerning the use of gene therapy in the treatment of glaucoma and explored the future directions that this innovation may offer. Three genes associated with glaucoma have been identified within these loci: myocilin/trabecular meshwork glucocorticoid response (TIGR) (GLC1A), optineurin (GLC1E), and WDR36 (GLC1G). Among these, the most extensively studied glaucoma gene is myocilin (a TM-inducible glucocorticoid response gene). Building on previous successes, researchers have begun to apply genetic therapeutic approaches to alleviate or reduce symptoms associated with ocular hypertension (OHT) and glaucoma-like optic neuropathy (GON). It is evident that several therapeutic strategies exist that modulate aqueous humor production and flow, thereby regulating intraocular pressure (IOP) and protecting retinal ganglion cells (RGCs) from apoptosis. With the emergence of gene therapy as a potentially viable approach to preserving vision, new methods for managing glaucoma may soon become available. Genomic therapy is a promising treatment option for glaucoma patients and has significant potential for widespread clinical application.

Drug delivery from a ring implant attached to intraocular lens: An in-silico investigation

Multiple iterations required to design ocular implants, which will last for the desired operational period of months or even years, necessitate the use of in-silico models for ocular drug delivery. In this study, we developed an in-silico model to simulate the flow of Aqueous Humor (AH) and drug delivery from an implant to the Trabecular Meshwork (TM). The implant, attached to the side of the intraocular lens (IOL), and the TM are treated as porous media, with their effects on AH flow accounted for using the Darcy equation. This model accurately predicts the physiological values of Intraocular Pressure (IOP) for both healthy individuals and glaucoma patients, as reported in the literature. Results reveal that the effective diffusivity of the drug within the implant is the critical parameter that can alter the bioavailability time period (BTP) from a few days to months. Intuitively, BTP should increase as effective diffusivity decreases. However, we discovered that with lower levels of initial drug loading, BTP declines when effective diffusivity falls below a specific threshold. Our findings further reveal that, while AH flow has a minimal effect on the drug release profile at the implant site, it significantly impacts drug availability at the TM.

Modelling gravity-driven aqueous humour flow and drug delivery in Descemet’s membrane detachment

Topical medications are common initial treatments for Descemet’s membrane detachment (DMD). It is crucial to understand the aqueous humour (AH) flow and drug transport to facilitate the DMD treatment. This paper presents a mathematical model to analyse AH flow and drug transport in the anterior of the human eye considering gravity orientation effects. Utilizing the finite element method, the model couples AH flow dynamics, temperature-induced buoyancy, and drug transport by convection-diffusion. COMSOL Multiphysics is used to simulate the spatial-temporal distribution of AH and drugs delivery. The findings indicate that the eye positioning influences the directional flow of AH, due to temperature differences, and impacts the delivery of drug concentrations. It is also discovered that eye drops diffuse faster due to tear turnover in the eye yet more eye ointment is delivered as it has a longer contact time in the cornea. By understanding the AH flow and transport process, this proposed model may offer appropriate guidelines for optimizing DMD treatment under various forms of topical drugs and eye positions.

A digoxin derivative that potently reduces intraocular pressure: efficacy and mechanism of action in different animal models.

Glaucoma is a blinding disease. Reduction of intraocular pressure (IOP) is the mainstay of treatment, but current drugs show side effects or become progressively ineffective, highlighting the need for novel compounds. We have synthesized a family of perhydro-1,4-oxazepine derivatives of digoxin, the selective inhibitor of Na,K-ATPase. The cyclobutyl derivative (DcB) displays strong selectivity for the human α2 isoform and potently reduces IOP in rabbits. These observations appeared consistent with a hypothesis that in ciliary epithelium DcB inhibits the α2 isoform of Na,K-ATPase, which is expressed strongly in nonpigmented cells, reducing aqueous humor (AH) inflow. This paper extends assessment of efficacy and mechanism of action of DcB using an ocular hypertensive nonhuman primate model (OHT-NHP) (Macaca fascicularis). In OHT-NHP, DcB potently lowers IOP, in both acute (24 h) and extended (7-10 days) settings, accompanied by increased aqueous humor flow rate (AFR). By contrast, ocular normotensive animals (ONT-NHP) are poorly responsive to DcB, if at all. The mechanism of action of DcB has been analyzed using isolated porcine ciliary epithelium and perfused enucleated eyes to study AH inflow and AH outflow facility, respectively. 1) DcB significantly stimulates AH inflow although prior addition of 8-Br-cAMP, which raises AH inflow, precludes additional effects of DcB. 2) DcB significantly increases AH outflow facility via the trabecular meshwork (TM). Taken together, the data indicate that the original hypothesis on the mechanism of action must be revised. In the OHT-NHP, and presumably other species, DcB lowers IOP by increasing AH outflow facility rather than by decreasing AH inflow.NEW & NOTEWORTHY When applied topically, a cyclobutyl derivative of digoxin (DcB) potently reduces intraocular pressure in an ocular hypertensive nonhuman primate model (Macaca fascicularis), associated with increased aqueous humor (AH) flow rate (AFR). The mechanism of action of DcB involves increased AH outflow facility as detected in enucleated perfused porcine eyes and, in parallel, increased (AH) inflow as detected in isolated porcine ciliary epithelium. DcB might have potential as a drug for the treatment of open-angle human glaucoma.

Statistical Investigations on Relationship of Intraocular Pressure with Environmental Factors

Clinical relevance: Intraocular pressure (IOP) has a significant role in glaucoma pathophysiology. There are factors that influence in the IOP value, such as central corneal thickness or the biomechanical properties of the cornea. However, other less studied factors may influence the IOP, such as environmental pollution.
 Background: The increase in air pollution is related to acute respiratory pathologies. Regarding the eyes, is related to conjunctivitis or dry eye disease. The purpose was to analyse the correlation of environmental factors (atmospheric pressure, temperature, O3, NO2, PM10 and PM2.5 concentrations) with intraocular pressure in young healthy patients.
 Methods: A cross-sectional study was carried out on patients treated at General Optica centres in Spain and Portugal in collaboration with the University of Valladolid. This study included healthy patients (between 18 and 40 years old). IOP measurements were taken with different air tonometers (CT-80, CT-800, NCT-200, NT-510 and NT-530) for one week and correlated with environmental factors (atmospheric pressure, temperature, O3, NO2, PM10 and PM2.5 concentrations). Correlation (Spearman’s Rho) analyses were performed between IOP and the different environmental parameters. Moreover, groupings were performed as a function of the values for healthy exposure levels recommended by the WHO. Different comparisons were performed using the Mann‒Whitney U test.
 Results: Statistically significant correlations were found (p < .04) between IOP and temperature (r = 0.37), atmospheric pressure (r = 0.20), NO2 (r = 0.14), PM10 (r = 0.21), O3 (r = 0.16) and PM2.5 concentrations (r = 0.16). Regarding the IOP values of people who were exposed to unhealthy concentrations (AQI > 20) versus those who were not, higher IOP values were only found in people exposed to PM2.5.
 Conclusion: Slight correlations were found between higher temperature, atmospheric pressure and concentrations of pollutant gases and increased IOP. More clinical studies are needed to understand the role that these environmental factors play in the aqueous humour flow and the value of IOP to know if and to what extent these factors may be risk of glaucoma.

A computational fluid dynamics investigation of endothelial cell damage from glaucoma drainage devices

Glaucoma drainage devices (GDDs) are prosthetic-treatment devices for treating primary open-angle glaucoma. Despite their effectiveness in reducing intraocular pressures (IOP), endothelial cell damage (ECD) is a commonly known side-effect. There have been different hypotheses regarding the reasons for ECD with one being an induced increase in shear on the corneal wall. A computational fluid dynamics (CFD) model was used to investigate this hypothesis in silico. The Ahmed Glaucoma Valve (AGV) was selected as the subject of this study using an idealised 3D model of the anterior chamber with insertion angles and positions that are commonly used in clinical practice. It was found that a tube-cornea distance of 1.27 mm or greater does not result in a wall shear stress (WSS) above the limit where ECD could occur. Similarly, a tube-cornea angle of 45° or more was shown to be preferable. It was also found that the ECD region has an irregular shape, and the aqueous humour flow fluctuates at certain insertion angles and positions. This study shows that pathological amounts of WSS may occur as a result of certain GDD placements. Hence, it is imperative to consider the associated fluid force interactions when performing the GDD insertion procedure.

Identifying Baseline Predictors of Selective Laser Trabeculoplasty Effectiveness: An Alternative Mathematical Approach.

Selective laser trabeculoplasty (SLT) emerges as a first-line treatment for newly diagnosed open-angle glaucoma and ocular hypertension. However, the interindividual response to SLT considerably varied. Large-scale clinical investigations concerning predictive factors for SLT effectiveness are limited. This study aimed to identify baseline predictors of the percentage intraocular pressure (IOP)-lowering effectiveness of SLT using an alternative mathematical approach. Mathematical equations of IOP under the steady state of aqueous humour flow were formulated. The conclusive equation integrates physiological variables, including trabecular outflow facility, uveoscleral outflow fraction, plasma protein concentration, albumin/globulin ratio, mean arterial pressure, episcleral venous pressure, and plasma osmolarity. The equation was employed to estimate the percentage of IOP reduction following SLT and subsequently subjected to global sensitivity analysis to determine significant predictors of the IOP-lowering effect of SLT using the Monte Carlo simulation of 8,192 samples. In the current model, a 50% improvement in the trabecular outflow facility impacted by SLT is associated with a mean percentage IOP reduction of 16.6%. Lower baseline trabecular outflow facilities were the strongest predictors, showing a correlation with greater effectiveness of SLT in terms of percentage of IOP reduction. The second most influential factor includes baseline uveoscleral outflow fraction, followed by baseline episcleral venous pressure. Specifically, lower baseline uveoscleral outflow fraction and episcleral venous pressure were found to be correlated with increased effectiveness of SLT. Baseline levels of plasma protein concentration, albumin/globulin ratio, mean arterial pressure, and plasma osmolarity have minimal impact on SLT success or failure. This study identifies baseline trabecular outflow facilities as the strongest predictor of SLT effectiveness. The results suggested that pre-SLT medical treatment that augments uveoscleral outflow and/or trabecular outflow facilities could compromise the effectiveness of subsequent SLT in terms of percentage IOP reduction compared to those who never received pre-SLT medication.

Pseudophakic Pupillary Block Following Cataract Extraction with Anterior Chamber Lens Implantation : A Case Report

Inteoduction : Pupillary block occurs when aqueous humor flow from posterior chamber to anterior chamber is obstructed by functional block between pupillary portion of iris and lens. It is relatively common when pupil is occluded by anterior chamber intraocular lens (IOL). This condition can lead to iris bombe, iridocorneal adhesion formation, increasing intraocular pressure (IOP), and optic nerve damage.
 Case Illustration : A 65-year-old woman came to local hospital with complaints of blurred left eye five days prior presentation. She had history of bilateral cataract surgery in 2013. On physical examination, BCVA was 6/6 on right eye and 1/300 on left eye. The IOP was 15. 3 on right eye and 31.5 on left eye. Slit lamp examination showed anterior chamber IOL on left eye, shallow camera oculi anterior (COA), no flare/cell, pupillary block was present, and no surgical iridectomy was found. She was previously given timolol 0.5% eye drop and added latanoprost 50 mcg eye drop, sodium chloride 4.4 mg- potassium chloride 0.8 mg eye drop for current therapy.
 Discussion : Pupillary block is a frequent complication of anterior chamber IOL implantation after cataract surgery. The anterior chamber in this patient was shallow, which indicates partial/total blocked aqueous flow from posterior chamber, causing an elevated IOP, and may disrupt optic nerve that cause decreased vision. Surgical iridectomy is suggested in high-risk procedures such as implantation of an anterior chamber IOL.
 Conclusion : Elevated IOP may cause visual dysfunction and damage to optic nerve. In cases of high-risk postoperative pupillary block, surgical iridectomy is suggested to prevent further complications

Self-generating electricity system driven by aqueous humor flow and trabecular meshwork contraction motion activated BCKa for glaucoma intraocular pressure treatment.

Primary open-angle glaucoma (POAG) is the most common form of glaucoma and the leading cause of irreversible vision loss and blindness worldwide. Intraocular pressure (IOP) is the only modifiable risk factor, and prompt treatment to lower IOP can effectively slow the rate of vision loss due to glaucoma. Trabecular meshwork (TM) cells can maintain IOP homeostasis by correcting and adjusting the resistance to aqueous humor outflow in response to sustained pressure changes. TM cells' function is reduced, and membrane ion channels are impaired in POAG. The dysfunction of Large conductance Ca2+-activated K+ (BKCa) plays a central role in the pathogenesis of POAG. In this work, we targeted MXene nanoparticles (MXene-RGD) with piezoelectric response to TM cells in a 3D model of glaucoma in vitro as well as in the rabbit Transient Ocular Hypertension (OHT) Model in vivo. MXene-RGD gives the TM electromechanical transfer properties, while the self-enhancing and self-generated electricity properties of the TM are determined by the aqueous humor flow rate and the size of the deformation of the TM. MXene-RGD is nontoxic, as illustrated by a cell toxicity study and histological examination. In a 3D in vitro model of high-pressure glaucoma, whole-cell patch-clamp confirmed that piezoelectric stimulation turns on BKCa, which reduces the volume of the cell. MXene-RGD was injected into the anterior chamber with minimal trauma, i.e., anterior chamber injection, and specifically targeted to TM cells. The OHT model in vivo confirmed the potential IOP-lowering ability of MXene-RGD. We evaluated the ion channels involved in the reduction of IOP by MXene-RGD by pre-treatment with a BKCa channel blocker (iberiotoxin, IbTX) and a voltage-gated Ca2+channel blocker (nifedipine). Quantitative qPCR analysis showed that MXene-RGD inhibited the upregulation of mRNA expression levels of the myofibroblast marker α-smooth muscle actin (α-SMA) and the inflammatory response marker interleukin-6 (IL-6) induced by IOP. Histology confirmed that MXene-RGD attenuated IOP-induced proliferation and collagen production in the TM. Taken together, we present for the first time a minimally invasive surgical approach for targeting TM cells for POAG by utilizing piezoresponse nanomaterials to target BKCa to repair or awaken the ability of TM cells to regulate IOP homeostasis on their own.

Microglial involvement in ocular hypertension

Glaucoma, a chronic and multifactorial neurodegenerative disease, is the leading cause of irreversible blindness. It is characterized by the degeneration of retinal ganglion cells (RGCs), loss of their axons, and damage to the lamina cribrosa. To study glaucomatous optic neuropathy, experimental rodent models are commonly used due to their low cost, ease of handling, and similarities to the human retina. The ideal model must reproduce tissue changes observed in human glaucoma, such as alterations of the optic nerve head, thinning of the retinal nerve fibre layer, activation of glial cells, and progressive degeneration of RGCs.The DBA/2J transgenic mouse model is the most commonly used genetic model, characterized by a gradual increase in intraocular pressure (IOP) with age, leading to rapid and progressive loss of RGCs and optic nerve degeneration. However, limitations such as iris atrophy and peripheral anterior synechiae can alter the anterior segment and influence IOP measurement. Induced models of ocular hypertension (OHT) have a predictable IOP increase following experimental procedures, but this increase is usually rapid and sustained for a relatively short time, which may not represent the slow and sustained IOP elevation observed in primary open‐angle glaucoma. Nonetheless, induced models produce similar pathophysiological mechanisms to genetic models. Other models include the injection of hypertonic saline into episcleral veins to cause scarring of the trabecular meshwork and elevate IOP, and the intracameral injection of polystyrene or magnetic microbeads to obstruct normal drainage flow of aqueous humour, resulting in an IOP increase. A new model employs an intracameral injection of a cross‐linking polymer that produces a viscosity increase, impeding normal drainage of the aqueous humour and resulting in an IOP increase and loss of RGCs.In this SIS, we review the different glaucoma models, their methods, and the retinal tissue changes, with a focus on microglial cell changes.

A novel effect of plasma rich in growth factors in the small leucine‐rich proteoglycans regulation in trabecular meshwork

Aims/Purpose: To analyse the effect of plasma rich in growth factors (PRGF) on the activity of small leucine‐rich proteoglycans (SRLPs) involved in extracellular matrix regulation in a trabecular meshwork fibrosis in vitro model.Methods: Trabecular meshwork cells were obtained from cadaveric donors in collaboration with the Blood and Tissue Centre of the Principality of Asturias (CEImPA2022.359). The cells were exposed to TGFβ2, which induces the expression of fibrosis markers. After 24 h in the presence of TGFβ2, the cells were treated with PRGF or human serum (control group) for 7 days. After the treatment period, samples were processed for immunocytochemistry or gene expression analysis by qPCR. Immunocytochemical techniques were used to examine the markers α‐sma, collagen I and collagen IV markers. The gene expression analysis included the genes lumican (LUM), decorin (DCN), biglycan (BGN) and fibromodulin (FMOD).Results: The induction of fibrosis in trabecular meshwork cells, characterized by an increase in extracellular matrix components such as α‐sma, collagen I and collagen IV, led to an increase in the expression of several SRLPs analysed, such as lumican, decorin, biglycan and fibromodulin. Treatment with PRGF for 7 days significantly reduced the expression of lumican, decorin and biglycan. In contrast, fibromodulin expression levels were slightly increased in the PRGF‐treated group.Conclusions: SRLPs play an important role in the regulation of the extracellular matrix in several ocular tissues. In glaucoma, altered expression of SRLPs such as lumican, decorin and biglycan leads to a glaucomatous phenotype in animal models. Changes in the expression of SRLPs have also been reported in the aqueous humour of glaucoma patients. PRGF treatment regulates the expression of SRLPs, as well as the expression and deposition of other fibrotic markers, and may promote aqueous humour flow and intraocular pressure control.

Acute Closed Angle Glaucoma : A Case Report

Glaucoma is an eye disorder characterized by disruption of the tissue and integrity of eye function. This study aims to describe a case of Glaucoma along with an explanation and management of its therapy so that it can help increase knowledge and detect it early. This type of research is a descriptive case study. The research was conducted at an eye clinic on February 12 2022 on patients who were diagnosed with acute angle closure glaucoma through anamnesis and direct physical examination of the patient. Based on the results of the anamnesis and physical examination obtained, Mrs. K was diagnosed with acute left angle closure glaucoma, an eye disorder that occurs due to a rapid increase in intraocular pressure as a sign of anterior eye closure. room, blocking the flow of aqueous humor. In this case, Timolol maleate 0.5% ED 2 dd gtt 1 OS therapy was given, a beta (?)-adrenergic receptor antagonist whose function is to reduce aqueous humor production. Apart from that, Acetazolamide 250 mg 3x1 therapy was also given, which is a class of carbonic anhydrase inhibitor which functions to suppress the production of aqueous humor. The conclusion of this study is that the most common cause of glaucoma is obstruction of aqueous humor outflow due to pupillary blockade, closure of the angle of the anterior chamber, narrowing of the trabecular meshwork and increased episcleral venous pressure thereby increasing intraocular pressure.

Myo/Nog Cells Increase in Response to Elevated Intraocular Pressure and Mitigate Ganglion Cell Death in a Mouse Model of Glaucoma

Glaucoma is one of the leading causes of blindness worldwide. Decreased aqueous humor drainage causes an increase in intraocular pressure (IOP), which in turn damages the ganglion cells of the retina and optic nerve. A mouse model of glaucoma was used to examine the behavior of Myo/Nog (M/N) cells, which were previously shown to respond to cataract surgery and retinopathy induced by hypoxia, light damage, and intravitreal injection of human retinal pigment epithelial cells. M/N cells express the skeletal-muscle-specific transcription factor MyoD, the bone morphogenetic protein inhibitor Noggin, and brain-specific angiogenesis inhibitor 1 (BAI1). Glaucoma was induced by injecting microbeads into the anterior chamber (AC) of the right eye to obstruct the flow of aqueous humor into the trabecular meshwork. IOP was elevated within three days of addition of microbeads. Loss of retinal ganglion cells (RGCs) and thinning of the ganglion cell layer–nerve fiber layer (GCL-NFL) was observed in tissue sections by day 32. The injection of microbeads resulted in an increase in BAI1-positive (+) M/N cells in the trabecular meshwork, ciliary body, canal of Schlemm, cornea, and ganglion cell layer (GCL). M/N cells ingested microbeads. The effect of further increasing the population of M/N cells on IOP and RGC loss was determined by injecting BAI1+ cells isolated from the brain into the AC of both eyes. Exogenous M/N cells prelabeled with CellTracker™ Red were found in the same tissues as the endogenous population of M/N cells in eyes with and without elevated IOP. The addition of M/N cells did not significantly reduce IOP in bead-injected eyes. However, there were significantly more RGCs and the NFL was thicker in glaucomatous eyes with M/N cell supplementation than eyes injected with phosphate-buffered saline. The numbers of RGCs and NFL thickness were similar in glaucomatous and non-glaucomatous eyes after adding M/N cells. These results demonstrate that endogenous M/N cells respond to elevated IOP in the anterior and posterior segments in response to induction of glaucoma. M/N cells’ mitigation of RGC loss may reflect a neuroprotective effect within the retina, as opposed to a significant drop in IOP.

Disorders of aqueous humor flow in the posterior part of the eye in the mechanisms of optic nerve damage development (literature review)

The study based on the literature search revealed that the peculiarities of fluid circulation in the posterior part of the eye have been studied insufficiently compared to the anterior part. It is suggested that the retina and optic nerve have their own cleansing system, which functions independently or in interaction with the brain's cleansing system. Of interest is the theory of the glymphatic system of the eye, which probably functions similarly to the glymphatic system of the brain, has four segments and ensures the exchange between intraocular, intracranial and interstitial fluids and the removal of metabolic waste products in the posterior part of the eye. Purpose. To determine the disorders of fluid circulation in the posterior part of the eye in the mechanisms of optic nerve damage development according to the literature. Methods: literature search of 48 sources. It is important to understand that the optic nerve under normal conditions passes a large amount of fluid from the eye to the brain and vice versa. The balance of perfusion (and, presumably, reperfusion in case of pathology) is ensured by the lamina cribrosa, the location of subarachnoid spaces in different parts of the nerve, and the AQP4 channels that support them. The question is whether the optic nerve has its own separate glymphatic system, or whether it interacts with the glymphatic system of the brain. It also remains unclear how the circulation of intraocular fluid, interstitial fluid of the retina and brain, and cerebrospinal fluid in the optic nerve is coordinated with blood, as well as with fluctuations in atmospheric pressure. Although this theory has not yet been recognized, it nevertheless has many supporters who explain optic nerve damage as a result of fluid circulation disturbances. The slowing of fluid flow, as well as the slowing of axonal transport, can be considered as the moment when neuropathy transforms into optic atrophy. That is why the study of the peculiarities of fluid flow and exchange in the posterior part of the eye is important when studying diseases of the optic nerve, whereas the correction of such circulation disorders could be used for therapeutic purposes. Conclusion. Impaired fluid circulation in the posterior part of the eye can occur in mechanisms of optic nerve damage. Improved diagnostics with the ability to assess hydrodynamics will help to understand the role of individual components, while their correction will likely contribute to the optic nerve recovery.

Possible dose-dependent effect of eplerenone on intraocular pressure.

Intraocular pressure (IOP) is the main modifiable risk factor for glaucoma. Current therapies target the anterior outflow of aqueous humor or its production. This study aims to demonstrate eplerenone could reduce IOP through a possible posterior outflow path via retinal pigment epithelium (RPE). In this retrospective study, IOP changes in patients undergoing eplerenone treatment were investigated. Inclusion criteria were IOP data immediately before and during treatment. Exclusion criteria included ophthalmic procedures, changes in topical glaucoma treatment, or taking systemic medications affecting IOP. After reviewing 162 charts, 41 subjects were eligible. Pearson correlation test was used to investigate the correlation between continuous IOP and eplerenone dosage. The mean ± SD IOP before eplerenone treatment was 14.31 ± 3.73 mmHg and decreased to 13.50 ± 4.04 mmHg; however, this was not statistically significant (P = 0.39). In subset of patients with eplerenone dose of more than 25 mg/day and baseline IOP equal to or less than 15 mmHg, the mean IOP before eplerenone treatment was 12.33 ± 2.59 mmHg and decreased to 10.33 ± 2.99, which is a trend toward IOP reduction with a 16% reduction in IOP (P = 0.055). A possible dose-dependent decrease in IOP with eplerenone provides indirect evidence for the posterior flow model and suggests the mineralocorticoid receptors (MRs) in RPE play a role in the posterior flow of aqueous humor. It can be deduced that the RPE pumps responsible for the posterior flow of aqueous humor are MR-regulated and their function can be enhanced with MR antagonists.

Clinical and Optical Coherence Tomography Evidence of Aqueous Humor Flow from the Suprachoroidal Space to Conjunctival Lymphatics.

A surgical technique was developed to enhance aqueous humor (AH) flow through the non-trabecular outflow pathway by rerouting it from the anterior chamber (AC) to the suprachoroidal space (SCS) without detaching the ciliary body from the scleral spur. Medium- and long-term surgical outcomes were retrospectively analyzed in a case series of 58 glaucoma patients. At 6, 12, and 24 months, the mean IOP decreased from 27.8 ± 8.3 to 14.9 ± 5.0 mmHg, median 15.0 (25th percentile (p25)13.0; 75th percentile (p75) 18.0) and 15.2 ± 3.3 mmHg, and hypotensive medication use reduced from a median (p25; p75) of 3 (2; 3) to 0 (0; 2), 0 (0; 2), and 0 (0; 1.5), respectively. Intra- and postoperative complications were few and manageable. Following surgery, no bleb formation occurred in any of the cases (as confirmed by optical coherence tomography). Conjunctival lymphatic vessels (CLVs) developed in 50% of eyes (29/58). Clinically, they developed directly from sclera and had no connection to the surgical site. Analysis further showed that the development of CLVs and their longer visibility period had poor prognostic value for IOP control. If the fluid flow from the SCS to CLVs was resistance-free, no CLV development was evident. However, if any resistance existed in the flow, the fluid accumulated in lymphatics, resulting in their engorgement. The proposed technique was safe and effective in decreasing IOP in glaucoma patients by enhancing AH flow from the SCS to CLVs via connecting intrascleral microchannels.

Effect of Fluid Flow Direction on Intravitreal Injections of Drugs into Eye

The amount of drug in the eye depends on various factors such as genetics, layers structure, temperature distribution, and aqueous humor flow field. The heat transfer, fluid flow field, and drug delivery in the eye are numerically simulated using a three-dimensional model. The results are compared with experimental data on human and rabbit eyes. The effect of ambient temperature on the flow field in standing and supine positions was investigated. Then the transfer of drug concentration by intravitreal injection method was simulated using the obtained flow field. The results showed that the temperature distribution and the position of the eye relative to the direction of gravity have a significant role in the process of concentration transfer in the anterior segment of the eye. The results showed that in an intravitreal injection method, the drug has a significant concentration in the posterior part of the eye. In the intravitreal injection method with the injection of 1.25 mg of the drug, the maximum concentration in the vitreous humor is 1575.5 μg/ml, and the drug vanishes into the eye after 30 days. In this case, the maximum drug concentration in the aqueous humor is 30.16 μg/ml, which occurs after 1.5 days.

Shear stress induces autophagy in Schlemm's canal cells via primary cilia-mediated SMAD2/3 signaling pathway.

The Schlemm's canal (SC) is a circular, lymphatic-like vessel located at the limbus of the eye that participates in the regulation of aqueous humor drainage to control intraocular pressure (IOP). Circumferential flow of aqueous humor within the SC lumen generates shear stress, which regulates SC cell behaviour. Using biochemical analysis and real-time live cell imaging techniques, we have investigated the activation of autophagy in SC cells by shear stress. We report, for the first time, the primary cilium (PC)-dependent activation of autophagy in SC cells in response to shear stress. Moreover, we identified PC-dependent shear stress-induced autophagy to be positively regulated by phosphorylation of SMAD2 in its linker and C-terminal regions. Additionally, SMAD2/3 signaling was found to transcriptionally activate LC3B, ATG5 and ATG7 in SC cells. Intriguingly, concomitant to SMAD2-dependent activation of autophagy, we also report here the activation of mTOR pathway, a classical autophagy inhibitor, in SC cells by shear stress. mTOR activation was found to also be dependent on the PC. Moreover, pharmacological inhibition of class I PI3K increased phosphorylation of SMAD2 at the linker and activated autophagy. Together, our data indicates an interplay between PI3K and SMAD2/3 signaling pathways in the regulation of PC-dependent shear stress-induced autophagy in SC cells.

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

PurposeSchlemm'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. MethodsAs 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. ResultsA 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. ConclusionsThis 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.