Aqueous Outflow Pathway Research Articles

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

Background and objectiveIntraocular pressure (IOP) is maintained via a dynamic balance between the production of aqueous humor and its drainage through the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway. Primary open angle glaucoma (POAG) is often associated with IOP elevation that occurs due to an abnormally high outflow resistance across the outflow pathway. Outflow tissues are viscoelastic and actively interact with aqueous humor dynamics through a two-way fluid-structure interaction coupling. While glaucoma affects the morphology and stiffness of the outflow tissues, their biomechanics and hydrodynamics in glaucoma eyes remain largely unknown. This research aims to develop an image-to-model method allowing the biomechanics and hydrodynamics of the conventional aqueous outflow pathway to be studied. MethodsWe used a combination of X-ray computed tomography and scanning electron microscopy to reconstruct high-fidelity, eye-specific, 3D microstructural finite element models of the healthy and glaucoma outflow tissues in cellularized and decellularized conditions. The viscoelastic TM/JCT/SC complex finite element models with embedded viscoelastic beam elements were subjected to a physiological IOP load boundary; the stresses/strains and the flow state were calculated using fluid-structure interaction and computational fluid dynamics. ResultsBased on the resultant hydrodynamics parameters across the outflow pathway, the primary site of outflow resistance in healthy eyes was in the JCT and immediate vicinity of the SC inner wall, while the majority of the outflow resistance in the glaucoma eyes occurred in the TM. The TM and JCT in the glaucoma eyes showed 1.32-fold and 1.13-fold larger beam thickness and smaller trabecular space size (2.24-fold and 1.50-fold) compared to the healthy eyes. ConclusionsCharacterizing the accurate morphology of the outflow tissues may significantly contribute to constructing more accurate, robust, and reliable models, that can eventually help to better understand the dynamic IOP regulation, hydrodynamics of the aqueous humor, and outflow resistance dynamic in the human eyes. This model demonstrates proof of concept for determining changes to outflow resistance in healthy and glaucomatous tissues and thus may be utilized in larger cohorts of donor tissues where disease specificity, race, age, and gender of the eye donors may be accounted for.

Analysis of Lipid Contents in Human Trabecular Meshwork Cells by Multiple Reaction Monitoring (MRM) Profiling Lipidomics.

Lipids are among the major constituents of cells and play many important cellular functions. Lipid levels in the trabecular meshwork (TM) aqueous humor outflow pathwayplay an important role in the maintenance of aqueous humor drainage and intraocular pressure (IOP) homeostasis. Therefore, it is important to characterize the changes in the lipid contents in the aqueous humor outflow pathway tissues to better understand their functional significance in the maintenance of IOP. The multiple reaction monitoring (MRM)-based profiling aids in the analysis of the metabolome as a collection of functional groups and is utilized as an exploratory metabolomics and lipidomics approach. The MRM-based profiling utilizes tandem mass spectrometry experiments carried out on a commercial triple quadrupole mass spectrometer with three aligned quadrupole mass filters (Q1, Q2, and Q3). This screening methodology can be utilized for targeted lipidomics screening. This chapter focuses on the methodology for isolation and culturing of the TM cells, lipid extraction, and the MRM-based lipidomics approach with data analysis.

Microbead-Induced Ocular Hypertension in a Rodent Model of Glaucoma.

Glaucoma is an irreversible blinding disease characterized by the loss of retinal ganglion cells. Development of therapeutics relies on suitable models and, given its complex nature, these are typically in vivo models. A widely used model, owing to its relative simplicity, is the microbead model. This model involves the injections of beads into the anterior chamber, which are suitably sized to block the aqueous outflow pathway, leading to an elevation in intraocular pressure and ultimately, retinal ganglion cell death. In this chapter, we describe in detail the materials and methods for modelling glaucoma using microbeads (both magnetic and nonmagnetic).

Changes to Outflow Structures After Pilocarpine in Primary Open Angle Glaucoma Compared With Healthy Individuals Using Optical Coherence Tomography.

Lower response of aqueous outflow pathway structures after pilocarpine could be observed in primary open angle glaucoma (POAG) patients, which is likely to be helpful for understanding intraocular pressure (IOP) evaluation in glaucoma. To evaluate the morphologic changes in the trabecular meshwork (TM), Schlemm canal (SC), scleral spur (SS), and ciliary muscle after miosis in patients with POAG and healthy individuals. A total of 30 patients with POAG and 26 healthy controls were recruited. All participants underwent complete ophthalmologic examinations, including IOP and swept-source optical coherence tomography (OCT), before and 1 hour after the local administration of pilocarpine (2%). OCT measurements included TM thickness and width, SC diameter and area, SS length, ciliary muscle thickness, and ciliary muscle angle (CMA). Pilocarpine administration induced a decline in IOP (15.6±2.3-14.6±2.2mmHg), decrease in nasal SS length (196.31±47.75-171.52±33.93μm), decrease in TM thickness (90.18±16.43-83.02±13.74μm), and increase in SC diameter (134.84±32.28-162.08±48.67μm) and SC area (3851.37±1455.07-4801.39±1762.37μm 2 ) among healthy controls. In contrast, no significant changes in IOP and OCT measurements were found in patients with POAG. At baseline, CMA was independently correlated with IOP in normal eyes. After miosis, the change in TM thickness was independently correlated with changes in IOP in normal eyes; in eyes with POAG, changes in SS length and CMA were independently associated with changes in IOP. Topical pilocarpine-induced morphologic changes to outflow pathway structures in healthy individuals without significant changes in POAG. The lower response observed in patients with glaucoma may be relevant to understanding IOP changes.

Modeling the Endothelial Glycocalyx Layer in the Human Conventional Aqueous Outflow Pathway.

A layer of proteoglycans and glycoproteins known as glycocalyx covers the surface of the trabecular meshwork (TM), juxtacanalicular tissue (JCT), and Schlemm's canal (SC) inner wall of the conventional aqueous outflow pathway in the eye. This has been shown to play a role in the mechanotransduction of fluid shear stress and in the regulation of the outflow resistance. The outflow resistance in the conventional outflow pathway is the main determinant of the intraocular pressure (IOP) through an active, two-way, fluid-structure interaction coupling between the outflow tissues and aqueous humor. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex with interspersed aqueous humor was constructed. A very thin charged double layer that represents the endothelial glycocalyx layer covered the surface of the elastic outflow tissues. The aqueous humor was modeled as electroosmotic flow that is charged when it is in contact with the outflow tissues. The electrical-fluid-structure interaction (EFSI) method was used to couple the charged double layer (glycocalyx), fluid (aqueous humor), and solid (outflow tissues). When the IOP was elevated to 15 mmHg, the maximum aqueous humor velocity in the EFSI model was decreased by 2.35 mm/s (9%) compared to the fluid-structure interaction (FSI) model. The charge or electricity in the living human conventional outflow pathway generated by the charged endothelial glycocalyx layer plays a minor biomechanical role in the resultant stresses and strains as well as the hydrodynamics of the aqueous humor.

In vivo identification of angle dysgenesis

AbstractAnterior segment Spectral domain–optical coherence tomography (SD‐OCT) is being increasingly used in glaucoma patients, primarily to investigate the anterior chamber angle and visualize the trabecular meshwork (TM) and Schlemm's canal (SC) in vivo. With the advent of angle surgery for glaucoma much interest has been generated in the aqueous outflow pathways. Our studies have shown that in vivo imaging of anterior chamber angle with ASOCT can been used to detect gross features of angle dysgenesis in primary congenital glaucoma (PCG), juvenile onset open angle glaucoma (JOAG) and adult onset primary open angle glaucoma (POAG), which has been described either as an absence of SC and/or the presence of abnormal tissue or a hyper‐reflective membrane within angle recess. This membrane is similar to what Barkan had described in PCG and was later described to be an angle cicatrization that portends a poorer success with goniotomy. Absence of development of SC was also shown by Hollander et al to be associated with a severe form of goniodysgenesis while its presence was seen in less severe goniodysgenesis on histopathological studies involving PCG. In fact, angle dysgenesis on ASOCT (ADoA), can be observed even in eyes with gonioscopically normal appearing angles. It is known that gonioscopy provides only a superficial representation of the histopathological anomalies affecting the angle. The presence of a thick compact tissue in the TM samples of Juvenile glaucoma patients has been observed, irrespective of whether they had an apparent goniodysgenesis or not. Hence, what appears to be morphologically normal angle on gonioscopy may harbour dysgenesis of the TM or even the SC. Primary congenital glaucoma, JOAG and adult onset POAG form a spectrum in terms of severity of angle dysgenesis. While most of the PCG eyes have features of ADoA, the same are present in 40% of JOAG eyes and in up to 35% of adult onset POAG. The size of the SC has also shown to be decreased in patients with adult‐onset open angle glaucoma based on in vivo OCT studies. We also present interesting observations of angle dysgenesis in fellow eyes of children with unilateral PCG.

The Effect of Intraocular Pressure Load Boundary on the Biomechanics of the Human Conventional Aqueous Outflow Pathway.

Aqueous humor outflow resistance in the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway actively contribute to intraocular pressure (IOP) regulation. Outflow resistance is actively affected by the dynamic outflow pressure gradient across the TM, JCT, and SC inner wall tissues. The resistance effect implies the presence of a fluid-structure interaction (FSI) coupling between the outflow tissues and the aqueous humor. However, the biomechanical interactions between viscoelastic outflow tissues and aqueous humor dynamics are largely unknown. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex was constructed with elastic and viscoelastic material properties for the bulk extracellular matrix and embedded elastic cable elements. The FE models were subjected to both idealized and a physiologic IOP load boundary using the FSI method. The elastic material model for both the idealized and physiologic IOP load boundary at equal IOPs showed similar stresses and strains in the outflow tissues as well as pressure in the aqueous humor. However, outflow tissues with viscoelastic material properties were sensitive to the IOP load rate, resulting in different mechanical and hydrodynamic responses in the tissues and aqueous humor. Transient IOP fluctuations may cause a relatively large IOP difference of ~20 mmHg in a very short time frame of ~0.1 s, resulting in a rate stiffening in the outflow tissues. Rate stiffening reduces strains and causes a rate-dependent pressure gradient across the outflow tissues. Thus, the results suggest it is necessary to use a viscoelastic material model in outflow tissues that includes the important role of IOP load rate.

AZD6738 decreases intraocular pressure and inhibits fibrotic response in trabecular meshwork through CHK1/P53 pathway

In this study, we report that AZD6738 (Ceralasertib), a novel potent ataxia telangiectasia and Rad3-related (ATR) kinase inhibitor, can decrease intraocular pressure (IOP) and inhibits fibrotic response in the trabecular meshwork (TM). We established mice TGF-β2-induced high IOP model and revealed that AZD6738 could effectively decrease IOP in the mice model and reduce TGF-β2-induced hyperplasia, collagen production, fibrosis, and extracellular matrix (ECM) remodeling in the TM by downregulating checkpoint kinase 1 (CHK1) level. Further, we demonstrated that AZD6738 reduces cell viability and migration, and inhibit the expression of fibrosis-related factors including fibronectin (FN), α-smooth muscle actin (α-SMA), laminin subunit beta 1 (LAMB1), matrix metallopeptidase (MMP) family including MMP2 and MMP9, collagen Ⅰ (COL1), and collagen Ⅳ (COL4), reduce gap junctions, altered cytoskeleton and nitric oxide production in TGF-β1-induced human trabecular meshwork cells (HTMCs) through the CHK1/P53 pathway, which were affected aqueous humor (AH) production and outflow pathway. In addition, we preliminarily verified the safety of the AZD6738 in topical ophthalmic use. Hence, our results demonstrate that AZD6738 may become a potential therapeutic option for anti-glaucoma.

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

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

The physiological and pathophysiological roles of the autophagy lysosomal system in the conventional aqueous humor outflow pathway: More than cellular clean up.

During the last few years, the autophagy lysosomal system is emerging as a central cellular pathway with roles in survival, acting as a housekeeper and stress response mechanism. Studies by our and other labs suggest that autophagy might play an essential role in maintaining aqueous humor outflow homeostasis, and that malfunction of autophagy in outflow pathway cells might predispose to ocular hypertension and glaucoma pathogenesis. In this review, we will collect the current knowledge and discuss the molecular mechanisms by which autophagy does or might regulate normal outflow pathway tissue function, and its response to different types of stressors (oxidative stress and mechanical stress). We will also discuss novel roles of autophagy and lysosomal enzymes in modulation of TGFβ signaling and ECM remodeling, and the link between dysregulated autophagy and cellular senescence. We will examine what we have learnt, using pre-clinical animal models about how dysregulated autophagy can contribute to disease and apply that to the current status of autophagy in human glaucoma. Finally, we will consider and discuss the challenges and the potential of autophagy as a therapeutic target for the treatment of ocular hypertension and glaucoma.

A novel glaucoma approach: Stem cell regeneration of the trabecular meshwork.

Glaucoma is the leading cause of global irreversible blindness, necessitating research for new, more efficacious treatment options than currently exist. Trabecular meshwork (TM) cells play an important role in the maintenance and function of the aqueous outflow pathway, and studies have found that there is decreased cellularity of the TM in glaucoma. Regeneration of the TM with stem cells has been proposed as a novel therapeutic option by several reports over the last few decades. Stem cells have the capacity for self-renewal and the potential to differentiate into adult functional cells. Several types of stem cells have been investigated in ocular regenerative medicine: tissue specific stem cells, embryonic stem cells, induced pluripotent stem cells, and adult mesenchymal stem cells. These cells have been used in various glaucoma animal models and ex vivo models and have shown success in IOP homeostasis and TM cellularity restoration. They have also demonstrated stability without serious side effects for a significant period of time. Based on current knowledge of TM pathology in glaucoma and existing literature regarding stem cell regeneration of this tissue, we propose a human clinical study as the next step in understanding this potentially revolutionary treatment paradigm. The ability to protect and replace TM cells in glaucomatous eyes could change the field forever.

Identifying Collector Channel Orifices In Vivo with Phase-Sensitive Optical Coherence Tomography: A Preliminary Study

Collector channels are openings located in the trabecular meshwork (TM) of the human eye that function as conduits, connecting the anterior chamber to the episcleral veins. Identifying the positions of collector channel orifices (CCOs) is essential for positioning implants in microinvasive canal-based glaucoma surgery, which is still not possible in vivo currently. Considerable evidence indicates that aqueous outflow becomes more active near the CCOs. Because the TM movement regulates the aqueous outflow, identification of the TM motion signal has the potential to locate the CCOs. Phase-sensitive optical coherence tomography (PhS-OCT) is an effective tool for the instantaneous detection of TM motion in vivo with sensitivity at the nanometer scale. However, the downside of this method is that phase measurement is prone to mix noises that negatively distinguish between biomedical signals. The TM motion was considered initially to be set up by the cardiac pulse. In this paper, a signal quality index related to blood pressure monitoring was applied to assess the validity of the TM motion signal. Measurements were carried out on two pairs of healthy human eyes. Quantitative measurements of the TM motion signal region such as size and frequency were recorded as the judgment indicator for CCOs. These results demonstrate that the PhS-OCT is a valuable tool capable of revealing the aqueous outflow pathway in vivo, offering a novel alternative to optimize glaucoma surgery.

Endothelial Glycocalyx Morphology in Different Flow Regions of the Aqueous Outflow Pathway of Normal and Laser-Induced Glaucoma Monkey Eyes.

Glycocalyx morphology was examined in the trabecular outflow pathway of monkey eyes with and without experimental glaucoma. Laser burns were administered along ~270 degrees of the trabecular meshwork (TM) of one eye (n = 6) or both eyes (n = 2) of each monkey until intraocular pressure remained elevated. Portions of the TM were not laser-treated. Unlasered eyes (n = 6) served as controls. Enucleated eyes were perfused at 15 mmHg to measure the outflow facility, perfused with fluorescein to evaluate the outflow pattern, perfusion-fixed for glycocalyx labeling, and processed for electron microscopy. Coverage and thickness of the glycocalyx were measured in the TM, Schlemm’s canal (SC), collector channels (CCs), intrascleral veins (ISVs), and episcleral veins (ESVs) in non-lasered regions and high- and low-flow regions of controls. Compared to controls, laser-treated eyes had decreased outflow facility (p = 0.02). Glycocalyx thickness increased from the TM to ESVs in non-lasered regions and controls (p < 0.05). Glycocalyx coverage was generally greater distally in non-lasered regions (p < 0.05). In lasered regions, TM, SC, and CCs were partly to completely obliterated, and ISVs and ESVs displayed minimal glycocalyx. Whether the glycocalyx is decreased in the trabecular outflow pathway of human glaucomatous eyes warrants investigation.

(Fish) tales of congenital diseases: molecularly distinguishing cranial neural crest cell populations

Congenital diseases that affect the anterior segment are typically due to cranial neural crest defects. This transient embryonic stem cell population ultimately gives rise to the bone, cartilage, and connective tissue of the jaw and mid face, and within the eye contributes to the corneal, iris, ciliary body, aqueous outflow pathways, and sclera. Thus, due to their common origin, congenital eye anomalies are often associated with facial defects.

Cell atlas of the human ocular anterior segment: Tissue-specific and shared cell types

The anterior segment of the eye consists of the cornea, iris, ciliary body, crystalline lens, and aqueous humor outflow pathways. Together, these tissues are essential for the proper functioning of the eye. Disorders of vision have been ascribed to defects in all of them; some disorders, including glaucoma and cataract, are among the most prevalent causes of blindness in the world. To characterize the cell types that compose these tissues, we generated an anterior segment cell atlas of the human eye using high-throughput single-nucleus RNA sequencing (snRNAseq). We profiled 195,248 nuclei from nondiseased anterior segment tissues of six human donors, identifying >60 cell types. Many of these cell types were discrete, whereas others, especially in the lens and cornea, formed continua corresponding to known developmental transitions that persist in adulthood. Having profiled each tissue separately, we performed an integrated analysis of the entire anterior segment, revealing that some cell types are unique to a single structure, whereas others are shared across tissues. The integrated cell atlas was then used to investigate cell type-specific expression patterns of more than 900 human ocular disease genes identified through either Mendelian inheritance patterns or genome-wide association studies.

Ultrasound biomicroscopy of the equine iridocorneal angle.

The iridocorneal angle (ICA) is the major pathway of aqueous humour outflow from the anterior chamber of the eye. Ultrasound biomicroscopy (UBM) has been utilised to characterise the morphology of this drainage pathway in numerous species. UBM may allow for early recognition of aqueous humour outflow obstructions in horses, allowing for earlier recognition of risk for glaucoma, a vision-threatening and painful disease. UBM morphology of the normal equine ICA has yet to be described. To determine the ultrasonographic morphology of the equine ICA by UBM in standing sedated horses. In vivo experimental study. Thirty healthy adult horses underwent UBM of the ICA at four locations (superior, temporal, inferior, nasal) of each eye utilising standing sedation, topical anaesthesia and auriculopalpebral perineural anaesthesia. Anatomic structures were defined on ultrasound images through comparison to published histologic photomicrographs of the equine ICA. Ultrasound imaging of the ICA at all four locations was easily performed in standing, sedated horses. High-resolution images of the ICA allowed for identification of the pectinate ligament, corneoscleral trabecular meshwork (TM), uveal TM and supraciliary TM. Pupil size was midrange in all eyes, but was not strictly controlled. Lighting conditions not controlled. Various breeds included. In vivo UBM of the equine ICA is feasible and provides high-resolution images of the structures of the aqueous humour outflow pathway.

Modeling the biomechanics of the conventional aqueous outflow pathway microstructure in the human eye

Background and objectiveIntraocular pressure (IOP) is determined by aqueous humor outflow resistance, which is a function of the combined resistance of Schlemm's canal (SC) endothelium and the trabecular meshwork (TM) and their interactions in the juxtacanalicular connective tissue (JCT) region. Aqueous outflow in the conventional outflow pathway results in pressure gradient across the TM, JCT, and SC inner wall, and induces mechanical stresses and strains that influence the geometry and homeostasis of the outflow system. The outflow resistance is affected by alteration in tissues’ geometry, so there is potential for active, two-way, fluid-structure interaction (FSI) coupling between the aqueous humor (fluid) and the TM, JCT, and SC inner wall (structure). However, our understanding of the biomechanical interactions of the aqueous humor with the outflow connective tissues and its contribution to the outflow resistance regulation is incomplete. MethodsIn this study, a microstructural finite element (FE) model of a human eye TM, JCT, and SC inner wall was constructed from a segmented, high-resolution histologic 3D reconstruction of the human outflow system. Three different elastic moduli (0.004, 0.128, and 51.5 MPa based on prior reports) were assigned to the TM/JCT complex while the elastic modulus of the SC inner wall was kept constant at 0.00748 MPa. The hydraulic conductivity was programmed separately for the TM, JCT, and SC inner wall using a custom subroutine. Cable elements were embedded into the TM and JCT extracellular matrix to represent the directional stiffness imparted by anisotropic collagen fibril orientation. The resultant stresses and strains in the outflow system were calculated using fluid-structure interaction method. ResultsThe higher TM/JCT stiffness resulted in larger stresses, but smaller strains in the outflow connective tissues, and resulted in a 4- and 5-fold larger pressure drop across the SC inner wall, respectively, compared to the most compliant model. Funneling through µm-sized SC endothelial pores was evident in the models at lower tissue stiffness, but aqueous flow was more turbulent in models with higher TM/JCT stiffness. ConclusionsThe mechanical properties of the outflow tissues play a crucial role in the hydrodynamics of the aqueous humor in the conventional outflow system.

Morphological changes to Schlemm's canal and the distal aqueous outflow pathway in monkey eyes with laser-induced ocular hypertension

Though roughly 30–50% of aqueous outflow resistance resides distal to Schlemm's canal (SC), the morphology of the conventional outflow pathway distal to SC has not been thoroughly evaluated. This study examined the morphological changes along proximal and distal aspects of the conventional aqueous outflow pathway and their association with decreased outflow facility in an experimental model of glaucoma in cynomolgus macaques. Nd:YAG laser burns were made to 270–340 degrees of the trabecular meshwork (TM) of one eye (n = 6) or both eyes (n = 2) of each monkey to induce ocular hypertension. Distinct regions of the TM were left unlasered. Contralateral eyes (n = 5) were not lasered and were utilized as controls. Monkeys were sacrificed ≥58 months after their last laser treatment. All eyes were enucleated and perfused at 15 mmHg for 30 min to measure outflow facility. Two pairs of eyes were also perfused with fluorescein to examine segmental outflow. All eyes underwent perfusion-fixation for 1 h. Anterior segments were cut into radial wedges and processed for light and electron microscopy. Width, height, and cross-sectional area (CSA) of SC were compared between high- and low-flow regions of control eyes, and between non-lasered regions of laser-treated eyes and control eyes. Number and CSA of intrascleral veins (ISVs) were compared between non-lasered and lasered regions of laser-treated eyes and control eyes, and between high- and low-flow regions of control eyes. Scleral collagen fibril diameter was compared between control eyes and lasered and non-lasered regions of laser-treated eyes. Median outflow facility was significantly decreased in laser-treated eyes compared to control eyes (P = 0.02). Median CSA and height of SC were smaller in high-flow regions than low-flow regions of control eyes (P < 0.05). Median width of SC was not significantly different between high- and low-flow regions of control eyes (P > 0.05). Median CSA, width, and height of SC were not different between non-lasered regions and control eyes (P > 0.05). SC was partially or completely obliterated in lasered regions. Median number of ISVs was significantly decreased in lasered regions compared to non-lasered regions (P < 0.01) and control eyes (P < 0.01). Median CSA of ISVs did not differ between these groups (P > 0.05). Median number and CSA of ISVs were not significantly different between high- and low-flow regions of control eyes (P > 0.05). Lasered regions displayed looser scleral stroma and smaller median diameter of collagen fibrils adjacent to the TM compared to non-lasered regions (P < 0.05) and control eyes (P < 0.05). Dense TM, partial to complete obliteration of SC, and a decreased number of patent ISVs may account in part for the decreased outflow facility in monkey eyes with laser-induced ocular hypertension. The significance of changes in scleral structure in laser-treated eyes warrants further investigation.

Impaired/dysfunctional aqueous collector channels may primarily contribute to the pathogenesis of primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is induced by elevated intraocular pressure (IOP) that arises due to increased resistance in conventional aqueous humor outflow pathway (AHOc) consisting of trabecular meshwork (TM), Schlemm’s canal (SC), and downstream vascular network including collector channels (CCs). Although it has been traditionally considered that most of the outflow resistance lies in TM and the inner wall of SC, recent studies identified that more than one third of the resistance lies on CCs and their connected vascular network. In addition, CCs draw more attention because minimally invasive glaucoma surgery (MIGS) whose success depends upon them has been recently spotlighted in the treatment of POAG. Despite the importance of CCs during the pathogenesis of POAG, glaucomatous changes in CCs of human patients have been only considered as secondary results without direct evidence due to the absence of glaucoma animal model primarily induced by CC impairment as well as difficulty in definitive visualization of AHOcin vivo. Here, we hypothesize that likewise in TM and SC inner wall, structural and functional impairment of CCs may also primarily contribute to the initiation and progression of POAG. This article introduces a potential strategy to investigate and treat CC-related POAG.

Direct Visualization of the Aqueous Outflow Pathway Using Indocyanine Green during Trabecular Microbypass Stent Implantation

Direct Visualization of the Aqueous Outflow Pathway Using Indocyanine Green during Trabecular Microbypass Stent Implantation