Unconventional aqueous humor outflow: A review

In vivo quantification of anterior and posterior chamber volumes in mice: implications for aqueous humor dynamics

Purpose

Aqueous humor inflow rate, a key parameter influencing aqueous humor dynamics, is typically measured by fluorophotometery. Analyzing fluorophotometric data depends, inter alia, on the volume of aqueous humor in the anterior, but not the posterior, chamber. Previous fluorophotometric studies of aqueous inflow rate in mice have assumed the ratio of anterior:posterior volumes in mice to be similar to those in humans. Our goal was to measure anterior and posterior chamber volumes in mice to facilitate better estimates of aqueous inflow rates.

Methods

We used standard near-infrared optical coherence tomography (OCT) and robotic visible-light OCT (vis-OCT) to visualize, reconstruct and quantify the volumes of the anterior and posterior chambers of the mouse eye in vivo. We used histology and micro-CT scans to validate relevant landmarks from ex vivo tissues to facilitate in vivo measurement.

Results

Posterior chamber volume is 1.1 times the anterior chamber volume in BALB/cAnNCrl mice, i.e. the anterior chamber constitutes about 47% of the total aqueous humor volume, which is very dissimilar to the situation in humans. Anterior chamber volumes in 2-month-old BALB/cAnNCrl and 7-month-old C57BL6/J mice were 1.55 ± 0.36 μL (n=10) and 2.41 ± 0.29 μL (n=8), respectively. This implies that previous studies likely over-estimated aqueous inflow rate by approximately two-fold.

Conclusions

It is necessary to reassess previously reported estimates of aqueous inflow rates, and thus aqueous humor dynamics in the mouse. For example, we now estimate that only 0-15% of aqueous humor drains via the pressure-independent (unconventional) route, similar to that seen in humans and monkeys.

Trends and hot spots in research related to aqueous humor from 2014 to 2023: A bibliometric analysis

Purpose

To analyze publication trends and investigate research hotspots of aqueous humor (AH) studies.

Methods

A bibliometric study was conducted based on the Web of Science Core Collection (WOSCC). VOSviewer v. 1.6.18 was utilized to create a knowledge map visualizing the number of annual publications, the distribution of countries, international collaborations, author productivity, source journals and keywords in the field.

Results

A grand total of 4020 peer-reviewed papers concerning AH were retrieved from 2014 to 2023. The United States of America secured the top position among the most published countries and Duke University emerged as the most active institution. Stamer, WD contributed the most papers in this area. Investigative Ophthalmology & Visual Science was the most prolific journal in AH research. Retrieved publications mainly concentrated on the correlation between AH as a biomarker carrier and different ocular disorders. Six clusters were formed based on the keywords: (1) the diagnosis of endophthalmitis and AH pharmacokinetics; (2) the association of AH with pathogenesis and prognosis of glaucoma; (3) diagnosis and treatment of AH associated with uveitis; (4) the relationship between AH and refractive diseases of the eye; (5) the association of AH with mechanism and biomarkers of ocular tumorigenesis; (6) the indicators of AH associated with fundus disease.

Conclusions

This study unveiled present patterns of global collaboration, emerging frontiers, fundamental knowledge, research hotspots and current trends in AH.

Using a Novel, Subconjunctival, Sustained-Release Mitomycin C Formulation in a Rabbit Model of Filtration Surgery with Gel Stent Implantation

Purpose: To investigate gel stent implantation with and without intraoperative sustained-release mitomycin C (MMC SR) in a rabbit model for gel stent implantation, and to examine aqueous humor outflow (AHO) postimplantation. Methods: Four groups of rabbits were included. Group 1 was untreated (control). Groups 2, 3, and 4 received the gel stent without MMC, with MMC solution (subconjunctival injection), and with MMC SR (subconjunctival injection), respectively. Intraocular pressure (IOP) and AHO were assessed via tonometry and indocyanine green-based angiography, respectively. The main efficacy measure was change in IOP from baseline. Results: Following gel stent implantation, Groups 2, 3, and 4 maintained ≥20% IOP reduction (response) for a median duration of 1 week, 6.5 weeks, and 30 weeks, respectively. Angiography showed normal aqueous humor drainage (Group 1) beginning at the perilimbal trabecular plexus and continuing posteriorly to episcleral outflow vessels. Following implantation, drainage occurred preferentially and directly into the subconjunctival bleb. Conclusions: Gel stent implantation with MMC SR was most effective in achieving sustained, long-term IOP reduction in the rabbit model, compared with implantation with or without MMC solution. Bleb presence and the postimplantation aqueous angiography results indicated redirection of the AHO to the subconjunctival vasculature and presumed lymphatics, suggesting efficient glaucoma filtration to lower IOP in this model. This rabbit model and aqueous angiography may help refine understanding of the mechanism of action of minimally invasive glaucoma surgeries and ultimately translate to improved surgical devices and procedures for patients with glaucoma.

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

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

The Ocular Glymphatic System-Current Understanding and Future Perspectives

The ocular glymphatic system subserves the bidirectional polarized fluid transport in the optic nerve, whereby cerebrospinal fluid from the brain is directed along periarterial spaces towards the eye, and fluid from the retina is directed along perivenous spaces following upon its axonal transport across the glial lamina. Fluid homeostasis and waste removal are vital for retinal function, making the ocular glymphatic fluid pathway a potential route for targeted manipulation to combat blinding ocular diseases such as age-related macular degeneration, diabetic retinopathy, and glaucoma. Several lines of work investigating the bidirectional ocular glymphatic transport with varying methodologies have developed diverging mechanistic models, which has created some confusion about how ocular glymphatic transport should be defined. In this review, we provide a comprehensive summary of the current understanding of the ocular glymphatic system, aiming to address misconceptions and foster a cohesive understanding of the topic.

Ultrasound biomicroscopy analysis of ciliary muscle dynamics and its relation to intra-ocular pressure after phacoemulsification in dogs

Introduction

This study investigates the relationship between ciliary muscle dynamics, thickness, and the regulation of intraocular pressure (IOP), focusing on the progression of cataracts and changes post-phacoemulsification. It explores how these factors impact canine ocular health, particularly in the context of cataract development and subsequent surgical intervention.

Materials and methods

Data was collected using Ultrasound Biomicroscopy (UBM) from dogs at the Veterinary Medical Teaching Hospital of Chungbuk National University, Korea. The study involved 57 eyes from 35 dogs, categorized into five groups: 13 normal eyes, 14 with incipient cataracts, 12 with immature cataracts, 6 with mature cataracts, and 12 post-phacoemulsification. UBM measurements assessed various ciliary muscle parameters including ciliary body axial length (CBAXL), ciliary process-sclera angle (CPSA), longitudinal fibers of ciliary muscle thickness (Lf-CMT), and longitudinal and radial fibers of ciliary muscle thickness (LRf-CMT).

Results

Findings indicated a decrease in CBAXL and an increase in Lf-CMT as cataracts progressed in severity. Post-phacoemulsification, there was a notable increase in CBAXL and a decrease in CPSA, Lf-CMT, and LRf-CMT, compared to both cataractous and normal eyes. Regression analysis revealed a significant positive association between CBAXL and IOP, alongside a negative association between Lf-CMT and IOP. These findings suggest that variations in ciliary muscle dynamics and thickness, as influenced by cataract progression and phacoemulsification, have distinct impacts on intraocular pressure.

Discussion

The study proposes that phacoemulsification leads to ciliary muscle contraction, causing an inward and anterior movement of the ciliary muscle. This movement results in the narrowing of the ciliary cleft and constriction of the unconventional outflow pathway, potentially causing an increased risk of glaucoma post-surgery. Our research contributes to understanding the anatomical and physiological changes in the canine eye following cataract surgery and underscores the importance of monitoring IOP and ciliary muscle dynamics in these patients.

Ferroptosis in Glaucoma: A Promising Avenue for Therapy

Glaucoma, a blind-leading disease largely since chronic pathological intraocular high pressure (ph-IOP). Hitherto, it is reckoned incurable for irreversible neural damage and challenges in managing IOP. Thus, it is significant to develop neuroprotective strategies. Ferroptosis, initially identified as an iron-dependent regulated death that triggers Fenton reactions and culminates in lipid peroxidation (LPO), has emerged as a focal point in multiple tumors and neurodegenerative diseases. Researches show that iron homeostasis play critical roles in the optic nerve (ON) and retinal ganglion cells (RGCs), suggesting targeted treatments could be effective. In glaucoma, apart from neural lesions, disrupted metal balance and increased oxidative stress in trabecular meshwork (TM) are observed. These disturbances lead to extracellular matrix excretion disorders, known as sclerotic mechanisms, resulting in refractory blockages. Importantly, oxidative stress, a significant downstream effect of ferroptosis, is also a key factor in cell senescence. It plays a crucial role in both the etiology and risk of glaucoma. Moreover, ferroptosis also induces non-infectious inflammation, which exacerbate glaucomatous injury. Therefore, the relevance of ferroptosis in glaucoma is extensive and multifaceted. In this review, the study delves into the current understanding of ferroptosis mechanisms in glaucoma, aiming to provide clues to inform clinical therapeutic practices.

Wound Modulations in Glaucoma Surgery: A Systematic Review

Excessive fibrosis and resultant poor control of intraocular pressure (IOP) reduce the efficacy of glaucoma surgeries. Historically, corticosteroids and anti-fibrotic agents, such as mitomycin C (MMC) and 5-fluorouracil (5-FU), have been used to mitigate post-surgical fibrosis, but these have unpredictable outcomes. Therefore, there is a need to develop novel treatments which provide increased effectiveness and specificity. This review aims to provide insight into the pathophysiology behind wound healing in glaucoma surgery, as well as the current and promising future wound healing agents that are less toxic and may provide better IOP control.

New suture probe canaloplasty combined with suprachoroidal collagen implantation

PURPOSE

To present the modified surgery technique of new suture probe canaloplasty with a specially prepared monofilament 4.0 polypropylene suture combined with suprachoroidal drainage (ScD) and collagen sheet implantation for non-penetrating glaucoma surgery.

METHODS

Prospective study with a twelve months follow-up. A standard 4/0 polypropylene suture (ProleneTM by Ethicon; thickness: approximately 250 m) is cut and shaped with an ophthalmic knife (MANI® Crescent Knife, Mani Inc 8-3 Kiyohara Industrial Park, Utsunomiya, Tochigi 321-3231, Japan) to create a blunt end without sharp or compressed edges. This improves suture probe canaloplasty by providing a more stable and smoother probing device. Schlemm's canal is prepared using the standard technique of canaloplasty with suprachoroidal drainage. Then, instead of using the canaloplasty microcatheter or the previously published 6/0 double-helix suture, Schlemm's canal is probed with the blunt ending of the 4/0 Prolene suture. After successful 360-degree probing, a doubled 10/0 polypropylene tension suture is threaded through the tip of the 4/0 suture. The 4/0 suture is then pulled back and the 10/0 tension sutures are tied at both ends to tension Schlemm's canal. A special collagen sheet (Ologen®) is placed in suprachoroidal space, and the scleral flap is firmly sewed.

RESULTS

115 eyes were included in this prospective study. In 113 cases the Schlemm's canal could completely be probed with the suture probe and canaloplasty with ScD and collagen sheet implantation succeeded. In two cases the intervention was transformed to 360-degree suture trabeculotomy due to an intraoperative cheese-wiring. Twelve months after successful new suture probe canaloplasty with ScD and Collagen Implantation the IOP had decreased by 37.1% (from 21.6 ± 6.0 mmHg with 3.3 different IOP lowering eye drops to 13.5 ± 3.5 mmHg with 1.0 eye drops). 16 Patients did not achieve sufficient IOP levels and underwent 360-degree suture trabeculotomy during the follow-up. One patient had to be treated with further glaucoma surgery to achieve a sufficient IOP level. Complications were hyphema, postoperative IOP elevation and transient hypotony. No serious or sight-threatening complications occurred.

CONCLUSION

New suture probe canaloplasty with ScD and collagen sheet implantation yields the opportunity to conduct a cost-effective canaloplasty easier and less complicated than with the previously described method with the twisted 6/0 suture. The safety profile and IOP lowering effect is comparable. In cases where complete probing fails, there is still the opportunity to switch to suture trabeculotomy over the majorly probed part of Schlemm's canal. The pressure lowering effect of the deep sclerectomy with ScD and suprachoroidal collagen sheet implant seems to have an additional impact on the sufficient pressure lowering procedure.

Compartmentalized ocular lymphatic system mediates eye-brain immunity

The eye, an anatomical extension of the central nervous system (CNS), exhibits many molecular and cellular parallels to the brain. Emerging research demonstrates that changes in the brain are often reflected in the eye, particularly in the retina1. Still, the possibility of an immunological nexus between the posterior eye and the rest of the CNS tissues remains unexplored. Here, studying immune responses to herpes simplex virus in the brain, we observed that intravitreal immunization protects mice against intracranial viral challenge. This protection extended to bacteria and even tumours, allowing therapeutic immune responses against glioblastoma through intravitreal immunization. We further show that the anterior and posterior compartments of the eye have distinct lymphatic drainage systems, with the latter draining to the deep cervical lymph nodes through lymphatic vasculature in the optic nerve sheath. This posterior lymphatic drainage, like that of meningeal lymphatics, could be modulated by the lymphatic stimulator VEGFC. Conversely, we show that inhibition of lymphatic signalling on the optic nerve could overcome a major limitation in gene therapy by diminishing the immune response to adeno-associated virus and ensuring continued efficacy after multiple doses. These results reveal a shared lymphatic circuit able to mount a unified immune response between the posterior eye and the brain, highlighting an understudied immunological feature of the eye and opening up the potential for new therapeutic strategies in ocular and CNS diseases.

Evaluating the effect of pulse energy on femtosecond laser trabeculotomy (FLT) outflow channels for glaucoma treatment in human cadaver eyes

BACKGROUND AND OBJECTIVES

Femtosecond laser trabeculotomy (FLT) creates aqueous humor outflow channels through the trabecular meshwork (TM) and is an emerging noninvasive treatment for open-angle glaucoma. The purpose of this study is to investigate the effect of pulse energy on outflow channel creation during FLT.

MATERIALS AND METHODS

An FLT laser (ViaLase Inc.) was used to create outflow channels through the TM (500 μm wide by 200 μm high) in human cadaver eyes using pulse energies of 10, 15, and 20 μJ. Following treatment, tissues were fixed in 4% paraformaldehyde. The channels were imaged using optical coherence tomography (OCT) and assessed as full thickness, partial thickness, or not observable.

RESULTS

Pulse energies of 15 and 20 μJ had a 100% success rate in creating full-thickness FLT channels as imaged by OCT. A pulse energy of 10 μJ resulted in no channels (n = 6), a partial-thickness channel (n = 2), and a full-thickness FLT channel (n = 2). There was a statistically significant difference in cutting widths between the 10 and 15 μJ groups (p < 0.0001), as well as between the 10 and 20 μJ groups (p < 0.0001). However, there was no statistically significant difference between the 15 and 20 μJ groups (p = 0.416).

CONCLUSIONS

Fifteen microjoules is an adequate pulse energy to reliably create aqueous humor outflow channels during FLT in human cadaver eyes. OCT is a valuable tool when evaluating FLT.

Drug Distribution After Intravitreal Injection: A Mathematical Model

Purpose

Intravitreal injection of drugs is commonly used for treatment of chorioretinal ocular pathologies, such as age-related macular degeneration. Injection causes a transient increase in the intraocular volume and, consequently, of the intraocular pressure (IOP). The aim of this work is to investigate how intravitreal flow patterns generated during the post-injection eye deflation influence the transport and distribution of the injected drug.

Methods

We present mathematical and computational models of fluid motion and mass transport in the vitreous chamber during the transient phase after injection, including the previously unexplored effects of globe deflation as ocular volume decreases.

Results

During eye globe deflation, significant fluid velocities are generated within the vitreous chamber, which can possibly contribute to drug transport. Pressure variations within the eye globe are small compared to IOP.

Conclusions

Even if significant fluid velocities are generated in the vitreous chamber after drug injection, these are found to have negligible overall effect on drug distribution.

New targets of nascent lymphatic vessels in ocular diseases

Recent advancements in the field of endothelial markers of lymphatic vessels and lymphangiogenic factors have shed light on the association between several ocular diseases and ocular nascent lymphatic vessels. The immune privilege of corneal tissue typically limits the formation of lymphatic vessels in a healthy eye. However, vessels in the eyes can potentially undergo lymphangiogenesis and be conditionally activated. It is evident that nascent lymphatic vessels in the eyes contribute to various ocular pathologies. Conversely, lymphatic vessels are present in the corneal limbus, ciliary body, lacrimal glands, optic nerve sheaths, and extraocular muscles, while a lymphatic vasculature-like system exists in the choroid, that can potentially cause several ocular pathologies. Moreover, numerous studies indicate that many ocular diseases can influence or activate nascent lymphatic vessels, ultimately affecting patient prognosis. By understanding the mechanisms underlying the onset, development, and regression of ocular nascent lymphatic vessels, as well as exploring related research on ocular diseases, this article aims to offer novel perspectives for the treatment of such conditions.

Macrophage-induced integrin signaling promotes Schlemm's canal formation to prevent intraocular hypertension and glaucomatous optic neuropathy

Schlemm's canal (SC) functions to maintain proper intraocular pressure (IOP) by draining aqueous humor and has emerged as a promising therapeutic target for glaucoma, the second-leading cause of irreversible blindness worldwide. However, our current understanding of the mechanisms governing SC development and functionality remains limited. Here, we show that vitronectin (VTN) produced by limbal macrophages promotes SC formation and prevents intraocular hypertension by activating integrin αvβ3 signaling. Genetic inactivation of this signaling system inhibited the phosphorylation of AKT and FOXO1 and reduced β-catenin activity and FOXC2 expression, thereby causing impaired Prox1 expression and deteriorated SC morphogenesis. This ultimately led to increased IOP and glaucomatous optic neuropathy. Intriguingly, we found that aged SC displayed downregulated integrin β3 in association with dampened Prox1 expression. Conversely, FOXO1 inhibition rejuvenated the aged SC by inducing Prox1 expression and SC regrowth, highlighting a possible strategy by targeting VTN/integrin αvβ3 signaling to improve SC functionality.

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

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

Currently available prostanoids for the treatment of glaucoma and ocular hypertension: A review

Recent advancements in prostaglandin analogs (PGAs) have reinforced their role in managing intraocular pressure (IOP). Latanoprost excels in 24-h IOP control, while various PGAs offer similar effectiveness and side effects, generic PGAs perform as well as branded ones, and a notable IOP rise observed upon PGA discontinuation. Formulations with or without preservatives show comparable IOP reduction and adherence, often surpassing benzalkonium chloride (BAK)-preserved options. Emergent PGAs, such as latanoprostene bunod, fixed-dose netarsudil combined with latanoprost, and omidenepag Isopropyl, offer enhanced or non-inferior IOP reduction. The bimatoprost implant introduces a novel administration method with effective IOP reduction. These developments underscore ongoing progress in PGA-focused ophthalmological research. This article offers a comprehensive review of available prostanoid analogs and explores new developments.

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

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

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

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

The use of benzalkonium chloride in topical glaucoma treatment: An investigation of the efficacy and safety of benzalkonium chloride-preserved intraocular pressure-lowering eye drops and their effect on conjunctival goblet cells

ENGLISH SUMMARY

Glaucoma is a leading cause of the global prevalence of irreversible blindness. The pathogenesis of glaucoma is not entirely known, but the major risk factors include advancing age, genetic predisposition, and increased intraocular pressure (IOP). The only evidence-based treatment is a lowering of IOP through the use of eye drops, laser procedures, or surgical interventions. Although laser treatment is gaining recognition as a first-choice treatment option, the most common approach for managing glaucoma is IOP-lowering eye drops. A major challenge in the treatment is the occurrence of adverse events and poor adherence. In this context, the ocular surface is an area of great concern, as most glaucoma patients have dry eye disease (DED), which is largely caused by eye drops. Preservation with benzalkonium chloride (BAK) is a controversial topic due to its potential role as a significant cause of DED. A systematic review and meta-analyses investigate potential differences in efficacy and safety between BAK-preserved and BAK-free anti-glaucomatous eye drops (I). Many of the included studies report on ocular surface damage caused by the application of BAK-preserved eye drops. However, the meta-analyses addressing hyperemia, number of ocular adverse events, and tear break-up time did not identify any significant differences. The latter is likely due to varying measurement methods, different endpoints, and study durations. It is, therefore, possible that the large variations between the studies conceal differences in the safety profiles. The efficacy meta-analysis finds that there are no differences in the IOP-lowering effect between BAK-preserved and BAK-free eye drops, indicating that BAK is not necessary for the effectiveness of eye drops. To promote more homogeneous choices of endpoints and methods when evaluating BAK-preserved and BAK-free glaucoma treatments, a Delphi consensus statement was performed. In this study, glaucoma experts and ocular surface disease experts reached consensus on the key factors to consider when designing such studies (II). The hope is to have more studies with comparable endpoints that can systematically show the potentially adverse effects of BAK. The preclinical studies in the current Ph.D. research focus on conjunctival goblet cells (GCs). GCs are important for the ocular surface because they release the mucin MUC5AC, which is an essential component of the inner layer of the tear film. BAK preservation may damage the GCs and result in a low GC density, leading to an unstable tear film and DED. The most commonly used IOP-lowering drugs are prostaglandin analogs (PGAs). Thus, the conducted studies investigate the effect of PGAs preserved in different ways on GCs. BAK-preserved latanoprost is cytotoxic to primary cultured human conjunctival GCs and results in a scattered expression of MUC5AC, in contrast to negative controls, where MUC5AC is localized around the cell nucleus (III). Preservative-free (PF) latanoprost is not cytotoxic and does not affect the MUC5AC expression pattern. Furthermore, BAK-preserved travoprost is found to be cytotoxic in a time-dependent manner, while Polyquad®-preserved travoprost does not affect GC survival at any measured time point (IV). Both Polyquad and BAK induce scattered expression of MUC5AC. The cytotoxicity of BAK-preserved PGA eye drops is higher compared to the safer profile of PF and Polyquad-preserved PGA eye drops (V). Additionally, PF latanoprost does not increase the release of the inflammatory markers interleukin (IL)-6 and IL-8, unlike BAK-preserved latanoprost. A review highlights the active and inactive components of IOP-lowering eye drops (VI). Several preclinical and clinical studies have identified adverse effects of BAK. Although other components, such as the active drug and phosphates, can also cause adverse events, the review clearly states that BAK alone is a major source of decreased tolerability. The conclusion of this thesis is that BAK preservation is unnecessary and harmful to the ocular surface. The preclinical studies demonstrate that GCs die when exposed to BAK. Furthermore, they find that BAK induces a pro-inflammatory response. The review included in the thesis concludes that BAK should be phased out of eye drops for chronic use. Overall, the inclusion of BAK poses a risk of developing DED and poor adherence, which can ultimately lead to disease progression and blindness.

Segmental Unconventional Outflow in Mouse Eyes

Purpose

To investigate the flow pattern in unconventional outflow and its correlation with conventional outflow in mouse eyes.

Methods

Fluorescent microspheres were injected into the anterior chamber of one eye of anesthetized C57BL/6J mice (n = 4), followed by perfused fixation with 4% paraformaldehyde in situ after 45 minutes. Post-euthanasia, the injected eyes were enucleated, further immersion fixed, and dissected into 12 equal radial segments. Both sides of each segment were imaged using a confocal microscope after nuclear counterstaining. Both unconventional and conventional outflow patterns of each eye were analyzed by ImageJ and ZEN 2.3 imaging software.

Results

Segmental outflow patterns were observed in both the ciliary body (CB) and the supraciliary space and suprachoroidal space (SCS). In the CB, the tracer intensity was the lowest at 12 o'clock and highest at 9 o'clock, whereas in the SCS it was the lowest at 2 o'clock and the highest at 10 o'clock. Consequently, a segmental unconventional outflow was observed, with the lowest and highest flow regions in the superior and temporal quadrants, respectively. The overall segmental uveoscleral outflow has no correlation with trabecular outflow (P > 0.05). Four different outflow patterns were observed: (1) low-flow regions in both outflows, (2) primarily a high-flow region in conventional outflow, (3) primarily a high-flow region in unconventional outflow, and (4) high-flow regions in both outflows.

Conclusions

Uveoscleral outflow is segmental and unrelated to the trabecular segmental outflow. These findings will lead to future studies to identify the best location for the placement of drainage devices and drug delivery.

Glaucoma: now and beyond

The glaucomas are a group of conditions leading to irreversible sight loss and characterised by progressive loss of retinal ganglion cells. Although not always elevated, intraocular pressure is the only modifiable risk factor demonstrated by large clinical trials. It remains the leading cause of irreversible blindness, but timely treatment to lower intraocular pressure is effective at slowing the rate of vision loss from glaucoma. Methods for lowering intraocular pressure include laser treatments, topical medications, and surgery. Although modern surgical innovations aim to be less invasive, many have been introduced with little supporting evidence from randomised controlled trials. Many cases remain undiagnosed until the advanced stages of disease due to the limitations of screening and poor access to opportunistic case finding. Future research aims to generate evidence for intraocular pressure-independent neuroprotective treatments, personalised treatment through genetic risk profiling, and exploration of potential advanced cellular and gene therapies.

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

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

Ciliary body size in chronic angle-closure glaucoma

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

The molecular aspect of anti-glaucomatous eye drops - are we harming our patients?

Glaucoma is one of the leading causes of irreversible blindness. Progression is halted with a reduction in intraocular pressure (IOP), which is most often achieved with eye drops. A major challenge in the topical treatment of glaucoma patients is the many side effects and the resulting reduced adherence. Side effects may of course be due to the molecular properties of the active pharmaceutical ingredients (APIs). There are currently six different APIs available: prostaglandin analogues, β-adrenergic inhibitors, α-adrenergic agonists, carbonic anhydrase inhibitors, rho-kinase inhibitors and muscarinic 3 agonists. But the additives used in eye drops are also known to cause damage to the ocular surface and to some extent also to the deeper tissues. Said additives are considered inactive molecular components and are added to secure for instance viscosity and pH value, and to prevent contamination. There has been an increasing focus on the harmful effects of preservatives, with the most commonly used preservative benzalkonium chloride (BAK) being particularly controversial. BAK has long been recognized as a toxin that increases the risk of ocular discomfort. This can affect the adherence and ultimately result in lack of disease control. Other issues include the addition of certain buffers, such as phosphates, and varying pH values. This review will address the different molecular components of the IOP-lowering eye drops and what to be aware of when prescribing topical glaucoma treatment.

Aqueous Outflow Facility after Periocular Triamcinolone Injection: A Preliminary Evaluation of the Falck Medical Applanation Tonometer

Aim

To evaluate the Falck Medical Applanation Tonometer 1 (FMAT-1) as a device for measuring intraocular pressure (IOP) and outflow facility (OF) in patients with uveitis after periocular triamcinolone injection in one eye.

Materials and methods

Retrospective observational comparison. IOP and OF measurements were recorded and analyzed, comparing Goldmann tonometry and FMAT-1 readings. Records were reviewed for adult patients with uveitis who had undergone recent periocular triamcinolone injection in one eye.

Results

A total of 19 patients' records were evaluated. In treated eyes, median IOPs (in mm Hg) by Goldmann and FMAT-1 were 21 and 21.0, respectively, and mean IOPs were 22.21 and 21.15, respectively. In untreated eyes, median IOPs by Goldmann and FMAT-1 were 15 and 15.7, respectively, and mean IOPs were 15.52 and 15.31, respectively. Median OF (in µL/mm Hg) in treated and untreated eyes was 0.17 and 0.22, respectively, and mean values were 0.17 and 0.23, respectively. Pearson correlation showed an inverse relationship between IOP and OF in treated eyes, and linear regression analysis showed that IOP strongly predicted outflow in this group.

Conclusion

The FMAT-1 generates IOP results substantially similar to Goldmann and OF readings with greater ease than prior tonography devices.

Clinical significance

The mechanism of corticosteroid-induced IOP elevation appears to be a reduction in aqueous OF, and its measurement is tonography. This technique has traditionally been cumbersome. FMAT-1 is a newly launched instrument that measures IOP and OF at the slit lamp simultaneously in a few seconds.

How to cite this article

Staso FD, Gaudio PA. Aqueous Outflow Facility after Periocular Triamcinolone Injection: A Preliminary Evaluation of the Falck Medical Applanation Tonometer. J Curr Glaucoma Pract 2023;17(4):197-204.

RNAi therapies: Expanding applications for extrahepatic diseases and overcoming delivery challenges

The era of RNA medicine has become a reality with the success of messenger RNA (mRNA) vaccines against COVID-19 and the approval of several RNA interference (RNAi) agents in recent years. Particularly, therapeutics based on RNAi offer the promise of targeting intractable and previously undruggable disease genes. Recent advances have focused in developing delivery systems to enhance the poor cellular uptake and insufficient pharmacokinetic properties of RNAi therapeutics and thereby improve its efficacy and safety. However, such approach has been mainly achieved via lipid nanoparticles (LNPs) or chemical conjugation with N-Acetylgalactosamine (GalNAc), thus current RNAi therapy has been limited to liver diseases, most likely to encounter liver-targeting limitations. Hence, there is a huge unmet medical need for intense evolution of RNAi therapeutics delivery systems to target extrahepatic tissues and ultimately extend their indications for treating various intractable diseases. In this review, challenges of delivering RNAi therapeutics to tumors and major organs are discussed, as well as their transition to clinical trials. This review also highlights innovative and promising preclinical RNAi-based delivery platforms for the treatment of extrahepatic diseases.

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.

The novel role of lymphatic vessels in the pathogenesis of ocular diseases

Historically, the eye has been considered as an organ free of lymphatic vessels. In recent years, however, it became evident, that lymphatic vessels or lymphatic-like vessels contribute to several ocular pathologies at various peri- and intraocular locations. The aim of this review is to outline the pathogenetic role of ocular lymphatics, the respective molecular mechanisms and to discuss current and future therapeutic options based thereon. We will give an overview on the vascular anatomy of the healthy ocular surface and the molecular mechanisms contributing to corneal (lymph)angiogenic privilege. In addition, we present (i) current insights into the cellular and molecular mechanisms occurring during pathological neovascularization of the cornea triggered e.g. by inflammation or trauma, (ii) the role of lymphatic vessels in different ocular surface pathologies such as dry eye disease, corneal graft rejection, ocular graft versus host disease, allergy, and pterygium, (iii) the involvement of lymphatic vessels in ocular tumors and metastasis, and (iv) the novel role of the lymphatic-like structure of Schlemm's canal in glaucoma. Identification of the underlying molecular mechanisms and of novel modulators of lymphangiogenesis will contribute to the development of new therapeutic targets for the treatment of ocular diseases associated with pathological lymphangiogenesis in the future. The preclinical data presented here outline novel therapeutic concepts for promoting transplant survival, inhibiting metastasis of ocular tumors, reducing inflammation of the ocular surface, and treating glaucoma. Initial data from clinical trials suggest first success of novel treatment strategies to promote transplant survival based on pretransplant corneal lymphangioregression.

A Physiology-Based Mathematical Model to Understand Drug Delivery from Contact Lenses to the Back of the Eye

OBJECTIVE

Therapeutic contact lenses, able to store drug and deliver it to the eye surface in a sustained fashion, gained interest as an effective and patient-friendly alternative to eye drops. Recent animal studies also demonstrated the presence of therapeutic drug levels in the back of the eye after wearing drug-loaded contact lenses, thus opening the possibility of treating the posterior segment without need of invasive intraocular injections. The drug pathways from contact lenses to the back of the eye require further investigation.

METHODS

A mechanistic mathematical model was developed to evaluate the drug concentration over time in the tears, sclera and choroid, retina, aqueous humor and vitreous humor after the application of a therapeutic contact lens. The main drug transport mechanisms of the eye and the barrier properties of the different tissues were included in the model. Validation was performed by comparison with experimental data in literature.

RESULTS

The model predictions of drug concentration over time reflected the experimental data both in the anterior and posterior segment of the eye. The model can differentiate between contributions to transport from different pathways.

CONCLUSIONS

The model constitutes a first step towards the possibility of predicting the ocular drug distribution and the treatment efficacy in the early stage of contact lens development, and it may help reduce both the need for in vivo tests (with ethical and economic advantages) and the gap between the lens design and clinical application. It also allows for an improved understanding of drug transport in the eye.

Aqueous Humor TGF-β2 and Its Association With Intraocular Pressure in a Naturally Occurring Large Animal Model of Glaucoma

Purpose

Transforming growth factor (TGF)-β2 has been widely implicated in human glaucoma pathology. The purpose of this study was to determine the source of TGF-β2 in aqueous humor (AH) and its relationship with intraocular pressure (IOP) in an inherited large animal model of glaucoma.

Methods

Sixty-six glaucomatous cats homozygous for LTBP2 mutation, and 42 normal cats were studied. IOP was measured weekly by rebound tonometry. AH was collected by anterior chamber paracentesis from each eye under general anesthesia, and serum samples collected from venous blood concurrently. Concentrations of total, active and latent TGF-β2 in AH and serum samples were measured by quantitative sandwich immunoassay. For comparisons between groups, unpaired t-test or Mann Whitney test were used, with P < 0.05 considered significant. The relationships between TGF-β2 concentrations and IOP values were examined by Pearson's correlation coefficient and generalized estimating equation.

Results

IOP and AH TGF-β2 concentrations were significantly higher in glaucomatous than in normal cats. AH TGF-β2 showed a significant, robust positive correlation with IOP in glaucomatous cats (r = 0.83, R2 = 0.70, P < 0.0001). Serum TGF-β2 did not correlate with AH TGF-β2 and was not significantly different between groups. TGF-β2 mRNA and protein expression were significantly increased in local ocular tissues in glaucomatous cats.

Conclusions

Enhanced, local ocular production of TGF-β2 with a robust positive association with IOP was identified in this spontaneous feline glaucoma model, providing a foundation for preclinical testing of novel therapeutics to limit disease-associated AH TGF-β2 elevation and signaling in glaucoma.

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

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

ALK5 inhibitor acts on trabecular meshwork cell and reduces intraocular pressure

Intraocular pressure (IOP) is the most important risk factor for the onset and progression of glaucoma. IOP reduction has been proven effective in the treatment of glaucoma. IOP is controlled by the production and outflow of the aqueous humor (AH), and the trabecular meshwork (TM) is the main pathway for AH drainage from the eye. However, there are few conventional IOP-lowering treatments that target TM, and there is a need for such treatments. In this study, we screened for the expression level of fibronectin as an indicator and identified an activin receptor-like kinase (ALK) 5 inhibitor. Western blot analysis showed that SB431542, an ALK 5 inhibitor, reduced fibronectin and α-SMA expression. Moreover, a single dose of the ALK5 inhibitor SB431542 reduced IOP in mice, and the IOP-lowering effect of the ALK5 inhibitor was greater than that of a Rho-associated coiled-coil-containing protein kinase inhibitor (Y-27632). Repeated dosing with ALK5 inhibitor eye drops (once daily) enhanced the murine IOP-lowering effect. Furthermore, ALK5 inhibition decreased the expression of extracellular matrix (ECM) mRNA and suppressed ECM production. These findings suggest that ALK5 inhibitors may contribute to the development of new treatments for glaucoma that target the TM.

A Mechanistic Model of Aqueous Humor Flow to Study Effects of Angle Closure on Intraocular Pressure

Purpose

To study the relationship between the circumferential extent of angle closure and elevation in intraocular pressure (IOP) using a novel mechanistic model of aqueous humor (AH) flow.

Methods

AH flow through conventional and unconventional outflow pathways was modeled using the unified Stokes and Darcy equations, which were solved using the finite element method. The severity and circumferential extent of angle closure were modeled by lowering the permeability of the outflow pathways. The IOP predicted by the model was compared with biometric and IOP data from the Chinese American Eye Study, wherein the circumferential extent of angle closure was determined using anterior segment OCT measurements of angle opening distance.

Results

The mechanistic model predicted an initial linear rise in IOP with increasing extent of angle closure which became nonlinear when the extent of closure exceeded around one-half of the circumference. The nonlinear rise in IOP was associated with a nonlinear increase in AH outflow velocity in the open regions of the angle. These predictions were consistent with the nonlinear relationship between angle closure and IOP observed in the clinical data.

Conclusions

IOP increases rapidly when the circumferential extent of angle closure exceeds 180°. Residual AH outflow may explain why not all angle closure eyes develop elevated IOP when angle closure is extensive.

Translational Relevance

This study provides insight into the extent of angle closure that is clinically relevant and confers increased risk of elevated IOP. The proposed model can be utilized to study other mechanisms of impaired aqueous outflow.

Intracameral Injection of AAV-DJ.COMP-ANG1 Reduces the IOP of Mice by Reshaping the Trabecular Outflow Pathway

Purpose

The angiopoietin-1 (ANG1)-TIE signaling pathway orchestrates the development and maintenance of the Schlemm's canal (SC). In this study, we investigated the impact of adeno-associated virus (AAV)-mediated gene therapy with cartilage oligomeric matrix protein-ANG1 (COMP-ANG1) on trabecular outflow pathway.

Methods

Different serotypes of AAVs were compared for transduction specificity and efficiency in the anterior segment. The selected AAVs encoding COMP-ANG1 or ZsGreen1 (control) were delivered into the anterior chambers of wild-type C57BL/6J mice. The IOP and ocular surface were monitored regularly. Ocular perfusion was performed to measure the outflow facility and label flow patterns of the trabecular drainage pathway. Structural features of SC as well as limbal, retinal, and skin vessels were visualized by immunostaining. Ultrastructural changes in the SC and trabecular meshwork were observed under transmission electron microscopy.

Results

AAV-DJ could effectively infect the anterior segment. Intracameral injection of AAV-DJ.COMP-ANG1 lowered IOP in wild-type C57BL/6J mice. No signs of inflammation or angiogenesis were noticed. Four weeks after AAV injection, the conventional outflow facility and effective filtration area were increased significantly (P = 0.005 and P = 0.04, respectively). Consistently, the area of the SC was enlarged (P < 0.001) with increased density of giant vacuoles in the inner wall (P = 0.006). In addition, the SC endothelia lay on a more discontinuous basement membrane (P = 0.046) and a more porous juxtacanalicular tissue (P = 0.005) in the COMP-ANG1 group.

Conclusions

Intracamerally injected AAV-DJ.COMP-ANG1 offers a significant IOP-lowering effect by remodeling the trabecular outflow pathway of mouse eyes.

Thrombospondin 1 missense alleles induce extracellular matrix protein aggregation and TM dysfunction in congenital glaucoma

Glaucoma is a highly heritable disease that is a leading cause of blindness worldwide. Here, we identified heterozygous thrombospondin 1 (THBS1) missense alleles altering p.Arg1034, a highly evolutionarily conserved amino acid, in 3 unrelated and ethnically diverse families affected by congenital glaucoma, a severe form of glaucoma affecting children. Thbs1R1034C-mutant mice had elevated intraocular pressure (IOP), reduced ocular fluid outflow, and retinal ganglion cell loss. Histology revealed an abundant, abnormal extracellular accumulation of THBS1 with abnormal morphology of juxtacanalicular trabecular meshwork (TM), an ocular tissue critical for aqueous fluid outflow. Functional characterization showed that the THBS1 missense alleles found in affected individuals destabilized the THBS1 C-terminus, causing protein misfolding and extracellular aggregation. Analysis using a range of amino acid substitutions at position R1034 showed that the extent of aggregation was correlated with the change in protein-folding free energy caused by variations in amino acid structure. Extracellular matrix (ECM) proteins, especially fibronectin, which bind to THBS1, also accumulated within THBS1 deposits. These results show that missense variants altering THBS1 p.Arg1034 can cause elevated IOP through a mechanism involving impaired TM fluid outflow in association with accumulation of aggregated THBS1 in the ECM of juxtacanalicular meshwork with altered morphology.

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

PRCIS

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Updates on the Diagnosis and Management of Glaucoma

Glaucoma is the leading cause of blindness throughout the world (after cataracts); therefore, general physicians should be familiar with the diagnosis and management of affected patients. Glaucomas are usually categorized by the anatomy of the anterior chamber angle (open vs narrow/closed), rapidity of onset (acute vs chronic), and major etiology (primary vs secondary). Most glaucomas are primary (ie, without a contributing comorbidity); however, several coexisting ophthalmic conditions may serve as the underlying etiologies of secondary glaucomas. Chronic glaucoma occurs most commonly; thus, regular eye examinations should be performed in at-risk patients to prevent the insidious loss of vision that can develop before diagnosis. Glaucoma damages the optic nerve and retinal nerve fiber layer, leading to peripheral and central visual field defects. Elevated intraocular pressure (IOP), a crucial determinant of disease progression, remains the only modifiable risk factor; thus, all current treatments (medications, lasers, and operations) aim to reduce the IOP. Pharmacotherapy is the usual first-line therapy, but noncompliance, undesirable adverse effects, and cost limit effectiveness. Laser and surgical treatments may lower IOP significantly over long periods and may be more cost effective than pharmacotherapy, but they are plagued by greater procedural risks and frequent treatment failures. Traditional incisional procedures have recently been replaced by several novel, minimally invasive glaucoma surgeries with improved safety profiles and only minimal decreases in efficacy. Minimally invasive glaucoma surgeries have dramatically transformed the surgical management of glaucoma; nevertheless, large, randomized trials are required to assess their long-term efficacy.

Suprachoroidal injection of polyzwitterion hydrogel for treating glaucoma

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

Ciliochoroidal effusion and its association with the outcomes of micropulse transscleral laser therapy in glaucoma patients: a pilot study

We investigate the development of ciliochoroidal effusion following micropulse transscleral laser therapy (MPTLT) and evaluate the relationship between the early postoperative ciliochoroidal effusion (ECE) and short-term treatment outcomes. Glaucoma patients who underwent MPTLT were assessed for ciliochoroidal effusion by anterior segment optical coherence tomography (AS-OCT) at postoperative 1, 4, 12 weeks. The subjects were classified based on AS-OCT findings at postoperative 1 week into eyes with and without ECE. The absolute intraocular pressure (IOP), IOP reduction and number of antiglaucoma medications were compared between eyes with and without ECE. A total of 50 eyes were included, of which 23 (46%) developed ciliochoroidal effusion at postoperative 1 week. Almost all effusion resolved at 4 weeks. At 12 weeks, the mean IOP (SD) significantly decreased from 28.5 (12.8) mmHg to 17.8 (10.5) mmHg (p < 0.001), and the mean number of medications (SD) decreased from 4.1 (0.9) to 3.3 (1.1) (p < 0.001). Eyes with ECE had significantly greater IOP reduction (p = 0.009) and lower absolute IOP (p = 0.008) at the 4-week visit. There was no significant difference in number of medications between the groups. In conclusion, ciliochoroidal effusion was commonly observed following MPTLT. Eyes with ECE had overall greater IOP reduction during early post-operation.

Ocular Lymphatic and Glymphatic Systems: Implications for Retinal Health and Disease

Clearance of ocular fluid and metabolic waste is a critical function of the eye in health and disease. The eye has distinct fluid outflow pathways in both the anterior and posterior segments. Although the anterior outflow pathway is well characterized, little is known about posterior outflow routes. Recent studies suggest that lymphatic and glymphatic systems play an important role in the clearance of fluid and waste products from the posterior segment of the eye. The lymphatic system is a vascular network that runs parallel to the blood circulatory system. It plays an essential role in maintenance of fluid homeostasis and immune surveillance in the body. Recent studies have reported lymphatics in the cornea (under pathological conditions), ciliary body, choroid, and optic nerve meninges. The evidence of lymphatics in optic nerve meninges is, however, limited. An alternative lymphatic system termed the glymphatic system was recently discovered in the rodent eye and brain. This system is a glial cell-based perivascular network responsible for the clearance of interstitial fluid and metabolic waste. In this review, we will discuss our current knowledge of ocular lymphatic and glymphatic systems and their role in retinal degenerative diseases.

Emerging drugs for the treatment of glaucoma: a review of phase II & III trials

INTRODUCTION

Glaucoma is a progressive optic neuropathy and the leading cause of irreversible vision loss. By 2040, the number of individuals with glaucoma is expected to nearly double. The only known modifiable risk factor for glaucoma is intraocular pressure. Topical medications are often used as first-line therapies. Although there are numerous available treatments, there continues to be a need for the development of new medical therapies due to variable response, intolerable side-effect profiles in some patients, and elevated intraocular pressure refractory to other treatments.

AREAS COVERED

This review will cover glaucoma medications currently undergoing phase II and III of drug development.

EXPERT OPINION

There are numerous drugs currently in development that have demonstrated significant and clinically relevant reduction of intraocular pressure. Differentiating factors include improved tolerability, novel mechanisms of action, multiple mechanisms of action, or superior IOP reduction. However, the availability of generic prostaglandin analogs may limit adoption of these novel compounds as first-line agents, except for certain subgroups of glaucoma patients. Use as adjuvant or second-line therapy appears more likely for the majority of glaucoma patients.

Minimally Invasive Glaucoma Surgery in Primary Angle-Closure Glaucoma

Primary angle-closure glaucoma (PACG) is responsible for half of the glaucoma-related blindness worldwide. Cataract surgery with or without trabeculectomy has been considered to be the first-line treatment in eyes with medically uncontrolled PACG. While minimally invasive glaucoma surgery has become an important surgical approach for primary open-angle glaucoma, its indications and benefits in PACG are less clear. This review summarizes the efficacy and safety profile of minimally invasive glaucoma surgery in PACG to unfold new insights into the surgical management of PACG.

Schlemm's canal: the outflow 'vessel'

In a healthy eye, the aqueous humour (AH) flows via the ciliary body and trabecular meshwork into the collector channels, which carry it to the episcleral veins. In glaucoma, a heterogeneous group of eye disorders affecting approximately 60 million individuals worldwide, the juxtacanalicular meshwork offers greater resistance to the outflow of the AH, leading to an increase in outflow resistance that gradually results in elevated intraocular pressure (IOP). The present review comprehensively covers the morphology of Schlemm’s canal (SC) and AH pathways. The path of the AH from the anterior chamber through the trabeculum into suprascleral and conjunctival veins via collector channels is described, and the role of SC in the development of glaucoma and outflow resistance is discussed. Finally, channelography is presented as a precise method of assessing the conventional drainage pathway and facilitating localization of an uncollapsed collector and aqueous veins. Attention is also given to the relationship between aqueous and episcleral veins and heartbeat. Possible directions of future research are proposed.

Potential Mechanisms of Intraocular Pressure Reduction by Micropulse Transscleral Cyclophotocoagulation in Rabbit Eyes

Purpose

To evaluate the histological changes associated with, and the potential mechanisms of, intraocular pressure (IOP) reduction by micropulse cyclophotocoagulation (MP-CPC) in rabbit eyes.

Methods

MP-CPC was performed on the right eyes of Dutch belted rabbits, whereas the left eyes served as controls. The laser power settings were 250, 500, 750, 1000, 1500, and 2000 mW, 10 seconds per sweep, 100 seconds in total. IOP, outflow facility, and uveoscleral outflow tract imaging, using a fluorescent tracer, were examined at one week after MP-CPC. Changes of morphology and protein expressions in the outflow tissues, conjunctiva, and sclera were also evaluated.

Results

Significant reductions in IOP after MP-CPC were observed at 500 to 1000 mW (P = 0.036 and P = 0.014, respectively). The pre-MP-CPC IOP was 11.35 ± 0.41 mm Hg. At one week after surgery, the respective IOP values in the eyes treated at 500 mW and 1000 mW were 9.45 ± 0.49 mm Hg and 7.4 ± 0.27 mm Hg, respectively. Severe ciliary body damage was observed at 1500 to 2000 mW. MMP1–3 and fibronectin expression levels in the outflow tract and ciliary body were upregulated after MP-CPC. The α-smooth muscle actin (α-SMA) was upregulated at higher power levels. MP-CPC significantly increased uveoscleral outflow, whereas the outflow facility did not change. The α-SMA, collagen, and fibronectin were significantly upregulated in the subconjunctiva and sclera.

Conclusions

Reactive fibrotic responses were observed in the outflow tract, conjunctiva, and sclera after MP-CPC. A potential mechanism of IOP reduction by MP-CPC in pigmented rabbit eyes may involve increased uveoscleral outflow related to MMP upregulation.

Measurement of postmortem outflow facility using iPerfusion

The key risk factor for glaucoma is elevation of intraocular pressure (IOP) and alleviating it is the only effective therapeutic approach to inhibit further vision loss. IOP is regulated by the flow of aqueous humour across resistive tissues, and a reduction in outflow facility C, is responsible for the IOP elevation in glaucoma. Measurement of C is therefore important when investigating the pathophysiology of glaucoma and testing candidate treatments for lowering IOP. Due to similar anatomy and response to pharmacological treatments, mouse eyes are a common model of human aqueous humour dynamics. The ex vivo preparation, in which an enucleated mouse eye is mounted in a temperature controlled bath and cannulated, has been well characterised and is widely used. The postmortem in situ model, in which the eyes are perfused within the cadaver, has received relatively little attention. In this study, we investigate the postmortem in situ model using the iPerfusion system, with a particular focus on i) the presence or absence of pressure-independent flow, ii) the effect of evaporation on measured flow rates and iii) the magnitude and pressure dependence of outflow facility and how these properties are affected by postmortem changes. Measurements immediately after cannulation and following multi-pressure facility measurement demonstrated negligible pressure-independent flow in postmortem eyes, in contrast to assumptions made in previous studies. Using a humidity chamber, we investigated whether the humidity of the surrounding air would influence measured flow rates. We found that at room levels of humidity, evaporation of saline droplets on the eye resulted in artefactual flow rates with a magnitude comparable to outflow, which were eliminated by a high relative humidity (>85%) environment. Average postmortem outflow facility was ∼4 nl/min/mmHg, similar to values observed ex vivo, irrespective of whether a postmortem delay was introduced prior to cannulation. The intra-animal variability of measured outflow facility values was also reduced relative to previous ex vivo data. The pressure-dependence of outflow facility was reduced in the postmortem relative to ex vivo model, and practically eliminated when eyes were cannulated >40 min after euthanisation. Overall, our results indicate that the moderately increased technical complexity associated with postmortem perfusion provides reduced variability and reduced pressure-dependence in outflow facility, when experimental conditions are properly controlled.

Modeling the Effects of Disease, Drug Properties, and Material on Drug Transport From Intraocular Lenses

Purpose

Surgically implanted intraocular lenses (IOLs) may be used as drug-delivery devices, but their effectiveness is not well defined. Computational fluid dynamics models were developed to investigate the capability of IOLs to release drugs at therapeutic concentrations.

Methods

Models were generated using COMSOL Multiphysics. Primary open-angle glaucoma (POAG) and wet age-related macular degeneration (AMD) were simulated by reducing aqueous vein and choroidal blood flow, respectively. Release of dexamethasone, ganciclovir, or dextran was studied using common IOL materials, polydimethylsiloxane (PDMS) and poly(2-hydroxyethyl methacrylate) (PHEMA).

Results

Drug clearance proceeds mainly through choroidal blood flow. When fully constricted, maximum concentration at the choroid (Cmax) values increased by 32.4% to 39,800%. Compared to dexamethasone, Cmax in different tissues decreased by 6.07% to 96.0% for ganciclovir and dextran, and clearance rates decreased by 16% to 69% for ganciclovir and by 92% to 100% for dextran. Using PDMS as the IOL reduced clearance rates by 91.3% to 94.6% compared to PHEMA.

Conclusions

In diseased eyes, drugs accumulate mainly in posterior tissue; thus, choroidal drug toxicity must be assessed prior to IOL implantation in POAG and AMD patients. Moreover, drug properties modulated concentration profiles in all ocular segments. The hydrophobic small-molecule dexamethasone attained the highest concentrations and cleared the fastest, whereas hydrophilic macromolecular dextran attained the lowest concentrations and cleared the slowest. Furthermore, high concentrations were achieved quickly following release from PHEMA, whereas PDMS allowed for sustained release.

Translational Relevance

In silico results can guide scientists and clinicians regarding important physiological and chemical factors that modulate tissue drug concentrations from drug-eluting IOLs.

Medical therapy for glaucoma: A review

A number of pharmacological targets are exploited to modify the parameters in the Goldmann equation and reduce the intraocular pressure (IOP). This strategy constitutes the foundation for the medical management of glaucoma, the evolution of which, until only recently, has been in relative stagnation. A burst of innovation has produced new ocular hypotensive drugs and long-acting delivery methods, including intracameral delivery, which are expanding the clinician's medical armamentarium. A number of IOP-independent neuroprotection strategies have shown strong potential in animal models of glaucoma, but translational attempts have been surprisingly limited. However, while pharmacological options are expanding, the traditional role of topical medical therapy is being challenged by selective laser trabeculoplasty, micro-invasive glaucoma surgery, and sustained delivery methods. A scientifically rigorous assessment of new treatments will be critical to empower clinicians with evidence-based information to optimise vision preservation and quality of life outcomes for their patients.

Specific Biomarkers in the Aqueous Humour of Glaucoma Patients

Glaucoma, a multifactorial neurodegenerative disease, is the second most common cause of blindness. Since early diagnosis facilitates timely treatment, it is therefore essential to identify appropriate markers. In the future, so-called biomarkers could be helpful in early detection and follow-up. In glaucoma, these parameters could be obtained in the aqueous humour. Altered antibodies, proteins, microRNA (miRNA) and trace element levels have already been identified. This review provides insight into possible changes in the aqueous humour of patients with primary open-angle glaucoma (POAG), normal tension glaucoma (NTG) or pseudoexfoliation glaucoma (PEXG). Studies on antibody changes in POAG patients identified an upregulation of immune system associated antibodies such as heat shock protein (HSP) 27. HSP27 was also upregulated in PEXG patients but decreased in NTG. In POAG and PEXG samples, the levels of certain proteins, including interleukins and endothelin-1, were elevated. The vasoconstrictor endothelin-1 may play a role in regulating intraocular pressure. By contrast, proteins playing a role in the response to oxidative stress were downregulated. In NTG patients, proteins responsible for the elimination of toxic by-products from the respiratory chain were downregulated. In addition, the aqueous humour of POAG and PEXG patients contained several miRNAs that have been linked to tissue development, neurological disease and cellular organisation. Other miRNAs regulated in glaucoma play a role in extracellular matrix remodelling and thus may affect drainage resistance in the trabecular meshwork. It is also interesting to note that the aqueous humour of glaucoma patients showed changes in the levels of trace elements such as zinc and selenium. The elevated zinc levels could be responsible for the imbalance of intraocular matrix metalloproteinases and thus for increased intraocular pressure. All these studies demonstrate the complex changes in aqueous humour in glaucoma. Some of these biomarkers may be useful in the future for early diagnosis of the disease.

Consensus Recommendation for Mouse Models of Ocular Hypertension to Study Aqueous Humor Outflow and Its Mechanisms

Due to their similarities in anatomy, physiology, and pharmacology to humans, mice are a valuable model system to study the generation and mechanisms modulating conventional outflow resistance and thus intraocular pressure. In addition, mouse models are critical for understanding the complex nature of conventional outflow homeostasis and dysfunction that results in ocular hypertension. In this review, we describe a set of minimum acceptable standards for developing, characterizing, and utilizing mouse models of open-angle ocular hypertension. We expect that this set of standard practices will increase scientific rigor when using mouse models and will better enable researchers to replicate and build upon previous findings.