Topical Glaucoma Therapy Is Associated With Alterations of the Ocular Surface Microbiome

Microbial Dynamics in Ophthalmic Health: Exploring the Interplay between Human Microbiota and Glaucoma Pathogenesis

The human microbiome has a crucial role in the homeostasis and health of the host. These microorganisms along with their genes are involved in various processes, among these are neurological signaling, the maturation of the immune system, and the inhibition of opportunistic pathogens. In this sense, it has been shown that a healthy ocular microbiota acts as a barrier against the entry of pathogens, contributing to the prevention of infections. In recent years, a relationship has been suggested between microbiota dysbiosis and the development of neurodegenerative diseases. In patients with glaucoma, it has been observed that the microbiota of the ocular surface, intraocular cavity, oral cavity, stomach, and gut differ from those observed in healthy patients, which may suggest a role in pathology development, although the evidence remains limited. The mechanisms involved in the relationship of the human microbiome and this neurodegenerative disease remain largely unknown. For this reason, the present review aims to show a broad overview of the influence of the structure and composition of the human oral and gut microbiota and relate its dysbiosis to neurodegenerative diseases, especially glaucoma.

Dry Eye Disease Symptoms Among Glaucoma Patients at a Portuguese Hospital

INTRODUCTION

Glaucoma-related dry eye disease (DED) is often underestimated, but it is an important comorbidity affecting 40% to 59% of glaucoma patients. It may be an exacerbation of a pre-existing condition or a novel disease starting after the initiation of topical medication. The cumulative effect of medication, preservatives and excipients leads to an alteration in tear film composition and ocular surface stability. The main purpose of this investigation was to study a group of Portuguese glaucoma patients regarding the presence of DED symptoms and correlate the severity of the symptoms with the usage of different types of glaucoma topical medications.

MATERIALS AND METHODS

This is a cross-sectional observational study of patients diagnosed with primary and secondary open-angle glaucoma. The questionnaire Standardized Patient Evaluation of Eye Dryness (SPEED) translated to Portuguese (SPEED-Vp) was taken by patients followed in the Glaucoma Department of Unidade Local de Saúde Entre Douro e Vouga, Santa Maria da Feira, Portugal. Data was collected regarding their age, gender, type of topical medication in use as well as frequency and duration of usage. A statistical analysis was performed.

RESULTS

A total of 75 patients answered the SPEED-Vp questionnaire. The mean age was 72 ± 7 years old. Fifty-two percent (n=39) were male, and 48% (n=36) were female patients. About 49.33% (n=37) had been on intraocular pressure (IOP)-lowering eyedrops for more than five years. About 61.43% (n=43) of patients used IOP-lowering eyedrops with preservatives. Most of the patients used prostaglandin analogs (75.71%, n=53) and beta-blockers (72.86%, n=51). SPEED score average was 2.75. About 25.33% (n=19) had no DED symptoms, 58.67% (n=44) had mild symptoms, 8% (n=6) had moderate symptoms and 8% (n=6) had severe symptoms. No statistically significant correlation was found between SPEED score and age, gender, number of eyedrop containers, number of active principles, application frequency, presence of preservatives, number of eyedrop containers with preservatives, duration of eyedrops usage or any of the medication groups.

CONCLUSION

Although a high percentage of patients were on eyedrops with preservatives, this low rate of symptoms might be because patients tended to devalue these symptoms; were already on treatment with artificial tears; or have an underestimation of the sensation of dry eye due to decreased neuronal corneal nerve responses and density. These results were surprisingly positive. This might also be the result of the healthcare provider's sensibilization to this issue (early diagnosis, early prescription of artificial tears and change from preservative to preservative-free medication).

Living with your biome: how the bacterial microbiome impacts ocular surface health and disease

Introduction

Microbiome research has grown exponentially but the ocular surface microbiome (OSM) remains an area in need of further study. This review aims to explore its complexity, disease-related microbial changes, and immune interactions, and highlights the potential for its manipulation as a therapeutic for ocular surface diseases.

Areas Covered

We introduce the OSM by location and describe what constitutes a normal OSM. Second, we highlight aspects of the ocular immune system and discuss potential immune microbiome interactions in health and disease. Finally, we highlight how microbiome manipulation may have therapeutic potential for ocular surface diseases.

Expert Opinion

The ocular surface microbiome varies across its different regions, with a core phyla identified, but with genus variability. A few studies have linked microbiome composition to diseases like dry eye but more research is needed, including examining microbiome interactions with the host. Studies have noted that manipulating the microbiome may impact disease presentation. As such, microbiome manipulation via diet, oral and topical pre and probiotics, and hygienic measures may provide new therapeutic algorithms in ocular surface diseases.

Comparison of Transcriptomic Analysis of the Conjunctiva in Glaucoma-Treated Eyes with Dry Eyes and Healthy Controls

Ocular surface disease (OSD) associated with topical glaucoma drugs is a common issue impacting treatment adherence. We aimed to identify conjunctival transcriptomic changes in glaucoma and dry eye patients, comparing them to healthy controls. Bulbar conjunctival specimens were collected via impression cytology from 33 patients treated for glaucoma, 9 patients with dry eye, and 14 healthy controls. RNA extraction and bulk RNA sequencing were performed, followed by bioinformatics analysis to detect gene dysregulation. Ingenuity pathways analysis (IPA) identified pathways and biological processes associated with these transcriptomic changes. Sequencing analysis revealed 200 modified genes in glaucoma patients compared to healthy individuals, 233 differentially expressed genes in dry eye patients versus controls, and 650 genes in treated versus dry eye samples. In glaucoma patients, 79% of altered pathways were related to host defense, while dry eye patients showed a 39% involvement of host response, 15% in cellular proliferation and integrity, and 16% of mitochondrial dysfunction. These findings were validated through qRT-PCR. Glaucoma patients showed an intensified conjunctival immune response as a potential cause of OSD, whereas in dry eye patients, in addition to the immune response, other mechanisms such as mitochondrial dysfunction or reduced cellular proliferation were observed.

The role of the microbiota in glaucoma

Glaucoma is a common irreversible vision loss disorder because of the gradual loss of retinal ganglion cells (RGCs) and the optic nerve axons. Major risk factors include elder age and high intraocular pressure (IOP). However, high IOP is neither necessary nor sufficient to cause glaucoma. Some non-IOP signaling cascades can mediate RGC degeneration. In addition, gender, diet, obesity, depression, or anxiety also contribute to the development of glaucoma. Understanding the mechanism of glaucoma development is crucial for timely diagnosis and establishing new strategies to improve current IOP-reducing therapies. The microbiota exerts a marked influence on the human body during homeostasis and disease. Many glaucoma patients have abnormal compositions of the microbiota (dysbiosis) in multiple locations, including the ocular surface, intraocular cavity, oral cavity, stomach, and gut. Here, we discuss findings in the last ten years or more about the microbiota and metabolite changes in animal models, patients with three risk factors (aging, obesity, and depression), and glaucoma patients. Antigenic mimicry and heat stress protein (HSP)-specific T-cell infiltration in the retina may be responsible for commensal microbes contributing to glaucomatous RGC damage. LPS-TLR4 pathway may be the primary mechanism of oral and ocular surface dysbiosis affecting glaucoma. Microbe-derived metabolites may also affect glaucoma pathogenesis. Homocysteine accumulation, inflammatory factor release, and direct dissemination may link gastric H. pylori infection and anterior chamber viral infection (such as cytomegalovirus) to glaucoma. Potential therapeutic protocols targeting microbiota include antibiotics, modified diet, and stool transplant. Later investigations will uncover the underlying molecular mechanism connecting dysbiosis to glaucoma and its clinical applications in glaucoma management.

Usability of an Eye Drop Delivery Aid for Single-Dose Instillation: Results from a Market Research Study

Background

One of the challenges of treating chronic ocular diseases like vernal keratoconjunctivitis (VKC), glaucoma, and ocular surface disease is patient adherence to topical medication. To support correct eye drop instillation, a variety of delivery aids have been developed for both single-dose and conventional multi-dose containers.

Methods

To evaluate Dropaid™ Single-dose, an eye drop delivery aid designed for single-dose containers, a usability study was conducted on 30 parents and caregivers of patients with VKC. After assessing the ability to squeeze a single eye drop from the single-dose container onto the eye of a pediatric medical dummy, the delivery aid was evaluated using an 11-point Likert scale on a variety of characteristics: from "very difficult" (-5) to "very easy" (+5).

Results

The majority of participants rated the task of opening the single-dose units (SDUs), preparing, and positioning the Dropaid™ Single-dose device as "very easy". When providing a single eye drop from the container, 87% of participants rated the Dropaid™ Single-dose device as either "very easy" or "easy", with a median rating score of +5.0 (interquartile range [IQR], 4.0-5.0). For general ease of use, 84% considered the delivery aid as either "very easy" or "easy", with a median score of +4.0 (IQR, 3.0-5.0). Most participants (93%) rated Dropaid™ Single-dose as either "very comfortable" or "comfortable" to hold, with a median score of +5.0 (IQR, 4.0-5.0).

Conclusion

The Dropaid™ Single-dose delivery aid demonstrated rapid learning and ease of use across all stages of application, including opening the container, eye drop administration, and handling comfort. Although designed for use with single-dose containers to help eye drop instillation in patients with VKC, Dropaid™ Single-dose may provide a wider utility across a range of other ocular diseases such as glaucoma and dry eye.

The Microbiome, Ocular Surface, and Corneal Disorders

The ocular surface microbiome is an emerging field of study that seeks to understand how the community of microorganisms found on the ocular surface may help maintain homeostasis or can potentially lead to disease and dysbiosis. Initial questions include whether the organisms detected on the ocular surface inhabit that ecological niche and, if so, whether there exists a core microbiome found in most or all healthy eyes. Many questions have emerged around whether novel organisms and/or a redistribution of organisms play a role in disease pathogenesis, response to therapies, or convalescence. Although there is much enthusiasm about this topic, the ocular surface microbiome is a new field with many technical challenges. These challenges are discussed in this review as well as a need for standardization to adequately compare studies and advance the field. In addition, this review summarizes the current research on the microbiome of various ocular surface diseases and how these findings may impact treatments and clinical decision-making.

Targeting the Gut-Eye Axis: An Emerging Strategy to Face Ocular Diseases

The human microbiota refers to a large variety of microorganisms (bacteria, viruses, and fungi) that live in different human body sites, including the gut, oral cavity, skin, and eyes. In particular, the presence of an ocular surface microbiota with a crucial role in maintaining ocular surface homeostasis by preventing colonization from pathogen species has been recently demonstrated. Moreover, recent studies underline a potential association between gut microbiota (GM) and ocular health. In this respect, some evidence supports the existence of a gut-eye axis involved in the pathogenesis of several ocular diseases, including age-related macular degeneration, uveitis, diabetic retinopathy, dry eye, and glaucoma. Therefore, understanding the link between the GM and these ocular disorders might be useful for the development of new therapeutic approaches, such as probiotics, prebiotics, symbiotics, or faecal microbiota transplantation through which the GM could be modulated, thus allowing better management of these diseases.

Effects of Carboxymethylcellulose Artificial Tears on Ocular Surface Microbiome Diversity and Composition, A Randomized Controlled Trial

Purpose

Carboxymethylcellulose is an artificial tear ingredient known to decrease gut microbiome diversity when ingested. This study examines the effect of carboxymethylcellulose on ocular surface microbiome diversity and composition.

Methods

Healthy adult participants without significant ophthalmic disease or concurrent carboxymethylcellulose artificial tear use were allocated randomly to take carboxymethylcellulose or control polyethylene glycol artificial tears for seven days. Conjunctival swabs were collected before and after artificial tear treatment. This trial is registered at clinicaltrials.gov (NCT05292755). Primary outcomes included abundance of bacterial taxa and microbiome diversity as measured by the Chao-1 richness estimate, Shannon's phylogenetic diversity index, and UniFrac analysis. Secondary outcomes included Ocular Surface Disease Index scores and artificial tear compliance.

Results

Of the 80 enrolled participants, 66 completed the trial. Neither intervention affected Chao-1 richness (analysis of variance [ANOVA], P = 0.231) or Shannon's diversity index (ANOVA, P = 0.224). Microbiome samples did not separate by time point (permutation multivariate analysis of variance [PERMANOVA], P = 0.223) or intervention group (PERMANOVA, P = 0.668). LEfSe taxonomic analysis revealed that carboxymethylcellulose depleted several taxa including Bacteroides and Lachnoclostridium, but enriched Enterobacteriaceae, Citrobacter, and Gordonia. Both interventions decreased OSDI scores (Wilcoxon signed rank test, P < 0.05), but there was no significant difference between interventions (Mann-Whitney U, P = 0.54).

Conclusions

Carboxymethylcellulose artificial tears increased Actinobacteriota but decreased Bacteroides and Firmicutes bacteria. Carboxymethylcellulose artificial tears do not affect ocular surface microbiome diversity and are not significantly more effective than polyethylene glycol artificial tears for dry eye treatment.

Translational Relevance

The 16S microbiome analysis has revealed small changes in the ocular surface microbiome associated with artificial tear use.

Perturbations of the ocular surface microbiome and their effect on host immune function

PURPOSE OF REVIEW

Current literature describing the ocular surface microbiome and host immunity are reviewed alongside experiments studying perturbations of the microbiome to explore the hypothesis that disruption of a healthy microbiome may predispose the ocular surface to inflammation and infection.

RECENT FINDINGS

The ocular surface of healthy subjects is colonized by stable, pauci-microbial communities that are tolerant to the host immune response and are dominated by the genera Corynebacterium , Propionibacterium , and Staphylococcus . In animal studies, commensal microbes on the ocular surface interact with toll-like receptors to regulate the immune system through immune cell and inflammatory cytokine production, promoting homeostasis and protecting against infection. Contact lens wear, lens wash solutions, and preserved topical medications can disrupt the native microbiome and alter the relative diversity and composition of microbes on the ocular surface.

SUMMARY

The ocular surface microbiome confers protection against pathogenic colonization and immune dysregulation. Disruption of this microbiome by exogenous factors may alter the resistance of the ocular surface to infection. Further study of the relationships between human ocular surface microbiome and the local immune response are needed.