Identification of an intraocular microbiota

Exploring the role of the ocular surface in the lung-eye axis: Insights into respiratory disease pathogenesis

Chronic respiratory diseases (CRDs) represent a significant proportion of global health burden, with a wide spectrum of varying, heterogenic conditions largely affecting the pulmonary system. Recent advances in immunology and respiratory biology have highlighted the systemic impact of these diseases, notably through the elucidation of the lung-eye axis. The current review focusses on understanding the pivotal role of the lung-eye axis in the pathogenesis and progression of chronic respiratory infections and diseases. Existing literature published on the immunological crosstalk between the eye and the lung has been reviewed. The various roles of the ocular microbiome in lung health are also explored, examining the eye as a gateway for respiratory virus transmission, and assessing the impact of environmental irritants on both ocular and respiratory systems. This novel concept emphasizes a bidirectional relationship between respiratory and ocular health, suggesting that respiratory diseases may influence ocular conditions and vice versa, whereby this conception provides a comprehensive framework for understanding the intricate axis connecting both respiratory and ocular health. These aspects underscore the need for an integrative approach in the management of chronic respiratory diseases. Future research should further elucidate the in-depth molecular mechanisms affecting this axis which would pave the path for novel diagnostics and effective therapeutic strategies.

Exploring the Ocular Surface Microbiome and Tear Proteome in Glaucoma

Although glaucoma is a leading cause of irreversible blindness worldwide, its pathogenesis is incompletely understood, and intraocular pressure (IOP) is the only modifiable risk factor to target the disease. Several associations between the gut microbiome and glaucoma, including the IOP, have been suggested. There is growing evidence that interactions between microbes on the ocular surface, termed the ocular surface microbiome (OSM), and tear proteins, collectively called the tear proteome, may also play a role in ocular diseases such as glaucoma. This study aimed to find characteristic features of the OSM and tear proteins in patients with glaucoma. The whole-metagenome shotgun sequencing of 32 conjunctival swabs identified Actinobacteria, Firmicutes, and Proteobacteria as the dominant phyla in the cohort. The species Corynebacterium mastitidis was only found in healthy controls, and their conjunctival microbiomes may be enriched in genes of the phospholipase pathway compared to glaucoma patients. Despite these minor differences in the OSM, patients showed an enrichment of many tear proteins associated with the immune system compared to controls. In contrast to the OSM, this emphasizes the role of the proteome, with a potential involvement of immunological processes in glaucoma. These findings may contribute to the design of new therapeutic approaches targeting glaucoma and other associated diseases.

Unveiling the gut-eye axis: how microbial metabolites influence ocular health and disease

The intricate interplay between the gut microbiota and ocular health has surpassed conventional medical beliefs, fundamentally reshaping our understanding of organ interconnectivity. This review investigates into the intricate relationship between gut microbiota-derived metabolites and their consequential impact on ocular health and disease pathogenesis. By examining the role of specific metabolites, such as short-chain fatty acids (SCFAs) like butyrate and bile acids (BAs), herein we elucidate their significant contributions to ocular pathologies, thought-provoking the traditional belief of organ sterility, particularly in the field of ophthalmology. Highlighting the dynamic nature of the gut microbiota and its profound influence on ocular health, this review underlines the necessity of comprehending the complex workings of the gut-eye axis, an emerging field of science ready for further exploration and scrutiny. While acknowledging the therapeutic promise in manipulating the gut microbiome and its metabolites, the available literature advocates for a targeted, precise approach. Instead of broad interventions, it emphasizes the potential of exploiting specific microbiome-related metabolites as a focused strategy. This targeted approach compared to a precision tool rather than a broad-spectrum solution, aims to explore the therapeutic applications of microbiome-related metabolites in the context of various retinal diseases. By proposing a nuanced strategy targeted at specific microbial metabolites, this review suggests that addressing specific deficiencies or imbalances through microbiome-related metabolites might yield expedited and pronounced outcomes in systemic health, extending to the eye. This focused strategy holds the potential in bypassing the irregularity associated with manipulating microbes themselves, paving a more efficient pathway toward desired outcomes in optimizing gut health and its implications for retinal diseases.

Differential Composition and Structure of the Microbiota from Active and Inactive Stages of HLA-B27-associated Uveitis by Paired Fecal Metagenomes

PURPOSE

To compare the diversities and abundances of bacterial taxa in the microbiome of patients with HLA B27-positive acute anterior uveitis (AAU) in the active and inactive phases.

METHODS

An observational descriptive prospective and comparative study was conducted in ten HLA-B27-positive AAU patients (44.6 ± 13.4 years). The microbiome of the stool samples obtained in the active and inactive stages was analyzed by sequencing the V3 region of the 16S rRNA gene.

RESULTS

The differences in the bacteria profile between active and inactive stages in each individual were confirmed (p < 0.0001). Ten OTUs were found exclusively in the active phase of 90% of the individuals, suggesting a proinflammatory association. Blautia OUT_4 and Faecalibacterium OUT_2 abundances showed a direct relationship between abundance and severity of ocular inflammation. Two OTUs were exclusive of the inactive stage, suggesting an anti-inflammatory role.

CONCLUSION

The metagenomic profile of the fecal microbiota differs in the acute phase of the AAU compared to when the inflammation subsides, despite being the same individual and a short time-lapse. AAU is a fertile field for studying the connection between subtle rapid changes in microbiota and their systemic consequences.

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.

CRB1-associated retinal degeneration is dependent on bacterial translocation from the gut

The Crumbs homolog 1 (CRB1) gene is associated with retinal degeneration, most commonly Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP). Here, we demonstrate that murine retinas bearing the Rd8 mutation of Crb1 are characterized by the presence of intralesional bacteria. While normal CRB1 expression was enriched in the apical junctional complexes of retinal pigment epithelium and colonic enterocytes, Crb1 mutations dampened its expression at both sites. Consequent impairment of the outer blood retinal barrier and colonic intestinal epithelial barrier in Rd8 mice led to the translocation of intestinal bacteria from the lower gastrointestinal (GI) tract to the retina, resulting in secondary retinal degeneration. Either the depletion of bacteria systemically or the reintroduction of normal Crb1 expression colonically rescued Rd8-mutation-associated retinal degeneration without reversing the retinal barrier breach. Our data elucidate the pathogenesis of Crb1-mutation-associated retinal degenerations and suggest that antimicrobial agents have the potential to treat this devastating blinding disease.

Altered ocular surface microbiota in obesity: a case-control study

Purpose

This study aimed to investigate the composition of ocular surface microbiota in patients with obesity.

Methods

This case-control study, spanning from November 2020 to March 2021 at Henan Provincial People's Hospital, involved 35 patients with obesity and an equivalent number of age and gender-matched healthy controls. By employing 16S rRNA sequencing, this study analyzed the differences in ocular surface microbiota between the two groups. The functional prediction analysis of the ocular surface microbiota was conducted using PICRUSt2.

Results

The alpha diversity showed no notable differences in the richness or evenness of the ocular surface microbiota when comparing patients with obesity to healthy controls (Shannon index, P=0.1003). However, beta diversity highlighted significant variances in the microbiota composition of these two groups (ANOSIM, P=0.005). LEfSe analysis revealed that the relative abundances of Delftia, Cutibacterium, Aquabacterium, Acidovorax, Caulobacteraceae unclassified, Comamonas and Porphyromonas in patients with obesity were significantly increased (P<0.05). Predictive analysis using PICRUSt2 highlighted a significant enhancement in certain metabolic pathways in patients with obesity, notably xenobiotics metabolism via cytochrome P450 (CYP450), lipid metabolism, and the oligomerization domain (NOD)-like receptor signaling pathway (P<0.05).

Conclusions

Patients with obesity exhibit a distinct ocular surface core microbiome. The observed variations in this microbiome may correlate with increased activity in CYP450, changes in lipid metabolism, and alterations in NOD-like receptor signaling pathways.

Moderate intensity exercise may protect cardiac function by influencing spleen microbiome composition

The beneficial effects of physical exercise on human cardiorespiratory fitness might be through reduced systemic inflammation, but the mechanism remains a controversy. Recent studies have highlighted the importance of spleen microbiomes in immune regulation. Hence, we conducted a study using a high-fat diet and exercise mouse model to investigate the relationships among different exercise intensities, spleen microbiome composition, and cardiac function. The mice spleen contained a diverse array of microbiota. Different intensities of exercise resulted in varying compositions of the spleen microbiome, Treg cell levels, and mouse heart function. Additionally, the abundance of Lactobacillus johnsonii in the mouse spleen exhibited a positive correlation with Treg cell levels, suggesting that Lactobacillus johnsonii may contribute to the production of Treg cells, potentially explaining the protective role of moderate-intensity exercise on cardiac function. In conclusion, our findings provide evidence that moderate-intensity exercise may promote cardiac function protection by influencing the spleen microbiome composition.

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.

Anti-VEGF Drugs in Age-Related Macular Degeneration: A Focus on Dosing Regimen-Related Safety and Efficacy

Age-related macular degeneration (AMD) is one of the main causes of visual impairment and severe visual loss, and can progress to two advanced forms-neovascularization and atrophic. The field of anti-AMD drugs has undergone huge developments in recent years, from single-target intravitreal administration to current clinical studies with multi-target and non-invasive agents, offering interesting new pharmacological opportunities for the treatment of this disease. Hence, we summarize some of the approved anti-vascular endothelial growth factor (VEGF) drugs for neovascular AMD, especially their structural characteristics, clinical manifestations, dosing regimens, and safety issues of the anti-VEGF drugs highlighted. In addition, advances in atrophic AMD drug research are also briefly described.

Emerging Roles of cGAS-STING Signaling in Mediating Ocular Inflammation

Cyclic GMP-AMP (cGAMP) synthase (cGAS), a sensor of cytosolic DNA, recognizes cytoplasmic nucleic acids to activate the innate immune responses via generation of the second messenger cGAMP and subsequent activation of the stimulator of interferon genes (STINGs). The cGAS-STING signaling has multiple immunologic and physiological functions in all human vital organs. It mediates protective innate immune defense against DNA-containing pathogen infection, confers intrinsic antitumor immunity via detecting tumor-derived DNA, and gives rise to autoimmune and inflammatory diseases upon aberrant activation by cytosolic leakage of self-genomic and mitochondrial DNA. Disruptions in these functions are associated with the pathophysiology of various immunologic and neurodegenerative diseases. Recent evidence indicates important roles of the cGAS-STING signaling in mediating inflammatory responses in ocular inflammatory and inflammation-associated diseases, such as keratitis, diabetic retinopathy, age-related macular degeneration, and uveitis. In this review, we summarize the recently emerging evidence of cGAS-STING signaling in mediating ocular inflammatory responses and affecting pathogenesis of these complex eye diseases. We attempt to provide insightful perspectives on future directions of investigating cGAS-STING signaling in ocular inflammation. Understanding how cGAS-STING signaling is modulated to mediate ocular inflammatory responses would allow future development of novel therapeutic strategies to treat ocular inflammation and autoimmunity.

Challenges and insights in the exploration of the low abundance human ocular surface microbiome

Purpose

The low microbial abundance on the ocular surface results in challenges in the characterization of its microbiome. The purpose of this study was to reveal factors introducing bias in the pipeline from sample collection to data analysis of low-abundant microbiomes.

Methods

Lower conjunctiva and lower lid swabs were collected from six participants using either standard cotton or flocked nylon swabs. Microbial DNA was isolated with two different kits (with or without prior host DNA depletion and mechanical lysis), followed by whole-metagenome shotgun sequencing with a high sequencing depth set at 60 million reads per sample. The relative microbial compositions were generated using the two different tools MetaPhlan3 and Kraken2.

Results

The total amount of extracted DNA was increased by using nylon flocked swabs on the lower conjunctiva. In total, 269 microbial species were detected. The most abundant bacterial phyla were Actinobacteria, Firmicutes and Proteobacteria. Depending on the DNA extraction kit and tool used for profiling, the microbial composition and the relative abundance of viruses varied.

Conclusion

The microbial composition on the ocular surface is not dependent on the swab type, but on the DNA extraction method and profiling tool. These factors have to be considered in further studies about the ocular surface microbiome and other sparsely colonized microbiomes in order to improve data reproducibility. Understanding challenges and biases in the characterization of the ocular surface microbiome may set the basis for microbiome-altering interventions for treatment of ocular surface associated diseases.

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.

The gut-retina axis: a new perspective in the prevention and treatment of diabetic retinopathy

Diabetic retinopathy (DR) is a microvascular lesion that occurs as a complication of diabetes mellitus. Many studies reveal that retinal neurodegeneration occurs early in its pathogenesis, and abnormal retinal function can occur in patients without any signs of microvascular abnormalities. The gut microbiota is a large, diverse colony of microorganisms that colonize the human intestine. Studies indicated that the gut microbiota is involved in the pathophysiological processes of DR and plays an important role in its development. On the one hand, numerous studies demonstrated the involvement of gut microbiota in retinal neurodegeneration. On the other hand, alterations in gut bacteria in RD patients can cause or exacerbate DR. The present review aims to underline the critical relationship between gut microbiota and DR. After a brief overview of the composition, function, and essential role of the gut microbiota in ocular health, and the review explores the concept of the gut-retina axis and the conditions of the gut-retina axis crosstalk. Because gut dysbiosis has been associated with DR, the review intends to determine changes in the gut microbiome in DR, the hypothesized mechanisms linking to the gut-retina axis, and its predictive potential.

Cutibacterium (Formerly Propionibacterium ) acnes Keratitis: A Review

ABSTRACT

Infectious keratitis is a devastating cause of vision loss worldwide. Cutibacterium acnes ( C. acnes ), a commensal bacterium of the skin and ocular surface, is an underrecognized but important cause of bacterial keratitis. This review presents the most comprehensive and up-to-date information for clinicians regarding the risk factors, incidence, diagnosis, management, and prognosis of C. acnes keratitis (CAK). Risk factors are similar to those of general bacterial keratitis and include contact lens use, past ocular surgery, and trauma. The incidence of CAK may be approximately 10%, ranging from 5% to 25% in growth-positive cultures. Accurate diagnosis requires anaerobic blood agar and a long incubation period (≥7 days). Typical clinical presentation includes small (<2 mm) ulcerations with deep stromal infiltrate causing an anterior chamber cell reaction. Small, peripheral lesions are usually resolved, and patients recover a high visual acuity. Severe infections causing VA of 20/200 or worse are common and often do not significantly improve even after treatment. Vancomycin is considered the most potent antibiotic against CAK, although other antibiotics such as moxifloxacin and ceftazidime are more commonly used as first-line treatment.

Intraocular Microbiome in Diabetes and Diabetic Retinopathy: A Pilot Study

INTRODUCTION

The objective of this study was to compare the microbiome in the aqueous humour and gut of people with diabetes mellitus (DM) with and without diabetic retinopathy (DR).

METHODS

This was a prospective controlled study. The study included 17 people undergoing intraocular surgery in their naïve eyes. Stool samples were obtained in the perioperative period; aqueous humour samples of sufficient quantity were obtained in 12 people during intraocular surgery. Dietary information was obtained using a previously validated questionnaire. The gut and aqueous humour samples were assessed for microbiome using 16S rRNA gene sequencing coupled with QIIME and R software.

RESULTS

Aqueous humour was analysed in 12 people: 4 each healthy controls, people with DM, and people with DR. There were minor differences at the phyla levels, but the aqueous humour microbiomes of healthy controls, DM, and DR formed three distinct clusters on heat map analysis with discriminatory genera. This genera-level clustering was more apparent for the intraocular than the gut microbiome. In people with DM and DR, we identified genera unique to the eye or the gut. There was a consistent reduction in the abundance of anti-inflammatory bacteria in people with DR than DM.

CONCLUSIONS

There is a difference in intraocular and gut microbiome regardless of disease or health. Our preliminary findings indicate distinctive features of the intraocular microbiome in people with DR compared with those without it. While this distinctiveness appears more evident in aqueous humour than in the gut, it needs further confirmation with larger studies.

The microbiome in HLA-B27-associated disease: implications for acute anterior uveitis and recommendations for future studies

The pathogenesis of human leukocyte antigen (HLA)-B27-associated diseases such as acute anterior uveitis (AAU) and ankylosing spondylitis (AS) remains poorly understood, though Gram-negative bacteria and subclinical bowel inflammation are strongly implicated. Accumulating evidence from animal models and clinical studies supports several hypotheses, including HLA-B27-dependent dysbiosis, altered intestinal permeability, and molecular mimicry. However, the existing literature is hampered by inadequate studies designed to establish causation or uncover the role of viruses and fungi. Moreover, the unique disease model afforded by AAU to study the gut microbiota has been neglected. This review critically evaluates the current literature and prevailing hypotheses on the link between the gut microbiota and HLA-B27-associated disease. We propose a new potential role for HLA-B27-driven altered antibody responses to gut microbiota in disease pathogenesis and outline recommendations for future well-controlled human studies, focusing on AAU.

Microbiome Dysbiosis: A Pathological Mechanism at the Intersection of Obesity and Glaucoma

The rate at which obesity is becoming an epidemic in many countries is alarming. Obese individuals have a high risk of developing elevated intraocular pressure and glaucoma. Additionally, glaucoma is a disease of epidemic proportions. It is characterized by neurodegeneration and neuroinflammation with optic neuropathy and the death of retinal ganglion cells (RGC). On the other hand, there is growing interest in microbiome dysbiosis, particularly in the gut, which has been widely acknowledged to play a prominent role in the etiology of metabolic illnesses such as obesity. Recently, studies have begun to highlight the fact that microbiome dysbiosis could play a critical role in the onset and progression of several neurodegenerative diseases, as well as in the development and progression of several ocular disorders. In obese individuals, gut microbiome dysbiosis can induce endotoxemia and systemic inflammation by causing intestinal barrier malfunction. As a result, bacteria and their metabolites could be delivered via the bloodstream or mesenteric lymphatic vessels to ocular regions at the level of the retina and optic nerve, causing tissue degeneration and neuroinflammation. Nowadays, there is preliminary evidence for the existence of brain and intraocular microbiomes. The altered microbiome of the gut could perturb the resident brain-ocular microbiome ecosystem which, in turn, could exacerbate the local inflammation. All these processes, finally, could lead to the death of RGC and neurodegeneration. The purpose of this literature review is to explore the recent evidence on the role of gut microbiome dysbiosis and related inflammation as common mechanisms underlying obesity and glaucoma.

The role of the gut microbiome in eye diseases

The gut microbiome is a complex ecosystem of microorganisms and their genetic entities colonizing the gastrointestinal tract. When in balanced composition, the gut microbiome is in symbiotic interaction with its host and maintains intestinal homeostasis. It is involved in essential functions such as nutrient metabolism, inhibition of pathogens and regulation of immune function. Through translocation of microbes and their metabolites along the epithelial barrier, microbial dysbiosis induces systemic inflammation that may lead to tissue destruction and promote the onset of various diseases. Using whole-metagenome shotgun sequencing, several studies have shown that the composition and associated functional capacities of the gut microbiome are associated with age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis. In this review, we provide an overview of the current knowledge about the gut microbiome in eye diseases, with a focus on interactions between the microbiome, specific microbial-derived metabolites and the immune system. We explain how these interactions may be involved in the pathogenesis of age-related macular degeneration, retinal artery occlusion, central serous chorioretinopathy and uveitis and guide the development of new therapeutic approaches by microbiome-altering interventions for these diseases.

Immune response in retinal degenerative diseases - Time to rethink?

Retinal degeneration comprises a group of diseases whereby either the retinal neurons or the neurovascular unit degenerates leading to the loss of visual function. Although the initial cause varies in different conditions, inflammation is known to play an important role in disease pathogenesis. Recent advances in molecular and cell biology and systems biology have yielded unexpected findings, including the heterogeneity of immune cells in the degenerative retina, bidirectional neuron-microglia cross talk, and links to the gut microbiome. Here we discuss the immune response in retinal degenerative conditions, taking into account both regional (retinal) and systemic factors. We propose to classify retinal degeneration into dry and wet forms based on whether the blood-retinal barrier (BRB) is breached and fluid is accumulated in retinal parenchyma. The dry form has a relatively intact BRB and is characterised by progressive retinal thinning. Immune response to degenerative insults is dominated by the retinal defence system, which remains to be regulated by neurons. In contrast, the wet form has retinal oedema due to BRB damaged. Inflammation is executed by infiltrating immune cells as well as the retinal defence system. The gut microbiome will have easy access to the retina in wet retinal degeneration and may affect significantly retinal immune response.

Inside out: Relations between the microbiome, nutrition, and eye health

Age-related macular degeneration (AMD) is a complex disease with increasing numbers of individuals being afflicted and treatment modalities limited. There are strong interactions between diet, age, the metabolome, and gut microbiota, and all of these have roles in the pathogenesis of AMD. Communication axes exist between the gut microbiota and the eye, therefore, knowing how the microbiota influences the host metabolism during aging could guide a better understanding of AMD pathogenesis. While considerable experimental evidence exists for a diet-gut-eye axis from murine models of human ocular diseases, human diet-microbiome-metabolome studies are needed to elucidate changes in the gut microbiome at the taxonomic and functional levels that are functionally related to ocular pathology. Such studies will reveal new ways to diminish risk for progression of- or incidence of- AMD. Current data suggest that consuming diets rich in dark fish, fruits, vegetables, and low in glycemic index are most retina-healthful during aging.

Application Progress of High-Throughput Sequencing in Ocular Diseases

Ocular diseases affect multiple eye parts and can be caused by pathogenic infections, complications of systemic diseases, genetics, environment, and old age. Understanding the etiology and pathogenesis of eye diseases and improving their diagnosis and treatment are critical for preventing any adverse consequences of these diseases. Recently, the advancement of high-throughput sequencing (HTS) technology has paved wide prospects for identifying the pathogenesis, signaling pathways, and biomarkers involved in eye diseases. Due to the advantages of HTS in nucleic acid sequence recognition, HTS has not only identified several normal ocular surface microorganisms but has also discovered many pathogenic bacteria, fungi, parasites, and viruses associated with eye diseases, including rare pathogens that were previously difficult to identify. At present, HTS can directly sequence RNA, which will promote research on the occurrence, development, and underlying mechanism of eye diseases. Although HTS has certain limitations, including low effectiveness, contamination, and high cost, it is still superior to traditional diagnostic methods for its efficient and comprehensive diagnosis of ocular diseases. This review summarizes the progress of the application of HTS in ocular diseases, intending to explore the pathogenesis of eye diseases and improve their diagnosis.

The STING pathway: An uncharacterized angle beneath the gut-retina axis

The gut-retina axis is an emerging concept that describes a close interaction between the gut host-microbiota interface and the retina. Stimulator of interferon genes (STING) is a universally expressed adaptor protein localized in the endoplasmic reticulum. When activated by the cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS), STING induces the activation of the transcription factor interferon regulatory factor 3 (IRF3) and nuclear factor-κB (NF-κB). Downstream effects include inflammation, autophagy, and programmed cell death. Dysregulation of the STING pathway has emerged as a crucial pathogenic mechanism underpinning a broad range of inflammatory diseases, autoimmune diseases, and cancer. Recently, a positive feedback loop between dysbiosis and aberrant activation of the intestinal STING pathway has been demonstrated, concurrently related to increased intestinal permeability. Alternations in the STING pathway have also been reported in the retina of patients with ocular diseases and retinal cells treated with pathological stimuli. Collectively, there is a chance that dysbiosis in patients with retinal diseases disrupts intestinal homeostasis and exacerbates barrier dysfunction through the erroneous accumulation of STING in the gut. Subsequent translocation of microbial products into the bloodstream allows access to the eye via the impaired blood-retina barrier, inducing the chronic activation of the STING pathway in the retina to participate in the disease progression. In this review, we explore how the alterations in the STING pathway could contribute to the gut disturbance and retinal pathologies and discuss its potential as a therapeutic target to treat the gut-retina axis-related diseases, which sheds some light on the better understanding of the crosstalk between the gut and retina.

Mucosal immunology of the ocular surface

The eye is a sensory organ exposed to the environment and protected by a mucosal tissue barrier. While it shares a number of features with other mucosal tissues, the ocular mucosal system, composed of the conjunctiva, Meibomian glands, and lacrimal glands, is specialized to address the unique needs of (a) lubrication and (b) host defense of the ocular surface. Not surprisingly, most challenges, physical and immunological, to the homeostasis of the eye fall into those two categories. Dry eye, a dysfunction of the lacrimal glands and/or Meibomian glands, which can both cause, or arise from, sensory defects, including those caused by corneal herpes virus infection, serve as examples of these perturbations and will be discussed ahead. To preserve vision, dense neuronal and immune networks sense various stimuli and orchestrate responses, which must be tightly controlled to provide protection, while simultaneously minimizing collateral damage. All this happens against the backdrop of, and can be modified by, the microorganisms that colonize the ocular mucosa long term, or that are simply transient passengers introduced from the environment. This review will attempt to synthesize the existing knowledge and develop trends in the study of the unique mucosal and immune elements of the ocular surface.

Epigenetic Modifications and Therapy in Uveitis

Uveitis is a sight-threatening intraocular inflammation, and the exact pathogenesis of uveitis is not yet clear. Recent studies, including multiple genome-wide association studies (GWASs), have identified genetic variations associated with the onset and progression of different types of uveitis, such as Vogt–Koyanagi–Harada (VKH) disease and Behcet’s disease (BD). However, epigenetic regulation has been shown to play key roles in the immunoregulation of uveitis, and epigenetic therapies are promising treatments for intraocular inflammation. In this review, we summarize recent advances in identifying epigenetic programs that cooperate with the physiology of intraocular immune responses and the pathology of intraocular inflammation. These attempts to understand the epigenetic mechanisms of uveitis may provide hope for the future development of epigenetic therapies for these devastating intraocular inflammatory conditions.

Gut microbiota and age-related macular degeneration: A growing partnership

Age-related macular degeneration (AMD) is a leading cause of severe, irreversible vision impairment in developed countries, and its prevalence is rising all over the world, increasing sharply with age. AMD represents an acquired degeneration of the retina that causes significant central visual impairment through a combination of noneovascular and neovascular derangement. The main risk factors for the development of advanced AMD are increasing age, genetic factors, and cigarette smoking; however, the exact pathophysiology of AMD is yet relatively poorly understood. In recent years, the gut microbiota has been intensively studied and linked to several pathologic processes, including ocular diseases. In this sense, the aim of this review is to gather published evidence about the relationship between gut microbiota and AMD.

Microbiota and Ocular Diseases

Recent advances have identified significant associations between the composition and function of the gut microbiota and various disorders in organ systems other than the digestive tract. Utilizing next-generation sequencing and multiomics approaches, the microbial community that possibly impacts ocular disease has been identified. This review provides an overview of the literature on approaches to microbiota analysis and the roles of commensal microbes in ophthalmic diseases, including autoimmune uveitis, age-related macular degeneration, glaucoma, and other ocular disorders. In addition, this review discusses the hypothesis of the "gut-eye axis" and evaluates the therapeutic potential of targeting commensal microbiota to alleviate ocular inflammation.

Atopobiosis and Dysbiosis in Ocular Diseases: Is Fecal Microbiota Transplant and Probiotics a Promising Solution?

PURPOSE

To highlight the role of atopobiosis and dysbiosis in the pathomechanism of autoimmune uveitis, therefore supporting fecal microbiota transplant (FMT) and probiotics as potential targeted-treatment for uveitis.

METHODS

This review synthesized literatures upon the relation between gut microbiota, autoimmune uveitis, FMT, and probiotics, published from January 2001 to March 2021 and indexed in PubMed, Google Scholar, CrossRef.

RESULTS

The basis of the gut-eye axis revolves around occurrences of molecular mimicry, increase in pro-inflammatory cytokines, gut epithelial barrier disruption, and translocation of microbes to distant sites. In patients with autoimmune uveitis, an increase of gut Fusobacterium and Enterobacterium were found. With current knowledge of aforementioned mechanisms, studies modifying the gut microbiome and restoring the physiologic gut barrier has been the main focus for pathomechanism-based therapy. In mice models, FMT and probiotics targeting repopulation of gut microbiota has shown significant improvement in clinical manifestations of uveitis. Consequently, a better understanding in the homeostasis of gut microbiome along with their role in the gut-eye axis is needed to develop practical targeted treatment.

CONCLUSION

Current preliminary studies are promising in establishing a causative gut-eye axis relationship and the possibility of conducting FMT and probiotics as targeted treatment to mitigate autoimmune uveitis, to shorten disease duration, and to prevent further complications.