Comparison of the Ocular Microbiomes of Dry Eye Patients With and Without Autoimmune Disease

What is the impact of microbiota on dry eye: a literature review of the gut-eye axis

BACKGROUND

Dry eye is a chronic and multifactorial ocular surface disease caused by tear film instability or imbalance in the microenvironment of the ocular surface. It can lead to various discomforts such as inflammation of the ocular surface and visual issues. However, the mechanism of dry eye is not clear, which results in dry eye being only relieved but not cured in clinical practice. Finding multiple environmental pathways for dry eye and exploring the pathogenesis of dry eye have become the focus of research. Studies have found that changes in microbiota may be related to the occurrence and development of dry eye disease.

METHODS

Entered the keywords "Dry eye", "Microbiota", "Bacteria" through PUBMED, summarised the articles that meet the inclusion criteria and then filtered them while the publication time range of the literature was defined in the past 5 years, with a deadline of 2023.A total of 13 clinical and 1 animal-related research articles were screened out and included in the summary.

RESULTS

Study found that different components of bacteria can induce ocular immune responses through different receptors present on the ocular surface, thereby leading to an imbalance in the ocular surface microenvironment. Changes in the ocular surface microbiota and gut microbiota were also found when dry eye syndrome occurs, including changes in diversity, an increase in pro-inflammatory bacteria, and a decrease in short-chain fatty acid-related bacterial genera that produce anti-inflammatory effects. Fecal microbiota transplantation or probiotic intervention can alleviate signs of inflammation on the ocular surface of dry eye animal models.

CONCLUSIONS

By summarizing the changes in the ocular surface and intestinal microbiota when dry eye occurs, it is speculated and concluded that the intestine may affect the occurrence of eye diseases such as dry eye through several pathways and mechanisms, such as the occurrence of abnormal immune responses, microbiota metabolites- intervention of short-chain fatty acids, imbalance of pro-inflammatory and anti-inflammatory factors, and release of neurotransmitters, etc. Analyzing the correlation between the intestinal tract and the eyes from the perspective of microbiota can provide a theoretical basis and a new idea for relieving dry eyes in multiple ways in the future.

Recommendations for nutritional supplements for dry eye disease: current advances

Dry eye disease (DED) represents a prevalent ocular surface disease. The development of effective nutritional management strategies for DED is crucial due to its association with various factors such as inflammation, oxidative stress, deficiencies in polyunsaturated fatty acids (PUFAs), imbalanced PUFA ratios, and vitamin insufficiencies. Extensive research has explored the impact of oral nutritional supplements, varying in composition and dosage, on the symptoms of DED. The main components of these supplements include fish oils (Omega-3 fatty acids), vitamins, trace elements, and phytochemical extracts. Beyond these well-known nutrients, it is necessary to explore whether novel nutrients might contribute to more effective DED management. This review provides a comprehensive update on the therapeutic potential of nutrients and presents new perspectives for combination supplements in DED treatment.

The Conjunctival Microbiome and Dry Eye: What We Know and Controversies

ABSTRACT

Dry eye disease is a common multifactorial condition that may be idiopathic or associated with autoimmune conditions, such as Sjogren syndrome. Commensal microorganisms modify immune responses, so it is relevant to understand how they modify such immune-mediated diseases. Microbiota in the gut regulate inflammation in the eye, and conversely, severe inflammation of the ocular surface results in alteration of gut microbiome. The conjunctiva microbiome can be analyzed using 16S or shotgun metagenomics. The amount of microbial DNA in ocular surface mucosa relative to human DNA is limited compared with the case of the intestinal microbiome. There are challenges in defining, harvesting, processing, and analyzing the microbiome in the ocular surface mucosa. Recent studies have shown that the conjunctiva microbiome depends on age, presence of local and systemic inflammation, and environmental factors. Microbiome-based therapy, such as the use of oral probiotics to manage dry eye disease, has initial promising results. Further longitudinal studies are required to investigate the alteration of the conjunctival microbiome after local therapy and surgery.

Analysis of the mucosal chemokines CCL28, CXCL14, and CXCL17 in dry eye disease: An in vitro and clinical investigation

Mucosal chemokines have antimicrobial properties and play an important role in mucosal immunity. However, little is known about their expression on the ocular surface. This study aimed to analyze the expression of the mucosal chemokines CCL28, CXCL14 and CXCL17 in corneal and conjunctival epithelial cells under in vitro dry eye (DE) conditions, and in conjunctival samples from healthy subjects and DE patients. Human corneal epithelial cells (HCE) and immortalized human conjunctival epithelial cells (IM-HConEpiC) were incubated under hyperosmolar (400-500 mOsM) or inflammatory (TNF-α 25 ng/mL) conditions for 6 h and 24 h to measure CCL28, CXCL14, and CXCL17 gene expression by RT-PCR and their secretion by immunobead-based analysis (CCL28, CXCL14) and ELISA (CXCL17). Additionally, twenty-seven DE patients and 13 healthy subjects were included in this study. DE-related questionnaires (OSDI, mSIDEQ and NRS) evaluated symptomatology. Ocular surface integrity was assessed using vital staining. Tactile sensitivity was measured with Cochet-Bonnet esthesiometer, and mechanic and thermal (heat and cold) sensitivity using Belmonte's non-contact esthesiometer. Subbasal nerve plexus and dendritic cell density were analyzed by in vivo confocal microscopy. Conjunctival cells from participants were collected by impression cytology to measure mucosal chemokines gene expression by RT-PCR. Our results showed that HCE and IM-HConEpiC cells increased CCL28, CXCL14, and CXCL17 secretion under hyperosmolar conditions. The gene expression of CCL28 was significantly upregulated in conjunctival samples from DE patients. CCL28 expression correlated positively with symptomatology, corneal staining, heat sensitivity threshold, and dendritic cell density. CXCL14 expression correlated positively with age, ocular pain, conjunctival staining, tactile sensitivity, and image reflectivity. CXCL17 expression correlated positively with corneal staining. These results suggest that corneal and conjunctival epithelial cells could be a source of CCL28, CXCL14, and CXCL17 on the ocular surface and that CCL28 might be involved in DE pathogenesis.

Novel treatments for dry eye syndrome

Dry eye syndrome (DES) is a prevalent and multifactorial disease that leads to a self-perpetuating cycle of inflammation and damage to the ocular surface. This results in symptoms such as redness, burning, and blurred vision, which can negatively affect a patient's quality of life. While treatments are available to manage DES, they only temporarily relieve symptoms. Furthermore, long-term use of certain medications can cause harm to the ocular surface. Therefore, there is a need for safer and effective treatments for DES. This review highlights the latest advancements in DES therapy, providing valuable insights into ongoing efforts to improve patient outcomes.

How does ocular graft-versus-host disease fit under the dry eye umbrella? A review

Graft-versus-host disease (GVHD) is a systemic disease that can affect multiple organs as a consequence of an allogeneic haematopoietic stem cell transplant. One organ system that is often affected in GVHD is the eyes. Ocular GVHD (oGVHD) may involve various structures within the eye including the lacrimal glands, eyelids, conjunctiva, cornea, and nasolacrimal ducts, and is a source of morbidity in patients with GVHD. Common presenting features of GVHD overlap with dry eye disease (DED), including decreased tear production, epithelial disruption, and Meibomian gland dysfunction (MGD). In this review, we aim to compare oGVHD and DED to better understand the similarities and differences between the conditions, with a focus on pathophysiology, risk factors, clinical features, and treatments.

Ocular surface microbiota in patients with varying degrees of dry eye severity

AIM

To elucidate the profiles of commensal bacteria on the ocular surfaces of patients with varying severity of dry eye (DE).

METHODS

The single-center, prospective, case-control, observational study categorized all participants into three distinct groups: 1) control group (n=61), 2) mild DE group (n=56), and 3) moderate-to-severe DE group (n=82). Schirmer's tear secretion strips were used, and the bacterial microbiota was analyzed using 16S ribosomal ribonucleic acid gene sequencing.

RESULTS

The three groups had significant differences in alpha diversity: the control group had the highest richness (Chao1, Faith's phylogenetic diversity), the mild DE group showed the highest diversity (Shannon, Simpson), and the moderate-to-severe DE group had the lowest of the above-mentioned indices. DE severity was positively correlated with a reduction in beta diversity of the microbial community, with the moderate-to-severe DE group exhibiting the lowest beta diversity. Linear discriminant analysis effect size presented distinct dominant taxa that significantly differed between each. Furthermore, the exacerbation of DE corresponded with the enrichment of certain pathogenic bacteria, as determined by random forest analysis.

CONCLUSION

As DE severity worsens, microbial community diversity tends to decrease. DE development corresponds with changes in microbial constituents, primarily characterized by reduced microbial diversity and a more homogenous species composition.

Temporal dynamics and composition of ocular surface microbiota in C57BL/6J mice: uncovering a 12h ultradian rhythm

Purpose

This study aimed to investigate the presence of rhythmic fluctuations in the composition, abundance, and functions of commensal core bacteria on the ocular surface of C57BL/6J mice.

Methods

Male C57BL/6J mice, aged 12 weeks, were subjected to a 12-hour light/12-hour dark cycle. Ocular surface tissue samples were collected at four time points (ZT) over a 24-hour period at six-hour intervals. The core ocular surface microbiota's oscillation cycles and frequencies were assessed using 16S rRNA gene sequencing targeting the V3-V4 region, along with the JTK_CYCLE algorithm. Functional predictions of these bacteria were conducted using PICRUSt2.

Results

Deep sequencing of the ocular surface microbiota highlighted the high abundance of commensal bacteria, with Proteobacteria, Actinobacteriota, and Firmicutes collectively constituting over 90% of the total sample abundance. Among the 22 core bacterial genera, 11 exhibited robust 12-hour rhythms, including Halomonas, Pelagibacterium, Pseudomonas, Nesterenkonia, norank_f_Hyphomonadaceae, Stenotrophomonas, Anoxybacillus, Acinetobacter, Zoogloea, Brevibacillus, and Ralstonia. Further taxonomic analysis indicated significant intra-cluster similarities and inter-cluster differences at the order, family, and genus levels during ZT0/12 and ZT6/18. Community interaction networks and functional prediction analyses revealed synchronized 12-hour rhythmic oscillations in neural, immune, metabolic, and other pathways associated with symbiotic bacteria.

Conclusion

This study demonstrates the presence of ultradian rhythmic oscillations in commensal bacteria on the ocular surface of normal C57BL/6J mice, with a 12-hour cycle. These findings suggest a crucial role for ultradian rhythms in maintaining ocular surface homeostasis in the host.

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.

Ocular surface microbiota dysbiosis contributes to the high prevalence of dry eye disease in diabetic patients

People with diabetes mellitus (DM) are at an increased risk for developing dry eye disease (DED). However, the mechanisms underlying this phenomenon remain unclear. Recent studies have found that the ocular surface microbiota (OSM) differs significantly between patients with DED and healthy people, suggesting that OSM dysbiosis may contribute to the pathogenesis of DED. This hypothesis provides a new possible explanation for why diabetic patients have a higher prevalence of DED than healthy people. The high-glucose environment and the subsequent pathological changes on the ocular surface can cause OSM dysbiosis. The unbalanced microbiota then promotes ocular surface inflammation and alters tear composition, which disturbs the homeostasis of the ocular surface. This "high glucose-OSM dysbiosis" pathway in the pathogenesis of DED with DM (DM-DED) is discussed in this review.

Contact lenses and ocular dysbiosis, from the transitory to the pathological

Normal ocular microbiota is composed of different Gram-negative and positive bacterial communities that act as commensals on the ocular surface. An imbalance in the homeostasis of the native species or dysbiosis triggers functional alterations that can eventually lead to ocular conditions, indicating the use of contact lenses as the most relevant predisposing factor. Through a bibliographic review that added scientific articles published between 2018 and 2022, the relationship between healthy ocular microbiota and dysbiosis associated with the use of contact lenses that trigger ocular conditions was analyzed. The ocular microbiota in healthy individuals is mainly composed of bacteria from the phyla: Proteobacteria, Actinobacteria and Firmicutes. These bacterial communities associated with the use of contact lenses develop dysbiosis, observing an increase in certain genera such as Staphylococcus spp. and Pseudomonas spp., which under normal conditions are commensals of the ocular surface, but as their abundance is increased, they condition the appearance of various ocular conditions such as corneal infiltrative events, bacterial keratitis and corneal ulcer. These pathologies tend to evolve rapidly, which, added to late detection and treatment, can lead to a poor visual prognosis. It is suggested that professionals in the ophthalmology area learn about the composition of the communities of microorganisms that make up this ocular microbiota, in order to correctly distinguish and identify the causative agent, thereby providing a adequate and effective treatment to the user.

Alterations of the bacterial ocular surface microbiome are found in both eyes of horses with unilateral ulcerative keratitis

Next generation sequencing (NGS) studies in healthy equine eyes have shown a more diverse ocular surface microbiota compared to culture-based techniques. This study aimed to compare the bacterial ocular surface microbiota in both eyes of horses with unilateral ulcerative keratitis (UK) with controls free of ocular disease. Conjunctival swabs were obtained from both ulcerated eyes and unaffected eyes of 15 client-owned horses with unilateral UK following informed consent, as well as from one eye of 15 healthy horses. Genomic DNA was extracted from the swabs and sequenced on an Illumina platform using primers that target the V4 region of bacterial 16S rRNA. Data were analyzed using Quantitative Insights Into Molecular Ecology (QIIME2). The ocular surface of ulcerated eyes had significantly decreased species richness compared with unaffected fellow eyes (Chao1 q = 0.045, Observed ASVs p = 0.045) with no differences in evenness of species (Shannon q = 0.135). Bacterial community structure was significantly different between either eye of horses with UK and controls (unweighted UniFrac: control vs. unaffected, p = 0.03; control vs. ulcerated, p = 0.003; unaffected vs. ulcerated, p = 0.016). Relative abundance of the gram-positive taxonomic class, Bacilli, was significantly increased in ulcerated eyes compared with controls (q = 0.004). Relative abundance of the taxonomic family Staphylococcaceae was significantly increased in ulcerated and unaffected eyes compared with controls (q = 0.030). The results suggest the occurrence of dysbiosis in infected eyes and reveal alterations in beta diversity and taxa of unaffected fellow eyes. Further investigations are necessary to better understand the role of the microbiome in the pathophysiology of ocular surface disease.

Conjunctival microbiome changes in soft contact lens users and contact lens discomfort patients

INTRODUCTION

Contact lens discomfort (CLD) acts as a challenging problem, and the associated conjunctival microbiome changes were unclear.

MATERIAL AND METHODS

Conjunctival sac swab samples were collected from 12 eyes of nonwearers (NW), 12 eyes of asymptomatic contact lens (ACL) wearers, and 11 eyes of CLD. The V3-V4 region of the 16S rRNA gene sequencing was used to investigate differences among three groups.

RESULTS

No differences in alpha diversity were observed among the three groups. The beta diversity showed a distinct microbiome composition between ACL and CLD group (P = 0.018) with principal coordinate analysis. The relative abundance of Firmicutes was significantly higher in CLD (48.18%) than in ACL (13.21%) group (P = 0.018). The abundance of Bacillus in patients with ACL (0.05%) or with CLD (0.02%) were significantly lower than that in the NW (1.27%) group (P = 0.024, 0.028, respectively). Moreover, the abundance of Firmicutes was positively correlated with the OSDI scores in CLD patients (r = 0.817, P < 0. 01, Spearman).

DISCUSSIONS

Patients with CLD have various degrees of bacterial microbiota imbalance in the conjunctival sac, compared with NW and ACL groups.

CONCLUSION

Firmicutes may serve as a potential biomarker for the CLD patients.

CDEMI: characterizing differences in microbial composition and function in microbiome data

Microbial communities influence host phenotypes through microbiota-derived metabolites and interactions between exogenous active substances (EASs) and the microbiota. Owing to the high dynamics of microbial community composition and difficulty in microbial functional analysis, the identification of mechanistic links between individual microbes and host phenotypes is complex. Thus, it is important to characterize variations in microbial composition across various conditions (for example, topographical locations, times, physiological and pathological conditions, and populations of different ethnicities) in microbiome studies. However, no web server is currently available to facilitate such characterization. Moreover, accurately annotating the functions of microbes and investigating the possible factors that shape microbial function are critical for discovering links between microbes and host phenotypes. Herein, an online tool, CDEMI, is introduced to discover microbial composition variations across different conditions, and five types of microbe libraries are provided to comprehensively characterize the functionality of microbes from different perspectives. These collective microbe libraries include (1) microbial functional pathways, (2) disease associations with microbes, (3) EASs associations with microbes, (4) bioactive microbial metabolites, and (5) human body habitats. In summary, CDEMI is unique in that it can reveal microbial patterns in distributions/compositions across different conditions and facilitate biological interpretations based on diverse microbe libraries. CDEMI is accessible at http://rdblab.cn/cdemi/.

Prevalence of Dry Eye Symptoms and Associated Risk Factors among University Students in Poland

Aim: The aim of the study was to demonstrate the prevalence and risk factors of dry eye symptoms (DES) among university students in Poland. Material and methods: A cross-sectional study survey was conducted among 312 Polish university students. The questionnaire consisted of the Ocular Surface Disease Index (OSDI), the 5-Item Dry Eye Questionnaire (DEQ-5) and questions regarding medical history and risk factors. Results: According to the OSDI, more than half of respondents (57.1%) have symptoms of ocular surface disease. Time spent using electronic devices is correlated with scores gathered in both OSDI and DEQ-5 (p < 0.001). There is a statistically significant dependence between psychotropics (p = 0.002), glucocorticosteroids usage (p = 0.026), the presence of depression (p < 0.001), diabetes (p = 0.01) or allergy (p = 0.008) and dry eye symptoms proved in both questionnaires. Respondents with refractive errors and those living in metropolitan areas have a statistically higher symptom intensity(p < 0.022). Stress felt by students is associated with higher DES risk. No correlation between DES and smoking habits was observed. The history of SARS-CoV-2 infection was associated with the severity of DES (p = 0.036). Conclusion: Pathogenesis of DES is multifactorial and its severity depends on several factors, both genetic and environmental. Its prevalence among the young population is underestimated. Determining risk factors will enable the implementation of appropriate prophylaxis and early diagnosis.

[Predictive significance of genetic analysis of the development of dry eye disease of different origin]

One of the etiological causes of dry eye disease (DED) is systemic autoimmune diseases (AID): primary Sjögren's syndrome (PSS), rheumatoid arthritis (RA); their manifestation may begin with ophthalmic symptoms. The relationship of PSS and RA with genetic factors is proven. The contribution of polymorphic markers of the genes THBS1, MUC1, TRIM21, STAT4, PTPN22 in the development of these diseases is established, as well as their connection with the development of DED. A panel of genetic markers for evaluating the risk of developing DED in PSS and RA is developed, and its sensitivity and specificity is determined.

PURPOSE

The aim of the study was to determine the prognostic significance of a panel of polymorphic gene markers in the development of dry eye syndrome in patients with primary Sjögren's syndrome and rheumatoid arthritis over a five-year follow-up period.

MATERIAL AND METHODS

Patients with a verified diagnosis of PSS and RA without signs of DED were examined (n=35 and n=42, respectively). The control group included 82 volunteers without AID and DED. The observation period was 5 years. Every year all study subjects underwent an ophthalmological clinical and functional examination.

RESULTS

Dry eye disease had developed in groups of patients with AID with predisposing genotypes of polymorphic markers of the genes THBS1, MUC1, TRIM21, STAT4, PTPN22. The peak of DED development in these patients was in the third year of the follow-up. As a result of ROC analysis, it was found that the sensitivity and specificity of determining the predisposing genotypes of polymorphic markers of the THBS1, MUC1, TRIM21, STAT4, PTPN22 genes was 68 and 87%, respectively (p<0.0001).

CONCLUSION

Genetic research methods are essential for minimally invasive early diagnosis of dry eye disease, and can subsequently become the basis for a personalized approach to its treatment.

The species-level microbiota of healthy eyes revealed by the integration of metataxonomics with culturomics and genome analysis

Objectives

To characterize the healthy ocular surface microbiota at the species level, including cultured and uncultured taxa.

Methods

We integrated the metataxonomic method with culturomics and genome sequencing analysis of selected isolated strains to better illustrate the taxonomic structure of the ocular surface microbiota. The metataxonomics used the full-length 16S rRNA gene sequences and the operational phylogenetic unit strategy, which can precisely identify the cultured and uncultured or potentially new taxa to species level based on the phylogenetic tree constructed.

Results

We detected 1,731 operational phylogenetic units (OPUs) in 196 healthy eyes from 128 people, affiliated to 796 cultured species, 784 potentially new species, and 151 potentially new higher taxa. The microbiota for each eye had 49.17 ± 35.66 OPUs. Of the 796 cultured species, 170 (21.36%) had previously caused clinical infections. Based on where they were initially isolated, the ocular surface microbiota mainly came from human body sites (34.55%), the environment (36.93%), plants (9.05%), animals (4.90%), and others; 428 strains were isolated from 20 eyes, affiliated to 42 species, and had come from the environment (33.33%) and the skin (16.67%). Of these, 47.62% had previously caused clinical infections. Genome analysis of 73 isolators revealed that 68.5% of them carried antibiotic resistance genes. The most frequently isolated genera, namely Staphylococcus, Streptococcus, and Moraxella, had an average of 5.30, four, and three resistance genes per strain, respectively.

Discussion

The study found that the ocular surface microbiota mainly came from the environment, plants, animals, food, and human body sites such as the skin, oral cavity, upper respiratory tract, etc. No core member of ocular surface microbiota was detected at the species level. The human eyes were invaded and colonized by bacteria from the exposed environment, some of which were capable of causing infections in humans and carried antibiotic resistance genes. Preventive measures should be developed to protect our eyes from danger.

Bacteria and Dry Eye: A Narrative Review

(1) Background: Dry eye is a multifactorial disease of the ocular surface, the incidence of which has been increasing sharply. The pathogenesis of dry eye, especially in terms of the bacterial flora, has drawn great attention. Additionally, the potential treatment methods need to be explored. (2) Methods: We reviewed more than 100 studies and summarized them briefly in a review. (3) Results: We summarized the bacterial communities found on the ocular surface in the general population and patients with dry eye and found a relationship between dry eye and antibiotic therapy. We identified the possible mechanisms of bacteria in the development of dry eye by discussing factors such as the destruction of the antibacterial barrier, infectious diseases, microbiome homeostasis, inflammatory factors on the ocular surface and vitamin deficiency. (4) Conclusion: We systematically reviewed the recent studies to summarize the bacterial differences between patients with dry eye and the general population and brought up several possible mechanisms and possible treatment targets.

Microbiome and immune-mediated dry eye: a review

In this review, we aim to summarise key articles that explore relationships between the gut and ocular surface microbiomes (OSMs) and immune-mediated dry eye. The gut microbiome has been linked to the immune system by way of stimulating or mitigating a proinflammatory or anti-inflammatory lymphocyte response, which may play a role in the severity of autoimmune diseases. Although the 'normal' gut microbiome varies among individuals and demographics, certain autoimmune diseases have been associated with characteristic gut microbiome changes. Less information is available on relationships between the OSM and dry eye. However, microbiome manipulation in multiple compartments has emerged as a therapeutic strategy, via diet, prebiotics and probiotics and faecal microbial transplant, in individuals with various autoimmune diseases, including immune-mediated dry eye.

Elevated Rheumatoid Factor Associates with Dry Eye in Patients with Common Autoimmune Diseases

Purpose

Patients and Methods

Results

Conclusion

Analysis of Conjunctival Sac Microbiome in Dry Eye Patients With and Without Sjögren's Syndrome

Purpose

To analyze the conjunctival sac microbial communities in patients with Sjögren's syndrome-associated dry eyes (SSDE) and non-Sjögren's syndrome-associated dry eyes (NSSDE), compared with normal controls (NC).

Methods

Conjunctival sac swab samples from 23 eyes of SSDE, 36 eyes of NSSDE, and 39 eyes of NC were collected. The V3–V4 region of the 16S ribosomal RNA (rRNA) gene high-throughput sequencing was performed on an Illumina MiSeq platform and analyzed using Quantitative Insights Into Microbial Ecology (QIIME). Alpha diversity was employed to analyze microbiome diversity through Chao1 and Shannon indexes. Beta diversity was demonstrated by the principal coordinates analysis (PCoA) and Partial Least Squares Discrimination Analysis (PLS-DA). The relative abundance was bioinformatically analyzed at the phylum and genus levels.

Results

The alpha diversity was lower in patients with dry eye disease (Shannon index: NC vs. SSDE: P = 0.020, NC vs. NSSDE: P = 0.029). The beta diversity showed divergent microbiome composition in different groups (NC vs. SSDE: P = 0.001, NC vs. NSSDE: P = 0.001, NSSDE vs. SSDE: P = 0.005). The top 5 abundant phyla were Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota, and Cyanobacteria in all three groups. The top five abundant genera included Acinetobacter, Staphylococcus, Bacillus, Corynebacterium, and Clostridium_sensu_stricto_1. The relative microbiome abundance was different between groups. The Firmicutes/Bacteroidetes (F/B) ratio was 6.42, 7.31, and 9.71 in the NC, NSSDE, and SSDE groups, respectively (NC vs. SSDE: P = 0.038, NC vs. NSSDE: P = 0.991, SSDE vs. NSSDE: P = 0.048).

Conclusion

The diversity of conjunctival sac microbiome in patients with NSSDE and SSDE was diminished compared with NC. The main microbiome at the phylum and genus level were similar between groups, but the relative abundance had variations. The Firmicutes/Bacteroidetes ratio was higher in the SSDE group.

Characterization of Conjunctival Sac Microbiome from Patients with Allergic Conjunctivitis

Conjunctival sac microbiome alterations have been reported to be closely associated with many ocular diseases. However, the characteristic of conjunctival sac microbiome in allergic conjunctivitis (AC) was scarcely described. In this study, we aimed to identify the differences of the conjunctival sac microbiome composition in AC patients compared with normal controls (NCs) using high-throughput 16S rDNA sequencing metagenomic analysis. The conjunctival sac microbiome samples from 28 AC patients and 39 NC patients were collected. The V3-V4 region of 16S rRNA gene high-throughput sequencing was performed on the illumina MiSeq platform. Alpha diversity, beta diversity and the relative abundance at the phylum and genus levels were analyzed using QIIME. Alpha diversity demonstrated by Chao1, Observed_species and PD_whole_tree indexes did not show significant difference between the AC and NC groups, while the Shannon index was higher in the AC group. Beta diversity showed divergent microbiome composition in different groups (p < 0.005). The top five abundant phyla were Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota and Cyanobacteria in both groups. The top five abundant genera were Bacillus, Staphylococcus, Corynebacterium, Acinetobacter and Ralstonia in the AC group and Acinetobacter, Staphylococcus, Bacillus, Clostridium_sensu_stricto_1, Corynebacterium and Geobacillus in the NC group. The Firmicutes/Bacteroidetes (F/B) ratio at the phylum level was similar between groups (p = 0.144). The Bacillus/Acinetobacter (B/A) ratio at the genus level was higher in the AC group (p = 0.021). The dysbiosis detected in this study might provide further evidence to investigate the mechanism and treatment methods for allergic conjunctivitis.