Clinically Relevant Immune-Cellular Metrics of Inflammation in Meibomian Gland Dysfunction

Quantitative Assessment of Lid Margin Vascularity Using Swept-Source Optical Coherence Tomography Angiography

Purpose

To evaluate the ability of swept-source optical coherence tomography angiography (SS-OCTA) to assess lid margin vascularity.

Methods

This prospective, cross-sectional trial enrolled 125 participants, including 15 control subjects and 110 meibomian gland dysfunction (MGD) patients. Lid margin blood flow density (LMBFD) was obtained using SS-OCTA. LMBFD was assessed for repeatability in 54 of 125 participants and for reproducibility in 23 of 125 participants. The efficacy of LMBFD was validated in the 125 participants, who were divided into mild (n = 46), moderate (n = 42), and severe groups (n = 37) according to the lid margin vascularity severity shown in the slit-lamp photographs. Correlations between LMBFD and MG-related parameters, such as ocular surface disease index (OSDI), fluorescein tear break-up time (FTBUT), cornea fluorescein staining (CFS), lid margin score (LMS), and meibomian gland expressibility (ME), were analyzed in all 125 participants.

Results

Repeatability and reproducibility coefficients were satisfactorily high in the scan mode with a scan area of 6 mm × 6 mm (intraclass correlation coefficient [ICC] repeatability = 0.905; ICC reproducibility = 0.986) and a scan area of 9 mm × 9 mm (ICC repeatability = 0.888; ICC reproducibility = 0.988). The LMBFD gradually increased in the mild, moderate, and severe groups (P < 0.001). LMBFD was significant correlated with OSDI (r = 0.290, P = 0.001), FTBUT (r = -0.195, P = 0.030), CFS (r = 0.352, P < 0.001), ME (r = 0.191, P = 0.033), and LMS (r = 0.370, P < 0.001).

Conclusions

LMBFD may be a noninvasive, repeatable, reproducible, and efficient index for the quantitative evaluation of eyelid margin vascularity in the future.

Translational Relevance

We demonstrated that SS-OCTA has the potential to evaluate the eyelid margin vascularity in MGD patients and guide future treatment strategies in clinics.

Urban Particulate Matter Triggers Meibomian Gland Dysfunction

Purpose

The meibomian gland (MG), as the largest modified sebaceous gland, is potentially damaged by urban particulate matter (UPM) based on epidemiological evidence, but the specific experimental mechanisms remain unknown. This study investigated the effects of UPM on MG dysfunction (MGD) in rodent models.

Methods

Female C57BL/6J mice received eye drops containing UPM suspension or PBS for 14 days. The proliferative capacity and progenitor of MG were evaluated by immunofluorescence. Cell apoptosis was confirmed by TUNEL assay, along with the analysis of caspase family expression. Lipid accumulation was visualized by Oil Red O staining and LipidTox staining. Ductal hyperkeratinization, neutrophil infiltration, and pyroptosis activation were detected through immunostaining. The relative gene expression and signaling pathway activation were determined by Western blot analysis.

Results

Administration of UPM caused MGD-like clinical signs, manifested as distinct corneal epithelial erosion, increased MG orifice occlusion, and glandular dropout. UPM exposure significantly induced progenitor loss, cellular apoptosis, and lipogenic disorder in MG, by reducing P63/Lrig1 expression and increasing cleaved caspase-8, -9, and -3 and meibum lipogenic protein (HMGCR/SREBP-1) expression. UPM-treated mice exhibited ductal hyperkeratinization and neutrophil recruitment. Simultaneously, pyroptosis was motivated, as indicated by the heightened expression of NLRP3 and the cleavage of caspase-1 and -4 and gasdermin D, as well as the increase in IL-1β and IL-18 downstream. The underlying pathological mechanisms of UPM involve the phosphorylation of mitogen-activated protein kinase and nuclear factor-κB.

Conclusions

These results provided direct evidence for the toxicity of UPM in MG. UPM-induced activation of pyroptosis and mitogen-activated protein kinase/nuclear factor-κB signaling pathway might account for the inflammatory MGD.

Dealing with the Persistent Pathogenic Issues of Dry Eye Disease: The Importance of External and Internal Stimuli and Tissue Responses

The immune system plays a central role in protecting the ocular surface from exogenous and endogenous insults, maintaining tissue homeostasis thanks to the mechanism of para-inflammation. This physiological adaptive response may induce resident macrophages/monocytes to produce cytokines and growth factors in order to promote epithelial cell recovery. In case of well-controlled para-inflammation, caused by a low amount of stress, cell viability and function are maintained. When stress becomes too intense, there is a response characterized by the activation of autophagic pathways and consequent cell death. Dysregulated homeostasis and chronic sub-clinical inflammation are the starting points for the development of a stable, chronic inflammatory disease, which leads to ocular surface damage, and, in turn, to the onset or progression of chronic dry eye disease (DED). The long-term management of DED should consider all of the pathogenic issues involved in the disease, including the control of persistent external or internal stresses that are capable of activating and maintaining the para-inflammatory adaptive mechanisms, potentially leading to full-blown inflammation. Dysregulated para-inflammation can be corrected by means of the prolonged use of tear substitutes containing minimal doses of safe corticosteroids or other anti-inflammatory molecules (e.g., corticosteroid, cyclosporine) in order to re-equilibrate ocular surface homeostasis.

Immune modulating nanoparticles for the treatment of ocular diseases

Ocular diseases are increasingly influencing people’s quality of life. Complicated inflammatory mechanisms involved in the pathogenic process of ocular diseases make inflammation-targeting treatment a potential therapeutic approach. The limited efficacy of conventional anti-inflammatory therapeutic strategies, caused by various objective factors, such as complex ocular biological barriers, and subjective factors, such as poor compliance, are promoting the development of new therapeutic methods. With the advantages of considerable tissue permeability, a controllable drug release rate, and selective tissue targeting ability, nanoparticles have successfully captured researchers’ attention and have become a research hotspot in treating ocular diseases. This review will focus on the advantages of nanosystems over traditional therapy, the anti-inflammation mechanisms of nanoparticles, and the anti-inflammatory applications of nanoparticles in different ocular diseases (ocular surface diseases, vitreoretinopathy, uveal diseases, glaucoma, and visual pathway diseases). Furthermore, by analyzing the current situation of nanotherapy and the challenges encountered, we hope to inspire new ideas and incentives for designing nanoparticles more consistent with human physiological characteristics to make progress based on conventional treatments. Overall, some progress has been made in nanoparticles for the treatment of ocular diseases, and nanoparticles have rather broad future clinical translation prospects.

Observation of Conjunctiva-Associated Lymphoid Tissue With In Vivo Confocal Microscopy in Healthy Patients and Patients With Meibomian Gland Dysfunction

PURPOSE

The purpose of this study was to assess the distribution and morphological variation of conjunctiva-associated lymphoid tissue (CALT) in healthy human subjects and patients with meibomian gland dysfunction (MGD) using laserscanningin vivo confocal microscopy.

METHODS

A total of 34 healthy subjects and 32 patients with MGD were enrolled. All subjects underwent a conventional examination consisting of slitlamp biomicroscopy, tear film break-up time, and the Schirmer test. In vivo microscopy was applied to analyze the morphological changes in the diffuse lymphoid layer and lymphoid follicles in CALT. Conjunctival impression cytology (CIC) of samples of patients' palpebral conjunctiva and immunofluorescence staining of CD4 and CD8 antibodies were also performed to indicate the immune response status of CALT.

RESULTS

In the MGD group, the density of diffuse lymphocytes ( P < 0.001), follicles ( P < 0.001), and perifollicular lymphocytes was higher ( P < 0.001) and the central reflection of the follicles was stronger ( P < 0.001) than in the control group, while there was no difference in the follicle area ( P = 0.758). Besides, diffuse lymphocyte density was correlated with telangiectasia, and follicular center reflection intensity was correlated with plugging. CIC immunofluorescence staining showed a higher percentage of CD4 + ( P < 0.001) and CD8 + ( P < 0.001) cells in the MGD group than in the control group.

CONCLUSIONS

Using laser scanning in vivo confocal microscopy and CIC immunofluorescence staining, we observed the activation of CALT in patients with MGD, and some CALT-related parameters correlated with the lid margin findings of patients with MGD.

Topographical Distribution and Phenotype of Resident Meibomian Gland Orifice Immune Cells (MOICs) in Mice and the Effects of Topical Benzalkonium Chloride (BAK)

Meibomian gland orifices (MGOs) are located along the eyelid margin and secrete meibum into the tear film. The profile of resident innate immune cells (ICs) at this site is not well understood. The distribution and phenotype of resident ICs around MGOs in mice was investigated and herein defined as MGO-associated immune cells (MOICs). The effect of topical 0.1% benzalkonium chloride (BAK) on MOICs was also assessed. Eyelids from healthy CD11ceYFP and Cx3cr1gfp/gfp mice aged three or seven months were compared. ICs were identified as CD11c+, Cx3cr1+, and MHC-II+ using four-colour immunostaining and confocal microscopy. MOIC density was variable but clustered around MGOs. There were more CD11c+ MOICs in three-month-old compared with seven-month-old mice (three-month-old: 893 ± 449 cells/mm2 vs. seven-month-old: 593 ± 493 cells/mm2, p = 0.004). Along the eyelid margin, there was a decreasing gradient of CD11c+ MOIC density in three-month-old mice (nasal: 1003 ± 369 cells/mm2, vs. central: 946 ± 574 cells/mm2, vs. temporal: 731 ± 353 cells/mm2, p = 0.044). Cx3cr1-deficient mice had two-fold fewer MHC-II+ MOICs, suggesting a role for Cx3cr1 receptor signaling in meibomian gland surveillance. CD11c+ MOIC density was lower in BAK-exposed eyes compared to saline-treated controls, suggesting a change in homeostasis. This study provides novel insight into resident ICs located at MGOs, and their contribution to MG homeostasis.

Automation of dry eye disease quantitative assessment: A review

Dry eye disease (DED) is a common eye condition worldwide and a primary reason for visits to the ophthalmologist. DED diagnosis is performed through a combination of tests, some of which are unfortunately invasive, non‐reproducible and lack accuracy. The following review describes methods that diagnose and measure the extent of eye dryness, enabling clinicians to quantify its severity. Our aim with this paper is to review classical methods as well as those that incorporate automation. For only four ways of quantifying DED, we take a deeper look into what main elements can benefit from automation and the different ways studies have incorporated it. Like numerous medical fields, Artificial Intelligence (AI) appears to be the path towards quality DED diagnosis. This review categorises diagnostic methods into the following: classical, semi‐automated and promising AI‐based automated methods.

Ocular Surface Inflammatory Disorders (OSID): A Collective of Systemic Etiologies Which Cause or Amplify Dry Eye Syndrome

The ocular surface inflammatory disorders (OSID) are caused by systemic disorders that conduct a persistent inflammatory reaction in the ocular adnexal connective tissues, such as the conjunctiva, lacrimal gland (LG) and meibomian glands (MGs), which cause an inflammatory dry eye. The etiologies of OSID are a subset of systemic pathologies such as graft versus host disease, Sjögren’s syndrome, allergies, cicatrizing conjunctivitis, and more. These cause a purely inflammatory dry eye syndrome as a consequence of the persistent surrounding inflammation in the adnexal tissues, which is distinct from the age-related dry eye disease. A limitation toward management of these conditions is the lack of available biomarkers that can detect presence of inflammation and quantify damage on the conjunctiva and LG, even though these are considered to be drivers of the inflammatory milieu. The OSID and dry eye syndrome are caused by different immune cells which are not exclusively limited to T cell lymphocytes, but rather derive from an orchestrated multicellular immunologic response. Recognition of this syndrome is crucial to direct research in a direction that clarifies the potential role of inflammation and its associated immune phenotype on the conjunctiva and adnexal ocular tissues in OSID and dry eye syndrome. On this paper, we review the basic and clinical research evidence for the existence of OSID with focus on the different immune cells involved, the target tissues and potential consequences and OSIDs diagnostic and therapeutic implications.

Candidate Molecular Compounds as Potential Indicators for Meibomian Gland Dysfunction

Meibomian gland dysfunction (MGD) is the leading cause of dry eye disease throughout the world. Studies have shown that several molecules in meibum, including but not limited to interleukins, amino acids, cadherins, eicosanoids, carbohydrates, and proteins, are altered in meibomian gland dysfunction compared with healthy normal controls. Some of these molecules such as antileukoproteinase, phospholipase A2, and lactoperoxidase also show differences in concentrations in tears between meibomian gland dysfunction and dry eye disease, further boosting hopes as candidate biomarkers. MGD is a complex condition, making it difficult to distinguish patients using single biomarkers. Therefore, multiple biomarkers forming a multiplex panel may be required. This review aims to describe molecules comprising lipids, proteins, and carbohydrates with the potential of serving various capacities as monitoring, predictive, diagnostic, and risk biomarkers for meibomian gland dysfunction.

In Vivo Confocal Microscopy in Different Types of Dry Eye and Meibomian Gland Dysfunction

In vivo confocal microscopy (IVCM) imaging is increasingly popular in ocular surface disease diagnosis and management. We conducted a systematic review to update the use of IVCM in the diagnosis and treatment of dry eye and meibomian gland dysfunction (MGD). A literature review was conducted on IVCM studies in MGD, dry eye disease, systemic disease causing dry eye, dry eye in glaucoma patients, contact lens-associated ocular conditions, graft-versus-host disease, and Sjogren’s syndrome-related dry eye. The articles were identified through PubMed and a total number of 63 eligible publications were analyzed in detail. All primary research studies on confocal microscopy on dry eye and related conditions from 2017 onwards were included. The reports were reviewed for their contribution to the existing literature as well as potential biases and drawbacks. Despite limitations such as small field of view, lack of population-based norms, and lack of standardization of image acquisition, interpretation, and quantification, IVCM is useful as a complementary technique for clinical diagnosis in various ocular surface disorders related to dry eye. With advances in hardware and software in the near future, it has the potential for further practical impact.

Recent Developments About the Pathogenesis of Dry Eye Disease: Based on Immune Inflammatory Mechanisms

Dry eye disease is a common and frequently occurring ophthalmology with complex and diverse causes, and its incidence is on the upward trend. The pathogenesis of DED is still completely clear. However, the immune response based on inflammation has been recognized as the core basis of this disease. In this review, we will systematically review the previous research on the treatment of DED in immune inflammation, analyze the latest views and research hotspots, and provide reference for the prevention and treatment of DED.

Alterations in corneal nerves in different subtypes of dry eye disease: An in vivo confocal microscopy study

PURPOSE

To evaluate corneal subbasal nerve alterations in evaporative and aqueous-deficient dry eye disease (DED) as compared to controls.

METHODS

In this retrospective, cross-sectional, controlled study, eyes with a tear break-up time of less than 10 s were classified as DED. Those with an anesthetized Schirmer's strip of less than 5 mm were classified as aqueous-deficient DED. Three representative in vivo confocal microscopy images were graded for each subject for total, main, and branch nerve density and numbers.

RESULTS

Compared to 42 healthy subjects (42 eyes), the 70 patients with DED (139 eyes) showed lower total (18,579.0 ± 687.7 μm/mm² vs. 21,014.7 ± 706.5, p = 0.026) and main (7,718.9 ± 273.9 vs. 9,561.4 ± 369.8, p < 0.001) nerve density, as well as lower total (15.5 ± 0.7/frame vs. 20.5 ± 1.3, p = 0.001), main (3.0 ± 0.1 vs. 3.8 ± 0.2, p = 0.001) and branch (12.5 ± 0.7 vs. 16.5 ± 1.2, p = 0.004) nerve numbers. Compared to the evaporative DED group, the aqueous-deficient DED group showed reduced total nerve density (19,969.9 ± 830.7 vs. 15,942.2 ± 1,135.7, p = 0.006), branch nerve density (11,964.9 ± 749.8 vs. 8,765.9 ± 798.5, p = 0.006), total nerves number (16.9 ± 0.8/frame vs. 13.0 ± 1.2, p = 0.002), and branch nerve number (13.8 ± 0.8 vs. 10.2 ± 1.1, p = 0.002).

CONCLUSIONS

Patients with DED demonstrate compromised corneal subbasal nerves, which is more pronounced in aqueous-deficient DED. This suggests a role for neurosensory abnormalities in the pathophysiology of DED.

Androgen and meibomian gland dysfunction: from basic molecular biology to clinical applications

Meibomian gland, the largest sebaceous gland of the body, is responsible for the biosynthesis of lipid layer of the tear film to prevent excessive evaporation. The loss of normal functions of meibomian gland, known as meibomian gland dysfunction (MGD), is a chronic disease and is the leading cause of dry eye symptoms in the clinics. Studies have found sex hormones, especially androgen, play vital roles in the regulation of the functions of meibomian gland. Recently, androgen has also been preliminarily applied in clinics for the treatment of MGD and showed promising results, especially in people with endogenous androgen deficiency. This review summarized the mechanisms of the function of androgen on meibomian gland based on molecular, animal, and clinical studies, and proposed evidence-based views about its potential applications for the treatment of MGD.

A Review of Imaging Biomarkers of the Ocular Surface

A biomarker is a "characteristic that is measured as an indicator of normal biological processes, pathogenic processes, or responses to an exposure or intervention, including therapeutic interventions." Recently, calls for biomarkers for ocular surface diseases have increased, and advancements in imaging technologies have aided in allowing imaging biomarkers to serve as a potential solution for this need. This review focuses on the state of imaging biomarkers for ocular surface diseases, specifically non-invasive tear break-up time (NIBUT), tear meniscus measurement and corneal epithelial thickness with anterior segment optical coherence tomography (OCT), meibomian gland morphology with infrared meibography and in vivo confocal microscopy (IVCM), ocular redness with grading scales, and cellular corneal immune cells and nerve assessment by IVCM. Extensive literature review was performed for analytical and clinical validation that currently exists for potential imaging biomarkers. Our summary suggests that the reported analytical and clinical validation state for potential imaging biomarkers is broad, with some having good to excellent intra- and intergrader agreement to date. Examples of these include NIBUT for dry eye disease, ocular redness grading scales, and detection of corneal immune cells by IVCM for grading and monitoring inflammation. Further examples are nerve assessment by IVCM for monitoring severity of diabetes mellitus and neurotrophic keratitis, and corneal epithelial thickness assessment with anterior segment OCT for the diagnosis of early keratoconus. However, additional analytical validation for these biomarkers is required before clinical application as a biomarker.

Latest evidences on meibomian gland dysfunction diagnosis and management

Meibomian gland dysfunction (MGD) can be considered the leading cause of dry eye disease (DED) and one of the most common ophthalmic disorders found in clinical practice. The growing body of literature provides a substantial amount of information on this condition, but more efforts are needed to better interpret research data and to properly apply them to daily clinical practice., In this article, we reviewed the most recent publications on MGD diagnosis and management, focusing on the highest available level of evidence, provided by well-designed and well-reported studies on humans., Latest evidences on MGD diagnosis are mainly focused on imaging techniques, including meibography, optical coherence tomography (OCT), and in vivo confocal microscopy. Meibographic parameters, such as drop-out and glands' distortion, show great diagnostic accuracy, which accounts for their widespread use in clinical practice and research., Recent randomized controlled clinical trials on MGD treatment provided data on the role of antibiotics, steroids, essential fatty acids, intraductal meibomian gland probing, electronic heating devices and intense pulsed light therapy.

Organotypic Culture of Mouse Meibomian Gland: A Novel Model to Study Meibomian Gland Dysfunction In Vitro

Purpose

Meibomian glands are essential in maintaining the integrity and health of the ocular surface. Meibomian gland dysfunction (MGD), mainly induced by ductal occlusion, is considered as the major cause of dry eye disease. In this study, a novel in vitro model was established for investigating the role of inflammation in the process of MGD.

Methods

Mouse tarsal plates were removed from eyelids after dissection and explants were cultured during various time ranging from 24 to 120 hours. Meibomian gland epithelial cells were further enzymatically digested and dissociated from tarsal plates before culturing. Both explants and cells were incubated in different media with or without serum or azithromycin (AZM). Furthermore, explants were treated with IL-1β or vehicle for 48 hours. Analyses for tissue viability, histology, biomarker expression, and lipid accumulation were performed with hematoxylin and eosin (H&E) staining, immunofluorescence staining, and Western blot.

Results

Higher viability was preserved when explants were cultured on Matrigel with immediate addition of culture medium. The viability, morphology, biomarker expression, and function of meibomian glands were preserved in explants cultured for up to 72 hours. Lipid accumulation and peroxisome proliferator-activated receptor γ (PPARγ) expression increased in both explants and cells cultured in media containing serum or AZM. Treatment with IL-1β induced overexpression of Keratin (Krt) 1 in meibomian gland ducts.

Conclusions

Intervention with pro-inflammatory cytokine IL-1β induces hyperkeratinization in meibomian gland ducts in vitro. This novel organotypic culture model can be used for investigating the mechanism of MGD.

Dihydrotestosterone suppression of proinflammatory gene expression in human meibomian gland epithelial cells

PURPOSE

We discovered that dihydrotestosterone (DHT) decreases the ability of lipopolysaccharide, a bacterial toxin, to stimulate the secretion of leukotriene B4, a potent proinflammatory mediator, by immortalized human meibomian gland epithelial cells (IHMGECs). We hypothesize that this hormone action reflects an androgen suppression of proinflammatory gene activity in these cells. Our goal was to test this hypothesis. For comparison, we also examined whether DHT treatment elicits the same effect in immortalized human corneal (IHC) and conjunctival (IHConj) ECs.

METHODS

Differentiated cells were cultured in media containing vehicle or 10 nM DHT. Cells (n = 3 wells/treatment group) were then processed for RNA isolation and the analysis of gene expression by using Illumina BeadChips, background subtraction, cubic spline normalization and Geospiza software.

RESULTS

Our results demonstrate that DHT significantly suppressed the expression of numerous immune-related genes in HMGECs, such as those associated with antigen processing and presentation, innate and adaptive immune responses, chemotaxis, and cytokine production. DHT also enhanced the expression of genes for defensin β1, IL-1 receptor antagonist, and the anti-inflammatory serine peptidase inhibitor, Kazal type 5. In contrast, DHT had no effect on proinflammatory gene expression in HCECs, and significantly increased 33 gene ontologies linked to the immune system in HConjECs.

CONCLUSIONS

Our findings support our hypothesis that androgens suppress proinflammatory gene expression in IHMGECs. This hormone effect may contribute to the typical absence of inflammation within the human meibomian gland.

Update on the role of impression cytology in ocular surface disease

Understanding of the molecular pathology of ocular surface disease (OSD) is poor, and treatment is highly unsatisfactory. To facilitate treatment of OSD, a relatively noninvasive procedure, i.e. impression cytology (IC) has been shown to be useful. Recently, the technologies employed in research studies using IC in OSD have vastly improved, and standardized IC has even been used in clinical trials of dry eye. Here, this review aims to describe the advances of IC in the last 10 years, which serves as an update on the progress in this field since the last major review of IC. OSD that has been recently evaluated include meibomian gland dysfunction, Sjogren's syndrome, Steven–Johnson syndrome, and postmenopausal dry eye. The recent studies (4 longitudinal, 18 cross-sectional analyses) which utilized IC analyzed DNA, RNA, proteins, and ocular surface cells, including memory T-lymphocytes, dendritic cells (DCs), neutrophils, conjunctival epithelial cells, and goblet cells. These studies employed quantification of transcripts associated with inflammation, proteins involved in oxidative stress, enzymes such as matrix metalloproteinases, and cell surface proteins by flow cytometry, such as HLA-DR, cytokine and chemokine receptors, markers for T cell differentiation, and DC activation, in addition to the more traditional morphological evaluation of squamous metaplasia and staining for goblet cells. Some challenges in the clinical use of IC have also been described, including issues related to storage and normalization of data. In summary, advances in IC have permitted a more robust evaluation of the ocular surface and will facilitate progress in the understanding and treatment of OSD.