A systematic review on the impact of diabetes mellitus on the ocular surface. Nutr Diabetes. 2017;7:e251. [PMID: 28319106 PMCID: PMC5380897 DOI: 10.1038/nutd.2017.4]

Tear Fluid Progranulin as a Noninvasive Biomarker for the Monitoring of Corneal Innervation Changes in Patients With Type 2 Diabetes Mellitus

Purpose

This study aimed to investigate the expression levels of progranulin (PGRN) in the tears of patients with diabetic retinopathy (DR) versus healthy controls. Additionally, we sought to explore the correlation between PGRN levels and the severity of ocular surface complications in patients with diabetes.

Methods

In this prospective, single-visit, cross-sectional study, patients with DR (n = 48) and age-matched healthy controls (n = 22) were included and underwent dry eye examinations. Tear fluid was collected, and its components were analyzed using the Luminex assay. The subbasal nerve plexus of all participants was evaluated by in vivo confocal microscopy.

Results

Patients with DR exhibited more severe dry eye symptoms, along with a reduction in nerve fiber density, length, and branch density within the subbasal nerve plexus, accompanied by an increase in the number of dendritic cells. Tear PGRN levels were also significantly lower in patients with diabetes than in normal controls, and the levels of some inflammatory factors (TNF-α, IL-6, and MMP-9) were higher in patients with DR. Remarkably, the PGRN level significantly correlated with nerve fiber density (R = 0.48, P < 0.001), nerve fiber length (R = 0.65, P < 0.001), and nerve branch density (R = 0.69, P < 0.001).

Conclusions

Tear PGRN levels might reflect morphological changes in the corneal nerve plexus under diabetic conditions, suggesting that PGRN itself is a reliable indicator for predicting the advancement of neurotrophic keratopathy in patients with diabetes.

Translational Relevance

PGRN insufficiency on the ocular surface under diabetic conditions was found to be closely associated with nerve impairment, providing a novel perspective to discover the pathogenesis of diabetic complications, which could help in developing innovative therapeutic strategies.

Immune-Mediated Ocular Surface Disease in Diabetes Mellitus-Clinical Perspectives and Treatment: A Narrative Review

Diabetes mellitus (DM) is a chronic metabolic disorder marked by hyperglycemia due to defects in insulin secretion, action, or both, with a global prevalence that has tripled in recent decades. This condition poses significant public health challenges, affecting individuals, healthcare systems, and economies worldwide. Among its numerous complications, ocular surface disease (OSD) is a significant concern, yet understanding its pathophysiology, diagnosis, and management remains challenging. This review aims to explore the epidemiology, pathophysiology, clinical manifestations, diagnostic approaches, and management strategies of diabetes-related OSD. The ocular surface, including the cornea, conjunctiva, and associated structures, is vital for maintaining eye health, with the lacrimal functional unit (LFU) playing a crucial role in tear film regulation. In DM, changes in glycosaminoglycan metabolism, collagen synthesis, oxygen consumption, and LFU dysfunction contribute to ocular complications. Persistent hyperglycemia leads to the expression of cytokines, chemokines, and cell adhesion molecules, resulting in neuropathy, tear film abnormalities, and epithelial lesions. Recent advances in molecular research and therapeutic modalities, such as gene and stem cell therapies, show promise for managing diabetic ocular complications. Future research should focus on pathogenetically oriented therapies for diabetic neuropathy and keratopathy, transitioning from animal models to clinical trials to improve patient outcomes.

Association Between Corneal Changes and Retinal Oximetry in Diabetes Mellitus

Purpose

Diabetes mellitus (DM) causes different corneal changes that are associated with the severity of diabetic retinopathy. To identify the pathophysiological reasons for this, corneal tomography and optical densitometry (COD) were combined with retinal oximetry.

Methods

Patients with DM and healthy subjects were included in this pilot study. Spatially resolved corneal thickness and COD were assessed using the Pentacam HR (Oculus). The pachymetry difference (PACDiff) was calculated as an indicator of an increase in the peripheral corneal thickness. Oxygen saturation (SO2) of the retinal vessels was measured using the Retinal Vessel Analyzer (Imedos Systems UG). Subsequently, the associations between corneal and retinal parameters were analyzed.

Results

Data from 30 patients with DM were compared with those from 30 age-matched healthy subjects. In DM, arterial (P = 0.048) and venous (P < 0.001) SO2 levels were increased, and arteriovenous SO2 difference was decreased (P < 0.001). In patients, PACDiff was higher than that in healthy subjects (P < 0.05), indicating a stronger increase in peripheral corneal thickness. The COD was reduced in DM (P = 0.004). The PACDiff of concentric rings with a diameter of 4 mm (r = -0.404; P = 0.033) to 8 mm (r = -0.522; P = 0.004) was inversely correlated with the arteriovenous SO2 difference. Furthermore, PACDiff 4 mm was negatively associated with arterial SO2 (r = -0.389; P = 0.041), and the COD of the peripheral corneal areas correlated positive with arterial SO2 (COD total 10-12 mm: r = 0.408; P = 0.025).

Conclusion

These associations might indicate a common pathogenesis of corneal and retinal changes in DM, which could be caused by reduced oxygen supply, mitochondrial dysfunction, oxidative stress, and cytokine effects.

Recent United States Developments in the Pharmacological Treatment of Dry Eye Disease

Dry eye disease (DED) can arise from a variety of factors, including inflammation, meibomian gland dysfunction (MGD), and neurosensory abnormalities. Individuals with DED may exhibit a range of clinical signs, including tear instability, reduced tear production, and epithelial disruption, that are driven by different pathophysiological contributors. Those affected often report a spectrum of pain and visual symptoms that can impact physical and mental aspects of health, placing an overall burden on an individual's well-being. This cumulative impact of DED on an individual's activities and on society underscores the importance of finding diverse and effective management strategies. Such management strategies necessitate an understanding of the underlying pathophysiological mechanisms that contribute to DED in the individual patient. Presently, the majority of approved therapies for DED address T cell-mediated inflammation, with their tolerability and effectiveness varying across different studies. However, there is an emergence of treatments that target additional aspects of the disease, including novel inflammatory pathways, abnormalities of the eyelid margin, and neuronal function. These developments may allow for a more nuanced and precise management strategy for DED. This review highlights the recent pharmacological advancements in DED therapy in the United States. It discusses the mechanisms of action of these new treatments, presents key findings from clinical trials, discusses their current stage of development, and explores their potential applicability to different sub-types of DED. By providing a comprehensive overview of products in development, this review aims to contribute valuable insights to the ongoing efforts in enhancing the therapeutic options available to individuals suffering from DED.

Analyzing the changing trend of corneal biomechanical properties under different influencing factors in T2DM patients

To analyze the changing trend of CH and CRF values under different influencing factors in T2DM patients. A total of 650 patients with T2DM were included. We discovered that the course of T2DM, smoking history, BMI, and FBG, DR, HbA1c, TC, TG, and LDL-C levels were common risk factors for T2DM, while HDL-C levels were a protective factor. Analyzing the CH and CRF values according to the course of diabetes, we discovered that as T2DM continued to persist, the values of CH and CRF gradually decreased. Moreover, with the increase in FBG levels and the accumulation of HbA1c, the values of CH and CRF gradually decreased. In addition, in patients with HbA1c (%) > 12, the values of CH and CRF decreased the most, falling by 1.85 ± 0.33 mmHg and 1.28 ± 0.69 mmHg, respectively. Compared with the non-DR group, the CH and CRF values gradually decreased in the mild-NPDR, moderate-NPDR, severe-NPDR and PDR groups, with the lowest CH and CRF values in the PDR group. In patients with T2DM, early measurement of corneal biomechanical properties to evaluate the change trend of CH and CRF values in different situations will help to identify and prevent diabetic keratopathy in a timely manner.

Corneal parameters in diabetics versus non-diabetics and correlation with various blood sugar parameters

Aim: To compare corneal parameters in diabetics versus age-group-matched non-diabetics; also, to correlate these parameters with the duration of diabetes, glycated haemoglobin (HbA1c) levels, and severity levels of diabetic retinopathy (DR). Materials and methods: A comparative study was conducted at a tertiary eye-care center from January 2020 to December 2020. Two-hundred patients (400 eyes) with type-2 diabetes (100) and age-sex-matched non-diabetics (100) were included. Corneal morphological parameters like central corneal thickness (CCT), endothelial cell density (ECD), coefficient of variance (CoV), hexagonality (6A), and average cell area were recorded by specular microscopy. These parameters were correlated with the duration of diabetes, severity of disease based upon fasting blood glucose levels, HbA1c, and grade of DR. Mean and standard deviation were calculated, and regular distribution of continuous data was tested using independent sample t-test and ANOVA. Results: Mean ECD (2447.32 ± 269.89/mm2), 6A (45.03 ± 6.71%), and IOP (15.47 ± 2.02 mmHg) changed in diabetic cases and were significantly low in diabetics, whereas, mean average cell area (413 ± 50.19 mm2), standard deviation (167.05 ± 77.91), CCT (525.81 ± 36.69) and CoV (39.84 ± 15.59%), were significantly high in diabetics. Mean CCT had insignificant variation. Subgroup analysis within diabetics showed a statistically significant reduction of ECD, cell count, and 6A with increased duration of diabetes, poor glycaemic control, and raised HbA1c. Discussion: The corneal endothelial analysis is vital in daily clinical practice and provides valuable evidence concerning the viability of corneal endothelium in various intraocular surgeries. Uncontrolled DM harms the cornea with 70% of diabetics resulting in complications like keratopathy. The study highlighted that the increased duration of diabetes raised HbA1c, and poor glycemic control negatively affected corneal morphology. Our study showed a definite reduction in ECD and 6A in diabetics compared to non-diabetics. Conclusion: A definite reduction in the corneal endothelial counts, cell density, and hexagonality was found in type-2 diabetics compared to non-diabetics. Abbreviations: DM = Diabetes Mellitus, CCT = central corneal thickness, ECC = endothelial cell counts, ECD = endothelial cell density, CoV = coefficient of variance, 6A = hexagonality, DR = Diabetic retinopathy, SD = Standard of deviation, IOP = Intraocular pressure.

Effects of Diabetes Mellitus on Corneal Immune Cell Activation and the Development of Keratopathy

Diabetes mellitus (DM) is one of the most prevalent diseases globally, and its prevalence is rapidly increasing. Most patients with a long-term history of DM present with some degree of keratopathy (DK). Despite its high incidence, the underlying inflammatory mechanism of DK has not been elucidated yet. For further insights into the underlying immunopathologic processes, we utilized streptozotocin-induced mice to model type 1 DM (T1D) and B6.Cg-Lepob/J mice to model type 2 DM (T2D). We evaluated the animals for the development of clinical manifestations of DK. Four weeks post-induction, the total frequencies of corneal CD45+CD11b+Ly-6G- myeloid cells, with enhanced gene and protein expression levels for the proinflammatory cytokines TNF-α and IL-1β, were higher in both T1D and T2D animals. Additionally, the frequencies of myeloid cells/mm2 in the sub-basal neural plexus (SBNP) were significantly higher in T1D and T2D compared to non-diabetic mice. DK clinical manifestations were observed four weeks post-induction, including significantly lower tear production, corneal sensitivity, and epitheliopathy. Nerve density in the SBNP and intraepithelial terminal endings per 40x field were lower in both models compared to the normal controls. The findings of this study indicate that DM alters the immune quiescent state of the cornea during disease onset, which may be associated with the progressive development of the clinical manifestations of DK.

High-throughput sequencing reveals differences in microbial community structure and diversity in the conjunctival tissue of healthy and type 2 diabetic mice

BACKGROUND

To investigate the differences in bacterial and fungal community structure and diversity in conjunctival tissue of healthy and diabetic mice.

METHODS

RNA-seq assays and high-throughput sequencing of bacterial 16 S rDNA and fungal internal transcribed spacer (ITS) gene sequences were used to identify differentially expressed host genes and fungal composition profiles in conjunctival tissues of diabetic BKS-db/db mice and BKS (control) mice. Functional enrichment analysis of differentially expressed genes and the correlation between the relative abundance of bacterial and fungal taxa in the intestinal mucosa were also performed.

RESULTS

Totally, 449 differential up-regulated genes and 1,006 down-regulated genes were identified in the conjunctival tissues of diabetic mice. The differentially expressed genes were mainly enriched in metabolism-related functions and pathways. A decrease in conjunctival bacterial species diversity and abundance in diabetic mice compared to control mice. In contrast, fungal species richness and diversity were not affected by diabetes. The microbial colonies were mainly associated with cellular process pathways regulating carbohydrate and lipid metabolism, as well as cell growth and death. Additionally, some interactions between bacteria and fungi at different taxonomic levels were also observed.

CONCLUSION

The present study revealed significant differences in the abundance and composition of bacterial and fungal communities in the conjunctival tissue of diabetic mice compared to control mice. The study also highlighted interactions between bacteria and fungi at different taxonomic levels. These findings may have implications for the diagnosis and treatment of diabetes.

Effects of hypoxia in the diabetic corneal stroma microenvironment

Corneal dysfunctions associated with Diabetes Mellitus (DM), termed diabetic keratopathy (DK), can cause impaired vision and/or blindness. Hypoxia affects both Type 1 (T1DM) and Type 2 (T2DM) surprisingly, the role of hypoxia in DK is unexplored. The aim of this study was to examine the impact of hypoxia in vitro on primary human corneal stromal cells derived from Healthy (HCFs), and diabetic (T1DMs and T2DMs) subjects, by exposing them to normoxic (21% O2) or hypoxic (2% O2) conditions through 2D and 3D in vitro models. Our data revealed that hypoxia affected T2DMs by slowing their wound healing capacity, leading to significant alterations in oxidative stress-related markers, mitochondrial health, cellular homeostasis, and endoplasmic reticulum health (ER) along with fibrotic development. In T1DMs, hypoxia significantly modulated markers related to membrane permeabilization, oxidative stress via apoptotic marker (BAX), and protein degradation. Hypoxic environment induced oxidative stress (NOQ1 mediated reduction of superoxide in T1DMs and Nrf2 mediated oxidative stress in T2DMs), modulation in mitochondrial health (Heat shock protein 27 (HSP27), and dysregulation of cellular homeostasis (HSP90) in both T1DMs and T2DMs. This data underscores the significant impact of hypoxia on the diabetic cornea. Further studies are warranted to delineate the complex interactions.

Rat Model of Type 2 Diabetes Mellitus Recapitulates Human Disease in the Anterior Segment of the Eye

Changes in the anterior segment of the eye due to type 2 diabetes mellitus (T2DM) are not well-characterized, in part due to the lack of a reliable animal model. This study evaluates changes in the anterior segment, including crystalline lens health, corneal endothelial cell density, aqueous humor metabolites, and ciliary body vasculature, in a rat model of T2DM compared with human eyes. Male Sprague-Dawley rats were fed a high-fat diet (45% fat) or normal diet, and rats fed the high-fat diet were injected with streptozotocin i.p. to generate a model of T2DM. Cataract formation and corneal endothelial cell density were assessed using microscopic analysis. Diabetes-related rat aqueous humor alterations were assessed using metabolomics screening. Transmission electron microscopy was used to assess qualitative ultrastructural changes ciliary process microvessels at the site of aqueous formation in the eyes of diabetic rats and humans. Eyes from the diabetic rats demonstrated cataracts, lower corneal endothelial cell densities, altered aqueous metabolites, and ciliary body ultrastructural changes, including vascular endothelial cell activation, pericyte degeneration, perivascular edema, and basement membrane reduplication. These findings recapitulated diabetic changes in human eyes. These results support the use of this model for studying ocular manifestations of T2DM and support a hypothesis postulating blood-aqueous barrier breakdown and vascular leakage at the ciliary body as a mechanism for diabetic anterior segment pathology.

Evaluation of the effect of intravitreal injections on corneal epithelial, scleral and limbal region changes in diabetic retinopathy by AS-OCT

PURPOSE

The aim of the study is to evaluate the effects of diabetic retinopathy and intravitreal injections on the corneal, limbal and scleral areas.

METHODS

Patients with diabetes mellitus at different diagnosis and treatment levels were compared among themselves and with the control group in terms of corneal, limbal and scleral aspects with the help of anterior segment optical coherence tomography. In addition, clinical tests such as tear break-up time, Schirmer test-I and ocular surface disease index questionnaire were applied to the patients and the difference between the groups was investigated.

RESULTS

When the groups were examined in terms of BUT, SCH-I and OSDI, there was a statistically significant difference between control group and diabetic group(p < 0.05). In the limbal region, all measurements are higher than in patients with diabetic eye involvement. Thinning was detected in the scleral area with intravitreal injection (p < 0.05).

CONCLUSION

It should be known that DM may cause undesirable changes in the limbal region, and the importance of non-invasive detection with AS-OCT should not be forgotten. Since intravitreal injections for DME cause thinning of the sclera, it can cause various complications, and it may be recommended to change the quadrant in repetitive injection applications.

Evaluation of Limbal Stem Cells in Patients With Type 2 Diabetes: An In Vivo Confocal Microscopy Study

PURPOSE

This study aimed to investigate corneal limbus changes in patients with type 2 diabetes mellitus (DM) using in vivo confocal microscopy (IVCM) and explore the correlation between their ocular manifestations and systemic status.

METHODS

Fifty-five patients with type 2 DM and 20 age-matched controls were included. The following IVCM parameters were compared between the 2 groups: palisades of Vogt (POV), corneal epithelial thickness (CET), basal cell density (BCD), subbasal nerve plexus, and dendritic cell density. All subjects underwent blood and urine sampling for laboratory analysis, including fasting blood glucose, glycated hemoglobin, total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, C-reactive protein, urinary albumin-to-creatinine ratio, urine albumin, and urine creatinine. The correlations between IVCM parameters and blood biomarkers were detected. Receiver operating characteristic curve was used for selecting the cutoff value of risk factors for corneal stem cell injury in patients with DM.

RESULTS

Compared with controls, patients with DM displayed a significant reduction of POV (superior region, P = 0.033; inferior region, P = 0.003; nasal region, P < 0.001; temporal region, P < 0.001), central CET (44.8 ± 3.6 μm vs. 51.9 ± 3.6 μm, P < 0.001), central corneal BCD (7415.5 ± 563.2 cells/mm 2 vs. 9177.9 ± 977.8 cells/mm 2 , P < 0.001), and peripheral corneal BCD (6181.3 ± 416.5 cells/mm 2 vs. 8576.3 ± 933.2 cells/mm 2 , P < 0.001). Dendritic cell density (41.0 ± 33.7 cells/mm 2 vs. 24.6 ± 7.8 cells/mm 2 , P = 0.001) was significantly higher in the DM group. The following weak correlations were shown between IVCM parameters and blood biomarkers: central corneal BCD was negatively correlated with DM duration (r = -0.3, P = 0.024), TC (r = -0.36, P = 0.007), and LDL (r = -0.39, P = 0.004). The presence of POV in the superior region was negatively correlated with TC (r = -0.34, P = 0.011) and LDL (r = -0.31, P = 0.022). Cutoff values of 1.215 mmol/L for HDL, 1.59 mmol/L for TG, or 4.75 mmol/L for TC were established to distinguish patients with a high risk from a low risk for stem cell damage.

CONCLUSIONS

Patients with type 2 DM displayed a lower positive rate of typical POV and a decrease in BCD, CET, and subbasal nerve density. The most relevant indicators for stem cell phenotypes were DM duration, TC, and LDL. Lipid status in diabetic patients could be a predictor of risk for developing corneal limbal stem cell deficiency. Further studies with larger sample sizes or basic research are needed to verify the results.

Increased expression of neutrophil CD15 correlates with the severity of anterior ocular surface damage in type II diabetes mellitus

BACKGROUND

Diabetes mellitus is associated with increased risk of ocular surface diseases in elderly. We consider neutrophil CD15 as a potential marker of ocular surface damage in type II diabetes mellitus patients.

AIM

We aimed to evaluate expression of neutrophil CD15 and correlate it with results of conjunctival impression cytology and routine objective anterior ocular surface tests (TMH, NIBUT, LLT, MGD) in T2DM patients.

MATERIALS AND METHODS

We prospectively enrolled sixty type II diabetes mellitus patients (120 eyes) into a study group. The control group included forty (80 eyes) age- and sex-matched healthy individuals. All patients underwent comprehensive ophthalmological examination, and tear meniscus height test (TMH), noninvasive tear break-up time (NIBUT), lipid layer thickness measurement (LLT), Meibomian gland dysfunction evaluation (MGD), conjunctival impression cytology (CIC) and expression of CD15.

RESULTS

Abnormal Nelson's grades of squamous metaplasia (grades 2 and 3) were observed in 50% (60 eyes) of the study group, and 13.8 (11 eyes) of the control group. Fifteen patients with type II diabetes mellitus suffered from grade 3 squamous metaplasia. Nelson's grades of squamous metaplasia have shown a positive correlation with the level of CD15 expression either in the study and control groups (rs = 0.628, p = <0.0001; rs = 0.746, p < 0.0001; respectively).

CONCLUSIONS

The research shows significantly reduced values of routine objective ocular tests in type II diabetes mellitus patients in comparison to healthy participants older than 60 y.o. Increased CD15 in the peripheral blood is associated with the development of squamous metaplasia and may be used to evaluate the severity of ocular surface damage in type II diabetes mellitus patients.

(Pre)diabetes and a higher level of glycaemic measures are continuously associated with corneal neurodegeneration assessed by corneal confocal microscopy: the Maastricht Study

AIMS/HYPOTHESIS

To assess the associations between glucose metabolism status and a range of continuous measures of glycaemia with corneal nerve fibre measures, as assessed using corneal confocal microscopy.

METHODS

We used population-based observational cross-sectional data from the Maastricht Study of N=3471 participants (mean age 59.4 years, 48.4% men, 14.7% with prediabetes, 21.0% with type 2 diabetes) to study the associations, after adjustment for demographic, cardiovascular risk and lifestyle factors, between glucose metabolism status (prediabetes and type 2 diabetes vs normal glucose metabolism) plus measures of glycaemia (fasting plasma glucose, 2 h post-load glucose, HbA1c, skin autofluorescence [SAF] and duration of diabetes) and composite Z-scores of corneal nerve fibre measures or individual corneal nerve fibre measures (corneal nerve bifurcation density, corneal nerve density, corneal nerve length and fractal dimension). We used linear regression analysis, and, for glucose metabolism status, performed a linear trend analysis.

RESULTS

After full adjustment, a more adverse glucose metabolism status was associated with a lower composite Z-score for corneal nerve fibre measures (β coefficients [95% CI], prediabetes vs normal glucose metabolism -0.08 [-0.17, 0.03], type 2 diabetes vs normal glucose metabolism -0.14 [-0.25, -0.04]; linear trend analysis showed a p value of 0.001), and higher levels of measures of glycaemia (fasting plasma glucose, 2 h post-load glucose, HbA1c, SAF and duration of diabetes) were all significantly associated with a lower composite Z-score for corneal nerve fibre measures (per SD: -0.09 [-0.13, -0.05], -0.07 [-0.11, -0.03], -0.08 [-0.11, -0.04], -0.05 [-0.08, -0.01], -0.09 [-0.17, -0.001], respectively). In general, directionally similar associations were observed for individual corneal nerve fibre measures.

CONCLUSIONS/INTERPRETATION

To our knowledge, this is the first population-based study to show that a more adverse glucose metabolism status and higher levels of glycaemic measures were all linearly associated with corneal neurodegeneration after adjustment for an extensive set of potential confounders. Our results indicate that glycaemia-associated corneal neurodegeneration is a continuous process that starts before the onset of type 2 diabetes. Further research is needed to investigate whether early reduction of hyperglycaemia can prevent corneal neurodegeneration.

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.

Diabetes-Associated Hyperglycemia Causes Rapid-Onset Ocular Surface Damage

Purpose

The metabolic alterations due to chronic hyperglycemia are well-known to cause diabetes-associated complications. Short-term hyperglycemia has also been shown to cause many acute changes, including hemodynamic alterations and osmotic, oxidative, and inflammatory stress. The present study was designed to investigate whether diabetes-associated hyperglycemia can cause rapid-onset detrimental effects on the tear film, goblet cells, and glycocalyx and can lead to activation of an inflammatory cascade or cellular stress response in the cornea.

Methods

Mouse models of type 1 and type 2 diabetes were used. Tear film volume, goblet cell number, and corneal glycocalyx area were measured on days 7, 14, and 28 after the onset of hyperglycemia. Transcriptome analysis was performed to quantify changes in 248 transcripts of genes involved in inflammatory, apoptotic, and stress response pathways.

Results

Our data demonstrate that type 1 and type 2 diabetes-associated hyperglycemia caused a significant decrease in the tear film volume, goblet cell number, and corneal glycocalyx area. The decrease in tear film and goblet cell number was noted as early as 7 days after onset of hyperglycemia. The severity of ocular surface injury was significantly more in type 1 compared to type 2 diabetes. Diabetes mellitus also caused an increase in transcripts of genes involved in the inflammatory, apoptotic, and cellular stress response pathways.

Conclusions

The results of the present study demonstrate that diabetes-associated hyperglycemia causes rapid-onset damage to the ocular surface. Thus, short-term hyperglycemia in patients with diabetes mellitus may also play an important role in causing ocular surface injury and dry eye.

Evaluation of corneal backward light scattering in type 2 diabetes mellitus

AIM

To compare the corneal backward light scattering values in type 2 diabetes mellitus (DM) patients with those of age and sex-matched healthy controls.

METHODS

The study included 30 patients (30 eyes) with type 2 DM and 30 control subjects (30 eyes). Duration of diabetes, most recent hemoglobin A1c levels, along with the status of diabetic retinopathy, and existing medical treatment of all subjects were recorded. All subjects underwent a complete ophthalmologic examination. In addition, backward light scattering (densitometry) was measured to assess changes in corneal transparency using tomography (Pentacam HR).

RESULTS

The type 2 DM patients included 12 males and 18 females and control subjects included 16 males and 14 females. The age was 50.40±7.80y (range: 40-68y) of the diabetic group and 49.30±9.50y (rang: 40-73y) of control group. The diabetic group demonstrated significantly higher mean densitometry values of the anterior (6-10 mm) zone (P=0.047), the total anterior layer (P=0.036) and the total cornea (P=0.043) than control group. The corneal densitometry of the diabetic eyes demonstrated no significant correlation with hemoglobin A1c levels and DM duration.

CONCLUSION

Diabetic group has higher densitometry in anterior corneal (6-10 mm) zone, total anterior cornea, and total cornea and with no correlation with hemoglobin A1c levels and DM duration.

Limbal Epithelial Stem Cells in the Diabetic Cornea

Continuous replenishment of the corneal epithelium is pivotal for maintaining optical transparency and achieving optimal visual perception. This dynamic process is driven by limbal epithelial stem cells (LESCs) located at the junction between the cornea and conjunctiva, which is otherwise known as the limbus. In patients afflicted with diabetes, hyperglycemia-induced impairments in corneal epithelial regeneration results in persistent epithelial and other defects on the ocular surface, termed diabetic keratopathy (DK), which progressively diminish vision and quality of life. Reports of delayed corneal wound healing and the reduced expression of putative stem cell markers in diabetic relative to healthy eyes suggest that the pathogenesis of DK may be associated with the abnormal activity of LESCs. However, the precise role of these cells in diabetic corneal disease is poorly understood and yet to be comprehensively explored. Herein, we review existing literature highlighting aberrant LESC activity in diabetes, focusing on factors that influence their form and function, and emerging therapies to correct these defects. The consequences of malfunctioning or depleted LESC stocks in DK and limbal stem cell deficiency (LSCD) are also discussed. These insights could be exploited to identify novel targets for improving the management of ocular surface complications that manifest in patients with diabetes.

Metagenomic analysis of microbiological changes on the ocular surface of diabetic children and adolescents with a dry eye

BACKGROUND

Microbiome changes on the ocular surface may cause dry eyes. A metagenome assay was used to compare the microbiome composition and function of the ocular surface between diabetic children and adolescents with dry eye, diabetic children and adolescents without dry eye, and normal children.

MATERIALS AND METHODS

Twenty children and adolescents aged 8 to 16 with diabetes were selected from the Shanghai Children and Adolescent Diabetes Eye Study. Ten healthy children and adolescents belonging to the same age group were selected from the outpatient clinic during the same period. The participants were classified into the dry eye group (DM-DE group, n = 10), the non-dry eye group (DM-NDE group, n = 10) and the normal group (NDM group, n = 10). A conjunctival sac swab was collected for metagenomic sequencing, and the relationship between the microbiome composition and functional gene differences on the ocular surface with dry eye was studied.

RESULTS

The classification composition and metabolic function of the microorganisms on the ocular surface of children in the 3 groups were analyzed. It was found that children's ocular microbiota was composed of bacteria, viruses and fungi. There were significant differences in α diversity and β diversity of microbial composition of ocular surface between DM-DE group and NDM group(P<0.05). There were significant differences in α and β diversity of metabolic pathways between the two groups(P<0.05). The functional pathways of ocular surface microorganisms in diabetic children with dry eyes were mainly derived from human disease, antibiotic resistance genes, carbohydrate, coenzyme and lipid transport and metabolism-related functional genes; In normal children, the functional pathways were mainly derived from replication, recombination, repair, signal transduction and defense-related functional genes.

CONCLUSION

The DM-DE group have unique microbial composition and functional metabolic pathways. The dominant species and unique metabolic pathways of the ocular surface in the DM-DE group may be involved in the pathogenesis of dry eye in diabetic children.

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.

TFOS Lifestyle: Impact of nutrition on the ocular surface

Nutrients, required by human bodies to perform life-sustaining functions, are obtained from the diet. They are broadly classified into macronutrients (carbohydrates, lipids, and proteins), micronutrients (vitamins and minerals) and water. All nutrients serve as a source of energy, provide structural support to the body and/or regulate the chemical processes of the body. Food and drinks also consist of non-nutrients that may be beneficial (e.g., antioxidants) or harmful (e.g., dyes or preservatives added to processed foods) to the body and the ocular surface. There is also a complex interplay between systemic disorders and an individual's nutritional status. Changes in the gut microbiome may lead to alterations at the ocular surface. Poor nutrition may exacerbate select systemic conditions. Similarly, certain systemic conditions may affect the uptake, processing and distribution of nutrients by the body. These disorders may lead to deficiencies in micro- and macro-nutrients that are important in maintaining ocular surface health. Medications used to treat these conditions may also cause ocular surface changes. The prevalence of nutrition-related chronic diseases is climbing worldwide. This report sought to review the evidence supporting the impact of nutrition on the ocular surface, either directly or as a consequence of the chronic diseases that result. To address a key question, a systematic review investigated the effects of intentional food restriction on ocular surface health; of the 25 included studies, most investigated Ramadan fasting (56%), followed by bariatric surgery (16%), anorexia nervosa (16%), but none were judged to be of high quality, with no randomized-controlled trials.

Immune Fingerprint in Diabetes: Ocular Surface and Retinal Inflammation

Diabetes is a prevalent global health issue associated with significant morbidity and mortality. Diabetic retinopathy (DR) is a well-known inflammatory, neurovascular complication of diabetes and a leading cause of preventable blindness in developed countries among working-age adults. However, the ocular surface components of diabetic eyes are also at risk of damage due to uncontrolled diabetes, which is often overlooked. Inflammatory changes in the corneas of diabetic patients indicate that inflammation plays a significant role in diabetic complications, much like in DR. The eye's immune privilege restricts immune and inflammatory responses, and the cornea and retina have a complex network of innate immune cells that maintain immune homeostasis. Nevertheless, low-grade inflammation in diabetes contributes to immune dysregulation. This article aims to provide an overview and discussion of how diabetes affects the ocular immune system's main components, immune-competent cells, and inflammatory mediators. By understanding these effects, potential interventions and treatments may be developed to improve the ocular health of diabetic patients.

Diabetes more than retinopathy, it’s effect on the anterior segment of eye

Diabetes mellitus (DM) is one of the chronic metabolic noncommunicable diseases that has attained worldwide epidemics. It threatens healthy life around the globe, with mild-to-severe secondary complications and leads to significant illness including nephropathy, neuropathy, retinopathy, and macrovascular abnormalities including peripheral vasculopathy, and ischaemic heart disease. Research into diabetic retinopathy (DR), which affects one-third of persons with diabetes, has made considerable strides in recent years. In addition, it can lead to several anterior segment complications such as glaucoma, cataract, cornea, conjunctiva, lacrimal glands and other ocular surface diseases. Uncontrolled DM also caused gradual damage to corneal nerves and epithelial cells, which raises the likelihood of anterior segment diseases including corneal ulcers, dry eye disease, and chronic epithelial abnormalities. Although DR and other associated ocular complications are well-known, the complexity of its aetiology and diagnosis makes therapeutic intervention challenging. Strict glycaemic control, early detection and regular screening, and meticulous management is the key to halting the progression of the disease. In this review manuscript, we aim to provide an in-depth understanding of the broad spectrum of diabetic complications in the anterior segment of the ocular tissues and illustrate the progression of diabetes and its pathophysiology, epidemiology, and prospective therapeutic targets. This first such review article will highlight the role of diagnosing and treating patients with a plethora of anterior segment diseases associated with diabetes, which are often neglected.

High Prevalence of Demodex Infestation is Associated With Poor Blood Glucose Control in Type 2 Diabetes Mellitus: A Cross-Sectional Study in the Guangzhou Diabetic Eye Study

PURPOSE

The aim of this study was to investigate the association between type 2 diabetes mellitus (T2DM) and ocular Demodex mite infection.

METHOD

About 381 patients with T2DM from nearby communities were enrolled, and 163 age-matched and sex-matched nondiabetic patients from the cataract clinic were included as the control group. All subjects underwent personal history and demographic data collection, ocular examination, and lash sampling, followed by microscopic identification and counting of Demodex mites. Binocular fundus photography was performed for diabetic patients. Statistical correlation between ocular Demodex infestation and T2DM and blood glucose control status was performed.

RESULTS

The Demodex mite infestation rate (62.5% vs. 44.8%, P < 0.001) and count [3 (0-12) vs. 2 (0-9.6), P = 0.01], especially of Demodex brevis (18.9% vs. 4.9%, P < 0.001) [0 (0-1) vs. 0 (0-0), P < 0.001], were significantly higher in the T2DM patient group than that in the control group. The ratio of Demodex brevis to Demodex folliculorum in the T2DM patient group was significantly higher than that in the control group (1:3 vs. 1:9, P < 0.001). Diabetic patients presented with more cylindrical dandruff (55.1% vs. 39.3%, P = 0.001). Ocular Demodex infestation was strongly associated with poor blood glucose control (HbA 1 c > 7%) (odds ratio = 1.82; 95% confidence interval, 1.12-2.94; P = 0.2) and female sex (odds ratio = 1.69, 95% confidence interval, 1.08-2.65, P = 0.02). No association was found between Demodex infestation and the severity of diabetic retinopathy.

CONCLUSIONS

Patients with T2DM, especially those with poor blood glucose control, tend to have a higher prevalence of ocular Demodex infestation, suggesting that high blood glucose is a risk factor for demodicosis .

The effect of a-Lipoic acid (ALA) on oxidative stress, inflammation, and apoptosis in high glucose-induced human corneal epithelial cells

PURPOSE

Oxidative stress and inflammation had been proved to play important role in the progression of diabetic keratopathy (DK). The excessive accumulation of AGEs and their bond to AGE receptor (RAGE) in corneas that cause the formation of oxygen radicals and the release of inflammatory cytokines, induce cell apoptosis. Our current study was aimed to evaluate the effect of ALA on AGEs accumulation as well as to study the molecular mechanism of ALA against AGE-RAGE axis mediated oxidative stress, apoptosis, and inflammation in HG-induced HCECs, so as to provide cytological basis for the treatment of DK.

METHODS

HCECs were cultured in a variety concentration of glucose medium (5.5, 10, 25, 30, 40, and 50 mM) for 48 h. The cell proliferation was evaluated by CCK-8 assay. Apoptosis was investigated with the Annexin V- fluorescein isothiocyanate (V-FITC)/PI kit, while, the apoptotic cells were determined by flow cytometer and TUNEL cells apoptosis Kit. According to the results of cell proliferation and cell apoptosis, 25 mM glucose medium was used in the following HG experiment. The effect of ALA on HG-induced HCECs was evaluated. The HCECs were treated with 5.5 mM glucose (normal glucose group, NG group), 5.5 mM glucose + 22.5 mM mannitol (osmotic pressure control group, OP group), 25 mM glucose (high glucose group, HG group) and 25 mM glucose + ALA (HG + ALA group) for 24 and 48 h. The accumulation of intracellular AGEs was detected by ELISA kit. The RAGE, catalase (CAT), superoxide dismutase 2 (SOD2), cleaved cysteine-aspartic acid protease-3 (Cleaved caspase-3), Toll-like receptors 4 (TLR4), Nod-like receptor protein 3 (NLRP3) inflammasome, interleukin 1 beta (IL-1 ß), and interleukin 18 (IL-18) were quantified by RT-PCR, Western blotting, and Immunofluorescence, respectively. Reactive oxygen species (ROS) production was evaluated by fluorescence microscope and fluorescence microplate reader.

RESULTS

When the glucose medium was higher than 25 mM, cell proliferation was significantly inhibited and apoptosis ratio was increased (P < 0.001). In HG environment, ALA treatment alleviated the inhibition of HCECs in a dose-dependent manner, 25 μM ALA was the minimum effective dose. ALA could significantly reduce the intracellular accumulation of AGEs (P < 0.001), activate protein and genes expression of CAT and SOD2 (P < 0.001), and therefore inhibited ROS-induced oxidative stress and cells apoptosis. Besides, ALA could effectively down-regulate the protein and gene level of RAGE, TLR4, NLRP3, IL-1B, IL-18 (P < 0.05), and therefore alleviated AGEs-RAGE-TLR4-NLRP3 pathway-induced inflammation in HG-induced HCECs.

CONCLUSION

Our study indicated that ALA could be a desired treatment for DK due to its potential capacity of reducing accumulation of advanced glycation end products (AGEs) and down-regulating AGE-RAGE axis-mediated oxidative stress, cell apoptosis, and inflammation in high glucose (HG)-induced human corneal epithelial cells (HCECs), which may provide cytological basis for therapeutic targets that are ultimately of clinical benefit.

Dry eye disease in mice activates adaptive corneal epithelial regeneration distinct from constitutive renewal in homeostasis

Many epithelial compartments undergo constitutive renewal in homeostasis but activate unique regenerative responses following injury. The clear corneal epithelium is crucial for vision and is renewed from limbal stem cells (LSCs). Using single-cell RNA sequencing, we profiled the mouse corneal epithelium in homeostasis, aging, diabetes, and dry eye disease (DED), where tear deficiency predisposes the cornea to recurrent injury. In homeostasis, we capture the transcriptional states that accomplish continuous tissue turnover. We leverage our dataset to identify candidate genes and gene networks that characterize key stages across homeostatic renewal, including markers for LSCs. In aging and diabetes, there were only mild changes with <15 dysregulated genes. The constitutive cell types that accomplish homeostatic renewal were conserved in DED but were associated with activation of cell states that comprise "adaptive regeneration." We provide global markers that distinguish cell types in homeostatic renewal vs. adaptive regeneration and markers that specifically define DED-elicited proliferating and differentiating cell types. We validate that expression of SPARC, a marker of adaptive regeneration, is also induced in corneal epithelial wound healing and accelerates wound closure in a corneal epithelial cell scratch assay. Finally, we propose a classification system for LSC markers based on their expression fidelity in homeostasis and disease. This transcriptional dissection uncovers the dramatically altered transcriptional landscape of the corneal epithelium in DED, providing a framework and atlas for future study of these ocular surface stem cells in health and disease.

The association between altered intestinal microbiome, impaired systemic and ocular surface immunity, and impaired wound healing response after corneal alkaline-chemical injury in diabetic mice

Purpose

We aim to investigate the effect of sustained hyperglycemia on corneal epithelial wound healing, ocular surface and systemic immune response, and microbiome indices in diabetic mice compared to controls after alkaline chemical injury of the eye.

Methods

Corneal alkaline injury was induced in the right eye of Ins2^Akita (Akita) mice and wild-type mice. The groups were observed at baseline and subsequently days 0, 3, and 7 after injury. Corneal re-epithelialization was observed under slit lamp with fluorescein staining using a cobalt blue light filter. Enucleated cornea specimens were compared at baseline and after injury for changes in cornea thickness under hematoxylin and eosin staining. Tear cytokine and growth factor levels were measured using protein microarray assay and compared between groups and time points. Flow cytometry was conducted on peripheral blood and ocular surface samples to determine CD3+CD4+ cell count. Fecal samples were collected, and gut microbiota composition and diversity pattern were measured using shotgun sequencing.

Results

Akita mice had significantly delayed corneal wound healing compared to controls. This was associated with a reduction in tear levels of vascular endothelial growth factor A, angiopoietin 2, and insulin growth factor 1 on days 0, 3, and 7 after injury. Furthermore, there was a distinct lack of upregulation of peripheral blood and ocular surface CD3+CD4+ cell counts in response to injury in Akita mice compared to controls. This was associated with a reduction in intestinal microbiome diversity indices in Akita mice compared to controls after injury. Specifically, there was a lower abundance of Firmicutes bacterium M10-2 in Akita mice compared to controls after injury.

Conclusion

In diabetic mice, impaired cornea wound healing was associated with an inability to mount systemic and local immune response to ocular chemical injury. Baseline and post-injury differences in intestinal microbial diversity and abundance patterns between diabetic mice and controls may potentially play a role in this altered response.

A systematic review of the safety of tirzepatide-a new dual GLP1 and GIP agonist - is its safety profile acceptable?

AIMS

Tirzepatide is a novel dual glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 receptor agonist (GLP-1 RA). At present, there is no controversy over its effectiveness, but its safety. We conducted a systematic review to assess the safety of tirzepatide.

METHODS

We searched PubMed, Embase and Cochrane databases for randomized controlled trials (RCTs) of tirzepatide from databases inception to August 28, 2022 and used the Cochrane Systematic Assessment Manual Risk of Bias Assessment Tool (version 5.1) and modified Jadad scale to assess risk of bias. The systematic review was conducted via Revman5.4.

RESULTS

Nine RCTs with a total of 9818 patients were included. The overall safety profile of tirzepatide is similar to GLP-1RAs, except for the hypoglycemia (tirzepatide 15mg, pooled RR=3.83, 95% CI [1.19- 12.30], P=0.02) and discontinuation (tirzepatide 10mg, pooled RR=1.75,95%CI[1.16-2.63], P=0.007 and 15mg, pooled RR=2.03, 95%CI [1.37-3.01], P=0.0004). It also showed that the dose escalation could not rise the occurrence rates of total, severe, gastrointestinal adverse events and hypoglycemia (P>0.05); Compared with 5mg, tirzepatide 10mg and 15mg were associated with more frequent nausea (P<0.001), discontinuation (P<0.05) and injection-site reaction (P<0.01); The rates of vomiting and diarrhea were dose-dependence at the range of 5-15mg.

CONCLUSION

The safety profile of tirzepatide is generally acceptable, similar to GLP-1 RAs. It is necessary to pay attention to its specific adverse events (hypoglycemia and discontinuation) at high doses (10mg or higher). Nausea, vomiting, diarrhea, discontinuation and injection-site reaction were dose-dependence among specific dose ranges.As the heterogeneity in different studies by interventions, the results may be with biases and the further confirmation is needed. Meanwhile, more well-designed trials are needed to control the confounding factors and ensure adequate sample size.

Microbiological Characteristics of Ocular Surface Associated With Dry Eye in Children and Adolescents With Diabetes Mellitus

Purpose

To analyze the characteristics of ocular surface microbial composition in children and adolescents with diabetes mellitus and dry eye (DE) by tear analysis.

Methods

We selected 65 children and adolescents aged 8 to 16 years with DE and non-DE diabetes mellitus and 33 healthy children in the same age group from the Shanghai Children and Adolescent Diabetes Eye Study. Tears were collected for high-throughput sequencing of the V3 and V4 region of 16S rRNA. The ocular surface microbiota in diabetic DE (DM-DE; n = 31), diabetic with non-DE (DM-NDE; n = 34), and healthy (NDM; n = 33) groups were studied. QIIME2 software was used to analyze the microbiota of each group.

Results

The DM-DE group had the highest amplicon sequence variants, and the differences in α-diversity and β-diversity of micro-organisms in the ocular surfaces of DM-DE, diabetic with non-DE, and healthy eyes were statistically significant (P < 0.05). Bacteroidetes (15.6%), Tenericutes (9.3%), Firmicutes (21.8%), and Lactococcus (7.9%), Bacteroides (7.8%), Acinetobacter (3.9%), Clostridium (0.8%), Lactobacillus (0.8%) and Streptococcus (0.2%) were the specific phyla and genera, respectively, in the DM-DE group.

Conclusions

Compared with the patients with non-DE and healthy children, the microbial diversity of the ocular surface in children and adolescents with diabetes mellitus and DE was higher with unique bacterial phyla and genera composition.

Ocular surface microbiome in diabetes mellitus

This cross-sectional, age- and gender-matched study included 20 eyes of non-diabetic subjects (non-DM group) and 60 eyes of type 2 diabetes mellitus (DM group). Subgroups of DM were classified by diabetic retinopathy (DR) staging into no DR (DM-no DR), non-proliferative DR (DM-NPDR), proliferative DR (DM-PDR), and by glycemic control (well-controlled DM; HbA1c < 7%, poorly controlled DM; HbA1c ≥ 7%). Conjunctival swabs were performed for ocular surface microbiome analysis using conventional culture and next-generation sequencing analysis (NGS). A higher culture-positive rate was found in DM (15%) than in non-DM group (5%) (p value = 0.437). Pathogenic organisms and antibiotic-resistant strains were detected in the DR groups (DM-NPDR and DM-PDR). The NGS analysis showed that potentially pathogenic bacteria such as Enterobacteriaceae, Neisseriaceae, Escherichia-Shigella, and Pseudomonas predominated in DM, especially in DR. There was dissimilarity in the ocular surface microbiome between DM and non-DM groups. The subgroup analysis showed that the DR group had significantly different microbial community from DM-no DR and non-DM groups (p value < 0.05). The microbial community in the poorly controlled DM was also significantly different from well-controlled DM and non-DM groups (p < 0.001). Using the NGS method, our study is the first to signify the importance of DR and glycemic control status, which affect the changes in the ocular surface microbiome.

Innate Immune System Activation, Inflammation and Corneal Wound Healing

Corneal wounds resulting from injury, surgeries, or other intrusions not only cause pain, but also can predispose an individual to infection. While some inflammation may be beneficial to protect against microbial infection of wounds, the inflammatory process, if excessive, may delay corneal wound healing. An examination of the literature on the effect of inflammation on corneal wound healing suggests that manipulations that result in reductions in severe or chronic inflammation lead to better outcomes in terms of corneal clarity, thickness, and healing. However, some acute inflammation is necessary to allow efficient bacterial and fungal clearance and prevent corneal infection. This inflammation can be triggered by microbial components that activate the innate immune system through toll-like receptor (TLR) pathways. In particular, TLR2 and TLR4 activation leads to pro-inflammatory nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) activation. Similarly, endogenous molecules released from disrupted cells, known as damage-associated molecular patterns (DAMPs), can also activate TLR2, TLR4 and NFκB, with the resultant inflammation worsening the outcome of corneal wound healing. In sterile keratitis without infection, inflammation can occur though TLRs to impact corneal wound healing and reduce corneal transparency. This review demonstrates the need for acute inflammation to prevent pathogenic infiltration, while supporting the idea that a reduction in chronic and/or excessive inflammation will allow for improved wound healing.

Impact of High Glucose on Ocular Surface Glycocalyx Components: Implications for Diabetes-Associated Ocular Surface Damage

Diabetes mellitus causes several detrimental effects on the ocular surface, including compromised barrier function and an increased risk of infections. The glycocalyx plays a vital role in barrier function. The present study was designed to test the effect of a high glucose level on components of glycocalyx. Stratified human corneal and conjunctival epithelial cells were exposed to a high glucose concentration for 24 and 72 h. Changes in Mucin (MUC) 1, 4, 16 expression were quantified using real-time PCR and ELISA. Rose bengal and jacalin staining were used to assess the spatial distribution of MUC16 and O-glycosylation. Changes in the gene expression of five glycosyltransferases and forty-two proteins involved in cell proliferation and the cell cycle were also quantified using PCR and a gene array. High glucose exposure did not affect the level or spatial distribution of membrane-tethered MUC 1, 4, and 16 either in the corneal or conjunctival epithelial cells. No change in gene expression in glycosyltransferases was observed, but a decrease in the gene expression of proteins involved in cell proliferation and the cell cycle was observed. A high-glucose-mediated decrease in gene expression of proteins involved in cellular proliferation of corneal and conjunctival epithelial cells may be one of the mechanisms underlying a diabetes-associated decrease in ocular surface's glycocalyx.

Monocarboxylate Transporters: Role and Regulation in Corneal Diabetes

Diabetes mellitus (DM) is a group of metabolic diseases that is known to cause structural and functional ocular complications. In the human cornea, DM-related complications affect the epithelium, stroma, and nerves. Monocarboxylate transporters (MCTs) are a family of proton-linked plasma membrane transporters that carry monocarboxylates across plasma membranes. In the context of corneal health and disease, their role, presence, and function are largely undetermined and solely focused on the most common MCT isoforms, 1 through 4. In this study, we investigated the regulation of MCT1, 2, 4, 5, 8, and 10, in corneal DM, using established 3D self-assembled extracellular matrix (ECM) in vitro models. Primary stromal corneal fibroblasts were isolated from healthy (HCFs), type I (T1DMs), and type II (T2DMs) DM donors. Monoculture 3D constructs were created by stimulating stromal cells on transwells with stable vitamin C for two or four weeks. Coculture 3D constructs were created by adding SH-SY5Y neurons at two different densities, 12 k and 500 k, on top of the monocultures. Our data showed significant upregulation of MCT1 at 4 weeks for HCF, T1DM, and T2DM monocultures, as well as the 500 k nerve cocultures. MCT8 was significantly upregulated in HCF and T1DM monocultures and all of the 500 k nerve cocultures. Further, MCT10 was only expressed at 4 weeks for all cocultures and was limited to HCFs and T1DMs in monocultures. Immunofluorescence analysis showed cytoplasmic MCT expression for all cell types and significant downregulation of both MCT2 and MCT4 in HCFs, when compared to T1DMs and T2DMs. Herein, we reveal the existence and modulation of MCTs in the human diabetic cornea in vitro. Changes appeared dependent on neuronal density, suggesting that MCTs are very likely critical to the neuronal defects observed in diabetic keratopathy/neuropathy. Further studies are warranted in order to fully delineate the role of MCTs in corneal diabetes.

Effects of Type 2 Diabetes Mellitus and Smoking on Changes in Corneal Endothelial Morphology and Cell Density

PURPOSE

The purpose of this study was to compare the corneal endothelial morphology and cell density of diabetic smokers and nonsmokers with 50 to 70 age-matched healthy subjects and to determine whether smoking increases the effects of type 2 diabetes mellitus (DM) on these corneal parameters.

METHODS

This prospective cohort study included 200 patients who were assigned to 4 groups, including smokers with type 2 DM (group 1), nonsmokers with type 2 DM (group 2), healthy smokers (group 3), and healthy nonsmokers (control group, group 4). Noncontact specular microscopy was used to measure central endothelial cell density (ECD), coefficient of variation of cell area, percentage of hexagonal cells, and central corneal pachymetry (CCT).

RESULTS

According to the ECD and CCT values ( P < 0.001 and P = 0.013, respectively), a significant difference was observed between the groups. The mean ECD was lowest in diabetic smokers (1917 ± 399 cells/mm 2 ). Healthy smokers and diabetic smokers had significantly lower ECD compared with the control group ( P = 0.03 and P < 0.001, respectively). Healthy smokers and diabetic smokers had significantly lower ECD compared with diabetic nonsmokers ( P = 0.012 and P < 0.001, respectively). The cornea was significantly thicker in the diabetic smokers than in the control group ( P = 0.013).

CONCLUSIONS

The coexistence of DM and smoking causes a significant decrease in ECD and an increase in CCT. Cigarette smoking is more harmful to corneal endothelial cells than DM alone.

Acute Foggy Corneal Epithelial Disease: Seeking Clinical Features and Risk Factors

(1) Purpose: Here, we describe the clinical characteristics and predisposing factors of acute foggy corneal epithelial disease, a rare disease newly found during COVID-19 pandemic; (2) Methods: In this single-arm, ambispective case series study, ten patients with acute foggy corneal epithelial disease admitted between May 2020 and March 2021 were enrolled. Their detailed medical history and clinical and ophthalmic findings were recorded and analyzed; (3) Results: All the patients were female (100%), aged from 28 to 61 years (mean age of 40.4 ± 9.3 years). Seven cases (70%) had excessive eye use, and six cases (60%) had stayed up late and were overworked. Ten subjects (100%) presented with acute onset and a self-healing tendency. There was a mild-to-moderate decrease in the corrected visual acuity (0.35 ± 0.21 (LogMAR)). Slit-lamp examination showed diffuse dust-like opacity and edema in the epithelial layer of the cornea. By in vivo confocal microscope, epithelial cells presented characteristically a “relief-like” appearance. Anterior segment optical coherence tomography examination revealed that the mean epithelial thickness was increased (69.25 ± 4.31 μm, p < 0.01); (4) Conclusions: Acute foggy corneal epithelial disease is a rare disease in clinic, which tends to occur in young and middle-aged females. The typical clinical symptom is sudden foggy vision, which occurs repeatedly and can be relieved without treatment. Sex, an abnormal menstrual cycle, overuse of the eyes, fatigue and pressure might be risk factors. Changes in lifestyle and eye use habit during the COVID-19 pandemic may have possibly contributed to this disease incidence.

Chronic Hyperglycemia Compromises Mitochondrial Function in Corneal Epithelial Cells: Implications for the Diabetic Cornea

Mitochondrial dysfunction is a major pathophysiological event leading to the onset of diabetic complications. This study investigated the temporal effects of hyperglycemia on mitochondrial metabolism in corneal epithelial cells. To accomplish this, human telomerase-immortalized corneal epithelial cells were cultured in a defined growth medium containing 6 mM glucose. To simulate hyperglycemia, cells were cultured in a medium containing 25 mM D-glucose, and control cells were cultured in mannitol. Using metabolic flux analysis, there was a hyperosmolar-mediated increase in mitochondrial respiration after 24 h. By day 5, there was a decrease in spare respiratory capacity in cells subject to high glucose that remained suppressed throughout the 14-day period. Although respiration remained high through day 9, glycolysis was decreased. Mitochondrial respiration was decreased by day 14. This was accompanied by the restoration of glycolysis to normoglycemic levels. These changes paralleled a decrease in mitochondrial polarization and cell cycle arrest. Together, these data show that chronic but not acute hyperglycemic stress leads to mitochondrial dysfunction. Moreover, the hyperglycemia-induced loss of spare respiratory capacity reduces the ability of corneal epithelial cells to respond to subsequent stress. Compromised mitochondrial function represents a previously unexplored mechanism that likely contributes to corneal complications in diabetes.

Salivary Biomarkers Associated with Psychological Alterations in Patients with Diabetes: A Systematic Review

The care of individuals with diabetes needs a holistic perspective, taking into account both the physical disease and the mental health problems that may be associated. Different studies show a higher prevalence of depression or anxiety issues in diabetes patients than in the general population, which is why diabetes can be considered one of the chronic diseases in which psychological care is crucial to maintain quality of life. The objective of this review is to examine the published articles that relate the bidirectional associations between objective and subjective measures of anxiety, depressive symptomatology, stress, sleep quality, and salivary biomarkers in patients with diabetes. For this, a search was carried out in the electronic databases PubMed, Cochrane, and SCOPUS using the keywords "diabetes", "saliva", "sleep", "anxiety", "depression", and "stress" for works published up until May 2022 and limited to the English and Spanish languages. The sample comprised 14 articles, 5 of which analysed the associations between depressive symptomatology and salivary biomarkers in people with diabetes. Among the salivary biomarkers most frequently used to evaluate psychological alterations in persons with diabetes are cortisol and melatonin. Thus, significant changes in the levels of these biomarkers were observed in most studies. Four out of five studies reported a statistically significant relationship between increased salivary cortisol in the evening/midnight or the cortisol awakening response and depressive symptoms. In contrast, lower cortisol levels upon waking in the morning were observed when there was no depression or anxiety. Regarding the association between salivary cortisol values and sleep quality in patients with diabetes, lower morning cortisol values related to prolonged nighttime sleep were common in the analysed studies. Low melatonin concentrations showed a negative correlation with sleep quality. As it is an easy-to-apply and non-invasive method, the measurement of salivary biomarkers can be very useful for predicting psychological alterations in patients with diabetes. Further scientific studies are required to determine the sensitivity of these biological substances acting as biomarkers for detecting sleep disorders and psychological alterations.

Technical Report: Automatic Measurement of Corneal Nerve Fiber Area Using Versatile Software

SIGNIFICANCE

In vivo confocal microscopy has become a popular method to observe the details of corneal structures. We consider the area of corneal structures to be a versatile index and have measured the areas of various corneal structures using commercially available software.

PURPOSE

To evaluate the accuracy of software used to measure the corneal nerve fiber area.

METHODS

The corneal structures of 11 healthy volunteers were visualized using in vivo confocal microscopy. The image that most clearly depicted the corneal nerve fibers of each participant was selected for analysis. The corneal nerve fiber area was automatically measured by the software. An experienced ophthalmologist then manually measured the corneal nerve fiber area in each image assessed by the software. The Pearson correlation test was used to determine the correlation coefficient between the corneal nerve fiber areas measured automatically and those measured manually. The correlation between the corneal nerve fiber area and the participant's age was also evaluated.

RESULTS

A strong correlation was found between the corneal nerve fiber area measured automatically and the corneal nerve fiber area measured manually (r = .98, P = 2.4 × 10-7). The corneal nerve fiber area was not correlated with participant age, regardless of whether the area was measured automatically (r = -.26, P = .44) or manually (r = -.13, P = .71).

CONCLUSIONS

The software used in this study automatically measures the corneal nerve fiber area with accuracy similar to that of manual measurement by an experienced ophthalmologist. This software has potential for use in quantifying the areas of various corneal structures.

The impact of sensory neuropathy and inflammation on epithelial wound healing in diabetic corneas

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes, with several underlying pathophysiological mechanisms, some of which are still uncertain. The cornea is an avascular tissue and sensitive to hyperglycemia, resulting in several diabetic corneal complications including delayed epithelial wound healing, recurrent erosions, neuropathy, loss of sensitivity, and tear film changes. The manifestation of DPN in the cornea is referred to as diabetic neurotrophic keratopathy (DNK). Recent studies have revealed that disturbed epithelial-neural-immune cell interactions are a major cause of DNK. The epithelium is supplied by a dense network of sensory nerve endings and dendritic cell processes, and it secretes growth/neurotrophic factors and cytokines to nourish these neighboring cells. In turn, sensory nerve endings release neuropeptides to suppress inflammation and promote epithelial wound healing, while resident immune cells provide neurotrophic and growth factors to support neuronal and epithelial cells, respectively. Diabetes greatly perturbs these interdependencies, resulting in suppressed epithelial proliferation, sensory neuropathy, and a decreased density of dendritic cells. Clinically, this results in a markedly delayed wound healing and impaired sensory nerve regeneration in response to insult and injury. Current treatments for DPN and DNK largely focus on managing the severe complications of the disease. Cell-based therapies hold promise for providing more effective treatment for diabetic keratopathy and corneal ulcers.

Anterior Segment-Optical Coherence Tomography and Diabetic Retinopathy: could it be an Early Biomarker?

INTRODUCTION

To measure the corneal thickness (CT), corneal epithelial thickness (CET), and corneal stromal thickness (CST) in patients affected by type 2 diabetes mellitus with good glycemic control and without any signs of diabetic retinopathy using anterior-segment optical coherence tomography (AS-OCT).

METHODS

60 eyes of 30 diabetic patients and 60 normal eyes of 30 healthy subjects underwent AS-OCT, evaluation of best-corrected visual acuity (BCVA), intraocular pressure (IOP), slit-lamp biomicroscopy, tear film breakup time (TBUT), Schirmer I test and fundus examination. The CT, CET, and CST maps generated corresponded to a 6-mm diameter area of the cornea that was divided into 17 sectors. We compared the CT, CET, and the CST of each sector obtained in the diabetic group with those obtained in the control group.

RESULTS

No significant difference in terms of age, gender, BCVA, IOP, TBUT, and Schirmer I test between the two study groups was observed. The CT, CET, and CST in the central section were significantly thickened in diabetic patients than in controls (p<0.001). Also, each paracentral and midperipheral sector was significantly increased in patients compared to controls (p<0.05).

CONCLUSIONS

The evaluation of the CT, CET, and CST by AS-OCT could be a valid and non-invasive biomarker in patients affected by diabetes mellitus, useful in early diagnosis of diabetic retinopathy.

Pathogenic Role of Diabetes-Induced Overexpression of Kallistatin in Corneal Wound Healing Deficiency Through Inhibition of Canonical Wnt Signaling

It was reported previously that circulation levels of kallistatin, an endogenous Wnt signaling inhibitor, are increased in patients with diabetes. The current study was conducted to determine the role of kallistatin in delayed wound healing in diabetic corneas. Immunostaining and Western blot analysis showed kallistatin levels were upregulated in corneas from humans and rodents with diabetes. In murine corneal wound healing models, the canonical Wnt signaling was activated in nondiabetic corneas and suppressed in diabetic corneas, correlating with delayed wound healing. Transgenic expression of kallistatin suppressed the activation of Wnt signaling in the cornea and delayed wound healing. Local inhibition of Wnt signaling in the cornea by kallistatin, an LRP6-blocking antibody, or the soluble VLDL receptor ectodomain (an endogenous Wnt signaling inhibitor) delayed wound healing. In contrast, ablation of the VLDL receptor resulted in overactivation of Wnt/β-catenin signaling and accelerated corneal wound healing. Activation of Wnt signaling in the cornea accelerated wound healing. Activation of Wnt signaling promoted human corneal epithelial cell migration and proliferation, which was attenuated by kallistatin. Our findings suggested that diabetes-induced overexpression of kallistatin contributes to delayed corneal wound healing by inhibiting the canonical Wnt signaling. Thus, kallistatin and Wnt/β-catenin signaling in the cornea could be potential therapeutic targets for diabetic corneal complications.

Changes of lysozyme content in the lacrimal fluid in patients with diabetic retinopathy (pilot study)

Background. Type 2 diabetes mellitus is one of the most common metabolic disorders in humans. Diabetes mellitus can lead to abnormalities in many tissues of the eye structure, exposing patients to the risk of developing a wide range of ocular pathologies associated with changes in its anterior and posterior segments. The most common complication is diabetic retinopathy.

The aim: to assess the potential clinical significance of lacrimal lysozyme as a minimally invasive biomarker of diabetic ophthalmic disorders.

Material and methods. Three groups were formed during the study. Group  1 (Control, n  =  10) included conditionally healthy people with no type  2 diabetes mellitus. Group 2 (Main 1, n = 15) included patients with type 2 diabetes mellitus, but  no  diabetic manifestations in the fundus. Group  3 (Main  2, n  =  15) included patients with type 2 diabetes mellitus and manifestations of diabetic retinopathy of varying degrees. In patients of all groups, the level of tear lysozyme was assessed.

Results. It was found that the concentration of lacrimal fluid lysozyme in patients with type 2 diabetes mellitus was significantly lower than in healthy patients. In patients with diabetic retinopathy of varying degrees of manifestation (non-proliferative and proliferative forms) against the background of type  2 diabetes mellitus, significantly lower values of lysozyme were observed compared to patients with type 2 diabetes mellitus, but without diabetic ophthalmic manifestations.

Conclusion. It is possible that local detection of lysozyme in the lacrimal fluid may be potential biomarkers of the progression of diabetic retinopathy. 

Corneal epithelial defects following vitreoretinal surgery: incidence and outcomes from the DISCOVER study

AIM

To investigate the incidence, risk factors, clinical course, and outcomes of corneal epithelial defects (CED) following vitreoretinal surgery in a prospective study setting.

METHODS

This was a post-hoc analysis of all participants in DISCOVER intraoperative optical coherence tomography study. Subjects with CED 1d after surgery without intraoperative corneal debridement was defined as the postoperative CED group. Subjects who underwent intraoperative debridement were defined as intraoperative debridement group. Eyes were matched 2:1 with controls (eyes without postoperative CED) for comparative assessment. The primary outcomes were the incidence of CED on postoperative day one and the incidence of required intraoperative debridement. Secondary outcomes included time to defect closure, delayed healing (>2wk), visual acuity (VA) and presence of scarring at one year and cornea consult.

RESULTS

This study included 856 eyes that underwent vitreoretinal surgery. Intraoperative corneal debridement was performed to 61 (7.1%) subjects and postoperative CED developed spontaneously in 94 (11.0%) subjects. Significant factors associated with postoperative CED included prolonged surgical duration (P=0.003), diabetes mellitus (P=0.04), postoperative ocular hypotension (P<0.001). Prolonged surgical duration was associated with intraoperative debridement. Delayed defect closure time (>2wk) was associated with corneal scar formation at the end of the 1y in all epithelial defect subjects (P<0.001). The overall rate of corneal scarring for all eyes undergoing vitrectomy was 1.8%.

CONCLUSION

Prolonged duration of surgery is the strongest factor associated with both intraoperative debridement and spontaneous postoperative CED. Delayed defect closure is associated with a greater risk of corneal scarring at one year. The overall rate of corneal scarring following vitrectomy is low at <2%.

Impact of Diquafosol Ophthalmic Solution on Tear Film and Dry Eye Symptom in Type 2 Diabetic Dry Eye: A Pilot Study

Background: Diquafosol ophthalmic solution (DQS) stimulates P2Y2 receptors on the ocular surface, which enhances mucin secretion from goblet cells. Therefore, tear film stability and hydration of the ocular surface can be achieved independent from lacrimal gland function. Methods: This prospective, open-label pilot study included 60 eyes of 30 diabetic patients diagnosed with dry eye disease (DED) and were randomly assigned to either DQS (n = 30 eyes) or hyaluronate (HA) group (n = 30 eyes). Participants in the DQS group received 3% diquafosol ophthalmic solution, whereas HA group received 0.1% sodium HA preservative-free artificial tears. The dosage for both drugs was 1 drop, 6 times per day for 4 weeks. Tear film lipid layer (TFLL), noninvasive breakup time (NITBUT), corneoconjunctival staining (CS) score, meibomian gland (MG), conjunctival hyperemia [redness score (RS)], ocular surface disease index (OSDI) was assessed and compared at baseline, day 14, and day 28. Results: Comparing baseline and day 28 measurements revealed that both groups found significant improvements in NITBUT, CS, MG quality, MG expressibility, and OSDI scores significantly (P < 0.05), in addition TFLL improvements were only found in the DQS group. At day 28, the magnitude of change in mean NITBUT was 1.74 (DQS) versus 0.31 (HA), 1.16 (DQS) versus 0.37 (HA) point grade reduction in corneoconjunctival staining score and 9.80 (DQS) versus 4.80 (HA) point grade in mean OSDI score. Conclusion: Three percent diquafosol ophthalmic solution treatment demonstrated the ability to improve the tear film dry eye parameters and clinically reduced sign and symptoms of DED in diabetic dry eye patients. Clinical Trials.gov ID: NCT04980144.

The use of androgen deprivation therapy for prostate cancer and its effect on the subsequent dry eye disease: a population-based cohort study

This study aimed to investigate the influence of androgen deprivation therapy (ADT) for the development of dry eye disease (DED) in subjects with prostate cancer via the use of national health insurance research database (NHIRD) of Taiwan. A retrospective cohort study was conducted and patients were selected as prostate cancer with ADT according to diagnostic and procedure codes. Each participant in that group was then matched to one patient with prostate cancer but without ADT and two subject s without prostate cancer and ADT. And a total of 1791, 1791 and 3582 participants were enrolled in each group. The primary outcome was set as the DED development according to the diagnostic codes. Cox proportional hazard regression was applied to calculate the adjusted hazard ratio (aHR) and 95% confidence interval (CI) of ADT and other parameters for DED development. There were 228, 126 and 95 new events of DED developed in the control group, the prostate cancer without ADT group and the prostate cancer with ADT group. The rate of DED in the prostate cancer with ADT group (aHR: 0.980, 95% CI: 0.771-1.246, P= 0.8696) and Prostate cancer without ADT group (aHR: 1.064, 95% CI: 0.855-1.325, P= 0.5766) were not significantly different compared to the control group. In addition, the patients aged 70-79 years old demonstrated a significantly higher incidence of developing DED compared to those aged 50-59 years old (aHR: 1.885, 95% CI: 1.188-2.989, P= 0.0071). In conclusion, the use of ADT did not alter the incidence of subsequent DED.

Risk factors for fluctuations in corneal endothelial cell density (Review)

The cornea is a transparent, avascular and abundantly innervated tissue through which light rays are transmitted to the retina. The innermost layer of the cornea, also known as the endothelium, consists of a single layer of polygonal endothelial cells that serve an important role in preserving corneal transparency and hydration. The average corneal endothelial cell density (ECD) is the highest at birth (~3,000 cells/mm²), which then decrease to ~2,500 cells/mm² at adulthood. These endothelial cells have limited regenerative potential and the minimum (critical) ECD required to maintain the pumping function of the endothelium is 400-500 cells/mm². ECD < the critical value can result in decreased corneal transparency, development of corneal edema and reduced visual acuity. The condition of the corneal endothelium can be influenced by a number of factors, including systemic diseases, such as diabetes or atherosclerosis, eye diseases, such as uveitis or dry eye disease (DED) and therapeutic ophthalmological interventions. The aim of the present article is to review the impact of the most common systemic disorders (pseudoexfoliation syndrome, diabetes mellitus, cardiovascular disease), eye diseases (DED, uveitis, glaucoma, intraocular lens dislocation) and widely performed ophthalmic interventions (cataract surgery, intraocular pressure-lowering surgeries) on corneal ECD.