Ultrastructural changes in corneas of diabetic patients: an electron-microscopy study

Comprehensive analysis of systemic, metabolic, and molecular changes following prospective change to low-carbohydrate diet in adults with type 2 diabetes mellitus in India

Purpose

South Asians, especially Indians, face higher diabetes-related risks despite lower body mass index (BMI) compared with the White population. Limited research connects low-carbohydrate high-fat (LCHF)/ketogenic diets to metabolic changes in this group. Systematic studies are needed to assess the long-term effects of the diet, such as ocular health.

Method

In this prospective, observational study, 465 candidates aged 25-75 years with type 2 diabetes included with institutional ethics approval. A total of 119 subjects were included in the final study assessment based on the availability of pathophysiological reports, tears, and blood samples collected at baseline, 3rd, and 6th months. Serum and tear samples were analyzed by an enzyme-linked lectinsorbent assay, to examine secreted soluble protein biomarkers, such as IL-1β (interleukin 1 Beta), IL-6 (interleukin 6), IL-10 (interleukin 10), IL-17A (interleukin 17A), MMP-9 (matrix metalloproteinase 9), ICAM-1 (intercellular adhesion molecule 1), VEGF-A (vascular endothelial growth factor A), and TNF-α (tumor necrosis factor-alpha). A Wilcoxon test was performed for paired samples. Spearman's correlation was applied to test the strength and direction of the association between tear biomarkers and HbA1c. p-value of < 0.05 was considered significant.

Results

After a 3- and 6-month LCHF intervention, fasting blood sugar decreased by 10% (Δ: -14 mg/dL; p < 0.0001) and 7% (Δ: -8 mg/dL; p < 0.0001), respectively. Glycated hemoglobin A1c levels decreased by 13% (Δ: -1%; p < 0.0001) and 9% (Δ: -0.6%; p < 0.0001). Triglycerides reduced by 22% (Δ: -27 mg/dL; p < 0.0001) and 14% (Δ: -19 mg/dL; p < 0.0001). Total cholesterol reduced by 5.4% (Δ: -10.5 mg/dL; p < 0.003) and 4% (Δ: -7 mg/dL; p < 0.03), while low-density lipoprotein decreased by 10% (Δ: -11.5 mg/dL; p < 0.003) and 9% (Δ: -11 mg/dL; p < 0.002). High-density lipoprotein increased by 11% (Δ: 5 mg/dL; p < 0.0001) and 17% (Δ: 8 mg/dL; p < 0.0001). At the first follow-up, tear proteins such as ICAM-1, IL-17A, and TNF-α decreased by 30% (Δ: -2,739 pg/mL; p < 0.01), 22% (Δ: -4.5 pg/mL; p < 0.02), and 34% (Δ: -0.9 pg/mL; p < 0.002), respectively. At the second follow-up, IL-1β and TNF-α reduced by 41% (Δ: -2.4 pg/mL; p < 0.05) and 34% (Δ: -0.67 pg/mL; p < 0.02). Spearman's correlation between HbA1c and tear analytes was not statistically significant.

Conclusion

The LCHF diet reduces the risk of hyperglycemia and dyslipidemia. Changes in tear fluid protein profiles were observed, but identifying promising candidate biomarkers requires validation in a larger cohort.

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.

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.

The soil and the seed: The relationship between Descemet's membrane and the corneal endothelium

Descemet's membrane (DM), the basement membrane of the corneal endothelium, is formed from the extracellular matrix (ECM) secreted by corneal endothelial cells. The ECM supports the growth and function of the corneal endothelial cells. Changes to DM are central to the diagnosis of the most common corneal endothelial disease, Fuchs endothelial corneal dystrophy (FECD). Changes in DM are also noted in systemic diseases such as diabetes mellitus. In FECD, the DM progressively accumulates guttae, "drop-like deposits" that disrupt the corneal endothelial cell monolayer. While the pathophysiologic changes to corneal endothelial cells in the course of FECD have been well described and reviewed, the changes to DM have received limited attention. The reciprocity of influence between the corneal endothelial cells and DM demands full attention to the latter in our search for novel treatment and preventive strategies. In this review, we discuss what is known about the formation and composition of DM and how it changes in FECD and other conditions. We review characteristics of guttae and the interplay between corneal endothelial cells and guttae, particularly as it might apply to future cell-based and genetic therapies for FECD.

The neuropeptide substance P/neurokinin-1 receptor system and diabetes: From mechanism to therapy

Diabetes is a significant public health issue known as the world's fastest-growing disease condition. It is characterized by persistent hyperglycemia and subsequent chronic complications leading to organ dysfunction and, ultimately, the failure of target organs. Substance P (SP) is an undecapeptide that belongs to the family of tachykinin (TK) peptides. The SP-mediated activation of the neurokinin 1 receptor (NK1R) regulates many pathophysiological processes in the body. There is also a relation between the SP/NK1R system and diabetic processes. Importantly, deregulated expression of SP has been reported in diabetes and diabetes-associated chronic complications. SP can induce both diabetogenic and antidiabetogenic effects and thus affect the pathology of diabetes destructively or protectively. Here, we review the current knowledge of the functional relevance of the SP/NK1R system in diabetes pathogenesis and its exploitation for diabetes therapy. A comprehensive understanding of the role of the SP/NK1R system in diabetes is expected to shed further light on developing new therapeutic possibilities for diabetes and its associated chronic conditions.

Pycnogenol a promising remedy for diabetic keratopathy in experimentally induced corneal alkali burns in diabetic rats

AIM

This study aimed to investigate the efficiency of topically applied pycnogenol (PYC) in healing the standardized alkaline corneal ulcer in diabetic and normal rats.

MATERIALS AND METHODS

The corneal alkali-burn injury (CA-I) model was unilaterally developed in Wistar rats by filter paper saturated with 0.01 M of NaOH and touching the eyes for 45 s. Rats were divided into four groups: Normal control (NC), normal PYC (NPYC), diabetic control (DC), and diabetic PYC (DPYC). Both NPYC and DPYC groups were daily treated with PY eye drops three times, whereas NC and DC ones were treated with ordinary saline for six successive days.

RESULTS

The wound healing of corneal epithelial was improved in the NPYC group compared to the NC group. Meanwhile, it was significantly improved (P < 0.05) in the DPYC group than in the DC group. Histological examination revealed that corneal re-epithelialization was more accomplished in the DPYC group than in the DC group. In addition, the inflammatory cells were augmented in the DC group more than those in the DPYC one.

CONCLUSION

The findings obtained revealed the efficiency of PYC for enhancing the corneal re-epithelialization and reducing the inflammatory reaction post alkali burn in rats, and thus it could be beneficially valuable as a treatment for the diabetic keratopathy.

Diabetic Corneal Neuropathy: Pathogenic Mechanisms and Therapeutic Strategies

Diabetes mellitus (DM) is a major global public health problem that can cause complications such as diabetic retinopathy, diabetic neuropathy, and diabetic nephropathy. Besides the reporting of reduction in corneal nerve density and decrease in corneal sensitivity in diabetic patients, there may be a subsequent result in delayed corneal wound healing and increased corneal infections. Despite being a potential cause of blindness, these corneal nerve changes have not gained enough attention. It has been proposed that corneal nerve changes may be an indicator for diabetic neuropathy, which can provide a window for early diagnosis and treatment. In this review, the authors aimed to give an overview of the relationship between corneal nerves and diabetic neuropathy as well as the underlying pathophysiological mechanisms of corneal nerve fiber changes caused by DM for improved prediction and prevention of diabetic neuropathy. In addition, the authors summarized current and novel therapeutic methods for delayed corneal wound healing, nerve protection and regeneration in the diabetic cornea.

Mechanistic investigations of diabetic ocular surface diseases

With the global prevalence of diabetes mellitus over recent decades, more patients suffered from various diabetic complications, including diabetic ocular surface diseases that may seriously affect the quality of life and even vision sight. The major diabetic ocular surface diseases include diabetic keratopathy and dry eye. Diabetic keratopathy is characterized with the delayed corneal epithelial wound healing, reduced corneal nerve density, decreased corneal sensation and feeling of burning or dryness. Diabetic dry eye is manifested as the reduction of tear secretion accompanied with the ocular discomfort. The early clinical symptoms include dry eye and corneal nerve degeneration, suggesting the early diagnosis should be focused on the examination of confocal microscopy and dry eye symptoms. The pathogenesis of diabetic keratopathy involves the accumulation of advanced glycation end-products, impaired neurotrophic innervations and limbal stem cell function, and dysregulated growth factor signaling, and inflammation alterations. Diabetic dry eye may be associated with the abnormal mitochondrial metabolism of lacrimal gland caused by the overactivation of sympathetic nervous system. Considering the important roles of the dense innervations in the homeostatic maintenance of cornea and lacrimal gland, further studies on the neuroepithelial and neuroimmune interactions will reveal the predominant pathogenic mechanisms and develop the targeting intervention strategies of diabetic ocular surface complications.

Segment-Long-Spacing (SLS) and the Polymorphic Structures of Fibrillar Collagen

The diverse and complex functions of collagen during the development of an organism are closely related to the polymorphism of its supramolecular structures in the extracellular matrix. SLS (segment-long-spacing) is one of the best understood alternative structures of collagen. SLS played an instrumental role in the original studies of collagen more than half a century ago that laid the foundation of nearly everything we know about collagen today. Despite being used mostly under in vitro conditions, the natural occurrence of SLS in tissues has also been reported. Here we will provide a brief overview of the major findings of the SLS and other structures of collagen based on a wealth of work published starting from the 1940s. We will discuss the factors that determine the stability and the structural specificity of the different molecular assemblies of collagen in light of the new studies using designed fibril forming collagen peptides. At the end of the chapter, we will summarize some recent discoveries of the alternative structures of collagen in tissues, especially those involved in pathogenic states. A revisit of SLS will likely inspire new understandings concerning the range of critical roles of fibrillar collagen in terms of its organizational diversity in the extracellular matrix.

Topical calcitriol application promotes diabetic corneal wound healing and reinnervation through inhibiting NLRP3 inflammasome activation

Vitamin D (VD) deficiency delays corneal wound healing in those with diabetes, which cannot be rescued with supplemental diet. Here, we employed topical calcitriol application to evaluate its efficiency in corneal wound healing and reinnervation in diabetic mice. Type 1 diabetic mice were topically administrated calcitriol, or subconjunctivally injected with NLRP3 antagonist MCC950 or IL-1β blocking antibody after epithelial debridement. Serum VD levels, corneal epithelial defect, corneal sensation and nerve density, NLRP3 inflammasome activation, neutrophil infiltration, macrophage phenotypes, and gene expressions were examined. Compared with those of normal mice, diabetic mice showed reduced serum VD levels. Topical calcitriol application promoted corneal wound healing and nerve regeneration, as well as sensation recovery in diabetic mice. Moreover, calcitriol ameliorated neutrophil infiltration and promoted the M1-to-M2 macrophage transition, accompanied by suppressed overactivation of the NLRP3 inflammasome. Treatment with NLRP3 antagonist or IL-1β blockage demonstrated similar improvements as those of topical calcitriol application. Additionally, calcitriol administration upregulated desmosomal and hemidesmosomal gene expression in the diabetic cornea. In conclusion, topical calcitriol application promotes corneal wound healing and reinnervation during diabetes, which may be related to the suppression of the overactivation of NLRP3 inflammasome.

Cell-Matrix Interactions in the Eye: From Cornea to Choroid

The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.

Systemic diseases and the cornea

There is a number of systemic diseases affecting the cornea. These include endocrine disorders (diabetes, Graves' disease, Addison's disease, hyperparathyroidism), infections with viruses (SARS-CoV-2, herpes simplex, varicella zoster, HTLV-1, Epstein-Barr virus) and bacteria (tuberculosis, syphilis and Pseudomonas aeruginosa), autoimmune and inflammatory diseases (rheumatoid arthritis, Sjögren's syndrome, lupus erythematosus, gout, atopic and vernal keratoconjunctivitis, multiple sclerosis, granulomatosis with polyangiitis, sarcoidosis, Cogan's syndrome, immunobullous diseases), corneal deposit disorders (Wilson's disease, cystinosis, Fabry disease, Meretoja's syndrome, mucopolysaccharidosis, hyperlipoproteinemia), and genetic disorders (aniridia, Ehlers-Danlos syndromes, Marfan syndrome). Corneal manifestations often provide an insight to underlying systemic diseases and can act as the first indicator of an undiagnosed systemic condition. Routine eye exams can bring attention to potentially life-threatening illnesses. In this review, we provide a fairly detailed overview of the pathologic changes in the cornea described in various systemic diseases and also discuss underlying molecular mechanisms, as well as current and emerging treatments.

Diseases of the corneal endothelium

The corneal endothelial monolayer and associated Descemet's membrane (DM) complex is a unique structure that plays an essential role in corneal function. Endothelial cells are neural crest derived cells that rest on a special extracellular matrix and play a major role in maintaining stromal hydration within a narrow physiologic range necessary for clear vision. A number of diseases affect the endothelial cells and DM complex and can impair corneal function and vision. This review addresses different human corneal endothelial diseases characterized by loss of endothelial function including: Fuchs endothelial corneal dystrophy (FECD), posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), bullous keratopathy, iridocorneal endothelial (ICE) syndrome, post-traumatic fibrous downgrowth, glaucoma and diabetes mellitus.

The Relationship Between Corneal Nerve Density and Hemoglobin A1c in Patients With Prediabetes and Type 2 Diabetes

Purpose

Decreased corneal nerve fiber density and higher corneal epithelial dendritic cells have been reported in established patients with type 2 diabetes; however, alterations in the subbasal nerve plexus in prediabetes with healthy subjects or subjects with diabetes is limited. The study aimed to determine corneal nerve fiber density and morphology and dendritic cell density between healthy subjects and those with prediabetes or type 2 diabetes.

Methods

Fifty-two subjects (aged 30-70 years) were recruited. Blood samples and body metrics were taken. Subjects were grouped as: healthy controls (hemoglobin A1c [HbA1c] < 5.7%), prediabetes (5.7-6.4%), and type 2 diabetes (> 6.4% or physician diagnosis). Central corneal subbasal nerve plexus was imaged using in vivo confocal microscopy. Corneal nerve fiber density and morphology, including interconnections and tortuosity, and dendritic cell density were assessed. Kruskal-Wallis tests were carried out to compare differences in the examined variables between groups. Spearman correlations were carried out to examine the associations between body metrics with HbA1c and corneal findings.

Results

Seventeen healthy controls, 20 subjects with prediabetes, and 15 subjects with type 2 diabetes completed this study. Central corneal nerve fiber density was significantly lower in type 2 diabetes compared to prediabetes (P = 0.045) and healthy controls (P = 0.001). No differences were found in central corneal nerve fiber interconnections, tortuosity, or dendritic cell density between groups. There was a significant association between HbA1c and corneal nerve fiber density (rho = -0.45, P = 0.001) and body mass index (BMI; rho = -0.30, P = 0.04).

Conclusions

Increased HbA1c values are associated with decreased corneal nerve fiber density across the spectrum of type 2 diabetes.

Eye care providers' emerging roles in early detection of diabetes and management of diabetic changes to the ocular surface: a review

US adults visit eye care providers more often than primary healthcare providers, placing these doctors in a prime position to help identify and manage patients with prediabetes and diabetes. Currently, diabetes is identified in eye clinics in an advanced stage, only after visible signs of diabetic retinopathy. Recent ophthalmic research has identified multiple subclinical and clinical changes that occur in the anterior segment of the eye with metabolic disease. The corneal epithelium exhibits increased defects and poor healing, including an increased risk of neurotrophic keratitis. Increased thickness and stiffness of the cornea artificially alters intraocular pressure. There is damage to the endothelial cells and changes to the bacterial species on the ocular surface, both of which can increase risk of complications with surgery. Decreased corneal sensitivity due to a loss of nerve density predispose patients with metabolic disease to further neurotrophic complications. Patients with diabetes have increased Meibomian gland dysfunction, blepharitis and reduced tear production, resulting in increased rates of dry eye disease and discomfort. Early detection of metabolic disease may allow eye care providers to be more proactive in recommending referral and intervention in order to reduce the risk of blindness and other diabetes-related morbidity. Continued research is needed to better understand the time course of changes to the anterior segment and what can be done to better detect and diagnose patients with prediabetes or undiagnosed diabetes and provide improved care for these patients.

Relationships of diabetes and hyperglycaemia with intraocular pressure in a Japanese population: the JPHC-NEXT Eye Study

Although a meta-analysis previously suggested a positive relationship between diabetes and intraocular pressure (IOP), the interrelationships among diabetes, IOP, and other ocular biometric parameters remain unclear. The present study investigated the relationships of diabetes, haemoglobin A1c (HbA1c), and serum glucose with IOP and ocular hypertension (IOP > 21 mmHg) in non-glaucomatous Japanese adults living in Chikusei City. Diabetes was defined as a self-reported history of diabetes, the use of antidiabetic medication, or HbA1c levels ≥6.5%. Among 6,786 enrolled participants aged 40 years and above, 734 were classified as diabetic (10.8%). After adjusting for several confounders, the IOP values were significantly higher in participants with diabetes than in those without diabetes (14.4 ± 0.1 vs. 13.9 ± 0.1 mmHg, P < 0.001) and were also significantly increased in those with elevated HbA1c and serum glucose levels (both P < 0.001). Moreover, diabetes was significantly related to ocular hypertension (multivariable-adjusted odds ratio, 1.75; 95% confidence interval, 1.09–2.81; P < 0.05). The positive influence of diabetes with ocular hypertension was consistent even after adjustment for central corneal thickness. In conclusion, diabetes, elevated HbA1c, and increased serum glucose are significant contributing factors for elevated IOP.

Relationship between dry eye and glycosylated haemoglobin among diabetics in Ibadan, Nigeria

Introduction

dry eye is a fairly common ocular surface disorder which significantly affects the quality of life of patients. This study aimed to determine the prevalence, and relationship between dry eye and glycosylated haemoglobin (HbA1c) among patients with diabetes mellitus.

Methods

this was a descriptive hospital-based study conducted among patients diagnosed with diabetes mellitus and attending the Diabetic Clinic at a tertiary health facility in Ibadan, south-western Nigeria. Dry eye was assessed using the standardized Ocular Surface Disease Index Questionnaire administered to the eligible respondents on dry eye symptoms. Detailed ocular examination including the tear break-up time (TBUT) and Schirmer I test were carried out and a recent glycosylated haemoglobin value was also obtained.

Results

one hundred and eighty-nine Type 2 diabetic patients were studied, with 68.8% female and a mean age of 60.2 ± 10.3 years. The frequency of dry eye among patients was 21.7% (95% CI, 15.8-27.6). The most commonly reported symptoms of dry eye were “feeling of gritty sensation” (78%, 95% CI, 65.4-90.7) and “blurred vision” (73.2%, 95% CI, 59.6-86.7) while “discomfort in windy areas” (61%, 95% CI, 46.0-75.9) was the most common environmental trigger. No statistically significant correlation was noted between dry eye and HbA1c (r = 0.086, p= 0.239), and age (r = 0.096, p = 0.1)

Conclusion

dry eye is fairly common among patients with diabetes mellitus with most frequent symptoms being gritty sensation and blurred vision. No significant correlation was noted between dry eye and glycosylated haemoglobin (HbA1c).

A Proteomic Approach for Understanding the Mechanisms of Delayed Corneal Wound Healing in Diabetic Keratopathy Using Diabetic Model Rat

Diabetes mellitus is a widespread metabolic disorder, and long-term hyperglycemia in diabetics leads to diabetic keratopathy. In the present study, we used a shotgun liquid chromatography/mass spectrometry-based global proteomic approach using the cornea of streptozotocin-induced diabetic (STZ) rats to examine the mechanisms of delayed corneal wound healing in diabetic keratopathy. Applying a label-free quantitation method based on spectral counting, we identified 188 proteins that showed expression changes of >2.0-fold in the cornea of STZ rats. In particular, the level of lumican expression in the cornea of STZ rats was higher than that of the normal rats. In the cornea of the normal rat, the expression level of lumican was elevated during the wound healing process, and it returned to the same expression level as before cornea injury after the wound was healed completely. On the other hand, a high expression level of lumican in the cornea of STZ rats was still maintained even after the wound was healed completely. In addition, adhesion deficiency in corneal basal cells and Bowman’s membrane was observed in the STZ rat. Thus, abnormally overexpressed lumican may lead to adhesion deficiency in the cornea of STZ rats.

Epithelial changes with corneal punctate epitheliopathy in type 2 diabetes mellitus and their correlation with time to healing

Background

To study basal epithelial cell (BEC), sub-basal nerve plexus (SBN) and Langerhans cell (LC) density in patients with type 2 diabetes mellitus (T2DM) with corneal punctate epitheliopathy (CPE) and to assess their association with time to healing of CPE.

Methods

Retrospective study of in vivo confocal microscopy (IVCM) in 160 eyes from 160 patients with T2DM diagnosed with CPE due to a single cause. Key exclusion criteria included multiple-causes for CPE or treatment with autologous serum. A total of 149 eyes from 149 gender- age- and aetiolgy-matched patients with CPE without T2DM comprised the control group. Electronic records were reviewed for demographic features, history of T2DM and aetiology of CPE. Density of BEC, SBN and LC were compared between the two groups.

Results

The healing time in days for CPE with different aetiologies in the T2DM and control groups were as follows: dry eye (21.56 ± 2.41; 7.00 ± 2.19; P = 0.001); meibomian gland dysfunction (26.42 ± 6.04; 9.21 ± 2.55; P = 0.001); cataract extraction (38.00 ± 19.62; 25.83 ± 11.49; P = 0.043); drug induced (53.19 ± 18.83; 41.86 ± 23.87; P = 0.018) and exposure (38.25 ± 14.13; 29.00 ± 13.67; P = 0.026). LC density was 38.70 ± 9.65 cells/mm² in the T2DM group comparedwith 25.53 ± 3.54 cells/mm² in the controls (P = 0.001). SBN density was 11.76 ± 1.69 mm/mm² in the T2DM group compared with 20.92 ± 1.43 mm/mm² in the controls (P = 0.001). BEC density in the T2DM group was 4982 ± 1178 cells/mm² compared with 5739 ± 394 cells/mm² in the control group (P = 0.018). Age and duration of T2DM had no relationship with healing time (multiple linear regression, P = 0.618; P = 0.787). The density of LC in the T2DM group showed a negative correlation with SBN density (r = 0.350; R² = 0.1225; P = 0.034). The density of SBN in the T2DM group showed a positive correlation with BEC density (r = 0.427; R² = 0.1823; P = 0.008). The density of BEC in the T2DM group showed a negative correlation with healing time (r = 0.931; R² = 0.8668; P = 0.001).

Conclusions

Utilising IVCM, we have demonstrated increased LC and decreased SBN in patients with T2DM and CPE. Both may be related to lower BEC density and nuclei enhanced reflection. Furthermore, decreased BEC density may lead to delay in cornea epithelium healing in the T2DM group comparedwith controls. An immune-mediated response may play a role in delayed wound closure in patients with T2DM.

Early central and peripheral corneal microstructural changes in type 2 diabetes mellitus patients identified using in vivo confocal microscopy: A case-control study

The aim of this study was to find early central and peripheral corneal microstructural changes in healthy subjects and type 2 diabetes mellitus (T2DM) patients with/without cornea fluorescein dot staining.This is a prospective case-control study of T2DM patients with/without cornea fluorescein dot staining. Age, sex, duration of diabetes, and serum glycosylated hemoglobin A1c (HbA1c) levels were recorded. Keratograph 5 M (K5 M) and in vivo confocal microscopy were performed on all subjects. The cornea was divided into 5 zones: central, superior, temporal, nasal, and inferior. Basal epithelial cell (BEC) density, the area of BEC, sub-basal nerve plexus (SBN) density, Langerhans cell (LC), and endothelial cell (EC) density were quantitatively analyzed.This study included a total of 87 individuals (28 males and 59 females; mean age, 62.30 ± 9.93 years) with T2DM, without (n = 48; T2DM group 1) and with (n = 39; T2DM group 2) cornea fluorescein staining, as well as 51 age- and sex-matched healthy subjects (18 males and 33 females; mean age, 61.53 ± 10.15 years). Ocular Surface Disease Index scores, Schirmer Ι test, tear meniscus height, the first breakup of tear film occurrence (NIKBUT-first), and the average time of all breakup incidents (NIKBUT-average) values were significantly lower for the T2DM groups than for the healthy group. The corneal sensations of all cornea positions in the T2DM groups were significantly different from the control group. The HbA1c in the T2DM groups showed a negative correlation with central BEC density (R = 0.348, P = .015; R = 0.91, P = .001); there was no correlation of HbA1c with BEC density in the control group. The BEC density, the area of BEC, SBN, and LC density of T2DM group 1 and T2DM group 2 were significantly different compared with the control group in all corneal positions (P < .001). The BEC density of T2DM group 2 was significantly different from T2DM group 1 in the central (P = .044) and inferior (P = .013) zones. The area of BEC in T2DM group 2 was significantly different from T2DM group 1 in inferior zone (P = .014) and other corneal positions showed was no significant difference (P > .05). The SBN density of T2DM group 2 was not significantly different from T2DM group 1 in all corneal positions (P > .05). The LC density of T2DM group 2 was significantly different from T2DM group 1 in the central (P = .006) and inferior (P = .006) zones. Although the LC density in the T2DM groups showed no significant difference in all corneal zones (P > .05), the LC density in the central zone was significantly lower compared with the peripheral zone in the control group (P = .001). The central ECs in the 3 groups were not significantly different (P > .05).LC induced an immune-mediated contribution to corneal nerve damage and may influence the early stages of BEC proliferation and differentiation in T2DM. BEC density was the reliable index for evaluating the early condition of diabetic corneal epitheliopathy. The BEC density of the central and inferior corneal zones was more sensitive.

Objective Evaluation of Corneal and Lens Clarity in Children With Type 1 Diabetes Mellitus

PURPOSE

To investigate whether abnormal glucose metabolism and duration of diabetes mellitus (DM) affected the corneal and lens clarity in children with well-controlled type 1 DM and to compare the results obtained with those in healthy children.

DESIGN

Cross-sectional prospective study.

METHODS

This multicenter study enrolled 56 patients with DM and 51 control subjects. The duration of DM and the glycosylated hemoglobin (HbA1c) levels of the patients in the DM group were recorded. The Pentacam HR imaging system was used for corneal densitometry (12-mm corneal diameter) measurements. Furthermore, the lens densitometry and lens thickness (LT) measurements were performed after dilation of the pupils, using the same Pentacam HR device.

RESULTS

The corneal densitometry values were similar in all concentric zones and layers in both groups (P > .05, for all). The mean values of the average and maximum lens densitometry measurements of the 2 groups, as well as the mean LT values, were statistically significantly different (P = .021, P = .011, and P < .001, respectively). There were statistically significant correlations between the lens densitometry values and the duration of DM (P < .05, for all). Conversely, no statistically significant relationship was found between the lens densitometry values and HbA1c levels (r = 0.743; P = .084).

CONCLUSIONS

The children with type 1 DM had decreased lens clarity and increased LT, even in cases of well-controlled DM, without DR. It is reasonable to think that these changes might have been caused by the type 1 DM.

Diabetic complications in the cornea

Diabetic corneal alterations, such as delayed epithelial wound healing, edema, recurrent erosions, neuropathy/loss of sensitivity, and tear film changes are frequent but underdiagnosed complications of both type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes mellitus. The disease affects corneal epithelium, corneal nerves, tear film, and to a lesser extent, endothelium, and also conjunctiva. These abnormalities may appear or become exacerbated following trauma, as well as various surgeries including retinal, cataract or refractive. The focus of the review is on mechanisms of diabetic corneal abnormalities, available animal, tissue and organ culture models, and emerging treatments. Changes of basement membrane structure and wound healing rates, the role of various proteinases, advanced glycation end products (AGEs), abnormal growth and motility factors (including opioid, epidermal, and hepatocyte growth factors) are analyzed. Experimental therapeutics under development, including topical naltrexone, insulin, inhibitors of aldose reductase, and AGEs, as well as emerging gene and cell therapies are discussed in detail.

Establishment of a 3D In Vitro Model to Accelerate the Development of Human Therapies against Corneal Diabetes

PURPOSE

To establish an in vitro model that would mirror the in vivo corneal stromal environment in diabetes (DM) patients.

METHODS

Human corneal fibroblasts from Healthy (HCFs), Type 1DM (T1DM) and Type 2DM (T2DM) donors were isolated and cultured for 4 weeks with Vitamin C stimulation in order to allow for extracellular matrix (ECM) secretion and assembly.

RESULTS

Our data indicated altered cellular morphology, increased cellular migration, increased ECM assembly, and severe mitochondrial damage in both T1DM and T2DMs when compared to HCFs. Furthermore, we found significant downregulation of Collagen I and Collagen V expression in both T1DM and T2DMs. Furthermore, a significant up regulation of fibrotic markers was seen, including α-smooth muscle actin in T2DM and Collagen III in both T1DM and T2DMs. Metabolic analysis suggested impaired Glycolysis and Tricarboxylic acid cycle (TCA) pathway.

CONCLUSION

DM has significant effects on physiological and clinical aspects of the human cornea. The benefits in developing and fully characterizing our 3D in vitro model are enormous and might provide clues for the development of novel therapeutics.

Splitting of the Recipient's Descemet Membrane in Descemet Membrane Endothelial Keratoplasty-Ultrastructure and Clinical Relevance

PURPOSE

In Descemet membrane endothelial keratoplasty (DMEK), lamellar splitting of the Descemet membrane (DM) may occur during stripping of host DM, leaving residual DM on the recipient's DMEK interface. The purpose of this study was to determine the incidence rate of lamellar splitting of DM during DMEK and to describe the ultrastructure of DM in these eyes.

DESIGN

Retrospective consecutive case series.

METHODS

setting: Institutional, single-center.

PATIENT POPULATION

Total of 664 eyes with Fuchs endothelial corneal dystrophy (FECD) scheduled for primary DMEK.

INTERVENTION

DMEK.

MAIN OUTCOME MEASURES

The incidence rate of lamellar DM splitting in the recipients' eyes; ultrastructural alterations of stripped DM specimens (transmission electron microscopy); preoperative best-corrected visual acuity (BCVA), central corneal thickness (CCT), and prevalence of diabetes mellitus.

RESULTS

Sixty-three of 664 eyes (9.5%) with FECD showed lamellar splitting of DM resulting in the dissociation of 2 separate layers. Transmission electron microscopy revealed accumulations of banded and wide-spaced collagen between the thicker posterior banded layer and the thin anterior banded layer, which is adhesive to the corneal stroma. Lamellar splitting occurred along these abnormal collagen inclusions, demarcating the borderline between both layers of DM.

CONCLUSIONS

Lamellar DM splitting occurs during DM stripping in almost 10% of eyes with FECD. This phenomenon appears to be caused by abnormal collagenous material deposits at the borderline between anterior and posterior layers of DM.

Complete metabolome and lipidome analysis reveals novel biomarkers in the human diabetic corneal stroma

Prolonged hyperglycemia during diabetes mellitus can cause severe ophthalmic complications affecting both the anterior and posterior ocular segments leading to impaired vision or blindness. Diabetes-induced corneal pathologies are associated with decreased wound healing capacity, corneal edema, and altered epithelial basement membrane. The mechanism by which diabetes modulates structure and function within the corneal stroma are unknown. In our study, we characterized the effects of diabetes on extracellular matrix, lipid transport, and cellular metabolism by defining the entire metabolome and lipidome of Type 1 and Type 2 human diabetic corneal stroma. Significant increases in Collagen I and III were found in diabetic corneas suggesting that diabetes promotes defects in matrix structure leading to scarring. Furthermore, increased lipid content, including sphingosine-1-phosphate and dihydrosphingosine, in diabetic corneas compared to healthy controls were measured suggesting altered lipid retention. Metabolomics analysis identified elevated tryptophan metabolites, independent of glucose metabolism, which correlated with upregulation of the Kynurenine pathway in diabetic corneas. We also found significant upregulation of novel biomarkers aminoadipic acid, D,L-pipecolic acid, and dihydroorotate. Our study links aberrant tryptophan metabolism to end-stage pathologies associated with diabetes indicating the potential of the Kynurenine pathway as a therapeutic target for inhibiting diabetes-associated defects in the eye.

Influence of Ultrastructural Corneal Graft Abnormalities on the Outcome of Descemet Membrane Endothelial Keratoplasty

PURPOSE

To investigate if ultrastructural alterations in the Descemet membrane (DM) are correlated with the clinical outcome after Descemet membrane endothelial keratoplasty (DMEK).

DESIGN

Retrospective cohort study.

METHODS

setting: Institutional, single-center.

STUDY POPULATION

One hundred and twelve residual DM specimens obtained after DM stripping.

MAIN OUTCOME MEASURES

Incidence of ultrastructural abnormalities in transmission electron microscopy, graft detachment rate, graft failure rate, best-corrected visual acuity (BCVA), endothelial cell density (ECD), and central corneal thickness (CCT). Examination dates were on the day before DMEK and 1, 3, 6, and 12 months after surgery.

RESULTS

Abnormalities in the ultrastructure of DM were found in 16 of 112 specimens (14%) (abnormal DM group), comprising deposits of long-spacing collagen, fine filaments (proteoglycans), a posterior collagenous layer, pseudoexfoliative material, and guttae. The secondary graft failure rate was significantly higher in the abnormal DM group compared with the normal DM group (P = .001). There was a trend for an increased graft detachment rate in the abnormal DM group (11/16) compared with the normal DM group (42/96) (P = .103). There was no significant difference in mean CCT and ECD after surgery. Mean CCT in the eyes with graft failure in the abnormal DM group at the last follow-up before regrafting was 850 μm, indicating endothelial failure with stromal edema.

CONCLUSION

This study reveals a correlation between ultrastructural alterations of DM in donor corneas and the graft failure rate after DMEK. Thus, graft failure after DMEK not only is determined by surgical trauma and postoperative events but may also be influenced by intrinsic, graft-specific features.

Early bone anchorage to micro- and nano-topographically complex implant surfaces in hyperglycemia

The aim of this work was to investigate the effect of implant surface design on early bone anchorage in the presence of hyperglycemia. 108 Wistar rats were separated into euglycemic (EG) controls and STZ-treated hyperglycemic (HG) groups, and received bilateral femoral custom rectangular implants of two surface topographies: grit blasted (GB) and grit-blast with a superimposed calcium phosphate nanotopography (GB-DCD). The peri-implant bone was subjected to a tensile disruption test 5, 7, and 9days post-operatively (n=28/time point); the force was measured; and the residual peri-implant bone was observed by scanning electron microscopy (SEM). Disruption forces at 5days were not significantly different from zero for the GB implants (p=0.24) in either metabolic group; but were for GB+DCD implants in both metabolic groups (p<0.001). Contact osteogenesis was greater on GB-DCD than the GB surface. The nano-and micro-surfaced implants showed significantly different disruption forces at all time points (e.g. >15N and <5N respectively at 9days). Such differences were not seen within the GB implants, as all values were very low (<5N). Even in hyperglycemia the GB-DCD surface outperformed the GB surfaces in both metabolic groups. Significantly, SEM of peri-implant bone showed compromised intra-fibrillar collagen mineralization in hyperglycemia, while inter-fibrillar and cement line mineralization remained unaffected. Enhanced bone anchorage to the implant surfaces was observed on the nanotopographically complex surface independent of metabolic group. The compromised intra-fibrillar mineralization observed provides a mechanism by which early bone mineralization is affected in hyperglycemia.

STATEMENT OF SIGNIFICANCE

It is generally accepted that the hyperglycemia associated with diabetes mellitus compromises bone quality, although the mechanism by which this occurs is unknown. Uncontrolled hyperglycemia is therefore a contra-indication for bone implant placement. It is also known that nano-topographically complex implant surfaces accelerate early peri-implant healing. In this report we show that, in our experimental model, nano-topographically complex surfaces can mitigate the compromised bone healing seen in hyperglycemia. Importantly, we also provide a mechanistic explanation for compromised bone quality in hyperglycemia. We show that intra-fibrillar collagen mineralization is compromised in hyperglycemia, but that interfibrillar and cement line mineralization, remain unaffected.

Hyperglycemia-suppressed expression of Serpine1 contributes to delayed epithelial wound healing in diabetic mouse corneas

PURPOSE

Patients with diabetes mellitus (DM) are at an increased risk for developing corneal complications, including delayed wound healing. The purpose of this study was to characterize the expression and the function of Serpine1 and other components of urokinase plasminogen activator (uPA)-proteolytic system in delayed epithelial wound healing in diabetic mouse corneas.

METHODS

Mice of the strain C57BL/6 were induced to develop diabetes by streptozotocin, and wound-healing assays were performed 10 weeks afterward. Gene expression and/or distribution were assessed by real-time PCR, Western blotting, and/or immunohistochemistry. The role of Serpine1 in mediating epithelial wound closure was determined by subconjunctival injections of neutralizing antibodies in either normal or recombinant protein in diabetic corneas. Enzyme assay for matrix metalloproteinase (MMP)-3 was also performed.

RESULTS

The expressions of Serpine1 (PAI-1), Plau (uPA), and Plaur (uPA receptor) were upregulated in response to wounding, and these upregulations were significantly suppressed by hyperglycemia. In healing epithelia, Plau and Serpine1 were abundantly expressed at the leading edge of the healing epithelia of normal and, to a lesser extent, diabetic corneas. Inhibition of Serpine1 delayed epithelial wound closure in normal corneas, whereas recombinant Serpine1 accelerated it in diabetic corneas. The Plau and MMP-3 mRNA levels and MMP-3 enzymatic activities were correlated to Serpine1 levels and/or the rates of epithelial wound closure.

CONCLUSIONS

Serpine1 plays a role in mediating epithelial wound healing and its impaired expression may contribute to delayed wound healing in DM corneas. Hence, modulating uPA proteolytic pathway may represent a new approach for treating diabetic keratopathy.

Sensory nerve regeneration after epithelium wounding in normal and diabetic cornea

The cornea is the most densely innervated mammalian tissue. The sensory nerves are responsible for sensations of dryness, temperature, touch, and pain, and play important roles in the blink reflex, wound healing, and tear production. Many ocular and systemic diseases can adversely affect corneal sensory nerve and consequently impair their function. One of such systemic diseases is diabetes mellitus (DM) which causes sensory degeneration, neurotrophic keratopathy (DNK), and delayed wound healing. In this review, we summarize recent discoveries revealing mechanisms underlying the pathogenesis of DNK and the impairment of sensory nerve regeneration in post wound diabetic corneas in using animal model of human diabetes. Because it is generally believed that common mechanisms are operative in the pathogenesis of diabetic peripheral neuropathy in different tissues, the findings in the corneas have implications in in other tissues such as the skin, which often leads to foot ulceration and amputation in diabetic patients.

Substance P promotes diabetic corneal epithelial wound healing through molecular mechanisms mediated via the neurokinin-1 receptor

Substance P (SP) is a neuropeptide, predominantly released from sensory nerve fibers, with a potentially protective role in diabetic corneal epithelial wound healing. However, the molecular mechanism remains unclear. We investigated the protective mechanism of SP against hyperglycemia-induced corneal epithelial wound healing defects, using type 1 diabetic mice and high glucose-treated corneal epithelial cells. Hyperglycemia induced delayed corneal epithelial wound healing, accompanied by attenuated corneal sensation, mitochondrial dysfunction, and impairments of Akt, epidermal growth factor receptor (EGFR), and Sirt1 activation, as well as decreased reactive oxygen species (ROS) scavenging capacity. However, SP application promoted epithelial wound healing, recovery of corneal sensation, improvement of mitochondrial function, and reactivation of Akt, EGFR, and Sirt1, as well as increased ROS scavenging capacity, in both diabetic mouse corneal epithelium and high glucose-treated corneal epithelial cells. The promotion of SP on diabetic corneal epithelial healing was completely abolished by a neurokinin-1 (NK-1) receptor antagonist. Moreover, the subconjunctival injection of NK-1 receptor antagonist also caused diabetic corneal pathological changes in normal mice. In conclusion, the results suggest that SP-NK-1 receptor signaling plays a critical role in the maintenance of corneal epithelium homeostasis, and that SP signaling through the NK-1 receptor contributes to the promotion of diabetic corneal epithelial wound healing by rescued activation of Akt, EGFR, and Sirt1, improvement of mitochondrial function, and increased ROS scavenging capacity.

A pilot study on total, corneal, and internal aberrations in insulin-dependent and non-insulin-dependent diabetes mellitus patients

PURPOSE

To explore the distribution of total, corneal, and internal higher-order aberrations (HOAs) in both insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetic patients.

METHODS

Pilot study including seven patients with IDDM (14 eyes) and 11 patients with NIDDM (22 eyes). Ocular HOAs were examined using ray tracing aberrometry (i-Trace, Tracey Technologies Corp., Houston, TX) and the measurements of anterior segment using Scheimpflug imaging (Pentacam, Oculus Inc. Germany).

RESULTS

Total HOAs was slightly higher in IDDM (0.634 ± 0.228 μm, 95% IC ± 0.131) than in NIDDM patients (0.527 ± 0.245 μm, 95% IC ± 0.108) (p = 0.267). The greatest contributor for total ocular HOAs was internal vertical coma (Z3 (- 1)) for both diabetic groups. In NIDDM, age and central corneal thickness (CCT) were correlated with total HOAs (p < 0.001, p = 0.0180 respectively); however, anterior chamber volume (ACV) was inversely correlated with total HOAs (p = 0.019). In IDDM, total HOAs were correlated with posterior asphericity (Q) (p = 0.002) and inversely correlated with ageing (p = 0.013).

CONCLUSIONS

Diabetic patients showed high values of total and internal vertical coma (Z3 (- 1)). There might be a role for optical quality measurements in monitoring changes due to DM.

Optical quality of the diabetic eye: a review

Diabetes mellitus is a metabolic disorder characterized by the presence of chronic hyperglycaemia. Several structural, morphological, and physiological changes in each of ocular component have been described in detail during the past decades. Due to these abnormalities, the diabetic patient undergoes a degradation of the retinal image by an increase of higher ocular aberrations and ocular scattering coming from mainly tear film, cornea, and crystalline lens. This review aims to provide an overview of current knowledge about the effects of diabetes mellitus in these optical phenomena and its consequence on the visual quality of the diabetic patient.

Corneal nerve fibre damage precedes diabetic retinopathy in patients with type 2 diabetes mellitus

AIMS

To quantify the morphological alterations in corneal nerve fibres and cells in patients with type 2 diabetes mellitus in relation to the severity of diabetic retinopathy.

METHODS

One hundred and thirty-two eyes of 132 patients with type 2 diabetes and 32 eyes of 32 healthy control subjects were evaluated with in vivo corneal confocal microscopy. Patients with diabetes were classified into three groups: patients without diabetic retinopathy, patients with non-proliferative diabetic retinopathy and patients with proliferative diabetic retinopathy. Anterior and posterior stromal keratocyte, endothelial cell and basal epithelial cell densities and sub-basal nerve fibre structure were evaluated.

RESULTS

Significant reductions in basal epithelial cell, anterior stromal keratocyte and endothelial cell densities were observed only in patients with diabetic retinopathy. However, nerve fibre density, nerve branch density and nerve fibre length were reduced in patients without diabetic retinopathy and worsened progressively with increasing severity of retinopathy.

CONCLUSIONS

Corneal cell pathology occurs in patients with diabetic retinopathy, but corneal nerve fibre damage seems to precede the development of diabetic retinopathy.

Age-related dystrophic changes in corneal endothelium from DNA repair-deficient mice

The corneal endothelium (CE) is a single layer of cells lining the posterior face of the cornea providing metabolic functions essential for maintenance of corneal transparency. Adult CE cells lack regenerative potential, and the number of CE cells decreases throughout life. To determine whether endogenous DNA damage contributes to the age-related spontaneous loss of CE, we characterized CE in Ercc1(-/Δ) mice, which have impaired capacity to repair DNA damage and age prematurely. Eyes from 4.5- to 6-month-old Ercc1(-/Δ) mice, age-matched wild-type (WT) littermates, and old WT mice (24- to 34-month-old) were compared by spectral domain optical coherence tomography and corneal confocal microscopy. Histopathological changes in CE were further identified in paraffin tissue sections, whole-mount immunostaining, and scanning electron and transmission electron microscopy. The CE of old WT mice displayed polymorphism and polymegathism, polyploidy, decreased cell density, increased cell size, increases in Descemet's thickness, and the presence of posterior projections originating from the CE toward the anterior chamber, similar to changes documented for aging human corneas. Similar changes were observed in young adult Ercc1(-/Δ) mice CE, demonstrating spontaneous premature aging of the CE of these DNA repair-deficient mice. CD45(+) immune cells were associated with the posterior surface of CE from Ercc1(-/Δ) mice and the tissue expressed increased IL-1α, Cxcl2, and TNFα, pro-inflammatory proteins associated with senescence-associated secretory phenotype. These data provide strong experimental evidence that DNA damage can promote aging of the CE and that Ercc1(-/Δ) mice offer a rapid and accurate model to study CE pathogenesis and therapy.

Dry eye and its correlation to diabetes microvascular complications in people with type 2 diabetes mellitus

AIMS

This study was performed to investigate the correlation between dry eye disease and diabetes microvascular complications.

METHODS

In this study 243 people with type 2 diabetes were enrolled. Tear osmolarity was measured using tear lab osmolarity system. All of the participants were evaluated for diabetes microvascular complications. The Michigan neuropathy screening instrument was used for detection of peripheral neuropathy, and the albumin/creatinine ratio in a spot urine sample was considered to diagnose diabetic nephropathy.

RESULTS

The prevalence of dry eye disease was 27.7%. The mean value for tear osmolarity was 301.97±13.52 mOsm/L. We found a significant correlation between dry eye disease and diabetic retinopathy (P=0.01). However no significant correlation was found between dry eye disease, diabetic neuropathy, and diabetic nephropathy. Dry eye disease was more prevalent in people with proliferative diabetic retinopathy and/or clinically significant macular edema (0.006). In a binary logistic regression analysis model, there was a significant correlation between dry eye disease and retinopathy (OR=2.29, CI=1.16-4.52, P=0.016). In addition, both dry eye and retinopathy had significant correlation with HbA1C.

CONCLUSIONS

Dry eye disease is common in people with type 2 diabetes, especially in those with diabetic retinopathy. In addition, it is more prevalent in people who suffer from advanced stages of diabetic retinopathy.

Advanced glycation end products and ultrastructural changes in corneas of long-term streptozotocin-induced diabetic monkeys

PURPOSE

The purpose of this study was to investigate the ultrastructural corneal changes of chronic diabetic monkeys and explore the relationship between advanced glycation end products and ultrastructural changes in diabetic corneas.

METHODS

A total of 8 cynomolgus monkeys were used in this experiment. Four monkeys were induced into insulin-dependent diabetes mellitus for 4 years. Four age-matched healthy monkeys were used as the controls. Ultrathin sections obtained from the corneas were examined by transmission electron microscopy.

RESULTS

Advanced glycation end product immunoreactivity was observed in the epithelial cells, epithelial basement membrane, and stromal keratocytes of diabetic corneas, whereas advanced glycation end product immunoreactivity was not found in the corresponding area in normal corneas. Abnormal collagen fibril bundles of variable thickness were identified in corneal stroma in all diabetic monkeys. Epithelial and endothelial cell degeneration was also observed in 1 diabetic monkey.

CONCLUSIONS

Abnormal aggregates of collagen fibrils in stromal matrix were common among long-term diabetic monkeys, and the formation of the abnormal collagen fibril aggregates might result from excessive nonenzymatic glycosylation.

Multimodal Highlighting of Structural Abnormalities in Diabetic Rat and Human Corneas

PURPOSE

This study aimed to highlight structural corneal changes in a model of type 2 diabetes, using in vivo corneal confocal microscopy (CCM). The abnormalities were also characterized by transmission electron microscopy (TEM) and second harmonic generation (SHG) microscopy in rat and human corneas.

METHODS

Goto-Kakizaki (GK) rats were observed at age 12 weeks (n = 3) and 1 year (n = 6), and compared to age-matched controls. After in vivo CCM examination, TEM and SHG microscopy were used to characterize the ultrastructure and the three-dimensional organization of the abnormalities. Human corneas from diabetic (n = 3) and nondiabetic (n = 3) patients were also included in the study.

RESULTS

In the basal epithelium of GK rats, CCM revealed focal hyper-reflective areas, and histology showed proliferative cells with irregular basement membrane. In the anterior stroma, extracellular matrix modifications were detected by CCM and confirmed in histology. In the Descemet's membrane periphery of all the diabetic corneas, hyper-reflective deposits were highlighted using CCM and characterized as long-spacing collagen fibrils by TEM. SHG microscopy revealed these deposits with high contrast, allowing specific detection in diabetic human and rat corneas without preparation and characterization of their three-dimensional organization.

CONCLUSION

Pathologic findings were observed early in the development of diabetes in GK rats. Similar abnormalities have been found in corneas from diabetic patients.

TRANSLATIONAL RELEVANCE

This multidisciplinary study highlights diabetes-induced corneal abnormalities in an animal model, but also in diabetic donors. This could constitute a potential early marker for diagnosis of hyperglycemia-induced tissue changes.

Hyperglycemia-induced abnormalities in rat and human corneas: the potential of second harmonic generation microscopy

Background

Second Harmonic Generation (SHG) microscopy recently appeared as an efficient optical imaging technique to probe unstained collagen-rich tissues like cornea. Moreover, corneal remodeling occurs in many diseases and precise characterization requires overcoming the limitations of conventional techniques. In this work, we focus on diabetes, which affects hundreds of million people worldwide and most often leads to diabetic retinopathy, with no early diagnostic tool. This study then aims to establish the potential of SHG microscopy for in situ detection and characterization of hyperglycemia-induced abnormalities in the Descemet’s membrane, in the posterior cornea.

Methodology/Principal Findings

We studied corneas from age-matched control and Goto-Kakizaki rats, a spontaneous model of type 2 diabetes, and corneas from human donors with type 2 diabetes and without any diabetes. SHG imaging was compared to confocal microscopy, to histology characterization using conventional staining and transmitted light microscopy and to transmission electron microscopy. SHG imaging revealed collagen deposits in the Descemet’s membrane of unstained corneas in a unique way compared to these gold standard techniques in ophthalmology. It provided background-free images of the three-dimensional interwoven distribution of the collagen deposits, with improved contrast compared to confocal microscopy. It also provided structural capability in intact corneas because of its high specificity to fibrillar collagen, with substantially larger field of view than transmission electron microscopy. Moreover, in vivo SHG imaging was demonstrated in Goto-Kakizaki rats.

Conclusions/Significance

Our study shows unambiguously the high potential of SHG microscopy for three-dimensional characterization of structural abnormalities in unstained corneas. Furthermore, our demonstration of in vivo SHG imaging opens the way to long-term dynamical studies. This method should be easily generalized to other structural remodeling of the cornea and SHG microscopy should prove to be invaluable for in vivo corneal pathological studies.

Laser refractive surgery in diabetic patients: a review of the literature

BACKGROUND

The purpose of this study was to evaluate the current recommendations regarding laser refractive surgery in patients with diabetes mellitus and to assess whether these patients make appropriate candidates for laser vision correction.

METHODS

A literature search was conducted to identify current research on the ocular complications of diabetes and original publications on laser refractive surgery in diabetic patients.

RESULTS

Diabetes was associated with several ocular complications. Initially the US Food and Drug Administration listed these complications as justification to advise against refractive surgery in patients with diabetes. However, recent studies on laser in situ keratomileusis in diabetic patients indicate that this procedure may be safe in diabetic patients with very well controlled systemic disease and no ocular manifestations.

CONCLUSION

Laser refractive surgery may be performed safely in a very selected group of patients with diabetes.

Exogenous endophthalmitis in diabetic patients: a systemic review

Diabetes mellitus is a systemic disease that increases the risk of infections. Exogenous endophthalmitis is an inflammatory disease to which diabetic patients are more predisposed to than nondiabetic patients undergoing any intraocular intervention. This might be because of the change in the immune and inflammatory factors that intervene in wound healing and in the bacterial flora of the ocular adnexa. We conducted a literature review to assess the risk of exogenous endophthalmitis in diabetic patients undergoing cataract extraction, pars plana vitrectomy, and intravitreal injections and to check whether its treatment differ from in non-diabetics. We found that diabetic patients are more predisposed to virulent organisms and that the incidence of ophthalmic symptoms was not substantially different in diabetic versus nondiabetic patients. Regarding treatment, all patients with light perception should receive pars plana vitrectomy, while those with hand motion and better vision should be given an intravitreal antibiotics injection. Some authors recommend vitrectomy to diabetic patients with even counting figure vision.

Reduced innervation and delayed re-innervation after epithelial wounding in type 2 diabetic Goto-Kakizaki rats

Patients with diabetes are at an increased risk for developing corneal complications including delayed wound healing and potential vision loss. To understand the cause of diabetic keratopathy, we investigated innervation and its correlation with delayed corneal epithelial wound healing in type 2 diabetic Goto-Kakizaki (GK) rats. GK rats are smaller than the age-matched control Wistar rats from which the GK rats were derived. The blood sugar levels of GK rats are significantly higher than those of Wistar rats. GK rats had increased rose bengal staining and cornea fragility. Fewer nerve fibers were detected compared with Wistar rats. Although nerve fiber densities detected by whole-mount immunohistochemistry were similar near the limbal region, in the central cornea the subbasal nerve plexuses were thinner, less abundant, and showed less branching in GK rats. Corneal epithelial wound closure was delayed and re-innervation was slow and incomplete in GK rats. These abnormalities were more apparent in older GK rats (12 months). Our data suggest that diabetic neuropathy occurs in the cornea of type 2 diabetic GK rats, and defects in the sensory nerve and/or tear film may contribute to diabetic keratopathy and delayed epithelial wound healing in diabetic corneas.

Mapping the nerve architecture of diabetic human corneas

OBJECTIVE

To investigate the entire human corneal nerve architecture of donors with different durations of insulin-dependent diabetes mellitus (IDDM).

DESIGN

Experimental study.

PARTICIPANTS AND CONTROLS

Sixteen fresh human eyes from 8 diabetic donors (aged 43-66 years, with IDDM for 2-17 years) and 12 eyes from 6 normal donors (aged from 44-67 years) were obtained from the National Disease Research Interchange (NDRI).

METHODS

After fixation, corneas were stained with mouse monoclonal anti-β-Tubulin III antibody, and images were acquired to build a whole view of the corneal nerve architecture. The same corneas were used for both whole-mount and cross-section examination.

MAIN OUTCOME MEASURES

Corneal epithelial nerve density was calculated on the basis of the whole-mount view of the central area. The number of stromal nerves was calculated by counting the nerve trunks at the corneoscleral limbus of the entire cornea. Differences between diabetic and normal corneas in epithelial nerve densities and main stromal nerve numbers were compared by paired-samples t test.

RESULTS

The diabetic eyes presented numerous neuropathies in areas where the epithelial nerve bundles emerged. A striking pathologic change was the presence of abundant nerve fiber loops in the stroma. These loops seemed to form by resistance presented by the basement membrane, which may prevent penetration of stromal nerve branches into epithelia. There was no difference in the numbers of main stromal nerve trunks between corneas from diabetic and normal donors, but there was a significant decrease in central epithelial nerve density in the diabetic corneas. We did not find an age effect on this decrease. Instead, it was significantly affected by 5 or more years of IDDM.

CONCLUSIONS

This is the first study to show an entire view of the nerve architecture in human diabetic corneas. The decreased epithelial nerve density may result from the abnormalities of stromal nerve architecture and is affected by 5 or more years of IDDM. Although compensation for some nerve regeneration takes place, the alterations in the stromal nerves can explain the poor healing and persistent epithelial defects seen in diabetic patients.

Impaired epithelial wound healing and EGFR signaling pathways in the corneas of diabetic rats

PURPOSE. The purpose of the study was to investigate the effects of hyperglycemia on EGFR (epidermal growth factor receptor)-mediated wound response and signal transduction in the corneal epithelium of rats with type I diabetes mellitus (DM). METHODS. Corneal epithelia were removed from streptozotocin (STZ)- and weight-matched normal rats. Wound healing was monitored by fluorescein staining at 24 or 48 hours after epithelial debridement. Phosphorylation of EGFR, AKT, ERK, and BAD was determined by Western blot analysis. The distribution of phospho-AKT and proliferating cell nuclear antigen (PCNA) in rat corneas was examined by immunohistochemistry. Cell death was evaluated by TUNEL staining. RESULTS. A significant delay in corneal epithelial wound healing was observed 48 hours after wounding in the diabetic rats compared with the weight-matched control rats. In the DM rat corneas, epithelial cells demonstrated diminished responses to wounding, as assessed by the phosphorylation of EGFR and its downstream signaling molecules, AKT and ERK. Furthermore, although the distribution pattern of phospho-AKT suggested a role for AKT in epithelial migration and proliferation in the normoglycemic rat corneas, it was abrogated in the healing epithelia of the DM rats. Consistent with impaired AKT activity, the number of PCNA-stained cells was also greatly reduced in the healing corneas of the diabetic rats. Finally, decreases in pBAD (Ser(136) and Ser(112)) and increases in TUNEL-positive cells were observed in both the uninjured and healing corneal epithelia of the DM rats, but not of the control rats. CONCLUSIONS. In the corneas of SZT rats, EGFR-PI3K-AKT and ERK, as well as their downstream BAD signaling pathways in migratory epithelium, were altered, resulting in increased apoptosis, decreased cell proliferation, and delayed wound closure.

Corneal biomechanical characteristics in patients with diabetes mellitus

PURPOSE

To compare the corneal biomechanical properties in eyes of patients with diabetes mellitus and in those of subjects without diabetes mellitus.

SETTING

Hospital eye clinic.

DESIGN

Comparative case series.

METHODS

Corneal hysteresis (CH) and corneal response factor (CRF) were measured in diabetic patients and nondiabetic subjects using the Ocular Response Analyzer. Central corneal thickness (CCT) and intraocular pressure (IOP) were also measured. Differences in corneal biomechanical properties were determined using a 1-way analysis of variance. Interassociations between ocular and diabetic parameters were also evaluated.

RESULTS

Sixty-one eyes of 61 diabetic patients and 123 eyes of 123 nondiabetic subjects were evaluated. The CRF was significantly greater in the eyes of diabetic patients (mean difference, 1.09 mm Hg; 95% confidence interval [CI], 0.49-1.69; P = .001). There were no significant differences in CCT or CH between groups (CH: mean difference, 0.38 mm Hg; 95% CI, -0.21 to 0.97 mm Hg; P = .21; CCT: mean difference, 0.13 μm; 95% CI, -10.6 to 10.8 μm; P =.98). Corneal hysteresis and CRF were weakly correlated with blood glucose concentration (slopes: CH: 0.28; 95% CI, 0.03-0.50; P = .03; CRF: 0.27; 95% CI 0.02-0.49; P = .04). In a multiple regression analysis, the effects of blood glucose concentration were reduced and age and CCT became significant predictors of CH and CRF.

CONCLUSIONS

The eyes in diabetic patients displayed altered corneal biomechanics that may be related to blood glucose concentration. Further studies are required to establish the effects of long-term poor glucose control on corneal biomechanical properties and how this might affect the diabetic patient's response to refractive surgery procedures.

In vivo confocal microscopy of corneal small fiber damage in diabetes mellitus

BACKGROUND

Advanced diabetic keratopathy includes impaired corneal sensation, reduced tear secretion, conjunctival squamous metaplasia, and goblet cell loss, as well as susceptibility to corneal erosions and ulcerations. It is thought to be a form of generalized diabetic neuropathy. Early diagnosis of nerve fiber degeneration is essential to prevent further damage.

METHODS

We examined the corneal innervation pattern of patients with diabetes mellitus type 1 and 2 of various durations by in vivo confocal microscopy, and correlated our findings to the severity of diabetic retinopathy, corneal sensation, peripheral diabetic neuropathy in the lower limb, and nephropathy.

RESULTS

Nerve fiber length (NFL) was significantly different between patients without diabetic retinopathy and controls (p = 0.028). In patients with non-proliferative diabetic retinopathy (NPDR) and patients with proliferative diabetic retinopathy (PDR), nerve fiber parameters including density (NFD), NFL, and corneal nerve branching (NB) showed a difference with increasing significance compared to healthy persons. A history of nephropathy and/or peripheral neuropathy (all p < 0.001), decreased corneal sensation (all p < or = 0.03), and pathological vibration sensation (p < or = 0.04) were significantly associated with a decrease in NFD, NFL, and NB (except vibration sensation). Unexpectedly, diabetic patients with normal corneal and vibration sensation demonstrated significant changes in NFD (p = 0.005), NFL, and NB (both p = 0.001) compared to healthy volunteers with intact corneal and vibration sensation.

CONCLUSION

Confocal microscopy is a valuable tool for demonstrating subtle corneal nerve alterations in vivo. It is capable of demonstrating diabetic nerve fiber damage earlier than corneal sensation testing and vibration perception assessment in the lower limb.

Role of epidermal growth factor receptor (EGFR) in corneal remodelling in diabetes

PURPOSE

This study examined the role of epidermal growth factor receptor (EGFR) signalling on the organization and remodelling of collagen fibrils (CFs) and proteoglycans (PGs) in the stroma of diabetic rat cornea.

METHODS

Diabetes was induced in female Wistar rats (n = 5) by streptozotocin (STZ) injection (55 mg/kg). Treatment with a selective inhibitor of EGFR tyrosine kinase, AG1478, was started on the same day as the induction of diabetes and administered every other day for 4 weeks. Corneas were fixed in 4% paraformaldehyde at 4 degrees to allow for analysis of CF diameters and in 2.5% glutaraldehyde in sodium acetate buffer containing cuprolinic blue to enable the study of PG distribution. AnalySIS soft imaging software was used to analyse CFs and PGs.

RESULTS

Epithelial thickness, and median diameter and area fraction of CF in corneal stroma were decreased in diabetic rat cornea compared with normal cornea (p < 0.001), whereas the median PG area and area fractions were significantly increased (p < 0.001). Treatment with AG1478, although it had no action on normal cornea, prevented these diameter and area fraction changes in CFs and PGs. The cornea of AG1478-treated diabetic rats showed a slight increase in CF diameter and area fraction and a decreased number density.

CONCLUSIONS

These data show that the distribution of corneal stroma CFs and PGs was altered after 4 weeks of diabetes and that, furthermore, treatment with an EGFR signalling inhibitor normalized these abnormalities. The data suggest that EGFR plays an important role in the development of diabetes-induced corneal remodelling.

LL-37 via EGFR transactivation to promote high glucose-attenuated epithelial wound healing in organ-cultured corneas

Purpose. Patients with diabetes are at higher risk for delayed corneal reepithelialization and infection. Previous studies indicated that high glucose (HG) impairs epidermal growth factor receptor (EGFR) signaling and attenuates ex vivo corneal epithelial wound healing. The authors investigated the effects of antimicrobial peptide LL-37 on HG-attenuated corneal epithelial EGFR signaling and wound closure. Methods. Human corneal epithelial cells (HCECs) were stimulated with LL-37. Heparin-binding EGF-like growth factor (HB-EGF) shedding was assessed by measuring the release of alkaline phosphatase (AP) in a stable HCEC line expressing HB-EGF-AP. Activation of EGFR, phosphoinositide 3-kinase (PI3K), and extracellular signal-regulated kinases 1/2 (ERK1/2) was determined by Western blot analysis. Corneal epithelial wound closure was assessed in cultured HCECs and porcine corneas. LL-37 expression was determined by immune dot blot. Results. LL-37 induced HB-EGF-AP release and EGFR activation in a dose-dependent manner. LL-37 prolonged EGFR signaling in response to wounding. LL-37 enhanced the closure of a scratch wound in cultured HCECs and partially rescued HG-attenuated wound healing in an EGFR- and a PI3K-dependent manner and restored HG-impaired EGFR signaling in cultured porcine corneas. HG attenuated wounding-induced LL-37 expression in cultured HCECs. Conclusions. LL-37 is a tonic factor promoting EGFR signaling and enhancing epithelial wound healing in normal and high glucose conditions. With both antimicrobial and regenerative capabilities, LL-37 may be a potential therapeutic for diabetic keratopathy.