Effects of diabetic keratopathy on corneal optical density, central corneal thickness, and corneal endothelial cell counts

Diabetic Keratopathy: Redox Signaling Pathways and Therapeutic Prospects

Diabetes mellitus, the most prevalent endocrine disorder, not only impacts the retina but also significantly involves the ocular surface. Diabetes contributes to the development of dry eye disease and induces morphological and functional corneal alterations, particularly affecting nerves and epithelial cells. These changes manifest as epithelial defects, reduced sensitivity, and delayed wound healing, collectively encapsulated in the context of diabetic keratopathy. In advanced stages of this condition, the progression to corneal ulcers and scarring further unfolds, eventually leading to corneal opacities. This critical complication hampers vision and carries the potential for irreversible visual loss. The primary objective of this review article is to offer a comprehensive overview of the pathomechanisms underlying diabetic keratopathy. Emphasis is placed on exploring the redox molecular pathways responsible for the aberrant structural changes observed in the cornea and tear film during diabetes. Additionally, we provide insights into the latest experimental findings concerning potential treatments targeting oxidative stress. This endeavor aims to enhance our understanding of the intricate interplay between diabetes and ocular complications, offering valuable perspectives for future therapeutic interventions.

Corneal optical density: Structural basis, measurements, influencing factors, and roles in refractive surgery

The cornea is the main refractive medium of the human eye, and its clarity is critical to visual acuity. Corneal optical density (COD) is an important index to describe corneal transparency. Intact corneal epithelial and endothelial cells, regular arrangement of collagen fibers in the stroma, and normal substance metabolism are all integral for the cornea to maintain its transparency. In the last two decades, the Pentacam Scheimpflug imaging system has emerged as a breakthrough for the measurement of COD (also called corneal densitometry). It has been found that a wide variety of factors such as age, refractive status, and corneal diseases can affect COD. Different corneal refractive surgery methods also change COD in different corneal regions and layers and affect visual acuity following the surgery. Thus, COD has gradually become a significant indicator to evaluate corneal health, one on which the attention of clinicians has been increasingly focused.

Corneal and lenticular clarity in children with inflammatory disease as assessed by Scheimpflug imaging

BACKGROUND

Corneal and lenticular optical properties are not well-documented in pediatric patients with inflammatory diseases. Here we aimed to evaluate corneal and lenticular optical density as well as corneal morphology in children with ocular and/or systemic inflammation by Scheimpflug imaging.

METHODS

Fifty-five eyes of 29 children with non-infectious uveitis, 56 eyes of 28 children with systemic inflammation without uveitis and 60 eyes of 31 healthy children were included. Corneal/lenticular optical density, corneal volume, central corneal thickness, keratometry were analyzed by Pentacam HR. Corneal endothelial cell density, hexagonal cell ratio and coefficient of variation were measured by specular microscope.

RESULTS

The mean age was 12.0±3.1 years, 11.9±4.0 years and 11.3±3.4 years whereas the female/ratio was 15/14, 15/13 and 14/17 in uveitis, systemic inflammation and control groups respectively. Uveitis type was anterior uveitis in 16 (29.1%) eyes, intermediate uveitis in 32 (58.2%) eyes and panuveitis in 7 (12.7%) eyes. Twenty-two (40%) eyes had active uveitis whereas 33 (60%) eyes had inactive uveitis. Corneal optical density was greater in uveitis group compared with other groups (p=0.001, Kruskal-Wallis test). Lenticular density and corneal parameters other than optical density were not different between the groups (p>0.05). Corneal optical density was higher in active uveitis than inactive uveitis (22/33 eyes, p=0.017).

CONCLUSION

Children with uveitis had decreased corneal clarity compared with systemic inflammation group and healthy controls, while lenticular clarity was similar between the groups. Corneal endothelial parameters did not change significantly based on ocular/systemic inflammation. Scheimpflug imaging provides objective corneal and lenticular optical density measurements.

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.

Improvement of Corneal Nerve Regeneration in Diabetic Rats Using Wharton's Jelly-Derived Mesenchymal Stem Cells and their Conditioned Medium

To investigate the efficacy of Wharton's jelly mesenchymal stem cells (WJSCs) and their conditioned medium (CM) for corneal nerve regeneration in rats with diabetic keratopathy. Streptozotocin (STZ)-induced male diabetic (DM) rats (250-300 g) were divided into four groups (n=7/group): Control, DM, DM with WJSCs (DM+WJ), and DM with CM treatment (DM+CM). DM+WJ and DM+CM group received WJSCs or CM, respectively, topically with eye drops. Corneal sensibility, corneal epithelial layer integrity, histology, expression of GAP-43 and TUBB3 on mRNA level and their immunohistochemical expression were examined after two weeks of treatment. There were changes in corneal sensibility and corneal integrity between normal control and diabetic groups with/without WJSC or CM injection. Total central corneal thickness was significantly higher in DM+CM (249.81 ± 43.85 μm) than in control (174.72 ± 44.12 μm, P=0.004) and DM groups (190.15 ± 9.63 μm, P=0.03). GAP-43 mRNA expression levels of DM+WJ and DM+CM groups were higher compared with DM and control groups. TUBB3 mRNA level was increased after CM (P=0.047), but not after WJSCs treatment (P=1.00). GAP-43 and TUBB3 immunohistochemical expression of nerve fibers along the epithelial layer significantly increased in DM+WJ and DM+CM compared with DM group. Our findings showed that WJSCs and their CM improved corneal nerve regeneration in rats with diabetic keratopathy.

Label-free Raman spectroscopy: A potential tool for early diagnosis of diabetic keratopathy

Diabetes has become a major public health problem worldwide, and the incidence of diabetes has been increasing progressively. Diabetes is prone to cause various complications, among which diabetic keratopathy (DK) emphasizes the significant impact on the cornea. The current diagnosis of DK lacks biochemical markers that can be used for early and non-invasive screening and detection. In contrast, in this study, Raman spectroscopy, which demonstrates non-destructive, label-free features, especially the unique advantage of providing molecular fingerprint information for target substances, were utilized to interrogate the intrinsic information of the corneal tissues from normal and diabetic mouse models, respectively. Visually, the Raman spectral response derived from the biochemical components and biochemical differences between the two groups were compared. Moreover, multivariate analysis methods such as principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were carried out for advanced statistical analysis. PCA yields a diagnostic results of 57.4% sensitivity, 89.2% specificity, 74.8% accuracy between the diabetic group and control group; Moreover, PLS-DA was employed to enhance the diagnostic ability, showing 76.1% sensitivity, 86.1% specificity, and 87.6% accuracy between the diabetic group and control group. Our proof-of-concept results show the potential of Raman spectroscopy-based techniques to help explore the underlying pathogenesis of DK disease and thus be further expanded for potential applications in the early screening of diabetic diseases.

Corneal dysfunction precedes the onset of hyperglycemia in a mouse model of diet-induced obesity

PURPOSE

The purpose of this study was to use a mouse model of diet-induced obesity to determine if corneal dysfunction begins prior to the onset of sustained hyperglycemia and if the dysfunction is ameliorated by diet reversal.

METHODS

Six-week-old male C57BL/6 mice were fed a high fat diet (HFD) or a normal diet (ND) for 5-15 weeks. Diet reversal (DiR) mice were fed a HFD for 5 weeks, followed by a ND for 5 or 10 weeks. Corneal sensitivity was determined using aesthesiometry. Corneal cytokine expression was analyzed using a 32-plex Luminex assay. Excised corneas were prepared for immunofluorescence microscopy to evaluate diet-induced changes and wound healing. For wounding studies, mice were fed a HFD or a ND for 10 days prior to receiving a central 2mm corneal abrasion.

RESULTS

After 10 days of HFD consumption, corneal sensitivity declined. By 10 weeks, expression of corneal inflammatory mediators increased and nerve density declined. While diet reversal restored nerve density and sensitivity, the corneas remained in a heightened inflammatory state. After 10 days on the HFD, corneal circadian rhythms (limbal neutrophil accumulation, epithelial cell division and Rev-erbα expression) were blunted. Similarly, leukocyte recruitment after wounding was dysregulated and accompanied by delays in wound closure and nerve recovery.

CONCLUSION

In the mouse, obesogenic diet consumption results in corneal dysfunction that precedes the onset of sustained hyperglycemia. Diet reversal only partially ameliorated this dysfunction, suggesting a HFD diet may have a lasting negative impact on corneal health that is resistant to dietary therapeutic intervention.

The findings of corneal specular microscopy in patients with type-2 diabetes mellitus

BACKGROUND

We aimed to compare the morphological characteristics of corneal endothelial cells in type 2 diabetic patients and age-matched healthy subjects by specular microscopy. We also aimed to determine the association of corneal morphological features with the general characteristics and laboratory data of diabetic patients, including disease duration, haemoglobin A1c (HbA1c) levels and urine albumin creatinine ratio.

METHODS

A total of 195 diabetic patients and 100 healthy controls were enrolled in the study. All participants underwent a complete ophthalmological examination. Corneal endothelial measurements were performed using a noncontact specular microscopy. Laboratory data including serum fasting glucose, haemoglobin A1c levels, creatinine levels, and the urinary albumin-to-creatinine ratio were recorded. Diabetic patients were further subdivided into 3 groups according to the presence and stage of diabetic retinopathy. Specular microscopy findings and central corneal thickness of all patients were compared.

RESULTS

The ECD and hexagonal cell ratio were significantly lower, while the average cell size, CV%, and central corneal thickness were determined to be significantly higher in diabetic patients than in healthy controls (p = 0.001). With the presence and advancement of diabetic retinopathy, the ECD and hexagonal cell ratio decreased, while the average cell size, CV%, and central corneal thickness increased. When correlation analysis was performed between corneal morphological features and laboratory data of diabetic patients, ECD showed a significant negative correlation with diabetes duration (p = 0.028). HbA1c levels, urinary albumin-creatinine ratio (p = 0.041), average cell size and CV showed a positive correlation with these parameters.

CONCLUSION

In conclusion, keratopathy is an important complication of type 2 diabetes. With an increase in the stage of diabetic retinopathy, alterations in corneal findings also increased. In that respect, we can suggest that keratopathy should be evaluated more cautiously in diabetic patients.

Light-Activatable Synergistic Therapy of Drug-Resistant Bacteria-Infected Cutaneous Chronic Wounds and Nonhealing Keratitis by Cupriferous Hollow Nanoshells

Due to the inability to spontaneously heal and vulnerability to bacterial infection, diabetic patients are frustrated by unexpected epithelium injuries in daily life. Notably, a drug-resistant bacterial infection may result in a long-term impact to the natural function of damaged organs. It is imperative to develop strategies that promote injury recovery and eradicate drug-resistant infection simultaneously. Here, we present a composite structured cupriferous hollow nanoshell (AuAgCu₂O NS) that consists of a hollow gold-silver (AuAg) core and Cu₂O shell as a photothermal therapeutic agent for a cutaneous chronic wound and nonhealing keratitis with drug-resistant bacterial infection. The controllable photothermal therapeutic effect and released silver ion from the hollow AuAg core possess a synergistic effect to eradicate multi-drug-resistant bacteria, including extended-spectrum β-lactamase Escherichia coli (ESBL E. coli) and methicillin-resistant Staphylococcus aureus (MRSA). Meanwhile, the released copper ion from the Cu₂O shell could expedite endothelial cell angiogenesis and fibroblast cell migration, thus boosting wound-healing effects. In both infection-complicated disease models, the ophthalmic clinical score, wound closure rates, and histopathology analysis demonstrate that the AuAgCu₂O NSs could facilitate the re-epithelialization at the wound area and eliminate the complicated bacterial infection from diabetic mice. A primary signal path involved in the promoted healing effect was further illustrated by comprehensive assays of immunohistochemical evaluation, Western blot, and quantitative polymerase chain reaction. Taken together, our AuAgCu₂O NSs are shown to be potent candidates for clinical utilization in the treatment of diabetic epithelium injuries.

The effects of diabetes mellitus on the corneal endothelium: A review

The corneal endothelium plays a critical role in maintaining corneal clarity. There is an expected decline in cell density with age and disease, and maintaining the health of this cell layer is important as corneal endothelial cells generally are amitotic in vivo. Diabetes mellitus is a highly prevalent disease that damages the corneal endothelium. Diabetes causes structural and functional impairments in the corneal endothelium that decrease cellular reserve in response to stress. These effects have implications to consider for diabetic patients undergoing anterior segment surgery, and for corneal surgeons who use diabetic donor tissue and treat diabetic patients. In this review, we discuss the specifics of how diabetes mellitus impacts the corneal endothelium including alterations in cell morphology, cell density, ultrastructure, pump and barrier function, cataract surgery outcomes, and corneal transplant outcomes with attention to the use of diabetic donor tissue and diabetic transplant recipients.

An Update on Corneal Biomechanics and Architecture in Diabetes

In the last decade, we have witnessed substantial progress in our understanding of corneal biomechanics and architecture. It is well known that diabetes is a systemic metabolic disease that causes chronic progressive damage in the main organs of the human body, including the eyeball. Although the main and most widely recognized ocular effect of diabetes is on the retina, the structure of the cornea (the outermost and transparent tissue of the eye) can also be affected by the poor glycemic control characterizing diabetes. The different corneal structures (epithelium, stroma, and endothelium) are affected by specific complications of diabetes. The development of new noninvasive diagnostic technologies has provided a better understanding of corneal tissue modifications. The objective of this review is to describe the advances in the knowledge of the corneal alterations that diabetes can induce.

Transforming growth factor-β blocks glucose-induced inflammation and apoptosis in corneal epithelial cells

Diabetic retinopathy is the most important ocular complication associated with diabetes. Corneal defects due to diabetes mellitus (DM) may cause severe vision impairments. This study aimed to identify the effect of transforming growth factor‐β (TGF‐β) on biological events, such as apoptosis and inflammation, in the diabetic cornea. High‐glucose treatment induced reactive oxygen species (ROS) production and several biological events, including apoptosis and inflammatory cytokine secretion, in human corneal epithelial cells. However, administration of TGF‐β significantly decreased ROS production, Annexin V‐positive cells, and levels of inflammatory cytokines. Sprague Dawley rats were injected with streptozotocin (STZ) as a model of DM. Inflammatory cytokine secretion, apoptosis, and inflammation were all increased by STZ treatment. However, apoptosis and inflammation were markedly reduced following TGF‐β treatment. In conclusion, TGF‐β can ameliorate the enhancement of apoptosis and inflammation in diabetic cornea in in vivo and in vitro.

A comparative study of risk factors for corneal infection in diabetic and non-diabetic patients

AIM

To compare the clinical characteristics of infectious keratopathy in type 2 diabetes mellitus (T2DM) and non-diabetes mellitus (NDM) and to investigate risk factors for infectious keratopathy in T2DM patients.

METHODS

Totally 230 patients with T2DM and 168 with NDM diagnosed as infectious keratopathy were hospitalized at Qingdao Eye Hospital from 2001 to 2015. Data including sex, age, occupation, season, smoking and alcohol consumption habits, duration between onset and treatments, duration of hospitalization were collected. Initially identified indicators were analyzed with a multivariate logistic regression. Glycosylated hemoglobin A1c (HbA1c) in patients with T2DM was analyzed. The infectious keratopathies in the two groups were categorized and compared.

RESULTS

The diabetic group consisted of 146 (63.5%) males and 84 (36.5%) females. The NDM group consisted of 111 (66.1%) males and 57 (33.9%) females. There was no signigicantly difference in sex distribution between the two groups (P>0.05). There were significant differences in age, occupation of patients, season of the onset of diseases, duration between onset and treatment, and durations of hospitalization between the two groups (P<0.05). In most of the patients in the diabetic group, the duration between onset and treatment was ≤3mo, and most was ≥3mo in the NDM group. Multivariate logistic regression analysis revealed that age and season were related to the development of corneal infection in the T2DM group (OR=1.709, 1.706). In the T2DM group, HbA1c was 9.09%±2.12%. There were statistically significant differences in the incidences of bacterial keratitis and herpes simplex keratitis in the two groups (P<0.05), but no significant statistical difference was found between fungal keratitis and amoebic keratitis (P>0.05).

CONCLUSION

Advanced age and the summer and winter seasons are identified as risk factors for infectious keratopathy in T2DM patients, and T2DM patients are more prone to bacterial keratitis.