Impact of SGLT2 Inhibitors on Corneal Nerve Morphology and Dendritic Cell Density in Type 2 Diabetes

PURPOSE

This study aims to determine the effects of SGLT2 inhibitors on corneal dendritic cell density and corneal nerve measures in type 2 diabetes.

METHODS

Corneal dendritic cell densities and nerve parameters were measured in people with type 2 diabetes treated with SGLT2 inhibitors (T2DM-SGLT2i) [n = 23] and those not treated with SGLT2 inhibitors (T2DM-no SGLT2i) [n = 23], along with 24 age and sex-matched healthy controls.

RESULTS

There was a reduction in all corneal nerve parameters in type 2 diabetes groups compared to healthy controls (All parameters: p < 0.05). No significant differences in corneal nerve parameters were observed between T2DM-SGLT2i and T2DM-no SGLT2i groups (All parameters: p > 0.05). Central corneal dendritic cells were significantly reduced [mature (p = 0.03), immature (p = 0.06) and total (p = 0.002)] in the T2DM-SGLT2i group compared to the T2DM-no SGLT2i group. Significantly, higher mature (p = 0.04), immature (p = 0.004), total (p = 0.002) dendritic cell densities in the T2DM-no SGLT2i group were observed compared to the healthy controls. In the inferior whorl, no significant difference in immature (p = 0.27) and total dendritic cell densities (p = 0.16) between T2DM-SGLT2i and T2DM-no SGLT2i were observed except mature dendritic cell density (p = 0.018). No differences in total dendritic cell density were observed in the central (p > 0.09) and inferior whorl (p = 0.88) between T2DM-SGLT2i and healthy controls.

CONCLUSION

The present study showed a reduced dendritic cell density in people with type 2 diabetes taking SGLT2 inhibitors compared to those not taking these medications.

The ability of face masks to reduce transmission of microbes

CLINICAL RELEVANCE

Optometrists have been advised to wear face masks during the COVID-19 pandemic. This study examined whether face masks were equally protective against transmission of microbes.

BACKGROUND

The aim of the current study was to examine the ability of face masks to reduce transmission of microbes in aerosols and during speech.

METHODS

Different face masks, surgical, medical 3-ply and cloth masks with different layers were used. The masks were tested under the ASTM standard F2101-1 to measure their ability to reduce the transmission of aerosolised Staphylococcus aureus. Bacterial cells in different sized aerosols were captured on agar plates. The ability of masks to reduce the transmission of bacteria during speech over 30 cm was measured. Bacteria were captured in masks or on agar plates at a distance of 30 cm during the speech.

RESULTS

All masks reduced the transmission of aerosolised S. aureus (p ≤ 0.007). The medical 3-ply and cloth masks with three layers reduced the transmission of S. aureus aerosols (3.3 μm) by 98% and surgical and seven-layer masks reduced this by 100%. An antibacterial silver mask showed significantly greater transmission of S. aureus in aerosols of 4.7 μm (16 ± 6 cells) and 3.3 μm (122 ± 66 cells) compared to all other masks (0-3 cells and 0-15 cells, respectively; p ≤ 0.016). Surgical and three-layer masks had significantly worse filtration of 1.1 μm aerosols than for other aerosol sizes. Wearing a mask reduced the transmission of bacteria during speech, but the inner surface of these masks became contaminated with 528-3060 bacterial cells.

CONCLUSIONS

Face masks effectively reduce the transmission of microbes in laboratory tests. Face masks made with seven layers were very effective at stopping transmission of S. aureus in all aerosol particle sizes. However, face masks become rapidly contaminated during wear. If masks are to be re-used, they should be regularly replaced or appropriately washed.

The role of nitric oxide in ocular surface physiology and pathophysiology

Nitric oxide (NO) has a wide array of biological functions including the regulation of vascular tone, neurotransmission, immunomodulation, stimulation of proinflammatory cytokine expression and antimicrobial action. These functions may depend on the type of isoform that is responsible for the synthesis of NO. NO is found in various ocular tissues playing a pivotal role in physiological mechanisms, namely regulating vascular tone in the uvea, retinal blood circulation, aqueous humor dynamics, neurotransmission and phototransduction in retinal layers. Unregulated production of NO in ocular tissues may result in production of toxic superoxide free radicals that participate in ocular diseases such as endotoxin-induced uveitis, ischemic proliferative retinopathy and neurotoxicity of optic nerve head in glaucoma. However, the role of NO on the ocular surface in mediating physiology and pathophysiological processes is not fully understood. Moreover, methods used to measure levels of NO in the biological samples of the ocular surface are not well established due to its rapid oxidation. The purpose of this review is to highlight the role of NO in the physiology and pathophysiology of ocular surface and propose suitable techniques to measure NO levels in ocular surface tissues and tears. This will improve the understanding of NO's role in ocular surface biology and the development of new NO-based therapies to treat various ocular surface diseases. Further, this review summarizes the biochemistry underpinning NO's antimicrobial action.

Antimicrobial resistance of ocular microbes and the role of antimicrobial peptides

Isolation of antimicrobial-resistant microbes from ocular infections may be becoming more frequent. Infections caused by these microbes can be difficult to treat and lead to poor outcomes. However, new therapies are being developed which may help improve clinical outcomes. This review examines recent reports on the isolation of antibiotic-resistant microbes from ocular infections. In addition, an overview of the development of some new antibiotic therapies is given. The recent literature regarding antibiotic use and resistance, isolation of antibiotic-resistant microbes from ocular infections and the development of potential new antibiotics that can be used to treat these infections was reviewed. Ocular microbial infections are a global public health issue as they can result in vision loss which compromises quality of life. Approximately 70 per cent of ocular infections are caused by bacteria including Chlamydia trachomatis, Staphylococcus aureus, and Pseudomonas aeruginosa and fungi such as Candida albicans, Aspergillus spp. and Fusarium spp. Resistance to first-line antibiotics such as fluoroquinolones and azoles has increased, with resistance of S. aureus isolates from the USA to fluoroquinolones reaching 32 per cent of isolates and 35 per cent being methicillin-resistant (MRSA). Lower levels of MRSA (seven per cent) were isolated by an Australian study. Antimicrobial peptides, which are broad-spectrum alternatives to antibiotics, have been tested as possible new drugs. Several have shown promise in animal models of keratitis, especially treating P. aeruginosa, S. aureus or C. albicans infections. Reports of increasing resistance of ocular isolates to mainstay antibiotics are a concern, and there is evidence that for ocular surface disease this resistance translates into worse clinical outcomes. New antibiotics are being developed, but not by large pharmaceutical companies and mostly in university research laboratories and smaller biotech companies. Antimicrobial peptides show promise in treating keratitis.

Associations between acute glucose control and peripheral nerve structure and function in type 1 diabetes

AIM

To examine the associations between continuous overlapping net glycaemic action (CONGA), percentage time in hyperglycaemia (%HG) or normoglycaemia (%NG) and peripheral nerve structure and function in type 1 diabetes.

METHODS

Twenty-seven participants with type 1 diabetes underwent continuous glucose monitoring followed by corneal confocal microscopy and nerve excitability assessments. CONGA, %HG (> 10.0 mmol/l) and %NG (3.9-10.0 mmol/l) were correlated against corneal nerve fibre length and density in the central cornea and inferior whorl region, corneal microneuromas, and a nerve excitability score while controlling for age, sex, diabetes duration and HbA_1c .

RESULTS

An increase in CONGA [median 2.5 (2.0-3.1) mmol/l] or %HG (mean 46 ± 18%) was associated with a worse nerve excitability score (r = -0.433, P = 0.036 and r = -0.670, P = 0.0012, respectively). By contrast, greater %NG (51 ± 17%) correlated with better nerve excitability scores (r = 0.672, P = 0.0011). Logistic regression revealed that increasing %HG increased the likelihood of abnormal nerve function [odds ratio (OR) 1.11, 95% confidence interval (CI) 1.01-1.23; P = 0.037). An increase in CONGA and %HG were associated with worsening nerve conduction measures, whereas longer %NG correlated with improved nerve conduction variables. CONGA and %HG were associated with inferior whorl corneal nerve fibre length (r = 0.483, P = 0.034 and r = 0.591, P = 0.021, respectively) and number of microneuromas (r = 0.433, P = 0.047 and r = 0.516, P = 0.020, respectively).

CONCLUSIONS

Short-term measures of glucose control are associated with impaired nerve function and alterations in corneal nerve morphology.

Relationship between corneal confocal microscopy and markers of peripheral nerve structure and function in Type 2 diabetes

AIMS

To investigate changes in corneal nerve morphology in Type 2 diabetes and to establish relationships between in vivo corneal confocal microscopy and markers of peripheral nerve structure and function.

PARTICIPANTS AND METHODS

We recruited 57 participants with Type 2 diabetes and 26 healthy controls of similar age and sex distribution. We also recruited a disease control group of 54 participants with Type 1 diabetes. All participants were assessed for distal symmetrical polyneuropathy using the Total Neuropathy Score. In vivo corneal confocal microscopy was used to assess corneal nerve fibre length, corneal nerve fibre density, corneal nerve branch density and inferior whorl length. Peripheral nerve structure was assessed using median nerve ultrasonography. Large fibre function was assessed according to median nerve axonal excitability. Small fibre function was assessed using Sudoscan^TM and the Survey of Autonomic Symptoms.

RESULTS

Corneal nerve fibre length, fibre density and branch density and inferior whorl length were significantly lower in individuals with Type 2 diabetes compared to controls (P<0.001 for all). In the Type 2 diabetes cohort, correlations were observed between neuropathy severity and corneal nerve fibre density (P=0.004), corneal nerve branch density (P=0.003), corneal nerve fibre length (P=0.002) and inferior whorl length (P=0.01). Significant correlations were observed between corneal confocal outcomes and axonal excitability measurements. No association was found between corneal confocal microscopy and median nerve cross-sectional area, Sudoscan measurements or the Survey of Autonomic Symptoms.

CONCLUSIONS

This study demonstrated significant changes in corneal nerves in individuals with Type 2 diabetes. Reductions in corneal nerve measures correlated with increasing neuropathy severity. Associations were found between corneal confocal microscopy and markers of voltage-gated potassium channel function.

Evaluation of corneal elevation and thickness indices in pellucid marginal degeneration and keratoconus

PURPOSE

To determine and compare corneal elevation and thickness indices, thereby formulating a reliable index to distinguish eyes with pellucid marginal degeneration (PMD) from keratoconus eyes and normal (control) eyes.

SETTING

LV Prasad Eye Institute, Hyderabad, India.

DESIGN

Initial model-building retrospective study.

METHODS

Anterior and posterior corneal elevations and thickness indices were obtained from the Orbscan IIz topographer. These values were analyzed and compared between PMD patients, keratoconus patients, and control subjects.

RESULTS

Of the indices, the mean values of anterior elevation (AE), ratio of the AE to the anterior best-fit sphere, ratio of the average power values of nasal quadrant to the average power values of inferior quadrant, and difference between maximum keratometry (K) and minimum K were significantly different between the 3 groups (P<.05). The highest area under the receiver-operating-characteristic (AROC) curve in discriminating PMD from keratoconus was for asphericity (0.974; cutoff ≥-0.07; sensitivity 93.3%; specificity 90.6%) followed by the ratio of average power values of the nasal and temporal quadrants to the average power values of the inferior and superior quadrants (Avg NT((D))/IS((D))) (0.959; cutoff ≥1.005; sensitivity 96.7%; specificity 90.6%). The PMD index (AROC curve, 0.935), with a cutoff of 3.45 or higher had 90% sensitivity and 93.7% specificity to distinguish PMD from keratoconus and had 100% sensitivity and 100% specificity to distinguish PMD from control eyes, with a cutoff of 2.46 or higher (AROC curve, 1.000).

CONCLUSIONS

The PMD index appeared to be highly sensitive and specific for diagnosing PMD. Asphericity and Avg NT((D))/IS((D)) were clinically relevant in discriminating PMD from other groups.