The acceptability and feasibility of corneal confocal microscopy to detect early diabetic neuropathy in children: a pilot study

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

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

Corneal nerve and nerve conduction abnormalities in children with type 1 diabetes

OBJECTIVE

In vivo corneal confocal microscopy (CCM) is a novel, rapid, and non-invasive technique that identifies early small fiber damage and can predict the progression and development of clinical neuropathy in adults with type 1 diabetes. However, its usefulness in children is not well established. This study compared corneal confocal microscopy with neuropathic symptoms, signs, and objective measures of neuropathy for the diagnosis of diabetic neuropathy in children with type 1 diabetes.

RESEARCH DESIGN AND METHODS

A total of 83 children with type 1 diabetes and 83 healthy participants of similar age underwent assessment of neuropathy symptoms, signs, nerve conduction studies, quantitative sensory and autonomic function testing, and in vivo CCM.

RESULTS

Only of 3/83 (4%) children with type 1 diabetes had subclinical neuropathy. However, corneal nerve fiber density (p = 0.001), branch density (p = 0.006), fiber length (p = 0.002), tibial motor nerve amplitude and conduction velocity, and sural sensory nerve amplitude and conduction velocity (all p < 0.004) were lower in participants with type 1 diabetes than in the controls. Vibration, cooling, and warm perception thresholds and deep breathing heart rate variability were not found to be different (all p > 0.05) between children with type 1 diabetes and healthy controls. Multivariate regression analysis identified a possible association between body mass index and decreased corneal nerves.

CONCLUSIONS

Decreased corneal nerves and abnormal nerve conduction were found in children with type 1 diabetes. CCM may allow rapid objective detection of subclinical diabetic neuropathy in children and adolescents with type 1 diabetes.

Large fibre, small fibre and autonomic neuropathy in adolescents with type 1 diabetes: A systematic review

AIMS

To estimate the prevalence of neuropathy in adolescents with type 1 diabetes.

METHODS

Systematic collection of published studies exploring the prevalence of large fibre neuropathy (LFN), small fibre neuropathy (SFN), and autonomic neuropathy in adolescents with type 1 diabetes. Following prospective registration (Prospero CRD42020206093), PubMed, EMBASE, and Cochrane Library were searched for studies from 2000 to 2020. PICO framework was used in the selection process (Population: adolescents aged 10-19 years with type 1 diabetes; Intervention: diagnostic methods for neuropathy; Comparison: reference data; Outcome: data on prevalence or comparison). Data were extracted concerning study quality based on available data and established methods for determining and diagnosing various neuropathy types.

RESULTS

From 2,017 initial citations, 27 studies (7589 participants) fulfilled eligibility criteria. The study population (47% males) had a diabetes duration between 4.0 and 10.6 years, and HbA1c level between 7.3 and 10.8%, 56-95 mmol/mol. The prevalence of LFN, based on nerve conduction studies, was 10-57%. Based on other tests for neuropathy, the prevalence of LFN and SFN was 12-62%, and that of cardiac autonomic neuropathy was 12-75%.

CONCLUSION

The described prevalence of neuropathy in adolescents with type 1 diabetes varied, which can be methodological due to different screening methods and classifications of neuropathy.

In vivo confocal microscopy study of corneal nerve alterations in children and youths with Type 1 diabetes

OBJECTIVE

To determine whether children and youths with Type 1 diabetes (T1D) have early alterations of the corneal subbasal nerve plexus detectable with in vivo confocal microscopy (IVCM) and to investigate the role of longitudinally measured major risk factors for diabetes complications associated with these alterations.

METHODS

One hundred and fifty children and youths with T1D and 51 age-matched controls were enrolled and underwent IVCM. Corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal fiber total branch density (CTBD), and corneal fiber fractal dimension (CNFrD) were measured. Risk factors for diabetes complications (blood pressure, BMI, HbA1c, lipoproteins, urinary albumin-creatinine ratio) were recorded at IVCM and longitudinally since T1D onset. Unpaired t-test was used to compare variables between the groups. Multiple regression models were calculated using IVCM parameters as dependent variables and risk factors as independent variables.

RESULTS

All IVCM parameters, except CTBD, were significantly lower in the T1D patients. Glycometabolic control (HbA1c, visit-to-visit HbA1c variability, and mean HbA1c), and blood pressure were inversely correlated with IVCM parameters. Multiple regression showed that part of the variability in CNFL, CNFD, CTBD, and CNFraD was explained by HbA1c, blood pressure percentiles and age at IVCM examination, independent of diabetes duration, BMI percentile and LDL cholesterol. Comparable results were obtained using the mean value of risk factors measured longitudinally since T1D onset.

CONCLUSIONS

Early signs of corneal nerve degeneration were found in children and youths with T1D. Glycometabolic control and blood pressure were the major risk factors for these alterations.

Corneal confocal microscopy demonstrates minimal evidence of distal neuropathy in children with celiac disease

OBJECTIVES

The aim of this study was to utilise corneal confocal microscopy to quantify corneal nerve morphology and establish the presence of sub-clinical small fibre damage and peripheral neuropathy in children with celiac disease.

METHODS

This is a cross-sectional cohort study of twenty children with celiac disease and 20 healthy controls who underwent clinical and laboratory assessments and corneal confocal microscopy. Corneal nerve fiber density (no.mm2), corneal nerve branch density (no.mm2), corneal nerve fiber length (mm.mm2), corneal nerve fiber tortuosity and inferior whorl length (mm.mm2) were quantified manually.

RESULTS

Corneal nerve fiber density (34.7±8.6 vs. 32.9±8.6; P = 0.5), corneal nerve branch density (47.2±24.5 vs. 47.3±20.0; P = 0.1) and corneal nerve fiber length (20.0±5.1 vs. 19.5±4.5; P = 0.8) did not differ between children with celiac disease and healthy controls. Corneal nerve fiber tortuosity (11.4±1.9 vs 13.5±3.0; P = 0.01) was significantly lower and inferior whorl length (20.0±5.5 vs 23.0±3.8; P = 0.06) showed a non-significant reduction in children with celiac disease compared to healthy controls. Inferior whorl length correlated significantly with corneal nerve fiber density (P = 0.005), corneal nerve branch density (P = 0.04), and corneal nerve fiber length (P = 0.002).

CONCLUSION

Corneal confocal microscopy demonstrates minimal evidence of neuropathy in children with celiac disease.

Corneal nerve loss in children with type 1 diabetes mellitus without retinopathy or microalbuminuria

Aims/Introduction

Corneal confocal microscopy is a rapid, non‐invasive ophthalmic technique to identify subclinical neuropathy. The aim of this study was to quantify corneal nerve morphology in children with type 1 diabetes mellitus compared with age‐matched healthy controls using corneal confocal microscopy.

Materials and Methods

A total of 20 participants with type 1 diabetes mellitus (age 14 ± 2 years, diabetes duration 4.08 ± 2.91 years, glycated hemoglobin 9.3 ± 2.1%) without retinopathy or microalbuminuria and 20 healthy controls were recruited from outpatient clinics. Corneal confocal microscopy was undertaken, and corneal nerve fiber density (n/mm²), corneal nerve branch density (n/mm²), corneal nerve fiber length (mm/mm²), corneal nerve fiber tortuosity and inferior whorl length (mm/mm²) were quantified manually.

Results

Corneal nerve fiber density (22.73 ± 8.84 vs 32.92 ± 8.59; P < 0.001), corneal nerve branch density (26.19 ± 14.64 vs 47.34 ± 20.01; P < 0.001), corneal nerve fiber length (13.26 ± 4.06 vs 19.52 ± 4.54; P < 0.001) and inferior whorl length (15.50 ± 5.48 vs 23.42 ± 3.94; P < 0.0001) were significantly lower, whereas corneal nerve fiber tortuosity (14.88 ± 5.28 vs 13.52 ± 3.01; P = 0.323) did not differ between children with type 1 diabetes mellitus and controls. Glycated hemoglobin correlated with corneal nerve fiber tortuosity (P < 0.006) and aspartate aminotransferase correlated with corneal nerve fiber density (P = 0.039), corneal nerve branch density (P = 0.003) and corneal nerve fiber length (P = 0.037).

Conclusion

Corneal confocal microscopy identifies significant subclinical corneal nerve loss, especially in the inferior whorl of children with type 1 diabetes mellitus without retinopathy or microalbuminuria.

Early corneal nerve fibre damage and increased Langerhans cell density in children with type 1 diabetes mellitus

Corneal confocal microscopy (CCM) has been used to identify corneal nerve damage and increased Langerhans cell (LC) density in adults with Type 1 diabetes mellitus (T1DM). The purpose of this study was to evaluate whether corneal confocal microscopy can identify early corneal nerve damage and change in LC density in children and adolescents with T1DM. 64 participants with T1DM (age-14.6 ± 2.5 years, duration of diabetes-9.1 ± 2.7 years, HbA1c-75.66 ± 2.53 mmol/mol [9.1 ± 1.8%]) and 48 age-matched healthy control subjects underwent CCM. Sub-basal corneal nerve morphology and the density of mature and immature LCs was quantified. Corneal nerve fibre length and branch density were lower, whilst fibre density and tortuosity did not differ and both immature and mature LC density was significantly higher in T1DM compared to control subjects. There was no association between HbA1c and duration of diabetes with nerve fibre parameters or LC's density. Children and adolescents with T1DM demonstrate early immune activation and nerve degeneration.

Corneal confocal microscopy: ready for prime time

Corneal confocal microscopy is a non-invasive ophthalmic imaging modality, which was initially used for the diagnosis and management of corneal diseases. However, over the last 20 years it has come to the forefront as a rapid, non-invasive, reiterative, cost-effective imaging biomarker for neurodegeneration. The human cornea is endowed with the densest network of sensory unmyelinated axons, anywhere in the body. A robust body of evidence shows that corneal confocal microscopy is a reliable and reproducible method to quantify corneal nerve morphology. Changes in corneal nerve morphology precede or relate to clinical manifestations of peripheral and central neurodegenerative conditions. Moreover, in clinical intervention trials, corneal nerve regeneration occurs early and predicts functional gains in trials of neuroprotection. In view of these findings, it is timely to summarise the knowledge in this area of research and to explain why the case for corneal confocal microscopy is sufficiently compelling to argue for its inclusion as a Food and Drug Administration endpoint in clinical trials of peripheral and central neurodegenerative conditions.

The corneal subbasal nerve plexus and thickness of the retinal layers in pediatric type 1 diabetes and matched controls

Optical coherence tomography (OCT) of the retina and corneal confocal laser scanning microscopy (CLSM) of the subbasal nerve plexus (SBP) are noninvasive techniques for quantification of the ocular neurodegenerative changes in individuals with type 1 diabetes mellitus (T1DM). In adult T1DM patients these changes are hardly related to T1DM only. Instead, ageing and/or lifestyle associated comorbidities have to be considered as putative confounding variables. Therefore, we investigated pediatric T1DM patients (n = 28; 14.2 ± 2.51 y; duration of disease: 5.39 ± 4.16 y) without clinical signs of diabetic retina disease, neuropathy, vasculopathy or nephropathy and compared our findings with those obtained in healthy controls (n = 46; 14.8 ± 1.89 y). The SBP was characterized by the averaged length, thickness, and tortuosity of nerve fibers as well as the number of branching and connecting points. OCT was used to determine the total thickness of the retina (ALL) and the thickness of each retinal layer. Both methods revealed signs of early neurodegenerative changes, e.g. thinning of distinct retinal layers at the pericentral ring and shortening of corneal nerve fibers that are already present in pediatric T1DM patients. Standardization of instruments and algorithms are urgently required to enable uniform comparison between different groups and define normative values to introduce in the clinical setting.

A systematic review on the impact of diabetes mellitus on the ocular surface

Diabetes mellitus is associated with extensive morbidity and mortality in any human community. It is well understood that the burden of diabetes is attributed to chronic progressive damage in major end-organs, but it is underappreciated that the most superficial and transparent organ affected by diabetes is the cornea. Different corneal components (epithelium, nerves, immune cells and endothelium) underpin specific systemic complications of diabetes. Just as diabetic retinopathy is a marker of more generalized microvascular disease, corneal nerve changes can predict peripheral and autonomic neuropathy, providing a window of opportunity for early treatment. In addition, alterations of immune cells in corneas suggest an inflammatory component in diabetic complications. Furthermore, impaired corneal epithelial wound healing may also imply more widespread disease. The non-invasiveness and improvement in imaging technology facilitates the emergence of new screening tools. Systemic control of diabetes can improve ocular surface health, possibly aided by anti-inflammatory and vasoprotective agents.

The Inferior Whorl For Detecting Diabetic Peripheral Neuropathy Using Corneal Confocal Microscopy

PURPOSE

In vivo corneal confocal microscopy (CCM) is increasingly used as a surrogate endpoint in studies of diabetic polyneuropathy (DPN). However, it is not clear whether imaging the central cornea provides optimal diagnostic utility for DPN. Therefore, we compared nerve morphology in the central cornea and the inferior whorl, a more distal and densely innervated area located inferior and nasal to the central cornea.

METHODS

A total of 53 subjects with type 1/type 2 diabetes and 15 age-matched control subjects underwent detailed assessment of neuropathic symptoms (NPS), deficits (neuropathy disability score [NDS]), quantitative sensory testing (vibration perception threshold [VPT], cold and warm threshold [CT/WT], and cold- and heat-induced pain [CIP/HIP]), and electrophysiology (sural and peroneal nerve conduction velocity [SSNCV/PMNCV], and sural and peroneal nerve amplitude [SSNA/PMNA]) to diagnose patients with (DPN+) and without (DPN-) neuropathy. Corneal nerve fiber density (CNFD) and length (CNFL) in the central cornea, and inferior whorl length (IWL) were quantified.

RESULTS

Comparing control subjects to DPN- and DPN+ patients, there was a significant increase in NDS (0 vs. 2.6 ± 2.3 vs. 3.3 ± 2.7, P < 0.01), VPT (V; 5.4 ± 3.0 vs. 10.6 ± 10.3 vs. 17.7 ± 11.8, P < 0.01), WT (°C; 37.7 ± 3.5 vs. 39.1 ± 5.1 vs. 41.7 ± 4.7, P < 0.05), and a significant decrease in SSNCV (m/s; 50.2 ± 5.4 vs. 48.4 ± 5.0 vs. 39.5 ± 10.6, P < 0.05), CNFD (fibers/mm2; 37.8 ± 4.9 vs. 29.7 ± 7.7 vs. 27.1 ± 9.9, P < 0.01), CNFL (mm/mm2; 27.5 ± 3.6 vs. 24.4 ± 7.8 vs. 20.7 ± 7.1, P < 0.01), and IWL (mm/mm2; 35.1 ± 6.5 vs. 26.2 ± 10.5 vs. 23.6 ± 11.4, P < 0.05). For the diagnosis of DPN, CNFD, CNFL, and IWL achieved an area under the curve (AUC) of 0.75, 0.74, and 0.70, respectively, and a combination of IWL-CNFD achieved an AUC of 0.76.

CONCLUSIONS

The parameters of CNFD, CNFL, and IWL have a comparable ability to diagnose patients with DPN. However, IWL detects an abnormality even in patients without DPN. Combining IWL with CNFD may improve the diagnostic performance of CCM.

Diabetes Complications in Childhood Diabetes-New Biomarkers and Technologies

A major challenge in preventing vascular complications in diabetes is the inability to identify high-risk patients at an early stage, emphasizing the importance of discovering new risk factors, technologies and therapeutic targets to reduce the development and progression of complications. Promising biomarkers which may improve risk stratification and serve as therapeutic targets, include: uric acid, insulin sensitivity, copeptin, SGLT-2 and Klotho/FGF-23. Non-invasive measures of macrovasuclar disease in youth, include: 1) pulse wave velocity to examine arterial stiffness; 2) carotid intima-media thickness to evaluate arterial thickness; 3) cardiac MRI to investigate cardiac function and structure. Novel microvascular measures include: GFR by iohexol clearance using filter paper to directly measure GFR, retinal vascular geometry to predict early retinal changes and corneal confocal microscopy to improve detection of early nerve loss to better predict diabetic neuropathy. Herein we will review technologies, novel biomarkers, and therapeutic targets in relation to vascular complications of diabetes.

Corneal confocal microscopy: Recent progress in the evaluation of diabetic neuropathy

The present brief review discusses recent progress with corneal confocal microscopy for the evaluation of diabetic sensorimotor polyneuropathy. Corneal confocal microscopy is a new, non-invasive and reproducible diagnostic modality, and it can also be easily applied for patient follow up. It enables new perspectives of studying the natural history of diabetic sensorimotor polyneuropathy, severity of nerve fiber pathology and documenting early nerve fiber regeneration after therapeutic intervention. It shows moderate to high sensitivity and specificity for the timely diagnosis of diabetic sensorimotor polyneuropathy. Currently, corneal confocal microscopy is mainly used in specialized centers, but deserves more widespread application for the assessment of diabetic sensorimotor polyneuropathy. Finally, further progress is required in terms of technical improvements for automated nerve fiber quantification and for analysis of larger images.

New vistas in the diagnosis of diabetic polyneuropathy

New modalities are now available to improve the diagnosis of diabetic polyneuropathy (DPN). The present review discusses the progress achieved in this area. First, the minimal diagnostic criteria have been better clarified. Moreover, there are now new bedside tests available, such as the indicator test Neuropad, NeuroQuick, Ipswich Touch Test (IpTT), Vibratip, NC-stat(®)/DPNCheck™ for automated nerve conduction study (NCS), tactile circumferential discriminator, steel ball-bearing, and SUDOSCAN(®), while more sophisticated modalities include skin biopsy and corneal confocal microscopy (CCM). Some tests can be used as screening tools, including primary care setting (Neuropad, IpTT, Vibratip, automated NCS), while others are more suitable for research, including evaluation of DPN in prospective studies (CCM, skin biopsy). Importantly, there is some evidence of earlier DPN diagnosis with the aid of some tests (Neuropad, skin biopsy, CCM). Further advantages provided by different tests are educational value and self-examination. Thus far, the potential of these tests has not been fully utilised. In particular, they have not been validated against standardised clinical examination scores in terms of predicting foot ulcers and amputations. Hence, it now remains to investigate the potential benefits from the widespread use of these tests for earlier and easier diagnosis of DPN in the everyday clinic.

Amplitude of sensory nerve action potential in early stage diabetic peripheral neuropathy: an analysis of 500 cases

Early diagnosis of diabetic peripheral neuropathy is important for the successful treatment of diabetes mellitus. In the present study, we recruited 500 diabetic patients from the Fourth Affiliated Hospital of Kunming Medical University in China from June 2008 to September 2013: 221 cases showed symptoms of peripheral neuropathy (symptomatic group) and 279 cases had no symptoms of peripheral impairment (asymptomatic group). One hundred healthy control subjects were also recruited. Nerve conduction studies revealed that distal motor latency was longer, sensory nerve conduction velocity was slower, and sensory nerve action potential and amplitude of compound muscle action potential were significantly lower in the median, ulnar, posterior tibial and common peroneal nerve in the diabetic groups compared with control subjects. Moreover, the alterations were more obvious in patients with symptoms of peripheral neuropathy. Of the 500 diabetic patients, neural conduction abnormalities were detected in 358 cases (71.6%), among which impairment of the common peroneal nerve was most prominent. Sensory nerve abnormality was more obvious than motor nerve abnormality in the diabetic groups. The amplitude of sensory nerve action potential was the most sensitive measure of peripheral neuropathy. Our results reveal that varying degrees of nerve conduction changes are present in the early, asymptomatic stage of diabetic peripheral neuropathy.

Corneal confocal microscopy to assess diabetic neuropathy: an eye on the foot

Accurate detection and quantification of human diabetic peripheral neuropathy are important to define at-risk patients, anticipate deterioration, and assess new therapies. Easily performed clinical techniques such as neuro-logical examination, assessment of vibration perception or insensitivity to the 10 g monofilament only assess advanced neuropathy, i.e., the at-risk foot. Techniques that assess early neuropathy include neurophysiology (which assesses only large fibers) and quantitative sensory testing (which assesses small fibers), but they can be highly subjective while more objective techniques, such as skin biopsy for intra-epidermal nerve fiber density quantification, are invasive and not widely available. The emerging ophthalmic technique of corneal confocal microscopy allows quantification of corneal nerve morphology and enables clinicians to diagnose peripheral neuropathy in diabetes patients, quantify its severity, and potentially assess therapeutic benefit. The present review provides a detailed critique of the rationale, a practical approach to capture images, and a basis for analyzing and interpreting the images. We also critically evaluate the diagnostic ability of this new noninvasive ophthalmic test to diagnose diabetic and other peripheral neuropathies.

Corneal confocal microscopy: a new technique for early detection of diabetic neuropathy

Corneal confocal microscopy (CCM) is a noninvasive method for the study of human cornea in vivo. It has increasingly been used to assess the morphology of the sub-basal corneal nerve plexus. CCM has good reproducibility and may contribute to the early diagnosis of diabetic polyneuropathy. It may also be useful to document favorable changes in nerve fiber structure early after therapeutic intervention. Corneal nerve pathology is more pronounced in patients with diabetic polyneuropathy and is associated with its clinical severity. The sensitivity and specificity of CCM for the diagnosis of polyneuropathy is moderate to high. CCM now merits further use in large longitudinal studies to provide more information on the natural history of diabetic neuropathy and effects of treatment. Moreover, there is a need for a larger normative database. Finally, technical progress is expected to enable visualization of larger corneal areas and improve nerve fiber quantification, increasing diagnostic accuracy.