Corneal confocal microscopy detects neuropathy in patients with type 1 diabetes without retinopathy or microalbuminuria

Corneal confocal microscopy in small and mixed fiber neuropathy-Comparison with skin biopsy and cold detection in a large prospective cohort

BACKGROUND AND AIMS

The diagnosis of small fiber neuropathy (SFN) is supported by reduced intraepidermal nerve fiber density (IENFD). The noninvasive method corneal confocal microscopy (CCM) has the potential to be a practical alternative. We aimed to estimate the diagnostic accuracy of CCM compared with IENFD and cold detection thresholds (CDT) in SFN and mixed fiber neuropathy (MFN).

METHODS

CCM was performed in an unselected prospective cohort of patients with a clinical suspicion of polyneuropathy. Predefined criteria were used to classify SFN and MFN. Neuropathy scores, including the Utah early neuropathy scale (UENS), were used to describe severity. Patients with established other diagnoses were used for diagnostic specificity calculations.

RESULTS

Data were taken from 680 patients, of which 244 had SFN or MFN. There was no significant difference in sensitivities [95%CI] of CCM (0.44 [0.38-0.51]), IEFND (0.43 [0.36-0.49]), and CDT (0.34 [0.29-0.41]). CCM specificity (0.75 [0.69-0.81]) was lower (p = .044) than for IENFD (0.99 [0.96-1.00]) but not than for CDT (0.81 [0.75-0.86]). The AUCs of the ROC curves of 0.63, 0.63 and 0.74 respectively, was lower for corneal nerve fiber density (p = .0012) and corneal nerve fiber length (p = .0015) compared with IENFD. While UENS correlated significantly with IENFD (p = .0016; R2  = .041) and CDT (p = .0002; R2  = .056), it did not correlate with CCM measures.

INTERPRETATION

The diagnostic utility of CCM in SNF and MFN is limited by the low specificity compared with skin biopsy. Further, CCM is less suitable than skin biopsy and CDT as a marker for neuropathy severity.

Corneal Confocal Microscopy Abnormalities in Children and Adolescents With Type 1 Diabetes

OBJECTIVE

Utility of corneal confocal microscopy (CCM) in children and adolescents with type 1 diabetes mellitus (T1DM) without neuropathic symptoms or signs and minimal abnormality in large and small nerve fiber function tests remains largely undetermined. This study aimed to evaluate the performance of CCM in comparison to thermal detection thresholds (TDT) testing and nerve conduction studies (NCS) for detecting neuropathy in children with T1DM.

METHODS

A cohort of children and adolescents with T1DM (n = 51) and healthy controls (n = 50) underwent evaluation for symptoms and signs of neurological deficits, including warm detection threshold, cold detection threshold, vibration perception threshold, NCS, and CCM.

RESULTS

Children with T1DM had no or very minimal neuropathic symptoms and deficits based on the Toronto Clinical Neuropathy Score, yet NCS abnormalities were present in 18 (35%), small fiber dysfunction defined by an abnormal TDT was found in 13 (25.5%) and CCM abnormalities were present in 25 (49%). CCM was abnormal in a majority of T1DM children with abnormal TDT (12/13, 92%) and abnormal NCS (16/18, 88%). CCM additionally was able to detect small fiber abnormalities in 13/38 (34%) in T1DM with a normal TDT and in 9/33 (27%) with normal NCS.

CONCLUSION

CCM was able to detect corneal nerve loss in children with and without abnormalities in TDT and NCS.

Visual Evoked Potentials for the Detection of Diabetic Retinal Neuropathy

Visual evoked potentials (VEP) are visually evoked signals that extract electroencephalographic activity in the visual cortex that can detect retinal ganglion cells, optic nerves, chiasmal and retrochiasmal dysfunction, including optic radiations, and the occipital cortex. Because diabetes causes diabetic retinopathy due to microangiopathy and neuropathy due to metabolic abnormalities and intraneural blood flow disorders, assessment of diabetic visual pathway impairment using VEP has been attempted. In this review, evidence on the attempts to assess the visual pathway dysfunction due to abnormal blood glucose levels using VEP is presented. Previous studies have provided significant evidence that VEP can functionally detect antecedent neuropathy before fundus examination. The detailed correlations between VEP waveforms and disease duration, HbA1c, glycemic control, and short-term increases and decreases in blood glucose levels are evaluated. VEP may be useful for predicting postoperative prognosis and evaluating visual function before surgery for diabetic retinopathy. Further controlled studies with larger cohorts are needed to establish a more detailed relationship between diabetes mellitus and VEP.

Methods for evaluation of corneal nerve fibres in diabetes mellitus by in vivo confocal microscopy: a scoping review protocol

INTRODUCTION

Globally, 422 million people have diabetes. Late complications of diabetes are blindness, kidney failure, heart attack, stroke and lower limb amputation. The prevalence of diabetic peripheral neuropathy and diabetic retinopathy is 50% and 35%, respectively. In vivo confocal microscopy (IVCM) is a rapid, non-invasive method to evaluate subbasal corneal nerve fibres, which are small fibres of the peripheral nervous system. Corneal nerve fibre changes can be a marker of diabetic peripheral neuropathy. There is currently no gold-standard procedure for IVCM imaging, image processing or quantitative analysis of the corneal nerve fibres in the subbasal plexus. This protocol describes a scoping review to map, summarise and critically evaluate current methods used with IVCM evaluation in people with diabetes mellitus.

METHODS

The scoping review will follow Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for scoping review. A comprehensive search of the literature will be conducted in MEDLINE, Embase, Cochrane, Scopus and Web of Science. The search strategy will include terms related to IVCM, diabetes and corneal nerve fibres. We will set inclusion and exclusion criteria prior to the search, and two reviewers will screen titles and abstracts independently. One reviewer will full text read eligible articles and chart data from the studies. A descriptive summary of the methods used in imaging, image processing and quantitative analysis of peripheral corneal nerve fibres by IVCM will be written.

ETHICS AND DISSEMINATION

Ethical approval is not required since this is a scoping review based on previously published articles. The findings will be published in a scientific peer-reviewed journal.

Diabetic Retinopathy: Soluble and Imaging Ocular Biomarkers

Diabetic retinopathy (DR), the most common microvascular complication of diabetes mellitus, represents the leading cause of acquired blindness in the working-age population. Due to the potential absence of symptoms in the early stages of the disease, the identification of clinical biomarkers can have a crucial role in the early diagnosis of DR as well as for the detection of prognostic factors. In particular, imaging techniques are fundamental tools for screening, diagnosis, classification, monitoring, treatment planning and prognostic assessment in DR. In this context, the identification of ocular and systemic biomarkers is crucial to facilitate the risk stratification of diabetic patients; moreover, reliable biomarkers could provide prognostic information on disease progression as well as assist in predicting a patient's response to therapy. In this context, this review aimed to provide an updated and comprehensive overview of the soluble and anatomical biomarkers associated with DR.

Diabetic corneal neuropathy as a surrogate marker for diabetic peripheral neuropathy

Diabetic neuropathy is a prevalent microvascular complication of diabetes mellitus, affecting nerves in all parts of the body including corneal nerves and peripheral nervous system, leading to diabetic corneal neuropathy and diabetic peripheral neuropathy, respectively. Diabetic peripheral neuropathy is diagnosed in clinical practice using electrophysiological nerve conduction studies, clinical scoring, and skin biopsies. However, these diagnostic methods have limited sensitivity in detecting small-fiber disease, hence they do not accurately reflect the status of diabetic neuropathy. More recently, analysis of alterations in the corneal nerves has emerged as a promising surrogate marker for diabetic peripheral neuropathy. In this review, we will discuss the relationship between diabetic corneal neuropathy and diabetic peripheral neuropathy, elaborating on the foundational aspects of each: pathogenesis, clinical presentation, evaluation, and management. We will further discuss the relevance of diabetic corneal neuropathy in detecting the presence of diabetic peripheral neuropathy, particularly early diabetic peripheral neuropathy; the correlation between the severity of diabetic corneal neuropathy and that of diabetic peripheral neuropathy; and the role of diabetic corneal neuropathy in the stratification of complications of diabetic peripheral neuropathy.

Corneal Confocal Microscopy as a Quantitative Imaging Biomarker of Diabetic Peripheral Neuropathy: A Review

Distal symmetric polyneuropathy (DPN), particularly chronic sensorimotor DPN, represents one of the most frequent complications of diabetes, affecting 50% of diabetic patients and causing an enormous financial burden. Whilst diagnostic methods exist to detect and monitor this condition, they have significant limitations, mainly due to their high subjectivity, invasiveness, and non-repeatability. Corneal confocal microscopy (CCM) is an in vivo, non-invasive, and reproducible diagnostic technique for the study of all corneal layers including the sub-basal nerve plexus, which represents part of the peripheral nervous system. We reviewed the current literature on the use of CCM as an instrument in the assessment of diabetic patients, particularly focusing on its role in the study of sub-basal nerve plexus alterations as a marker of DPN. CCM has been demonstrated to be a valid in vivo tool to detect early sub-basal nerve plexus damage in adult and pediatric diabetic patients, correlating with the severity of DPN. Despite its great potential, CCM has still limited application in daily clinical practice, and more efforts still need to be made to allow the dissemination of this technique among doctors taking care of diabetic patients.

Corneal Nerve Changes Observed by In Vivo Confocal Microscopy in Patients Receiving Oxaliplatin for Colorectal Cancer: The COCO Study

An objective method of early identification of people at risk of chemotherapy-induced peripheral neuropathy is needed to minimize long-term toxicity and maximize dose intensity. The aims of the study were to observe corneal nerve microstructure and corneal sensitivity changes and peripheral neuropathy in patients receiving oxaliplatin, and to determine its association with corneal parameters at different stages of treatment and assess utility as non-invasive markers to detect and monitor peripheral neuropathy. Twenty-three patients scheduled to receive oxaliplatin chemotherapy with intravenous 5-FU for gastro-intestinal cancer were recruited and followed up with for 12 months. Ocular examinations including corneal and retinal evaluations, alongside peripheral neuropathy assessment, were performed. The corneal nerve density did not show significant change after chemotherapy when measured with a widely used semi-automated program or an automated analysis technique. Macula and optic nerve function did not change during or after oxaliplatin chemotherapy. However, the corneal nerve density modestly correlated with clinical peripheral neuropathy after 20 weeks of chemotherapy (r = 0.61, p = 0.01) when peripheral neuropathy is typical most profound, and corneal nerve sensitivity correlated with neuropathy at 12 (r = 0.55, p = 0.01) and 20 weeks (r = 0.64, p = 0.006). In conclusion, corneal changes detected on confocal microscopy show moderate association with peripheral neuropathy, indicating their potential to identify the development of oxaliplatin-induced peripheral neuropathy. However, further studies are required to confirm these findings.

A Novel Algorithm for the Evaluation of Corneal Nerve Beadings by in vivo Confocal Microscopy in Patients With Type 1 Diabetes Mellitus

Purpose

Peripheral neuropathy could complicate diabetes mellitus (DM). In vivo confocal microscopy (IVCM) is an ocular examination for the diagnosis of small fiber neuropathies and the detection of the earliest corneal sub-basal nerve plexus (SBP) alterations. Corneal SBP characteristics include focal enlargement along with the nerve fiber, called corneal beadings. These dilatations represent a mitochondrial accumulation induced by the reactive oxygen stress, as a consequence of hyperglycemia. For this reason, corneal beadings are considered indicative of metabolic activity. This study aimed to describe the corneal characteristics of a population of type 1 diabetes mellitus (T1DM) well metabolically controlled, using a new algorithm for the analysis of corneal beading size (BS).

Methods

Patients aged ≥18 years affected by T1DM were compared with healthy subjects who underwent IVCM (Confoscan 4; Nidek Technologies Padova, Italy). Starting from the coordinates of the beadings detected by the IVCM, we implemented a new algorithm for automatically measuring BS in corneal SBP images.

Results

We compared 20 eyes of T1DM patients with 26 healthy controls. The corneal nerves' fiber length (p = 0.008), corneal nerves' fiber length density (p = 0.008), and the number of fibers (p = 0.017) were significantly lower in the diabetic group compared with controls. There was no difference between diabetic and healthy eyes in the mean number of corneal beadings both in the frame of analysis (p = 0.606) and for 0.1 mm of SBP nerve (p = 0.145). Regarding the BS, patients with T1DM had corneal beadings larger than controls (p = 0.036).

Conclusions

We found that the corneal beadings parameters are similar in healthy and T1DM individuals. Nevertheless, measuring the BS with our algorithm, we showed that corneal beadings are enlarged in patients affected by T1DM when compared with healthy controls. Identifying beading expansion in corneal nerve fiber using IVCM should become a useful tool to predict peripheral neuropathy at an early stage.

Corneal in vivo Confocal Microscopy for Assessment of Non-Neurological Autoimmune Diseases: A Meta-Analysis

Purpose

This study aimed to evaluate the features of corneal nerve with in vivo confocal microscopy (IVCM) among patients with non-neurological autoimmune (NNAI) diseases.

Methods

We systematically searched PubMed, Web of Science, and Cochrane Central Register of Controlled Trials for studies published until May 2021. The weighted mean differences (WMDs) of corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), tortuosity, reflectivity, and beadings per 100 μm with a 95% CI between NNAI and control group were analyzed using a random-effects model.

Results

The results showed 37 studies involving collective totals of 1,423 patients and 1,059 healthy controls were ultimately included in this meta-analysis. The pooled results manifested significantly decreased CNFL (WMD: −3.94, 95% CI: −4.77–−3.12), CNFD (WMD: −6.62, 95% CI: −8.4–−4.85), and CNBD (WMD: −9.89, 95% CI: −14–−5.79) in NNAI patients. In addition, the NNAI group showed more tortuous corneal nerve (WMD: 1.19, 95% CI:0.57–1.81). The comparison between NNAI patients and healthy controls in beadings per 100 μm corneal nerve length was inconsistent. No significant difference was found in the corneal nerve fiber reflectivity between NNAI and the control group (WMD: −0.21, 95% CI: −0.65–0.24, P = 0.361).

Conclusions

The parameters and morphology of corneal nerves observed by IVCM proved to be different in NNAI patients from healthy controls, suggesting that IVCM may be a non-invasive technique for identification and surveillance of NNAI diseases.

Corneal Confocal Microscopy to Image Small Nerve Fiber Degeneration: Ophthalmology Meets Neurology

Neuropathic pain has multiple etiologies, but a major feature is small fiber dysfunction or damage. Corneal confocal microscopy (CCM) is a rapid non-invasive ophthalmic imaging technique that can image small nerve fibers in the cornea and has been utilized to show small nerve fiber loss in patients with diabetic and other neuropathies. CCM has comparable diagnostic utility to intraepidermal nerve fiber density for diabetic neuropathy, fibromyalgia and amyloid neuropathy and predicts the development of diabetic neuropathy. Moreover, in clinical intervention trials of patients with diabetic and sarcoid neuropathy, corneal nerve regeneration occurs early and precedes an improvement in symptoms and neurophysiology. Corneal nerve fiber loss also occurs and is associated with disease progression in multiple sclerosis, Parkinson's disease and dementia. We conclude that corneal confocal microscopy has good diagnostic and prognostic capability and fulfills the FDA criteria as a surrogate end point for clinical trials in peripheral and central neurodegenerative diseases.

Neurodegeneration of the cornea and retina in patients with type 1 diabetes without clinical evidence of diabetic retinopathy

AIM

Diabetic retinopathy (DR) is widely considered the earliest and most common microvascular complication of diabetes. However, recent studies have shown that retinal nerve fiber layer and corneal nerve abnormalities may be present in diabetic patients without retinopathy. This preliminary study aimed to establish if structural and functional changes in the nerve fiber layer of the retina and cornea occur in patients with type 1 diabetes (T1DM) without retinopathy.

METHODS

Twenty patients with T1DM, without clinical evidence of retinopathy (Age: 47.0 ± 2.5 years; Duration diabetes: 27.0 ± 3 years) and 15 age-matched healthy control subjects underwent detailed medical neurological examinations. Ophthalmic examinations using Spectral Domain Optical coherence tomography (SD-OCT), Standard Automated Perimetry (SAP), Flicker Defined Form High Edge Perimetry (FDF), Corneal Confocal Microscopy (CCM) and Non-contact corneal Aesthesiometry (NCCA) were performed to quantify the structure and function of the nerves in the retina and cornea, respectively.

RESULTS

At the structural level, retinal nerve fiber layer thickness (RNFL) was significantly reduced in the superior nasal (p=0.001) and inferior temporal (p=0.004) sectors, in diabetic patients. Retinal ganglion layer function was reduced in the patient group when assessed using Flicker Defined Form Perimetry (FDF), but this was not significant. The function of the cornea assessed by corneal sensitivity, using a non-contact corneal aesthesiometer (NCCA), was significantly reduced (p=0.001). Structural assessment of corneal nerves using corneal confocal microscopy (CCM) showed reduction at corneal nerve fiber density (CNFD) (p=0.01), branch density (CNBD) (p=0.006) and length (CNFL) (p=0.01) in patients with diabetes. Compared to control subjects, the percentage of abnormality in patients with T1DM for RNFL was 32% while the FDF was abnormal in 61% of patients. Corneal abnormality was observed in 47% for NCCA, 28% for CNFD, and 17% for CNFL. There was no correlation between neuronal damage in the retina and cornea.

CONCLUSIONS

Neuronal abnormalities were observed in both the retina and cornea of diabetic patients without evidence of retinopathy. The prevalence of structural and functional changes was higher in the retina compared to the cornea. This preliminary study suggests that structural neuronal changes may occur in parallel and correlate with functional changes. The assessment of corneal and retinal nerve structure may be clinically useful for detecting and monitoring the earliest stages of diabetic microvascular abnormalities.

Implementation of corneal confocal microscopy for screening and early detection of diabetic neuropathy in primary care alongside retinopathy screening: Results from a feasibility study

OBJECTIVE

Screening for diabetic peripheral neuropathy (DPN) is essential for early detection and timely intervention. Quantitative assessment of small nerve fiber damage is key to the early diagnosis and assessment of its progression. Corneal confocal microscopy (CCM) is a non-invasive, in-vivo diagnostic technique that provides an accurate surrogate biomarker for small-fiber neuropathy. In this novel study for the first time, we introduced CCM to primary care as a screening tool for DPN alongside retinopathy screening to assess the level of neuropathy in this novel cohort.

RESEARCH DESIGN AND METHODS

450 consecutive subjects with type 1 or type 2 diabetes attending for annual eye screening in primary care optometry settings underwent assessment with CCM to establish the prevalence of sub-clinical diabetic peripheral neuropathy. Subjects underwent assessment for neurological and ocular symptoms of diabetes and a history of diabetic foot disease, neuropathy and diabetic retinopathy (DR).

RESULTS

CCM examination was completed successfully in 427 (94.9%) subjects, 22% of whom had neuropathy according to Diabetic Neuropathy Symptom (DNS) score. The prevalence of sub-clinical neuropathy as defined by abnormal corneal nerve fiber length (CNFL) was 12.9%. In the subjects with a short duration of type 2 diabetes, 9.2% had abnormal CNFL. CCM showed significant abnormalities in corneal nerve parameters in this cohort of subjects with reduction of corneal nerve fiber density (CNFD, p<0.001), CNFL (p<0.001) and corneal nerve branch density (CNBD, p<0.001) compared to healthy subjects. In subjects who had no evidence of DR (67% of all subjects), 12.0% had abnormal CNFL.

CONCLUSIONS

CCM may be a sensitive biomarker for early detection and screening of DPN in primary care alongside retinopathy screening.

Corneal nerve loss is related to the severity of painful diabetic neuropathy

Background and purpose

Previously it has been shown that patients with painful diabetic neuropathy (PDN) have greater corneal nerve loss compared to patients with painless diabetic neuropathy. This study investigated if the severity of corneal nerve loss was related to the severity of PDN.

Methods

Participants with diabetic neuropathy (n = 118) and healthy controls (n = 38) underwent clinical and neurological evaluation, quantitative sensory testing, nerve conduction testing and corneal confocal microscopy and were categorized into those with no (n = 43), mild (n = 34) and moderate‐to‐severe (n = 41) neuropathic pain.

Results

Corneal nerve fibre density (p = 0.003), corneal nerve fibre length (p < 0.0001) and cold perception threshold (p < 0.0001) were lower and warm perception threshold was higher (p = 0.002) in patients with more severe pain, but there was no significant difference in the neuropathy disability score (p = 0.5), vibration perception threshold (p = 0.5), sural nerve conduction velocity (p = 0.3) and amplitude (p = 0.7), corneal nerve branch density (p = 0.06) and deep breathing heart rate variability (p = 0.08) between patients with differing severity of PDN. The visual analogue scale correlated significantly with corneal nerve fibre density (r = −0.3, p = 0.0002), corneal nerve branch density (r = −0.3, p = 0.001) and corneal nerve fibre length (r = −0.4, p < 0.0001). Receiver operating curve analysis showed that corneal nerve fibre density had an area under the curve of 0.78 with a sensitivity of 0.73 and specificity of 0.72 for the diagnosis of PDN.

Conclusions

Corneal confocal microscopy reveals increasing corneal nerve fibre loss with increasing severity of neuropathic pain and a good diagnostic outcome for identifying patients with PDN.

Corneal Confocal Microscopy: A Biomarker for Diabetic Peripheral Neuropathy

PURPOSE

Diagnosing early diabetic peripheral neuropathy remains a challenge due to deficiencies in currently advocated end points. The cornea is densely innervated with small sensory fibers, which are structurally and functionally comparable to intraepidermal nerve fibers. Corneal confocal microscopy is a method for rapid, noninvasive scanning of the living cornea with high resolution and magnification.

METHODS

This narrative review presents the framework for the development of biomarkers and the literature on the use and adoption of corneal confocal microscopy as an objective, diagnostic biomarker in experimental and clinical studies of diabetic peripheral neuropathy. A search was performed on PubMed and Google Scholar based on the terms "corneal confocal microscopy," "diabetic neuropathy," "corneal sensitivity," and "clinical trials."

FINDINGS

A substantial body of evidence underpins the thesis that corneal nerve loss predicts incident neuropathy and progresses with the severity of diabetic peripheral neuropathy. Corneal confocal microscopy also identifies early corneal nerve regeneration, strongly arguing for its inclusion as a surrogate end point in clinical trials of disease-modifying therapies.

IMPLICATIONS

There are sufficient diagnostic and prospective validation studies to fulfill the US Food and Drug Administration criteria for a biomarker to support the inclusion of corneal confocal microscopy as a primary end point in clinical trials of disease-modifying therapies in diabetic neuropathy.

Early detection of neuropathy in patients with type 2 diabetes with or without microalbuminuria in the absence of peripheral neuropathy and retinopathy

PURPOSE

Our goal is early detection of neuropathy in patients with type 2 diabetes with or without microalbuminuria in the absence of diabetic retinopathy and peripheral neuropathy by using in vivo corneal confocal microscopy (IVCCM).

METHODS

A total of 60 type-2 diabetic patients, assigned to either a diabetes mellitus (DM) with microalbuminuria group (DM/MA+, n=30) or a DM without microalbuminuria group (DM/MA-, n=30), and 30 age-matched control subjects were enrolled in this study. All cases underwent evaluation of blood glucose level, HbA_1c, lipid fractions, body mass index (BMI), and corneal sensitivity (CS). Corneal nerve fiber length (NFL), nerve fiber density (NFD), nerve branch density (NBD), and tortuosity coefficient (TC) were quantified by IVCCM. None of the patients had peripheral neuropathy or retinopathy.

RESULTS

Compared with the healthy subjects, NFL and NFD were reduced in both diabetic groups (P<0.0001), while NBD was significantly reduced in the DM/MA+ group. Between the diabetic groups, NFL, NFD, and NBD were significantly higher in the DM/MA- group (all P's<0.001). CS was significantly lower in DM/MA+ compared with DM/MA- and controls (both P's<0.0001). NFD and NFL were inversely correlated with age, triglyceride level, and BMI.

CONCLUSION

These results indicate that significant damage to small nerves, quantified using IVCCM, can be detected in the absence of retinopathy, peripheral neuropathy or microalbuminuria in type 2 diabetic patients. The severity of corneal nerve involvement may further increase in the presence of nephropathy. This feature may also be valuable for early detection of microvascular complications of DM, allowing for the prevention of progression of life threatening microvascular complications.

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.

Improvements in Diabetic Neuropathy and Nephropathy After Bariatric Surgery: a Prospective Cohort Study

PURPOSE

There are limited data on the impact of bariatric surgery on microvascular complications of type 2 diabetes (T2D), particularly diabetic neuropathy. We assessed microvascular complications (especially neuropathy) in obese patients with T2D before and 12 months after bariatric surgery.

MATERIALS AND METHODS

This was a prospective observational cohort study. Measurements of neuropathy symptom profile (NSP), neuropathy disability score (NDS), vibration (VPT), cold (CPT) and warm (WPT) perception thresholds, nerve conduction studies (NCS) and corneal confocal microscopy (CCM) to quantify corneal nerve fibre density (CNFD), branch density (CNBD) and fibre length (CNFL); urinary albumin/creatinine ratio (uACR), estimated glomerular filtration rate (eGFRcyst-creat) and retinal grading were taken.

RESULTS

Twenty-six (62% female; median age 52 years) obese patients with T2D were recruited. Body mass index (BMI) (47.2 to 34.5 kg/m2; p < 0.001) decreased post-operatively. There were improvements in CNFD (27.1 to 29.2/mm2; p = 0.005), CNBD (63.4 to 77.8/mm2; p = 0.008), CNFL (20.0 to 20.2/mm2; p = 0.001), NSP (3 to 0/38; p < 0.001) and eGFRcyst-creat (128 to 120 ml/min; p = 0.015) post-bariatric surgery. Changes in (Δ) triglycerides were independently associated with ΔCNFL (β = - 0.53; p = 0.024) and Δsystolic blood pressure (β = 0.62;p = 0.017), and %excess BMI loss (β = - 0.004; p = 0.018) were associated with ΔeGFRcyst-creat. There was no significant change in NDS, VPT, CPT, WPT, NCS, uACR or retinopathy status. Glomerular hyperfiltration resolved in 42% of the 12 patients with this condition pre-operatively.

CONCLUSION

Bariatric surgery results in improvements in small nerve fibres and glomerular hyperfiltration in obese people with T2D, which were associated with weight loss, triglycerides and systolic blood pressure, but with no change in retinopathy or uACR at 12 months.

A Review of Imaging Biomarkers of the Ocular Surface

A biomarker is a "characteristic that is measured as an indicator of normal biological processes, pathogenic processes, or responses to an exposure or intervention, including therapeutic interventions." Recently, calls for biomarkers for ocular surface diseases have increased, and advancements in imaging technologies have aided in allowing imaging biomarkers to serve as a potential solution for this need. This review focuses on the state of imaging biomarkers for ocular surface diseases, specifically non-invasive tear break-up time (NIBUT), tear meniscus measurement and corneal epithelial thickness with anterior segment optical coherence tomography (OCT), meibomian gland morphology with infrared meibography and in vivo confocal microscopy (IVCM), ocular redness with grading scales, and cellular corneal immune cells and nerve assessment by IVCM. Extensive literature review was performed for analytical and clinical validation that currently exists for potential imaging biomarkers. Our summary suggests that the reported analytical and clinical validation state for potential imaging biomarkers is broad, with some having good to excellent intra- and intergrader agreement to date. Examples of these include NIBUT for dry eye disease, ocular redness grading scales, and detection of corneal immune cells by IVCM for grading and monitoring inflammation. Further examples are nerve assessment by IVCM for monitoring severity of diabetes mellitus and neurotrophic keratitis, and corneal epithelial thickness assessment with anterior segment OCT for the diagnosis of early keratoconus. However, additional analytical validation for these biomarkers is required before clinical application as a biomarker.

Early Detection of Diabetic Peripheral Neuropathy: A Focus on Small Nerve Fibres

Diabetic peripheral neuropathy (DPN) is the most common complication of both type 1 and 2 diabetes. As a result, neuropathic pain, diabetic foot ulcers and lower-limb amputations impact drastically on quality of life, contributing to the individual, societal, financial and healthcare burden of diabetes. DPN is diagnosed at a late, often pre-ulcerative stage due to a lack of early systematic screening and the endorsement of monofilament testing which identifies advanced neuropathy only. Compared to the success of the diabetic eye and kidney screening programmes there is clearly an unmet need for an objective reliable biomarker for the detection of early DPN. This article critically appraises research and clinical methods for the diagnosis or screening of early DPN. In brief, functional measures are subjective and are difficult to implement due to technical complexity. Moreover, skin biopsy is invasive, expensive and lacks diagnostic laboratory capacity. Indeed, point-of-care nerve conduction tests are convenient and easy to implement however questions are raised regarding their suitability for use in screening due to the lack of small nerve fibre evaluation. Corneal confocal microscopy (CCM) is a rapid, non-invasive, and reproducible technique to quantify small nerve fibre damage and repair which can be conducted alongside retinopathy screening. CCM identifies early sub-clinical DPN, predicts the development and allows staging of DPN severity. Automated quantification of CCM with AI has enabled enhanced unbiased quantification of small nerve fibres and potentially early diagnosis of DPN. Improved screening tools will prevent and reduce the burden of foot ulceration and amputations with the primary aim of reducing the prevalence of this common microvascular complication.

Diagnostic utility of corneal confocal microscopy in type 2 diabetic peripheral neuropathy

Aims/Introduction

The early pathological changes of diabetic peripheral neuropathy (DPN) are mainly small nerve fiber injuries. Corneal confocal microscopy (CCM) is an easy, rapid, non‐invasive and repeatable technique to detect the damage of small nerve fibers. The purpose of this study was to explore the application of CCM in DPN and other chronic complications of type 2 diabetes mellitus.

Materials and Methods

A total of 220 individuals (48 normal healthy control participants and 172 patients with type 2 diabetes mellitus) were included in the study. All participants were assessed and scored for neurological symptoms and neurological deficits, quantitative sensory test, neuroelectrophysiological test, and CCM.

Results

Corneal nerve fiber density, corneal nerve fiber length and corneal nerve branch density were significantly reduced in patients with type 2 diabetes mellitus compared with normal healthy control subjects (P < 0.001, P < 0.001 and P < 0.001, respectively). In the DPN group, corneal nerve fiber density, corneal nerve branch density and corneal nerve fiber length were significantly lower than for patients without DPN (P < 0.001, P < 0.001 and P < 0.001, respectively). Receiver operating characteristic analysis showed that the optimal cut‐off values were 24.68, 39 and 15.315, respectively, in which corneal nerve fiber density and corneal nerve fiber length had moderate sensitivity and specificity.

Conclusion

This study provides more support for the clinical use of CCM to diagnose type 2 diabetes mellitus‐related complications, especially DPN.

Corneal nerves in diabetes-The role of the in vivo corneal confocal microscopy of the subbasal nerve plexus in the assessment of peripheral small fiber neuropathy

The cornea's intense innervation is responsible for corneal trophism and ocular surface hemostasis maintenance. Corneal diabetic neuropathy affects subbasal nerve plexus, with progressive alteration of nerves' morphology and density. The quantitative analysis of nerve fibers can be performed with in vivo corneal confocal microscopy considering the main parameters such as corneal nerve fibers length, corneal nerve fibers density, corneal nerve branching density, tortuosity coefficient, and beadings frequency. As the nerve examination permits the detection of early changes occurring in diabetes, the invivo corneal confocal microscopy becomes, over time, an important tool for diabetic polyneuropathy assessment and follow-up. In this review, we summarize the actual evidence about corneal nerve changes in diabetes and the relationship between the grade of alterations and the duration and severity of the disease. We aim at understanding how diabetes impacts corneal nerves and how it correlates with sensorimotor peripheral polyneuropathy and retinal complications. We also attempt to analyze the safety of the most common surgical procedures such as cataract and refractive surgery in diabetic patients and to highlight the specific risk factors. We believe that information about the corneal nerve fibers' condition obtained from the in vivo subbasal nerve plexus investigation may be crucial in monitoring peripheral small fiber polyneuropathy and that it will help with decision-making in ophthalmic surgery in diabetic patients.

Clinical and confocal imaging findings in congenital corneal anaesthesia

BACKGROUND/AIMS

Congenital corneal anaesthesia (CCA) is an uncommon cause of corneal ulceration in young patients, with a reported poor visual prognosis. We correlated clinical findings in patients with CCA with corneal sub-basal nerve plexus (SBNP) morphology and dendritiform cell density (DCD) on confocal microscopy.

METHODS

A prospective, case-control study was conducted at a referral clinic. History includied presenting features in patients with CCA, clinical course and examination findings. Differences in SBNP morphology and DCD on in vivo confocal microscopy (IVCM) were compared in cases and control subjects with healthy corneas.

RESULTS

Eight patients with CCA were examined, of which three had a diagnosis of familial dysautonomia. Age at initial diagnosis of corneal disease ranged from infancy to 22 years, the most common presentation being corneal ulceration. All patients with CCA except one with optic neuropathy had corrected visual acuity 6/18 (logMAR 0.35) or better in at least one eye. Measured corneal sensation was minimal in all patients. Major abnormalities were found on confocal microscopy in all patients with CCA, whether or not inherited, including statistically significant reduction in SBNP nerve fibre density, fibre length and branch density. Increased DCD in superficial cornea was found in all patients with CCA.

CONCLUSION

Good visual acuity can be maintained in eyes with corneal anaesthesia present from birth. IVCM provides direct evidence of a morphological correlate for measured corneal anaesthesia. Increased DCD may indicate an enhanced role for innate immune cells in superficial cornea in protection of the anaesthetic ocular surface.

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.

Diabetic Neuropathy Is Characterized by Progressive Corneal Nerve Fiber Loss in the Central and Inferior Whorl Regions

Purpose

We hypothesized that longitudinal changes in corneal nerve morphology would differ between the central cornea and inferior whorl in relation to other measures of diabetic neuropathy.

Methods

Thirty patients with diabetes (age: 54.08 ± 15.86, duration: 23.95 ± 14.2, HbA1c: 7.51 ± 1.37) and 19 age-matched healthy controls (age: 49.47 ± 13.25) underwent assessment of neuropathy disability score (NDS), vibration perception threshold (VPT), cold (CPT) and warm (WPT) perception thresholds, peroneal motor nerve conduction velocity (PMNCV), corneal nerve fiber density (CNFD), branch density (CNBD), fiber length (CNFL), inferior whorl length (IWL), and the average of CNFL and IWL (ANFL) at baseline and after 1 to 8 years.

Results

In patients with diabetes, between baseline and follow-up, there was a significant reduction in CNBD (57.72 ± 30.08 vs. 44.04 ± 23.69; P = 0.02), CNFL (21.77 ± 5.19 vs. 15.65 ± 4.7; P < 0.0001), IWL (24.69 ± 8.67 vs. 14.23 ± 6.13; P < 0.0001), ANFL (23.26 ± 5.53 vs. 15.09 ± 4.48; P < 0.0001), and WPT (43.56 ± 4.43 vs. 40.78 ± 4.93; P = 0.01), and an increase in VPT (12.9 ± 8.96 vs. 13.78 ± 8.99; P = 0.02). There was no significant change in CNFD (27.12 ± 8.2 vs. 25.43 ± 7.11; P = 0.2), NDS (3.38 ± 3.35 vs. 2.61 ± 2.8; P = 0.08), CPT (17.7 ± 10.59 vs. 22.45 ± 9.23; P = 0.06), or PMNCV (42.4 ± 4.21 vs. 42.16 ± 6.3; P = 0.2).

Conclusions

There is evidence of corneal nerve loss in patients with diabetes, particularly at the inferior whorl during follow-up.

Region of interest and directional analysis of subbasal nerves in wide-area corneal nerve plexus mosaics in type 2 diabetes mellitus

In vivo confocal microscopy (IVCM) imaging of the corneal subbasal nerve plexus (SBNP) is a clinical imaging modality gaining popularity for the diagnosis and follow-up of corneal neuropathy in various conditions such as diabetes mellitus. There remain, however, major limitations to the method, hindering its widespread clinical use. Finding the same exact area of the central cornea to standardize image acquisition is difficult without a reference point. Alternatively, creating wide-area mosaics of the SBNP is resource-intensive and has not yet been developed for routine clinical use. Here, we investigated whether IVCM analysis of the corneal SBNP in a predetermined, anatomically standardized region of interest (ROI) could be applied as an equivalent substitution for wide-area SBNP mosaic generation and analysis. Furthermore, we investigated nerve patterns outside the central corneal region for a possible relationship to type 2 diabetes mellitus status using a publicly available dataset. We found that corneal nerve fibre length density (CNFL) based on the ROI underestimated the mosaic-based CNFL by an average of 34% in 90% of cases (150 eyes), and did not exhibit a significant reduction with diabetes, as seen in the full SBNP. Outside the central cornea, nerve orientation differed depending on the anatomic region (left, central or right superior plexus, P < 0.001). Moreover, in long-term type 2 diabetes mellitus (≥ 10 years, 28 subjects), nerve density in the left superior sector of the SBNP was decreased (P < 0.001) while that in the central superior SBNP increased (P = 0.01) relative to 35 age-matched healthy subjects with normal glucose tolerance. These results indicate that subbasal nerve degeneration in type 2 diabetes mellitus can vary according to anatomic location, and regions with potential diagnostic value outside the central SBNP may warrant further investigation.

Diabetic peripheral neuropathy in people with type 2 diabetes: too little too late

Diabetic peripheral neuropathy in people with type 2 diabetes is poorly managed because of its insidious onset, delayed diagnosis and more complex aetiology resulting from the contribution of not only hyperglycaemia, but also ageing, hyperlipidaemia, hypertension and obesity. Because there is no US Food and Drug Adminstration-approved disease-modifying therapy for diabetic peripheral neuropathy, the key to ameliorating it in type 2 diabetes has to be through earlier diagnosis and timely multi-factorial risk factor reduction. The management of painful diabetic peripheral neuropathy also requires a detailed appraisal of the choice of therapy, taking into account efficacy, patient wishes, comorbidities, side effect profile and potential for abuse.

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.

Multifocal electroretinogram in diabetic macular edema and its correlation with different optical coherence tomography features

PURPOSE

To evaluate multifocal electroretinogram (mfERG) parameters in eyes with diabetic macular edema (DME) and its correlation with vision and optical coherence tomography (OCT) features.

METHODS

Fifty-four eyes of 27 subjects with DME due to nonproliferative diabetic retinopathy were evaluated. MfERG responses were measured in three concentric rings. Macular thickness was measured by OCT in each segment of the three concentric rings, and mfERG rings were superimposed on the macular thickness map. The correlation between macular thickness in specific points of the thickness map and changes of the mfERG parameters in the corresponding points of the mfERG field map was evaluated and the relationship between the OCT and mfERG changes and changes of best-corrected visual acuity (BCVA) was investigated. The central foveal B-scans of SD-OCT were used to evaluate any correlation between the external limiting membrane (ELM) status, ellipsoid zone (EZ) status, presence of cysts or disorganization of retinal inner layers (DRIL), and mfERG parameters at the central corresponding area.

RESULTS

The mean of BCVA was 0.5 ± 0.3 in logMAR, and the central macular thickness was 392.6 ± 123.4 microns. The central ring P1 and N2 amplitudes had a significant correlation with BCVA in univariate and multivariate analyses (P = 0.001 for both, r = - 0.346 and r = - 0.646, respectively). There was a significant correlation between retinal thickness and the N1 amplitude in the central ring (P = 0.02, r = - 0.343). Outer retinal layer disruption (ELM and EZ) correlated with prolonged P1 implicit time at the corresponding location (P = 0.005, r = 0.068). The presence of the DRIL was associated with reduced P1 and N2 amplitudes (P = 0.037, r = - 0.284 and P = 0.019, r = - 0.562, respectively). A significant correlation was also found between the presence of cysts and a lower central P1 amplitude (P = 0.033, r = - 0.376).

CONCLUSION

In diabetic patients, discrete changes of some parameters in the central ring of the mfERG field map (e.g., P1 and N2 amplitudes) have a significant correlation with both structural OCT abnormalities in the corresponding points of the thickness map (like DRIL, intraretinal cyst and ELM/EZ disruption) and BCVA. Predictive models such as those described in this report may make it possible to identify the relationship between specific anatomical and functional characteristics in diabetic retinopathy.

Latent autoimmune diabetes of adulthood (LADA) is associated with small fibre neuropathy

AIM

To assess if latent autoimmune diabetes of adulthood (LADA) is associated with small fibre neuropathy.

METHODS

Participants with LADA (n=31), Type 2 diabetes (n=31) and healthy control participants without diabetes (n=31) underwent a detailed assessment of neurologic deficits, quantitative sensory testing, electrophysiology, skin biopsy and corneal confocal microscopy.

RESULTS

The groups were matched for age (healthy control without diabetes: 53.5±9.1 vs. Type 2 diabetes: 58.0±6.5 vs. LADA: 53.2±11.6 years), duration of diabetes (Type 2 diabetes: 10.0±8.3 vs. LADA: 11.0±9.1 years) and blood pressure. However, BMI (P=0.01) and triglycerides (P=0.0008) were lower and HbA_1c (P=0.0005), total cholesterol (P=0.01) and HDL (P=0.002) were higher in participants with LADA compared with Type 2 diabetes. Peroneal motor nerve conduction velocity (P=0.04) and sural sensory nerve conduction velocity (P=0.008) were lower in participants with latent autoimmune diabetes in adults compared with Type 2 diabetes. Intra-epidermal nerve fibre density (P=0.008), corneal nerve fibre density (P=0.003) and corneal nerve branch density (P=0.006) were significantly lower in participants with LADA compared with Type 2 diabetes. There were no significant differences in the other neuropathy parameters.

CONCLUSIONS

Despite comparable age and duration of diabetes, participants with LADA demonstrate more severe neuropathy and particularly small fibre neuropathy, compared with participants with Type 2 diabetes.

ASSOCIATIONS BETWEEN INDIVIDUAL RETINAL LAYER THICKNESSES AND DIABETIC PERIPHERAL NEUROPATHY USING RETINAL LAYER SEGMENTATION ANALYSIS

PURPOSE

To evaluate clinical correlations between the thicknesses of individual retinal layers in the foveal area of diabetic patients and the presence of diabetic peripheral neuropathy (DPN).

METHODS

This retrospective, observational, cross-sectional study enrolled a total of 120 eyes from 120 patients. The eyes were divided into 3 groups: normal controls (n = 42 eyes), patients with diabetes mellitus (n = 42 eyes) but no DPN, and patients with diabetes mellitus and DPN (n = 36 eyes). The primary outcome measures were the thickness of all retinal layers in the central 1-mm zone measured using the segmentation analysis of spectral-domain optical coherence tomography. Correlations between the thicknesses of the individual retinal layers and the presence of DPN were also analyzed. Logistic regression analyses were used to determine which change in layer thickness had the most significant association with the presence of DPN.

RESULTS

The mean thicknesses and the ratios of retinal nerve fiber layers to total retina thicknesses in the DPN group were 10.77 ± 1.79 μm and 4.10 ± 0.55%, which was significantly lower than those in normal controls and the diabetes mellitus with no DPN group (P = 0.014 and P = 0.001, respectively). Logistic regression analyses also showed that the decrease in thicknesses of the retinal nerve fiber layers and the inner nuclear layer are significant factors for predicting a higher risk for DPN development (odds ratio = 7.407 and 1.757; P < 0.001 and P = 0.001, respectively).

CONCLUSION

A decrease in the retinal nerve fiber layer and the inner nuclear layer thickness was significantly associated with the presence of DPN.

Early Alterations of Corneal Subbasal Plexus in Uncomplicated Type 1 Diabetes Patients

Purpose

The purpose of our study is to describe the in vivo corneal confocal microscopy characteristics of subbasal nerve plexus in a highly selected population of patients affected by type 1 diabetes mellitus (T1DM) without any microvascular diabetes complications.

Methods

We included 19 T1DM patients without diabetic peripheral neuropathy, diabetic autonomic neuropathy, diabetic retinopathy, and microalbuminuria. All patients underwent in vivo corneal confocal microscopy and blood analysis to determine subbasal nerve plexus parameters and their correlation with clinical data. We compared the results with 19 healthy controls.

Results

The T1DM group showed a significant decrease of the nerve fiber length (P=0.032), the nerve fiber length density (P=0.034), the number of fibers (P=0.005), and the number of branchings (P=0.028), compared to healthy subjects. The nerve fiber length, nerve fiber length density, and number of fibers were directly related to the age at onset of diabetes and inversely to the duration of DM. BMI (body mass index) was highly related to the nerve fiber length (r = −0.6, P=0.007), to the nerve fiber length density (r = −0.6, P=0.007), and to the number of fibers (r = −0.587, P=0.008). No significant correlations were found between the corneal parameters and HbA1c.

Conclusions

Early subclinical fiber corneal variation could be easily detected using in vivo corneal confocal microscopy, even in type 1 diabetes without any microvascular diabetes complications, including diabetic peripheral neuropathy, diabetic autonomic neuropathy, diabetic retinopathy, and 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.

Glycemia Lowering Effect of an Aqueous Extract of Hedychium coronarium Leaves in Diabetic Rodent Models

Hedychium coronarium has a long history of use worldwide as a food and in folk medicine. In this study, we aimed to investigate the effect of an aqueous extract of H. coronarium leaves (HC) on type 2 diabetes mellitus (T2DM). Two types of animal models were used in this study: Streptozotocin (STZ)-induced T2DM (Wistar rats; N = 8) and C57BKSdb/db mice (N = 5). After treatment with HC for 28 days, glucose tolerance improved in both of the diabetic animal models. As significant effects were shown after 14 days of treatment in the STZ-induced T2DM model, we carried out the experiments with it. After 28 days of treatment with HC, the levels of cholesterol, triglyceride, high-density lipoprotein, and low-density lipoprotein were significantly improved in the STZ-induced T2DM model. The lesions degree of islet β-cells was decreased after the HC treatment. Although the insulin level increased moderately, the aldosterone level was significantly decreased in the HC-treated groups, suggesting that aldosterone might play an important role in this effect. In summary, HC is a natural product and it is worth exploring its effect on T2DM.

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.

In Vivo Characterization of Corneal Changes in a Type 1 Diabetic Animal Model

Diabetes mellitus (DM) is a metabolic disease that affects 9% of the adult population, promoting an increase in glucose concentration that affects the corneal structure, namely, its thickness, as well as the constituents and flow of the aqueous humor. In this study, high-frequency transducers (20-MHz and 50-MHz) were used to measure and characterize changes in the corneal and aqueous humor in streptozotocin-induced type 1 diabetic rats followed over 8 weeks. Increases of 24.6 and 15.4 μm in central corneal thickness were measured with the 20-MHz and 50-MHz probes, respectively, in DM rats (p < 0.001). The increases in thickness of the different corneal layers ranged from 7% to 17%. Structural alterations of the aqueous humor were also studied by relating the amplitudes of the anterior lens and posterior cornea boundary signals, the result of which was denominated by pseudo-attenuation. The results revealed an increase of 49% at week 8 compared with the baseline values (p < 0.020, with the 50-MHz probe). This study illustrated that high-frequency ultrasound can be used to measure corneal layer thickness and study the alterations promoted by diabetes in the eye's anterior segment. Those assessments may allow early detection of DM, improving the monitoring of diabetic patients.

Prevalence and Determinants of Painful and Painless Neuropathy in Type 1 Diabetes Mellitus

Aims: To evaluate (1) the prevalence of diabetic distal symmetrical sensory-motor polyneuropathy (DSPN) and painful DSPN among patients with type 1 diabetes mellitus (DM1) aged over 18 years and (2) the determinant factors of neuropathy and pain in those patients. Materials and Methods: An epidemiological, cross-sectional, observational study was performed; 330,386 people were included, and a total of 444 people were diagnosed with DM1. After exclusion of possible confounders, 360 patients were assessed for painless and painful DSPNs using neurological examination and questionnaires for neuropathy and pain. Odds ratio (OR) and confidence intervals (95% CI) were estimated using multinomial logistic regression models. The analysis was based on a framework with four conceptual levels that consider feasible pathways between several risk factors: (1) socio-demographic factors and diabetes duration, (2) patient habits, (3) co-morbidities, and (4) metabolic factors and disease complications. Results: The prevalence of DSPN and painful DSPN were 42.8 and 18.9%, respectively. Diabetes duration was positively associated with painful (OR = 1.107, 95% CI: 1.107-1.139) and painless DSPN (OR = 1.069, 95% CI: 1.043-1.096). Education level was negatively associated with painful DSPN (OR = 0.889, 95% CI: 0.826-0.957). Sex (female) was positively associated only with painless DSPN (OR = 1.769, 95% CI: 1.007-3.107). Being a current or former smoker was positively associated only with painless DSPN (OR = 1.940, 95% CI: 1.069-3.518). Hypertension was positively associated with painful DSPN (OR = 2.474, 95% CI: 1.110-5.512) and painless DSPN (OR = 2.565, 95% CI: 1.252-5.256). Glycated hemoglobin (HbA1c) was positively associated only with painless DSPN (OR = 1.193, 95% CI: 1.018-1.399). Conclusions: Diabetes duration and hypertension have a direct impact on the development of painful and painless DSPN. However, female sex and HbA1c have a direct effect only on the development of painless DSPN, and education level has an indirect effect on the development of painful DSPN. Therefore, it can be concluded that different etiological factors have different contributions to the development of neuropathy and pain.

Effect of Diabetes Mellitus Type 1 Diagnosis on the Corneal Cell Densities and Nerve Fibers

Relation of diabetes mellitus (DM) to the various stages of corneal nerve fiber damage is well accepted. A possible association between changes in the cornea of diabetic patients and diabetic retinopathy (DR), DM duration, and age at the time of DM diagnosis were evaluated. The study included 60 patients with DM type 1 (DM1) and 20 healthy control subjects. The density of basal epithelial cells, keratocytes and endothelial cells, and the status of the subbasal nerve fibers were evaluated using in vivo corneal confocal microscopy. Basal epithelial cell density increased with age (p=0.026), while stromal and endothelial cell density decreased with age (p=0.003, p=0.0005, p<0.0001). After the DM1 diagnosis was established, this association with age weaken. We showed nerve fiber damage in DM1 patients (p˂0.0001). The damage correlated with the degree of DR. DM1 patients with higher age at DM1 diagnosis had a higher nerve fiber density (p=0.0021). These results indicated that age at DM1 diagnosis potentially has an important effect on final nerve fiber and corneal cell density.

Corneal Nerve Fractal Dimension: A Novel Corneal Nerve Metric for the Diagnosis of Diabetic Sensorimotor Polyneuropathy

Objective

Corneal confocal microscopy (CCM), an in vivo ophthalmic imaging modality, is a noninvasive and objective imaging biomarker for identifying small nerve fiber damage. We have evaluated the diagnostic performance of previously established CCM parameters to a novel automated measure of corneal nerve complexity called the corneal nerve fiber fractal dimension (ACNFrD).

Methods

A total of 176 subjects (84 controls and 92 patients with type 1 diabetes) with and without diabetic sensorimotor polyneuropathy (DSPN) underwent CCM. Fractal dimension analysis was performed on CCM images using purpose-built corneal nerve analysis software, and compared with previously established manual and automated corneal nerve fiber measurements.

Results

Manual and automated subbasal corneal nerve fiber density (CNFD) (P < 0.0001), length (CNFL) (P < 0.0001), branch density (CNBD) (P < 0.05), and ACNFrD (P < 0.0001) were significantly reduced in patients with DSPN compared to patients without DSPN. The areas under the receiver operating characteristic curves for identifying DSPN were comparable: 0.77 for automated CNFD, 0.74 for automated CNFL, 0.69 for automated CNBD, and 0.74 for automated ACNFrD.

Conclusions

ACNFrD shows comparable diagnostic efficiency to identify diabetic patients with and without DSPN.

Diagnosing Diabetic Neuropathy: Something Old, Something New

There are potentially many ways of assessing diabetic peripheral neuropathy (DPN). However, they do not fulfill U.S. Food and Drug Administration (FDA) requirements in relation to their capacity to assess therapeutic benefit in clinical trials of DPN. Over the past several decades symptoms and signs, quantitative sensory and electrodiagnostic testing have been strongly endorsed, but have consistently failed as surrogate end points in clinical trials. Therefore, there is an unmet need for reliable biomarkers to capture the onset and progression and to facilitate drug discovery in DPN. Corneal confocal microscopy (CCM) is a non-invasive ophthalmic imaging modality for in vivo evaluation of sensory C-fibers. An increasing body of evidence from multiple centers worldwide suggests that CCM fulfills the FDA criteria as a surrogate endpoint of DPN.

Cornea and anterior eye assessment with slit lamp biomicroscopy, specular microscopy, confocal microscopy, and ultrasound biomicroscopy

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple, and several devices and technologies show signs that help in identification of different diseases thereby, helping in diagnosis, management, and follow-up of patients. The purpose of this review is to present and update readers on the evaluation of cornea and ocular surface. This first part reviews a description of slit lamp biomicroscopy (SLB), endothelial specular microscopy, confocal microscopy, and ultrasound biomicroscopy examination techniques and the second part describes the corneal topography and tomography, providing up-to-date information on the clinical recommendations of these techniques in eye care practice. Although the SLB is a traditional technique, it is of paramount importance in clinical diagnosis and compulsory when an eye test is conducted in primary or specialist eye care practice. Different techniques allow the early diagnosis of many diseases, especially when clinical signs have not yet become apparent and visible with SLB. These techniques also allow for patient follow-up in several clinical conditions or diseases, facilitating clinical decisions and improving knowledge regarding the corneal anatomy.

Impaired vibrotactile sense in children and adolescents with type 1 diabetes - Signs of peripheral neuropathy

Objective

To investigate whether multi-frequency vibrometry can identify individuals with elevated vibration perception thresholds (VPTs), reflecting impaired vibrotactile sense, among children and adolescents with type 1 diabetes.

Methods

In 72 pediatric patients with type 1 diabetes, VPTs were evaluated for seven frequencies on two sites of the hand, and five frequencies on two sites of the foot. Z-scores, based on previously collected reference data, were calculated. Perception to light touch was investigated using monofilaments. Subjects’ characteristics were analyzed in comparison to normal and impaired vibrotactile sense.

Results

Subjects’ median age, disease duration and age at disease onset were 12.8, 5.3 and 6.9 years, respectively. A total of 13 out of 72 (18%) subjects had impaired vibrotactile sense on at least one foot site. Impaired vibrotactile sense was more common among subjects treated with multiple daily insulin injections (MDI) compared to subjects treated with continuous subcutaneous insulin infusion (CSII) (p = 0.013). Age at disease onset was higher among subjects with impaired vibrotactile sense (p = 0.046). No significant correlations were found with gender, HbA1c or duration of diabetes.

Conclusions

Impaired vibrotactile sense, mirroring diabetic peripheral neuropathy, was found in 1/5 of the children and adolescents in the study, and was more common in patients treated with MDI than in subjects treated with CSII.

Corneal Innervation and Sensation: The Eye and Beyond

The cornea is one of the most densely innervated and sensitive tissues in the body. In addition to their important sensory functions, corneal nerves induce reflex tear production, blinking, and the release of trophic factors - all of which combined help to maintain the structural and functional integrity of the surface of the eye. Consequently, damage to corneal nerves as a result of disease, surgery, or trauma can lead to diminished corneal sensitivity, epithelial defects, and possible blindness. In this review, we describe commonly used tools that have provided considerable new information on corneal architecture and sensation in healthy and diseased corneas, with special emphasis on changes seen in herpes zoster ophthalmicus, corneal and other therapeutic ocular procedures, antiglaucoma medical therapy, aging, and diabetes. With its potential applications ranging from managing ocular-specific to systemic diseases, the study of corneal innervation has implications for future therapies extending beyond just the eye itself.

Ophthalmic and clinical factors that predict four-year development and worsening of diabetic retinopathy in type 1 diabetes

AIMS

To investigate the role of ophthalmic imaging markers - namely retinal thickness measures and corneal nerve morphology - in predicting four-year development and worsening of diabetic retinopathy (DR) in type 1 diabetes (T1DM).

METHODS

126 eyes of 126 participants with T1DM were examined at baseline and after four years. Diabetic retinopathy (DR) was graded using the Early Treatment Diabetic Retinopathy Study scale. HbA_1c, nephropathy, neuropathy, cardiovascular factors, and retinal thickness using optical coherence tomography (OCT) and corneal nerve fiber length (CNFL) using corneal confocal microscopy at baseline were assessed by univariate and step-wise multiple logistic regression, and their diagnostic capabilities for single and combined measures.

RESULTS

Four-year development of DR was 19% (13 of 68 without DR at baseline). Worsening of DR was seen in 43% (25 of 58 with DR at baseline). When adjusted for potential confounders, a lower CNFL (AUC=0.637, p=0.040, 64% sensitivity and 64% specificity at 14.9mm/mm² cut-off), higher triglycerides (AUC=0.669, p=0.012, 64% sensitivity, 62% specificity at 0.85mmol/L) and an elevated vibration threshold (AUC=0.708, p=0.002, 96% sensitivity, 40% specificity at 3.55Hz) were significant predictors for four-year worsening of DR.

CONCLUSIONS

Reduced CNFL, elevated vibration perception threshold and higher triglycerides can predict future worsening of DR.

Tear Levels of Insulin-Like Growth Factor Binding Protein 3 Correlate With Subbasal Nerve Plexus Changes in Patients With Type 2 Diabetes Mellitus

Purpose

This study investigated the expression of insulin-like growth factor binding protein-3 (IGFBP-3) in basal tears of patients with type 2 diabetes mellitus compared to nondiabetic controls; and correlated tear levels of IGFBP-3 with morphologic changes in the subbasal nerve plexus and density of basal corneal epithelial cells.

Methods

This was a single visit, cross-sectional study. Diabetic and control subjects were matched for age, sex, smoking status, and body mass index. Tear levels of IGFBP-3 were measured using ELISA. Corneal nerve and basal epithelial cell changes were measured using in vivo confocal microscopy.

Results

Tear levels of IGFBP-3 were 3.5-fold higher in those with diabetes. Patients with diabetes also showed a reduction in nerve fiber layer, nerve branch density, and corneal basal epithelial cell density. There was no significant difference in corneal sensitivity. IGFBP-3 levels were highly correlated with nerve fiber length and branch density; while hemoglobin (Hb)A1c was only moderately correlated. There were no significant differences in the clinical or subjective signs of dry eye between groups, indicating that tear levels of IGFBP-3 and corneal nerve changes were not due to the presence of mild dry eye.

Conclusions

These findings indicate that tear levels of IGFBP-3 are more tightly correlated to nerve fiber changes in diabetes than HbA1c. Future studies that stratify the severity of diabetic disease with tear levels of IGFBP-3 are needed to validate this finding.

Corneal confocal microscopy is a rapid reproducible ophthalmic technique for quantifying corneal nerve abnormalities

PURPOSE

To assess the effect of applying a protocol for image selection and the number of images required for adequate quantification of corneal nerve pathology using in vivo corneal confocal microscopy (IVCCM).

METHODS

IVCCM was performed in 35 participants by a single examiner. For each participant, 4 observers used a standardized protocol to select 6 central corneal nerve images to assess the inter-observer variability. Furthermore, images were selected by a single observer on two occasions to assess intra-observer variability and the effect of sample size was assessed by comparing 6 with 12 images. Corneal nerve fiber density (CNFD), branch density (CNBD) and length (CNFL) were quantified using fully automated software. The data were compared using the intra class correlation coefficient (ICC) and Bland-Altman agreement plots for all experiments.

RESULTS

The ICC values for CNFD, CNBD and CNFL were 0.93 (P<0.0001), 0.96 (P<0.0001) and 0.95 (P<0.0001) for inter-observer variability and 0.95 (P<0.0001), 0.97 (P<0.001) and 0.97 (P<0.0001) for intra-observer variability. For sample size variability, ICC values were 0.94 (P<0.0001), 0.95 (P<0.0001), and 0.96 (P<0.0001) for CNFD, CNBD and CNFL. Bland-Altman plots showed excellent agreement for all parameters.

CONCLUSIONS

This study shows that implementing a standardized protocol to select IVCCM images results in high intra and inter-observer reproducibility for all corneal nerve parameters and 6 images are adequate for analysis. IVCCM could therefore be deployed in large multicenter clinical trials with confidence.