Corneal nerve tortuosity in diabetic patients with neuropathy

Comprehensive assessment of ocular parameters for identifying diagnostic indicators of diabetic peripheral neuropathy

PURPOSE

To explore variations in systemic and ocular parameters among patients with diabetes, both with and without diabetic peripheral neuropathy (DPN) and to identify sensitive indicators for DPN diagnosis.

METHODS

Ninty-five patients with type 2 diabetes mellitus (T2DM) were involved in this cross-sectional study, including 49 without DPN and 46 with DPN. Ocular parameters were obtained using optical coherence tomography angiography (OCTA) and corneal confocal microscopy (CCM).

RESULT

Patients with DPN presented with significantly higher HbA1c (p < 0.05) and glycated albumin (GA, p < 0.01) levels, increased prevalence of diabetic retinopathy (DR, p < 0.05), and lower serum albumin (ALB, p < 0.01) and red blood cell (RBC, p < 0.05) levels. Ocular assessments revealed reduced corneal nerve fiber length (CNFL, p < 0.001) and enlarged foveal avascular zone (FAZ) area (p < 0.05) in DPN group. Logistic regression analysis indicated a significant association of presence of DR, RBC, GA, ALB, CNFL and DPN (p < 0.05, respectively). In the binary logistic regression for DPN risk, all three models including the presence of DR and CNFL exhibited the area under the curve (AUC) exceeding 0.8.

CONCLUSION

The study establishes a strong correlation between ocular parameters and DPN, highlighting CCM's role in early diagnosis. Combining systemic and ocular indicators improves DPN risk assessment and early management.

The inferocentral whorl region and its directional patterns in the corneal sub-basal nerve plexus: A review

There has been a growing application of in vivo confocal microscopy (IVCM) in the examination of corneal microstructure, including different corneal layers and corneal nerve fibers in health and in pathological conditions. Corneal nerves forming the sub-basal nerve plexus (SBNP) beneath the corneal basal epithelial cell layer in particular have been intensively researched in health and disease as a marker for corneal neurophysioanatomical and degenerative changes. One intriguing feature in the SBNP that is found inferior to the corneal apex, is a whorl-like pattern (or vortex) of nerves, which represents an anatomical landmark. Evidence has indicated that the architecture of this 'whorl region' is dynamic, changing with time in healthy individuals but also in disease conditions such as in diabetic neuropathy and keratoconus. This review summarizes the known information regarding the characteristics and significance of the whorl region of nerves in the corneal SBNP, as a potential area of high relevance for future disease monitoring and diagnostics.

Chronic intermittent hypoxia remodels catecholaminergic nerve innervation in mouse atria

Chronic intermittent hypoxia (CIH, a model for sleep apnoea) is a major risk factor for several cardiovascular diseases. Autonomic imbalance (sympathetic overactivity and parasympathetic withdrawal) has emerged as a causal contributor of CIH-induced cardiovascular disease. Previously, we showed that CIH remodels the parasympathetic pathway. However, whether CIH induces remodelling of the cardiac sympathetic innervation remains unknown. Mice (male, C57BL/6J, 2-3 months) were exposed to either room air (RA, 21% O2 ) or CIH (alternating 21% and 5.7% O2 , every 6 min, 10 h day-1 ) for 8-10 weeks. Flat-mounts of their left and right atria were immunohistochemically labelled for tyrosine hydroxylase (TH, a sympathetic marker). Using a confocal microscope (or fluorescence microscope) and Neurlocudia 360 digitization and tracing system, we scanned both the left and right atria and quantitatively analysed the sympathetic axon density in both groups. The segmentation data was mapped onto a 3D mouse heart scaffold. Our findings indicated that CIH significantly remodelled the TH immunoreactive (-IR) innervation of the atria by increasing its density at the sinoatrial node, the auricles and the major veins attached to the atria (P < 0.05, n = 7). Additionally, CIH increased the branching points of TH-IR axons and decreased the distance between varicosities. Abnormal patterns of TH-IR axons around intrinsic cardiac ganglia were also found following CIH. We postulate that the increased sympathetic innervation may further amplify the effects of enhanced CIH-induced central sympathetic drive to the heart. Our work provides an anatomical foundation for the understanding of CIH-induced autonomic imbalance. KEY POINTS: Chronic intermittent hypoxia (CIH, a model for sleep apnoea) causes sympathetic overactivity, cardiovascular remodelling and hypertension. We determined the effect of CIH on sympathetic innervation of the mouse atria. In vivo CIH for 8-10 weeks resulted in an aberrant axonal pattern around the principal neurons within intrinsic cardiac ganglia and an increase in the density, branching point, tortuosity of catecholaminergic axons and atrial wall thickness. Utilizing mapping tool available from NIH (SPARC) Program, the topographical distribution of the catecholaminergic innervation of the atria were integrated into a novel 3D heart scaffold for precise anatomical distribution and holistic quantitative comparison between normal and CIH mice. This work provides a unique neuroanatomical understanding of the pathophysiology of CIH-induced autonomic remodelling.

Pathogenesis of Alkali Injury-Induced Limbal Stem Cell Deficiency: A Literature Survey of Animal Models

Limbal stem cell deficiency (LSCD) is a debilitating ocular surface disease that eventuates from a depleted or dysfunctional limbal epithelial stem cell (LESC) pool, resulting in corneal epithelial failure and blindness. The leading cause of LSCD is a chemical burn, with alkali substances being the most common inciting agents. Characteristic features of alkali-induced LSCD include corneal conjunctivalization, inflammation, neovascularization and fibrosis. Over the past decades, animal models of corneal alkali burn and alkali-induced LSCD have been instrumental in improving our understanding of the pathophysiological mechanisms responsible for disease development. Through these paradigms, important insights have been gained with regards to signaling pathways that drive inflammation, neovascularization and fibrosis, including NF-κB, ERK, p38 MAPK, JNK, STAT3, PI3K/AKT, mTOR and WNT/β-catenin cascades. Nonetheless, the molecular and cellular events that underpin re-epithelialization and those that govern long-term epithelial behavior are poorly understood. This review provides an overview of the current mechanistic insights into the pathophysiology of alkali-induced LSCD. Moreover, we highlight limitations regarding existing animal models and knowledge gaps which, if addressed, would facilitate development of more efficacious therapeutic strategies for patients with alkali-induced LSCD.

Corneal confocal microscopy identifies corneal nerve fiber loss in patients with migraine

BACKGROUND/HYPOTHESIS

Migraine affects >1 billion people but its pathophysiology remains poorly understood. Alterations in the trigeminovascular system play an important role. We have compared corneal nerve morphology in patients with migraine to healthy controls.

METHODS

Sixty patients with episodic (n = 32) or chronic (n = 28) migraine and 20 age-matched healthy control subjects were studied cross-sectionally. Their migraine characteristics and signs and symptoms of dry eyes were assessed. Manual and automated quantification of corneal nerves was undertaken by corneal confocal microscopy.

RESULTS

In patients with migraine compared to controls, manual corneal nerve fiber density (P < 0.001), branch density (P = 0.015) and length (P < 0.001); and automated corneal nerve fiber density (P < 0.001), branch density (P < 0.001), length (P < 0.001), total branch density (P < 0.001), nerve fiber area (P < 0.001), nerve fiber width (P = 0.045) and fractal dimension (P < 0.001) were lower. Automated corneal nerve fiber density was higher in patients with episodic migraine and aura (P = 0.010); and fractal dimension (P = 0.029) was lower in patients with more headache days in the last three months. Automated corneal nerve fiber density predicted a significant amount of the observed variance in pain intensity (adjusted r² = 0.14, partial r = -0.37, P = 0.004) in patients with migraine.

CONCLUSIONS

Corneal confocal microscopy reveals corneal nerve loss in patients with migraine. It may serve as an objective imaging biomarker of neurodegeneration in migraine.

Is Corneal Subbasal Nerve Loss Associated With Meibomian Gland Loss in Inactive Mild and Moderate-to-Severe Graves' Ophthalmopathy?

PURPOSE

To evaluate meibomian gland and subbasal nerve plexus parameters in Graves' Ophthalmopathy (GO) and association of meibomian gland loss with corneal subbasal nerve plexus loss.

METHODS

Fifty-two eyes of 52 mild and moderate-to-severe GO patients and 32 eyes of 32 healthy controls were enrolled. The meibomian gland dropout area (MGDA) and meibography scores were evaluated using noncontact meibography. In vivo confocal microscopy of corneal subbasal nerve plexus were conducted. ACCMetrics was used to obtain corneal parameters.

RESULTS

Compared with healthy subjects, GO patients had worse upper and lower eyelid MGDA ( p < 0.001, for all) and upper, lower and total meibography scores ( p < 0.001, p = 0.001, and p < 0.001, respectively). Eyelid margin scores were worse in the GO group ( p < 0.001) and showed correlation with all noncontact meibography parameters ( p < 0.001 for all). All corneal subbasal nerve parameters were significantly lower in the GO group compared with the controls ( p < 0.05 for all). Subbasal nerve parameters of GO patients did not reveal a correlation with MGDA and meibography scores but showed correlations with ocular surface disease index score and Schirmer I test (r = -0.304; p = 0.042 and r = 0.336; p = 0.021, respectively).

CONCLUSION

Meibomian gland and corneal nerve loss could be observed even in the inactive phase and mild GO. The lack of a correlation between meibomian gland loss and subbasal nerve loss suggests that meibomian gland loss is not a significant additional component in the pathogenesis of subbasal nerve damage in GO. Furthermore, our study revealed new evidence regarding the use of eyelid margin score to represent meibomian gland loss in GO.

Corneal Sub-Basal Nerve Plexus in Non-Diabetic Small Fiber Polyneuropathies and the Diagnostic Role of In Vivo Corneal Confocal Microscopy

In vivo corneal confocal microscopy (IVCM) allows the immediate analysis of the corneal nerve quantity and morphology. This method became, an indispensable tool for the tropism examination, as it evaluates the small fiber plexus in the cornea. The IVCM provides us with direct information on the health of the sub-basal nerve plexus and indirectly on the peripheral nerve status. It is an important tool used to investigate peripheral polyneuropathies. Small-fiber neuropathy (SFN) is a group of neurological disorders characterized by neuropathic pain symptoms and autonomic complaints due to the selective involvement of thinly myelinated Aδ-fibers and unmyelinated C-fibers. Accurate diagnosis of SFN is important as it provides a basis for etiological work-up and treatment decisions. The diagnosis of SFN is sometimes challenging as the clinical picture can be difficult to interpret and standard electromyography is normal. In cases of suspected SFN, measurement of intraepidermal nerve fiber density through a skin biopsy and/or analysis of quantitative sensory testing can enable diagnosis. The purpose of the present review is to summarize the current knowledge about corneal nerves in different SFN. Specifically, we explore the correlation between nerve density and morphology and type of SFN, disease duration, and follow-up. We will discuss the relationship between cataracts and refractive surgery and iatrogenic dry eye disease. Furthermore, these new paradigms in SFN present an opportunity for neurologists and clinical specialists in the diagnosis and monitoring the peripheral small fiber polyneuropathies.

Evaluation of central corneal epithelial thickness with anterior segment OCT in patients with type 2 diabetes mellitus

BACKGROUND

This study aimed to evaluate the central corneal thickness (CCT) and central corneal epithelial thickness (CCET) in patients with Type 2 diabetes mellitus (DM), and the effect of the duration of diabetes, the degree of diabetic retinopathy (DR), and HbA1c level.

METHODS

CCT and CCET values of 72 patients diagnosed with type 2 DM and 72 healthy individuals were measured by anterior segment optical coherence tomography. The eye tear function was evaluated with the Tear Break-up Time test (TBUT) and the Schirmer test. From the results of fundus examination, the diabetic patients were grouped as those without DR, non-proliferative DR, and proliferative DR. The disease duration and the HbA1c levels were recorded.

RESULTS

In the diabetic patients, the mean CCT was determined to be thicker (p = 0.025), the CCET was thinner (p = 0.003), and the TBUT and Schirmer values were lower (p <0.001, p <0.001, respectively). The duration of diabetes and the HbA1c level was not found to have any statistically significant effect on these parameters (p >0.05). The presence of retinopathy had no significant effect on CCT, TBUT, and Schirmer values. The CCET was determined to be thinner in patients with retinopathy (p <0.001).

CONCLUSIONS

As the corneal epithelial thickness is reduced in patients with advanced diabetic retinopathy, corneal epithelial pathologies can be seen more often. Therefore, early and effective treatment can be started by taking into consideration the complications which may develop associated with the corneal epithelium following surgical procedures, especially those applied to the cornea.

Corneal dendritic cells in diabetes mellitus: A narrative review

Diabetes mellitus is a global public health problem with both macrovascular and microvascular complications, such as diabetic corneal neuropathy (DCN). Using in-vivo confocal microscopy, corneal nerve changes in DCN patients can be examined. Additionally, changes in the morphology and quantity of corneal dendritic cells (DCs) in diabetic corneas have also been observed. DCs are bone marrow-derived antigen-presenting cells that serve both immunological and non-immunological roles in human corneas. However, the role and pathogenesis of corneal DC in diabetic corneas have not been well understood. In this article, we provide a comprehensive review of both animal and clinical studies that report changes in DCs, including the DC density, maturation stages, as well as relationships between the corneal DCs, corneal nerves, and corneal epithelium, in diabetic corneas. We have also discussed the associations between the changes in corneal DCs and various clinical or imaging parameters, including age, corneal nerve status, and blood metabolic parameters. Such information would provide valuable insight into the development of diagnostic, preventive, and therapeutic strategies for DM-associated ocular surface complications.

Update on Corneal Confocal Microscopy Imaging

In vivo corneal confocal microscopy (IVCM) is a non-invasive ophthalmic imaging technique that provides images of the cornea at the cellular level. Despite the uses in ocular surface pathologies, in the last decades IVCM has been used to provide more knowledge in refractive surgery wound healing, in neuropathies diagnosis, etc. The observation of the corneal cells, both normal and inflammatory, and the possibility of quantification of the corneal nerve density with manual or automated tools, makes IVCM have a significant potential to improve the diagnosis and prognosis in several systemic and corneal conditions.

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 confocal microscopy in patients with distal symmetric polyneuropathy compared to controls

BACKGROUND

Diabetic neuropathy (DN) is a very common clinical condition throughout the world. The diagnostic tests currently recommended have low sensitivity, such as electromyography, or are invasive, such as skin biopsy. New techniques have been developed to identify the early involvement of the peripheral nerve. With the advent of corneal confocal microscopy (CCM), a reduction in corneal innervation in patients with DN has been observed.

OBJECTIVE

To compare, through CCM, diabetic patients with symptomatic distal symmetric polyneuropathy (DSP) and controls.

METHODS

In the present study, through CCM, we compared the morphological changes in the sub-basal epithelial corneal plexus of 35 diabetic patients with symptomatic DSP with 55 controls. Moreover, we sought to determine a pattern of change regarding the severity stages of DSP, comparing the clinical, laboratory, and nerve-conduction (NC) variables.

RESULTS

Differences between the control and diabetic groups were observed for the following variables, respectively: age (44.9 ± 13.24 years versus 57.02 ± 10.4 years; p < 0.001); fiber density (29.7 ± 10.2 versus 16.6 ± 10.2; p < 0.001); number of fibers (4.76 ± 1.30 versus 3.14 ± 1.63; p < 0.001); number of Langerhans cells (4.64 ± 8.05 versus 7.49 ± 10.3; p = 0.035); tortuosity (p < 0.05); and thickness (p < 0.05). Furthermore, inverse relationships were found regarding fiber density and age (p < 0.01) and fiber density and the severity of the disease (p < 0.05). A positive relationship between the conduction velocity of the fibular nerve and fiber density (p < 0.05) was also observed.

CONCLUSION

Corneal confocal microscopy proved to be a fast, noninvasive and reproducible method for the diagnosis, staging, and monitoring of diabetic DSP.

In vivo confocal microscopic study of corneal innervation in Sjögren's Syndrome with or without small fiber neuropathy

PURPOSE

To study changes in the subbasal nerve plexus by In vivo confocal microscopy (IVCM) in Sjögren's Syndrome (SS) with or without associated Small Fiber Neuropathy (SFN), in order to prevent diagnostic delay.

METHODS

Seventy-one patients with SS, including 19 with associated SFN, 20 healthy volunteers and 20 patients with Meibomian gland dysfunction (MGD) were included in this retrospective case-control study. IVCM was used to investigate subbasal nerve plexus density and morphology.

RESULTS

Corneal sensitivity as evaluated with the Cochet-Bonnet aesthesiometer was significantly reduced in the SS group versus the control group (P = 0.026) and the MGD group (P = 0.037). The number of inflammatory cells was significantly increased in the SS group to 86.2 ± 82.1 cells/mm² compared to the control group (P < 0.001). The density of the subbasal nerve plexus was significantly reduced to 16.7 ± 6.5 mm/mm² in the SS group compared to the control group (P < 0.005) and the MGD group (P = 0.042). The tortuosity of the nerves in the SS group was significantly increased compared to the control group (P < 0.001) and the MGD group (P = 0.025). The average number of subbasal nerve plexus neuromas was significantly increased in the SS group compared to the control group (P = 0.001), with a significant increase in the average number of neuromas in SS patients with associated SFN compared to SS patients without SFN (P = 0.008).

CONCLUSION

IVCM can be useful to detect corneal nerve changes in SS patients and may allow earlier diagnosis of the disease and to consider new therapeutic approaches.

The impact of sensory neuropathy and inflammation on epithelial wound healing in diabetic corneas

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes, with several underlying pathophysiological mechanisms, some of which are still uncertain. The cornea is an avascular tissue and sensitive to hyperglycemia, resulting in several diabetic corneal complications including delayed epithelial wound healing, recurrent erosions, neuropathy, loss of sensitivity, and tear film changes. The manifestation of DPN in the cornea is referred to as diabetic neurotrophic keratopathy (DNK). Recent studies have revealed that disturbed epithelial-neural-immune cell interactions are a major cause of DNK. The epithelium is supplied by a dense network of sensory nerve endings and dendritic cell processes, and it secretes growth/neurotrophic factors and cytokines to nourish these neighboring cells. In turn, sensory nerve endings release neuropeptides to suppress inflammation and promote epithelial wound healing, while resident immune cells provide neurotrophic and growth factors to support neuronal and epithelial cells, respectively. Diabetes greatly perturbs these interdependencies, resulting in suppressed epithelial proliferation, sensory neuropathy, and a decreased density of dendritic cells. Clinically, this results in a markedly delayed wound healing and impaired sensory nerve regeneration in response to insult and injury. Current treatments for DPN and DNK largely focus on managing the severe complications of the disease. Cell-based therapies hold promise for providing more effective treatment for diabetic keratopathy and corneal ulcers.

In Vivo Confocal Microscopy in Different Types of Dry Eye and Meibomian Gland Dysfunction

In vivo confocal microscopy (IVCM) imaging is increasingly popular in ocular surface disease diagnosis and management. We conducted a systematic review to update the use of IVCM in the diagnosis and treatment of dry eye and meibomian gland dysfunction (MGD). A literature review was conducted on IVCM studies in MGD, dry eye disease, systemic disease causing dry eye, dry eye in glaucoma patients, contact lens-associated ocular conditions, graft-versus-host disease, and Sjogren’s syndrome-related dry eye. The articles were identified through PubMed and a total number of 63 eligible publications were analyzed in detail. All primary research studies on confocal microscopy on dry eye and related conditions from 2017 onwards were included. The reports were reviewed for their contribution to the existing literature as well as potential biases and drawbacks. Despite limitations such as small field of view, lack of population-based norms, and lack of standardization of image acquisition, interpretation, and quantification, IVCM is useful as a complementary technique for clinical diagnosis in various ocular surface disorders related to dry eye. With advances in hardware and software in the near future, it has the potential for further practical impact.

A Population-Based Study of Social Demographic Factors, Associated Diseases and Recurrent Corneal Erosion in Taiwan

Purpose

To investigate the association of recurrent corneal erosion (RCE) with sociodemographic factors and associated ocular conditions or systemic diseases.

Methods

This nationwide, population-based, retrospective, matched case-controlled study included 98,895 RCE patients, identified by the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code 371.42, were selected from the Taiwan National Health Insurance Research Database. The age-, sex-, and index date- matched control group included 98,895 non-RCE control group also selected from the Taiwan Longitudinal Health Insurance Database 2000. Sociodemographic factors and associated ocular conditions or systemic diseases were examined using univariate logistic regression analyses, and continuous variables were analyzed using paired t-test. The odds ratio (OR) of developing RCE were compared using adjusted logistic regression analysis.

Results

Patients with ocular conditions including corneal abrasion, ocular allergic conditions, and corneal dystrophy were more likely to have RCE than the control group (adjusted OR = 63.56, 95% CI = 42.06-96.06, p < 0.0001; adjusted OR = 24.27, 95% CI = 20.51-28.72, p < 0.0001; adjusted OR = 17.10, 95% CI = 5.14-59.93, p < 0.0001, respectively). Patients with systemic diseases such as diabetes mellitus, hyperlipidaemia, and atopy trait have significantly higher ORs for RCE development. Patients residing in either Northern Taiwan or a metropolis city had higher odds of developing RCE; however, there were no significant differences in income or occupation on the probability to develop RCE.

Conclusion

RCE is strongly associated with corneal abrasion, ocular allergic conditions, corneal dystrophy, diabetes mellitus, hyperlipidaemia, and atopy trait.

Small Fibre Peripheral Alterations Following COVID-19 Detected by Corneal Confocal Microscopy

A large spectrum of neurological manifestations has been associated with coronavirus disease 2019 (COVID-19), and recently, the involvement of small fibers has been suggested. This study aims to investigate the involvement of small peripheral nervous fibers in recovered COVID-19 patients using in-vivo corneal confocal microscopy (CCM). Patients recovered from COVID-19 and a control group of healthy subjects underwent in-vivo CCM. Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), corneal nerve fiber total branch density (CTBD), corneal nerve fiber area (CNFA), corneal nerve fiber width (CNFW), fiber tortuosity (FT), number of beadings (NBe), and dendritic cells (DC) density were quantified. We enrolled 302 eyes of 151 patients. CNBD and FT were significantly higher (p = 0.0131, p < 0.0001), whereas CNFW and NBe were significantly lower (p = 0.0056, p = 0.0045) in the COVID-19 group compared to controls. Only CNBD and FT resulted significantly correlated to antiviral drugs (increased) and corticosteroids (decreased). No significant relationship with disease severity parameters was found. COVID-19 may induce peripheral neuropathy in small fibers even months after recovery, regardless of systemic conditions and therapy, and CCM may be a useful tool to identify and monitor these morphological changes.

Corneal and Epidermal Nerve Quantification in Chemotherapy Induced Peripheral Neuropathy

Chemotherapy-induced neurotoxicity is an increasingly recognized clinical issue in oncology. in vivo confocal microscopy (IVCM) of corneal nerves has been successfully used to diagnose peripheral neuropathies, including diabetic neuropathy. The purpose of this study was to test if the combination of corneal nerve density and morphology assessed by IVCM is useful to monitor the neurotoxic effects of chemotherapy compared to epidermal nerve quantification. Overall, 95 adult patients with different cancer types were recruited from the oncology and hematology departments of the San Raffaele Hospital. Neurological examination, including clinical Total Neuropathy Score, and in vivo corneal confocal microscopy (IVCM), were performed before and after chemotherapy. In a group of 14 patients, skin biopsy was performed at the first and last visit. In the group of 14 patients who underwent both skin biopsy and corneal nerve imaging, clinical worsening (+69%, p = 0.0018) was paralleled by corneal nerve fiber (CNF) density reduction (−22%, p = 0.0457). Clinical Total neuropathy score significantly worsened from the first to the last visit (+62%, p < 0.0001). CNF length was not significantly reduced overall. However, CNF density/tortuosity ratio significantly decreased after therapy. Correlation analysis showed that the CNF density/tortuosity ratio was also correlated with the number of chemotherapy cycles (r = −0.04790, P = 0.0009). Our data confirm that in vivo corneal confocal microscopy is a helpful, non-invasive tool which shows promise for the diagnosis of chemotherapy-induced peripheral neuropathies. IVCM could allow a rapid, reproducible and non-invasive quantification of peripheral nerve pathology in chemotherapy-associated neuropathy.

Mechanistic investigations of diabetic ocular surface diseases

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

The Corneal Changes in Diabetic Patients

Diabetes mellitus (DM) represents a systemic disorder which afects different organs. Ocular complications of the DM are the worldwide leading cause of blindness. The most common complications are diabetic retinopathy, diabetic cataract, neovascular glaucoma. Recently many investigations point out that DM can cause comlications at ocular surface as well. Condition such as decreased corneal sensitivity, dry eye or neurotrophic corneal ulceraction are the main clinical manifestations of the diabetic keratopathy (DK). Untreated, these conditions can lead to serious visual acuity decrease. Pathological processes, based on chronic inflammation, due to chronic hyperglycemia, are the main step in the process of DK development. Adequate treatment of the main disease - DM is an imperative in maintaining the healthy cornea without subjective sensations of diabetic patients.

Corneal Nerve Abnormalities in Painful Dry Eye Disease Patients

Background: This study aimed to compare the corneal nerve structural abnormalities detected using in vivo confocal microscopy (IVCM) in patients with neuropathic corneal pain (NCP) secondary to primary meibomian gland dysfunction (MGD) or autoimmune dry eye (AIDE). Methods: A two-stage retrospective nested case-control study was conducted. First, data from patients with either MGD or AIDE were assessed, selecting only cases with no corneal pain (VAS = 0) or severe pain (VAS ≥ 8). Ocular signs and symptoms of the 238 selected patients were compared between painful and painless cases. Next, painful patients with no corneal damage (Oxford score ≤ 1) were selected within each study group, defining the cases with NCP (i.e., "pain without stain"). IVCM images from all groups were compared with prospectively-recruited healthy controls, focusing on dendritiform cell density and nerve abnormalities (density, tortuosity, microneuromas). Results: AIDE patients had more ocular signs/symptoms than MGD patients. Compared with healthy controls, AIDE-related NCP patients showed increased nerve tortuosity and number of neuromas, whereas MGD-related NCP patients had reduced nerve density and increased number, perimeter, and area of microneuromas. Microneuromas were also observed in healthy controls. Furthermore, a higher number of microneuromas was found in MGD-related NCP compared to AIDE-related NCP or painless MGD. Conclusions: MGD-related NCP was associated with significantly more corneal nerve abnormalities than AIDE-related NCP or healthy controls. Although IVCM can be useful to detect NCP-related corneal nerve changes in such patients, the diagnosis of dry eye disease-related NCP will require an association of several IVCM-based criteria without relying solely on the presence of microneuromas.

Comparing the results of manual and automated quantitative corneal neuroanalysing modules for beginners

This study aimed to evaluate the reliability of in vivo confocal microscopic neuroanalysis by beginners using manual and automated modules. Images of sub-basal corneal nerve plexus (SCNP) from 108 images of 18 healthy participants were analyzed by 7 beginner observers using manual (CCMetrics, [CCM]) and automated (ACCMetrics, [ACCM]) module. SCNP parameters analyzed included corneal nerve fiber density (NFD), corneal nerve branch density (NBD), corneal nerve fiber length (NFL), and tortuosity coefficient (TC). The intra-observer repeatability, inter-observer reliability, inter-module agreement, and left–right eye symmetry level of SCNP parameters were examined. All observers showed good intra-observer repeatability using CCM (intraclass correlation coefficient [ICC] > 0.60 for all), except when measuring TC. Two observers demonstrated especially excellent repeatability in analyzing NFD, NBD, and NFL using manual mode, indicating the quality of interpretation may still be observer-dependent. Among all SCNP parameters, NFL had the best inter-observer reliability (Spearman’s rank-sum correlation coefficient [SpCC] and ICC > 0.85 for the 3 original observers) and left–right symmetry level (SpCC and ICC > 0.60). In the additional analysis of inter-observer reliability using results by all 7 observers, only NFL showed good inter-observer reliability (ICC = 0.79). Compared with CCM measurements, values of ACCM measurements were significantly lower, implying a poor inter-module agreement. Our result suggested that performance of quantitative corneal neuroanalysis by beginners maybe acceptable, with NFL being the most reliable parameter, and automated method cannot fully replace manual work.

Characteristics of Corneal Subbasal Nerves in Different Age Groups: An in vivo Confocal Microscopic Analysis

Purpose

To determine the normative characteristics of corneal subbasal nerves in different age groups using laser scanning in vivo confocal microscopy (IVCM).

Patients and Methods

This descriptive observational study recruited healthy subjects (aged 20–60 years) from Siriraj Health-Screening Center. Excluded were individuals who had abnormal ocular symptoms, previous ocular surgery, a history of any diseases related to systemic and/or corneal neuropathy, or abnormal corneal sensitivity. Corneal IVCM (HRT3/Rostock Corneal Module) was performed at the central cornea to analyze the subbasal nerve plexus. The corneal nerve characteristics, comprising the number and density of nerves (main nerve trunks, branches, and total nerves) were analyzed using the NeuronJ program, and the corneal nerve tortuosity was graded. The correlations between the subbasal nerve density, tortuosity and age were then analyzed.

Results

Eighty subjects were enrolled, with twenty in each of four age groups (20–30, >30–40, >40–50, and >50–60 years). Overall, the mean number and density of main nerve trunks were 27.93±0.81/mm² and 11.22±0.30 mm/mm², respectively. As of the nerve branches, the average number and density were 103.56±2.37/mm² and 9.15±0.30 mm/mm², respectively. The total nerve density was 20.37±0.39 mm/mm². There were no significant differences between subbasal nerve parameters of the four age groups. It is noteworthy that 65% of the subjects aged over 40 years revealed high-grade nerve tortuosity.

Conclusion

The corneal subbasal nerve numbers and densities were not significantly different among a healthy population aged 20–60 years. However, there was a trend towards high tortuosity of the corneal nerve in people aged over 40 years.

Corneal Nerve Fiber and Sensitivity Loss After Repeated Intravitreal Anti-VEGF Injections: An In Vivo Confocal Microscopy Study

PURPOSE

The purpose of this study was to investigate corneal sensation, subbasal nerve plexus (SBNP), and ocular surface symptoms in patients who underwent multiple intravitreal antivascular endothelial growth factor (anti-VEGF) injections for age-related macular degeneration (AMD) and diabetic macular edema (DME).

METHODS

Forty patients with previous anti-VEGF intravitreal injections (20 AMD and 20 DME) and 30 healthy controls were included in this study. In vivo corneal confocal microscopy (IVCM) of the SBNP, corneal sensitivity measurement with a Cochet-Bonnet esthesiometer, noninvasive tear break-up times, and ocular surface disease score index (OSDI) calculation were performed for each participant. Corneal nerve fiber density, corneal nerve branch density, total length of all nerve fibers, corneal total branch density, corneal nerve fiber area, corneal nerve fiber width, and corneal nerve fiber fractal dimension parameters were obtained by automatic digital analysis.

RESULTS

Corneal nerve fiber density, corneal nerve branch density, total length of all nerve fibers, and corneal nerve fiber fractal dimension in IVCM imaging and corneal sensitivity were significantly decreased in both AMD and DME groups compared with the control group. Corneal nerve fiber width and OSDI scores were significantly increased in AMD and DME groups compared with the control group. None of the IVCM parameters were significantly different between AMD and DME groups. Corneal sensitivity was decreased in patients with DME compared with patients with AMD. Tear break-up time was not different among the groups.

CONCLUSIONS

Corneal SBNP parameters were affected, corneal sensitivity was decreased, and OSDI scores were increased in patients with multiple intravitreal anti-VEGF injections. IVCM parameters were not significantly different between AMD and DME groups.

The pattern of the inferocentral whorl region of the corneal subbasal nerve plexus is altered with age

PURPOSE

To describe the pattern of the nerves in the inferocentral whorl region of the human corneal subbasal nerve plexus (SBNP) in health and diseases known to affect the subbasal nerves.

METHODS

Laser-scanning in vivo confocal microscopy (IVCM) was used to image the SBNP bilaterally in 91 healthy subjects, 39 subjects with type 2 diabetes mellitus (T2DM), and 43 subjects with Parkinson's disease (PD). Whorl regions were classified according to nerve orientation relative to age and health/disease status.

RESULTS

Of 346 examined eyes, 300 (86.7%) had an identifiable whorl pattern. In healthy subjects, a clockwise nerve orientation of the whorl was most common (67.9%), followed by non-rotatory or 'seam' morphology (21.4%), and counterclockwise (10.7%). The clockwise orientation was more prevalent in healthy subjects than in T2DM or PD (P < 0.001). Healthy individuals below 50 years of age had a predominantly clockwise orientation (93.8%) which was reduced to 51.9% in those over 50 years (P < 0.001). Age but not disease status explained whorl orientation in T2DM and PD groups. Moreover, whorl orientation is bilaterally clockwise in the young, but adopts other orientations and becomes asymmetric across eyes with age. Finally, we report reflective 'dot-like' features confined to the whorl region of the subbasal plexus, sometimes appearing in close association with subbasal nerves and present in 84-93% of examined eyes regardless of disease status, eye or sex.

CONCLUSION

Subbasal nerves in the inferocentral whorl region are predominantly clockwise in young, healthy corneas. With aging and conditions of T2DM and PD, counterclockwise and non-rotatory configurations increase in prevalence, and bilateral symmetry is lost. Mechanisms regulating these changes warrant further investigation.

Cross-sectional Study on Corneal Denervation in Contralateral Eyes Following SMILE Versus LASIK

PURPOSE

To compare long-term corneal nerve status following small incision lenticule extraction (SMILE) versus laser in situ keratomileusis (LASIK).

METHODS

Twenty-four patients were randomized to receive SMILE in one eye and LASIK in the other eye. In vivo confocal microscopy examination and dry eye assessments were performed at a mean of 4.1 years postoperatively. The patients were further divided into two groups based on the mean assessment time: 2.7 years postoperatively (2.7 years group) and 5.5 years postoperatively (5.5 years group). Another 6 age-matched normal patients were recruited.

RESULTS

At 4.1 years, LASIK eyes had significantly less corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and corneal total branch density and significantly more nerves with beading than SMILE eyes. The CNFD, CNBD, CNFL, and number of nerves with sprouting were significantly higher in the 5.5 years group than in the 2.7 years group, in both types of surgery, suggesting persistent nerve regeneration. The CNBD and CNFD in the 5.5 years group, regardless of surgical types, were significantly lower than those in the control group, indicating the nerve status had not recovered to normal ranges even at 5.5 years. High myopic treatment resulted in significantly reduced CNFD with LASIK but not with SMILE. There were no significant differences in the dry eye parameters between the two procedures at 4.1 years postoperatively.

CONCLUSIONS

The impact on corneal nerves following refractive surgery is long-lasting. SMILE had better nerve preservation and regeneration than LASIK, but neither procedure had recovered nerve status to normal levels even at 5.5 years. [J Refract Surg. 2020;36(10):653-660.].

A Review On digital image processing techniques for in-Vivo confocal images of the cornea

This work reviews the scientific literature regarding digital image processing for in vivo confocal microscopy images of the cornea. We present and discuss a selection of prominent techniques designed for semi- and automatic analysis of four areas of the cornea (epithelium, sub-basal nerve plexus, stroma and endothelium). The main context is image enhancement, detection of structures of interest, and quantification of clinical information. We have found that the preprocessing stage lacks of quantitative studies regarding the quality of the enhanced image, or its effects in subsequent steps of the image processing. Threshold values are widely used in the reviewed methods, although generally, they are selected empirically and manually. The image processing results are evaluated in many cases through comparison with gold standards not widely accepted. It is necessary to standardize values to be quantified in terms of sensitivity and specificity of methods. Most of the reviewed studies do not show an estimation of the computational cost of the image processing. We conclude that reliable, automatic, computer-assisted image analysis of the cornea is still an open issue, constituting an interesting and worthwhile area of research.

Corneal Nerves Alteration Associated with Corneal Complications after Pars Plana Vitrectomy

Purpose

To evaluate the effect of corneal nerves assessment on predicting corneal complications following pars plana vitrectomy (PPV).

Methods

In this prospective single-center cohort study, 94 patients (94 eyes) received PPV, and were divided into postoperative groups with and without corneal complications. All eyes had corneal nerve fiber length (CNFL), corneal nerve fiber density, and branch density of corneal nerve fibers assessed and calculated with Image J preoperatively. Multivariate logistic regression analysis was used to identify corneal nerve fiber parameters that correlated to post-operative corneal complications. Receiver operator characteristic curve analysis was performed to identify the optimal cut-off point of the corneal fibers’ parameters for predicting corneal complications after PPV.

Results

Eleven eyes (11.70%) developed corneal complications at 1 week after PPV. There was significant difference between CNFL (19.44 ± 6.88 vs. 26.84 ± 7.53, p = 0.003), corneal nerve fiber density (28.82 ± 9.91 vs. 37.10 ± 10.16, p = 0.013) and branch density of corneal nerve fibers (55.84 ± 21.08 vs. 82.04 ± 31.89, p = 0.01) in two groups, respectively. Receiver operator characteristic analysis showed that the optimal cutoff value of CNFL to predict corneal complications following PPV was <26.495 mm/mm².

Conclusions

The decrease of CNFL may predict corneal complications following PPV. Regular preoperative corneal confocal microscopy test in PPV patients could be considered.

Quantification of Increased Corneal Subbasal Nerve Tortuosity in Dry Eye Disease and Its Correlation With Clinical Parameters

Purpose

This study quantified corneal subbasal nerve tortuosity in dry eye disease (DED) and investigated its correlation with clinical parameters by proposing an aggregated measure of tortuosity (Tagg).

Methods

The sample consisted of 26 eyes of patients with DED and 23 eyes of healthy volunteers, which represented separately the dry eye group and the control group. Clinical evaluation of DED and in vivo confocal microscopy analysis of the central cornea were performed. Tagg incorporated six metrics of tortuosity. Corneal subbasal nerve images of subjects and a validation data set were analyzed using Tagg. Spearman's rank correlation was performed on Tagg and clinical parameters.

Results

Tagg was validated using 1501 corneal nerve images. Tagg was higher in patients with DED than in healthy volunteers (P < 0.001). Tagg was positively correlated with the ocular surface disease index (r = 0.418, P = 0.003) and negatively correlated with tear breakup time (r = -0.398, P = 0.007). There was no correlation between Tagg and visual analog scale scores, corneal fluorescein staining scores, or the Schirmer I test.

Conclusions

Tagg was validated for quantification of corneal subbasal nerve tortuosity and was higher in patients with DED than in healthy volunteers. A higher Tagg may be linked to ocular discomfort, visual function disturbance, and tear film instability.

Translational Relevance

Corneal subbasal nerve tortuosity is a potential biomarker for corneal neurobiology in DED.

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.

Impact of corneal parameters, refractive error and age on density and morphology of the subbasal nerve plexus fibers in healthy adults

The purpose of this study was to analyze corneal sub-basal nerve plexus (SBNP) density and morphology and their relationships with corneal parameters and refractive status. In this single center study, in vivo confocal microscopy (IVCM) was performed in 76 eyes of 38 healthy subjects aged 19–87 (mean age 34.987 ± 1.148). Nerve fiber analysis was performed using Confoscan 4 microscope with semi-automated software (Nidek Technologies, Italy) The nerve fiber length (NFL) µm/mm², nerve fiber density (NFD) no./mm², tortuosity coefficient (TC), and nerve beadings density (NBD) no./mm were considered. Relationship between SBNP parameters and corneal curvature, thickness, diameter, and refraction were analyzed. Additionally, the association with gender, laterality and age were determined. NFL was inversely correlated with age (r = − 0.528, p < 0.001), myopic refractive error (spherical value) (r = − 0.423, p < 0.001), and cylindrical power (r = − 0.340, p = 0.003). NFD was inversely correlated with age (r = − 0.420, p < 0.001) and myopic refractive error (r = − 0.341, p = 0.003). NBD showed a low inverse correlation with cylindrical power (r = − 0.287, p = 0.012) and a slight positive correlation with K (r = 0.230, p = 0.047). TC showed a significant negative correlation between age (r = − 0.500, p < 0.001) and myopic refractive error (r = − 0.351, p = 0.002). Additionally, there were strong positive correlations between NFL and NFD (r = 0.523, p < 0.001), NFL and TI (r = 0.603, p < 0.001), and NFD and TC (r = 0.758, p < 0.001). Multiple regression analysis revealed age to be the most significant factor affecting SBNP density (B = − 0.467, p = 0.013) and length (B = − 61.446, p < 0.001); myopic refractive error reduced both SBNP density (B = − 2.119, p = 0.011) and length (B = − 158.433, p = 0.016), while gender and laterality had no significant effects (p > 0.005). SBNP fiber length decreases with age, myopic refractive error and cylindrical power. SBNP fiber density reduces with age and myopic refractive error. Corneal nerve parameters are not influenced by gender or laterality.

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.

Corneal confocal microscopy compared with quantitative sensory testing and nerve conduction for diagnosing and stratifying the severity of diabetic peripheral neuropathy

INTRODUCTION

Diabetic neuropathy can be diagnosed and assessed using a number of techniques including corneal confocal microscopy (CCM).

RESEARCH DESIGN AND METHODS

We have undertaken quantitative sensory testing, nerve conduction studies and CCM in 143 patients with type 1 and type 2 diabetes without neuropathy (n=51), mild neuropathy (n=47) and moderate to severe neuropathy (n=45) and age-matched controls (n=30).

RESULTS

Vibration perception threshold (p<0.0001), warm perception threshold (WPT) (p<0.001), sural nerve conduction velocity (SNCV) (p<0.001), corneal nerve fiber density (CNFD) (p<0.0001), corneal nerve branch density (CNBD) (p<0.0001), corneal nerve fiber length (CNFL) (p=0.002), inferior whorl length (IWL) (p=0.0001) and average nerve fiber length (ANFL) (p=0.0001) showed a progressive abnormality with increasing severity of diabetic neuropathy. Receiver operating characteristic curve analysis for the diagnosis of diabetic neuropathy showed comparable performance in relation to the area under the curve (AUC) but differing sensitivities and specificities for vibration perception threshold (AUC 0.79, sensitivity 55%, specificity 90%), WPT (AUC 0.67, sensitivity 50%, specificity 76%), cold perception threshold (AUC 0.64, sensitivity 80%, specificity 47%), SNCV (AUC 0.70, sensitivity 76%, specificity 54%), CNFD (AUC 0.71, sensitivity 58%, specificity 83%), CNBD (AUC 0.70, sensitivity 69%, specificity 65%), CNFL (AUC 0.68, sensitivity 64%, specificity 67%), IWL (AUC 0.72, sensitivity 70%, specificity 65%) and ANFL (AUC 0.72, sensitivity 71%, specificity 66%).

CONCLUSION

This study shows that CCM identifies early and progressive corneal nerve loss at the inferior whorl and central cornea and has comparable utility with quantitative sensory testing and nerve conduction in the diagnosis of diabetic neuropathy.

Association between alterations of corneal sub-basal nerve plexus analyzed with in vivo confocal microscopy and long-term glycemic variability

Purpose:

The effect of long-term glycemic variability upon corneal sub-basal nerve plexus (CSNP) morphology analyzed by in vivo confocal microscopy (IVCM) has been poorly investigated in the setting of type 1 diabetes mellitus (T1DM). Our purpose was to analyze the association between morphometric parameters of CSNP and new markers of glycemic variability in a population of patients with T1DM.

Methods:

Forty patients with T1DM underwent: assessment of diabetic neuropathy (DN); analysis of subcutaneous advanced glycated end-products; IVCM scans of CSNP. The fully automated software ACCMetrics was employed to analyze IVCM images and calculate seven corneal nerve parameters. Data of diabetes duration, mean and standard deviation (SD) of either last-year and all-time glycated hemoglobin (HbA1C) were retrieved.

Results:

Diabetes duration and all-time SD of HbA1C were independently associated with CNFD (R = –0.26, p = 0.01; R = –0.27, p = 0.047 respectively), CNFL (R = –0.12; p = 0.01; R = –0.17, p = 0.01 respectively) and CNFrD (R = –0.001, p = 0.009; R = –0.002, p = 0.007 respectively). The analysis of the association among IVCM parameters and specific subtypes of DN showed that altered cold sensitivity was independently associated with CNFD (B = –0.24, p = 0.01), CNFL (B = –0.46, p = 0.01) and CNFrD (B = –28.65, p = 0.03).

Conclusions:

All-time SD of HbA1C and disease duration were found to be independent predictors of damage to CSNP in patients with T1DM.

Biophotonics methods for functional monitoring of complications of diabetes mellitus

The prevalence of diabetes complications is a significant public health problem with a considerable economic cost. Thus, the timely diagnosis of complications and prevention of their development will contribute to increasing the length and quality of patient life, and reducing the economic costs of their treatment. This article aims to review the current state-of-the-art biophotonics technologies used to identify the complications of diabetes mellitus and assess the quality of their treatment. Additionally, these technologies assess the structural and functional properties of biological tissues, and they include capillaroscopy, laser Doppler flowmetry and hyperspectral imaging, laser speckle contrast imaging, diffuse reflectance spectroscopy and imaging, fluorescence spectroscopy and imaging, optical coherence tomography, optoacoustic imaging and confocal microscopy. Recent advances in the field of optical noninvasive diagnosis suggest a wider introduction of biophotonics technologies into clinical practice and, in particular, in diabetes care units.

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 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.

Automated Tortuosity Analysis of Nerve Fibers in Corneal Confocal Microscopy

Precise characterization and analysis of corneal nerve fiber tortuosity are of great importance in facilitating examination and diagnosis of many eye-related diseases. In this paper we propose a fully automated method for image-level tortuosity estimation, comprising image enhancement, exponential curvature estimation, and tortuosity level classification. The image enhancement component is based on an extended Retinex model, which not only corrects imbalanced illumination and improves image contrast in an image, but also models noise explicitly to aid removal of imaging noise. Afterwards, we take advantage of exponential curvature estimation in the 3D space of positions and orientations to directly measure curvature based on the enhanced images, rather than relying on the explicit segmentation and skeletonization steps in a conventional pipeline usually with accumulated pre-processing errors. The proposed method has been applied over two corneal nerve microscopy datasets for the estimation of a tortuosity level for each image. The experimental results show that it performs better than several selected state-of-the-art methods. Furthermore, we have performed manual gradings at tortuosity level of four hundred and three corneal nerve microscopic images, and this dataset has been released for public access to facilitate other researchers in the community in carrying out further research on the same and related topics.

Corneal nerve tortuosity grading via ordered weighted averaging-based feature extraction

PURPOSE

Tortuosity of corneal nerve fibers acquired by in vivo Confocal Microscopy (IVCM) are closely correlated to numerous diseases. While tortuosity assessment has conventionally been conducted through labor-intensive manual evaluation, this warrants an automated and objective tortuosity assessment of curvilinear structures. This paper proposes a method that extracts the image-level features for corneal nerve tortuosity grading.

METHODS

For an IVCM image, all corneal nerve fibers are first segmented and then, their tortuosity are calculated by morphological measures. The ordered weighted averaging (OWA) approach, and the k-Nearest-Neighbor guided dependent ordered weighted averaging (kNNDOWA) approach are proposed to aggregate the tortuosity values and form a set of extracted features. This is followed by running the Wrapper method, a supervised feature selection, with an aim to identify the most informative attributes for tortuosity grading.

RESULTS

Validated on a public and an in-house benchmark data sets, experimental results demonstrate superiority of the proposed method over the conventional averaging and length-weighted averaging methods with performance gain in accuracy (15.44% and 14.34%, respectively).

CONCLUSIONS

The simultaneous use of multiple aggregation operators could extract the image-level features that lead to more stable and robust results compared with that using average and length-weighted average. The OWA method could facilitate the explanation of derived aggregation behavior through stress functions. The kNNDOWA method could mitigate the effects of outliers in the image-level feature extraction.

Validation of the Use of Automated and Manual Quantitative Analysis of Corneal Nerve Plexus Following Refractive Surgery

Following refractive surgery, the cornea is denervated and re-innervated, hence a reproducible tool to objectively quantify this change is warranted. This study aimed to determine the repeatability and reproducibility of corneal nerve quantification between automated (ACCMetrics) and manual software (CCMetrics) following refractive surgery. A total of 1007 in vivo confocal microscopy images from 20 post-small incision lenticule extraction (SMILE) or post-laser-assisted in situ keratomileusis (LASIK) patients were evaluated by two independent observers using CCMetrics for corneal nerve fibre density (CNFD), corneal nerve branch density (CNBD), and corneal nerve fibre length (CNFL). Intra-observer and inter-observer reproducibility and repeatability, as well as agreement and correlation between the measurements obtained by ACCMetrics and CCMetrics, were assessed. We found that CNFL demonstrated the best intra- and inter-observer agreement followed by CNFD (intra-class correlation coefficient (ICC) = 0.799 and 0.740, respectively for CNFL; 0.757 and 0.728 for CNFD). CNBD demonstrated poorest intra- and inter-observer ICC. There was an underestimation in ACCMetrics measurements compared to CCMetrics measurements, although the differences were not significant. Our data suggested that both automated and manual methods can be used as reliable tools for the evaluation of corneal nerve status following refractive surgery. However, the measurements obtained with different methods are not interchangeable.

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.

Risk of recurrent corneal erosion in patients with diabetes mellitus in Taiwan: a population-based cohort study

OBJECTIVE

To investigate the risk of recurrent corneal erosion (RCE) in patients with diabetes mellitus (DM).

DESIGN, SETTING AND PARTICIPANTS

This retrospective, nationwide, matched cohort study included 239 854 patients with DM recruited between 2003 and 2005 from the Longitudinal Cohort of Diabetes Patients database. The control group included the same number of age-matched and sex-matched patients without DM selected from the Taiwan Longitudinal Health Insurance Database, 2000. Data for each patient were collected from the index date until December 2013.

MAIN OUTCOMES AND MEASURES

The incidence and risk of RCE were compared between the two groups. Cox proportional hazards regression was used to calculate the HR for RCE after adjustment for potential confounders. The cumulative RCE incidence rate was calculated using Kaplan-Meier analysis.

RESULTS

In total, 1236 patients with DM and 884 controls developed RCE during the follow-up period, resulting in an incidence rate of RCE in patients with DM (5.87/10 000 person-years (PY)) higher than that in the controls (4.23/10 000 PY). After adjustment for potential confounders, including hypertension, hyperlipidaemia, chronic renal disease and keratoconjunctivitis sicca, patients with DM were 1.35 times (95% CI, 1.24 to 1.48) more likely to develop RCE than the total sample cohort.

CONCLUSIONS

DM increases the risk of RCE, which is an interdisciplinary issue. Therefore, close collaboration between endocrinologists and ophthalmologists is important in managing RCE following DM.

Stromal Nerve Imaging and Tracking Using Micro-Optical Coherence Tomography

Purpose

To image, track and map the nerve fiber distribution in excised rabbit corneas over the entire stromal thickness using micro-optical coherence tomography (µOCT) to develop a screening tool for early peripheral neuropathy.

Methods

Excised rabbit corneas were consecutively imaged by a custom-designed µOCT prototype and a commercial laser scanning fluorescence confocal microscope. The µOCT images with a field of view of approximately 1 × 1 mm were recorded with axial and transverse resolutions of approximately 1 µm and approximately 4 µm, respectively. In the volumetric µOCT image data, network maps of hyper-reflective, branched structures traversing different stromal compartments were segmented using semiautomatic image processing algorithms. Furthermore, the same corneas received βIII-tubulin antibody immunostaining before digital confocal microscopy, and a comparison between µOCT image data and immunohistochemistry analysis was performed to validate the nerval origin of the tracked network structures.

Results

Semiautomatic tracing of the nerves with a high range of different thicknesses was possible through the whole corneal volumes, creating a skeleton of the traced nerves. There was a good conformity between the hyper-reflective structures in the µOCT data and the stained nerval structures in the immunohistochemistry data.

Conclusions

This article demonstrates nerval imaging and tracking as well as a spatial correlation between µOCT and a fluorescence corneal nerve standard for larger nerves throughout the full thickness of the cornea ex vivo.

Translational Relevance

Owing to its advantageous properties, µOCT may become useful as a noncontact method for assessing nerval structures in humans to screen for early peripheral neuropathy.

U-Net Segmented Adjacent Angle Detection (USAAD) for Automatic Analysis of Corneal Nerve Structures

Measurement of corneal nerve tortuosity is associated with dry eye disease, diabetic retinopathy, and a range of other conditions. However, clinicians measure tortuosity on very different grading scales that are inherently subjective. Using in vivo confocal microscopy, 253 images of corneal nerves were captured and manually labelled by two researchers with tortuosity measurements ranging on a scale from 0.1 to 1.0. Tortuosity was estimated computationally by extracting a binarised nerve structure utilising a previously published method. A novel U-Net segmented adjacent angle detection (USAAD) method was developed by training a U-Net with a series of back feeding processed images and nerve structure vectorizations. Angles between all vectors and segments were measured and used for training and predicting tortuosity measured by human labelling. Despite the disagreement among clinicians on tortuosity labelling measures, the optimised grading measurement was significantly correlated with our USAAD angle measurements. We identified the nerve interval lengths that optimised the correlation of tortuosity estimates with human grading. We also show the merit of our proposed method with respect to other baseline methods that provide a single estimate of tortuosity. The real benefit of USAAD in future will be to provide comprehensive structural information about variations in nerve orientation for potential use as a clinical measure of the presence of disease and its progression.