Automatic analysis of diabetic peripheral neuropathy using multi-scale quantitative morphology of nerve fibres in corneal confocal microscopy imaging

Tear film hTERT and corneal nerve characteristics in dry eye disease

CLINICAL RELEVANCE

The behaviour of human telomerase reverse transcriptase (hTERT) in tears reflects its role in maintaining the ocular surface homoeostasis, as it is increased after the initial fitting of contact lenses and post-overnight lid closure.

BACKGROUND

hTERT has been shown to respond to cellular stress in neurodegenerative diseases and to enhance axonal regeneration after peripheral axotomy in an animal model. This work investigated whether the behaviour of hTERT in the tear film reflects ocular surface inflammation and neuronal changes in the presence of dry eye disease.

METHODS

Flush tears were collected from 18 participants with dry eye disease (14 females, 4 males, mean age 34.7 ± 5.2 years) and from 18 healthy participants without dry eye disease (8 females, 10 males, mean age 31.9 ± 5.8 years). Dry eye disease status was defined using the TFOS DEWS II diagnostic criteria. hTERT levels in tears were measured using enzyme-linked immunosorbent assays. Confocal images were taken at the level of the subbasal nerve plexus at the central cornea and at the inferior whorl, and the densities of corneal immune cells were evaluated as well as corneal nerve morphology metrics using a fully automated technique (University of Manchester, United Kingdom).

RESULTS

In participants with dry eye disease, hTERT levels were significantly higher compared to controls (median [interquartile range]: 434 [320-600] ng/ml, and 184 [42-390] ng/ml, respectively, p = 0.01). Increased nerve fibre width at the inferior whorl, was seen in those with dry eyes (0.0219 [0.0214-0.0236] mm/mm compared to controls 0.0217 [0.0207 0.0222] p < 0.001), but no significant differences were found in the density of corneal immune cells.

CONCLUSIONS

hTERT levels were elevated in participants with dry eye disease, and this was accompanied by increased nerve thickness in the inferior cornea. The hTERT response may reflect the stress induced to the ocular surface and corneal nerves due to having dry eye disease.

Analysis of the ocular surface functional unit in episodic migraine

AIM

Migraine is a chronic neurovascular disease that affects the trigeminovascular system. The purpose of this study was to evaluate corneal subbasal nerve fibers, dendritic cells and to measure tear film parameters in migraine.

PATIENTS AND METHODS

87 eyes of 44 patients suffering from migraine with a mean age of 33.23 ± 11.41 years were included in our study. 25 age-matched controls (mean age of 30.16 ± 12.59 years; P = 0.162) were recruited. The corneal subbasal plexus and the dendritic cells (DC) were analyzed using in vivo confocal microscopy (Heidelberg Retina Tomograph II Rostock Cornea Module; Heidelberg Engineering GmbH), and the tear film was imaged using LacryDiag (Quantel Medical, France).

RESULTS

Regarding the subbasal nerve fibers of the cornea, none of the examined parameters differed significantly in migraine patients from controls. We found a significant increase in the corneal DC density (P < 0.0001) and DC area (P < 0.0001) in migraine patients compared to healthy volunteers. DC density showed a positive correlation with the monthly attack frequency (r = 0.32, P = 0.041) and the DC area a negative correlation with corneal nerve branch density (r = -0.233, P = 0.039), nerve fiber length (r = -0.232, P = 0.04) and total branch density (r = -0.233, P = 0.039). Using LacryDiag a significant loss of Meibomian gland area could be detected on the superior eyelid (P = 0.005) in migraine.

CONCLUSIONS

Our results suggest the presence of neuroinflammation in the cornea of migraine patients affecting the peripheral trigeminal system. Dendritic cells surrounding the subbasal plexus may be involved in the activation and modulation of pain in migraine.

Morphological Differentiation of Corneal Inflammatory Cells: Proposal of Pragmatic Protocol

PURPOSE

Corneal confocal microscopy is a noninvasive imaging technique to analyze corneal nerve fibers and corneal inflammatory cells (CICs). The amount of CICs is a potential biomarker of disease activity in chronic autoinflammatory diseases. To date, there are no standardized criteria for the morphological characterization of CICs. The aim was to establish a protocol for a standardized morphological classification of CICs based on a literature search and to test this protocol for applicability and reliability.

METHODS

A systematic review of the literature about definitions of CICs was conducted. Existing morphological descriptions were translated into a structured algorithm and applied by raters. Subsequently, the protocol was optimized by reducing and defining the criteria of the cell types. The optimized algorithm was applied by 4 raters. The interrater reliability was calculated using Fleiss kappa (K).

RESULTS

A systematic review of the literature revealed no uniform morphological criteria for the differentiation of the individual cell types in CICs. Our first protocol achieved only a low level of agreement between 3 raters (K = 0.09; 1062 rated cells). Our revised protocol was able to achieve a higher interrater reliability with 3 (K = 0.64; 471 rated cells) and 4 (K = 0.61; 628 rated cells) raters.

CONCLUSIONS

The indirect use of criteria from the literature leads to a high error rate. By clearly defining the individual cell types and standardizing the protocol, reproducible results were obtained, allowing the introduction of this protocol for the future evaluation of CICs in the corneal confocal microscopy.

Artificial-Intelligence-Enhanced Analysis of In Vivo Confocal Microscopy in Corneal Diseases: A Review

Artificial intelligence (AI) has seen significant progress in medical diagnostics, particularly in image and video analysis. This review focuses on the application of AI in analyzing in vivo confocal microscopy (IVCM) images for corneal diseases. The cornea, as an exposed and delicate part of the body, necessitates the precise diagnoses of various conditions. Convolutional neural networks (CNNs), a key component of deep learning, are a powerful tool for image data analysis. This review highlights AI applications in diagnosing keratitis, dry eye disease, and diabetic corneal neuropathy. It discusses the potential of AI in detecting infectious agents, analyzing corneal nerve morphology, and identifying the subtle changes in nerve fiber characteristics in diabetic corneal neuropathy. However, challenges still remain, including limited datasets, overfitting, low-quality images, and unrepresentative training datasets. This review explores augmentation techniques and the importance of feature engineering to address these challenges. Despite the progress made, challenges are still present, such as the "black-box" nature of AI models and the need for explainable AI (XAI). Expanding datasets, fostering collaborative efforts, and developing user-friendly AI tools are crucial for enhancing the acceptance and integration of AI into clinical practice.

Discontinuity third harmonic generation microscopy for label-free imaging and quantification of intraepidermal nerve fibers

Label-free imaging methodologies for nerve fibers rely on spatial signal continuity to identify fibers and fail to image free intraepidermal nerve endings (FINEs). Here, we present an imaging methodology-called discontinuity third harmonic generation (THG) microscopy (dTHGM)-that detects three-dimensional discontinuities in THG signals as the contrast. We describe the mechanism and design of dTHGM and apply it to reveal the bead-string characteristics of unmyelinated FINEs. We confirmed the label-free capability of dTHGM through a comparison study with the PGP9.5 immunohistochemical staining slides and a longitudinal spared nerve injury study. An intraepidermal nerve fiber (IENF) index based on a discontinuous-dot-connecting algorithm was developed to facilitate clinical applications of dTHGM. A preliminary clinical study confirmed that the IENF index was highly correlated with skin-biopsy-based IENF density (Pearson's correlation coefficient R = 0.98) and could achieve differential identification of small-fiber neuropathy (p = 0.0102) in patients with diabetic peripheral neuropathy.

Neuropathic Corneal Pain after Coronavirus Disease 2019 (COVID-19) Infection

INTRODUCTION

This is a case report of a patient with neuropathic corneal pain after coronavirus disease 2019 (COVID-19) infection.

METHODS

A previously healthy 27-year-old female presented with bilateral eye pain accompanied by increased light sensitivity 5 months after COVID-19 infection. She was diagnosed with neuropathic corneal pain based on clear corneas without fluorescein staining, alongside the presence of microneuromas, dendritic cells, and activated stromal keratocytes identified bilaterally on in vivo confocal microscopy.

RESULTS

The patient's tear nerve growth factor, substance P, and calcitonin gene-related peptide levels were 5.9 pg/mL, 2978.7 pg/mL, and 1.1 ng/mL, respectively, for the right eye and 23.1 pg/mL, 4798.7 pg/mL, and 1.2 ng/mL, respectively, for the left eye, suggesting corneal neuroinflammatory status. After 6 weeks of topical 0.1% flurometholone treatment, decreased microneuroma size, less extensive dendritic cells, and reduced tear nerve growth factor and substance P levels were observed. The scores on the Ocular Pain Assessment Survey showed an improvement in burning sensation and light sensitivity, decreasing from 80% and 70% to 50% for both.

CONCLUSIONS

Neuropathic corneal pain is a potential post-COVID-19 complication that warrants ophthalmologists' and neurologists' attention.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Fully Automatic, Semiautomatic, and Manual Corneal Nerve Fiber Analysis in Patients With Sarcoidosis

Purpose

No guidelines are available on the preferred method for analyzing corneal confocal microscopy (CCM) data. Manual, semiautomatic, and automatic analyzes are all currently in use. The purpose of the present study was threefold. First, we aimed to investigate the different methods for CCM analysis in patients with and without small fiber neuropathy (SFN). Second, to determine the correlation of different methods for measuring corneal nerve fiber length (CNFL) and nerve fiber area (NFA). Finally, we investigated the added value of automatic NFA analysis.

Methods

We included 20 healthy controls and 80 patients with sarcoidosis, 31 with established SFN and 49 without SFN. The CNFL was measured using CCMetrics, ACCMetrics, and NeuronJ. NFA was measured with NFA FIJI and ACCMetrics NFA.

Results

CNFL and NFA could not distinguish sarcoidosis with and without SFN or healthy controls. CCMetrics, NeuronJ, and ACCMetrics CNFL highly correlated. Also, NFA FIJI and ACCMetrics NFA highly correlated. Reproducing a nonlinear formula between CNFL and NFA confirmed the quadratic relation between NFA FIJI and ACCMetrics CNFL. CCMetrics and NeuronJ instead showed a square root relationship and seem to be less comparable owing to differences between automatic and manual techniques.

Conclusions

ACCMetrics can be used for fully automatic analysis of CCM images to optimize efficiency. However, CNFL and NFA do not seem to have a discriminatory value for SFN in sarcoidosis. Further research is needed to determine the added value and normative values of NFA in CCM analysis.

Translational Relevance

Our study improves the knowledge about CCM software and pathophysiology of SFN.

Ophthalmological involvement in wild-type transthyretin amyloidosis: A multimodal imaging study

BACKGROUND AND AIMS

Ophthalmological abnormalities have been reported in hereditary transthyretin-related amyloidosis (ATTRv, v for variant) but not in wild-type transthyretin-related amyloidosis (ATTRwt).

METHODS

Patients with ATTRwt, ATTRv, and light chain amyloidosis (AL) and healthy subjects (controls) underwent complete eye examination, including optical coherence tomography (OCT), OCT angiography (OCTA), and in vivo corneal confocal microscopy (CCM).

RESULTS

Seventeen ATTRwt, nine ATTRv, two ATTRv carriers, and seven AL patients were enrolled. Compared with other groups, ATTRwt patients had 10 letters lower visual acuity and a higher prevalence of glaucoma, cataract, and retinal pigment epithelium alterations. In the whole group of patients, especially in ATTRwt, we observed (1) a reduced corneal nerve fiber length and more tortuous stromal nerves at CCM, (2) a reduced macular volume and peripapillary nerve fiber layer thickness at OCT, and (3) impairment of peripapillary and macular vascularization at OCTA.

INTERPRETATION

Ophthalmological abnormalities are common in ATTRwt, significantly impairing visual acuity. Noninvasive imaging modalities allow for the identification of small nerve fibers and small vessel damage, which may represent further warning signs for early diagnosis of ATTRwt.

Decreased corneal subbasal nerve fiber length and density in diabetic dogs with cataracts using in vivo confocal microscopy

OBJECTIVE

To determine whether there is a difference in corneal sensitivity and corneal subbasal nerve plexus (CSNP) morphology in cataractous dogs with diabetes mellitus (DM) versus without DM.

ANIMALS STUDIED

Twenty six domestic dogs with cataracts of various breeds presented for phacoemulsification, 13 with DM and 13 without DM.

PROCEDURE

The inclusion criteria for the study were dogs with bilateral cataracts and no clinical evidence of corneal disease. The diabetic group had documented hyperglycemia and was currently treated with insulin. The non-diabetic group had no evidence of DM on examination and bloodwork. Complete ophthalmic examination, corneal esthesiometry, and in vivo confocal microscopy of the CSNP was performed for both eyes of each dog. The CSNP was evaluated using a semi-automated program and statistically analyzed.

RESULTS

The mean (±SD) CSNP fiber length was significantly decreased in diabetic (3.8 ± 3.0 mm/mm2 ) versus non-diabetic (6.7 ± 1.9 mm/mm2 ) dogs. Likewise, the mean (±SD) fiber density was significantly decreased in diabetic (8.3 ± 3.1 fibers/mm2 ) versus non-diabetic (15.5 ± 4.9 fibers/mm2 ) dogs. The corneal touch threshold was significantly reduced in diabetic (2.1 ± 0.8 cm) versus non-diabetic (2.8 ± 0.4 cm) dogs. There was a non-significant trend towards subclinical keratitis in diabetic (9/13) versus non-diabetic (4/13) dogs.

CONCLUSIONS

Morphological and functional abnormalities of the CSNP were present in dogs with DM, including decreased fiber length, fiber density, and corneal sensitivity. These findings are consistent with diabetic neuropathy and could contribute to clinically significant corneal complications after cataract surgery.

Corneal nerve loss and increased Langerhans cells are associated with disease severity in patients with rheumatoid arthritis

BACKGROUND/OBJECTIVES

Rheumatoid arthritis (RA) is a multisystem autoimmune disorder characterized by articular and extra-articular manifestations. Neuropathy is a poorly studied manifestation of RA. The aim of this study was to utilize the rapid non-invasive ophthalmic imaging technique of corneal confocal microscopy to identify whether there is evidence of small nerve fibre injury and immune cell activation in patients with RA.

SUBJECTS/METHODS

Fifty consecutive patients with RA and 35 healthy control participants were enrolled in this single-centre, cross-sectional study conducted at a university hospital. Disease activity was assessed with the 28-Joint Disease Activity Score and erythrocyte sedimentation rate (DAS28-ESR). Central corneal sensitivity was measured with a Cochet-Bonnet contact corneal esthesiometer. A laser scanning in vivo corneal confocal microscope was used to quantify corneal nerve fibre density (CNFD), nerve branch density (CNBD), nerve fibre length (CNFL), and Langerhans cell (LC) density.

RESULTS

Corneal sensitivity (P = 0.01), CNFD (P = 0.02), CNBD (P < 0.001), and CNFL (P < 0.001) were lower, and mature (P = 0.001) and immature LC densities (P = 0.011) were higher in patients with RA compared to control subjects. CNFD (P = 0.016) and CNFL (P = 0.028) were significantly lower in patients with moderate to high (DAS28-ESR > 3.2) compared to mild (DAS28-ESR ≤ 3.2) disease activity. Furthermore, the DAS28-ESR score correlated with CNFD (r = -0.425; P = 0.002), CNBD (ρ = -0.362; P = 0.010), CNFL (r = -0.464; P = 0.001), total LC density (ρ = 0.362; P = 0.010) and immature LC density (ρ = 0.343; P = 0.015).

CONCLUSIONS

This study demonstrates reduced corneal sensitivity, corneal nerve fibre loss and increased LCs which were associated with the severity of disease activity in patients with RA.

Optimizing examination time and diagnostic performance of the histamine-induced axon-reflex flare response in diabetes

INTRODUCTION/AIMS

The axon-reflex flare response is a reliable method for functional assessment of small fibers in diabetic peripheral neuropathy (DPN), but broad adoption is limited by the time requirement. The aims of this study were to (1) assess diagnostic performance and optimize time required for assessing the histamine-induced flare response and (2) associate with established parameters.

METHODS

A total of 60 participants with type 1 diabetes with (n = 33) or without (n = 27) DPN participated. The participants underwent quantitative sensory testing (QST), corneal confocal microscopy (CCM), and flare intensity and area size assessments by laser-Doppler imaging (FLPI) following an epidermal skin-prick application of histamine. The flare parameters were evaluated each minute for 15 min, and the diagnostic performance compared to QST and CCM were assessed using area under the curve (AUC). Minimum time-requirements until differentiation and to achieve results comparable with a full examination were assessed.

RESULTS

Flare area size had better diagnostic performance compared with CCM (AUC 0.88 vs. 0.77, p < 0.01) and QST (AUC 0.91 vs. 0.81, p = 0.02) than mean flare intensity, and could distinguish people with and without DPN after 4 min compared to after 6 min (both p < 0.01). Flare area size achieved a diagnostic performance comparable to a full examination after 6 and 7 min (CCM and QST respectively, p > 0.05), while mean flare intensity achieved it after 5 and 8 min (CCM and QST respectively, p > 0.05).

DISCUSSION

The flare area size can be evaluated 6-7 min after histamine-application, which increases diagnostic performance compared to mean flare intensity.

Evaluation of Corneal Nerve Regeneration After Minimally Invasive Corneal Neurotization

PURPOSE

To evaluate the corneal nerve regeneration after minimally invasive corneal neurotization (MICN) and to further clarify the recovery patterns of sensory and trophic functions of the corneal nerves.

DESIGN

A retrospective cohort study based in the Shanghai Ninth People's Hospital.

METHODS

Eighteen patients (18 eyes) who underwent MICN for neurotrophic keratopathy due to intracranial surgery was conducted to analyze their follow-up data at 6, 12, 18, and 24 months after surgery.

RESULTS

At 12 months postoperatively, the growth of the central and peripheral corneal nerve fiber density (CNFD) was 11.47±8.56 and 14.73±8.08 n/mm 2 with subsequent improvement slowing down, and the patient's corneal epithelium defect was healed ahead of the accomplishment of corneal nerve regeneration. The number of dendritic cells also reached its peak. At 18 months postoperatively, the recovery of central and peripheral corneal sensation was 37.22±23.06 mm and 39.38±18.08 mm with no subsequent improvement, and the growth of the central and peripheral corneal nerve branch density (CNBD) was 29.69±11.05 and 43.75±1.41 n/mm 2 , with a positive and significant correlation between corneal sensation and CNBD (at central r =0.632, P <0.005; at peripheral r =0.645, P <0.005). At 24 months postoperatively, mean CNFD, CNBD, and corneal sensation recovered significantly compared with preoperative, but a few patients' corneal sensation recovered insignificantly with good CNFD recovery and poor CNBD recovery.

CONCLUSIONS

After MICN, the trophic function of the corneal nerve recovers before the sensory function, and in particular, the recovery of sensation is based on the coexistence of the corneal nerve trunk and branches.

Skin-Only Versus Skin-Plus-Orbicularis Resection Blepharoplasty: An Elaborated Analysis of Early- and Long-Term Effects on Corneal Nerves, Meibomian Glands, Dry Eye Parameters, and Eyebrow Position

PURPOSE

To evaluate the early- and long-term effects of 2 different blepharoplasty techniques on corneal nerves, meibomian gland morphology, clinical parameters of dry eye disease (DED), and eyebrow position.

METHODS

This prospective, interventional study included age-sex-matched blepharoplasty patients who had a skin-only resection (24 eyes of 12 patients; Group-S) or a skin-plus-orbicularis muscle resection (24 eyes of 12 patients; Group-M) procedure. Preoperative and postoperative parameters of in vivo corneal confocal microscopy (IVCCM; corneal nerve fiber density [CNFD], nerve branch density [CNBD], and nerve fiber length), meibomian gland area loss (MGAL), DED (Schirmer I test and noninvasive tear breakup time), and eyebrow heights (lateral [LBH] and central [CBH]) were evaluated and compared between the intervention groups ( ClinicalTrials.gov , NCT05528016).

RESULTS

Compared with baseline, the CNBD of Group-S (19.91 ± 7.66 vs. 16.05 ± 7.28 branches/mm 2 , p = 0.049) and CNFD of Group-M (19.52 ± 7.45 vs. 16.80 ± 6.95 fibers/mm 2 , p = 0.028) was significantly decreased at postoperative first week. However, in both groups, IVCCM parameters returned to baseline values at postoperative first month and first year ( p > 0.05). A significant MGAL increase was observed in Group-S (18.47 ± 5.43 vs. 19.94 ± 5.31, p = 0.030) and Group-M (18.86 ± 7.06 vs. 20.12 ± 7.01, p = 0.023) at the postoperative first year, demonstrating meibomian gland atrophy. Only significant changes were observed in Group-M in LBH (16.17 ± 2.45 vs. 16.67 ± 2.28 mm, p = 0.044) and CBH (17.33 ± 2.35 vs. 17.96 ± 2.31 mm, p = 0.004) at postoperative first year.

CONCLUSIONS

Blepharoplasty with or without orbicularis resection seems to have similar effects on IVCCM, DED, and MGAL parameters. However, incorporating an orbicularis muscle resection in a blepharoplasty operation could slightly elevate the eyebrow position.

Real-World Effectiveness and Safety of Hydrogen Inhalation in Chinese Patients with Type 2 Diabetes: A Single-Arm, Retrospective Study

Aim

To evaluate the real-life effectiveness and safety of Chinese patients with type 2 diabetes mellitus (T2DM) receiving hydrogen inhalation (HI) treatment as a supplementary treatment.

Methods

This retrospective, multicenter, observational 6-months clinical study included T2DM patients maintaining HI, visited at 4 time points. The primary outcome is the mean change in glycated hemoglobin (HbA1c) at the end of the study compared to baseline. The secondary outcome is analyzing the mean change of fasting plasma glucose (FPG), weight, lipid profile, insulin dose and homeostasis model assessment. Linear regression and logistics regression are applied to evaluate the effect of HI after the treatment.

Results

Of the 431 patients comprised, it is observed a significant decrease in HbA1c level (9.04±0.82% at baseline to 8.30±0.99% and 8.00±0.80% at the end, p<0.001), FPG (165.6±40.2 mg/dL at baseline to 157.1±36.3mg/dL and 143.6±32.3mg/dL at the end, p<0.001), weight (74.7±7.1kg at baseline to 74.8±10.0kg and 73.6±8.1kg at the end, p<0.001), insulin dose (49.3±10.8U/d at baseline to 46.7±8.0U/d and 45.2±8.7U/d, p<0.001). The individuals in subgroup with higher baseline HbA1c and longer daily HI time duration gain greater HbA1c decrease after 6 months. Linear regression shows that higher baseline HbA1c level and shorter diabetes duration are significantly in relation to greater HbA1c reduction. Logistics regression reveals that lower weight is associated with a higher possibility of reaching HbA1c<7%. The most common adverse event is hypoglycemia.

Conclusion

HI therapy significantly improves glycemic control, weight, insulin dose, lipid metabolism, β-cell function and insulin resistance of patients with type 2 diabetes after 6 months. Higher baseline HbA1c level and shorter diabetes duration is related to greater clinical response to HI.

Where Art Thou O treatment for diabetic neuropathy: the sequel

INTRODUCTION

Having lived through a pandemic and witnessed how regulatory approval processes can evolve rapidly; it is lamentable how we continue to rely on symptoms/signs and nerve conduction as primary endpoints for clinical trials in DPN.

AREAS COVERED

Small (Aδ and C) fibers are key to the genesis of pain, regulate skin blood flow, and play an integral role in the development of diabetic foot ulceration but continue to be ignored. This article challenges the rationale for the FDA insisting on symptoms/signs and nerve conduction as primary endpoints for clinical trials in DPN.

EXPERT OPINION

Quantitative sensory testing, intraepidermal nerve fiber density, and especially corneal confocal microscopy remain an after-thought, demoted at best to exploratory secondary endpoints in clinical trials of diabetic neuropathy. If pharma are to be given a fighting chance to secure approval for a new therapy for diabetic neuropathy, the FDA needs to reassess the evidence rather than rely on 'opinion' for the most suitable endpoint(s) in clinical trials of diabetic neuropathy.

In-vivo corneal confocal microscopy: Imaging analysis, biological insights and future directions

In-vivo corneal confocal microscopy is a powerful imaging technique which provides clinicians and researcher with the capabilities to observe microstructures at the ocular surfaces in significant detail. In this Mini Review, the optics and image analysis methods with the use of corneal confocal microscopy are discussed. While novel insights of neuroanatomy and biology of the eyes, particularly the ocular surface, have been provided by corneal confocal microscopy, some debatable elements observed using this technique remain and these are explored in this Mini Review. Potential improvements in imaging methodology and instrumentation are also suggested.

Segmentation and Classification Approaches of Clinically Relevant Curvilinear Structures: A Review

Detection of curvilinear structures from microscopic images, which help the clinicians to make an unambiguous diagnosis is assuming paramount importance in recent clinical practice. Appearance and size of dermatophytic hyphae, keratitic fungi, corneal and retinal vessels vary widely making their automated detection cumbersome. Automated deep learning methods, endowed with superior self-learning capacity, have superseded the traditional machine learning methods, especially in complex images with challenging background. Automatic feature learning ability using large input data with better generalization and recognition capability, but devoid of human interference and excessive pre-processing, is highly beneficial in the above context. Varied attempts have been made by researchers to overcome challenges such as thin vessels, bifurcations and obstructive lesions in retinal vessel detection as revealed through several publications reviewed here. Revelations of diabetic neuropathic complications such as tortuosity, changes in the density and angles of the corneal fibers have been successfully sorted in many publications reviewed here. Since artifacts complicate the images and affect the quality of analysis, methods addressing these challenges have been described. Traditional and deep learning methods, that have been adapted and published between 2015 and 2021 covering retinal vessels, corneal nerves and filamentous fungi have been summarized in this review. We find several novel and meritorious ideas and techniques being put to use in the case of retinal vessel segmentation and classification, which by way of cross-domain adaptation can be utilized in the case of corneal and filamentous fungi also, making suitable adaptations to the challenges to be addressed.

Morphological alterations in corneal nerves of patients with dry eye and associated biomarkers

The purposes of the present study were to (1) identify the relationship between dry eye symptoms and morphological changes in corneal subbasal nerves/ocular surfaces, and (2) discover tear film biomarkers indicating morphological changes in the subbasal nerves. This was a prospective cross-sectional study conducted between October and November 2017. Adults with dry eye disease (DED, n = 43) and healthy eyes (n = 16) were evaluated based on their subjective symptoms and ophthalmological findings. Corneal subbasal nerves were observed using confocal laser scanning microscopy. Nerve lengths, densities, branch numbers, and nerve fiber tortuosity were analyzed using ACCMetrics and CCMetrics image analysis systems; tear proteins were quantified by mass spectroscopy. Compared with the control group, the DED group had significantly lower tear breakup times (TBUT) and pain tolerance capacity, and significantly higher corneal nerve branch density (CNBD) and corneal nerve total branch density (CTBD). CNBD and CTBD showed significant negative correlations with TBUT. Six biomarkers (cystatin-S, immunoglobulin kappa constant, neutrophil gelatinase-associated lipocalin, profilin-1, protein S100-A8, and protein S100-A9) showed significant positive correlations with CNBD and CTBD. The significantly higher CNBD and CTBD in the DED group suggests that DED is associated with morphological alterations in corneal nerves. The correlation of TBUT with CNBD and CTBD further supports this inference. Six candidate biomarkers that correlate with morphological changes were identified. Thus, morphological changes in corneal nerves are a hallmark of DED, and confocal microscopy may help in the diagnosis and treatment of dry eyes.

Pre-Ophthalmoscopic Quantitative Biomarkers in Diabetes Mellitus

Purpose

The purpose of this study was to assess whether retinal microvascular or corneal nerve abnormalities occur earlier in diabetes mellitus (DM) and to identify imaging biomarkers in order to help prevent the subsequent irreversible retinal and corneal complications.

Methods

The study comprised 35 eyes of 35 healthy volunteers and 52 eyes of 52 patients with type 1 and type 2 DM. Swept-source optical coherence tomography (OCT), OCT angiography, and in vivo corneal confocal microscopy were performed in both groups. Corneal sub-basal nerve plexus and vessel density (VD) of superficial capillary plexus (SCP) and deep capillary plexus (DCP) were evaluated.

Results

All corneal sub-basal nerve fiber parameters were decreased in patients with DM compared with healthy subjects and the difference was significant for each result except for nerve fiber width (P = 0.586). No significant correlation was obtained between any nerve fiber morphology parameters and disease duration or HbA1C. VD in SCP was significantly decreased in the superior (P < 0.0001), temporal (P = 0.001), and nasal quadrant (P = 0.003) in the diabetes group. In DCP, only superior VD (P = 0.036), decreased significantly in the diabetes group. Ganglion cell layer thickness in the inner ring showed a significantly lower value in patients with DM (P < 0.0001).

Conclusions

Our results implicate a more pronounced and earlier damage to the corneal nerve fibers compared to the retinal microvasculature in patients with DM.

Translational Relevance

In DM, an earlier and more pronounced damage to the corneal nerve fibers was observed compared to the retinal microvasculature.

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.

Diagnostic Accuracy of Perception Threshold Tracking in the Detection of Small Fiber Damage in Type 1 Diabetes

AIM

An objective assessment of small nerve fibers is key to the early detection of diabetic peripheral neuropathy (DPN). This study investigates the diagnostic accuracy of a novel perception threshold tracking technique in detecting small nerve fiber damage.

METHODS

Participants with type 1 diabetes (T1DM) without DPN (n = 20), with DPN (n = 20), with painful DPN (n = 20) and 20 healthy controls (HCs) underwent perception threshold tracking on the foot and corneal confocal microscopy. Diagnostic accuracy of perception threshold tracking compared to corneal confocal microscopy was analyzed using logistic regression.

RESULTS

The rheobase, corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and corneal nerve fiber length (CNFL) (all P < .001) differed between groups. The diagnostic accuracy of perception threshold tracking (rheobase) was excellent for identifying small nerve fiber damage, especially for CNFL with a sensitivity of 94%, specificity 94%, positive predictive value 97%, and negative predictive value 89%. There was a significant correlation between rheobase with CNFD, CNBD, CNFL, and Michigan Neuropathy Screening Instrument (all P < .001).

CONCLUSION

Perception threshold tracking had a very high diagnostic agreement with corneal confocal microscopy for detecting small nerve fiber loss and may have clinical utility for assessing small nerve fiber damage and hence early DPN.

CLINICAL TRIALS

NCT04078516.

A Retinex-based variational model for noise suppression and nonuniform illumination correction in corneal confocal microscopy images

Objective.Corneal confocal microscopy (CCM) image analysis is a non-invasivein vivoclinical technique that can quantify corneal nerve fiber damage. However, the acquired CCM images are often accompanied by speckle noise and nonuniform illumination, which seriously affects the analysis and diagnosis of the diseases.Approach.In this paper, first we propose a variational Retinex model for the inhomogeneity correction and noise removal of CCM images. In this model, the Beppo Levi space is introduced to constrain the smoothness of the illumination layer for the first time, and the fractional order differential is adopted as the regularization term to constrain reflectance layer. Then, a denoising regularization term is also constructed with Block Matching 3D (BM3D) to suppress noise. Finally, by adjusting the uneven illumination layer, we obtain the final results. Second, an image quality evaluation metric is proposed to evaluate the illumination uniformity of images objectively.Main results.To demonstrate the effectiveness of our method, the proposed method is tested on 628 low-quality CCM images from the CORN-2 dataset. Extensive experiments show the proposed method outperforms the other four related methods in terms of noise removal and uneven illumination suppression.SignificanceThis demonstrates that the proposed method may be helpful for the diagnostics and analysis of eye diseases.

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.

Impact of Chronic Kidney Disease on Corneal Neuroimmune Features in Type 2 Diabetes

Aim: To determine the impact of chronic kidney disease on corneal nerve measures and dendritic cell counts in type 2 diabetes. Methods: In vivo corneal confocal microscopy images were used to estimate corneal nerve parameters and compared in people with type 2 diabetes with chronic kidney disease (T2DM-CKD) (n = 29) and those with type 2 diabetes without chronic kidney disease (T2DM-no CKD) (n = 29), along with 30 healthy controls. Corneal dendritic cell densities were compared between people with T2DM-CKD and those with T2DM-no CKD. The groups were matched for neuropathy status. Results: There was a significant difference in corneal nerve fiber density (p < 0.01) and corneal nerve fiber length (p = 0.04) between T2DM-CKD and T2DM-no CKD groups. The two diabetes groups had reduced corneal nerve parameters compared to healthy controls (all parameters: p < 0.01). Immature central dendritic cell density was significantly higher in the T2DM-CKD group compared to the T2DM-no CKD group ((7.0 (3.8−12.8) and 3.5 (1.4−13.4) cells/mm2, respectively, p < 0.05). Likewise, central mature dendritic cell density was significantly higher in the T2DM-CKD group compared to the T2DM-no CKD group (0.8 (0.4−2.2) and 0.4 (0.6−1.1) cells/mm2, respectively, p = 0.02). Additionally, total central dendritic cell density was increased in the T2DM-CKD group compared to T2DM-no CKD group (10.4 (4.3−16.1) and 3.9 (2.1−21.0) cells/mm2, respectively, p = 0.03). Conclusion: The study showed that central corneal dendritic cell density is increased in T2DM-CKD compared to T2DM-no CKD, with groups matched for peripheral neuropathy severity. This is accompanied by a loss of central corneal nerve fibers. The findings raise the possibility of additional local factors exacerbating central corneal nerve injury in people with diabetic chronic kidney disease.

Impact of Peripheral and Corneal Neuropathy on Markers of Ocular Surface Discomfort in Diabetic Chronic Kidney Disease

SIGNIFICANCE

There is a reduction in corneal nerve fiber density and length in type 2 diabetes mellitus with chronic kidney disease compared with type 2 diabetes mellitus alone; however, this difference does not result in worse ocular surface discomfort or dry eye disease.

PURPOSE

This study aimed to determine the clinical impact of corneal nerve loss on ocular surface discomfort and markers of ocular surface homeostasis in people with type 2 diabetes mellitus without chronic kidney disease (T2DM-no CKD) and those with type 2 diabetes mellitus with concurrent chronic kidney disease (T2DM-CKD).

METHODS

Participants were classified based on estimated glomerular filtration rates into two groups: T2DM-CKD (n = 27) and T2DM-no CKD (n = 28).

RESULTS

There was a significant difference between the T2DM-CKD and T2DM-no CKD groups in corneal nerve fiber density (14.9 ± 8.6 and 21.1 ± 7.1 no./mm 2 , respectively; P = .005) and corneal nerve fiber length (10.0 ± 4.6 and 12.3 ± 3.7 mm/mm 2 , respectively; P = .04). Fluorescein tear breakup time was significantly reduced in T2DM-CKD compared with T2DM-no CKD (8.1 ± 4.4 and 10.7 ± 3.8 seconds, respectively; P = .01), whereas ocular surface staining was not significantly different (3.5 ± 1.7 and 2.7 ± 2.3 scores, respectively; P = .12). In terms of ocular surface discomfort, there were no significant differences in the ocular discomfort score scores (12.5 ± 11.1 and 13.6 ± 12.1, respectively; P = .81) and Ocular Pain Assessment Survey scores (3.3 ± 5.4 and 4.3 ± 6.1, respectively; P = .37) between the T2DM-CKD and T2DM-no CKD.

CONCLUSIONS

The current study demonstrated that corneal nerve loss is greater in T2DM-CKD than in T2DM-no CKD. However, these changes do not impact ocular surface discomfort or markers of ocular surface homeostasis.

Mosaic vs. Single Image Analysis with Confocal Microscopy of the Corneal Nerve Plexus for Diagnosis of Early Diabetic Peripheral Neuropathy

INTRODUCTION

The assessment of the corneal nerve fibre plexus with corneal confocal microscopy (CCM) is an upcoming but still experimental method in the diagnosis of early stage diabetic peripheral neuropathy (DPN). Using an innovative imaging technique-Heidelberg Retina Tomograph equipped with the Rostock Cornea Module (HRT-RCM) and EyeGuidance module (EG)-we were able to look at greater areas of subbasal nerve plexus (SNP) in order to increase the diagnostic accuracy. The aim of our study was to evaluate the usefulness of EG instead of single image analysis in diagnosis of early stage DPN.

METHODS

This prospective study was performed on 60 patients with type 2 diabetes mellitus, classified equally into two subgroups based on neuropathy deficient score (NDS): patients without DPN (group 1) or with mild DPN (group 2). The following parameters were analysed in the two subgroups: corneal nerve fibre length (CNFL; mm/mm²), corneal nerve fibre density (CNFD; no./mm²), corneal nerve branch density (CNBD; no./mm²). Furthermore, we compared the data calculated with the novel mosaic, EG-based method with those received from single image analysis using different quantification tools.

RESULTS

Using EG we did not find a significant difference between group 1 and group 2: CNFL (16.81 ± 5.87 mm/mm² vs. 17.19 ± 7.19 mm/mm², p = 0.895), CNFD (254.05 ± 115.36 no./mm² vs. 265.91 ± 161.63 no./mm², p = 0.732) and CNBD (102.68 ± 62.28 no./mm² vs. 115.38 ± 96.91 no./mm², p = 0.541). No significant difference between the EG method of analysing the SNP and the single image analysis of 10 images per patient was detected.

CONCLUSION

On the basis of our results it was not possible to differentiate between early stages of large nerve fibre DPN in patients with type 2 diabetes mellitus via SNP analysis. To improve sensitivity and specificity of this method newer technologies are under current evaluation.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT05326958.

Association between systemic omega-3 polyunsaturated fatty acid levels, and corneal nerve structure and function

BACKGROUND

Omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have anti-inflammatory and neuroprotective properties. This study sought to determine the relationship between corneal parameters and systemic omega-3 fatty acid levels.

METHODS

Forty-seven participants with no/mild peripheral neuropathy (26 with diabetes and 21 without) underwent comprehensive ocular surface and systemic PUFA assessments. Corneal anatomical parameters were assessed using in vivo confocal microscopy. Corneal sensitivity was measured using non-contact esthesiometry. Relationships between systemic PUFA levels and corneal parameters were evaluated with multiple linear regression, adjusted for age, sex, neuropathy symptom score, and presence of diabetes and dry eye disease. The relationship between corneal nerve fibre length (CNFL) and corneal sensitivity threshold was evaluated.

RESULTS

The median Omega-3 Index, a measure of erythrocyte EPA and DHA, was 5.21% (interquartile range: 4.44-5.94%) in the study population. Mean ( ± SD) CNFL was 13.53 ± 3.37 mm/mm². Multiple linear regression showed that Omega-3 Index (β = 0.33; p = 0.02), age (β = -0.46; p = 0.001) and diabetes (β = -0.30; p = 0.03) were independently associated with CNFL (R² = 0.39, p = 0.002). In a separate model, DHA (β = 0.32; p = 0.027) and age (β = -0.41; p = 0.003) were associated with CNFL (R² = 0.37, p = 0.003). Neither systemic EPA nor omega-6 fatty acid levels correlated with CNFL. There was no association between PUFA levels and corneal sensitivity or corneal immune cell density. A negative correlation was found between CNFL and corneal sensation thresholds to a cooled stimulus in diabetes participants, in the central (ρ = -0.50; p = 0.009) and peripheral (ρ = -0.50; p = 0.01) cornea.

CONCLUSIONS

A positive relationship between the systemic Omega-3 Index and corneal nerve parameters suggests omega-3 PUFA intake may influence corneal nerve architecture.

Tear film substance P in patients treated with neurotoxic chemotherapy

Neurotoxic chemotherapy has been shown to be associated with reduced corneal nerves and ocular surface discomfort. Substance P is a neuropeptide expressed by sensory nerves including those in the densely innervated cornea. It is involved in both pain signaling and the regulation of epithelial and neural health. While its levels in tear fluids have been used as a neuropathic biomarker in diabetes, investigations of tear concentrations of substance P in chemotherapy-induced peripheral neuropathy have not been explored. The current cross-sectional study assessed substance P expression in tears of patients following neurotoxic chemotherapy treatment. Patients treated with paclitaxel (n = 35) or oxaliplatin (n = 30) 3-24 months prior to assessment were recruited along with healthy controls (n = 25). Flush tear collection, in-vivo corneal confocal microscopy and neurotoxicity assessments were also conducted. Enzyme-linked immunosorbent assays were used to measure substance P concentrations in collected tears, while total protein content (TPC) was measured with the bicinchoninic acid method (BCA). General linear models were used for statistical analysis. Substance P concentration was reduced in paclitaxel-treated patients [Median (Interquartile range, IQR): 1.11 (0.20-2.24) ng/ml)] compared to the oxaliplatin group [4.28 (1.01-10.73) ng/ml, p = 0.02]. Substance P expressed as a proportion of TPC was also lower in the paclitaxel group [0.00006 (0.00001-0.00010) %] compared to the oxaliplatin group [0.00018 (0.00008-0.00040) %, p = 0.005]. Substance P concentration and its percentage in TPC were also reduced in the paclitaxel group when compared to healthy controls [4.61 (1.35-18.51) ng/ml, p = 0.02; 0.00020 (0.00006-0.00060) %, p = 0.04, respectively]. Higher cumulative dose of paclitaxel was correlated with a reduction in substance P concentrations (r = -0.40, p = 0.037), however no associations were found with corneal nerve parameters or neuropathy severity (p > 0.05). While these findings show evidence for the dysregulation of tear film substance P following paclitaxel treatment, longitudinal studies should be conducted to investigate how substance P levels in tears change during treatment.

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.

Technical Report: Automatic Measurement of Corneal Nerve Fiber Area Using Versatile Software

SIGNIFICANCE

In vivo confocal microscopy has become a popular method to observe the details of corneal structures. We consider the area of corneal structures to be a versatile index and have measured the areas of various corneal structures using commercially available software.

PURPOSE

To evaluate the accuracy of software used to measure the corneal nerve fiber area.

METHODS

The corneal structures of 11 healthy volunteers were visualized using in vivo confocal microscopy. The image that most clearly depicted the corneal nerve fibers of each participant was selected for analysis. The corneal nerve fiber area was automatically measured by the software. An experienced ophthalmologist then manually measured the corneal nerve fiber area in each image assessed by the software. The Pearson correlation test was used to determine the correlation coefficient between the corneal nerve fiber areas measured automatically and those measured manually. The correlation between the corneal nerve fiber area and the participant's age was also evaluated.

RESULTS

A strong correlation was found between the corneal nerve fiber area measured automatically and the corneal nerve fiber area measured manually (r = .98, P = 2.4 × 10-7). The corneal nerve fiber area was not correlated with participant age, regardless of whether the area was measured automatically (r = -.26, P = .44) or manually (r = -.13, P = .71).

CONCLUSIONS

The software used in this study automatically measures the corneal nerve fiber area with accuracy similar to that of manual measurement by an experienced ophthalmologist. This software has potential for use in quantifying the areas of various corneal structures.

Corneal toxicity associated with belantamab mafodotin is not restricted to the epithelium: neuropathy studied with confocal microscopy

PURPOSE

The purpose of this study was to investigate epithelial and neuronal changes in patients with refractory/relapsed multiple myeloma (RRMM) before/during belantamab mafodotin (belamaf) treatment using confocal microscopy.

DESIGN

Retrospective case series.

METHODS

RRMM patients underwent best corrected visual acuity (BCVA) testing and slit-lamp examination/photography, followed by corneal confocal microscopy (CCM) to evaluate the epithelium and subbasal nerve plexus (SNP) to measure corneal nerve fiber density (CNFD), -branch density (CNBD), and -fiber length (CNFL) before and during belamaf treatment.

RESULTS

In 14 eyes of 7 patients (4 female, 68±10 years) with complete follow-up (4±2 months), the median BCVA dropped from 20/25 (20/25-20/20) to 20/40 (20/200-20/32) in the worse eye at the end of follow-up. Microcystic epithelial changes and ocular surface disease were demonstrated biomicroscopically. CCM showed "grape-like" hyperreflective spots in the central basal epithelium that changed to polymorphous-structured cysts in the superficial epithelium, with no pathology detected at the(peri-)limbal structures. The baseline, normal SNP morphology with a mean CNFD, CNBD, and CNFL of 20.25±7.06/mm², 19.49±12.34/mm², and 11.8±3.74mm/mm² respectively, showed severe fiber fragmentation during follow-up, and an observed complete loss of the SNP at the end of follow-up in all eyes.

CONCLUSIONS

This study is the first to illustrate neurotoxic effects of belamaf on the human cornea.

Progressive loss of corneal nerve fibers is associated with physical inactivity and glucose lowering medication associated with weight gain in type 2 diabetes

Aims/Introduction

Limited studies have identified risk factors linked to the progression of diabetic peripheral neuropathy (DPN) in type 2 diabetes. This study examined the association of risk factors with change in neuropathy measures over 2 years.

Materials and Methods

Participants with type 2 diabetes (n = 78) and controls (n = 26) underwent assessment of clinical and metabolic parameters and neuropathy using corneal confocal microscopy (CCM), vibration perception threshold (VPT), and the DN4 questionnaire at baseline and 2 year follow‐up.

Results

Participants with type 2 diabetes had a lower corneal nerve fiber density (CNFD), branch density (CNBD), and fiber length (CNFL) (P ≤ 0.0001) and a higher VPT (P ≤ 0.01) compared with controls. Over 2 years, despite a modest reduction in HbA1c (P ≤ 0.001), body weight (P ≤ 0.05), and LDL (P ≤ 0.05) the prevalence of DPN (P = 0.28) and painful DPN (P = 0.21) did not change, but there was a significant further reduction in CNBD (P ≤ 0.0001) and CNFL (P ≤ 0.05). CNFD, CNBD, and CNFL decreased significantly in physically inactive subjects (P < 0.05–0.0001), whilst there was no change in CNFD (P = 0.07) or CNFL (P = 0.85) in physically active subjects. Furthermore, there was no change in CNFD (P = 0.82), CNBD (P = 0.08), or CNFL (P = 0.66) in patients treated with glucose lowering medication associated with weight loss, whilst CNBD (P = 0.001) decreased in patients on glucose lowering medication associated with weight gain.

Conclusions

In participants with type 2 diabetes, despite a modest improvement in HbA1c, body weight, and LDL there was a progressive loss of corneal nerve fibers; except in those who were physically active or on glucose lowering medication associated with weight loss.

Corneal Sensation and Nerve Fiber Changes in Patients With Interstitial Cystitis

PURPOSE

Central sensitization syndromes are associated with ocular surface discomfort and certain changes in corneal sensation. The aim of this study was to evaluate corneal changes in patients with interstitial cystitis (IC).

METHODS

Thirty patients with IC and 32 healthy control subjects were included in this study. All patients had a detailed ophthalmological examination including measurement of corneal sensation with Cochet-Bonnet esthesiometer, tear breakup time, Schirmer I test, and Ocular Surface Disease Index questionnaire. After these examinations, corneal subbasal nerve plexus of the patients was evaluated with in vivo corneal confocal microscopy (IVCM) and the images were analyzed using fully automated software (ACC Metrics Corneal Nerve Fiber Analyzer V.2).

RESULTS

There was no significant difference between the groups regarding age and gender distribution. Corneal sensation was significantly higher in patients with IC (P = 0.03), whereas tear breakup time, Schirmer I test, and Ocular Surface Disease Index scores were similar between the patients and controls. IVCM demonstrated nerve fiber loss in patients with IC. Corneal nerve fiber density, corneal nerve branch density, and corneal nerve fiber length were significantly reduced in patients with IC compared with healthy controls (P < 0.001, P = 0.04, and P < 0.001, respectively).

CONCLUSIONS

Patients with IC had increased corneal sensation and decreased nerve fiber density in IVCM analysis. Corneal nerve fiber loss might decrease the induction threshold of the remaining fibers to induce peripheral sensitization, which may also trigger central sensitization in long term.

Segmentation and Evaluation of Corneal Nerves and Dendritic Cells From In Vivo Confocal Microscopy Images Using Deep Learning

Purpose

Segmentation and evaluation of in vivo confocal microscopy (IVCM) images requires manual intervention, which is time consuming, laborious, and non-reproducible. The aim of this research was to develop and validate deep learning–based methods that could automatically segment and evaluate corneal nerve fibers (CNFs) and dendritic cells (DCs) in IVCM images, thereby reducing processing time to analyze larger volumes of clinical images.

Methods

CNF and DC segmentation models were developed based on U-Net and Mask R-CNN architectures, respectively; 10-fold cross-validation was used to evaluate both models. The CNF model was trained and tested using 1097 and 122 images, and the DC model was trained and tested using 679 and 75 images, respectively, at each fold. The CNF morphology, number of nerves, number of branching points, nerve length, and tortuosity were analyzed; for DCs, number, size, and immature–mature cells were analyzed. Python-based software was written for model training, testing, and automatic morphometric parameters evaluation.

Results

The CNF model achieved on average 86.1% sensitivity and 90.1% specificity, and the DC model achieved on average 89.37% precision, 94.43% recall, and 91.83% F₁ score. The interclass correlation coefficient (ICC) between manual annotation and automatic segmentation were 0.85, 0.87, 0.95, and 0.88 for CNF number, length, branching points, and tortuosity, respectively, and the ICC for DC number and size were 0.95 and 0.92, respectively.

Conclusions

Our proposed methods demonstrated reliable consistency between manual annotation and automatic segmentation of CNF and DC with rapid speed. The results showed that these approaches have the potential to be implemented into clinical practice in IVCM images.

Translational Relevance

The deep learning–based automatic segmentation and quantification algorithm significantly increases the efficiency of evaluating IVCM images, thereby supporting and potentially improving the diagnosis and treatment of ocular surface disease associated with corneal nerves and dendritic cells.

Performance Analysis of Conventional Machine Learning Algorithms for Diabetic Sensorimotor Polyneuropathy Severity Classification Using Nerve Conduction Studies

Background

Diabetic sensorimotor polyneuropathy (DSPN) is a major form of complication that arises in long-term diabetic patients. Even though the application of machine learning (ML) in disease diagnosis is very common and well-established in the field of research, its application in DSPN diagnosis using nerve conduction studies (NCS), is very limited in the existing literature.

Method

In this study, the NCS data were collected from the Diabetes Control and Complications Trial (DCCT) and its follow-up Epidemiology of Diabetes Interventions and Complications (EDIC) clinical trials. The NCS variables are median motor velocity (m/sec), median motor amplitude (mV), median motor F-wave (msec), median sensory velocity (m/sec), median sensory amplitude (μV), Peroneal Motor Velocity (m/sec), peroneal motor amplitude (mv), peroneal motor F-wave (msec), sural sensory velocity (m/sec), and sural sensory amplitude (μV). Three different feature ranking techniques were used to analyze the performance of eight different conventional classifiers.

Results

The ensemble classifier outperformed other classifiers for the NCS data ranked when all the NCS features were used and provided an accuracy of 93.40%, sensitivity of 91.77%, and specificity of 98.44%. The random forest model exhibited the second-best performance using all the ten features with an accuracy of 93.26%, sensitivity of 91.95%, and specificity of 98.95%. Both ensemble and random forest showed the kappa value 0.82, which indicates that the models are in good agreement with the data and the variables used and are accurate to identify DSPN using these ML models.

Conclusion

This study suggests that the ensemble classifier using all the ten NCS variables can predict the DSPN severity which can enhance the management of DSPN patients.

Corneal Confocal Microscopy Identifies People with Type 1 Diabetes with More Rapid Corneal Nerve Fibre Loss and Progression of Neuropathy

There is a need to accurately identify patients with diabetes at higher risk of developing and progressing diabetic peripheral neuropathy (DPN). Fifty subjects with Type 1 Diabetes Mellitus (T1DM) and sixteen age matched healthy controls underwent detailed neuropathy assessments including symptoms, signs, quantitative sensory testing (QST), nerve conduction studies (NCS), intra epidermal nerve fiber density (IENFD) and corneal confocal microscopy (CCM) at baseline and after 2 years of follow-up. Overall, people with type 1 diabetes mellitus showed no significant change in HbA1c, blood pressure, lipids or neuropathic symptoms, signs, QST, neurophysiology, IENFD and CCM over 2 years. However, a sub-group (n = 11, 22%) referred to as progressors, demonstrated rapid corneal nerve fiber loss (RCNFL) with a reduction in corneal nerve fiber density (CNFD) (p = 0.0006), branch density (CNBD) (p = 0.0002), fiber length (CNFL) (p = 0.0002) and sural (p = 0.04) and peroneal (p = 0.05) nerve conduction velocities, which was not related to a change in HbA1c or cardiovascular risk factors. The majority of people with T1DM and good risk factor control do not show worsening of neuropathy over 2 years. However, CCM identifies a sub-group of people with T1DM who show a more rapid decline in corneal nerve fibers and nerve conduction velocity.

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.

Analysis of microvascular and neurodegenerative complications of mild COVID-19

Purpose

To examine retinal and corneal neurodegenerative and retinal microvascular changes in patients after mild or asymptomatic COVID-19 disease compared to age-matched controls.

Methods

Thirty-five (35) patients after PCR-proven SARS-CoV-2 infection and 28 age-matched controls were enrolled. Swept-source optical coherence tomography (OCT), OCT angiography, and in vivo corneal confocal microscopy were performed in both groups. Corneal subbasal nerve plexus was quantified. Vessel density for superficial (SCP) and deep capillary plexus (DCP) and structural OCT parameters were recorded.

Results

Significantly lower nerve branch density (P = 0.0004), nerve fiber area (P = 0.0001), nerve fiber density (P = 0.0009), nerve fiber length (P < 0.0001), and total nerve branch density (P = 0.002) values were observed in patients after COVID-19 compared to healthy controls. VD of the temporal SCP was significantly different between the two groups (P = 0.019). No other SCP and DCP vessel density parameter differed significantly between the two groups.

Conclusions

Our results suggest that peripheral neurodegenerative changes may occur even after mild or asymptomatic SARS-CoV-2 infection. No relevant microvascular changes were seen with OCT angiography and structural OCT parameters did not show any signs of optic neuropathy in post-COVID patients. In vivo confocal microscopy seems to be an important tool in monitoring peripheral neuropathy in patients after COVID-19.

Small Fiber Neuropathy in Diabetes Polyneuropathy: Is It Time to Change?

Diabetes polyneuropathy is an important complication of diabetes polyneuropathy, and its notable sequelae of foot ulceration, autonomic dysfunction, and neuropathic pain are associated with significant morbidity and mortality. Despite the major impact on quality of life and health economic costs, it remains underdiagnosed until late in its natural history, and there is lack of any intervention that can reverse its clinical progress. Assessment of small fiber neuropathy (SFN) in diabetes offers an opportunity to detect abnormalities at an early stage so that both interventional studies and preventative measures can be enacted to prevent progression to the devastating complications of foot ulceration and cardiac dysautonomic death. Over the last two decades, significant advances have been made in understanding the pathophysiology of diabetes neuropathy and its assessment. In this review, we discuss limitations of the screening methods recommended in current clinical guidelines which are based on large nerve fiber assessments. Thereafter, we discuss in detail the various methods currently available to assess small fiber structure and function and examine their individual strength and limitations. Finally, we discuss the reasons why despite the considerable body of evidence available, legislators and global experts have yet to incorporate the assessment of SFN as routine clinical surveillance in diabetes management. We hope that these insights will stimulate further discussion and be instrumental in the early adoption of these methods so as to reduce the burden of complications arising due to diabetes polyneuropathy.

Artificial intelligence utilising corneal confocal microscopy for the diagnosis of peripheral neuropathy in diabetes mellitus and prediabetes

AIMS/HYPOTHESIS

We aimed to develop an artificial intelligence (AI)-based deep learning algorithm (DLA) applying attribution methods without image segmentation to corneal confocal microscopy images and to accurately classify peripheral neuropathy (or lack of).

METHODS

The AI-based DLA utilised convolutional neural networks with data augmentation to increase the algorithm's generalisability. The algorithm was trained using a high-end graphics processor for 300 epochs on 329 corneal nerve images and tested on 40 images (1 image/participant). Participants consisted of healthy volunteer (HV) participants (n = 90) and participants with type 1 diabetes (n = 88), type 2 diabetes (n = 141) and prediabetes (n = 50) (defined as impaired fasting glucose, impaired glucose tolerance or a combination of both), and were classified into HV, those without neuropathy (PN-) (n = 149) and those with neuropathy (PN+) (n = 130). For the AI-based DLA, a modified residual neural network called ResNet-50 was developed and used to extract features from images and perform classification. The algorithm was tested on 40 participants (15 HV, 13 PN-, 12 PN+). Attribution methods gradient-weighted class activation mapping (Grad-CAM), Guided Grad-CAM and occlusion sensitivity displayed the areas within the image that had the greatest impact on the decision of the algorithm.

RESULTS

The results were as follows: HV: recall of 1.0 (95% CI 1.0, 1.0), precision of 0.83 (95% CI 0.65, 1.0), F₁-score of 0.91 (95% CI 0.79, 1.0); PN-: recall of 0.85 (95% CI 0.62, 1.0), precision of 0.92 (95% CI 0.73, 1.0), F₁-score of 0.88 (95% CI 0.71, 1.0); PN+: recall of 0.83 (95% CI 0.58, 1.0), precision of 1.0 (95% CI 1.0, 1.0), F₁-score of 0.91 (95% CI 0.74, 1.0). The features displayed by the attribution methods demonstrated more corneal nerves in HV, a reduction in corneal nerves for PN- and an absence of corneal nerves for PN+ images.

CONCLUSIONS/INTERPRETATION

We demonstrate promising results in the rapid classification of peripheral neuropathy using a single corneal image. A large-scale multicentre validation study is required to assess the utility of AI-based DLA in screening and diagnostic programmes for diabetic neuropathy.

Eight months follow-up of corneal nerves and sensitivity after treatment with cenegermin for neurotrophic keratopathy

Backgroud

Cenegermin (Oxervate, Dompè Farmaceutici, Milan, IT), a recombinant human NGF, is a potentially healing new drug for neurotrophic keratopathy (NK), a rare but challenging disease affecting the cornea. To date, studies that evaluate its mid-term effect on corneal nerves and sensitivity are lacking.

Objective

To evaluate the recovery and morphology of subbasal corneal nerves in patients treated with Cenegermin for NK and assess their correlation with corneal sensitivity.

Methods

This prospective, observational case series study was carried out between May 2018 and August 2020 at the Ophthalmic Clinic of the University of Verona. Clinical evaluation, sensitivity, and in vivo confocal microscopy (IVCM) were performed in the central and all four corneal sectors at baseline, the end of therapy (8 weeks), and 2, 4, and 8 months after therapy. Consecutive patients with NK (stage 2–3), treated with Cenegermin (1 drop 6 times daily for 8 weeks), were enrolled. During each visit, Corneal nerve fiber length (CNFL), corneal nerve fiber total branch density (CTBD), corneal nerve fiber fractal dimension (CNFraD) and Cochet-Bonnet esthesiometry (CBE) were measured.

Results

We enrolled 18 patients. Complete NK healing was noted in 14/18(78%) patients after 8 weeks of treatment; then in 14(78%), 15(83%), and 13(72%) patients at 2-, 4-, and 8-months, respectively. Starting at 8 weeks through 4-month follow-up there was progressive improvement in CBE in all corneal sectors (p ≤ 0.01), which continued thereafter. There was significant corneal nerve regrowth especially in the peripheral cornea: centripetal progression starting at 8 weeks (CNFL and CNFrad) and significant branching starting at 2 months (CTBD), which continued through to the end of follow up. Sector-coupled IVCM and CBE findings correlated at all evaluations (all r ≥ 0.62 starting at 2 months, with highest values in the peripheral sectors).

Conclusions

After Cenegermin we observed a subbasal corneal nerve regeneration, a recovery of sensitivity and a lasting epithelial healing, suggesting that the effect of its action persists several months after discontinuation in patients with NK.

Abnormal corneal nerve morphology and brain volume in patients with schizophrenia

Neurodevelopmental and neurodegenerative pathology occur in Schizophrenia. This study compared the utility of corneal confocal microscopy (CCM), an ophthalmic imaging technique with MRI brain volumetry in quantifying neuronal pathology and its relationship to cognitive dysfunction and symptom severity in schizophrenia. Thirty-six subjects with schizophrenia and 26 controls underwent assessment of cognitive function, symptom severity, CCM and MRI brain volumetry. Subjects with schizophrenia had lower cognitive function (P ≤ 0.01), corneal nerve fiber density (CNFD), length (CNFL), branch density (CNBD), CNBD:CNFD ratio (P < 0.0001) and cingulate gyrus volume (P < 0.05) but comparable volume of whole brain (P = 0.61), cortical gray matter (P = 0.99), ventricle (P = 0.47), hippocampus (P = 0.10) and amygdala (P = 0.68). Corneal nerve measures and cingulate gyrus volume showed no association with symptom severity (P = 0.35–0.86 and P = 0.50) or cognitive function (P = 0.35–0.86 and P = 0.49). Corneal nerve measures were not associated with metabolic syndrome (P = 0.61–0.64) or diabetes (P = 0.057–0.54). The area under the ROC curve distinguishing subjects with schizophrenia from controls was 88% for CNFL, 84% for CNBD and CNBD:CNFD ratio, 79% for CNFD and 73% for the cingulate gyrus volume. This study has identified a reduction in corneal nerve fibers and cingulate gyrus volume in schizophrenia, but no association with symptom severity or cognitive dysfunction. Corneal nerve loss identified using CCM may act as a rapid non-invasive surrogate marker of neurodegeneration in patients with schizophrenia.

Imaging in experimental models of diabetes

Translational medicine, experimental medicine and experimental animal models, in particular mice and rats, represent a multidisciplinary field that has made it possible to achieve, in the last decades, important scientific progress. In this review, we have summarized the most frequently used imaging animal models, such as ultrasound (US), micro-CT, MRI and the optical imaging methods, and their main implications in diagnostic and therapeutic fields, with a particular focus on diabetes mellitus, a multifactorial disease extremely widespread among the general population.

Loss of corneal nerves and brain volume in mild cognitive impairment and dementia

Introduction

This study compared the capability of corneal confocal microscopy (CCM) with magnetic resonance imaging (MRI) brain volumetry for the diagnosis of mild cognitive impairment (MCI) and dementia.

Methods

In this cross‐sectional study, participants with no cognitive impairment (NCI), MCI, and dementia underwent assessment of Montreal Cognitive Assessment (MoCA), MRI brain volumetry, and CCM.

Results

Two hundred eight participants with NCI (n = 42), MCI (n = 98), and dementia (n = 68) of comparable age and gender were studied. For MCI, the area under the curve (AUC) of CCM (76% to 81%), was higher than brain volumetry (52% to 70%). For dementia, the AUC of CCM (77% to 85%), was comparable to brain volumetry (69% to 93%). Corneal nerve fiber density, length, branch density, whole brain, hippocampus, cortical gray matter, thalamus, amygdala, and ventricle volumes were associated with cognitive impairment after adjustment for confounders (All P’s < .01).

Discussion

The diagnostic capability of CCM compared to brain volumetry is higher for identifying MCI and comparable for dementia, and abnormalities in both modalities are associated with cognitive impairment.

Corneal Confocal Microscopy in the Diagnosis of Small Fiber Neuropathy: Faster, Easier, and More Efficient Than Skin Biopsy?

Chronic pain may affect 30–50% of the world’s population and an important cause is small fiber neuropathy (SFN). Recent research suggests that autoimmune diseases may be one of the most common causes of small nerve fiber damage. There is low awareness of SFN among patients and clinicians and it is difficult to diagnose as routine electrophysiological methods only detect large fiber abnormalities, and specialized small fiber tests, like skin biopsy and quantitative sensory testing, are not routinely available. Corneal confocal microscopy (CCM) is a rapid, non-invasive, reproducible method for quantifying small nerve fiber degeneration and regeneration, and could be an important tool for diagnosing SFN. This review considers the advantages and disadvantages of CCM and highlights the evolution of this technique from a research tool to a diagnostic test for small fiber damage, which can be a valuable contribution to the study and management of autoimmune disease.

Biomarkers of in vivo limbal stem cell function

PURPOSE

To evaluate in vivo parameters as biomarkers of limbal stem cell function and to establish an objective system that detects and stage limbal stem cell deficiency (LSCD).

METHODS

A total of 126 patients (172 eyes) with LSCD and 67 normal subjects (99 eyes) were included in this observational cross-sectional comparative study. Slit-lamp biomicroscopy, in vivo laser scanning confocal microscopy (IVCM), and anterior segment optical coherence tomography (AS-OCT) were performed to obtain the following: clinical score, cell morphology score, basal cell density (BCD), central corneal epithelial thickness (CET), limbal epithelial thickness (LET), total corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and tortuosity coefficient. Their potential correlations with the severity of LSCD were investigated, and cutoff values were determined.

RESULTS

An increase clinical score correlated with a decrease in central cornea BCD, limbal BCD, CET, mean LET, maximum LET, CNFL, CNFD, CNBD, and tortuosity coefficient. Regression analyses showed that central cornea BCD, CET and CNFL were the best parameters to differentiate LSCD from normal eyes (Coef = 3.123, 3.379, and 2.223; all p < 0.05). The rank correlation analysis showed a similar outcome between the clinical scores and the central cornea BCD (ρ = 0.79), CET (ρ = 0.82), and CNFL (ρ = 0.71). A comprehensive LSCD grading formula based on a combination of these parameters was established.

CONCLUSIONS

A comprehensive staging system combining clinical presentation, central cornea BCD, CET, and CNFL is established to accurately and objectively diagnose LSCD and stage its severity.

PIAS1 alleviates diabetic peripheral neuropathy through SUMOlation of PPAR-γ and miR-124-induced downregulation of EZH2/STAT3

Diabetic peripheral neuropathy (DPN) is a frequently occurring chronic complication of diabetes. In this study, we aim to explore the regulatory mechanism of protein inhibitor of activated STAT1 (PIAS1) in DPN in terms of autophagy and apoptosis of Schwann cells. The SUMOlation of PPAR-γ by PIAS1 was examined, and ChIP was performed to verify the binding of PPAR-γ to miR-124 promoter region. Dual-luciferase gene reporter assay was used to validate the binding affinity between miR-124 and EZH2/STAT3. Following loss‐ and gain‐of-function experiments, in vitro assays in high glucose-treated Schwann cells (SC4) and in vivo assays in db/db and ob/ob mice were performed to detect the effects of PIAS1 on autophagy and apoptosis of Schwann cells as well as symptoms of DPN by regulating the PPAR-γ-miR-124-EZH2/STAT3. The expression of PIAS1, PPAR-γ, and miR-124 was downregulated in the sciatic nerve tissue of diabetic mice. PIAS1 enhanced the expression of PPAR-γ through direct binding and SUMOlation of PPAR-γ. PPAR-γ enhanced the expression of miR-124 by enhancing the promoter activity of miR-124. Furthermore, miR-124 targeted and inversely modulated EZH2 and STAT3, promoting the autophagy of Schwann cells and inhibiting their apoptosis. In vivo experiments further substantiated that PIAS1 could promote the autophagy and inhibit the apoptosis of Schwann cells through the PPAR-γ-miR-124-EZH2/STAT3 axis. In conclusion, PIAS1 promoted SUMOlation of PPAR-γ to stabilize PPAR-γ expression, which upregulated miR-124 to inactivate EZH2/STAT3, thereby inhibiting apoptosis and promoting autophagy of Schwann cells to suppress the development of DPN.

Corneal nerve fiber loss relates to cognitive impairment in patients with Parkinson’s disease

Cognitive impairment in Parkinson’s disease (PD) adversely influences quality of life. There is currently no available biomarker to predict cognitive decline in PD. Corneal confocal microscopy (CCM) has been used as a non-invasive tool for quantifying small nerve damage in PD. The present study investigated whether corneal nerve measures were associated with cognitive function in PD. Patients with PD were classified into those with normal cognitive function (PD-CN), mild cognitive impairment (PD-MCI), and dementia (PDD). Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and corneal nerve fiber length (CNFL) were quantified with CCM and compared with a control group. Sixty-five PD patients and thirty controls were studied. CNFD was decreased and CNBD was increased in PD patients compared to controls (P < 0.05). CNBD and CNBD/CNFD ratio was higher in PD-CN compared to controls. CNFD was positively correlated with the Montreal cognitive assessment (MoCA) score (r = 0.683, P < 0.001), but negatively associated with unified Parkinson disease rating scale (UPDRS)-part III (r = −0.481, P < 0.001) and total UPDRS scores (r = −0.401, P = 0.001) in PD patients. There was no correlation between CNFD and Levodopa equivalent daily dose (LEDD) (r = 0.176, P = 0.161). CNFD, CNBD, CNFL, and CNBD/CNFD ratio was lower with increasing Hoehn and Yahr stage. PD patients show evidence of corneal nerve loss compared with controls and corneal nerve parameters are associated with the severity of cognitive and motor dysfunction in PD. CCM could serve as an objective in vivo ophthalmic imaging technique to assess neurodegeneration in PD.