Repeatability of In Vivo Corneal Confocal Microscopy to Quantify Corneal Nerve Morphology

Differences in corneal nerve fiber density and fiber length in patients with painful chronic idiopathic axonal polyneuropathy and diabetic polyneuropathy

INTRODUCTION/AIMS

Corneal confocal microscopy (CCM) detects small nerve fiber loss and correlates with skin biopsy findings in diabetic neuropathy. In chronic idiopathic axonal polyneuropathy (CIAP) this correlation is unknown. Therefore, we compared CCM and skin biopsy in patients with CIAP to healthy controls, patients with painful diabetic neuropathy (PDN) and diabetics without overt neuropathy (DM).

METHODS

Participants with CIAP and suspected small fiber neuropathy (n = 15), PDN (n = 16), DM (n = 15), and healthy controls (n = 16) underwent skin biopsy and CCM testing. Inter-center intraclass correlation coefficients (ICC) were calculated for CCM parameters.

RESULTS

Compared with healthy controls, patients with CIAP and PDN had significantly fewer nerve fibers in the skin (IENFD: 5.7 ± 2.3, 3.0 ± 1.8, 3.9 ± 1.5 fibers/mm, all p < .05). Corneal nerve parameters in CIAP (fiber density 23.8 ± 4.9 no./mm2, branch density 16.0 ± 8.8 no./mm2, fiber length 13.1 ± 2.6 mm/mm2) were not different from healthy controls (24.0 ± 6.8 no./mm2, 22.1 ± 9.7 no./mm2, 13.5 ± 3.5 mm/mm2, all p > .05). In patients with PDN, corneal nerve fiber density (17.8 ± 5.7 no./mm2) and fiber length (10.5 ± 2.7 mm/mm2) were reduced compared with healthy controls (p < .05). CCM results did not correlate with IENFD in CIAP patients. Inter-center ICC was 0.77 for fiber density and 0.87 for fiber length.

DISCUSSION

In contrast to patients with PDN, corneal nerve parameters were not decreased in patients with CIAP and small nerve fiber damage. Therefore, CCM is not a good biomarker for small nerve fiber loss in CIAP patients.

Corneal nerve fiber morphology following COVID-19 infection in vaccinated and non-vaccinated population

To examine corneal subbasal nerve changes in patients who received vaccination against SARS-CoV-2 virus and underwent COVID-19 infection compared to infected non-vaccinated patients and healthy controls. Twenty-nine eyes of 29 vaccinated patients (mean age: 36.66 ± 12.25 years) within six months after PCR or Ag test proven COVID-19 infection and twenty-eight eyes of 28 age-matched infected, non-vaccinated patients (mean age: 42.14 ± 14.17 years) were enrolled. Twenty-five age-matched healthy individuals (mean age: 47.52 ± 18.45 years) served as controls. In vivo confocal microscopy (Heidelberg Retina Tomograph II Rostock Cornea Module, Germany) was performed in each group. Corneal subbasal nerve plexus morphology and corneal dendritic cells (DC) were evaluated. Significantly higher corneal nerve fiber density (P < 0.001), nerve branch density (P < 0.001), nerve fiber length (P < 0.001), total branch density (P = 0.007), nerve fiber area (P = 0.001) and fractal dimension (P < 0.001) values were observed in vaccinated patients after COVID-19 infection compared to the non-vaccinated group. Significantly higher DC density was observed in the non-vaccinated group compared to the control group (P = 0.05). There was a statistically significant difference in the size of mature DCs (P < 0.0001) but the size of immature DCs did not differ significantly among the 3 groups (P = 0.132). Our results suggest that SARS-CoV-2 vaccination may have a protective effect against the complications of COVID-19 disease on the corneal subbasal nerve fibers.

Sustained corneal nerve loss predicts the development of diabetic neuropathy in type 2 diabetes

Introduction

This study was undertaken to investigate whether sustained rather than a single measure of corneal nerve loss was associated with the onset of diabetic peripheral neuropathy (DPN) and the progression of neuropathic symptoms and deficits in individuals with type 2 diabetes (T2D).

Methods

Participants underwent clinical, metabolic testing and assessment of neuropathic symptoms, vibration perception threshold (VPT), sudomotor function, and corneal confocal microscopy (CCM) at baseline, 1, 2, and 4-7 years. Sustained corneal nerve loss was defined as abnormal corneal nerve fiber density (CNFD, <24 fibers/mm2), corneal nerve branch density (CNBD, <21 branches/mm2), and corneal nerve fiber length (CNFL, <16 mm/mm2) persisting for ≥50% of the study duration.

Results

A total of 107 participants with a mean duration of T2D of 13.3 ± 7.3 years, aged 54.8 ± 8.5 years, underwent baseline and follow-up assessments over a median duration of 4 years, ranging from 1 to 7 years. The DPN prevalence at baseline was 18/107 (16.8%), and of the 89 participants without DPN at baseline, 13 (14.6%) developed DPN during follow-up. Approximately half of the cohort had sustained corneal nerve damage, and corneal nerve measures were significantly lower in this group than those without sustained damage (p < 0.0001). Sustained corneal nerve damage was associated with the development of DPN (p < 0.0001), a progressive loss of vibration perception (p ≤ 0.05), an increased incidence of burning pain, numbness, or a combination of both (p = 0.01-0.001), and a borderline association with progressive sudomotor dysfunction (p = 0.07). Sustained abnormal CNFL effectively distinguished between participants who developed DPN and those who did not (AUC: 76.3, 95% CI: 65.9-86.8%, p < 0.0001), while baseline and other sustained measures did not predict DPN onset.

Conclusion

Sustained abnormal CCM is associated with more severe corneal nerve damage, DPN development, and the progression of neuropathic symptoms and deficits. Regular CCM monitoring may enable the identification of those at greater risk of developing and worsening DPN who may benefit from more aggressive risk factor reduction.

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.

Corneal nerves and amyotrophic lateral sclerosis: an in vivo corneal confocal imaging study

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a severe motor neuron disorder. Diagnosis is challenging due to its clinical heterogeneity and the absence of definitive diagnostic tools, leading to delays averaging between 9.1 and 27 months. In vivo corneal confocal microscopy, assessing the sub-basal nerve plexus of the cornea, has been proposed as a potential biomarker for ALS. We aimed to determine whether the assessment of corneal nerves using in vivo confocal microscopy can serve as an imaging biomarker for ALS.

METHODS

A single-centre prospective case-control study was conducted in France from September 2021 to March 2023 including patients with ALS according to the revised EI Escorial criteria. The corneal sub-basal nerve plexus was analysed using in vivo confocal microscopy. An automated algorithm (ACCMetrics) was used to evaluate corneal parameters: nerve fibre density, nerve branch density, nerve fibre length, nerve fibre area, nerve total branch density, nerve fibre width, and nerve fractal dimension.

RESULTS

Twenty-two patients with ALS and 30 controls were included. No significant differences were found between ALS and control groups for all corneal parameters (p > 0.05). Corneal sensitivity did not differ between groups, and no correlation was identified between corneal nerve parameters and ALS disease duration, severity and rate of progression (p > 0.05).

CONCLUSIONS

The present study does not support the use of in vivo corneal confocal microscopy as an early diagnostic or prognostic tool for ALS. Further research, especially longitudinal investigations, is needed to understand any potential corneal innervation changes as ALS progresses.

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.

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.

A protocol for a single center, randomized, controlled trial comparing the clinical efficacy of 3% diquafosol and 0.1% hyaluronic acid in diabetic patients with dry eye disease

BACKGROUND

The global prevalence of diabetes mellitus (DM) continues to rise and 70% of diabetic individuals have dry eye disease (DED) that leads to subsequent abnormalities of the corneal epithelium, corneal nerves, tear film, or corneal endothelium. In addition, persons with diabetes produce fewer tear secretions than healthy individuals. While several anti-inflammatory drug-based therapies for dry eye in diabetic individuals are currently being administered, their efficacy has not been studied in detail. Therefore, the aim of this study was to compare the effectiveness of 3% diquafosol (DQS) vs 0.1% hyaluronic acid (HA) eye drops in diabetic dry eye patients.

METHODS

This triple-blind randomized, control trial will include 202 diabetic-related DED and will be assigned to DQS (n = 101) and HA (n = 101) one drop, six times per day for 8 weeks. Tear film lipid layer, non-invasive breakup time, conjunctivocorneal staining score, corneal sensitivity, tear MMP-9 levels, meibomian gland expression and quality, tear meniscus height, corneal nerves, immune/inflammatory cell change, conjunctival hyperemia, and ocular surface disease index questionnaire score will be assessed and compared at baseline, week 4, and week 8.

DISCUSSION

This study will be a standardized, scientific, clinical trial designed to evaluate the therapeutic effects and safety of DQS and HA for diabetic dry eye treatment.

TRIAL REGISTRATION

ClinicalTrials.govNCT05682547. Registered on December 05, 2022.

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.

Corneal characteristics of Mongolian population with type 2 diabetic peripheral neuropathy in inner Mongolia, China: an assessment using corneal confocal microscopy

OBJECTIVE

To quantify corneal nerve fiber parameters in a Mongolian population with diabetic peripheral neuropathy (DPN) by corneal confocal microscopy.

METHODS

This study conducted a comprehensive evaluation of 114 participants from Hulunbuir between January 2020 and December 2021. The participants included healthy controls, Mongolian and Han patients with type 2 diabetes mellitus. Demographic, medical, and laboratory data were collected, and neuropathy was evaluated by confocal corneal microscopy. And compare various parameters between Han and Mongolian were performed using SPSS software.

RESULTS

The average waist circumference of Mongolian diabetic patients was larger than that of Han diabetic patients (P < 0.05). The mean HbA1c of Mongolian was 9.30 (8.15, 10.30) %, and that of Han was 8.30 (7.20, 9.40) % (P = 0.023). The average values of Corneal Nerve Fiber Density (CNFD), Corneal Nerve Fiber Length (CNFL) and corneal nerve branch density (CNBD) in Mongolian diabetic patients were significantly lower than those in Han diabetic patients (P < 0.05). The correlation coefficient between CNFL and age was - 0.368. ROC results show that CNBD has a certain diagnostic value for DPN in Mongolian patients with type 2 diabetes and the optimal cut-off point value is 24.99(no./mm2), the sensitivity is 80.0%, and the specificity is 77.8%.

CONCLUSION

The corneal confocal microscopy could possibly represent a promising adjuvant technique for the early diagnosis and assessment of PDN in Mongolian T2DM patients.

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.

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.

Multimodal testing reveals subclinical neurovascular dysfunction in prediabetes, challenging the diagnostic threshold of diabetes

AIM

To explore if novel non-invasive diagnostic technologies identify early small nerve fibre and retinal neurovascular pathology in prediabetes.

METHODS

Participants with normoglycaemia, prediabetes or type 2 diabetes underwent an exploratory cross-sectional analysis with optical coherence tomography angiography (OCT-A), handheld electroretinography (ERG), corneal confocal microscopy (CCM) and evaluation of electrochemical skin conductance (ESC).

RESULTS

Seventy-five participants with normoglycaemia (n = 20), prediabetes (n = 29) and type 2 diabetes (n = 26) were studied. Compared with normoglycaemia, mean peak ERG amplitudes of retinal responses at low (16-Td·s: 4.05 μV, 95% confidence interval [95% CI] 0.96-7.13) and high (32-Td·s: 5·20 μV, 95% CI 1.54-8.86) retinal illuminance were lower in prediabetes, as were OCT-A parafoveal vessel densities in superficial (0.051 pixels/mm² , 95% CI 0.005-0.095) and deep (0.048 pixels/mm² , 95% CI 0.003-0.093) retinal layers. There were no differences in CCM or ESC measurements between these two groups. Correlations between HbA_1c and peak ERG amplitude at 32-Td·s (r = -0.256, p = 0.028), implicit time at 32-Td·s (r = 0.422, p < 0.001) and 16-Td·s (r = 0.327, p = 0.005), OCT parafoveal vessel density in the superficial (r = -0.238, p = 0.049) and deep (r = -0.3, p = 0.017) retinal layers, corneal nerve fibre length (CNFL) (r = -0.293, p = 0.017), and ESC-hands (r = -0.244, p = 0.035) were observed. HOMA-IR was a predictor of CNFD (β = -0.94, 95% CI -1.66 to -0.21, p = 0.012) and CNBD (β = -5.02, 95% CI -10.01 to -0.05, p = 0.048).

CONCLUSIONS

The glucose threshold for the diagnosis of diabetes is based on emergent retinopathy on fundus examination. We show that both abnormal retinal neurovascular structure (OCT-A) and function (ERG) may precede retinopathy in prediabetes, which require confirmation in larger, adequately powered studies.

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.

Recovery of Corneal Innervation after Treatment in Dry Eye Disease: A Confocal Microscopy Study

PURPOSE

To analyze the changes in corneal innervation by means of in vivo corneal confocal microscopy (IVCM) in patients diagnosed with Evaporative (EDE) and Aqueous Deficient Dry Eye (ADDE) and treated with a standard treatment for Dry Eye Disease (DED) in combination with Plasma Rich in Growth Factors (PRGF).

METHODS

Eighty-three patients diagnosed with DED were enrolled in this study and included in the EDE or ADDE subtype. The primary variables analyzed were the length, density and number of nerve branches, and the secondary variables were those related to the quantity and stability of the tear film and the subjective response of the patients measured with psychometric questionnaires.

RESULTS

The combined treatment therapy with PRGF outperforms the standard treatment therapy in terms of subbasal nerve plexus regeneration, significantly increasing length, number of branches and nerve density, as well as significantly improving the stability of the tear film (p < 0.05 for all of them), and the most significant changes were located in the ADDE subtype.

CONCLUSIONS

the corneal reinnervation process responds in a different way depending on the treatment prescribed and the subtype of dry eye disease. In vivo confocal microscopy is presented as a powerful technique in the diagnosis and management of neurosensory abnormalities in DED.

Corneal axonal loss as an imaging biomarker of neurodegeneration in multiple sclerosis: a longitudinal study

Background

Resourceful endpoints of axonal loss are needed to predict the course of multiple sclerosis (MS). Corneal confocal microscopy (CCM) can detect axonal loss in patients with clinically isolated syndrome and established MS, which relates to neurological disability.

Objective

To assess corneal axonal loss over time in relation to retinal atrophy, and neurological and radiological abnormalities in MS.

Methods

Patients with relapsing-remitting (RRMS) (n = 68) or secondary progressive MS (SPMS) (n = 15) underwent CCM and optical coherence tomography. Corneal nerve fibre density (CNFD-fibres/mm²), corneal nerve branch density (CNBD-branches/mm²), corneal nerve fibre length (CNFL-mm/mm²) and retinal nerve fibre layer (RNFL-μm) thickness were quantified along with neurological and radiological assessments at baseline and after 2 years of follow-up. Age-matched, healthy controls (n = 20) were also assessed.

Results

In patients with RRMS compared with controls at baseline, CNFD (p = 0.004) and RNFL thickness (p < 0.001) were lower, and CNBD (p = 0.003) was higher. In patients with SPMS compared with controls, CNFD (p < 0.001), CNFL (p = 0.04) and RNFL thickness (p < 0.001) were lower. For identifying RRMS, CNBD had the highest area under the receiver operating characteristic (AUROC) curve (0.99); and for SPMS, CNFD had the highest AUROC (0.95). At follow-up, there was a further significant decrease in CNFD (p = 0.04), CNBD (p = 0.001), CNFL (p = 0.008) and RNFL (p = 0.002) in RRMS; in CNFD (p = 0.04) and CNBD (p = 0.002) in SPMS; and in CNBD (p = 0.01) in SPMS compared with RRMS. Follow-up corneal nerve loss was greater in patients with new enhancing lesions and optic neuritis history.

Conclusion

Progressive corneal and retinal axonal loss was identified in patients with MS, especially those with more active disease. CCM may serve as an imaging biomarker of axonal loss in MS.

Artificial Intelligence Based Analysis of Corneal Confocal Microscopy Images for Diagnosing Peripheral Neuropathy: A Binary Classification Model

Diabetic peripheral neuropathy (DPN) is the leading cause of neuropathy worldwide resulting in excess morbidity and mortality. We aimed to develop an artificial intelligence deep learning algorithm to classify the presence or absence of peripheral neuropathy (PN) in participants with diabetes or pre-diabetes using corneal confocal microscopy (CCM) images of the sub-basal nerve plexus. A modified ResNet-50 model was trained to perform the binary classification of PN (PN+) versus no PN (PN-) based on the Toronto consensus criteria. A dataset of 279 participants (149 PN-, 130 PN+) was used to train (n = 200), validate (n = 18), and test (n = 61) the algorithm, utilizing one image per participant. The dataset consisted of participants with type 1 diabetes (n = 88), type 2 diabetes (n = 141), and pre-diabetes (n = 50). The algorithm was evaluated using diagnostic performance metrics and attribution-based methods (gradient-weighted class activation mapping (Grad-CAM) and Guided Grad-CAM). In detecting PN+, the AI-based DLA achieved a sensitivity of 0.91 (95%CI: 0.79-1.0), a specificity of 0.93 (95%CI: 0.83-1.0), and an area under the curve (AUC) of 0.95 (95%CI: 0.83-0.99). Our deep learning algorithm demonstrates excellent results for the diagnosis of PN using CCM. A large-scale prospective real-world study is required to validate its diagnostic efficacy prior to implementation in screening and diagnostic programmes.

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.

Peripheral Neuropathy in Beta-Thalassemia: Corneal Confocal Microscopy-Based Study

Background Peripheral neuropathy is a controversial but serious complication of beta-thalassemia (β-Th). Although few studies have reported no relationship between neuropathy and thalassemia, many have linked it with increasing age, iron overload, and iron chelator toxicity. This study aims to investigate the presence of neuropathy in β-Th using corneal nerve fibers. Methodology A cross-sectional study was conducted using corneal confocal microscopy on individuals with intermediate and major β-Th who were compared to healthy individuals. The main outcome variables were corneal main nerve and branch nerve densities which were calculated using Image J software. The comparison between groups was done using the independent-samples F-test and Bonferroni post-hoc analysis. Results There was reduced corneal main nerve and branch nerve density in β-Th intermediate and major patients compared to the control group, and the results were statistically significant (p-value <0.05). However, a significant correlation was not observed between serum ferritin levels and corneal nerve parameters. Conclusions The reduction in corneal nerve parameters in β-Th patients compared to healthy controls can be an indication of peripheral neuropathy in β-Th. Further work is needed to confirm these findings.

Centerline extraction by neighborhood-statistics thinning for quantitative analysis of corneal nerve fibers

Objective. Corneal nerve fiber (CNF) has been found to exhibit morphological changes associated with various diseases, which can therefore be utilized to aid in the early diagnosis of those diseases. CNF is usually visualized under corneal confocal microscopy (CCM) in clinic. To obtain the diagnostic biomarkers from CNF image produced from CCM, image processing and quantitative analysis are needed. Usually, CNF is segmented first and then CNF’s centerline is extracted, allowing for measuring geometrical and topological biomarkers of CNF, such as density, tortuosity, and length. Consequently, the accuracy of the segmentation and centerline extraction can make a big impact on the biomarker measurement. Thus, this study is aimed to improve the accuracy and universality of centerline extraction. Approach. We developed a new thinning algorithm based on neighborhood statistics, called neighborhood-statistics thinning (NST), to extract the centerline of CNF. Compared with traditional thinning and skeletonization techniques, NST exhibits a better capability to preserve the fine structure of CNF which can effectively benefit the biomarkers measurement above. Moreover, NST incorporates a fitting process, which can make centerline extraction be less influenced by image segmentation. Main results. This new method is evaluated on three datasets which are segmented with five different deep learning networks. The results show that NST is superior to thinning and skeletonization on all the CNF-segmented datasets with a precision rate above 0.82. Last, NST is attempted to be applied for the diagnosis of keratitis with the quantitative biomarkers measured from the extracted centerlines. Longer length and higher density but lower tortuosity were found on the CNF of keratitis patients as compared to healthy patients. Significance. This demonstrates that NST has a good potential to aid in the diagnostics of eye diseases in clinic.

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.

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.

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.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

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.

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.

Is Nerve Electrophysiology a Robust Primary Endpoint in Clinical Trials of Treatments for Diabetic Peripheral Neuropathy?

There is currently no FDA-approved disease-modifying therapy for diabetic peripheral neuropathy (DPN). Nerve conduction velocity (NCV) is an established primary endpoint of disease-modifying therapies in DPN and clinical trials have been powered with an assumed decline of 0.5 m/s/year. This paper sought to establish the time-dependent change in NCV associated with a placebo, compared to that observed in the active intervention group. A literature search identified twenty-one double-blind, randomised controlled trials in DPN of ≥1 year duration conducted between 1971 and 2021. We evaluated changes in neurophysiology, with a focus on peroneal motor and sural sensory NCV and amplitude in the placebo and treatment groups. There was significant variability in the change and direction of change (reduction/increase) in NCV in the placebo arm, as well as variability influenced by the anatomical site of neurophysiological measurement within a given clinical trial. A critical re-evaluation of efficacy trials should consider placebo-adjusted effects and present the placebo-subtracted change in NCV rather than assume a universal annual decline of 0.5 m/s/year. Importantly, endpoints such as corneal confocal microscopy (CCM) have demonstrated early nerve repair, whilst symptoms and NCV have not changed, and should thus be considered as a viable alternative.

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.

Corneal confocal microscopy: A useful tool for diagnosis of small fiber neuropathy in type 2 diabetes

AIM

To investigate the diagnostic utility of corneal confocal microscopy (CCM) for small fiber neuropathy in type 2 diabetes.

MATERIALS AND METHODS

There were 186 participants with type 2 diabetes enrolled in this cross-sectional research. Pure small fiber neuropathy and mixed fiber neuropathy were defined using clinical examination, electromyography, and quantitative sensory testing. Demographics and clinical data, corneal confocal microscopy parameters, and other neuropathy measures were compared among the groups. The diagnostic utility of corneal confocal microscopy for small fiber neuropathy was assessed by the receiver operating curve.

RESULTS

Of the 186 patients, 24.7% had a pure small fiber neuropathy and 17.2% of patients were diagnosed with mixed fiber neuropathy. The corneal nerve fiber density (CNFD), corneal nerve fiber branch density (CNBD), and corneal nerve fiber length (CNFL) were significantly lower in subjects with pure small fiber neuropathy compared with those without diabetic peripheral neuropathy (all P < 0.05). The receiver operating curve analysis for corneal confocal microscopy diagnosing small fiber neuropathy demonstrated the area under the curve for CNFD of 0.791, CNFL of 0.778, CNBD of 0.710.

CONCLUSIONS

Patients with type 2 diabetes with pure small fiber neuropathy showed more corneal nerve loss compared with those without diabetic peripheral neuropathy. It was revealed that corneal confocal microscopy can be a reasonable marker in the diagnosis of small fiber neuropathy in type 2 diabetes.

Characteristics of ocular findings of patients with neuronal intranuclear inclusion disease

PURPOSE

This study aimed to explore the ocular characteristics of neuronal intranuclear inclusion disease (NIID), caused by GGC repeat expansion in the NOTCH2NLC gene, combined with the systemic clinical manifestations, and propose early diagnostic features of NIID.

METHODS

Six patients (12 eyes) were enrolled in this study. In vivo corneal confocal microscopy (IVCCM), fundus photography, fundus autofluorescence (FAF) imaging, optical coherence tomography (OCT), full-field electroretinography (ERG), and electromyography were performed.

RESULTS

The average corneal nerve fiber density (CNFD) was 6.83 ± 4.96 number/mm², and the corneal nerve fiber length (CNFL) was 6.76 ± 1.96 mm/mm². The nerves were looser and more curved in affected individuals. Dendritic cells were observed in patients with NIID. Chorioretinal atrophy, hyper-AF spots, and outer retinal abnormalities were observed during FAF imaging and OCT examinations. In full-field ERGs, the amplitudes of the a-wave and b-wave reduced or extinguished over time. The compound muscle action potential and motor nerve conduction velocity of the left common peroneal nerve decreased substantially.

CONCLUSION

The findings of IVCCM and retinal changes should be included in the diagnostic criteria for NIID. Corneal confocal characteristics may precede the systemic neurological manifestations and provide a clinical basis for the early treatment and staging of the disease. ClincalTrials.gov. Identifier: ChiCTR21000500227.

Small fiber neuropathy in the cornea of Covid-19 patients associated with the generation of ocular surface disease

Purpose

To describe the association between Sars-CoV-2 infection and small fiber neuropathy in the cornea identified by in vivo corneal confocal microscopy.

Methods

Twenty-three patients who had overcome COVID-19 were recruited to this observational retrospective study. Forty-six uninfected volunteers were also recruited and studied as a control group. All subjects were examined under in vivo confocal microscopy to obtain images of corneal subbasal nerve fibers in order to study the presence of neuroma-like structures, axonal beadings and dendritic cells. The Ocular Surface Disease Index (OSDI) questionnaire and Schirmer tear test were used as indicators of Dry Eye Disease (DED) and ocular surface pathology.

Results

Twenty-one patients (91.31%) presented alterations of the corneal subbasal plexus and corneal tissue consistent with small fiber neuropathy. Images from healthy subjects did not indicate significant nerve fiber or corneal tissue damage. Eight patients reported increased sensations of ocular dryness after COVID-19 infection and had positive DED indicators. Beaded axons were found in 82.60% of cases, mainly in patients reporting ocular irritation symptoms. Neuroma-like images were found in 65.22% patients, more frequently in those with OSDI scores >13. Dendritic cells were found in 69.56% of patients and were more frequent in younger asymptomatic patients. The presence of morphological alterations in patients up to 10 months after recovering from Sars-CoV-2 infection points to the chronic nature of the neuropathy.

Conclusions

Sars-CoV-2 infection may be inducing small fiber neuropathy in the ocular surface, sharing symptomatology and morphological landmarks with DED and diabetic neuropathy.

Corneal confocal microscopy demonstrates axonal loss in different courses of multiple sclerosis

Axonal loss is the main determinant of disease progression in multiple sclerosis (MS). This study aimed to assess the utility of corneal confocal microscopy (CCM) in detecting corneal axonal loss in different courses of MS. The results were confirmed by two independent segmentation methods. 72 subjects (144 eyes) [(clinically isolated syndrome (n = 9); relapsing–remitting MS (n = 20); secondary-progressive MS (n = 22); and age-matched, healthy controls (n = 21)] underwent CCM and assessment of their disability status. Two independent algorithms (ACCMetrics; and Voxeleron deepNerve) were used to quantify corneal nerve fiber density (CNFD) (ACCMetrics only), corneal nerve fiber length (CNFL) and corneal nerve fractal dimension (CNFrD). Data are expressed as mean ± standard deviation with 95% confidence interval (CI). Compared to controls, patients with MS had significantly lower CNFD (34.76 ± 5.57 vs. 19.85 ± 6.75 fibers/mm², 95% CI − 18.24 to − 11.59, P < .0001), CNFL [for ACCMetrics: 19.75 ± 2.39 vs. 12.40 ± 3.30 mm/mm², 95% CI − 8.94 to − 5.77, P < .0001; for deepNerve: 21.98 ± 2.76 vs. 14.40 ± 4.17 mm/mm², 95% CI − 9.55 to − 5.6, P < .0001] and CNFrD [for ACCMetrics: 1.52 ± 0.02 vs. 1.45 ± 0.04, 95% CI − 0.09 to − 0.05, P < .0001; for deepNerve: 1.29 ± 0.03 vs. 1.19 ± 0.07, 95% − 0.13 to − 0.07, P < .0001]. Corneal nerve parameters were comparably reduced in different courses of MS. There was excellent reproducibility between the algorithms. Significant corneal axonal loss is detected in different courses of MS including patients with clinically isolated syndrome.

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.

Corneal Nerve and Brain Imaging in Mild Cognitive Impairment and Dementia

Background:

Visual rating of medial temporal lobe atrophy (MTA) is an accepted structural neuroimaging marker of Alzheimer’s disease. Corneal confocal microscopy (CCM) is a non-invasive ophthalmic technique that detects neuronal loss in peripheral and central neurodegenerative disorders.

Objective:

To determine the diagnostic accuracy of CCM for mild cognitive impairment (MCI) and dementia compared to medial temporal lobe atrophy (MTA) rating on MRI.

Methods:

Subjects aged 60–85 with no cognitive impairment (NCI), MCI, and dementia based on the ICD-10 criteria were recruited. Subjects underwent cognitive screening, CCM, and MTA rating on MRI.

Results:

182 subjects with NCI (n = 36), MCI (n = 80), and dementia (n = 66), including AD (n = 19, 28.8%), VaD (n = 13, 19.7%), and mixed AD (n = 34, 51.5%) were studied. CCM showed a progressive reduction in corneal nerve fiber density (CNFD, fibers/mm²) (32.0±7.5 versus 24.5±9.6 and 20.8±9.3, p < 0.0001), branch density (CNBD, branches/mm²) (90.9±46.5 versus 59.3±35.7 and 53.9±38.7, p < 0.0001), and fiber length (CNFL, mm/mm²) (22.9±6.1 versus 17.2±6.5 and 15.8±7.4, p < 0.0001) in subjects with MCI and dementia compared to NCI. The area under the ROC curve (95% CI) for the diagnostic accuracy of CNFD, CNBD, CNFL compared to MTA-right and MTA-left for MCI was 78% (67–90%), 82% (72–92%), 86% (77–95%) versus 53% (36–69%) and 40% (25–55%), respectively, and for dementia it was 85% (76–94%), 84% (75–93%), 85% (76–94%) versus 86% (76–96%) and 82% (72–92%), respectively.

Conclusion:

The diagnostic accuracy of CCM, a non-invasive ophthalmic biomarker of neurodegeneration, was high and comparable with MTA rating for dementia but was superior to MTA rating for MCI.

The effect of Rho Kinase inhibition on corneal nerve regeneration in vitro and in vivo

PURPOSE

Impairment of corneal nerves can lead to neurotrophic keratopathy accompanied with severe ocular surface damage, which due to limited treatment options, can result in severe visual deterioration. This study evaluates a possible new treatment by enhancing the corneal nerve regeneration using a Rho Kinase inhibitor (Y27632). ROCK is known to play an important role in regulating cell morphology, adhesion and motility but little is known about its role in corneal nerve regeneration.

METHODS

Effects of ROCK inhibition on murine peripheral nerves was assessed in single cell- and wound healing assays as well as a 3D in vitro model. Furthermore, Sholl analysis evaluating neuronal branching and life-death assays evaluating toxicity of the inhibitor were performed. An in vivo mouse model was established, with monitoring weekly corneal nerve regrowth using confocal microscopy. Additionally, corneal nerve fiber length was evaluated by immunofluorescence staining. Underlying pathways were examined by qrtPCR.

RESULTS

ROCK inhibition leads to a significant enhancement of fiber growth in vitro. Sholl analysis revealed a higher degree of branching of treated fibers. Cytotoxicity assay showed no influence of Y27632 on cellular survival. In vivo measurement revealed significant enhanced regeneration after injury in the treated group. QrtPCR of trigeminal ganglia confirmed ROCK knock-down as well as altered pathways.

CONCLUSION

The inhibition of ROCK after corneal nerve injury resulted in an enhanced regrowth of fibers in vitro and in vivo. This might be a step towards a new therapeutic concept for the treatment of impaired corneal nerves in diseases such as neurotrophic keratopathy.

Corneal inflammatory cell infiltration predicts disease activity in chronic inflammatory demyelinating polyneuropathy

The assessment of disease activity is fundamental in the management of chronic inflammatory demyelinating polyneuropathy (CIDP). Previous studies with small patient numbers found an increase of corneal immune cell infiltrates as a potential marker of inflammation in patients with CIDP. However, its clinical relevance remained unclear. The present study aimed to determine whether the amount of corneal inflammatory cells (CIC) measured by corneal confocal microscopy (CCM) detects disease activity in CIDP. CIC were measured in 142 CCM-investigations of 97 CIDP-patients. Data on clinical disease activity, disability (INCAT-ODSS) and need for therapy escalation at the timepoint of CCM, 3 and 6 months later were analyzed depending CIC-count. Pathological spontaneous activity during electromyography was examined as another possible biomarker for disease activity in comparison to CIC-count. An increased CIC-count at baseline was found in patients with clinical disease activity and disability progression in the following 3-6 months. An increase to more than 25 CIC/mm² had a sensitivity of 0.73 and a specificity of 0.71 to detect clinical disease activity and a sensitivity of 0.77 and a specificity of 0.64 to detect disability progression (increasing INCAT-ODSS) in the following 6 months. An increase to more than 50 CIC/mm² had a sensitivity of about 0.51 and a specificity of 0.91 to detect clinical disease activity and a sensitivity of 0.53 and a specificity of 0.80 to detect disability progression. CIC count is a non-invasive biomarker for the detection of disease activity in the following 6 months in CIDP.

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.

Clinical Applications of In Vivo Confocal Microscopy in Keratorefractive Surgery

PURPOSE

To review the contribution of in vivo confocal microscopy (IVCM) to the understanding of corneal wound healing following refractive surgery, and its role in the diagnosis and management of complications arising from keratorefractive procedures.

METHODS

Review of the basic science and clinical literature relating to the study of keratorefractive surgical procedures using IVCM.

RESULTS

Extensive research using IVCM has generated a comprehensive understanding of tissue responses after corneal refractive surgery. Epithelial thickness and stromal keratocyte density can be quantified postoperatively and studied longitudinally. Corneal nerve loss and subsequent reinnervation has been characterized and differs significantly between laser refractive techniques. IVCM has also been used to study complications arising from postoperative inflammation (diffuse lamellar keratitis, central toxic keratopathy, ring keratitis, and ectasia), infection (microbial keratitis), and neuropathy (dry eye and neuralgia). This imaging technique can have a critical role in the diagnosis of these complications and subsequent monitoring of treatment response. Manual processing of IVCM images is time-consuming and there may be significant interobserver and intraobserver variability with poor repeatability. However, increasing automation and the use of artificial intelligence is improving the speed and accuracy of image analysis.

CONCLUSIONS

IVCM has historically been confined to a research setting because image capture and subsequent processing was extremely labor intensive. However, advances in both hardware and software capabilities promise to allow the use of IVCM in routine clinical practice. Real-time evaluation of the cornea at a cellular level will be particularly useful in patients with inflammatory, infectious, or neuropathic complications of keratorefractive surgery. [J Refract Surg. 2021;37(7):493-503.].

An in vivo confocal microscopy study of corneal changes in patients with systemic sclerosis

To investigate corneal microstructure of systemic sclerosis (SSc) patients using in vivo confocal microscopy (IVCM). 33 patients with SSc and 30 age-matched healthy subjects were recruited. All participants underwent comprehensive ophthalmic examination including IVCM (Heidelberg Retina Tomograph III, Heidelberg Engineering GmbH, Heidelberg, Germany) and ocular surface evaluation. Subbasal nerve plexus morphology was investigated using automated software analysis (ACCMetrics V3; University of Manchester, Manchester, UK). Keratocyte cell densities in the anterior stroma were significantly lower in patients with SSc compared to controls (P < 0.0001). In 7 SSc patients no keratocyte nuclei were identified in the anterior stroma and in most patients scattered hyperreflective punctate material were observed in the anterior stroma. Significantly lower subbasal nerve fiber parameters were found in patients with SSc compared to healthy subjects (P < 0.05). There were no significant correlations between the duration of SSc and any of the corneal cell density values. Tear break-up time values (4.82 ± 3.15 s) and Ocular Surface Disease Index scores (33.27 ± 30.11) were abnormal, Schirmer values (6.78 ± 5.82 mm) were borderline in SSc patients. In SSc, corneal morphological changes and accumulation of punctate material in the stroma was detected with confocal microscopy. Severe ocular surface disease was observed in SSc patients with significant impairment in subbasal nerve plexus morphology resembling peripheral neuropathy.

Corneal Confocal Microscopy: A Biomarker for Diabetic Peripheral Neuropathy

PURPOSE

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

METHODS

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

FINDINGS

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

IMPLICATIONS

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

Validation of a Novel Confocal Microscopy Imaging Protocol With Assessment of Reproducibility and Comparison of Nerve Metrics in Dry Eye Disease Compared With Controls

PURPOSE

The purposes of this study were to assess the reproducibility of a novel standardized technique for capturing corneal subbasal nerve plexus images with in vivo corneal confocal microscopy and to compare nerve metrics captured with this method in participants with dry eye and control participants.

METHODS

Cases and controls were recruited based on their International Statistical Classification of Diseases and Related Health Problems (ICD-10) diagnoses. Participants completed the following 3 ocular symptom questionnaires: the Ocular Surface Disease Index, Neuropathic Pain Symptom Inventory, and Dry Eye Questionnaire 5. A novel eye fixation-grid system was used to capture 30 standardized confocal microscopy images of the central cornea. Each participant was imaged twice by different operators. Seven quantitative nerve metrics were analyzed using automated software (ACCmetrics, Manchester, United Kingdom) for all 30 images and a 6-image subset.

RESULTS

Forty-seven participants were recruited (25 classified as dry eye and 22 controls). The most reproducible nerve metrics were corneal nerve fiber length [intraclass correlation (ICC) = 0.86], corneal nerve fiber area (ICC = 0.86), and fractal dimension (ICC = 0.90). Although differences were not statistically significant, all mean nerve metrics were lower in those with dry eye compared with controls. Questionnaire scores did not significantly correlate with nerve metrics. Reproducibility of nerve metrics was similar when comparing the entire 30-image montage to a central 6-image subset.

CONCLUSIONS

A standardized confocal imaging technique coupled with quantitative assessment of corneal nerves produced reproducible corneal nerve metrics even with different operators. No statistically significant differences in in vivo corneal confocal microscopy nerve metrics were observed between participants with dry eye and control participants.

Short-Term Impact of FS-LASIK and SMILE on Dry Eye Metrics and Corneal Nerve Morphology

PURPOSE

To analyze the short-term (up to 1 month) clinical outcomes in patients undergoing corneal laser refractive surgery and the impact on dry eye disease (DED) metrics and corneal nerves using in vivo confocal microscopy (IVCM).

METHODS

The unaided distance visual acuity, corrected distance visual acuity, and spherical equivalent refraction (SEQ) were determined in 16 and 13 patients undergoing FS-LASIK and SMILE, respectively. DED metrics assessed were Ocular Surface Disease Index, Dry Eye Questionnaire 5-items (DEQ-5), tear film osmolarity, tear meniscus height, noninvasive keratograph breakup time (NIKBUT), ocular staining, and meibomian gland atrophy. An automated analysis of corneal nerve fiber density, corneal nerve branch density, corneal nerve fiber length (CNFL), and corneal nerve fiber fractal dimension were obtained from the IVCM scans using ACCMetrics software (University of Manchester).

RESULTS

Both surgical techniques provided good refractive and visual outcomes. DED symptoms were found to be higher after FS-LASIK compared with SMILE (P < 0.05). A decrease in tear meniscus height (∼31%) and NIKBUT (∼40%) was reported after FS-LASIK (P = 0.005 and P = 0.001, respectively) but not after SMILE. Both procedures affected corneal nerve fiber density, corneal nerve branch density, CNFL, and corneal nerve fiber fractal dimension, but the impact was significantly greater with FS-LASIK (P = 0.001). Only CNFL correlated with the reported symptoms (DEQ-5) after FS-LASIK (r = -0.545, P = 0.029).

CONCLUSIONS

FS-LASIK and SMILE provided good refractive and visual outcomes. There was an increased impact on DED symptoms after FS-LASIK compared with SMILE, although there were no significant differences between the procedures for most of the other ocular surface metrics assessed. The IVCM findings showed that SMILE had less impact on corneal nerves compared with FS-LASIK.

Corneal Subbasal Nerve Plexus Evaluation by in Vivo Confocal Microscopy in Multiple Sclerosis: A Potential New Biomarker

Purpose/Aim: Our study aims to evaluate corneal subbasal nerve plexus morphology by in vivo corneal confocal microscopy (CCM) in Multiple Sclerosis (MS) patients and to explore its potential ability to distinguish between MS patients and healthy subjects.Materials and methods: Cross-sectional study, including 60 MS patients and 22 healthy subjects. Expanded Disability Status Scale (EDSS) was used to assess neurological disability. All participants underwent full ophthalmology evaluation, CCM and optical coherence tomography (OCT). Corneal nerve fibre density (CNFD), branch density (CNBD), fibre length (CNFL) and fibre tortuosity (CNFT) were analysed. Generalized additive regression models were used to analyse the data.Results: Compared to controls, MS patients had lower CNFD, CNBD and CNFL (p < .001) and higher CNFT (p = .002). The area under the ROC curve to distinguish MS patients from healthy controls with CNFD and CNBD was 0.84 (95%CI: 0.75 to 0.93; 95%CI: 0.75 to 0.92, respectively). A nonlinear association between EDSS and CNFD was found, with an initial density increase followed by a significant decrease until more severe disability status. EDSS was associated with CNFL and CNBD, with values being significantly lower for patients with an EDSS > 2.5 (-2.06 mm/mm2; 95%CI: -3.84 to -0.28; p = .027 and -8.70 branches/mm2; 95%CI: -14.69 to -2.71; p = .006, respectively). An optic neuritis (ON) history did not influence CCM parameters.Conclusions: Our results confirm CCM parameters' potential to differentiate MS patients from healthy subjects, not being influenced by a previous ON history. A significant relationship between patient's disability and corneal nerve morphology was also found.

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 identifies small fibre damage and progression of diabetic neuropathy

Accurately quantifying the progression of diabetic peripheral neuropathy is key to identify individuals who will progress to foot ulceration and to power clinical intervention trials. We have undertaken detailed neuropathy phenotyping to assess the longitudinal utility of different measures of neuropathy in patients with diabetes. Nineteen patients with diabetes (age 52.5 ± 14.7 years, duration of diabetes 26.0 ± 13.8 years) and 19 healthy controls underwent assessment of symptoms and signs of neuropathy, quantitative sensory testing, autonomic nerve function, neurophysiology, intra-epidermal nerve fibre density (IENFD) and corneal confocal microscopy (CCM) to quantify corneal nerve fibre density (CNFD), branch density (CNBD) and fibre length (CNFL). Mean follow-up was 6.5 years. Glycated haemoglobin (p = 0.04), low-density lipoprotein-cholesterol (LDL-C) (p = 0.0009) and urinary albumin creatinine ratio (p < 0.0001) improved. Neuropathy symptom profile (p = 0.03), neuropathy disability score (p = 0.04), vibration perception threshold (p = 0.02), cold perception threshold (p = 0.006), CNFD (p = 0.03), CNBD (p < 0.0001), CNFL (p < 0.0001), IENFD (p = 0.04), sural (p = 0.02) and peroneal motor nerve conduction velocity (p = 0.03) deteriorated significantly. Change (∆) in CNFL correlated with ∆CPT (p = 0.006) and ∆Expiration/Inspiration ratio (p = 0.002) and ∆IENFD correlated with ∆CNFD (p = 0.005), ∆CNBD (p = 0.02) and ∆CNFL (p = 0.01). This study shows worsening of diabetic neuropathy across a range of neuropathy measures, especially CCM, despite an improvement in HbA1c and LDL-C. It further supports the utility of CCM as a rapid, non-invasive surrogate measure of diabetic neuropathy.

Small Fibre Neuropathy Is Associated With Impaired Vascular Endothelial Function in Patients With Type 2 Diabetes

Diabetic polyneuropathy (DPN) and endothelial dysfunction are prevalent complications of diabetes mellitus. Currently, there are two non-invasive markers for endothelial dysfunction: flow-mediated dilation and reactive hyperaemia peripheral arterial tonometry (RH-PAT). However, the relationship between diabetic small fibre neuropathy and macroangiopathy remains obscure thus far. Corneal confocal microscopy (CCM) has emerged as a new diagnostic modality to assess DPN, especially of small fibre. To clarify the relationship between diabetic small fibre neuropathy and vascular dysfunction, we aimed to determine the functions of peripheral nerves and blood vessels through clinical tests such as nerve conduction study, coefficient of variation in the R-R interval, CCM, and RH-PAT in 82 patients with type 2 diabetes. Forty healthy control subjects were also included to study corneal nerve parameters. Correlational and multiple linear regression analyses were performed to determine the associations between neuropathy indices and markers for vascular functions. The results revealed that patients with type 2 diabetes had significantly lower values for most variables of CCM than healthy control subjects. RH-PAT solely remained as an explanatory variable significant in multiple regression analysis for several CCM parameters and vice versa. Other vascular markers had no significant multiple regression with any CCM parameters. In conclusion, endothelial dysfunction as revealed by impaired RH-PAT was significantly associated with CCM parameters in patients with type 2 diabetes. This association may indicate that small fibre neuropathy results from impaired endothelial dysfunction in type 2 diabetes. CCM parameters may be considered surrogate markers of autonomic nerve damage, which is related to diabetic endothelial dysfunction. This study is the first to report the relationship between corneal nerve parameter as small fibre neuropathy in patients with type 2 diabetes and RH-PAT as a marker of endothelial dysfunction.