Corneal confocal microscopy detects corneal nerve damage and increased dendritic cells in Fabry disease

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

BACKGROUND AND AIMS

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

METHODS

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

RESULTS

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

INTERPRETATION

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

Corneal 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.

Ophthalmic Manifestations in Fabry Disease: Updated Review

Fabry disease (FD) is an X-linked lysosomal storage disorder, causing Gb-3 (globotriaosylceramide) buildup in cellular lysosomes throughout the body, in particular in blood vessel walls, neuronal cells, and smooth muscle. The gradual accumulation of this glycosphingolipid in numerous eye tissues causes conjunctival vascular abnormalities, corneal epithelial opacities (cornea verticillata), lens opacities, and retinal vascular abnormalities. Although a severe vision impairment is rare, these abnormalities are diagnostic indicators and prognostics for severity. Cornea verticillata is the most common ophthalmic feature in both hemizygous men and heterozygous females. Vessel tortuosity has been linked to a faster disease progression and may be useful in predicting systemic involvement. New technologies such as optical coherence tomography angiography (OCTA) are useful for monitoring retinal microvasculature alterations in FD patients. Along with OCTA, corneal topographic analysis, confocal microscopy, and electro-functional examinations, contributed to the recognition of ocular abnormalities and have been correlated with systemic involvement. We offer an update regarding FD ocular manifestations, focusing on findings derived from the most recent imaging modalities, to optimize the management of this pathology.

In vivo confocal microscopy of corneal nerve fiber damage in early course of multiple sclerosis

PURPOSE

To evaluate the corneal nerve fiber morphology in patients with multiple sclerosis (MS) by in vivo corneal confocal microscopy (CCM).

METHODS

Retinal nerve fiber layer thickness (RNFLT), central macular thickness (CMT), corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD) and corneal nerve fiber tortuosity (CNFT) were measured. Correlation of corneal nerve findings with duration and clinical severity of MS was calculated.

RESULTS

CNFL (9.50 ± 0.60 vs. 11.20 ± 0.57 mm/mm², P = 0.046) and CNBD (57.46 ± 5.04 vs. 77.65 ± 3.41 no/mm², P = 0.001) were significantly lower with no significant difference in CNFD (21.24 ± 1.20 vs. 23.62 ± 0.95 no/mm², P = 0.125), CNFT (2.00 ± 0.15 vs. 1.73 ± 0.12, P = 0.180), CMT (269.57 ± 12.53 vs. 271.10 ± 18.84 μm, P = 0.716) or RNFLT (102.82 ± 6.98 vs. 105.33 ± 12.70 μm, P = 0.351) between patients with RRMS compared to controls. There was no significant correlation between CCM parameters with EDSS and duration of disease in MS patients.

CONCLUSION

The current study demonstrated that a decrease in CNFL, CNFD and CNBD in CCM analysis in the early course of MS.

Narrative Review Concerning the Clinical Spectrum of Ophthalmological Impairments in Parkinson's Disease

Ophthalmic non-motor impairments are common in Parkinson's disease patients, from the onset of the neurodegenerative disease and even prior to the development of motor symptoms. This is a very crucial component of the potential for early detection of this disease, even in its earliest stages. Since the ophthalmological disease is extensive and impacts all extraocular and intraocular components of the optical analyzer, a competent assessment of it would be beneficial for the patients. Because the retina is an extension of the nervous system and has the same embryonic genesis as the central nervous system, it is helpful to investigate the retinal changes in Parkinson's disease in order to hypothesize insights that may also be applicable to the brain. As a consequence, the detection of these symptoms and signs may improve the medical evaluation of PD and predict the illness' prognosis. Another valuable aspect of this pathology is the fact that the ophthalmological damage contributes significantly to the decrease in the quality of life of patients with Parkinson's disease. We provide an overview of the most significant ophthalmologic impairments associated with Parkinson's disease. These results certainly constitute a large number of the prevalent visual impairments experienced by PD patients.

In Vivo Corneal Confocal Microscopy in Multiple Sclerosis: Can it Differentiate Disease Relapse in Multiple Sclerosis?

PURPOSE

This study aims to investigate the role of in vivo corneal confocal microscopy (IVCCM) in the detection of corneal inflammatory activity and subbasal nerve alterations in patients with multiple sclerosis (MS) and to further determine whether IVCCM can be used to detect (acute) disease relapse.

DESIGN

Prospective cross-sectional study, with a subgroup follow-up.

METHODS

This single-center study included 58 patients with MS (MS-Relapse group [n = 27] and MS-Remission group [n = 31]), and 30 age- and sex-matched healthy control subjects. Patients with a history of optic neuritis or trigeminal symptoms were excluded. Corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), and dendritic cell (DC) density were evaluated in all patients with MS and control subjects by IVCCM. Patients in the MS-Relapse group who were in remission for ≥6 months after the MS incident underwent a repeat IVCCM.

RESULTS

No statistical difference was observed between the MS-Relapse and MS-Remission groups regarding age, sex, MS duration, and the number of relapses (P > .05). Compared with healthy control subjects, all subbasal nerve parameters were significantly lower (CNFD: P < .001, CNFL: P < .001, CNBD: P < .001), and the DC density was significantly higher (P = .023) in patients with MS. However, no significant difference was observed between MS-Relapse and MS-Remission groups in terms of CNFD (mean [SE] difference -2.05 [1.69] fibers/mm² [95% confidence interval {CI} -1.32 to 5.43]; P < .227), CNFL (mean [SE] difference -1.10 [0.83] mm/mm² [95% CI -0.56 to 2.75]; P < .190), CNBD (mean [SE] difference -3.91 [2.48] branches/mm² [95% CI -1.05 to 8.87]; P < .120), and DC density (median [IQR], 59.38 [43.75-85.0] vs 75.0 [31.25-128.75]; P = .596). The repeat IVCCM in relapse patients (n = 16 [59.3%]) showed a significant increase in CNFD (P = .036) and CNBD (P = .018), but no change was observed in CNFL (P = .075) and DC density (P = .469).

CONCLUSION

Although increased inflammation and neurodegeneration can be demonstrated in patients with MS compared with healthy control subjects, a single time point evaluation of IVCCM does not seem to be sufficient to confirm the occurrence of relapse in patients with MS. However, IVCCM holds promise for demonstrating early neuroregeneration in patients with MS.

Autophagy-lysosome pathway alteration in ocular surface manifestations in Fabry disease patients

Background

Fabry disease (FD) is a rare X-linked, lysosomal storage disorder caused by mutations in the alpha-galactosidase gene and characterized by neurological, cutaneous, renal, cardiovascular, cochleo-vestibular and ocular manifestations. The aim of this study is to characterize morphological, functional and autophagy-lysosome pathway alterations of the ocular surface in FD patients.

Methods

Eleven subjects with a diagnosis of FD and fifteen healthy control subjects were examined. All patients underwent ocular surface slit lamp examination, corneal aesthesiometry and in vivo confocal laser-scanning microscopy (CCM). Conjunctival impression cytology was performed in six FD patients and six controls, to assess for expression of two markers of the autophagy-lysosome pathway: the microtubule-associated protein light chain 3 (LC3) and lysosome-associated membrane protein 2 (LAMP2).

Results

Cornea verticillata and increased conjunctival vessel tortuosity were detected respectively in 67% and 33% of patients with FD. Compared with healthy subjects, patients affected by FD showed a significant reduction in corneal nerve fiber length, density and nerve branching on CCM and a significantly increased expression of LC3 on conjunctival impression cytology (p < 0.001). No changes were observed in the conjunctival expression of LAMP2 between the two groups.

Conclusions

This study shows that FD is associated with ocular surface alterations including corneal and conjunctival morphology, innervation and vascularization changes. Our data demonstrate an increased expression of LC3 protein in patients with FD, suggesting that alteration of the autophagy-lysosome pathway may play a role in the occurrence of ocular manifestations.

Corneal epithelial dendritic cells, tear neuropeptides and corneal nerves continue to be affected more than 12 months after LASIK

PURPOSE

LASIK causes corneal nerve damage and may affect the neuro-immune crosstalk. This study examined the effects of LASIK on corneal epithelial dendritic cells (CEDC) density and morphology and explored their relationships with corneal nerves and tear neuropeptides. A grading system was developed to assess CEDC morphology.

METHODS

Intra- and inter-observer repeatability of the CEDC morphology grading system was established using kappa (κ). In vivo confocal microscope images of the central cornea were captured from 20 participants who had undergone LASIK 12-16 months earlier and 20 controls (age 18-32 years, 55%F). CEDC density was counted manually, and CEDC morphology was assessed using a new grading system. CEDC sub-types (contacting nerves [CEDCc] and not contacting nerves [CEDCnc]) were also assessed. Differences in CEDC density and morphology were examined using mixed models and chi-squared test. Relationships between CEDC and corneal nerve parameters and tear substance P were explored using Spearman's correlation.

RESULTS

Excellent intra- and inter-observer repeatability was demonstrated for the grading system (κ = 0.82-0.97). In post-LASIK participants, CEDC density was lower compared with controls (5 [0-34] vs. 21 [7-77] cells/mm² ; p = 0.01), and the proportion of CEDC with thick dendrites was higher (55%-73% vs. 11%-21%, p < 0.003). Higher tear substance P levels were associated with higher CEDC density (rho = 0.48, p = 0.003). Fewer nerve interconnections were observed in participants in whom CEDC had dendrites (p = 0.03). CEDC sub-types followed a similar pattern to CEDC.

CONCLUSIONS

The findings suggest that CEDC may remain altered more than 12 months post-LASIK. The association with substance P suggests a role for CEDC in corneal neurogenic inflammation.

Density and distribution of dendritiform cells in the peripheral cornea of healthy subjects using in vivo confocal microscopy

PURPOSE

To establish dendritiform cell (DC) density and morphological parameters in the central and peripheral cornea in a large healthy cohort, using in vivo confocal microscopy (IVCM).

METHODS

A prospective, cross-sectional, observational study was conducted in 85 healthy volunteers (n = 85 eyes). IVCM images of corneal center and four peripheral zones were analyzed for DC density and morphology to compare means and assess correlations (p < 0.05 being statistically significant).

RESULTS

Central cornea had lower DC density (40.83 ± 5.14 cells/mm²; mean ± SEM) as compared to peripheral cornea (75.42 ± 2.67 cells/mm², p < 0.0001). Inferior and superior zones demonstrated higher DC density (105.01 ± 7.12 and 90.62 ± 4.62 cells/mm²) compared to the nasal and temporal zones (59.93 ± 3.42 and 51.77 ± 2.98 cells/mm², p < 0.0001). Similarly, lower DC size, field and number of dendrites were observed in the central as compared to the average peripheral cornea (p < 0.0001), with highest values in the inferior zone (p < 0.001 for all, except p < 0.05 for number of dendrites in superior zone). DC parameters did not correlate with age or gender. Inter-observer reliability was 0.987 for DC density and 0.771-0.922 for morphology.

CONCLUSION

In healthy individuals, the peripheral cornea demonstrates higher DC density and larger morphology compared to the center, with highest values in the inferior zone. We provide the largest normative cohort for sub-stratified DC density and morphology, which can be used in future clinical trials to compare differential changes in diseased states. Furthermore, as DC parameters in the peripheral zones are dissimilar, random sampling of peripheral cornea may be inaccurate.

Charcot-Marie-Tooth Disease and Implications on Corneal Refractive Surgery

Charcot–Marie–Tooth (CMT) disease is the most common inherited polyneuropathy, with a characteristic phenotype of distal muscle weakness, atrophy, and sensory loss. Variable ocular involvement has been documented in patients with CMT, with optic atrophy as the most frequently reported symptom. Although the Charcot–Marie–Tooth Association has generally deemed laser-assisted in situ keratomileuses (LASIK) a safe option for patients with CMT, reports of corneal refractive surgery are lacking in this patient population. This commentary discusses the current understanding of CMT, including its ocular manifestations, and additional specific testing to consider when evaluating these patients for corneal refractive surgery.

Trigeminal Nerve Affection in Patients with Neuro-Sjögren Detected by Corneal Confocal Microscopy

Background: Patients with Sjögren’s syndrome and polyneuropathy more frequently develop cranial nerve affection when compared to patients with chronic inflammatory demyelinating polyneuropathy (CIDP). We therefore aimed to analyze trigeminal corneal nerve fibre characteristics in both patient groups. Methods: A total of 26 patients with Sjögren’s syndrome associated neuropathy and 29 patients with CIDP were recruited at our university hospital and compared to 6 healthy controls. Dry eye symptoms and signs were assessed via clinical examination and the Ocular Disease Surface Index questionnaire. Trigeminal corneal nerve fibres were analyzed via corneal confocal microscopy (CCM) as a non-invasive in vivo microscopy. Results: CCM revealed significantly reduced corneal nerve fibre density and corneal nerve fibre main branch density in the Neuro-Sjögren group when compared with healthy controls. There were no significant group differences between the Neuro-Sjögren and the CIDP group for any of the microscopic parameters. Dry eye assessment showed similarly reduced scores for both patient groups, while healthy controls showed better results for objective dry eye signs. There was no correlation between microscopic parameters of the corneal confocal microscopy and parameters of dry eye assessment. Conclusions: Our data revealed trigeminal corneal nerve affection in patients with neuropathy associated with Sjögren’s syndrome and patients with CIDP detected by CCM. No difference was found between both neuropathy groups indicating that CCM is not able to distinguish between both entities.

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.

Neuroimmune crosstalk in the cornea: The role of immune cells in corneal nerve maintenance during homeostasis and inflammation

In the cornea, resident immune cells are in close proximity to sensory nerves, consistent with their important roles in the maintenance of nerves in both homeostasis and inflammation. Using in vivo confocal microscopy in humans, and ex vivo immunostaining and fluorescent reporter mice to visualize corneal sensory nerves and immune cells, remarkable progress has been made to advance our understanding of the physical and functional interactions between corneal nerves and immune cells. In this review, we summarize and discuss recent studies relating to corneal immune cells and sensory nerves, and their interactions in health and disease. In particular, we consider how disrupted corneal nerve axons can induce immune cell activity, including in dendritic cells, macrophages and other infiltrating cells, directly and/or indirectly by releasing neuropeptides such as substance P and calcitonin gene-related peptide. We summarize growing evidence that the role of corneal intraepithelial immune cells is likely different in corneal wound healing versus other inflammatory-dominated conditions. The role of different types of macrophages is also discussed, including how stromal macrophages with anti-inflammatory phenotypes communicate with corneal nerves to provide neuroprotection, while macrophages with pro-inflammatory phenotypes, along with other infiltrating cells including neutrophils and CD4⁺ T cells, can be inhibitory to corneal re-innervation. Finally, this review considers the bidirectional interactions between corneal immune cells and corneal nerves, and how leveraging this interaction could represent a potential therapeutic approach for corneal neuropathy.

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

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

Implications of Corneal Refractive Surgery in Patients with Fabry Disease

Fabry disease is an X-linked lysosomal storage disorder involving abnormal metabolism of glycosphingolipids, resulting in a range of multisystem organ dysfunction and ocular manifestations. Reports of laser-assisted in situ keratomileuses (LASIK) and photorefractive keratectomy (PRK) are lacking in this patient population. Proceeding with corneal refractive surgery in patients with Fabry disease raises concerns regarding the pre-existing corneal manifestations, reduced mesopic visual acuity, the potential for conjunctival lymphangiectasia, and predisposition to dry eye syndrome. This commentary discusses the current understanding of Fabry disease, including its ocular manifestations, and explores factors to consider when evaluating these patients for LASIK or PRK.

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

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

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Subclinical Corneal Nerve Fiber Damage and Immune Cell Activation in Systemic Lupus Erythematosus: A Corneal Confocal Microscopy Study

Purpose

The purpose of this study was to evaluate the utility of corneal confocal microscopy (CCM) in identifying small nerve fiber damage and immune cell activation in patients with systemic lupus erythematosus (SLE).

Methods

This cross-sectional comparative study included 39 consecutive patients with SLE and 30 healthy control participants. Central corneal sensitivity was assessed using a Cochet-Bonnet contact corneal esthesiometer and a laser scanning CCM (Heidelberg, Germany) was used to quantify corneal nerve fiber density (CNFD), nerve branch density (CNBD), nerve fiber length (CNFL), and Langerhans cell (LC) density.

Results

Age was comparable among patients with SLE (33.7 ± 12.7) and controls (35.0 ± 13.7 years, P = 0.670) and the median duration of disease was 3.0 years (2.0–10.0 years). CNBD (P = 0.003) and CNFL (P = 0.019) were lower and mature LC density (P = 0.002) was higher, but corneal sensitivity (P = 0.178) and CNFD (P = 0.198) were comparable in patients with SLE compared with controls. The SELENA-SLEDAI score correlated with CNFD (ρ = −0.319, P = 0.048) and CNFL (ρ = −0.373, P = 0.019), and the total and immature LC densities correlated with CNBD (ρ = −0.319. P = 0.048, and ρ = −0.328, P = 0.041, respectively). Immature LC density was higher (P = 0.025), but corneal sensitivity and nerve fiber parameters were comparable between patients with (33%) and without neuropsychiatric symptoms and SLE.

Conclusions

Corneal confocal microscopy identifies distal corneal nerve fiber loss and increased immune cell density in patients with SLE and corneal nerve loss was associated with disease activity.

Translational Relevance

Corneal confocal microscopy may enable the detection of subclinical corneal nerve loss and immune cell activation in SLE.

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.

Distribution of Corneal TRPV1 and Its Association With Immune Cells During Homeostasis and Injury

Purpose

Given the role of corneal sensory nerves during epithelial wound repair, we sought to examine the relationship between immune cells and polymodal nociceptors following corneal injury.

Methods

Young C57BL/6J mice received a 2 mm corneal epithelial injury. One week later, corneal wholemounts were immunostained using β-tubulin-488, TRPV1 (transient receptor potential ion channel subfamily V member-1, a nonselective cation channel) and immune cell (MHC-II, CD45 and CD68) antibodies. The sum length of TRPV1⁺ and TRPV1^– nerve fibers, and their spatial association with immune cells, was quantified in intact and injured corneas.

Results

TRPV1⁺ nerves account for ∼40% of the nerve fiber length in the intact corneal epithelium and ∼80% in the stroma. In the superficial epithelial layers, TRPV1⁺ nerve terminal length was similar in injured and intact corneas. In intact corneas, the density (sum length) of basal epithelial TRPV1⁺ and TRPV1⁻ nerve fibers was similar, however, in injured corneas, TRPV1⁺ nerve density was higher compared to TRPV1⁻ nerves. The degree of physical association between TRPV1⁺ nerves and intraepithelial CD45⁺ MHC-II⁺ CD11c⁺ cells was similar in intact and injured corneas. Stromal leukocytes co-expressed TRPV1, which was partially localized to CD68⁺ lysosomes, and this expression pattern was lower in injured corneas.

Conclusions

TRPV1⁺ nerves accounted for a higher proportion of corneal nerves after injury, which may provide insights into the pathophysiology of neuropathic pain following corneal trauma. The close interactions of TRPV1⁺ nerves with intraepithelial immune cells and expression of TRPV1 by stromal macrophages provide evidence of neuroimmune interactions in the cornea.

Corneal Immune Cells Are Increased in Patients With Multiple Sclerosis

Purpose

Corneal confocal microscopy (CCM) is an ophthalmic imaging technique that has been used to identify increased corneal immune cells in patients with immune-mediated peripheral neuropathy. Given that multiple sclerosis has an immune-mediated etiology, we have compared corneal immune cell (IC) density and near-nerve distance in different subtypes of patients with multiple sclerosis (MS) to controls.

Methods

This is a blinded, cross-sectional study conducted at a tertiary hospital. Patients with clinically isolated syndrome (CIS) (n = 9), relapsing-remitting multiple sclerosis (RRMS) (n = 43), secondary progressive multiple sclerosis (SPMS) (n = 22), and control subjects (n = 20) underwent CCM. The total, mature, and immature corneal IC density and their nearest nerve distance were quantified.

Results

The total IC density was higher in patients with MS (P = 0.02), RRMS (P = 0.01), and SPMS (P = 0.04) but not CIS (P = 0.99) compared to controls. Immature IC density was higher in patients with MS (P = 0.03) and RRMS (P = 0.02) but not SPMS (P = 0.10) or CIS (P = 0.99) compared to controls. Mature IC density (P = 0.15) did not differ between patients with MS and controls. The immature IC near-nerve distance was significantly greater in patients with MS (P = 0.001), RRMS (P = 0.007), and SPMS (P = 0.002) compared to controls. Immature IC density correlated with the Symbol Digit Modalities Test (r = –0.281, P = 0.02) and near-nerve distance correlated with the Expanded Disability Status Scale (r = 0.289, P = 0.005).

Conclusions

In vivo CCM demonstrates an increase in immature IC density and the near-nerve distance in patients with MS. These observations merit further studies to assess the utility of CCM in assessing neuroimmune alterations in MS.

Translational Relevance

Multiple sclerosis is an immune-mediated neurodegenerative disease. Dendritic cells mediate communication between the innate and adaptive immune systems. We have used in vivo CCM to show increased corneal ICs and suggest it may act as an imaging biomarker for disease status in patients with MS.

Altered pupillary light responses are associated with the severity of autonomic symptoms in patients with Fabry disease

Symptoms of autonomic dysfunction are common in Fabry disease. In this study we aimed to evaluate alterations in the pupillary response to white light stimulation in patients with Fabry disease and their association with the severity of autonomic symptoms. Fourteen consecutive patients with Fabry disease and 14 healthy control participants were enrolled in this cross-sectional study. The Mainz Severity Score Index (MSSI) was used to measure the severity of Fabry disease and the Composite Autonomic Symptom Scale 31 (COMPASS 31) questionnaire was used to evaluate the severity of autonomic symptoms. The pupil light responses were assessed with an infrared dynamic pupillometry unit. There were significant reductions in the amplitude (P = 0.048) and duration (P = 0.048) of pupil contraction, and the latency of pupil dilation (P = 0.048) in patients with Fabry disease compared to control subjects. The total weighted COMPASS 31 score correlated with MSSI (r = 0.592; P = 0.026) and the duration of pupil dilation (ρ = 0.561; P = 0.037). The pupillomotor weighted sub-score of the COMPASS 31 correlated inversely with the duration of pupil contraction (r = − 0.600; P = 0.023) and latency of pupil dilation (ρ = − 0.541; P = 0.046), and directly with the duration of pupil dilation (ρ = 0.877; P < 0.001) and MSSI (r = 0.533; P = 0.049). In conclusion, abnormal pupillary function is demonstrated in patients with Fabry disease, which is associated with the severity of autonomic symptoms.

Advances in Screening, Early Diagnosis and Accurate Staging of Diabetic Neuropathy

The incidence of both type 1 and type 2 diabetes is increasing worldwide. Diabetic peripheral neuropathy (DPN) is among the most distressing and costly of all the chronic complications of diabetes and is a cause of significant disability and poor quality of life. This incurs a significant burden on health care costs and society, especially as these young people enter their peak working and earning capacity at the time when diabetes-related complications most often first occur. DPN is often asymptomatic during the early stages; however, once symptoms and overt deficits have developed, it cannot be reversed. Therefore, early diagnosis and timely intervention are essential to prevent the development and progression of diabetic neuropathy. The diagnosis of DPN, the determination of the global prevalence, and incidence rates of DPN remain challenging. The opinions vary about the effectiveness of the expansion of screenings to enable early diagnosis and treatment initiation before disease onset and progression. Although research has evolved over the years, DPN still represents an enormous burden for clinicians and health systems worldwide due to its difficult diagnosis, high costs related to treatment, and the multidisciplinary approach required for effective management. Therefore, there is an unmet need for reliable surrogate biomarkers to monitor the onset and progression of early neuropathic changes in DPN and facilitate drug discovery. In this review paper, the aim was to assess the currently available tests for DPN's sensitivity and performance.

Progressive Loss of Corneal and Retinal Nerve Fibers in Patients With Multiple Sclerosis: A 2-Year Follow-up Study

Purpose

To determine longitudinal alterations in corneal nerve fiber morphology, dendritic cell (DC) density, and retinal nerve fiber layer (RNFL) thickness over 2 years in patients with multiple sclerosis (MS).

Methods

Thirty-one consecutive patients with relapsing-remitting MS (RRMS) underwent assessment of the Kurtzke Expanded Disability Status Scale (EDSS), Multiple Sclerosis Severity Score (MSSS), corneal confocal microscopy to quantify corneal subbasal nerve morphology and DC density, and spectral-domain optical coherence tomography to quantify RNFL thickness at baseline and after 2 years.

Results

There was a significant reduction in corneal nerve fiber area (CNFA) (P = 0.003), nerve fiber width (CNFW) (P = 0.005), and RNFL thickness (P = 0.004) with an increase in EDSS (P = 0.01) over 2 years. The change in corneal nerve fiber density (CNFD) correlated with the change in EDSS (ρ = -0.468; P = 0.008), MSSS (ρ = -0.442; P = 0.01), DC density (ρ = -0.550; P = 0.001), and RNFL (ρ = 0.472; P = 0.007). The change in corneal nerve fiber length (CNFL) correlated with the change in EDSS (ρ = -0.445; P = 0.01) and MSSS (ρ = -0.490; P = 0.005). Furthermore, there was a significant decrease in CNFL (P < 0.001), CNFA (P = 0.02), CNFW (P = 0.04), corneal total branch density (P = 0.01), and RNFL thickness (P = 0.02) and a significant increase in DC density (P = 0.04) in patients with worsening EDSS (n = 15).

Conclusions

Corneal confocal microscopy can be used to detect progressive corneal nerve fiber loss that relates to a progression of disability in patients with RRMS.

Translational Relevance

Corneal confocal microscopy acts as a sensitive imaging biomarker for progressive nerve degeneration in patients with MS.

The Utility of Corneal Nerve Fractal Dimension Analysis in Peripheral Neuropathies of Different Etiology

Purpose

Quantification of corneal confocal microscopy (CCM) images has shown a significant reduction in corneal nerve fiber length (CNFL) in a range of peripheral neuropathies. We assessed whether corneal nerve fractal dimension (CNFrD) analysis, a novel metric to quantify the topological complexity of corneal subbasal nerves, can differentiate peripheral neuropathies of different etiology.

Methods

Ninety patients with peripheral neuropathy, including 29 with diabetic peripheral neuropathy (DPN), 34 with chronic inflammatory demyelinating polyneuropathy (CIDP), 13 with chemotherapy-induced peripheral neuropathy (CIPN), 14 with human immunodeficiency virus-associated sensory neuropathy (HIV-SN), and 20 healthy controls (HCs), underwent CCM for estimation of corneal nerve fiber density (CNFD), CNFL, corneal nerve branch density (CNBD), CNFrD, and CNFrD adjusted for CNFL (ACNFrD).

Results

In patients with DPN, CIDP, CIPN, or HIV-SN compared to HCs, CNFD (P = 0.004-0.0001) and CNFL (P = 0.05-0.0001) were significantly lower, with a further significant reduction among subgroups. CNFrD was significantly lower in patients with CIDP compared to HCs and patients with HIV-SN (P = 0.02-0.0009) and in patients with DPN compared to HCs and patients with HIV-SN, CIPN, or CIDP (P = 0.001-0.0001). ACNFrD was lower in patients with CIPN, CIDP, or DPN compared to HCs (P = 0.03-0.0001) and in patients with DPN compared to those with HIV-SN, CIPN, or CIDP (P = 0.01-0.005).

Conclusions

CNFrD can detect a distinct pattern of corneal nerve loss in patients with DPN or CIDP compared to those with CIPN or HIV-SN and controls.

Translational Relevance

Various peripheral neuropathies are characterized by a comparable degree of corneal nerve loss. Assessment of corneal nerve topology by CNFrD could be useful in differentiating neuropathies based on the pattern of loss.

Optical coherence tomography angiography analysis of fabry disease

PURPOSE

Fabry disease (FD) is characterized by a deficiency in α-galactosidase A activity that leads to the cumulative deposition of unmetabolized glycosphingolipids within organs, including the vascular endothelium and the eyes. The purpose of this study was to assess the effects of FD on the retinal microvasculature, foveal avascular zone (FAZ), macular thickness and retinal nerve fiber layer (RNFL) using optical coherence tomography angiography (OCT-A).

METHODS

Twenty-five patients (14 female and 11 male; mean age 33.16 ± 11.44) with genetically verified FD were compared with 37 age- and sex-matched healthy controls (mean age 32.36 ± 15.54). The vessel density (VD) values of the superficial and deep capillary plexuses (SCP and DCP), the area of the FAZ, the density of radial peripapillary capillaries (RPC), the macular thickness and the retinal nerve fiber layer thickness were measured by OCT-A examination.

RESULTS

The patients showed significantly lower VD values than controls in the foveal regions of both SCP and the DCP (21.15 ± 5.56 vs. 23.79 ± 4.64 (p = 0.048), 37.92 ± 6.78 vs. 41.11 ± 5.59 (p = 0.048), respectively). The FAZ was significantly larger in the FD group than in the control group (0.3 ± 0.1 vs. 0.24 ± 0.08 (p = 0.011)). No significant difference was identified in measurements of RPC density, peripapillary RNFL thickness or macular thickness between the two groups (p > 0.05 for all).

CONCLUSION

Decreased VD and an enlarged foveal avascular area suggest possible changes in the retinal microvasculature of patients with FD. OCT-A can serve as a useful, noninvasive, quantitative tool for diagnosing FD and monitoring its progression.

Fabry disease due to G171S GLA mutation: An atypical small nerve fiber sparing variant?

INTRODUCTION

To describe the ocular manifestations and in vivo confocal microscopic findings in a patient carrying the recently described hemizygous G171S GLA gene mutation.

CASE DESCRIPTION

A 63-year-old Albanian male patient was evaluated for cataract surgery. Anamnesis showed pacemaker implantation in left ventricular hypertrophy, chronic kidney disease, family history for kidney transplantation, and late onset of sporadic acroparesthesias. Bilateral cornea verticillata, and increased tortuosity in conjunctival and retinal vessels were present. In vivo confocal microscopy revealed clusters of hyper-reflective corneal epithelial cells centripetally extending from the limbus. Interestingly, the nerve fiber number, density, and length in the corneal sub-basal nerve plexus were preserved. Alpha-galactosidase A activity was almost absent and hemizygous c.511G>A mutation (G171S - p.Gly171Ser) of the GLA gene was identified. The patient was referred for initiation of enzyme replacement therapy, and genetic counseling was recommended for at-risk family members.

CONCLUSION

This is the third reported case of Fabry disease due to GLA G171S mutation. All patients are of Albanian descent. Cornea verticillata and vascular anomalies remain common ocular manifestations, as well as cardiac and renal involvement. Confirming its pathogenicity, this mutation results in a "classic" Fabry disease phenotype, but it seems to be associated with a relative small nerve fiber sparing that may delay a correct diagnosis. The diagnosis of Fabry disease still remains challenging due to its clinical heterogeneity, but a thorough ophthalmological examination can promote early detection and, consequently, early initiation of enzyme replacement therapy.

Role of Gangliosides in Peripheral Pain Mechanisms

Gangliosides are abundantly occurring sialylated glycosphingolipids serving diverse functions in the nervous system. Membrane-localized gangliosides are important components of lipid microdomains (rafts) which determine the distribution of and the interaction among specific membrane proteins. Different classes of gangliosides are expressed in nociceptive primary sensory neurons involved in the transmission of nerve impulses evoked by noxious mechanical, thermal, and chemical stimuli. Gangliosides, in particular GM1, have been shown to participate in the regulation of the function of ion channels, such as transient receptor potential vanilloid type 1 (TRPV1), a molecular integrator of noxious stimuli of distinct nature. Gangliosides may influence nociceptive functions through their association with lipid rafts participating in the organization of functional assemblies of specific nociceptive ion channels with neurotrophins, membrane receptors, and intracellular signaling pathways. Genetic and experimentally induced alterations in the expression and/or metabolism of distinct ganglioside species are involved in pathologies associated with nerve injuries, neuropathic, and inflammatory pain in both men and animals. Genetic and/or pharmacological manipulation of neuronal ganglioside expression, metabolism, and action may offer a novel approach to understanding and management of pain.

The 2017 Banting Memorial Lecture The diabetic lower limb - a forty year journey: from clinical observation to clinical science

A series of clinical research projects conducted over the past 40 years, all of which were informed by clinical observation or discussions with people with diabetes and staff colleagues are described in this review. A study of necrobiosis lipoidica diabeticorum confirmed that this rare skin complication occurs predominantly in young women with Type 1 diabetes and other microvascular complications. Biopsies of necrobiotic lesions showed destruction of superficial nerve fibres by inflammatory tissue, which likely causes the sensory loss in lesions that is pathognomonic of the condition. The development of corneal confocal microscopy as a new non-invasive surrogate marker of peripheral neuropathy in diabetes is described next and several small studies of the use of this new technique in clinical research are reported. The influence of blood glucose instability on the genesis of neuropathic pain is then explained, with results suggesting that the stability of glycaemic control may be more important than the level of control achieved. Lastly, in neuropathy, studies of gustatory sweating are discussed, including the observation that sweating in the head and neck region is more common in people with end-stage diabetic nephropathy than in those with neuropathy. The disappearance of gustatory sweating after renal transplantation suggests a metabolic cause and for those with troublesome sweating, use of the anticholinergic, anti-muscarinic, topical cream glycopyrrolate is confirmed in a randomized control trial. In the area of diabetic foot research, distended dorsal foot veins were observed to be a clinical sign of sympathetic autonomic neuropathy: raised venous Po₂ and Doppler abnormalities of blood flow are highly suggestive of arteriovenous shunting. A series of studies of the abnormalities of pressures and loads under the neuropathic diabetic foot are described: high dynamic plantar pressures are highly predictive of subsequent ulceration in the neuropathic foot. Lastly, a number of recent studies on unsteadiness and gait abnormalities when climbing and descending stairs are described. It is hoped that the art of clinical observation survives in the highly technological 21st century.

Topographical and Morphological Differences of Corneal Dendritic Cells during Steady State and Inflammation

PURPOSE

We report novel differences in mouse corneal DC morphology and density during local and systemic inflammation.

METHODS

Local inflammation was induced by topical application of saline or TLR9 agonist CpG-ODN on abraded C57BL6J mouse corneas. Systemic inflammation was induced by intraperitoneal injection of lipopolysaccharide (LPS) in CD11c-YFP mice. Corneal epithelial DCs from uninjured, injured and contralateral eyes were analysed by confocal microscopy.

RESULTS

Following local CpG delivery on the injured cornea, the DC density and size increased in both central and peripheral regions. Contralateral uninjured eyes displayed enlarged DC morphology in the central cornea compared to naïve cohorts. After systemic LPS, the size of DCs in the central cornea was lower at 2 hours, returning to baseline after 24 hours.

CONCLUSIONS

Corneal DCs respond differently in terms of shape and distribution during local and systemic inflammation. These features can serve as in vivo indicators in ocular and systemic diseases.

Rats deficient in α-galactosidase A develop ocular manifestations of Fabry disease

Fabry disease is an X-linked lysosomal storage disease caused by deficiency of α-galactosidase A. Ocular findings, such as cornea verticillata, cataracts, and retinal vascular tortuosity, serve as important diagnostic markers. We aimed to evaluate ocular phenotypes in α-galactosidase A-deficient (Fabry) rats and hypothesized that these rats would manifest ocular signs similar to those observed in patients. Slit lamp biomicroscopy was used to evaluate the cornea and lens, and retinal vasculature was examined by fluorescein angiography in WT and Fabry rats. Mass spectrometry was used to characterize and quantify ocular glycosphingolipids, and histology and electron microscopy revealed the location of the glycosphingolipid storage. We found that Fabry rats developed corneal and lenticular opacities to a statistically greater degree than WT rats. Retinal vascular morphology did not appear grossly different, but there was vascular leakage in at least one Fabry rat. Fabry rat eyes accumulated substrates of α-galactosidase A, and these α-galactosyl glycoconjugates were found in corneal keratocytes, lens fibers, and retinal vascular endothelial cells. Electron-dense lamellar inclusions were observed in keratocytes. Because Fabry rats recapitulate many ocular phenotypes observed in patients, they can be used to study disease pathogenesis and determine whether ocular findings serve as noninvasive indicators of therapeutic efficacy.

Corneal confocal microscopy: ready for prime time

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

Association of corneal nerve fiber measures with cognitive function in dementia

Objectives

Corneal confocal microscopy (CCM) is a noninvasive ophthalmic technique that identifies corneal nerve degeneration in a range of peripheral neuropathies and in patients with multiple sclerosis, Parkinson's disease, and amyotrophic lateral sclerosis. We sought to determine whether there is any association of corneal nerve fiber measures with cognitive function and functional independence in patients with MCI and dementia.

Methods

In this study, 76 nondiabetic participants with MCI (n = 30), dementia (n = 26), and healthy age‐matched controls (n = 20) underwent assessment of cognitive and physical function and CCM.

Results

There was a progressive reduction in corneal nerve fiber density (CNFD), branch density (CNBD), and fiber length (CNFL) (P < 0.0001) in patients with MCI and dementia compared to healthy controls. Adjusted for confounders, all three corneal nerve fiber measures were significantly associated with cognitive function (P < 0.05) and functional independence (P < 0.01) in MCI and dementia. The area under the ROC curve to distinguish MCI with CNFD, CNBD, and CNFL was 69.1%, 73.2%, and 73.0% and for dementia it was 84.8%, 84.2%, and 86.2%, respectively.

Interpretation

CCM demonstrates corneal nerve fiber loss, which is associated with a decline in cognitive function and functional independence in patients with MCI and dementia.