Comparison of Standard Versus Wide-Field Composite Images of the Corneal Subbasal Layer by In Vivo Confocal Microscopy

[Chromatic Swept-Source Laser Scanning - Concept for a Cell-Resolving Confocal Laser Slit Lamp?]

BACKGROUND

The in vivo characterisation of corneal epithelial tissue morphology is of considerable importance for diagnosis, disease prognosis, and the development of a treatment strategy for ocular surface diseases. In contrast to many alternative methods, in vivo corneal confocal microscopy (CCM) not only provides a macroscopic description of the corneal tissue but also allows its visualisation with cellular resolution. However, the translation of CCM from research to clinical practice is significantly limited by the complex and still largely manual operation of available CCM systems. In addition, for cross-sectional images, and analogously to conventional slit lamp microscopy, volume data must be acquired in time-consuming depth scans due to the frontal orientation of the image field in CCM, from which depth slices can subsequently be calculated. The pure acquisition time is already in the range of seconds, and additionally, motion artefacts have to be corrected in a sophisticated way.

MATERIALS AND METHODS

This paper presents the concept and optics simulation of a new imaging technique based on a swept-source laser in combination with special chromatic optics. Here, the laser periodically changes its wavelength and is focused at different depths due to the wavelength-dependent aberration of the chromatic optics.

RESULTS

The optics simulation results promise good optical resolution at a total imaging depth of 145 µm.

CONCLUSION

The long-term goal is cell-resolving in vivo corneal confocal microscopy in real time with differently oriented sectioning directions.

Increased dendritic cell density and altered morphology in allergic conjunctivitis

BACKGROUND

Corneal and conjunctival epithelial dendritic cells (DC) have an established role in vernal keratoconjunctivitis, however, their role in more prevalent forms of allergic eye disease remains unclear. This study evaluated corneal and conjunctival epithelial DC density, morphology, and distribution observed using in vivo confocal microscopy (IVCM) in allergic conjunctivitis.

METHODS

In this prospective, observational study, 66 participants (mean age 36.6 ± 12.0 years, 56% female): 33 with allergic conjunctivitis and 33 controls were recruited. IVCM was performed at the corneal centre, inferior whorl, corneal periphery, corneal limbus, and temporal bulbar conjunctiva. DC were counted and their morphology was assessed as follows: largest cell body size, presence of dendrites, and presence of long and thick dendrites. Mixed model analysis (DC density) and non-parametric tests (DC morphology) were used.

RESULTS

DC density was higher in allergic participants at all locations (p ≤ 0.01), (corneal centre median (IQR) 21.9 (8.7-50.9) cells/mm2 vs 13.1 (2.8-22.8) cells/mm2; periphery 37.5 (15.6-67.2) cells/mm2 vs 20 (9.4-32.5) cells/mm2; limbus 75 (60-120) cells/mm2 vs 58.1 (44.4-66.2) cells/mm2; conjunctiva 10 (0-54.4) cells/mm2 vs 0.6 (0-5.6) cells/mm2, but not at the inferior whorl 21.9 (6.2-34.4) cells/mm2 vs 12.5 (1.9-37.5) cells/mm2, p = 0.20. At the corneal centre, allergic participants had larger DC bodies (p = 0.02), a higher proportion of DC with dendrites (p = 0.02) and long dendrites (p = 0.003) compared to controls.

CONCLUSIONS

Corneal and conjunctival DC density was increased, and morphology altered in allergic conjunctivitis. These findings imply that the ocular surface immune response was upregulated and support an increased antigen-capture capacity of DC in allergic conjunctivitis.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSION

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

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT05326958.

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.

Defining an Optimal Sample Size for Corneal Epithelial Immune Cell Analysis Using in vivo Confocal Microscopy Images

Purpose

In vivo confocal microscopy (IVCM) images are frequently used to quantify corneal epithelial immune cell (IC) density in clinical studies. There is currently limited evidence to inform the selection of a representative image sample size to yield a reliable IC density estimate, and arbitrary numbers of images are often used. The primary aim of this study was to determine the number of randomly selected, unique IVCM images required to achieve an acceptable level of accuracy when quantifying epithelial IC density, in both the central and peripheral cornea. The secondary aim was to evaluate the consistency and precision of an image selection approach where corneal epithelial IC density was quantified from "three representative images" selected independently by three experienced observers.

Methods

All combinations of two to 15 non-overlapping IVCM images were used for deriving IC density estimates, for both the central and peripheral cornea, in 20 healthy participants; the density value from averaging quantifications in the 16 images was defined as the "true mean". IC density estimates were compared with the true mean in each corneal region using a mean ratio. Intraclass correlation coefficients (ICCs) were used to evaluate the consistency of the mean ratios of IC density estimates derived from the method involving the manual selection of "three representative images" by the observers. The precision of the IC density estimates was compared to a scenario involving three randomly selected images.

Results

A total of 12 randomly selected, non-overlapping IVCM images were found to be required to produce a corneal epithelial IC density estimate that was within 30% of the true mean, 95% of the time, for the central cornea; seven such images produced an equivalent level of precision in the peripheral cornea. Mean ratios of corneal IC density estimates derived from "three representative images" methods had poor consistency between observers (ICC estimates <0.5) and similar levels of precision when compared with using three randomly selected images (p > 0.05 for all comparisons), in both the central and peripheral cornea.

Conclusions

Data presented in this study can inform image selection methods, and the sample size required for a preferred level of accuracy, when quantifying IC densities in the central and peripheral corneal epithelium using IVCM images.

Evaluation of corneal nerves and dendritic cells by in vivo confocal microscopy after Descemet's membrane keratoplasty for bullous keratopathy

This study evaluated changes in corneal nerves and the number of dendritic cells (DCs) in corneal basal epithelium following Descemet membrane endothelial keratoplasty (DMEK) surgery for bullous keratopathy (BK). Twenty-three eyes from 16 consecutive patients that underwent DMEK for BK were included. Eyes of age-matched patients that underwent pre-cataract surgery (12 eyes) were used as controls. In vivo confocal microscopy was performed pre- and postoperatively at 6, 12, and 24 months. Corneal nerve length, corneal nerve trunks, number of branches, and the number of DCs were determined. The total corneal nerve length of 1634.7 ± 1389.1 μm/mm² before surgery was significantly increased in a time-dependent manner to 4485.8 ± 1403.7 μm/mm², 6949.5 ± 1477.1 μm/mm², and 9389.2 ± 2302.2 μm/mm² at 6, 12, and 24 months after DMEK surgery, respectively. The DC density in BK cornea pre- and postoperatively at 6 months was significantly higher than in the controls, and decreased postoperatively at 12 and 24 months and was significantly lower than that at 6 months postoperatively. Thus, our results suggest that DMEK can repair and normalize the corneal environment.

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.

Semiautomated and Automated Quantitative Analysis of Corneal Sub-Basal Nerves in Patients With DED With Ocular Pain Using IVCM

Purpose

Investigate the correlation and agreement between the results of semiautomated and fully automated quantitative analysis of the corneal sub-basal nerve plexus (SNP) in patients with dry eye disease (DED) with ocular pain using in vivo confocal microscopy (IVCM).

Method

A total of 50 voluntary participants were enrolled in this study, i.e., 25 DED patients with ocular pain and 25 healthy controls. Each patient underwent an evaluation of ocular symptoms that utilized: the Ocular Surface Disease Index (OSDI), the Ocular Pain Assessment Survey (OPAS), the tear film breakup time (TBUT) test, the Schirmer test, corneal staining, and IVCM. Five SNP images of the cornea of each eye were selected and analyzed using a semiautomated analysis software (NeuronJ) and a fully automated method (ACCMetrics) to quantify corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and corneal nerve fiber length (CNFL).

Results

The intraclass correlation coefficient (ICC) of the CNFD (0.460 [0.382–0.532], p < 0.001), CNBD (0.608 [0.545–0.665], p < 0.001), and CNFL (0.851 [0.822–0.875], p < 0.001) represents the repeatability and consistency of measurements by the NeuronJ and ACCMetrics software. The CNFL values (r = 0.881, p < 0.001) obtained using the two methods have extremely high correlation, and similarly, the CNFD values (r = 0.669, p < 0.001) and CNBD values (r = 0.703, p < 0.001) are highly correlated. The CNFL had the biggest area under the curve (AUC; 0.747 [0.700–0.793], p < 0.001) when using ACCMetrics. In DED patients with ocular pain, the mean CNFD values for semiautomated and fully automated quantization were 23.5 ± 8.1 and 23.8 ± 8.6 n/mm²; the mean CNBD values were 46.0 ± 21.3, 35.7 ± 23.3 n/mm²; and the mean CNFL values were 19.3 ± 4.3 and 15.2 ± 3.8 mm/mm², which were significantly lower than healthy subjects (p < 0.001).

Conclusion

There is a significant correlation between the measurements obtained via ACCMetrics and NeuronJ, especially for CNFL, which can be considered as the primary indicator in the diagnosis of DED with ocular pain. The SNP of the disease was significantly lower than that of healthy subjects.

Quantifying corneal immune cells from human in vivo confocal microscopy images: Can manual quantification be improved with observer training?

Manually quantifying immune cells (ICs), commonly considered dendritic cells, in the corneal epithelium from in vivo confocal microscopy (IVCM) images can be influenced by observer bias. This study sought to evaluate the repeatability of manual IC quantification. Cell counts were first performed for 184 non-overlapping IVCM images by a single observer. Quantifications were undertaken to establish the total cell numbers per image, and the numbers of three cell morphological subtypes: mature ICs (with elongated dendrites), immature ICs (with short- or non-discernible dendrites) and globular cells (with large bodies and no visible dendrites). Cell counts were then repeated by the same observer, and independently undertaken by a second observer. Prior to these counts, both observers undertook an agreement 'training' process to define IC appearance and delineate the morphological subtypes. Total IC counts demonstrated excellent intra- and inter-observer reliability (intraclass correlation coefficients (ICC) > 0.90). Bland-Altman plots showed that interobserver measurement bias increased as a function of the total IC number in the image prior to consensus training. For total IC counts after the observer training process, there was no significant interobserver measurement bias. For IC morphological subtypes, there was a positive relationship between the mean inter-observer difference and average cell count for mature ICs and globular cells, but not immature ICs. In conclusion, higher variability in manual corneal IC counts exists when more cells are present in an IVCM image. Implementing an observer training process reduced inter-observer variability and minimised systematic measurement error.

Corneal nerve structure in patients with primary Sjögren's syndrome in China

Background

The aim of this study was to evaluate the in vivo confocal microscopic morphology of corneal subbasal nerves and its relationship with clinical parameters in patients with primary Sjögren’s syndrome in China.

Methods

This was a case control study of 22 dry eye disease (DED) patients with primary Sjögren’s syndrome (pSS) and 20 control subjects with non-Sjögren dry eye disease (NSDE). Each patient underwent an evaluation of ocular surface disease using the tear film break-up time (TBUT), noninvasive tear film break-up time (NIKBUT), noninvasive tear meniscus height (NIKTMH), corneal staining (National Eye Institute scale, NEI), Schirmer I test, meibography, and corneal subbasal nerve analysis with in vivo confocal microscopy (IVCM). The right eye of each subject was included in this study.

Results

SS patients showed a shorter TBUT (P = 0.009) and Schirmer I test results (P = 0.028) than the NSDE group. However, there was no significant difference in NIKBUT between the two groups (P = 0.393). The nerve density of subbasal nerves, number of nerves and tortuosity of the SS group were significantly lower than those of the NSDE group (P = 0.001, P < 0.001 and P = 0.039, respectively). In the SS group, the mean nerve length was correlated with age and the Schirmer I test (r = − 0.519, P = 0.013 and r = 0.463, P = 0.035, respectively). Corneal staining was correlated with nerve density and the number of nerves (r = − 0.534, P = 0.013 and r = − 0.487, P = 0.025, respectively).

Conclusions

Sjögren syndrome dry eye (SSDE) patients have more severe clinical dry eye parameters than non-Sjögren dry eye disease (NSDE) patients. Compared with NSDE patients, we found that SSDE patients showed decreased corneal subbasal nerve density and numbers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-01967-7.

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.

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.

Parkinson's disease with restless legs syndrome-an in vivo corneal confocal microscopy study

Small fiber neuropathy (SFN) has been suggested as a trigger of restless legs syndrome (RLS). An increased prevalence of peripheral neuropathy has been demonstrated in Parkinson's disease (PD). We aimed to investigate, in a cross-sectional manner, whether SFN is overrepresented in PD patients with concurrent RLS relative to PD patients without RLS, using in vivo corneal confocal microscopy (IVCCM) and quantitative sensory testing (QST) as part of small fiber assessment. Study participants comprised of age- and sex-matched PD patients with (n = 21) and without RLS (n = 21), and controls (n = 13). Diagnosis of RLS was consolidated with the sensory suggested immobilization test. Assessments included nerve conduction studies (NCS), Utah Early Neuropathy Scale (UENS), QST, and IVCCM, with automated determination of corneal nerve fiber length (CNFL) and branch density (CNBD) from wide-area mosaics of the subbasal nerve plexus. Plasma neurofilament light (p-NfL) was determined as a measure of axonal degeneration. No significant differences were found between groups when comparing CNFL (p = 0.81), CNBD (p = 0.92), NCS (p = 0.82), and QST (minimum p = 0.54). UENS scores, however, differed significantly (p = 0.001), with post-hoc pairwise testing revealing higher scores in both PD groups relative to controls (p = 0.018 and p = 0.001). Analysis of all PD patients (n = 42) revealed a correlation between the duration of L-dopa therapy and CNBD (ρ = -0.36, p = 0.022), and p-NfL correlated with UENS (ρ = 0.35, p = 0.026) and NCS (ρ = -0.51, p = 0.001). Small and large fiber neuropathy do not appear to be associated with RLS in PD. Whether peripheral small and/or large fiber pathology associates with central neurodegeneration in PD merits further longitudinal studies.

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

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

Correlation of corneal immune cell changes with clinical severity in dry eye disease: An in vivo confocal microscopy study

PURPOSE

To evaluate corneal immune dendritiform cell (DC) changes in dry eye disease (DED) using in vivo confocal microscopy (IVCM) and to correlate IVCM parameters with clinical severity.

METHODS

This was a retrospective, cross-sectional study including 300 eyes of 150 DED patients and 49 eyes of 49 age-matched controls. Severity of DED was based on the Dry Eye Workshop (DEWS) classification. IVCM images of subbasal layer of the central cornea were analyzed for DC density and morphology (including number of dendrites per DC, DC size and DC field).

RESULTS

DC density was significantly higher in DED compared to controls (93.4 ± 6.3 vs. 25.9 ± 3.9 cells/mm²; P < 0.001). Morphologically, number of dendrites, DC size and field were significantly larger in DED (3.3 ± 0.1, 106.9 ± 4.7 μm², 403.8 ± 20.1 μm² than controls (2.3 ± 0.1, 62.5 ± 5.7 μm², 241.4 ± 24.4 μm², P < 0.001). Significantly higher DC density compared to controls was observed as early as Level 1 DED severity (87 ± 10 cells/mm², p < 0.001. Significant morphological changes in DC were detected for Levels 2 to 4 (p=<0.001, and p =< 0.05) for dendrites and DC field, respectively. Similarly, DC size showed significant increase at DED level 3-4. (p < 0.05). Linear regression analysis showed that both conjunctival and corneal staining were independently associated with DC density, while corneal staining was independently associated with DC morphology.

CONCLUSION

DC density and morphology correlated with clinical severity of DED. While, DC density is increased in mild DED, morphological changes are seen only in severe cases. IVCM may be a powerful tool to detect early immune changes and may complement clinical examination in DED.

Reduced association between dendritic cells and corneal sub-basal nerve fibers in patients with fibromyalgia syndrome

In our study, we aimed at investigating corneal langerhans cells (LC) in patients with fibromyalgia syndrome (FMS) and small fiber neuropathy (SFN) as potential contributors to corneal small fiber pathology. We enrolled women with FMS (n = 134) and SFN (n = 41) who underwent neurological examination, neurophysiology, prostaglandin analysis in tear fluid, and corneal confocal microscopy (CCM). Data were compared with those of 60 age-matched female controls. After screening for dry eye disease, corneal LC were counted and sub-classified as dendritic (dLC) and non-dendritic (ndLC) cells with or without nerve fiber association. We further analyzed corneal nerve fiber density (CNFD), length (CNFL), and branch density (CNBD). Neurological examination indicated deficits of small fiber function in patients with SFN. Nerve conduction studies were normal in all participants. Dry eye disease was more prevalent in FMS (17%) and SFN (28%) patients than in controls (5%). Tear fluid prostaglandin levels did not differ between FMS patients and controls. While corneal LC density in FMS and SFN patients was not different from controls, there were fewer dLC in association with nerve fibers in FMS and SFN patients than in controls (P < .01 each). Compared to controls, CNFL was lower in FMS and SFN patients (P < .05 each), CNFD was lower only in FMS patients (P < .05), and CNBD was lower only in SFN patients (P < .001). There was no difference in any CCM parameter between patients with and without dry eyes. Our data indicate changes in corneal innervation and LC distribution in FMS and SFN, potentially based on altered LC signaling.

Dysregulated Tear Fluid Nociception-Associated Factors, Corneal Dendritic Cell Density, and Vitamin D Levels in Evaporative Dry Eye

Purpose

The purpose of this study was to study the status and association among tear-soluble factors, corneal dendritic cell density, vitamin D, and signs and symptoms in dry eye disease (DED).

Methods

A total of 33 control subjects and 47 evaporative dry eye patients were included in the study. DED diagnosis and classification was based on the 2017 Report of the Tear Film & Ocular Surface Society International Dry Eye Workshop (TFOS DEWS II). DED workup, including tear film break-up time (TBUT), Schirmer's test I (STI), corneal and conjunctival staining, ocular surface disease index (OSDI) scoring, and in vivo confocal microscopy (to assess corneal dendritic cell density [cDCD] and subbasal nerve plexus [SBNP] features) was performed in the study subjects. Tear fluid using Schirmer's strip and serum were collected from the subjects. Multiplex ELISA or single analyte ELISA was performed to measure 34 tear-soluble factors levels including vitamin D.

Results

Significantly higher OSDI discomfort score, lower TBUT, and lower STI were observed in DED patients. cDCD was significantly higher in DED patients. No significant difference was observed in SBNP features. Tear fluid IL-1β, IL-17A, MMP9, MMP10, MMP9/TIMP ratio, and VEGF-B were significantly higher in DED patients. Significantly lower tear fluid IL-2, IP-10, NPY, VEGF-A, and vitamin D was observed in DED patients. These dysregulated tear factors showed significant associations with DED signs and symptoms.

Conclusions

Altered tear fluid soluble factors with potential to modulate nociception exhibited a distinct association with ocular surface discomfort status, TBUT, STI, and cDCD. This implies a functional relationship between the various tear-soluble factors and dry eye pathogenesis, indicating new molecular targets for designing targeted therapies.

C-Fiber Assays in the Cornea vs. Skin

C-fibers are unmyelinated nerve fibers that transmit high threshold mechanical, thermal, and chemical signals that are associated with pain sensations. This review examines current literature on measuring altered peripheral nerve morphology and discusses the most relevant aspects of corneal microscopy, especially whether corneal imaging presents significant method advantages over skin biopsy. Given its relative merits, corneal confocal microscopy would seem to be a more practical and patient-centric approach than utilizing skin biopsies.

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.

Efficacy of autologous serum tears for treatment of neuropathic corneal pain

OBJECTIVE

Corneal nerve damage may result in neuropathic corneal pain (NCP). Autologous serum tears (AST) have been shown to results in nerve regeneration and may help alleviate corneal pain. This study aimed to evaluate the efficacy of AST in the treatment of NCP.

METHODS

This was a retrospective case-control study. Sixteen patients suffering from severe NCP and no current ocular surface disease were compared to 12 controls. In vivo confocal microscopy (IVCM) (HRT3/RCM; Heidelberg Engineering GmbH, Germany) of the central corneas was performed bilaterally. Change in pain severity (scale of 0-10), corneal nerve density, tortuosity, reflectivity and presence of beading and micro-neuromas before and after treatment were recorded.

RESULTS

All patients had severe pain, with a mean of 9.1 ± 0.2 (range 8-10). Subbasal nerves were significantly decreased before treatment as compared to controls, including total nerve length (10,935.5 ± 1264.3 vs. 24,714.4 ± 1056.2 μm/mm²; p < 0.0001) and total number of nerves (10.5 ± 1.4 vs. 28.6 ± 2.0; p < 0.0001), respectively. Morphologically, significantly increased reflectivity (2.9 ± 0.2 vs. 1.2 ± 0.1; p = 0.00008) and tortuosity (2.4 ± 0.2 vs. 1.7 ± 0.1; p = 0.001), both graded on a scale of 0-4, were noted. After a mean of 3.8 ± 0.5 months (range 1-8 months) of AST treatment, pain severity decreased to 3.1 ± 0.3 (range 0-4), (p < 0.0001). Further, IVCM demonstrated a significant improvement (p < 0.005) in total nerve length (17,351.3 ± 1395.6  μm/mm²) and number (15.1 ± 1.6), as well as significant decrease in reflectivity (2.4 ± 0.2; p = 0.001) and tortuosity (2.2 ± 0.2; p = 0.001).

CONCLUSION

IVCM demonstrates underlying alterations of the subbasal corneal nerve plexus in patients suffering from debilitating NCP. AST-induced nerve regeneration is seen following treatment with AST, which correlates with improvement in patient symptoms of NCP.

In Vivo Confocal Microscopy Shows Alterations in Nerve Density and Dendritiform Cell Density in Fuchs' Endothelial Corneal Dystrophy

PURPOSE

To evaluate corneal nerve and immune cell alterations in Fuchs' endothelial corneal dystrophy (FECD) and pseudophakic bullous keratopathy (PBK) by laser in vivo confocal microscopy (IVCM) as correlated to corneal sensation and endothelial cell loss.

DESIGN

Prospective, cross-sectional, controlled study.

METHODS

Thirty-three eyes with FECD were compared to 13 eyes with PBK and 17 normal age-matched control eyes at a tertiary referral center. FECD was classified into early (without edema) and late stage (with edema). Corneal IVCM and esthesiometry were performed. Corneal nerve and immune dendritiform cell (DC) alterations were evaluated and correlated to clinical parameters.

RESULTS

FECD and PBK eyes showed significantly (P = .001) diminished total nerve length (11.5 ± 1.3 and 2.9 ± 0.7 mm/mm²) and number (8.8 ± 1.1 and 2.2 ± 0.4 n/frame), compared to controls (23.3 ± 8.1 mm/mm² and 25.9 ± 1.3 n/frame). Decreased nerves corresponded to diminished sensation in FECD (4.9 ± 0.2 cm; R = 0.32; P = .045), compared to controls (5.9 ± 0.04 cm). Early- and late-stage FECD showed significantly reduced total nerve length (13.1 ± 1.4 and 9.9 ± 1.2 mm/mm², respectively) and number (8.2 ± 2.5 and 6.5 ± 2.1 n/frame), compared to controls (P < .001). DC density was significantly increased in FECD (57.8 ± 10.4 cells/mm²; P = .01), but not in PBK (47.7 ± 11.6 cells/mm²; P = .60) compared to controls (22.5 ± 4.5 cells/mm²). A subset of early FECD patients (7/22) demonstrated very high DC density (>100/mm²).

CONCLUSION

IVCM demonstrates profound diminishment of subbasal corneal nerves in early- and late-stage FECD and in PBK, correlating to decreased sensation. Increased DC density in early FECD demonstrates potential subclinical inflammation. The data suggest that reduction in subbasal nerves and increased immune activation may play a role in the pathophysiology of FECD.

Diagnosing Diabetic Neuropathy: Something Old, Something New

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

3D confocal laser-scanning microscopy for large-area imaging of the corneal subbasal nerve plexus

The capability of corneal confocal microscopy (CCM) to acquire high-resolution in vivo images of the densely innervated human cornea has gained considerable interest in using this non-invasive technique as an objective diagnostic tool for staging peripheral neuropathies. Morphological alterations of the corneal subbasal nerve plexus (SNP) assessed by CCM have been shown to correlate well with the progression of neuropathic diseases and even predict future-incident neuropathy. Since the field of view of single CCM images is insufficient for reliable characterisation of nerve morphology, several image mosaicking techniques have been developed to facilitate the assessment of the SNP in large-area visualisations. Due to the limited depth of field of confocal microscopy, these approaches are highly sensitive to small deviations of the focus plane from the SNP layer. Our contribution proposes a new automated solution, combining guided eye movements for rapid expansion of the acquired SNP area and axial focus plane oscillations to guarantee complete imaging of the SNP. We present results of a feasibility study using the proposed setup to evaluate different oscillation settings. By comparing different image selection approaches, we show that automatic tissue classification algorithms are essential to create high-quality mosaic images from the acquired 3D datasets.

Wide-field corneal subbasal nerve plexus mosaics in age-controlled healthy and type 2 diabetes populations

A dense nerve plexus in the clear outer window of the eye, the cornea, can be imaged in vivo to enable non-invasive monitoring of peripheral nerve degeneration in diabetes. However, a limited field of view of corneal nerves, operator-dependent image quality, and subjective image sampling methods have led to difficulty in establishing robust diagnostic measures relating to the progression of diabetes and its complications. Here, we use machine-based algorithms to provide wide-area mosaics of the cornea's subbasal nerve plexus (SBP) also accounting for depth (axial) fluctuation of the plexus. Degradation of the SBP with age has been mitigated as a confounding factor by providing a dataset comprising healthy and type 2 diabetes subjects of the same age. To maximize reuse, the dataset includes bilateral eye data, associated clinical parameters, and machine-generated SBP nerve density values obtained through automatic segmentation and nerve tracing algorithms. The dataset can be used to examine nerve degradation patterns to develop tools to non-invasively monitor diabetes progression while avoiding narrow-field imaging and image selection biases.

Improved sampling and analysis of images in corneal confocal microscopy

INTRODUCTION

Corneal confocal microscopy (CCM) is a noninvasive clinical method to analyse and quantify corneal nerve fibres in vivo. Although the CCM technique is in constant progress, there are methodological limitations in terms of sampling of images and objectivity of the nerve quantification. The aim of this study was to present a randomized sampling method of the CCM images and to develop an adjusted area-dependent image analysis. Furthermore, a manual nerve fibre analysis method was compared to a fully automated method.

METHODS

23 idiopathic small-fibre neuropathy patients were investigated using CCM. Corneal nerve fibre length density (CNFL) and corneal nerve fibre branch density (CNBD) were determined in both a manual and automatic manner. Differences in CNFL and CNBD between (1) the randomized and the most common sampling method, (2) the adjusted and the unadjusted area and (3) the manual and automated quantification method were investigated.

RESULTS

The CNFL values were significantly lower when using the randomized sampling method compared to the most common method (p = 0.01). There was not a statistical significant difference in the CNBD values between the randomized and the most common sampling method (p = 0.85). CNFL and CNBD values were increased when using the adjusted area compared to the standard area. Additionally, the study found a significant increase in the CNFL and CNBD values when using the manual method compared to the automatic method (p ≤ 0.001).

CONCLUSION

The study demonstrated a significant difference in the CNFL values between the randomized and common sampling method indicating the importance of clear guidelines for the image sampling. The increase in CNFL and CNBD values when using the adjusted cornea area is not surprising. The observed increases in both CNFL and CNBD values when using the manual method of nerve quantification compared to the automatic method are consistent with earlier findings. This study underlines the importance of improving the analysis of the CCM images in order to obtain more objective corneal nerve fibre measurements.

Translational Immunoimaging and Neuroimaging Demonstrate Corneal Neuroimmune Crosstalk

Corneal immunoimaging and neuroimaging approaches facilitate in vivo analyses of the cornea, including high-resolution imaging of corneal immune cells and nerves. This approach facilitates the analyses of underlying immune and nerve alterations not detected by clinical slit-lamp examination alone. In this review, we describe recent work performed in our translational ocular immunology center with a focus on "bench-to-bedside" and "bedside-to-bench" research. The ability to visualize dendritiform immune cells (DCs) in patients with laser in vivo confocal microscopy (IVCM), recently discovered in the central murine cornea, has allowed us to demonstrate their utility as a potential surrogate biomarker for inflammatory ocular surface diseases. This biomarker for inflammation allows the measurement of therapeutic efficacy of anti-inflammatory drugs and its utility as an endpoint in clinical trials with high interobserver agreement. IVCM image analyses from our studies has demonstrated a significant increase in DC density and size in ocular disease, a positive correlation between DC density and clinical signs and symptoms of disease and pro-inflammatory tear cytokines, and a strong negative correlation between DC density and subbasal nerve density. In conjunction with preclinical research investigating the inflammatory state in a partial or fully denervated cornea, our results indicated that corneal nerves are directly involved in the regulation of homeostasis and immune privilege in the cornea.

In Vivo Confocal Microscopy of Corneal Nerves in Health and Disease

In vivo confocal microscopy (IVCM) is becoming an indispensable tool for studying corneal physiology and disease. Enabling the dissection of corneal architecture at a cellular level, this technique offers fast and noninvasive in vivo imaging of the cornea with images comparable to those of ex vivo histochemical techniques. Corneal nerves bear substantial relevance to clinicians and scientists alike, given their pivotal roles in regulation of corneal sensation, maintenance of epithelial integrity, as well as proliferation and promotion of wound healing. Thus, IVCM offers a unique method to study corneal nerve alterations in a myriad of conditions, such as ocular and systemic diseases and following corneal surgery, without altering the tissue microenvironment. Of particular interest has been the correlation of corneal subbasal nerves to their function, which has been studied in normal eyes, contact lens wearers, and patients with keratoconus, infectious keratitis, corneal dystrophies, and neurotrophic keratopathy. Longitudinal studies have applied IVCM to investigate the effects of corneal surgery on nerves, demonstrating their regenerative capacity. IVCM is increasingly important in the diagnosis and management of systemic conditions such as peripheral diabetic neuropathy and, more recently, in ocular diseases. In this review, we outline the principles and applications of IVCM in the study of corneal nerves in various ocular and systemic diseases.

Comparative quantitative assessment of the human corneal sub-basal nerve plexus by in vivo confocal microscopy and histological staining

PurposeThis study was designed to compare and contrast quantitative data of the human corneal sub-basal nerve plexus (SBP) evaluated by two different methods: in vivo confocal microscopy (IVCM), and immunohistochemical staining of ex vivo donor corneas.MethodsSeven parameters of the SBP in large-scale IVCM mosaicking images from healthy subjects were compared with the identical parameters in ex vivo donor corneas stained by β-III-tubulin immunohistochemistry. Corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), average weighted corneal nerve fiber tortuosity (CNFTo), corneal nerve connection points (CNCP), average corneal nerve single-fiber length (CNSFL), and average weighted corneal nerve fiber thickness (CNFTh) were calculated using a dedicated, published algorithm and compared.ResultsOur experiments showed significantly higher values for CNFL (50.2 vs 21.4 mm/mm²), CNFD (1358.8 vs 277.3 nerve fibers/mm²), CNBD (847.6 vs 163.5 branches/mm²), CNFTo (0.095 vs 0.081 μm^-1), and CNCP (49.4 vs 21.6 connections/mm²) in histologically staining specimens compared with IVCM images. In contrast, CNSFL values were higher in IVCM images than in histological specimens (32.1 vs 74.1 μm). No significant difference was observed in CNFTh (2.22 vs 2.20 μm) between the two groups.ConclusionsThe results of this study have shown that IVCM has an inherently lower resolution compared with ex vivo immunohistochemical staining of the corneal SBP and that this limitation leads to a systematic underestimation of several SBP parameters. Despite this shortcoming, IVCM is a vital clinical tool for in vivo characterization, quantitative clinical imaging, and evaluation of the human corneal SBP.

Patients with multiple sclerosis demonstrate reduced subbasal corneal nerve fibre density

BACKGROUND

Many studies in multiple sclerosis (MS) have investigated the retina. Little, however, is known about the effect of MS on the cornea, which is innervated by the trigeminal nerve. It is the site of neural-immune interaction with local dendritic cells reacting in response to environmental stimuli.

OBJECTIVE

This study aims to investigate the effect of MS on corneal nerve fibres and dendritic cells in the subbasal nerve plexus using in vivo confocal microscopy (IVCM).

METHODS

We measured the corneal nerve fibre and dendritic cell density in 26 MS patients and matched healthy controls using a Heidelberg Retina Tomograph with cornea module. Disease severity was assessed with the Multiple Sclerosis Functional Composite, Expanded Disability Status Scale, visual acuity and retinal optical coherence tomography.

RESULTS

We observed significant reduction in total corneal nerve fibre density in MS patients compared to controls. Dendritic cell density was similar in both groups. Reduced total nerve fibre density was associated with worse clinical severity but not with previous clinical trigeminal symptoms, retinal neuro-axonal damage, visual acuity or disease duration.

CONCLUSION

Corneal nerve fibre density is a promising new imaging marker for the assessment of disease severity in MS and should be investigated further.

A Novel Approach to Analyze the Progression of Measured Corneal Sub-Basal Nerve Fiber Length in Continuously Expanding Mosaic Images

Purpose/Aim of the study: A recently proposed technique enables the generation of continuously increasing mosaic images of the corneal sub-basal nerve plexus (SNP) using in vivo corneal confocal microscopy (CCM). The aim of the present study was to investigate the progression of the corneal nerve fiber length (CNFL) measured in the growing mosaic images with regard to their increasing area.

MATERIALS AND METHODS

Five large datasets from three healthy volunteers were examined using the proposed CCM technique. Intermediate mosaic images were created and assessed for CNFL.

RESULTS

The measured CNFL progression shows both over- and underestimation of the CNFL for small observed areas. Increasing the mosaic image area stabilizes the CNFL values and reduces the moving variance in all five datasets. The relative deviation of means from values of first and second examination of two of the subjects shows high differences for an observed area of <1.5 mm².

CONCLUSIONS

The present examination provides two measures to quantify different area-dependent aspects of the CNFL measured in an expanding mosaic image. The moving variance measures how stable the CNFL can be considered at a certain mosaic size. The relative deviation of means from two repeated CCM examinations on the other hand gives some indication on the level of reliability that can be expected from the measured CNFL. The progression of CNFL in the examined datasets manifests a potentially very high variability for mosaic sizes of less than about 1.5 mm². Above that size, CNFL progression and the intra-patient relative deviations both stabilize significantly in all five datasets. The results of the present examination suggest a recommendation for a minimum sampled area of the central SNP of 1.5 mm² for reliable and meaningful measurement of CNFL.

Corneal Epithelial Immune Dendritic Cell Alterations in Subtypes of Dry Eye Disease: A Pilot In Vivo Confocal Microscopic Study

PURPOSE

To evaluate density and morphology of corneal epithelial immune dendritic cells (DCs) in different subtypes of dry eye disease (DED) using in vivo confocal microscopy (IVCM).

METHODS

This retrospective study included 59 eyes of 37 patients with DED and 40 eyes of 20 age-matched healthy controls. Based on clinical tests, eyes with DED were categorized into two subtypes: aqueous-deficient (n = 35) and evaporative (n = 24). For all subjects, images of laser scanning in vivo confocal microscopy (IVCM) of the central cornea were analyzed for DC density and DC morphology (DC size, number of dendrites, and DC field). These DC parameters were compared among all dry eye and control groups.

RESULTS

Compared with the controls, patients with DED had significantly higher DC density, larger DC size, higher number of dendrites, and larger DC field (all P < 0.001). Comparison between aqueous-deficient and evaporative subtypes demonstrated that DC density was significantly higher in aqueous-deficient subtype (189.8 ± 36.9 vs. 58.9 ± 9.4 cells/mm2, P = 0.001). However, there were no significant differences in morphologic parameters between DED subtypes. When aqueous-deficient DED with underlying systemic immune disease (Sjögren's syndrome and graft versus host disease) were compared with nonimmune conditions, the immunologic subgroup showed significantly higher DC density, DC size, and number of dendrites (all P < 0.05).

CONCLUSIONS

Corneal IVCM demonstrated differential changes in DC density and morphologic DC parameters between subtypes of DED. These changes, which reflect the degree of immune activation and inflammation in DED, can be used for clinical practice and endpoints in clinical trials.

Corneal Dendritic Cell Density Is Associated with Subbasal Nerve Plexus Features, Ocular Surface Disease Index, and Serum Vitamin D in Evaporative Dry Eye Disease

Dry eye disease (DED) has evolved into a major public health concern with ocular discomfort and pain being responsible for significant morbidity associated with DED. However, the etiopathological factors contributing to ocular pain associated with DED are not well understood. The current IVCM based study investigated the association between corneal dendritic cell density (DCD), corneal subbasal nerve plexus (SBNP) features, and serum vitamin D and symptoms of evaporative dry eye (EDE). The study included age and sex matched 52 EDE patients and 43 heathy controls. A significant increase in the OSDI scores (discomfort subscale) was observed between EDE (median, 20.8) and control (median, 4.2) cohorts (P < 0.001). Similarly, an increase in DCD was observed between EDE (median, 48.1 cells/mm²) patients and controls (median, 5.6 cells/mm²) (P < 0.001). A significant decrease in SBNP features (corneal nerve fiber length, fiber density, fiber width, total branch density, nerve branch density, and fiber area) was observed in EDE patients with OSDI score >23 (P < 0.05). A positive correlation was observed between DCD and OSDI discomfort subscale (r = 0.348; P < 0.0003) and SBNP features. An inverse correlation was observed between vitamin D and OSDI scores (r = −0.332; P = 0.0095) and DCD with dendritic processes (r = −0.322; P = 0.0122). The findings implicate DCD, SBNP features, and vitamin D with EDE symptoms.