Degeneration and Regeneration of Subbasal Corneal Nerves after Infectious Keratitis: A Longitudinal In Vivo Confocal Microscopy Study

Diagnosing and monitoring the characteristics of Acanthamoeba keratitis using slit scanning and laser scanning in vivo confocal microscopy

INTRODUCTION

Acanthamoeba keratitis (AK) is a serious and potentially blinding ocular infection caused by the free-living amoeba, Acanthamoeba. In vivo confocal microscopy (IVCM) is a non-invasive device which has been proven of great use to diagnose Acanthamoeba infections immediately. The aim of this review was to establish different patterns and signs of AK that appear on the IVCM both before and after treatment.

METHODS

A systematic review of the literature from 1974 until September 2021 was performed using Embase and PubMed, following The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Twenty different signs of AK were observed using IVCM. The included studies used vastly different criteria to diagnose infections, ranging from just 1 to 13 of the signs, demonstrating the current lack of a standardised diagnosis of this infection using the IVCM. The appearance of double wall cysts, trophozoites, signet rings, target signs and clusters were shown to be pathognomonic to AK infections. Bright spots located in the corneal epithelium were demonstrated as non-reliable predictors of AK. The presence of cysts in clusters and single file can predict the need for corneal transplantation. The morphological changes in cysts using the IVCM following treatment were described as breaking down to hollow forms and occasionally surrounded by black cavities. Using this information, a visual guideline for identifying AK signs in diagnosis and follow-up using IVCM was created.

CONCLUSION

Increased awareness of the different signs and patterns of AK that appear on the IVCM is crucial in order to correctly identify an infection and increase the potential of this device. Our guidelines presented here can be used, but further studies are needed in order to determine the relationship and aetiology of these signs and cellular changes on the IVCM both before and after anti-amoeba treatment.

Effect of recombinant human nerve growth factor treatment on corneal nerve regeneration in patients with neurotrophic keratopathy

Introduction

Neurotrophic Keratopathy (NK) is a neurodegenerative corneal disease that results in diminished corneal sensation. Previous studies have found that Cenegermin 0.002%, a recombinant human nerve growth factor (rhNGF), improves corneal epithelial healing in stage 2 and 3 NK patients. However, rhNGF effect on corneal sensation and nerve regeneration has not been well established. Thus, this study aims to analyze the effect of rhNGF on corneal nerve regeneration using in vivo confocal microscopy (IVCM) and on corneal sensitivity in NK patients.

Methods

This is a retrospective, longitudinal, case-control study that included patients with NK, treated with rhNGF for at least 4 weeks, with pre- and post-treatment IVCM images available for analysis. Chart reviews were conducted documenting prior medical and surgical history, clinical signs and symptoms, and corneal sensation using Cochet-Bonnet esthesiometry. Corneal nerve parameters were assessed by IVCM. Sex- and age-matched reference controls were selected from a database of healthy subjects for comparison.

Results

The study included 25 patients, with 22 (88%) stage 1, two (8%) stage 2, and 1 (4%) stage 3 NK patients, with a median age of 64 years (range: 30-93 years). Total, main, and branch nerve densities [median (range) in mm/mm2] were lower in the NK group pre-treatment [2.3 (0.0-21.1); 1.7 (0.0-13.0); 0.5 (0.0-10.2); respectively] vs. controls [22.3 (14.9-29.0); 10.1 (3.2-15.4); and 12.1 (6.2-18.4), (p < 0.0001 for all), respectively]. Post-treatment nerve densities increased compared to pre-treatment to 5.3 (0.0-19.4, p = 0.0083) for total, 3.5 (0.0-13.2, p = 0.0059) for main, and 2.0 (0.0-10.4, p = 0.0251) for branch nerves, but remained lower than controls (p < 0.0001 for all). Corneal sensation increased from 2.3 ± 1.1 cm pre-treatment to 4.1 ± 1.4 cm post-treatment (p = 0.001). Median best corrected visual acuity significantly increased following rhNGF treatment from 0.4 (0.0-1.6) to 0.12 (-0.1 to 1.6) (p = 0.007).

Conclusion

Patients with NK treated with at least 4 weeks of rhNGF, showed a significant increase in corneal nerve densities after treatment. A significant increase in corneal sensation, as well as best corrected visual acuity, was observed following treatment.

Corneal nerve regeneration is affected by scar location in herpes simplex keratitis: A longitudinal in vivo confocal microscopy study

PURPOSE

To assess the effect of corneal scar location on corneal nerve regeneration in patients with herpes simplex virus (HSV) keratitis in their affected and contralateral eyes over a 1-year period by in vivo confocal microscopy (IVCM), and to correlate these findings to corneal sensation measured by Cochet-Bonnet Esthesiometer.

METHODS

Prospective, longitudinal, case-control study. Bilateral corneal nerve density and corneal sensation were analyzed centrally and peripherally in 24 healthy controls and 23 patients with unilateral HSV-related corneal scars using IVCM.

RESULTS

In the central scar (CS) group, total nerve density in the central cornea remained significantly lower compared to controls at follow-up (11.05 ± 1.97mm/mm2, p < 0.001), and no significant nerve regeneration was observed (p = 0.090). At follow-up, total nerve density was not significantly different from controls in the central and peripheral cornea of the peripheral scar (PS) group (all p > 0.05), but significant nerve regeneration was observed in central corneas (16.39 ± 2.39mm/mm2, p = 0.007) compared to baseline. In contralateral eyes, no significant corneal nerve regeneration was observed in central or peripheral corneas of patients with central scars or peripheral scars at 1-year follow-up, compared to baseline (p > 0.05). There was a positive correlation between corneal nerve density and sensation in both central (R = 0.53, p < 0.0001) and peripheral corneas (R = 0.27, p = 0.0004). In the CS group, the corneal sensitivity was <4 cm in 4 (30.8%) and 7 (53.8%) patients in the central and peripheral corneas at baseline, and in 5 (38.5%) and 2 subjects (15.4%) at follow-up, whereas in the PS group only 1 patient (10%) showed a corneal sensation < 4 cm in the central cornea at baseline, and only 1 (10.0%), 3 (30.0%) and 1 (10.0%) patients at follow-up in the central, affected and opposite area of the cornea, respectively.

CONCLUSION

The location of HSV scarring in the cornea affects the level of corneal nerve regeneration. Eyes with central corneal scar have a diminished capacity to regenerate nerves in central cornea, show a more severe reduction in corneal sensation in the central and peripheral corneas that persist at follow-up, and have a reduced capability to restore the corneal sensitivity above the cut-off of 4 cm. Thus, clinicians should be aware that CS patients would benefit from closer monitoring for potential complications associated with neurotrophic keratopathy, as they have a lower likelihood for nerve regeneration.

Identifying Meibomian Gland Dysfunction Biomarkers in a Cohort of Patients Affected by DM Type II

(1) Background: Meibomian gland dysfunction (MGD) among patients with diabetes mellitus (DM) is a common manifestation of dry eye syndrome (DES). (2) Methods: The purpose of this study is to identify clinical parameters and biomarkers useful to improve the follow-up and the treatment of these patients. We have used an ocular surface disease index (OSDI) questionnaire, Schirmer test I/II, tear film break-up time (TF-BUT), fluorescein plus lissamine green staining, Marx's line (ML), and meibomian gland (MGs) morphology using Sirius^® Topographer (CSO, Costruzione Strumenti Oftalmici, Florence, Italy). Blood sample analysis included glucose, glycated hemoglobin, lipid profile, cortisol, dehydroepiandrosterone sulfate (DHEA-S), androstenedione (ASD) and testosterone. (3) Results: Cortisol and ASD were positively correlated with an increase of MG tortuosity, and an Increased level of triglycerides was associated with a reduction of MGs length. DHEAS levels lowered with age and were associated with ocular surface staining. (4) Conclusions: Future studies, perhaps including meibum lipid analysis and tear cytokine levels, may also further elucidate the connection between these parameters, MG architecture and function.

Clinical Observation of Corneal Endothelial Plaques With Fungal and Bacterial Keratitis by Anterior Segment Optical Coherence Tomography and In Vivo Confocal Microscopy

PURPOSE

Endothelial plaque is an important sign of fungal keratitis and is related to diagnosis, surgical indications, and prognosis. However, bacterial keratitis sometimes involves fibrin formation on the back corneal surface, similar to endothelial plaques. Because corneal infiltration interferes with precise observation of the posterior corneal plaque, distinguishing pathogens with a slitlamp is difficult. We hope to assist clinicians in early diagnosis and timely treatment by observing the connection state of endothelial plaques and the corneal endothelium through anterior segment optical coherence tomography (AS-OCT) and the different forms of endothelial plaques in infectious keratopathy through in vivo confocal microscopy (IVCM).

METHODS

We analyzed 52 patients in the Eye Hospital of the First Affiliated Hospital of Harbin Medical University who were clearly diagnosed with fungal or bacterial keratitis with endothelial plaques. All patients underwent AS-OCT and IVCM on admission.

RESULTS

According to the smear, IVCM, or fungal and bacterial culture results, the patients were diagnosed with fungal (28 patients) or bacterial keratitis (24 patients). AS-OCT in 25 patients diagnosed with fungal keratitis revealed that the corneal endothelium-endothelial plaque boundary was unclear and wavy, and 24 patients had unclear cell boundaries and a large number of compactly distributed inflammatory cells in the endothelial layer according to IVCM. AS-OCT in 23 patients diagnosed with bacterial keratitis revealed clear corneal endothelium-endothelial plaque boundaries, and insufficient endothelial cell boundaries with a large number of visible and scattered inflammatory cell structures were observed through IVCM in 22 patients.

CONCLUSIONS

Corneal endothelial plaque detection by AS-OCT and IVCM can be used for early diagnosis of infectious keratitis.

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.

A history of over 40 years of potentially pathogenic free-living amoeba studies in Brazil - a systematic review

Free-living amoeba (FLA) group includes the potentially pathogenic genera Acanthamoeba, Naegleria, Balamuthia, Sappinia, and Vermamoeba, causative agents of human infections (encephalitis, keratitis, and disseminated diseases). In Brazil, the first report on pathogenic FLA was published in the 70s and showed meningoencephalitis caused by Naegleria spp. FLA studies are emerging, but no literature review is available to investigate this trend in Brazil critically. Thus, the present work aims to integrate and discuss these data. Scopus, PubMed, and Web of Science were searched, retrieving studies from 1974 to 2020. The screening process resulted in 178 papers, which were clustered into core and auxiliary classes and sorted into five categories: wet-bench studies, dry-bench studies, clinical reports, environmental identifications, and literature reviews. The papers dating from the last ten years account for 75% (134/178) of the total publications, indicating the FLA topic has gained Brazilian interest. Moreover, 81% (144/178) address Acanthamoeba-related matter, revealing this genus as the most prevalent in all categories. Brazil’s Southeast, South, and Midwest geographic regions accounted for 96% (171/178) of the publications studied in the present work. To the best of our knowledge, this review is the pioneer in summarising the FLA research history in Brazil.

Clinicopathological Correlation of Microbial Keratitis and Ahead: Is There a Corneal Sepsis?

Microbial, infectious keratitis is a relevant indication for penetrating keratoplasty. The requirement for transplantation results in histopathological examination of the entire thickness of the cornea. Although the clinical diagnosis is not always possible to confirm, pathology can support diagnostic evidence of clinical presentation and pathogenesis. This is achieved with multiple methods from cytology, histochemistry, immunohistology, molecular pathology and in rare cases electron microscopy. These allow tissue-based detection of previous and parallel diseases and the responsible pathogens. The failure of satisfactory clinicopathological correlation raises the question whether a suspected pathogen was not ultimately responsible for destroyed corneal tissue. The pathogenesis of keratitis requiring transplantation is not yet completely understood, also on the experimental level. The development of such a keratitis can lead to a clinical symptomatology which can be described as "threatening organ dysfunction", a term used in sepsis research. Considering recent literature, possible correlations between sepsis and microbial keratitis and their relation to histopathology are discussed.

The use of in vivo confocal microscopy in fungal keratitis - Progress and challenges

Fungal keratitis (FK) is a serious and sight-threatening corneal infection with global reach. The need for prompt diagnosis is paramount, as a delay in initiation of treatment could lead to irreversible vision loss. Current "gold standard" diagnostic methods, namely corneal smear and culture, have limitations due to diagnostic insensitivity and their time-consuming nature. PCR is a newer, complementary method used in the diagnosis of fungal keratitis, whose results are also sample-dependent. In vivo confocal microscopy (IVCM) is a promising complementary diagnostic method of increasing importance as it allows non-invasive real-time direct visualization of potential fungal pathogens and manifesting infection directly in the patient's cornea. In numerous articles and case reports, FK diagnosis by IVCM has been evaluated, and different features, approaches, sensitivity/specificity, and limitations have been noted. Here, we provide an up-to-date, comprehensive review of the current literature and present the authors' combined recommendations for fungal identification in IVCM images, while also looking to the future of FK assessment by IVCM using artificial intelligence methods.

Epidemiology of Corneal Neovascularization and Its Impact on Visual Acuity and Sensitivity: A 14-Year Retrospective Study

Purpose: To quantify the severity and location of corneal neovascularization (cNV) and its impact on the visual acuity and corneal sensitivity in a cohort of the patients referred to a specialist cornea clinic and also to describe the etiology of cNV in the cohort.

Methods: We retrospectively evaluated the charts of 13,493 subjects referred to the San Raffaele Cornea Unit between January 2004 and December 2018 to search for cNV diagnosis. The corneal neovascularization severity was measured in the quadrants (range: 1–4) and location was defined as superficial, deep, or both. Best spectacle corrected visual acuity (BSCVA) was measured in logMar. We used the multiple regression analysis to identify the independent predictors of logMAR, after adjusting for age, gender, keratoconus, herpes keratitis, penetrating keratoplasty, trauma, and cataract surgery.

Results: Corneal neovascularization was diagnosed in 10.4% of the patients analyzed. The most prevalent etiology of cNV in our population was non-infectious corneal dystrophies/degenerations followed by herpes simplex virus infection. cNV affected OD, OS, or both eyes in 35.6, 40.2, and 24.2 of cases, respectively. Mean BSCVA (SD) was 0.59 (0.76), 0.74 (0.94), and 1.24 (1.08) in cNV one, two, and three or four of the quadrant groups. Superficial, deep, or mixed cNV occurred in 1,029, 348, and 205 eyes. Severe cNV (three or four of the quadrants) was a significant predictor of low visual acuity (p < 0.001) and reduced corneal sensitivity (p < 0.05). cNV location and its severity were associated (p < 0.05). In addition, corneal anesthesia was associated with lower BSCVA (p < 0.001).

Conclusion: Severe and deep cNV are associated with the reduced visual acuity and corneal sensitivity. Our data strongly support the relevance of appropriate follow-up as cNV is a major risk factor for graft rejection.

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

Purpose

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

Patients and Methods

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

Results

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

Conclusion

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

Multi-discriminator adversarial convolutional network for nerve fiber segmentation in confocal corneal microscopy images

Quantitative measurements of corneal sub-basal nerves are biomarkers for many ocular surface disorders, and are also important for early diagnosis and assessment of progression of neurodegenerative diseases. This paper aims to develop an automatic method for nerve fiber segmentation from in vivo corneal confocal microscopy (CCM) images, which is fundamental for nerve morphology quantification. A novel multi-discriminator adversarial convolutional network (MDACN) is proposed, where both the generator and the two discriminators emphasize multi-scale feature representations. The generator is a U-shaped fully convolutional network with multi-scale split and concatenate blocks, and the two discriminators have different effective receptive fields, sensitive to features of different scales. A novel loss function is also proposed which enables the network to pay more attention to thin fibers. The MDACN framework was evaluated on four datasets. Experiment results show that our method has excellent segmentation performance for corneal nerve fibers and outperforms some state-of-the-art methods.

Production of the Cytokine VEGF-A by CD4+ T and Myeloid Cells Disrupts the Corneal Nerve Landscape and Promotes Herpes Stromal Keratitis

Herpes simplex virus type 1 (HSV-1)-infected corneas can develop a blinding immunoinflammatory condition called herpes stromal keratitis (HSK), which involves the loss of corneal sensitivity due to retraction of sensory nerves and subsequent hyperinnervation with sympathetic nerves. Increased concentrations of the cytokine VEGF-A in the cornea are associated with HSK severity. Here, we examined the impact of VEGF-A on neurologic changes that underly HSK using a mouse model of HSV-1 corneal infection. Both CD4⁺ T cells and myeloid cells produced pathogenic levels of VEGF-A within HSV-1-infected corneas, and CD4⁺ cell depletion promoted reinnervation of HSK corneas with sensory nerves. In vitro, VEGF-A from infected corneas repressed sensory nerve growth and promoted sympathetic nerve growth. Neutralizing VEGF-A in vivo using bevacizumab inhibited sympathetic innervation, promoted sensory nerve regeneration, and alleviated disease. Thus, VEGF-A can shape the sensory and sympathetic nerve landscape within the cornea, with implications for the treatment of blinding corneal disease.

Neuronal-epithelial cell alignment: A determinant of health and disease status of the cornea

PURPOSE

How sensory neurons and epithelial cells interact with one another, and whether this association can be considered an indicator of health or disease is yet to be elucidated.

METHODS

Herein, we used the cornea, Confetti mice, a novel image segmentation algorithm for intraepithelial corneal nerves which was compared to and validated against several other analytical platforms, and three mouse models to delineate this paradigm. For aging, eyes were collected from 2 to 52 week-old normal C57BL/6 mice (n ≥ 4/time-point). For wound-healing and limbal stem cell deficiency, 7 week-old mice received a limbal-sparing or limbal-to-limbal epithelial debridement to their right cornea, respectively. Eyes were collected 2-16 weeks post-injury (n=4/group/time-point), corneas procured, immunolabelled with βIII-tubulin, flat-mounted, imaged by scanning confocal microscopy and analyzed for nerve and epithelial-specific parameters.

RESULTS

Our data indicate that nerve features are dynamic during aging and their curvilinear arrangement align with corneal epithelial migratory tracks. Moderate corneal injury prompted axonal regeneration and recovery of nerve fiber features. Limbal stem cell deficient corneas displayed abnormal nerve morphology, and fibers no longer aligned with corneal epithelial migratory tracks. Mechanistically, we discovered that nerve pattern restoration relies on the number and distribution of stromal-epithelial nerve penetration sites.

CONCLUSIONS

Microstructural changes to innervation may explain corneal complications related to aging and/or disease and facilitate development of new assays for diagnosis and/or classification of ocular and systemic diseases.

Application of Artificial Intelligence in the Diagnosis and Management of Corneal Diseases

Diagnosis and treatment planning in ophthalmology heavily depend on clinical examination and advanced imaging modalities, which can be time-consuming and carry the risk of human error. Artificial intelligence (AI) and deep learning (DL) are being used in different fields of ophthalmology and in particular, when running diagnostics and predicting outcomes of anterior segment surgeries. This review will evaluate the recent developments in AI for diagnostics, surgical interventions, and prognosis of corneal diseases. It also provides a brief overview of the newer AI dependent modalities in corneal diseases.

Corneal Nerve Abnormalities in Ocular and Systemic Diseases

The trigeminal nerve gives rise to the corneal subbasal nerve system, which plays a crucial role in sensations of touch, pain, and temperature and in ocular healing processes. Technological advancements in instruments, in particular in vivo confocal microscopy and aethesiometry, have allowed for the structural and functional evaluation of corneal nerves in health and disease. Through application of these technologies in humans and animal models, structural and functional abnormalities have been detected in several ocular and systemic disorders, including dry eye disease (DED), glaucoma, migraine, and fibromyalgia. However, studies across a number of conditions have found that structural abnormalities do not always relate to functional abnormalities. This review will discuss instruments used to evaluate corneal nerves and summarize data on nerve abnormalities in a number of ocular and systemic conditions. Furthermore, it will discuss potential treatments that can alleviate the main manifestations of nerve dysfunction, namely ocular surface pain and persistent epithelial defects.

In Vivo Confocal Microscopy Morphologic Features and Cyst Density in Acanthamoeba Keratitis

PURPOSE

To correlate in vivo confocal microscopy morphologic features (IVCM-MF) and Acanthamoeba cyst density (ACD) with final best-corrected visual acuity (BCVA) in Acanthamoeba keratitis (AK).

DESIGN

Retrospective cohort study.

METHODS

Patient demographics, treatment outcome, and corresponding IVCM-MF performed at the acute stage of infection were analyzed. Inclusion criteria were microbiological positive AK cases seen at Moorfields Eye Hospital between February 2013 and October 2017. Statistical significance was assessed by multinomial regression and multiple linear regression analysis. Main outcome measure was final BCVA.

RESULTS

A total of 157 eyes (157 patients) had AK. Absence of single-file round/ovoid objects was associated with a BCVA of 6/36 to 6/9 (odds ratio [OR] 8.13; 95% confidence interval [CI], 1.55-42.56, P = .013) and ≥6/6 (OR 10.50; 95% CI, 2.12-51.92, P = .004) when compared to no perception of light to 6/60. Absence of rod/spindle objects was associated with a BCVA of ≥6/6 (OR 4.55; 95% CI, 1.01-20.45, P = .048). Deep stromal/ring infiltrate was associated with single-file round/ovoid objects (OR 7.78; 95% CI, 2.69-22.35, P < .001), rod/spindle objects (OR 7.05; 95% CI, 2.11-23.59, P = .002), and binary round/ovoid objects (OR 3.45; 95% CI, 1.17-10.14, P = .024). There was a positive association between ACD and treatment duration (β = 0.14, P = .049), number of IVCM-MF (β = 0.34, P = .021), and clusters of round/ovoid objects (β = 0.29, P = .002).

CONCLUSIONS

Specific IVCM-MF correlate with ACD and clinical staging of disease, and are prognostic indicators for a poorer visual outcome.

Plasmacytoid dendritic cells in the eye

Plasmacytoid dendritic cells (pDCs) are a unique subpopulation of immune cells, distinct from classical dendritic cells. pDCs are generated in the bone marrow and following development, they typically home to secondary lymphoid tissues. While peripheral tissues are generally devoid of pDCs during steady state, few tissues, including the lung, kidney, vagina, and in particular ocular tissues harbor resident pDCs. pDCs were originally appreciated for their potential to produce large quantities of type I interferons in viral immunity. Subsequent studies have now unraveled their pivotal role in mediating immune responses, in particular in the induction of tolerance. In this review, we summarize our current knowledge on pDCs in ocular tissues in both mice and humans, in particular in the cornea, limbus, conjunctiva, choroid, retina, and lacrimal gland. Further, we will review our current understanding on the significance of pDCs in ameliorating inflammatory responses during herpes simplex virus keratitis, sterile inflammation, and corneal transplantation. Moreover, we describe their novel and pivotal neuroprotective role, their key function in preserving corneal angiogenic privilege, as well as their potential application as a cell-based therapy for ocular diseases.

Visualization of microneuromas by using in vivo confocal microscopy: An objective biomarker for the diagnosis of neuropathic corneal pain?

PURPOSE

The diagnosis of neuropathic corneal pain (NCP) is challenging, as it is often difficult to differentiate it from conventional dry eye disease (DED). In addition to eye pain, NCP can present with similar signs and symptoms of DED. The purpose of this study is to find an objective diagnostic sign to identify patients with NCP, using in vivo confocal microscopy (IVCM).

METHODS

This was a comparative, retrospective, case-control study. Patients with clinical diagnosis of NCP (n = 25), DED (n = 30), and age- and sex-matched healthy controls (n = 16), who underwent corneal imaging with IVCM (HRT3/RCM) were included. Central corneal IVCM scans were analyzed by 2 masked observers for nerve density and number, presence of microneuromas (terminal enlargements of subbasal corneal nerve) and/or nerve beading (bead-like formation along the nerves), and dendritiform cell (DC) density.

RESULTS

There was a decrease in total nerve density in both NCP (14.14 ± 1.03 mm/mm²) and DED patients (12.86 ± 1.04 mm/mm²), as compared to normal controls (23.90 ± 0.92 mm/mm²; p < 0.001). However, total nerve density was not statistically different between NCP and DED patients (p = 0.63). Presence of nerve beading was not significantly different between patients and normal controls (p = 0.15). Interestingly, microneuromas were observed in all patients with NCP, while they were not present in any of the patients with conventional DED (sensitivity and specificity of 100%). DC density was significantly increased in both NCP (71.89 ± 16.91 cells/mm²) and DED patients (111.5 ± 23.86 cells/mm²), as compared to normal controls (24.81 ± 4.48 cells/mm² (p < 0.05). However, there was no significant difference in DC density between DED and NCP patients (p = 0.31).

CONCLUSION

IVCM may be used as an adjunct diagnostic tool for the diagnosis of NCP in the presence of neuropathic symptoms. Microneuromas may serve as a sensitive and specific biomarker for the diagnosis of NCP.

A Deep Learning Model for Automated Sub-Basal Corneal Nerve Segmentation and Evaluation Using In Vivo Confocal Microscopy

Purpose

The purpose of this study was to establish a deep learning model for automated sub-basal corneal nerve fiber (CNF) segmentation and evaluation with in vivo confocal microscopy (IVCM).

Methods

A corneal nerve segmentation network (CNS-Net) was established with convolutional neural networks based on a deep learning algorithm for sub-basal corneal nerve segmentation and evaluation. CNS-Net was trained with 552 and tested on 139 labeled IVCM images as supervision information collected from July 2017 to December 2018 in Peking University Third Hospital. These images were labeled by three senior ophthalmologists with ImageJ software and then considered ground truth. The areas under the receiver operating characteristic curves (AUCs), mean average precision (mAP), sensitivity, and specificity were applied to evaluate the efficiency of corneal nerve segmentation. The relative deviation ratio (RDR) was leveraged to evaluate the accuracy of the corneal nerve fiber length (CNFL) evaluation task.

Results

The model achieved an AUC of 0.96 (95% confidence interval [CI] = 0.935-0.983) and an mAP of 94% with minimum dice coefficient loss at 0.12. For our dataset, the sensitivity was 96% and specificity was 75% in the CNF segmentation task, and an RDR of 16% was reported in the CNFL evaluation task. Moreover, the model was able to segment and evaluate as many as 32 images per second, much faster than skilled ophthalmologists.

Conclusions

We established a deep learning model, CNS-Net, which demonstrated a high accuracy and fast speed in sub-basal corneal nerve segmentation with IVCM. The results highlight the potential of the system in assisting clinical practice for corneal nerves segmentation and evaluation.

Translational Relevance

The deep learning model for IVCM images may enable rapid segmentation and evaluation of the corneal nerve and may provide the basis for the diagnosis and treatment of ocular surface diseases associated with corneal nerves.

Use of white light in vivo confocal microscopy for the detection of spatial changes in the corneal nerves in cases of early-stage Acanthamoeba keratitis with radial keratoneuritis

Purpose:

Radial keratoneuritis (RK) is a common feature of Acanthamoeba keratitis (AK). In vivo confocal microscopy (IVCM) is noninvasive and provides real-time images for the diagnosis of corneal diseases by allowing the visualization of corneal structures and morphologies of living organisms at the cellular level. Images of AK with RK obtained using commercial white light IVCM devices have not been frequently evaluated. In the present study, a white light IVCM device was used to evaluate the corneal findings and describe spatial changes in the corneal nerves at different depths in cases of early-stage AK with RK.

Methods:

In this retrospective, observational study, white light IVCM images focused on RK were evaluated for Acanthamoeba cysts/trophozoites, corneal deposits, and altered corneal nerves, with special emphasis on three-dimensional spatial changes in the corneal nerves at different depths.

Results:

Seventeen eyes of 17 patients exhibiting early-stage AK with RK were included in the study. Acanthamoeba cysts/trophozoites were observed in the corneal epithelium of 13 eyes and stroma of 7 eyes. Alterations in the corneal nerve morphology and density were observed from the basal epithelial layer to the stromal layer in 12 eyes. Acanthamoeba trophozoites were attached to the corneal stromal nerves in five eyes.

Conclusion:

These findings suggest that white light IVCM can identify consistent corneal findings, particularly spatial changes in the corneal nerves, in cases of early-stage AK with RK.

Stromal Nerve Imaging and Tracking Using Micro-Optical Coherence Tomography

Purpose

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

Methods

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

Results

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

Conclusions

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

Translational Relevance

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

Central corneal basal cell density and nerve parameters in ocular surface disease and limbal stem cell deficiency: a review and meta-analysis

OBJECTIVE

To conduct a review and meta-analysis for investigating the relative reduction of central corneal basal cell density (BCD) and nerve parameters in ocular surface disease (OSD) and limbal stem cell deficiency (LSCD).

METHODS

A systematic literature search using the terms ((1) "ocular surface disease" or "ocular surface disorder"; (2) "in vivo confocal microscopy"; (3) "limbal stem cell deficiency"; (4) "basal cell density" or "corneal basal cell density" or "central corneal basal cell density"; (5) "corneal nerves" or "corneal nerve parameters" or "central corneal nerve parameters") was performed. The results are presented as weighted mean difference (WMD) with corresponding 95% CI.

RESULTS

16 studies that reported the central corneal BCD and 21 studies that reported the central corneal nerve parameters in OSD (including LSCD) were included. A significant reduction in central corneal BCD was observed in patients with various OSDs (WMD=-9.50, 95% CI -14.04 to -4.97, p<0.01) as well as in patients with LSCD (WMD=-22.14, 95% CI -37.91 to -6.37, p<0.01) compared with healthy controls, however, no significant difference in BCD was observed between the two groups (WMD=-11.61, 95% CI -15.96 to -7.26, p=0.13). There was no conclusive difference in various central corneal nerve parameters between OSDs and LSCD.

CONCLUSION

Central corneal BCD and nerve parameters are reduced in LSCD, there is a similar reduction in other OSDs.

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.

Healing characteristics of acellular porcine corneal stroma following therapeutic keratoplasty

BACKGROUND

Acellular porcine corneal stroma (APCS) has proven to be a promising alternative to traditional corneal grafts. This prospective case series was conducted to further investigate the healing characteristics of APCS following keratoplasty.

METHODS

Twenty-seven patients undergoing APCS implantation to treat infectious keratitis were included. The patients were followed up for 12 months after surgery. The main outcome measures included visual acuity, corneal transparency, graft thickness, and cellular and nerve regeneration.

RESULTS

In the operated eyes, the best-corrected visual acuity (BCVA, in logarithm of the minimal angle of resolution [logMAR] units) increased from 1.23 ± 0.95 logMAR before surgery to 0.23 ± 0.18 logMAR at 12 months after surgery (P < .001). The contrast sensitivity was still evidently reduced, especially at higher spatial frequencies. Gradual transparency improvement was observed in APCS grafts post-operatively. After implantation, the APCS graft thickness initially increased (day 1 = 592.41 ± 52.69 µm) but then continuously decreased until 3 months after surgery (1 month = 449.26 ± 50.38 µm; 3 months = 359.63 ± 34.14 µm, P < .001). Graft reepithelialization was completed within 1 week. In the in vivo confocal microscopy scans, host keratocytes began to repopulate the APCS grafts between 3 and 6 months post-operatively; subbasal nerve regeneration was only noted in 18.52% (5/27) of the eyes by 12 months after surgery.

CONCLUSIONS

Acellular porcine corneal stroma functions as an effective alternative to human corneal tissue in lamellar keratoplasty. However, APCS is somewhat different from fresh human cornea in term of the post-operative healing process, which warrants the attention of both clinicians and patients.

The PACAP-derived peptide MPAPO facilitates corneal wound healing by promoting corneal epithelial cell proliferation and trigeminal ganglion cell axon regeneration

It is well known that the cornea plays an important role in providing protection to the eye, but it is fragile and vulnerable. To clarify the biological effects and molecular mechanisms of the pituitary adenylate cyclase activating polypeptide (PACAP)-derived peptide MPAPO (named MPAPO) to promote corneal wound healing, we applied a mechanical method to establish a corneal injury model and analyzed the repair effects of MPAPO on corneal injury. MPAPO significantly promoted corneal wound repair in C57BL/6 mice. In addition, we established injury models of epithelial cells and trigeminal ganglion cells with H₂O₂. The results show that when the concentration of MPAPO is 1 μM, it can significantly promote the repair of injured corneal epithelial cells and the regeneration of trigeminal ganglion cell axons. MPAPO repairs epithelial cells through the promotion of GSK3β phosphorylation by binding to PAC1 and activating AKT. β-catenin escapes the phosphorylation of GSK3β and enters the nucleus to promote the expression of cyclin D1, accelerate cell cycle progression and promote cell proliferation. MPAPO promotes axonal regeneration by binding to the PAC1 receptor and activating adenylate cyclase activity, followed by the cAMP activation of protein kinase A activity and the promotion of CREB phosphorylation. Phosphorylated CREB promotes Bcl₂ expression and axonal regeneration. In conclusion, our data support the role of MPAPO to facilitate corneal wound healing by promoting corneal epithelial cell proliferation and trigeminal ganglion cell axon regeneration.

In Vivo Confocal Microscopy Demonstrates Increased Immune Cell Densities in Corneal Graft Rejection Correlating With Signs and Symptoms

PURPOSE

Diagnosis of graft rejection is based on patient symptoms and on clinical signs detected by slit-lamp biomicroscopy. This study investigated whether laser in vivo confocal microscopy (IVCM) can aid in the diagnosis of corneal graft rejection by detecting cellular corneal changes that take place after transplantation.

DESIGN

Prospective case-control study.

SUBJECTS

Thirty-eight eyes of 38 patients with penetrating keratoplasty (15 eyes with corneal graft rejection, 23 eyes without rejection) and 9 age-matched normal controls.

METHODS

Laser IVCM was performed in the corneal grafts centrally. The density of immune cells (IC) was assessed for epithelial, sub-epithelial, stromal, and endothelial layers by 2 masked observers. IC density was compared among different groups and correlated to clinical signs and symptoms of corneal graft rejection.

MAIN OUTCOME MEASUREMENTS

Outcome measurement was the IC density in the corneal layers and its associations with the presence of clinical signs and symptoms of corneal graft rejection.

RESULTS

The IC density was significantly different between rejected and non-rejected grafts (P = 0.004) and different from that of normal controls (P = 0.001). Among corneal layers, IC density was significantly higher in rejected grafts than in non-rejected grafts in only the sub-basal (611.54 ± 573.74 vs. 340.61 ± 268.60 cells/mm², respectively; P = 0.049) and endothelial layers (250.62 ± 267.13 vs. 103.47 ± 81.91 cells/mm², respectively; P = 0.001). Patients with decreased best corrected visual acuity, Khodadoust line, and anterior chamber cells demonstrated a significant increase in total IC density (P < 0.05), whereas patients with symptoms of irritation, light sensitivity, and pain revealed a specific increase in IC density in the sub-basal layer (P < 0.05). Patients with ocular pain had higher IC density in the epithelial layer than those without pain (P = 0.03).

CONCLUSIONS

Patients with corneal graft rejection demonstrate a significant increase in corneal immune cells, particularly, in the sub-basal and endothelial layers compared to patients with non-rejected grafts and controls. Although symptoms associated with endothelial rejection demonstrate a general increase in IC, pain, irritation, and light sensitivity are associated with increased IC in the sub-basal layer. Assessment of patients with corneal graft rejection by IVCM may serve as an adjunctive tool in the diagnosis and management of corneal graft rejection.

Degeneration of Corneal Sensation and Innervation in Patients with Facial Paralysis: A Cross-Sectional Study Using in Vivo Confocal Microscopy

Purpose: Facial paralysis (FP) leads to diverse periocular complications which threats visual acuity and affects corneal nerve functionally and morphologically. This study aims to summarize the clinical ophthalmic outcomes, corneal sensation, and morphological alterations of subbasal nerve and dendritic cells (DCs) in patients with facial paralysis.Methods: We performed a cross-sectional study of 48 consecutive patients with facial paralysis at one tertiary hospital. Forty-eight healthy participants were enrolled as controls. The images of corneal nerves and epithelial DCs were detected by in vivo confocal microscopy (IVCM). Each patient received thorough ophthalmic examination, tear film function tests, corneal fluorescence staining and Cochet-Bonnet esthesiometry test. Clinical and morphologic data were compared with controls.Results: Forty patients (83.3%) showed corneal injuries from punctate epithelial defects to corneal ulcers and scars. Visual impairment and eyelid malposition were observed. Corneal sensitivity remarkably decreased (25.1 ± 23.8 mm) in the affected eyes and was correlated to diminished subbasal nerve density (P = .019, r = 0.387). Numbers of corneal main nerve trunks and branches were significantly reduced (P < .0001) while DCs were increased (P < .0001) in patients with FP when compared with controls. Nerve fiber density showed inverse association with DC density (P = .019, r = -0.389).Conclusions: Ocular complications including corneal erosions, loss of corneal sensation, visual impairment and eyelid malposition have largely affected patients with facial paralysis. Morphological changes of diminished corneal subbasal nerve and increased DCs were detected by IVCM. Corneal epithelial defect, corneal opacity, corneal sensation, dendritic cell density are factors associated with corneal subbasal nerve density. Patients with FP are suggested to have complete ophthalmic evaluation and early instruction on ocular prevention.

Corneal subbasal nerve plexus changes in patients with episodic migraine: an in vivo confocal microscopy study

Background and purpose: It has been generally thought that activation and sensitization of the trigeminovascular system may contribute to the pathogenesis of migraine. Nevertheless, there is little evidence on abnormalities in peripheral trigeminal afferent nerves from humans in vivo. Alterations of corneal nerves from the ophthalmic branch of the trigeminal nerve may support the notion that trigeminal afferent nerves are involved in migraine pathophysiology. The aim of the present study was to investigate the structural changes in corneal subbasal nerve plexus in patients with episodic migraine (EM) with in vivo confocal microscope (IVCM).

Methods: In this cross-sectional observational study, 10 EM patients and 10 age- and sex-matched healthy controls were included. Analysis of IVCM images with Image J software was performed to quantify the changes in the corneal subbasal nerve plexus.

Results: EM patients showed an increase in nerve fiber length (25.0±2.65 vs 22.3±2.41 mm/mm², p=0.047) and nerve fiber density (36.3±7.29 vs 30.5±6.19 fibers/mm², p=0.104) as compared with normal controls, but this difference was not statistically significant. Nerve branching and tortuosity were significantly increased in the EM subjects compared to the normal subjects (91.3±13.8 vs 75.0±14.2 branches/mm², p=0.030 and 2.30±0.46 versus 1.63±0.52, p=0.011, respectively). In addition, nerve sprouts and increased number of Langerhans cells were observed in the EM patients.

Conclusion: The morphologic changes of corneal subbasal nerve plexus and Langerhans cell aggregation suggest the presence of nerve regeneration and inflammation in EM. Furthermore, the alterations of corneal nerves from the ophthalmic branch of the trigeminal nerve offer support for the hypothesis that the peripheral trigeminal system may be involved in the pathogenesis of migraine.

Corneal esthesiometry and sub-basal nerves morphological changes in herpes simplex virus keratitis/uveitis patients

AIM

To describe and compare corneal sensation and morphological changes of sub-basal corneal nerves by in vivo laser scanning confocal microscopy (LSCM) in herpes simplex virus (HSV) keratitis/uveitis and contralateral, clinically unaffected eyes.

METHODS

A prospective clinical study included 30 HSV eyes and 30 contralateral eyes of 30 patients, diagnosed with unilateral HSV keratitis/uveitis. Both eyes underwent a complete ophthalmological examination, Cochet-Bonnet aesthesiometry and LSCM of the central cornea, using the Heidelberg Retina Tomograph III Rostock Cornea Module. After 6mo, the same examination of the HSV affected and contralateral, clinically unaffected eyes was performed.

RESULTS

HSV eyes, as compared to contralateral eyes, demonstrated a significant decrease in mean corneal sensation (3.1±1.6 vs 5.3±0.8 cm), total nerve fibres number (5.7±4.4 vs 15.1±5.4), nerve branches (3.4±3.0 vs 8.4±4.7), main nerve trunks (2.3±1.6 vs 5.8±2.2), and nerve fibres density (7.5±5.6 vs 18.1±5.3 mm/mm², P<0.05). There was no significant difference between keratitis and uveitis eyes in mean corneal sensation and nerve fibres parameters. After 6mo, corneal sensation and sub-basal nerve fibres parameters were increased significantly, but did not reach the parameters of contralateral, clinically unaffected eyes.

CONCLUSION

Corneal aesthesiometry and LSCM in HSV affected eyes reveals a significant decrease of corneal sensation and sub-basal nerve fibres which recovers at 6mo but does not reach the normal level.

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.

Understanding the Role of Pro-resolving Lipid Mediators in Infectious Keratitis

Keratitis is a sight-threatening inflammatory condition of the cornea that can be caused by both infectious and non-infectious agents. Physical or chemical trauma are typically related to non-infectious keratitis, which may then become secondarily infected or remain non-infected. Etiology of infectious keratitis is most often associated with bacteria; but viruses, fungi, and parasites are common causative pathogens as well. As a global concern, common risk factors include: systemic immunosuppression (secondary to malnutrition, alcoholism, diabetes, steroid use), previous corneal surgery (refractive corneal surgery, penetrating keratoplasty), extended wear contact lens use, pre-existing ocular surface diseases (dry eye, epithelial defect) and ocular trauma (agriculture- or farm-related) [1-8]. Annual rates of incidence include nearly one million clinical visits due to keratitis in the United States, while it has been reported that roughly two million people develop corneal ulcers in India. Clinically, patients may show signs of eye pain (ranging from mild to severe), blurred vision, photophobia, chemosis and redness. Pathogenesis is generally characterized by rapid progression, focal white infiltrates with underlying stromal inflammation, corneal thinning, stromal edema, mucopurulent discharge and hypopyon, which can lead to corneal scarring, endophthalmitis, and perforation. In fact, corneal opacity is not only a complication of keratitis, but among the leading causes of legal blindness worldwide. Despite that empirical treatment effectively controls most of the pathogens implicated in infectious keratitis, improved clinical outcomes are not guaranteed. Further, if treatment is not initiated in a timely manner, good visual outcome is reduced to approximately 50% of keratitis patients [9]. Moreover, resultant structural alterations, loss of tissue and an unresolved host response remain unaddressed through current clinical management of this condition.

En Face and Cross-sectional Corneal Tomograms Using Sub-micron spatial resolution Optical Coherence Tomography

Accurate diagnosis of corneal pathology and morphological identification of different corneal layers require clear delineation of corneal three-dimensional structures and en face or cross-sectional imaging of palisade of Vogt (POV), neovascularization (NV) or corneal nerves. Here we report a prototype of full-field optical coherence tomography (FF-OCT) system with isotropic sub-micron spatial resolution in the en face and cross-sectional views. It can also provide three-dimensional reconstructed images and a large field of view (FOV) by stitching tomograms side by side. We validated the imaging power of this prototype in in vivo rat and rabbit eyes, and quantified anatomical characteristics such as corneal layer thickness, endothelial cell density and the intensity profile of different layers. This FF-OCT delineated the ridge-like structure of POV, corneal nerve bundles, and conjunctival vessels in rat eyes. It also clearly identified the vessel walls and red blood cells in rabbit model of corneal NV. The findings provided by this FF-OCT are expected to facilitate corneal disease diagnosis and treatment.

A Novel Murine Model of Radiation Keratopathy

Purpose

Radiation therapy results in severe chronic keratopathy and dry eye disease. We developed a novel mouse model for radiation keratopathy to allow future mechanistic studies.

Methods

Six to 8-week-old BALB/c mice underwent sublethal irradiation to the head only from a Cesium-137 irradiator, 2 × 550 rad, 3-hours apart. Irradiated mice were clinically evaluated by corneal fluorescein staining (CFS) at 1, 2, and 3 months, after which corneas were excised and immunofluorescence histochemistry performed with anti-CD45, anti-MHC class II, and anti-β-tubulin antibodies.

Results

The survival rate after irradiation was 100%. Mice demonstrated significant CFS and hair loss around the eyes. Corneal nerve density decreased in the central and peripheral corneas (P < 0.01) at 2 and 3 months, respectively. CD45+ immune cell densities increased in the central and peripheral corneas (P < 0.005, P < 0.001) at 2 and 3 months, respectively. MHC class II, a sign of antigen presenting cell activation, significantly increased after irradiation in the central and peripheral corneas at 2 and 3 months (P = 0.02). A strong inverse correlation was noted between decreased corneal nerves and increase in CD45+ cells in the central cornea at 2 (P = 0.04, r = -0.89) and 3 months (P = 0.03, r = -0.91) after irradiation.

Conclusions

We present a model of radiation keratopathy and demonstrate significant nerve loss and increase in immune cell influx and activation within months. This model will enable future investigations to understand the effects of radiation therapy on the eye, and to study mechanisms of neuro-immune crosstalk in the cornea.

Corneal confocal sub-basal nerve plexus evaluation: a review

The aim of this study was to review the most recent data about corneal sub-basal nerve plexus (SNP) evaluated with the use of corneal confocal microscopy (CCM). For this purpose, an electronic search was conducted based on PubMed and Google Scholar and Web of Science databases from 2008 up to the end of 2016. Ninety-eight articles in English were cited, as well as abstracts in other languages, concerning the morphology and function of corneal SNP in various diseases. Changes in corneal SNP as a result of local treatment were also introduced. Figures with scans from confocal microscopy from our Department were included. The main conclusion of this review was that both corneal SNP diminishment and high tortuosity as well as low sensitivity are in principle related to the presence or level of pathology. In addition, increased nerve tortuosity may represent a morphological determinant of nerve regeneration. However, the presented literature shows that SNP changes are not characteristic for one unified corneal pathology; rather, they reflect the non-specific pathological process present in many diseases. Future studies should use automatized biometric software and also examine the effects of new treatments on SNP.

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.

Quantitative Analysis of Depth, Distribution, and Density of Cysts in Acanthamoeba Keratitis Using Confocal Microscopy

PURPOSE

To quantify the density, distribution, and depth of invasion of cysts in the corneas of eyes with acanthamoeba keratitis (AK) by in vivo confocal microscopy (IVCM) with a novel scanning pattern.

METHODS

The medical records of patients with AK evaluated at the Doheny Eye Center UCLA between September 2014 and July 2016 were reviewed retrospectively. Patients with clinically diagnosed AK underwent IVCM at various time points during their clinical course. Five corneal locations were scanned at each time point: the central area and 4 standard points on the peripheral cornea corresponding to temporal, nasal, inferior, and superior locations. The IVCM scans were manually graded to quantify the maximum depth of invasion and density of cysts.

RESULTS

Twenty-one eyes of 18 patients with visible cysts on IVCM were included. Mean cyst density at presentation was 214.1 ± 120.2/mm (range: 64-484 cells/mm), and the average cyst depth was 164.3 ± 81.2 μm (range: 17-290 μm). In 17 eyes, the average cyst depth was 139.4 ± 68.6 μm (range: 17-245 μm), mean cyst density was 177.9 ± 99.6/mm, and an average of 1.4 ± 1.3 quadrants was infiltrated at presentation, and reached clinical resolution with medical treatment without surgical intervention. Four eyes that ultimately underwent therapeutic penetrating keratoplasty had cysts in all 4 quadrants and deeper cyst infiltration; the average cyst depth in these corneas was 270.5 ± 17.5 μm (range: 252-290).

CONCLUSIONS

Eyes with AK requiring therapeutic keratoplasty were more likely to have a deeper and more diffuse penetration of cysts in the cornea compared with those resolving with medical treatment.

Corneal Subbasal Nerve Recovery in an Acute Case of Ultraviolet Keratitis Treated with Autologous Serum Eye Drops

Purpose

To report degeneration of subbasal corneal nerves and the subsequent neuroregeneration in a case of acute ultraviolet (UV) keratitis, treated with autologous serum eye drops.

Methods

Case report.

Results

A 37-year-old female presented with ocular discomfort and blurred vision in both eyes, after exposure to UV-C light in a laboratory. On exam, she had bilateral conjunctival injection and superficial punctate keratitis (SPK), worse in the left, consistent with acute, bilateral, but asymmetric UV-C keratitis. She was initially started on antibiotic ointment and lubricant eye drops. On her follow-up visit 3 days later, corneas had persistent SPK bilaterally. Laser scanning in vivo confocal microscopy (IVCM) showed beading of subbasal corneal nerves in the right eye and decreased subbasal corneal nerve density and numerous amputated nerves in the left eye. Autologous serum eye drops 20%, eight times a day, and loteprednol 0.5% ophthalmic solution were commenced in both eyes. Twelve weeks later, her symptoms fully resolved; IVCM revealed near-normal subbasal corneal nerve density in both eyes.

Conclusions

IVCM demonstrated dramatic damage to subbasal corneal nerves after brief UV-C exposure. The patient, treated with autologous serum eye drops in both eyes, achieved resolution of symptoms and recovery of subbasal corneal nerves.

Corneal nerve regeneration after herpes simplex keratitis: A longitudinal in vivo confocal microscopy study

PURPOSE

To evaluate the long-term alterations of corneal nerves in patients with herpes simplex virus (HSV) keratitis using in vivo confocal microscopy (IVCM).

DESIGN

Prospective, longitudinal, cross sectional.

METHODS

This study included 16 patients with a history of HSV keratitis and 15 age-matched normal controls. Slit-scanning IVCM was performed in all subjects at baseline and then after a mean follow-up of 37.3 ± 1.7 months in the patient group. Corneal subbasal nerve density and corneal sensation were compared between groups at baseline and follow-up.

RESULTS

At baseline, the mean subbasal nerve density was significantly lower in both affected eyes (1.4 ± 0.6 mm/mm²) and contralateral unaffected eyes (6.4 ± 0.7 mm/mm²) compared with the controls (14.1 ± 1.6 mm/mm²; all P < .001). At the end of follow-up, the mean nerve density in affected eyes increased to 2.8 ± 0.7 mm/mm² (P = .006), with no significant change in contralateral unaffected eyes (6.5 ± 1.0 mm/mm², P = .72). However, both eyes had lower nerve density than controls (all P < .001). Corneal sensation was significantly lower in affected eyes (2.6 ± 0.6 cm) than in the control group (6.0 ± 0.0, P < .001) and showed no significant change at the end of follow-up (2.5 ± 0.6 cm, P = .80). Corneal sensation in contralateral unaffected eyes was not different in comparison with controls at both baseline and follow up (all p > .05).

CONCLUSIONS

Our results demonstrate that although corneal nerve regeneration occurs in patients with HSV keratitis, this change is not clinically significant and does not results in changes of corneal sensation. Therefore, these patients need to be followed closely for complications of neurotrophic keratopathy and might benefit from neuro-regenerative therapies.

In Vivo Confocal Microscopy Evaluation of Ocular Surface with Graft-Versus-Host Disease-Related Dry Eye Disease

Dry eye disease (DED) is often elicited by graft-versus-host disease (GVHD), an extensive complication of hematopoietic stem cell transplantation (HSCT). To unravel the mechanism of this type of DED, in vivo confocal microscopy (IVCM) was used to investigate alterations in the state of the sub-basal nerves, dendritic cells (DCs) and globular immune cells (GICs) in the central cornea and limbal epithelia. In this study, we examined 12 HSCT recipients with GVHD-caused DED and 10 HSCT recipients without GVHD-associated DED and evaluated the clinical parameters in the 2 groups. Analysis of the central cornea and limbal epithelia using IVCM was conducted to investigate the density of the corneal sub-basal nerves, DCs and GICs as well as the tortuosity and branching of the sub-basal nerves. As suggested by our data, the clinical variables in the GVHD group were significantly different from those in the non-GVHD group. Additionally, GVHD-triggered DED conceivably increased the density of DCs and GICs in the central cornea and the density of DCs in limbal epithelia and altered the morphology of the sub-basal nerves. These phenomena are presumably correlated with the degree of inflammation. Thus, our findings may be translated into non-invasive diagnostic methods that indicate the severity of inflammation on the ocular surface in HSCT recipients.

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.

Two-Dimensional Plane for Multi-Scale Quantification of Corneal Subbasal Nerve Tortuosity

PURPOSE

To assess the performance of a novel system for automated tortuosity estimation and interpretation.

METHODS

A supervised strategy (driven by observers' grading) was employed to automatically identify the combination of tortuosity measures (i.e., tortuosity representation) leading to the best agreement with the observers. We investigated 18 tortuosity measures including curvature and density of inflection points, computed at multiple spatial scales. To leverage tortuosity interpretation, we propose the tortuosity plane (TP) onto which each image is mapped. Experiments were carried out on 140 images of subbasal nerve plexus of the central cornea, covering four levels of tortuosity. Three experienced observers graded each image independently.

RESULTS

The best tortuosity representation was the combination of mean curvature at spatial scales 2 and 5. These tortuosity measures were the axes of the proposed TP (interpretation). The system for tortuosity estimation revealed strong agreement with the observers on a global and per-level basis. The agreement with each observer (Spearman's correlation) was statistically significant (αs = 0.05, P < 0.0001) and higher than that of at least one of the other observers in two out of three cases (ρOUR = 0.7594 versus ρObs3 = 0.7225; ρOUR = 0.8880 versus ρObs1 = 0.8017, ρObs3 = 0.7315). Based on paired-sample t-tests, these improvements were significant (P < 0.001).

CONCLUSIONS

Our automated system stratifies images by four tortuosity levels (discrete scale) matching or exceeding the accuracy of experienced observers. Of importance, the TP allows the assessment of tortuosity on a two-dimensional continuous scale, thus leading to a finer discrimination among images.

In vivo confocal microscopic corneal images in health and disease with an emphasis on extracting features and visual signatures for corneal diseases: a review study

There is an evolution in the demands of modern ophthalmology from descriptive findings to assessment of cellular-level changes by using in vivo confocal microscopy. Confocal microscopy, by producing greyscale images, enables a microstructural insight into the in vivo cornea in both health and disease, including epithelial changes, stromal degenerative or dystrophic diseases, endothelial pathologies and corneal deposits and infections. Ophthalmologists use acquired confocal corneal images to identify health and disease states and then to diagnose which type of disease is affecting the cornea. This paper presents the main features of the healthy confocal corneal layers and reviews the most common corneal diseases. It identifies the visual signatures of each disease in the affected layer and extracts the main features of this disease in terms of intensity, certain regular shapes with both their size and diffusion, and some specific region of interest. These features will lead towards the development of a complete automatic corneal diagnostic system that predicts abnormalities in the confocal corneal data sets.