Morphological Analysis of Quiescent and Activated Keratocytes: A Review ofEx VivoandIn VivoFindings

Neuropathic Corneal Pain: Tear Proteomic and Neuromediator Profiles, Imaging Features, and Clinical Manifestations

PURPOSE

To investigate the tear proteomic and neuromediator profiles, in vivo confocal microscopy (IVCM) imaging features, and clinical manifestations in neuropathic corneal pain (NCP) patients.

DESIGN

Cross-sectional study.

METHODS

A total of 20 NCP patients and 20 age-matched controls were recruited. All subjects were evaluated by corneal sensitivity, Schirmer test, tear break-up time, and corneal and ocular surface staining, Ocular Surface Disease Index and Ocular Pain Assessment Survey questionnaires were administered, as well as IVCM examinations for corneal nerves, microneruomas, and epithelial and dendritic cells. Tears were collected for neuromediator and proteomic analysis using enzyme-linked immunosorbent assay and data-independent acquisition mass spectrometry.

RESULTS

Burning and sensitivity to light were the 2 most common symptoms in NCP. A total of 188 significantly dysregulated proteins, such as elevated metallothionein-2, creatine kinases B-type, vesicle-associated membrane protein 2, neurofilament light polypeptide, and myelin basic protein, were identified in the NCP patients. The top 10 dysregulated biological pathways in NCP include neurotoxicity, axonal signaling, wound healing, neutrophil degradation, apoptosis, thrombin signaling mitochondrial dysfunction, and RHOGDI and P70S6K signaling pathways. Compared to controls, the NCP cohort presented with significantly decreased corneal sensitivity (P < .001), decreased corneal nerve fiber length (P = .003), corneal nerve fiber density (P = .006), and nerve fiber fractal dimension (P = .033), as well as increased corneal nerve fiber width (P = .002), increased length, total area and perimeter of microneuromas (P < .001, P < .001, P = .019), smaller corneal epithelial size (P = .017), and higher nerve growth factor level in tears (P = .006).

CONCLUSIONS

These clinical manifestations, imaging features, and molecular characterizations would contribute to the diagnostics and potential therapeutic targets for NCP.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

In vivo confocal microscopy evaluation of infiltrated immune cells in corneal stroma treated with cell therapy in advanced keratoconus

PURPOSE

This study investigates immune cell (ICs) infiltration in advanced keratoconus patients undergoing autologous adipose-derived adult stem cell (ADASC) therapy with recellularized human donor corneal laminas (CL).

METHODS

A prospective clinical trial included fourteen patients divided into three groups: G-1, ADASCs; G-2, decellularized CL (dCL); and G-3, dCL recellularized with ADASCs (ADASCs-rCL). Infiltrated ICs were assessed using in vivo confocal microscopy (IVCM) at 1,3,6, and12 months post-transplant.

RESULTS

Infiltrated ICs, encompassing granulocytes and agranulocytes, were observed across all groups, categorized by luminosity, structure, and area. Stromal ICs infiltration ranged from 1.19% to 6.62%, with a consistent increase in group-related cell density (F = 10.68, P < .0001), independent of post-op time (F = 0.77, P = 0.511); the most substantial variations were observed in G-3 at 6 and 12 months (2.0 and 1.87-fold, respectively). Similarly, significant size increases were more group-dependent (F = 5.76, P < .005) rather than time-dependent (F = 2.84, P < .05); G-3 exhibited significant increases at 6 and 12 months (3.70-fold and 2.52-fold, respectively). A lamina-induced shift in IC size occurred (F = 110.23, P < .0001), primarily with 50-100 μm2 sizes and up to larger cells > 300μm2, presumably macrophages, notably in G-3, indicating a potential role in tissue repair and remodeling, explaining reductions in cells remnants < 50μm2.

CONCLUSIONS

ADASCs-rCL therapy may lead to increased IC infiltration compared to ADASCs alone, impacting cell distribution and size due to the presence of the lamina. The findings reveal intricate immune patterns shaped by the corneal microenvironment and highlight the importance of understanding immune responses for the development of future therapeutic strategies.

Exosomes and their miRNA/protein profile in keratoconus-derived corneal stromal cells

Keratoconus (KC) is a corneal thinning disorder and a leading cause of corneal transplantation worldwide. Exosomes are small, secreted extracellular vesicles (30-150 nm) that mediate cellular communication via their protein, lipid, and nucleic acid content. We aimed to characterize the exosomes secreted by primary corneal fibroblasts from subjects with or without KC. Using human keratoconus stromal fibroblast cells (HKC, n = 4) and healthy stromal fibroblasts (HCF, n = 4), we collected and isolated exosomes using serial ultracentrifugation. Using nanoparticle tracking analysis (NTA) with ZetaView®, we compared the size and concentration of isolated exosomes. Different exosomal markers were identified and quantified using a transmission electron microscope (TEM) (CD81) and Western blot (CD9 and CD63). Exosomal miRNA profiles were determined by qRT-PCR using Exiqon Human panel I miRNA assays of 368 pre-selected miRNAs. Proteomic profiles were determined using a label-free spectral counting method with mass spectrometry. Differential expression analysis for miRNAs and proteins was done using student's t-test with a significance cutoff of p-value ≤0.05. We successfully characterized exosomes isolated from HCFs using several complementary techniques. We found no significant differences in the size, quantity, or morphology between exosomes secreted by HCFs with or without KC. Expression of CD81 was confirmed by immuno-EM, and expression of CD63 and CD9 with western blots in all exosome samples. We detected the expression of 72-144 miRNAs (threshold cycle Ct < 36) in all exosome samples. In HKC-derived exosome samples, miR-328-3p, miR-532-5p, miR-345-5p, and miR-424-5p showed unique expression, while let-7c-5p and miR-665 have increased expression. Protein profiling identified 157 proteins in at least half of the exosome samples, with 38 known exosomal proteins. We identified 12 up- and 2 down-regulated proteins in HKC-derived exosomes. The proteins are involved in membrane-bounded vesicles, cytoskeletal, calcium binding, and nucleotide binding. These proteins are predicted to be regulated by NRF2, miR-205, and TGF-β1, which are involved in KC pathogenesis. We successfully characterized the HKC-derived exosomes and profiled their miRNA and protein contents, suggesting their potential role in KC development. Further studies are necessary to determine if and how these exosomes with differential protein/miRNA profiles contribute to the pathogenesis of KC.

Diagnosis of Acanthamoeba Keratitis: Past, Present and Future

Acanthamoeba keratitis (AK) is a painful and sight-threatening parasitic corneal infection. In recent years, the incidence of AK has increased. Timely and accurate diagnosis is crucial during the management of AK, as delayed diagnosis often results in poor clinical outcomes. Currently, AK diagnosis is primarily achieved through a combination of clinical suspicion, microbiological investigations and corneal imaging. Historically, corneal scraping for microbiological culture has been considered to be the gold standard. Despite its technical ease, accessibility and cost-effectiveness, the long diagnostic turnaround time and variably low sensitivity of microbiological culture limit its use as a sole diagnostic test for AK in clinical practice. In this review, we aim to provide a comprehensive overview of the diagnostic modalities that are currently used to diagnose AK, including microscopy with staining, culture, corneal biopsy, in vivo confocal microscopy, polymerase chain reaction and anterior segment optical coherence tomography. We also highlight emerging techniques, such as next-generation sequencing and artificial intelligence-assisted models, which have the potential to transform the diagnostic landscape of AK.

Ultrastructural Examination of the Corneal Interface after Predescemetic Deep Anterior Lamellar Keratoplasty (DALK) - A Case Report with Light and Transmission Electron Microscopy

PURPOSE

To examine corneal buttons with light and transmission electron microscopy (TEM) to visualize the interface area and highlight the ultrastructural corneal changes after deep anterior lamellar keratoplasty (DALK).

METHODS

Two patients underwent excimer laser-assisted penetrating repeat keratoplasty after predescemetic DALK. The corneal buttons were examined by light microscopy and TEM.

RESULTS

The light microscopic examination of the corneal buttons revealed fragments of a second Descemet's membrane in the central and midperipheral areas (Case 1). In both cases, visualization of the interface area was not possible by light microscopy. The donor and host stroma were tightly attached without dehiscence. TEM identified the interface area by irregularities in the collagen distribution between the donor and host stroma. The thickness of the remaining recipient corneal stroma measured approximately 30 µm (Case 1) and 100 µm (Case 2), respectively. In the host stroma, TEM revealed the absence or degeneration of keratocytes, accumulation of amorphous material between the collagen lamellae, and vacuolar inclusions dispersed in the stroma, forming a band-like zone anterior to Descemet's membrane.

CONCLUSION

The interface area after DALK has been mainly investigated by in vivo confocal microscopy. Light microscopy and TEM findings indicate remodeling processes after DALK that are associated with increased keratocyte degeneration and structural alterations of the extracellular matrix in the host stroma. The choice of surgical method may influence the postoperative morphological and functional outcome since these findings were primarily apparent in the remaining host stroma. Therefore, complete exposure of Descemet's membrane is an important prognostic factor for the postoperative visual outcome.

In vivo Confocal Microscopic Evaluation of Corneal Changes in Acute Endothelial Rejection

Purpose

To evaluate the microstructural corneal changes during acute endothelial graft rejection and following treatment using in vivo confocal microscopy (IVCM).

Methods

Patients with a clinical diagnosis of severe acute endothelial graft rejection following penetrating keratoplasty were included in this study. IVCM was performed on the 1^st day the patient presented with rejection signs and at the time of clinical resolution.

Results

Twenty-three patients were included in this study. Inflammatory cells appeared as dendritic cells (DCs) and less frequently, as non-DCs in basal epithelial and subbasal areas. Activated keratocytes (AKs) (type 1: large cells with visible cytoplasmic processes; type 2: elongated and spindle-shaped keratocytes) were visible in acute phase. Following resolution, type 1 AKs considerably reduced, but type 2 cells were more often persisted. Multiple types of keratic precipitates (KPs) were also visible in acute phase which resolved following resolution of rejection.

Conclusions

Acute graft rejection was associated with an increase in the number of DCs, activation of keratocytes, and aggregation of various types of KPs. Inflammatory process subsided in almost all cases, but the IVCM changes did not return to normal early after clinical resolution of rejection.

Evaluation of pterygium severity with en face anterior segment optical coherence tomography and correlations with in vivo confocal microscopy

PURPOSE

To describe en face anterior segment optical coherence tomography (EF-OCT) characteristics of pterygia and their correlation with in vivo confocal microscopy (IVCM).

PATIENTS AND METHODS

In this observational case series, we prospectively included 21 eyes of 17 subjects with pterygium. All subjects underwent detailed ophthalmic examination, anterior segment photography, an ocular surface disease index (OSDI) questionnaire, IVCM, and EF-OCT. Eyes were divided into two groups according to pterygium severity (Modified Pterygium Classification System) and OSDI score. EF-OCT images for both groups were analyzed for surface area of Fuchs Patches (FP). The IVCM activity score was based on the number of inflammatory cells, blood vessels, activated keratocytes and the appearance of the cornea/pterygium at the head of the pterygium. The correlations between EF-OCT and IVCM images were then analyzed and compared in both groups.

RESULTS

EF-OCT permits clear visualization and evaluation of FPs and the border between the pterygium and the adjacent cornea. The severe pterygium group was characterized by irregular borders and larger FPs (0.13±0.06 mm² versus 0.06±0.02 mm² respectively) (P=0.003). The mean IVCM activity score was 2.36±0.81 in the severe pterygium group and 1.2±0.42 in the mild pterygium group (P=0.0013). There was a positive correlation between FP surface area and IVCM activity score. A larger FP surface area was associated with a higher activity score on IVCM.

CONCLUSION

EF-OCT allows good evaluation of pterygium extension, borders and FP surface area. EF-OCT analysis of pterygium could represent a simple, non-invasive and reproducible method to evaluate pterygium severity and activity.

In vivo Histology of the Cornea - from the "Rostock Cornea Module" to the "Rostock Electronic Slit Lamp" - a Clinical "Proof of Concept" Study

INTRODUCTION

Confocal in vivo microscopy is an established method in ophthalmology research. As it requires contact coupling and calibration of the instruments is suboptimal, this method has been only rarely used in clinical routine work. As a result of close collaboration between physicists, information scientists and ophthalmologists, confocal laser scanning microscopy (CLSM) of the eye has been developed in recent years and a prototype can now be used in patients. The present study evaluates possible clinical uses of this method.

MATERIAL AND METHODS

The essential innovations in CLSM are (1) a newly designed coupling element with superficial adaptation to corneal curvature and (2) the use of a dual computerised piezo drive for rapid and precise focusing. In post-processing and after elastic imaging registration of the individual images parallel to the surface, it is also possible to produce sagittal sections resembling a split lamp and with resolution in the micrometer range. The concept was tested on enucleated pig bulbi and tested on normal volunteers and selected patients with diseases of the cornea.

RESULTS

Simultaneous imaging in planes parallel to the surface and in sagittal planes provided additional information that can help us to understand the processes of wound healing in all substructures of the cornea and the role of immune competent cells. Possible clinical uses were demonstrated in a volunteer with healthy eyes and several groups of patients (keratoconus after CXL, recurrent keratitis, status after PRK). These show that this new approach can be used in morphological studies at cellular level in any desired and appropriate test plane.

CONCLUSIONS

It could be shown that this new concept of CLSM can be used clinically. It can provide valuable and novel information to both preclinical researchers and to ophthalmologists interested in corneal disease, e.g. density of Langerhans cells and epithelial stratification in ocular surface diseases.

Femtosecond Laser-Assisted Allogenic Lenticule Implantation for Corneal Ectasia After LASIK: A 3-Year In Vivo Confocal Microscopic Investigation

PURPOSE

To investigate morphological changes in the cornea and the implanted lenticule in patients with corneal ectasia after laser in situ keratomileusis (LASIK) and implantation using a lenticule from small incision lenticule extraction (SMILE).

METHODS

Eight eyes of 8 patients with ectasia after LASIK from 2015 to 2018 at the Eye and ENT Hospital of Fudan Unversity were analyzed. For recipient eyes, lenticules were transferred with a mean cryopreserved time of 20 ± 21 days extracted from SMILE donors to the exposed stromal bed after lifting the flaps and the flap was repositioned. Uncorrected and corrected distance visual acuity, manifest refraction, and corneal topography were performed. Patients were followed up for 3 years. Changes in lenticules and recipient corneas were analyzed using in vivo confocal microscopy.

RESULTS

Activated keratocytes in the anterior and posterior stroma were observed near the lenticule at the first 6 months. Elongated, deformed keratocyte nuclei were found in the implanted lenticules in postoperative year 1. The anterior and posterior interfaces showed an absence or decrease of keratocytes and the presence of small particles of varying brightness. Nerve fibers in the implanted lenticules were detected in one case. No obvious difference was detected between cryopreserved and fresh lenticules.

CONCLUSIONS

The preliminary findings suggest that recipient keratocytes repopulate the lenticules and the keratocytes in lenticules gradually return to their normal morphology. [J Refract Surg. 2020;36(11):714-722.].

Fibroblastic and bone marrow-derived cellularity in the corneal stroma

The unwounded, normal corneal stroma is a relatively simple, avascular tissue populated with quiescent keratocytes, along with corneal nerves and a few resident dendritic and monocyte/macrophage cells. In the past, the resting keratocytes were thought of as a homogenous cellular population, but recent work has shown local variations in vimentin and nestin expression, and responsiveness to transforming growth factor (TGF)-β1. Studies have also supported there being "stromal stem cells" in localized areas. After corneal wounding, depending on the site and severity of injury, profound changes in stromal cellularity occur. Anterior or posterior injuries to the epithelium or endothelium, respectively, trigger apoptosis of adjacent keratocytes. Many contiguous keratocytes transition to keratocan-negative corneal fibroblasts that are proliferative and produce limited amounts of disorganized extracellular matrix components. Simultaneously, large numbers of bone marrow-derived cells, including monocytes, neutrophils, fibrocytes and lymphocytes, invade the stroma from the limbal blood vessels. Ongoing adequate levels of TGFβ1, TGFβ2 and platelet-derived growth factor (PDGF) from epithelium, tears, endothelium and aqueous humor that penetrate defective or absent epithelial barrier function (EBF) and epithelial basement membrane (EBM) and/or Descemet's basement membrane (DBM) drive corneal fibroblasts and fibrocytes to differentiate into alpha-smooth muscle actin (SMA)-positive myofibroblasts. If the EBF, EBM and/or DBM are repaired or replaced in a timely manner, typically measured in weeks, then corneal fibroblast and fibrocyte progeny, deprived of requisite levels of TGFβ1 and TGFβ2, undergo apoptosis or revert to their precursor cell-types. If the EBF, EBM and/or DBM are not repaired or replaced, stromal levels of TGFβ1 and TGFβ2 remain elevated, and mature myofibroblasts are generated from corneal fibroblasts and fibrocyte precursors that produce prodigious amounts of disordered extracellular matrix materials associated with scarring fibrosis. This fibrotic stromal matrix persists, at least until the EBF, EBM and/or DBM are regenerated or replaced, and keratocytes remove and reorganize the affected stromal matrix.

Corneal fibroblasts: Function and markers

Corneal stromal keratocytes contribute to the maintenance of corneal transparency and shape by synthesizing and degrading extracellular matrix. They are quiescent in the healthy cornea, but they become activated in response to insults from the external environment that breach the corneal epithelium, with such activation being associated with phenotypic transformation into fibroblasts. Corneal fibroblasts (activated keratocytes) act as sentinel cells to sense various external stimuli-including damage-associated molecular patterns derived from injured cells, pathogen-associated molecular patterns of infectious microorganisms, and inflammatory mediators such as cytokines-under pathological conditions such as trauma, infection, and allergy. The expression of various chemokines and adhesion molecules by corneal fibroblasts determines the selective recruitment and activation of inflammatory cells in a manner dependent on the type of insult. In infectious keratitis, the interaction of corneal fibroblasts with various components of microbes and with cytokines derived from infiltrated inflammatory cells results in excessive degradation of stromal collagen and consequent corneal ulceration. Corneal fibroblasts distinguish between type 1 and type 2 inflammation through recognition of corresponding cytokines, with their activation by type 2 cytokines contributing to the pathogenesis of corneal lesions in severe ocular allergic diseases. Pharmacological targeting of corneal fibroblast function is thus a potential novel therapeutic approach to prevention of excessive corneal stromal inflammation, damage, and scarring.

Topical Corneal Cross-Linking Solution Delivered Via Corneal Reservoir in Dutch-Belted Rabbits

Purpose

A topical corneal cross-linking solution that can be used as an adjunct or replacement to standard photochemical cross-linking (UV-riboflavin) methods remain an attractive possibility. Optimal concentration and delivery method for such topical corneal stabilization in the living rabbit eye were developed.

Methods

A series of experiments were carried out using Dutch-belted rabbits (3 months old, weighing 1.0–1.5 kg) and topical cross-linking solutions (sodium hydroxymethylglycinate) (10–250 mM) delivered via corneal reservoir. The application regimen included a one-time 30-minute application (10–40 mM sodium hydroxymethylglycinate) as well as a once per week 5-minute application (250 mM sodium hydroxymethylglycinate) for 7 weeks. Animals were evaluated serially for changes in IOP, pachymetry, epithelial integrity, and endothelial cell counts. Keratocyte changes were identified using intravital laser scanning confocal microscopy. Post mortem efficacy was evaluated by mechanical inflation testing.

Results

Overall, there were very few differences observed in right eye treated versus left eye controls with respect to intraocular pressure, pachymetry, and endothelial cell counts, although 30-minute cross-linking techniques did cause transient increases in thickness resolving within 7 days. Epithelial damage was noted in all of the 30-minute applications and fully resolved within 72 hours. Keratocyte changes were significant, showing a wound healing pattern similar to that after riboflavin UVA photochemical cross-linking in rabbits and humans. Surprisingly, post mortem inflation testing showed that the lower concentration of 20 mM delivered over 30 minutes showed the most profound stiffening/strengthening effect.

Conclusions

Topical cross-linking conditions that are safe and can increase corneal stiffness/strength in the living rabbit eye have been identified.

Translational Relevance

A topical corneal cross-linking solution delivered via corneal reservoir is shown to be both safe and effective at increasing tissue strength in living rabbit eyes and could now be tested in patients suffering from keratoconus and other conditions marked by corneal tissue weakness.

Keratocyte biology

The study of corneal stromal keratocytes is motivated by its strong association with corneal health and visual function. They play a dominant role in the maintenance of corneal homeostasis and transparency through the production of collagens, proteoglycans and corneal crystallins. Trauma-induced apoptosis of keratocytes and replacement by fibroblasts and myofibroblasts disrupt the stromal matrix organization, resulting in corneal haze formation and vision loss. It is, therefore, important to understand the biology and behaviours of keratocytes and the associated stromal cell types (like fibroblasts, myofibroblasts, stromal stem cells) in wound healing, corneal pathologies (including keratoconus, keratitis, endothelial disorders) as well as different ophthalmic situations (such as collagen crosslinking/photodynamic treatment, keratoplasty and refractive surgery, and topical medications). The recent development of ex vivo propagation of keratocytes and stromal stem cells, and their translational applications, either via stromal injection or incorporated in bioscaffold, have been shown to restore the corneal transparency and regenerate native stromal tissue in animal models of corneal haze and other disorders.

In Vivo Corneal Confocal Microscopy and Histopathology of Keratitis Fugax Hereditaria From a Pathogenic Variant in NLRP3

PURPOSE

To apply in vivo corneal confocal microscopy (IVCM) to study the pathogenesis of keratitis (keratoendotheliitis) fugax hereditaria, an autosomal dominant cryopyrin-associated periodic keratitis, associated with the c.61G>C pathogenic variant in the NLRP3 gene, in its acute and chronic phase, and to report histopathologic findings after penetrating keratoplasty.

DESIGN

This was an observational case series.

METHODS

The study population included 6 patients during an acute attack, 18 patients in the chronic phase, and 1 patient who underwent penetrating keratoplasty. Interventions included Sanger sequencing for the NLRP3 variant c.61C>G, a clinical examination, corneal photography, IVCM, light microscopy, and immunohistochemistry. Our primary outcome measures included IVCM and histopathologic findings.

RESULTS

During the acute attack, hyperreflective cellular structures consistent with inflammatory cells transiently occupied the anterior to middle layers of the corneal stroma. Other corneal layers were unremarkable. With recurring attacks, central oval stromal opacities accumulated. IVCM revealed that they contained long, hyperreflective, needle-shaped structures in the extracellular matrix. Using light microscopy, the anterior half of the stroma displayed thin and finely vacuolated lamellae, and keratocytes throughout the stroma were immunopositive for syndecan.

CONCLUSIONS

The acute attacks and chronic stromal deposits mainly involve the anterior to middle layers of the corneal stroma, and the disease is primarily a keratitis rather than a keratoendotheliitis. IVCM shows that inflammatory cells invade only the stroma during an acute attack. IVCM and light microscopic findings suggest that the central corneal opacities represent gradual deposition of extracellular lipids. The disease could make a good in vivo model to study activation of the NLRP3 inflammasome in cryopyrin-associated periodic syndromes.

Uptake of cell debris and enhanced expression of inflammatory factors in response to dead cells in corneal fibroblast cells

Keratocytes synthesize stromal proteins and participate in wound healing through successive differentiation into corneal fibroblasts and myofibroblasts. Cultured keratocytes or corneal fibroblasts are also known as non-professional phagocytes and innate immune cells. However, whether the corneal fibroblasts phagocytize their dead cells and whether the associated innate immunity is enhanced remains unknown. We initially characterized immortalized corneal fibroblast cells with the expression of specific genes. The corneal fibroblasts strongly expressed extracellular matrix molecules (FN and COL1A1) and low or medium levels of macrophage markers (CD14, CD68, and CD36), inflammatory cytokines (IL1A, IL1B, and IL6), and chemokines (IL8 and CCL2), but not CD11b, suggesting that corneal fibroblasts are macrophage-like fibroblasts. We confirmed the phagocytic activity of the corneal fibroblasts with fluorescent dye labeled-dead E. coli and S. aureus bacteria using confocal microscopy and flow cytometry. To test corneal fibroblast phagocytosis of apoptotic and necrotic cells we co-cultured corneal fibroblasts with fluorescent dye labeled-apoptotic and -necrotic cells and analyzed their uptake using fluorescence and confocal microscopy. We observed that corneal fibroblasts can engulf digested or processed cellular debris and entire dead cells. Co-cultured dying and dead cells strongly enhanced the expression of cytokine (IL1A, IL1B, and IL6), chemokine (CCL2, CCL5, CCL20, IL8, and CXCL10), and MMP (MMP1, MMP3, and MMP9) genes through the NF-κB signaling pathway. Our findings suggest that dying and dead cells stimulate corneal fibroblasts to further induce inflammatory factors and that corneal fibroblasts contribute to the clearing of cell debris as non-professional phagocytes.

Variable Responses to Corneal Grafts: Insights from Immunology and Systems Biology

Corneal grafts interact with their hosts via complex immunobiological processes that sometimes lead to graft failure. Prediction of graft failure is often a tedious task due to the genetic and nongenetic heterogeneity of patients. As in other areas of medicine, a reliable prediction method would impact therapeutic decision-making in corneal transplantation. Valuable insights into the clinically observed heterogeneity of host responses to corneal grafts have emerged from multidisciplinary approaches, including genomics analyses, mechanical studies, immunobiology, and theoretical modeling. Here, we review the emerging concepts, tools, and new biomarkers that may allow for the prediction of graft survival.

Cellular Factor XIII, a Transglutaminase in Human Corneal Keratocytes

Cellular factor XIII (cFXIII, FXIII-A₂), a transglutaminase, has been demonstrated in a few cell types. Its main function is to cross-link proteins by isopeptide bonds. Here, we investigated the presence of cFXIII in cells of human cornea. Tissue sections of the cornea were immunostained for FXIII-A in combination with staining for CD34 antigen or isopeptide cross-links. Isolated corneal keratocytes were also evaluated by immunofluorescent microscopy and flow cytometry. FXIII-A in the corneal stroma was quantified by Western blotting. FXIII-A mRNA was detected by RT-qPCR. The cornea of FXIII-A-deficient patients was evaluated by cornea topography. FXIII-A was detected in 68 ± 13% of CD34+ keratocytes. Their distribution in the corneal stroma was unequal; they were most abundant in the subepithelial tertile. cFXIII was of cytoplasmic localization. In the stroma, 3.64 ng cFXIII/mg protein was measured. The synthesis of cFXIII by keratocytes was confirmed by RT-qPCR. Isopeptide cross-links were detected above, but not within the corneal stroma. Slight abnormality of the cornea was detected in six out of nine FXIII-A-deficient patients. The presence of cFXIII in human keratocytes was established for the first time. cFXIII might be involved in maintaining the stability of the cornea and in the corneal wound healing process.

The Use of Digital Microscopy to Compare the Thicknesses of Normal Corneas and Ex Vivo Rejected Corneal Grafts with a Focus on the Descemet's Membrane

Objective

To compare the thickness of corneal layers, specifically the Descemet's membrane (DM), in normal corneas and in failed grafts due to rejection (FGRs) using the digital histopathology and to propose a model for the measurement of corneal layers using this method.

Methods

This is a prospective, cross-sectional study performed at the MUHC-McGill University Ocular Pathology & Translational Research Laboratory (McGill University, Montreal, Canada). Histopathological sections of 25 normal human corneas and 40 FGRs were fully digitalized and examined. Inclusion criteria: samples diagnosed as normal corneas or FGRs, from patients older than 18 years of age. Exclusion criteria: histopathological sections without adequate tissue or missing epidemiological information. For each sample, the thicknesses of the epithelium, stroma, and DM were acquired. From a perpendicular plane of reference, two central measurements and two nasal and two temporal peripheral measurements were obtained.

Results

There were differences between the normal and FGR groups in the mean central thickness of the epithelium (p < 0.001), the nasal and temporal stromal regions (p < 0.001), and of the DM in the nasal and temporal regions (p < 0.001). Compared with the extremities of the sample (nasal and temporal), the mean thickness of the DM in normal corneas was lower in the central region (p < 0.001), and this difference was not found in the FGR group.

Conclusions

Normal corneas have a thinner epithelium in the central region than the FGR group. In addition, the stroma and DM thicknesses of the nasal and temporal periphery were significantly higher in normal corneas than in those from the FGR group. The digital microscopy protocol applied in this study may be useful for further research studies regarding cornea and other tissues.

Clinical and in vivo confocal microscopic features of neuropathic corneal pain

Aims

To describe clinical and in vivo confocal microscopy (IVCM) features of neuropathic corneal pain (NCP) without clinically visible signs.

Methods

Prospective, observational study of 27 eyes of 14 patients who had continuous severe ocular pain for one or more years, with minimal or no ocular surface signs and were non-responsive to topical lubricants, steroids and/or ciclosporin. All patients were evaluated using Ocular Surface Disease Index, Oxford grading scale, Schirmer test 1, Cochet Bonnet esthesiometry and response to topical anaesthesia. Central and paracentral regions of the cornea of patients and seven healthy controls were studied by IVCM. Corneal epithelial thickness and sub-basal nerve density were measured in patients and controls.

Results

Four patients responded to topical anaesthesia (responsive group (RG)), indicating peripheral NCP while 10 patients did not show any improvement (non-responsive group (NRG)), indicating central NCP. Schirmer-1 test was within normal limits in the RG but significantly greater in the NRG (p<0.001). None of the other clinical parameters nor corneal epithelial thickness were statistically significantly different. The sub-basal nerve density was significantly reduced (p<0.008) in patients compared with controls. Stroma of all patients demonstrated activated keratocytes and spindle, lateral and stump microneuromas. There was a statistically significant greater number of microneuromas (p<0.0001) and activated keratocytes in RG compared with NRG.

Conclusion

NCP without visible clinical signs does not represent typical dry eye disease. Distinct signs demonstrated on IVCM suggest that peripheral NCP, which responds to topical anaesthesia, and central NCP, which does not, are separate entities.

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.

Cellular morphological changes detected by laser scanning in vivo confocal microscopy associated with clinical outcome in fungal keratitis

HRT3 in vivo confocal microscopy (IVCM) images may indicate clinical outcome, but few studies have analysed this in fungal keratitis (FK). Adults with FK (diameter ≥3 mm) presenting to Aravind Eye Hospital, India from 2012-3 were enrolled prospectively. IVCM was performed at baseline, days 7, 14 and 21 post-enrolment (+/- 3 days where possible). Specific morphologies were identified in IVCM images by a grader masked to microbiology and clinical outcome (defined as good: healed/improving, or poor: enlarged ulcer, perforation or transplant/glue). Associations with final visit outcome assessed using logistic regression. 143 FK participants were enrolled; 87 had good outcome, 56 had poor outcome. Poor outcomes were associated with stellate interconnected cellular processes with no visible nuclei (OR 2.28, 95% CI: 1.03-5.06, p = 0.043) in baseline IVCM images, and fungal filaments (OR 6.48, 95% CI:2.50-16.78, p < 0.001) or honeycomb distribution of inflammatory cells (OR 5.24, 95% CI: 1.44-19.06, p = 0.012) in final visit images. Fungal filaments (OR 3.61, 95% CI:1.64-7.95, p = 0.001), stromal dendritiform cells (OR 2.88, 95% CI:1.17-7.11, p = 0.022), or stellate cellular processes with no visible nuclei (OR 2.09, 95% CI:1.14-3.82, p = 0.017) were associated with poor outcome if not in baseline but present in final visit images. IVCM can reveal morphological changes associated with clinical outcome.

Quantitative Analysis of the Corneal Collagen Distribution after In Vivo Cross-Linking with Second Harmonic Microscopy

Corneal cross-linking (CXL) is a surgical procedure able to modify corneal biomechanics and stabilize keratoconus progression. Although it is known that CXL produces changes in corneal collagen distribution, these are still a topic of discussion. Here we quantitatively compare the corneal stroma architecture between two animal models four weeks after in vivo conventional CXL treatment, with second harmonic generation (SHG) imaging microscopy and the structure tensor (ST). The healing stage and the stroma recovery were also analyzed by means of histological sections. Results show that the CXL effects depend on the initial arrangement of the corneal collagen. While the treatment increases the order in corneas with a low level of initial organization, corneas presenting a fairly regular pattern are hardly affected. Histological samples showed active keratocytes in anterior and middle stroma, what means that the recovery is still in progress. The combination of SHG imaging and the ST is able to objectively discriminate the changes suffered by the collagen arrangement after the CXL treatment, whose effectiveness depends on the initial organization of the collagen fibers within the corneal stroma.

In Vivo Confocal Microscopy Cellular Features of Host and Organism in Bacterial, Fungal, and Acanthamoeba Keratitis

PURPOSE

To determine cellular features of fungal (FK), Acanthamoeba (AK), and bacterial keratitis (BK) using HRT3 in vivo confocal microscopy (IVCM).

DESIGN

Prospective observational cross-sectional study.

METHODS

Eligible participants were adults with microbiologically positive FK, AK, or BK, of size ≥ 3 mm, attending Aravind Eye Hospital from February 2012 to February 2013. Exclusion criteria were descemetocele or perforation. At presentation, IVCM imaging was performed, then corneal scrapes were obtained for culture/light microscopy. An experienced grader (masked to microbiology/clinical features) assessed IVCM images for presence/absence of normal keratocyte-like morphology, stellate interconnected cells with/without visible nuclei, dendritiform cells (DFCs), inflammatory cells in a honeycomb distribution, and organism features. Statistical significance was assessed by logistic regression, adjusted for age, sex, ulcer size, and symptom duration. Main outcome measures were presence/absence of IVCM features in FK, AK, BK.

RESULTS

A total of 183 participants had FK, 18 AK, 17 BK. Acanthamoeba appeared as bright spots (16/18, 89%), double-walled cysts (15/18, 83%), or signet rings (3/18, 17%), and often formed clusters after topical steroid use (univariable odds ratio [OR] 9.98, 95% confidence interval [CI] 1.02-97.96, P = .048). BK was associated with bullae in anterior stroma (OR 9.99, 95% CI: 3.11-32.06, P < .001). Honeycomb distribution of anterior stromal inflammatory cells was associated with FK (univariable OR 2.74, 95% CI: 1.01-7.40, P = .047). Aspergillus ulcers were associated with stromal DFCs (OR 11.05, 95% CI: 1.49-82.13, P = .019) and Fusarium ulcers with stellate appearance of interconnected cell processes with nuclei (OR 0.24, 95% CI: 0.09-0.65, P = .005).

CONCLUSION

Specific cellular and structural features observed using IVCM in microbial keratitis may be associated with organism.

Development and Assessment of a Novel Canine Ex Vivo Corneal Model

PURPOSE

To develop a novel ex vivo extended culture model of canine corneal epithelial cell wound healing.

MATERIALS AND METHODS

Canine corneoscleral rims (CSR) were obtained and, after preparation for culture, were placed on a nutating scaffold and incubated in physiological conditions. In experiment 1, eight CSR in a serum-containing antimicrobial-fortified medium were monitored for epithelial integrity and bacterial infection up to 28 days in culture. CSR were assessed histologically at the end of the culture period end points 0, 7, 14, and 28 days with accompanying scanning electron microscopic (SEM) and transmission electron microscopic (TEM) evaluation. Samples for microbial culture were obtained at days 0, 3, 7, 14, and 28. In experiment 2, uniform 8-mm-diameter superficial corneal epithelial wounds were created and monitored for re-epithelialization in the same culture conditions or in a serum-free protein equivalent medium, with four CSR per group. Standardized digital images were obtained with cobalt filter at the time of fluorescein staining and media change every six hours. Image J imaging software was used to measure the area of fluorescein retention. Re-epithelialization rates were calculated and CSR then fixed for immunohistochemistry (IHC).

RESULTS

All corneas survived to end points as described in experiment 1 with no evidence of contamination or compromised epithelial integrity. Histologically, a multilayered epithelium was maintained and corneal edema was not appreciated until day 14. SEM examination revealed epithelial cell layer confluence and migrating epithelial cells of normal cellular morphology with normal cell-cell interactions on TEM. In experiment 2, all eight corneas healed with a healing rate of 0.702 ± 0.130 mm²/h (1.25 mm/day epithelial cell migration rate) and were positive in IHC evaluation for markers of corneal fibrosis.

CONCLUSION

This ex vivo canine corneal wound healing model is an appropriate and clinically relevant tool for assessment and modulation of epithelial wound healing.

Effect of fibrin glue on corneal lamellar healing and how it correlates to biomechanical properties: biomechanical wavefront analysis and confocal study

Background

To evaluate, using a rabbit model, the influence of the wound healing process at the flap edge on corneal biomechanics after sutured, glued, and non-augmented microkeratome flaps.

Methods

Unilateral 160 μm thick laser in situ keratomileusis (LASIK) flaps using a mechanical microkeratome were performed on the corneas of the left eyes of 36 rabbits. Animals were then divided into 3 groups of 12 rabbits each: A: the flaps were glued with human fibrin tissue adhesive (Tisseel); B: the flaps were sutured; and C: the flaps were allowed to heal without the use of sutures or glue (non-augmented). The contralateral eyes served as controls. Reichert ocular response analyzer (ORA) was used to measure corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and cornea-compensated IOP (IOPcc) at 6 weeks and 3 months postoperatively. In vivo confocal microscopy (IVCM) was also used to study the corneal wound healing process in all groups.

Results

Both mean CH and mean CRF were significantly higher in sutured and glued groups compared with the non-augmented group at 6 weeks and 3 months postoperatively (P  < 0.0001). No statistically significant difference in corneal biomechanics was found between controls and groups A and B at any time points. Activated keratocytes were detected at the wound edge and peripheral flap interface in sutured and glued groups.

Conclusion

The healing process at the wound edge is critical for optimal corneal integrity. Fibrin glue may serve as a safe and effective substitute to sutures in enhancing the corneal flap edge healing response and in increasing its mechanical strength.

Predicting Corneal Graft Rejection by Confocal Microscopy

PURPOSE

This study aims at estimating corneal healing by activated keratocyte (AK) counting with in vivo confocal microscopy after perforating keratoplasty (PK). It assesses the value of AK counting in predicting corneal graft rejection.

METHODS

This prospective single-center observational study included 45 patients who benefited from PK in 2013 and were followed up over 2 years. All were monitored by confocal microscopy at day 1, day 7, and monthly thereafter. The AKs were counted in 5 optical sections in each of the anterior, middle, and posterior stroma. The ability of AKs in predicting the occurrence of corneal rejection was assessed by comparison of AK counts between patients with and without clinical signs of rejection.

RESULTS

In patients with graft rejection, the AK counts increased significantly 2 months before the clinical diagnosis of rejection, whereas it remained stable after 4 months in patients without rejection. In patient with graft rejection, the AK count reached a maximum at the rejection diagnosis and antirejection treatment initiation but decreased significantly 1 month after treatment initiation.

CONCLUSIONS

This study confirmed the predictive value of AK counting in corneal graft rejection. The increase in the AK count allowed predicting graft rejection 2 months before the clinical diagnosis of rejection; it may then be the first sign of subclinical rejection.

1,25-dihydroxyvitamin D3 inhibits corneal wound healing in an ex-vivo mouse model

PURPOSE

Impaired healing of corneal injuries can result in ulceration and complete loss of vision, especially in the elderly. Such patients frequently also exhibit vitamin D insufficiency. 1,25-dihydroxyvitamin D3 is the active vitamin D metabolite. As it affects cell proliferation and inflammation, we herein aimed at elucidating its influence on corneal wound healing after alkali burn by using in vitro and ex vivo techniques.

METHODS

mRNA abundance in human corneal epithelial cells in response to vitamin D3 was determined by RT-PCR. Corneal re-epithelialization after alkaline burn was analyzed using enucleated mouse eyes and fluorescein staining.

RESULTS

Human corneal epithelial cells (HCEC) expressed the vitamin D receptor (VDR) and retinoid x receptor (RXR) and were responsive to 1,25- dihydroxyvitamin D3, as shown by induction of the 1,25- dihydroxyvitamin D3 responsive gene cyp-24A1 and slightly reduced abundance of IL-6 mRNA. However, no effect on cell vitality and migration was observed. In contrast, re-epithelialization of mouse corneas ex vivo was dose dependently inhibited by 1,25- dihydroxyvitamin D3.

CONCLUSIONS

These data indicate that topically applied 1,25- dihydroxyvitamin D3 does not seem to be suitable for therapy of corneal lesions.