In vivo imaging of corneal inflammation: new tools for clinical practice and research

Photoactivated Chromophore Corneal Collagen Cross-Linking for Infectious Keratitis (PACK-CXL)-A Comprehensive Review of Diagnostic and Prognostic Factors Involved in Therapeutic Indications and Contraindications

Infectious keratitis is a severe infection of the eye, which requires urgent care in order to prevent permanent complications. Typical cases are usually diagnosed clinically, whereas severe cases also require additional tools, such as direct microscopy, corneal cultures, molecular techniques, or ophthalmic imaging. The initial treatment is empirical, based on the suspected etiology, and is later adjusted as needed. It ranges from topical administration of active substances to oral drugs, or to complex surgeries in advanced situations. A novel alternative is represented by Photoactivated Chromophore Corneal Collagen Cross-Linking (PACK-CXL), which is widely known as a minimally invasive therapy for corneal degenerations. The purpose of this review is to identify the main diagnostic and prognostic factors which further outline the indications and contraindications of PACK-CXL in infectious keratitis. Given the predominantly positive outcomes in the medical literature, we ponder whether this is a promising treatment modality, which should be further evaluated in a systematic, evidence-based manner in order to develop a clear treatment protocol for successful future results, especially in carefully selected cases.

A novel combination of corneal confocal microscopy, clinical features and artificial intelligence for evaluation of ocular surface pain

OBJECTIVES

To analyse various corneal nerve parameters using confocal microscopy along with systemic and orthoptic parameters in patients presenting with ocular surface pain using a random forest artificial intelligence (AI) model.

DESIGN

Observational, cross-sectional.

METHODS

Two hundred forty eyes of 120 patients with primary symptom of ocular surface pain or discomfort and control group of 60 eyes of 31 patients with no symptoms of ocular pain were analysed. A detailed ocular examination included visual acuity, refraction, slit-lamp and fundus. All eyes underwent laser scanning confocal microscopy (Heidelberg Engineering, Germany) and their nerve parameters were evaluated. The presence or absence of orthoptic issues and connective tissue disorders were included in the AI. The eyes were grouped as those (Group 1) with symptom grade higher than signs, (Group 2) with similar grades of symptoms and signs, (Group3) without symptoms but with signs, (Group 4) without symptoms and signs. The area under curve (AUC), accuracy, recall, precision and F1-score were evaluated.

RESULTS

Over all, the AI achieved an AUC of 0.736, accuracy of 86%, F1-score of 85.9%, precision of 85.6% and recall of 86.3%. The accuracy was the highest for Group 2 and least for Group 3 eyes. The top 6 parameters used for classification by the AI were microneuromas, immature and mature dendritic cells, presence of orthoptic issues and nerve fractal dimension parameter.

CONCLUSIONS

This study demonstrated that various corneal nerve parameters, presence or absence of systemic and orthoptic issues coupled with AI can be a useful technique to understand and correlate the various clinical and imaging parameters of ocular surface pain.

Corneal Confocal Microscopy Features and Tear Molecular Profile in Study Participants with Discordance between Ocular Surface Disease Clinical Signs and Discomfort

Various ocular surface conditions such as dry eye disease can present with severe discomfort and pain. However, it is clinically challenging to establish etiology and prescribe correct treatment in patients who have a lot of discordance between symptoms and signs. To understand the basis of such discordance, we stratified subjects with ocular surface pain based on concordance between the severity of signs and symptoms and evaluated corneal structural features and tear molecular factors. All subjects underwent slit lamp examination, dry eye evaluation, and ocular surface disease index (OSDI) scoring. Subjects were stratified into group 1—without symptoms or clinical signs; group 2—without symptoms but with signs; group 3—with similar severity of symptoms and signs; and group 4—with symptom severity greater than that of the signs. Laser scanning in vivo confocal microscopy (IVCM) and tear fluid analysis for soluble factors by multiplex ELISA was performed for all subjects. Patients with a higher grade of symptoms and signs showed increased corneal dendritic cell (cDC) density (p < 0.05) which was more pronounced in subjects with discordance between the symptoms and signs (group 4). A significantly higher proportion of microneuroma-like structures and cDC were observed in group 4. IL-17A levels were significantly elevated in the tears of subjects with more discomfort. Our results demonstrate that corneal IVCM and the measurement of tear film factors can help clinicians improve diagnosis and treatment choice. Stratifying patients with ocular surface discomfort on the basis of discordance between symptoms and clinical signs may help identify patients who need additional adjunctive targeted therapy to resolve their condition.

How Should Corneal Nerves be Incorporated Into the Diagnosis and Management of Dry Eye?

Purpose

a)Confocal microscopy and aethesiometry have allowed clinicians to assess the structural and functional integrity of corneal nerves in health and disease. This review summarizes literature on nerves in dry eye disease (DED) and discusses how this data can be applied to DED diagnosis and treatment.

Recent findings

b)Subjects with DED have a heterogenous symptom and sign profile along with variability in nerve structure and function. Most studies have reported lower nerve density and sensitivity in aqueous tear deficiency, while findings are more inconsistent for other DED subtypes. Examining nerve status, along with profiling symptoms and signs of disease, can help categorize subjects into disease phenotypes (structural and functional patterns) that exist under the umbrella of DED. This, in turn, can guide therapeutic decision-making.

Summary

c)Due to the heterogeneity in symptoms and signs of DED, corneal nerve evaluations can be valuable for categorizing individuals into disease sub-types and for guiding clinical decision making.

Repository Corticotropin Injection (Acthar® Gel) for Refractory Severe Noninfectious Keratitis: Efficacy and Safety from a Phase 4, Multicenter, Open-Label Study

Introduction

Noninfectious keratitis is a painful corneal inflammation treated with topical cyclosporine and other immunosuppressants. Additional treatment options are needed for keratitis that does not improve with standard therapies. Repository corticotropin injection (RCI; Acthar^® Gel) is approved to treat severe acute and chronic allergic and inflammatory processes involving the eye and its adnexa, including keratitis. This phase 4, multicenter, open-label study assessed the efficacy and safety of RCI for refractory severe noninfectious keratitis.

Methods

Patients were ≥ 18 years old with persistent severe keratitis despite treatment with topical immunosuppressants. Patients received 80 U of RCI subcutaneously twice weekly for 12 weeks followed by a 4-week taper. Assessments included all domains of the Impact of Dry Eye on Everyday Life (IDEEL) Questionnaire, Ocular Discomfort and 4-Symptom Questionnaire, and Visual Analog Scale (VAS). Corneal fluorescein and conjunctival lissamine green staining, Conjunctival Redness Scale, tear production (Schirmer’s test), visual acuity, slit lamp examination, and intraocular pressure were also assessed. Safety was evaluated via treatment-emergent adverse events. Analyses were performed using the modified intent-to-treat (mITT) population (patients who received ≥ 1 dose of RCI and contributed any post-baseline efficacy data).

Results

In the mITT population (N = 35), 50.0% (95% confidence interval, 33.2% to 66.8%) of patients experienced clinically important improvements in the symptom bother domain of the IDEEL Questionnaire at week 12 of RCI therapy. All domains of the IDEEL and the Ocular Discomfort and 4-Symptom Questionnaire showed improvements at week 12 of RCI treatment. The most pronounced improvements in the VAS at week 12 were for eye dryness and eye discomfort. Corneal staining, conjunctival staining, conjunctival redness, and tear production showed early improvements that were sustained through week 12. No new safety signals for RCI were identified.

Conclusions

RCI is safe and effective for refractory severe noninfectious keratitis that has not improved with other approved therapies.

Trial registration number

ClinicalTrials.gov NCT04169061.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40123-021-00400-y.

A Review of Imaging Biomarkers of the Ocular Surface

A biomarker is a "characteristic that is measured as an indicator of normal biological processes, pathogenic processes, or responses to an exposure or intervention, including therapeutic interventions." Recently, calls for biomarkers for ocular surface diseases have increased, and advancements in imaging technologies have aided in allowing imaging biomarkers to serve as a potential solution for this need. This review focuses on the state of imaging biomarkers for ocular surface diseases, specifically non-invasive tear break-up time (NIBUT), tear meniscus measurement and corneal epithelial thickness with anterior segment optical coherence tomography (OCT), meibomian gland morphology with infrared meibography and in vivo confocal microscopy (IVCM), ocular redness with grading scales, and cellular corneal immune cells and nerve assessment by IVCM. Extensive literature review was performed for analytical and clinical validation that currently exists for potential imaging biomarkers. Our summary suggests that the reported analytical and clinical validation state for potential imaging biomarkers is broad, with some having good to excellent intra- and intergrader agreement to date. Examples of these include NIBUT for dry eye disease, ocular redness grading scales, and detection of corneal immune cells by IVCM for grading and monitoring inflammation. Further examples are nerve assessment by IVCM for monitoring severity of diabetes mellitus and neurotrophic keratitis, and corneal epithelial thickness assessment with anterior segment OCT for the diagnosis of early keratoconus. However, additional analytical validation for these biomarkers is required before clinical application as a biomarker.

Imaging Biomarkers for Dry Eye Disease

The clinical, scientific, economic, and regulatory impact of validated biomarkers and surrogate endpoints has the potential to revolutionize the approach to ocular surface diseases. At present, there is a growing interest in developing biomarkers for dry eye disease, and other ocular surface disorders and imaging are of the most promising approaches to this issue. Among the several and constantly evolving imaging technologies, some tools that are aimed to assess tear film stability and volume, meibomian gland morphology and function, and ocular surface microanatomy are now supported by a good body of evidence. To date, clinical trials on ocular surface diseases have slowly started incorporating imaging biomarkers for disease diagnosis and stratification and as surrogate endpoints. Major efforts are still needed, mainly aimed to improve automatic acquisition and quantitative analysis, standardization (standard operating procedures, normative databases etc.), and validation of imaging biomarkers.

Treatment of Corneal Infections Utilizing an Ocular Wound Chamber

Purpose

To demonstrate that the ocular wound chamber (OWC) can be used for the treatment of bacterial keratitis (BK).

Methods

A blepharotomy was performed on anesthetized, hairless guinea pigs to induce exposure keratopathy 72 hours before corneal wound creation and Pseudomonas aeruginosa inoculation. Twenty-four hours postinoculation, eyes were treated with an OWC filled with 500 µL 0.5% moxifloxacin hydrochloride ophthalmic solution (OWC), 10 µL 0.5% moxifloxacin hydrochloride drops (DROPS) four times daily, or not treated (NT). White light, fluorescein, and spectral domain optical coherence tomography (SD-OCT) images; ocular and periocular tissues samples for colony-forming units (CFU) quantification; and plasma samples were collected at 24 and 72 hours posttreatment.

Results

White light, fluorescein, and SD-OCT imaging suggests OWC-treated eyes are qualitatively healthier than those in DROPS or NT groups. At 24 hours, the median number of CFUs (interquartile range) measured was 0 (0-8750), 150,000 (106,750-181,250), and 8750 (2525-16,000) CFU/mL for OWC, NT, and DROPS, respectively. While 100% of NT and DROPS animals remained infected at 24 hours, only 25% of OWC-treated animals showed infection. Skin samples at 24 hours showed infection percentages of 50%, 75%, and 0% in DROPS, NT, and OWC groups, respectively. OWC-treated animals had higher moxifloxacin plasma concentrations at 24 and 72 hours than those treated with drops.

Conclusions

OWC use resulted in a more rapid decrease of CFUs when compared to DROPS or NT groups and was associated with qualitatively healthier ocular and periocular tissue.

Translational Relevance

The OWC could be used clinically to continuously and rapidly deliver antimicrobials to infected ocular and periocular tissues, effectively lowering bacterial bioburdens and mitigating long-term complications.

The gamut of perspectives, challenges, and recent trends for in situ hydrogels: a smart ophthalmic drug delivery vehicle

Polymers have a major role in the controlled delivery of pharmaceutical compounds to a targeted portion of the body. In this quest, a high priority research area is the targeted delivery of ophthalmic drugs to the interior regions of the eyes. Due to their complex anatomical/biochemical nature. This necessitates an advanced drug delivery cargo that could administer a therapeutic agent to the targeted location by evading various obstacles. The ongoing focus is to design an ophthalmic formulation by coupling it with a smart in situ forming polymeric hydrogel. These smart macromolecules have an array of unique theranostic properties and can utilize the in vivo biological parameters as a stimulus to change their macromolecular state from liquid to gel. The fast gelling hydrogel improves the corneal contact time, facilitates sustained drug release, resists the burst-out effect, and assists drug permeability to anterior regions. This review summarizes the rationale, scientific objectives, properties, and classification of the biologically important in situ hydrogels in the niche of ophthalmic drug delivery. The current trends and prospectives of the array of stimulus-responsive polymers, copolymers, and nanomaterials are discussed broadly. The crucial biointerfacial attributes with pros and cons are reviewed by investigating the effect of the nature of polymers as well as the ratio/percentage of additives and copolymers that influence the overall performance.

Comparing in-vivo confocal microscopy and ex-vivo light and scanning electron microscopy images of the hairs of the pine processionary caterpillar embedded in the cornea: Report of three cases

This report describes three cases of pine processionary caterpillar hairs (setae) embedded in the cornea: one in a 69-year-old man with acute keratouveitis, a second case in a 65-year-old man with an epithelial defect and a stromal infiltrate, and the third case affecting a 54-year-old woman with mild keratitis. The two first patients had one hair embedded in the anterior corneal layers while the last one had several hairs deeply embedded in the stroma. By comparing in-vivo confocal microscopy (IVCM) with ex-vivo light microscopy (LM) and scanning electron microscopy (SEM) images, the morphology of the setae was identified and confirmed.

Multi-modal Anterior Eye Imager Combining Ultra-High Resolution OCT and Microvascular Imaging for Structural and Functional Evaluation of the Human Eye

To establish complementary information for the diagnosis and evaluation of ocular surface diseases, we developed a multi-modal, non-invasive optical imaging platform by combining ultra-high resolution optical coherence tomography (UHR-OCT) with a microvascular imaging system based on slit-lamp biomicroscopy. Our customized UHR-OCT module achieves an axial resolution of ≈2.9 μm in corneal tissue with a broadband light source and an A-line acquisition rate of 24 kHz with a line array CCD camera. The microvascular imaging module has a lateral resolution of 3.5 μm under maximum magnification of ≈187.5× with an imaging rate of 60 frames/s, which is sufficient to image the conjunctival vessel network and record the movement trajectory of clusters of red blood cells. By combining the imaging optical paths of different modules, our customized multi-modal anterior eye imaging platform is capable of performing real-time cross-sectional UHR-OCT imaging of the anterior eye, conjunctival vessel network imaging, high-resolution conjunctival blood flow videography, fluorescein staining and traditional slit-lamp imaging on a single device. With self-developed software, a conjunctival vessel network image and blood flow videography were further analyzed to acquire quantitative morphological and hemodynamics parameters, including vessel fractal dimensions, blood flow velocity and vessel diameters. The ability of our multi-modal anterior eye imager to provide both structural and functional information for ophthalmic clinical applications was demonstrated on a healthy human subject and a keratitis patient.

Kinetics of corneal leukocytes by intravital multiphoton microscopy

Corneal immune privilege is integral in maintaining the clear avascular window to the foreign world. The presence of distinct populations of corneal leukocytes (CLs) in the normal cornea has been firmly established. However, their precise function and kinetics remain, as of yet, unclear. Through intravital multiphoton microscopy (IV-MPM), allowing the means to accumulate critical spatial and temporal cellular information, we provide details for long-term investigation of CL morphology and kinetics under steady state and following inflammation. Significant alterations in size and morphology of corneal CD11c+ dendritic cells (DCs) were noted following acute sterile inflammation, including cell volume (4364.4 ± 489.6 vs. 1787.6 ± 111.0 μm3, P < 0.001) and sphericity (0.82 ± 0.01 vs. 0.42 ± 0.02, P < 0.001) compared with steady state. Furthermore, IV-MPM analyses revealed alterations in both the CD11c+ DC and major histocompatibility complex class II (MHC)-II+ mature antigen-presenting cell population kinetics during inflammation, including track displacement length (CD11c: 16.57 ± 1.41 vs. 4.64 ± 0.56 μm, P < 0.001; MHC-II: 9.03 ± 0.37 vs. 4.09 ± 0.39, P < 0.001) and velocity (CD11c: 1.91 ± 0.07 μm/min vs. 1.73 ± 0.1302 μm/min; MHC-II: 2.97 ± 0.07 vs. 1.62 ± 0.08, P < 0.001) compared with steady state. Our results reveal in vivo evidence of sessile CL populations exhibiting dendritic morphology under steady state and increased velocity of spherical leukocytes following inflammation. IV-MPM represents a powerful tool to study leukocytes in corneal diseases in context.-Seyed-Razavi, Y., Lopez, M. J., Mantopoulos, D., Zheng, L., Massberg, S., Sendra, V. G., Harris, D. L., Hamrah, P. Kinetics of corneal leukocytes by intravital multiphoton microscopy.

What's new in dry eye disease diagnosis? Current advances and challenges

Dry eye disease (DED) is a commonly encountered condition in general ophthalmology practice and imparts a significant socioeconomic burden. Despite its prevalence, there remain challenges regarding its diagnosis and management. A major reason behind these challenges is the fact that DED represents an umbrella term that encompasses many different underlying conditions and pathophysiological mechanisms. The purpose of this article is to highlight aspects of DED pathophysiology and focus on targeted diagnostic and therapeutic approaches to this multifactorial, chronic condition.

Two-photon microscopy of fungal keratitis-affected rabbit cornea ex vivo using moxifloxacin as a labeling agent

Two-photon microscopy (TPM) is a three dimensional (3D) microscopic technique based on nonlinear two-photon fluorescence, which has been tested as an alternative to reflectance confocal microscopy (RCM) for detecting fungal keratitis via optical imaging. Although TPM provided images with better contrast than RCM for fungal keratitis, its imaging speed was relatively low because of weak intrinsic signal. Moxifloxacin, a Food and Drug Administration (FDA)-approved antibiotic, was recently used as a cell-labeling agent for TPM. In this study, moxifloxacin was used to label fungal cells for TPM imaging of fungal keratitis models. Fungal cell suspensions and ex vivo fungal keratitis-affected rabbit corneas were prepared using two types of fungal pathogens, Aspergillus fumigatus and Candida albicans, and TPM imaging was performed both with and without moxifloxacin treatment. Fungal cells with enhanced fluorescence were clearly visible by TPM of moxifloxacin-treated fungal cell suspensions. TPM of moxifloxacin-treated fungal keratitis rabbit corneas revealed both the infecting fungal cells and corneal cells similar to those observed in TPM without moxifloxacin treatment, albeit with approximately 10-times enhanced fluorescence. Fungal cells were distinguished from corneal cells on the basis of their distinct morphologies. Thus, TPM with moxifloxacin labeling might be useful for the detection of fungal keratitis at the improved imaging speed.

Corneal Innervation and Sensation: The Eye and Beyond

The cornea is one of the most densely innervated and sensitive tissues in the body. In addition to their important sensory functions, corneal nerves induce reflex tear production, blinking, and the release of trophic factors - all of which combined help to maintain the structural and functional integrity of the surface of the eye. Consequently, damage to corneal nerves as a result of disease, surgery, or trauma can lead to diminished corneal sensitivity, epithelial defects, and possible blindness. In this review, we describe commonly used tools that have provided considerable new information on corneal architecture and sensation in healthy and diseased corneas, with special emphasis on changes seen in herpes zoster ophthalmicus, corneal and other therapeutic ocular procedures, antiglaucoma medical therapy, aging, and diabetes. With its potential applications ranging from managing ocular-specific to systemic diseases, the study of corneal innervation has implications for future therapies extending beyond just the eye itself.

Neutrophil migration in infection and wound repair: going forward in reverse

Neutrophil migration and its role during inflammation has been the focus of increased interest in the past decade. Advances in live imaging and the use of new model systems have helped to uncover the behaviour of neutrophils in injured and infected tissues. Although neutrophils were considered to be short-lived effector cells that undergo apoptosis in damaged tissues, recent evidence suggests that neutrophil behaviour is more complex and, in some settings, neutrophils might leave sites of tissue injury and migrate back into the vasculature. The role of reverse migration and its contribution to resolution of inflammation remains unclear. In this Review, we discuss the different cues within tissues that mediate neutrophil forward and reverse migration in response to injury or infection and the implications of these mechanisms to human disease.

Understanding Neuropathic Corneal Pain--Gaps and Current Therapeutic Approaches

The richly innervated corneal tissue is one of the most powerful pain generators in the body. Corneal neuropathic pain results from dysfunctional nerves causing perceptions such as burning, stinging, eye-ache, and pain. Various inflammatory diseases, neurological diseases, and surgical interventions can be the underlying cause of corneal neuropathic pain. Recent efforts have been made by the scientific community to elucidate the pathophysiology and neurobiology of pain resulting from initially protective physiological reflexes, to a more persistent chronic state. The goal of this clinical review is to briefly summarize the pathophysiology of neuropathic corneal pain, describe how to systematically approach the diagnosis of these patients, and finally summarizing our experience with current therapeutic approaches for the treatment of corneal neuropathic pain.

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

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Small-Fiber Neuropathy Is Associated With Corneal Nerve and Dendritic Cell Alterations: An In Vivo Confocal Microscopy Study

PURPOSE

In patients with small-fiber neuropathy (SFN), noninvasive diagnostic tests that allow accurate monitoring of disease progression are urgently needed. The aim of this study was to assess corneal trigeminal small sensory nerves and immune cells by in vivo corneal confocal microscopy (CCM) in SFN.

METHODS

In this prospective single-center study, 14 patients with histologically confirmed SFN were analyzed. CCM parameters [corneal nerve fiber density (NFD); the total number of nerves, main trunks, and branches; nerve tortuosity; and dendritic cell density] were compared with 14 age-matched healthy controls and correlated with clinical symptoms, disease course, and histopathological findings.

RESULTS

Corneal NFD (15,489.3 ± 5927.6 μm/mm² vs. 22,687.1 ± 4328.7 μm/mm²; P = 0.001) and the total number of nerves (10.4 ± 4.6/frame vs. 18.5 ± 4.8/frame; P < 0.0001) were significantly reduced in patients with SFN. In contrast, nerve tortuosity was significantly increased (2.2 ± 0.3 vs. 1.7 ± 0.5; P = 0.02). Corneal NFD did not correlate with intraepidermal NFD (ρ = -0.158; P = 0.5) or clinical symptoms (cold P = 0.1; prickling P = 0.2; burning P = 0.8; formication P = 0.7; stabbing P = 0.4; rubbing 0.1; pressure P = 0.1). The average dendritic cell density was increased in SFN (33.5 ± 57.5 cells/mm² vs. 16.1 ± 13.7 cells/mm²) but did not reach significance (P = 0.7).

CONCLUSIONS

CCM provides parameters that reliably indicate injury to sensory afferents of the trigeminal nerve in patients with SFN. Our data suggest that CCM may serve both as a noninvasive diagnostic test and as a surrogate marker in SFN.

Comparison of reflectance confocal microscopy and two-photon second harmonic generation microscopy in fungal keratitis rabbit model ex vivo

Fungal keratitis is an infection of the cornea by fungal pathogens. Diagnosis methods based on optical microscopy could be beneficial over the conventional microbiology method by allowing rapid and non-invasive examination. Reflectance confocal microscopy (RCM) and two-photon second harmonic generation microscopy (TPSHGM) have been applied to pre-clinical or clinical studies of fungal keratitis. In this report, RCM and TPSHGM were characterized and compared in the imaging of a fungal keratitis rabbit model ex vivo. Fungal infection was induced by using two strains of fungi: aspergillus fumigatus and candida albicans. The infected corneas were imaged in fresh condition by both modalities sequentially and their images were analyzed. Both RCM and TPSHGM could detect both fungal strains within the cornea based on morphology: aspergillus fumigatus had distinctive filamentous structures, and candida albicans had round structures superficially and elongated structures in the corneal stroma. These imaging results were confirmed by histology. Comparison between RCM and TPSHGM showed several characteristics. Although RCM and TPSHGM images had good correlation each other, their images were slightly different due to difference in contrast mechanism. RCM had relatively low image contrast with the infected turbid corneas due to high background signal. TPSHGM visualized cells and collagen in the cornea clearly compared to RCM, but used higher laser power to compensate low autofluorescence. Since these two modalities provide complementary information, combination of RCM and TPSHGM would be useful for fungal keratitis detection by compensating their weaknesses each other.

New Details of the Human Corneal Limbus Revealed With Second Harmonic Generation Imaging

PURPOSE

To report novel findings of the human corneal limbus by using second harmonic generation (SHG) imaging.

METHODS

Corneal limbus was imaged by using an inverted two-photon excitation fluorescence microscope. Laser (Ti:Sapphire) was tuned at 850 nm for two-photon excitation. Backscatter signals of SHG and autofluorescence (AF) were collected through a 425/30-nm emission filter and a 525/45-emission filter, respectively. Multiple, consecutive, and overlapping image stacks (z-stack) were acquired for the corneal limbal area.

RESULTS

Two novel collagen structures were revealed by SHG imaging at the limbus: an anterior limbal cribriform layer and presumed anchoring fibers. Anterior limbal cribriform layer is an intertwined reticular collagen architecture just beneath the limbal epithelial niche and is located between the peripheral cornea and Tenon's/scleral tissue. Autofluorescence imaging revealed high vascularity in this structure. Central to the anterior limbal cribriform layer, radial strands of collagen were found to connect the peripheral cornea to the limbus. These presumed anchoring fibers have both collagen and elastin and were found more extensively in the superficial layers than deep layer and were absent in very deep limbus near Schlemm's canal.

CONCLUSIONS

By using SHG imaging, new details of the collagen architecture of human corneal limbal area were elucidated. High resolution images with volumetric analysis revealed two novel collagen structures.

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

PURPOSE

To investigate the longitudinal alterations of subbasal corneal nerves in patients with infectious keratitis (IK) during the acute phase, cessation of treatment, and the recovery phase by in vivo confocal microscopy (IVCM).

DESIGN

Prospective, longitudinal, case-control, single-center study.

PARTICIPANTS

Fifty-six eyes of 56 patients with the diagnosis of bacterial (n=28), fungal (n=15), or Acanthamoeba (n=13) keratitis were included in the study. Thirty eyes of 30 normal volunteers constituted the control group.

METHODS

Corneal sensation and serial IVCM of the central cornea were performed prospectively using the Heidelberg Retina Tomograph 3/Rostock Cornea Module (Heidelberg Engineering, Heidelberg, Germany). The IVCM images were assessed at 3 time points: at the acute phase (first visit to the cornea service), at cessation of antimicrobial treatment, and up to 6 months after the resolution of infection.

MAIN OUTCOME MEASURES

Total nerve number and length, main nerve trunks, branching, and corneal sensation were assessed during the follow-up period.

RESULTS

Corneal nerves were reduced significantly during the acute phase in eyes with IK compared with controls across all subgroups, with total nerve length of 5.47±0.69 mm/mm2 versus 20.59±1.06 mm/mm2 (P<0.0001). At the cessation of treatment, corneal nerves in patients with IK had regenerated, including total nerve length (8.49±0.94 mm/mm2; P=0.02) and nerve branch length (4.80±0.37 mm/mm2; P=0.005). During the recovery phase, after resolution of infection, corneal nerves regenerated further, including total nerve length (12.13±1.97 mm/mm2; P=0.005), main nerve trunk length (5.80±1.00 mm/mm2; P=0.01), and nerve branch length (6.33±0.76 mm/mm2; P=0.003) as compared with the acute phase, but were still significantly lower when compared with controls (P<0.05 for all parameters). Corneal degeneration and regeneration correlated with corneal sensation (r=0.47; P=0.0009).

CONCLUSIONS

Patients with IK who sustain profound loss of corneal nerves during the acute phase of infection demonstrate increased corneal nerve density during the first 6 months after the resolution of infection. However, despite significant nerve regeneration, corneal nerve density does not recover fully and remains low compared to controls. By providing an objective methodology to monitor corneal re-innervation, IVCM adds potentially important findings that may have implications for clinical management and surgical planning.

The role and treatment of inflammation in dry eye disease

Dry eye syndrome is a common ocular surface problem, affects 10-30 % of the population, especially in those who are older than 40 years. As a consequence of the demographic pressure created by the aging population, its prevalence is expected to increase as well as its burden on ophthalmologic practices. Thus, understanding the complex underlying mechanisms and development of thoughtful, effective strategies that involve these mechanisms are critical. Many factors causing ocular surface damage and inflammation have been shown to contribute to the etiopathogenesis. Increased osmolarity induces ocular surface inflammation leading to disruption of both the quality and quantity of tears. Pathologic tear function and the ocular surface inflammation affects the neural arcade and increases apoptosis in the ocular surface cells thus creating a viscous cycle for dry eye by causing unstable and hyperosmolar tears. Thus, the treatment objective is to prevent severe dry eye complications via preventing inflammation and apoptosis of the ocular surface cells. The ultimate target is a normalized ocular surface, increased tear stability, and decreased osmolarity of the tear film. In the light of current literature, this review aims to elucidate the role of inflammation as the main etiological factor in dry eye disease and discuss current therapeutic approaches to overcome it.

En-face optical coherence tomography as a novel tool for exploring the ocular surface: a pilot comparative study to conventional B-scans and in vivo confocal microscopy

PURPOSE

To explore the potential of spectral-domain optical coherence tomography (SD-OCT) using the en-face technology for the imaging of ocular surface diseases and to correlate the findings with in vivo confocal microscopy (IVCM) images.

PATIENTS AND METHODS

113 eyes of 75 subjects with various ocular surface diseases were investigated with the RTVue(®) anterior-segment en face OCT. En face OCT images were compared to B-scan OCT and IVCM images.

RESULTS

Patients with corneal dystrophies, corneal deposits, keratitis, pterygium, conjunctivochalasis, or ocular surface squamous neoplasia and patients who underwent lamellar corneal surgeries were included. En-face OCT images showed ocular surface tissue changes that were not discernible using conventional B-scan OCT. Nevertheless, there was a good correlation with IVCM analysis. Compared with IVCM, the major advantages of en-face OCT included easy operation and rapid image acquisition, with minimal operator experience required. In addition, the non-contact method avoided patient discomfort and external pressure on the globe, which was especially useful in patients with corneal dystrophies, ulcers, or corneal abscesses. Although the resolution of en-face OCT was lower than that of IVCM, it allowed useful overall visualization of corneal lesions due to the larger areas analyzed.

CONCLUSION

En-face SD-OCT is a novel, valuable tool to assess a wide variety of ocular surface diseases. It can provide additional information and new insight into different ocular surface conditions with no corneal contact.

In vivo confocal evaluation of the ocular surface morpho-functional unit in dry eye

PURPOSE

To study, by a new, integrated, laser scanning confocal microscopy approach, the ocular surface morpho-functional unit in patients with primary Sjogren syndrome (SSI), non-Sjogren syndrome dry eye (non-SSDE), and meibomian gland disease (MGD).

METHODS

Patients and age- and sex-matched control subjects (N = 60; 15 each) were consecutively enrolled in a prospective case-control study. Laser scanning confocal microscopy was used to obtain simultaneous optical sampling of the ocular surface components: cornea, bulbar and tarsal conjunctiva, MGs, and eyelid margin.

RESULTS

For all superficial epithelia, except eyelid margins, there were reduced cell densities in each group compared with that in controls (p < 0.001). The lowest cell densities were in the SSI group (p < 0.001). Eyelid margin superficial cell density was decreased only in MGD (p < 0.001). Basal epithelial cell density at the corneal apex was increased in both SSI and non-SSDE compared with that in controls (p < 0.01). In the conjunctiva, it was decreased in each group compared with that in controls (p < 0.01). Subbasal dendritic cell density was significantly increased in both SSI and MGD compared with that in controls (p < 0.01). Conjunctival inflammatory cell density and MG inflammation were increased in each group compared with those in controls (p < 0.001), with the highest values in SSI. Subbasal nerve plexi had fewer fibers and higher bead density in each group compared with those in controls (p < 0.001). There was increased tortuosity in both SSI and MGD (p < 0.001). Patients with MGD had the lowest MG acinar density, the largest diameter of acini and acinar orifices, and the highest secretion reflectivity (p < 0.001).

CONCLUSIONS

Laser scanning confocal microscopy can provide an in vivo, noninvasive, high-resolution overview of the ocular surface morpho-functional unit. This confocal integrated approach may be useful in both research and clinical settings.

Anterior segment optical coherence tomography in evaluation of severe fungal keratitis infections treated by corneal crosslinking

PURPOSE

Anterior segment optical coherence tomography (OCT) is a relevant diagnostic tool in the evaluation of corneal changes following corneal crosslinking (CXL) treatment in patients infected by a severe fungal corneal infection.

METHODS

Two patients with severe fungal keratitis that was unresponsive to medical treatment were treated with CXL. Corneal melting was present in all cases. Anterior segment OCT showed the preoperative depth and extension of the infiltrate and the modification during the follow-up.

RESULTS

Blockage of the melting was achieved in one patient and one patient developed a corneal perforation. Anterior segment OCT allowed control of the evolution of fungal infection and evaluation of the corneal tissue response to the CXL. It is also able to identify the extent and depth of the inflammation. This parameter seems more important than corneal pachymetry to ensure the safety of CXL procedures in infectious keratitis.

CONCLUSIONS

The different behavior of inflamed tissue with respect to UVA irradiance could be the main point to understand the different postoperative outcome.

An in vivo method for visualizing flow dynamics of cells within corneal lymphatics

BACKGROUND

Monitoring the trafficking of specific cell populations within lymphatics could improve our understanding of processes such as transplant rejection and cancer metastasis. Current methods, however, lack appropriate image resolution for single-cell analysis or are incompatible with in vivo and longitudinal monitoring of lymphatics in their native state. We therefore sought to achieve high-resolution live imaging of the dynamic behavior of cells within lymph vessels in the rat cornea.

METHODS/RESULTS

Inflammatory angiogenesis was induced by suture placement in corneas of Wistar rats. Pre- and up to 3 weeks post-induction, corneas were noninvasively examined by laser-scanning in vivo corneal confocal microscopy (IVCM) using only endogenous contrast. Lymph vessels and the cells harbored therein were documented by still images, real-time video, and 3D confocal stack reconstruction of live tissue. In vivo, conjunctival and corneal lymphatics were morphologically distinct, those with corneal location being one-quarter the diameter of those in the conjunctiva (p<0.001). Cells were recruited to initially empty pre-existing lymph vessels during the first day of inflammation and maintained a dense occupation of vessels for up to 7 days. A diverse population of cells (diameter range: 1.5-27.5 μm) with varying morphology was observed, and exhibited variable flow patterns and were transported singly and in clusters of at least 2-9 adherent cells.

CONCLUSIONS

The in vivo microscopic technique presented enables lymph vessels and cell trafficking to be studied in high resolution in a minimally-perturbed physiologic milieu.

In vivo imaging of therapy-induced anti-cancer immune responses in humans

Immunotherapy aims to re-engage and revitalize the immune system in the fight against cancer. Research over the past decades has shown that the relationship between the immune system and human cancer is complex, highly dynamic, and variable between individuals. Considering the complexity, enormous effort and costs involved in optimizing immunotherapeutic approaches, clinically applicable tools to monitor therapy-induced immune responses in vivo are most warranted. However, the development of such tools is complicated by the fact that a developing immune response encompasses several body compartments, e.g., peripheral tissues, lymph nodes, lymphatic and vascular systems, as well as the tumor site itself. Moreover, the cells that comprise the immune system are not static but constantly circulate through the vascular and lymphatic system. Molecular imaging is considered the favorite candidate to fulfill this task. The progress in imaging technologies and modalities has provided a versatile toolbox to address these issues. This review focuses on the detection of therapy-induced anticancer immune responses in vivo and provides a comprehensive overview of clinically available imaging techniques as well as perspectives on future developments. In the discussion, we will focus on issues that specifically relate to imaging of the immune system and we will discuss the strengths and limitations of the current clinical imaging techniques. The last section provides future directions that we envision to be crucial for further development.

Ocular surface immunity: homeostatic mechanisms and their disruption in dry eye disease

The tear film, lacrimal glands, corneal and conjunctival epithelia and Meibomian glands work together as a lacrimal functional unit (LFU) to preserve the integrity and function of the ocular surface. The integrity of this unit is necessary for the health and normal function of the eye and visual system. Nervous connections and systemic hormones are well known factors that maintain the homeostasis of the ocular surface. They control the response to internal and external stimuli. Our and others' studies show that immunological mechanisms also play a pivotal role in regulating the ocular surface environment. Our studies demonstrate how anti-inflammatory factors such as the expression of vascular endothelial growth factor receptor-3 (VEGFR-3) in corneal cells, immature corneal resident antigen-presenting cells, and regulatory T cells play an active role in protecting the ocular surface. Dry eye disease (DED) affects millions of people worldwide and negatively influences the quality of life for patients. In its most severe forms, DED may lead to blindness. The etiology and pathogenesis of DED remain largely unclear. Nonetheless, in this review we summarize the role of the disruption of afferent and efferent immunoregulatory mechanisms that are responsible for the chronicity of the disease, its symptoms, and its clinical signs. We illustrate current anti-inflammatory treatments for DED and propose that prevention of the disruption of immunoregulatory mechanisms may represent a promising therapeutic strategy towards controlling ocular surface inflammation.