In vivoconfocal microscopy, an inner vision of the cornea - a major review

Assessment of Corneal Epithelial Changes and Related Factors in Ocular Chronic Graft-Versus-Host Disease (GVHD) by in Vivo Confocal Microscopy

PURPOSE

To evaluate corneal epithelial changes and related factors in chronic ocular graft-versus-host disease (oGVHD) patients.

METHODS

21 patients (35 eyes) with chronic oGVHD and 8 patients (12 eyes) without oGVHD after bone marrow transplantation were recruited for assessment involving in vivo confocal microscopy (IVCM) analysis, ocular surface parameter determination and tear cytokine level analysis. The IVCM corneal epithelial scoring system was used to evaluate corneal epithelial changes.

RESULTS

There was a significant difference in the corneal epithelial score (p = .001) between the two groups. The corneal epithelial scores were significantly correlated with the corneal fluorescein staining scores (CFS, r = 0.463, p < .001), Schirmer's test (r = -0.389, p = .009) and tear cytokine levels of EGF (r = -0.491, p < .001) and APRIL (r = -0.318, p = .030).

CONCLUSIONS

The depth of corneal epithelial defects can be estimated by the CFS. Corneal epithelial changes of chronic oGVHD are considered to be associated with lacrimal deficiency and a lack of EGF.

Evaluation of aqueous-deficient and evaporative dry eye cases with confocal microscopy

INTRODUCTION

Dry eye disease (DED) is an important health problem affecting hundreds of millions of people worldwide. In vivo confocal microscopy (IVCM) is a non-invasive imaging tool that can visualize ocular surface diseases. In this study, we aimed to evaluate corneal structures and inflammatory cells with IVCM in DED patients.

MATERIAL AND METHODS

The patients were divided into three subgroups: group 1, consisting of 22 patients with aqueous tear insufficiency; group 2, consisting of 21 patients with evaporative type DED; and group 3, consisting of 20 healthy patients. Imaging was performed with IVCM. The corneal epithelium, nerves, stroma, endothelial and inflammatory cells were compared between groups.

RESULTS

There was a significant decrease in corneal epithelial cell density in cases with DED, and there was a significant increase in corneal basal epithelial cell density in the aqueous-deficient type. Keratocyte density was significantly increased in the aqueous-deficient type. A significant decrease in the number and density of sub-basal nerves was found in aqueous-deficient cases, and an increase was found in neural pilling and folding. Dendritic cell density, size, number and area were significantly increased in the aqueous-deficient type. There was also decreased corneal endothelial cell density in DED.

CONCLUSION

We evaluated pathological changes in DED on the corneal surface by IVCM. This methodology is valuable in terms of objectively evaluating how the corneal surface is affected in accordance with disease severity and in predicting poor response to treatment.

Ocular microbial dysbiosis and its linkage with infectious keratitis patients in Northwest China: A cross-sectional study

OBJECTIVES

To evaluate the alteration of ocular surface microbiome of patients with infectious keratitis in northwest of China.

METHODS

The corneal scrapings, eyelid margin and conjunctiva samples were collected from 57 participants, who were divided into bacterial keratitis, fungal keratitis, viral keratitis and control group. The V3-V4 region of bacterial 16S rDNA in each sample was amplified and sequenced on the Illumina HiSeq 2500 sequencing platform, and the differences among different groups were compared bioinformatically.

RESULTS

Significant alterations of the microbiome were observed in alpha-diversity and beta-diversity analysis between the keratitis groups and the control group (p < 0.05). There was no significant differences between eyelid margin and conjunctiva samples in Alpha-Diversity analysis, but a significant difference between eyelid margin and corneal scraping samples in the keratitis group (p < 0.05, independent t-test). The abundances of Bacillus, Megamonas, Acinetobacter, and Rhodococcu were significantly elevated, while the abundance of Staphylococcus was decreased in the keratitis group compared to the control group.

CONCLUSIONS

The abundance of the ocular microbiome in patients with bacterial keratitis, fungal keratitis, or viral keratitis was significantly higher than those in the control group. Keratitis patients may have ecological disorder on ocular surface microbiome compared with controls. We believe that the conjunctiva and eyelid margin microbiome combined analysis can more comprehensively reflect the composition and abundance of ocular surface microbiome.

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.

Methods for evaluation of corneal nerve fibres in diabetes mellitus by in vivo confocal microscopy: a scoping review protocol

INTRODUCTION

Globally, 422 million people have diabetes. Late complications of diabetes are blindness, kidney failure, heart attack, stroke and lower limb amputation. The prevalence of diabetic peripheral neuropathy and diabetic retinopathy is 50% and 35%, respectively. In vivo confocal microscopy (IVCM) is a rapid, non-invasive method to evaluate subbasal corneal nerve fibres, which are small fibres of the peripheral nervous system. Corneal nerve fibre changes can be a marker of diabetic peripheral neuropathy. There is currently no gold-standard procedure for IVCM imaging, image processing or quantitative analysis of the corneal nerve fibres in the subbasal plexus. This protocol describes a scoping review to map, summarise and critically evaluate current methods used with IVCM evaluation in people with diabetes mellitus.

METHODS

The scoping review will follow Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for scoping review. A comprehensive search of the literature will be conducted in MEDLINE, Embase, Cochrane, Scopus and Web of Science. The search strategy will include terms related to IVCM, diabetes and corneal nerve fibres. We will set inclusion and exclusion criteria prior to the search, and two reviewers will screen titles and abstracts independently. One reviewer will full text read eligible articles and chart data from the studies. A descriptive summary of the methods used in imaging, image processing and quantitative analysis of peripheral corneal nerve fibres by IVCM will be written.

ETHICS AND DISSEMINATION

Ethical approval is not required since this is a scoping review based on previously published articles. The findings will be published in a scientific peer-reviewed journal.

Corneal dendritic cells in diabetes mellitus: A narrative review

Diabetes mellitus is a global public health problem with both macrovascular and microvascular complications, such as diabetic corneal neuropathy (DCN). Using in-vivo confocal microscopy, corneal nerve changes in DCN patients can be examined. Additionally, changes in the morphology and quantity of corneal dendritic cells (DCs) in diabetic corneas have also been observed. DCs are bone marrow-derived antigen-presenting cells that serve both immunological and non-immunological roles in human corneas. However, the role and pathogenesis of corneal DC in diabetic corneas have not been well understood. In this article, we provide a comprehensive review of both animal and clinical studies that report changes in DCs, including the DC density, maturation stages, as well as relationships between the corneal DCs, corneal nerves, and corneal epithelium, in diabetic corneas. We have also discussed the associations between the changes in corneal DCs and various clinical or imaging parameters, including age, corneal nerve status, and blood metabolic parameters. Such information would provide valuable insight into the development of diagnostic, preventive, and therapeutic strategies for DM-associated ocular surface complications.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Label free optical transmission tomography for biosystems: intracellular structures and dynamics

There is an increasing need for label free methods that could reveal intracellular structures and dynamics. In this context, we develop a new optical tomography method working in transmission - full-field optical transmission tomography (FF-OTT). The method can measure the forward scattering signals and reveals the time-dependent metabolic signals in living cells. FF-OTT is a common path interferometer taking advantage of the Gouy phase shift - a π phase shift that the light wave experiences around the focus. By modulating the position of the focus one can alter the phase of the scattered light. Demodulation of images with different phases rejects the background and enhances the light from the depth-of-field, thus producing an optical section. We test FF-OTT by imaging single-cell diatoms and ex vivo biological samples. In fresh samples, we show that the intracellular motions create visible intensity fluctuations in FF-OTT so that the method is able to reveal a metabolic dynamic contrast. FF-OTT was found to be an efficient label free technique that can be readily implemented thanks to a robust common-path speckle-free interferometer design using an incoherent light source.

Corneal in vivo Confocal Microscopy for Assessment of Non-Neurological Autoimmune Diseases: A Meta-Analysis

Purpose

This study aimed to evaluate the features of corneal nerve with in vivo confocal microscopy (IVCM) among patients with non-neurological autoimmune (NNAI) diseases.

Methods

We systematically searched PubMed, Web of Science, and Cochrane Central Register of Controlled Trials for studies published until May 2021. The weighted mean differences (WMDs) of corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), tortuosity, reflectivity, and beadings per 100 μm with a 95% CI between NNAI and control group were analyzed using a random-effects model.

Results

The results showed 37 studies involving collective totals of 1,423 patients and 1,059 healthy controls were ultimately included in this meta-analysis. The pooled results manifested significantly decreased CNFL (WMD: −3.94, 95% CI: −4.77–−3.12), CNFD (WMD: −6.62, 95% CI: −8.4–−4.85), and CNBD (WMD: −9.89, 95% CI: −14–−5.79) in NNAI patients. In addition, the NNAI group showed more tortuous corneal nerve (WMD: 1.19, 95% CI:0.57–1.81). The comparison between NNAI patients and healthy controls in beadings per 100 μm corneal nerve length was inconsistent. No significant difference was found in the corneal nerve fiber reflectivity between NNAI and the control group (WMD: −0.21, 95% CI: −0.65–0.24, P = 0.361).

Conclusions

The parameters and morphology of corneal nerves observed by IVCM proved to be different in NNAI patients from healthy controls, suggesting that IVCM may be a non-invasive technique for identification and surveillance of NNAI diseases.

In Vivo Confocal Microscopy Evaluation in Patients with Keratoconus

Keratoconus is the most common primary corneal ectasia characterized by progressive focal thinning. Patients experience increased irregular astigmatism, decreased visual acuity and corneal sensitivity. Corneal collagen crosslinking (CXL), a minimally invasive procedure, is effective in halting disease progression. Historically, keratoconus research was confined to ex vivo settings. In vivo confocal microscopy (IVCM) has been used to examine the corneal microstructure clinically. In this review, we discuss keratoconus cellular changes evaluated by IVCM before and after CXL. Cellular changes before CXL include decreased keratocyte and nerve densities, disorganized subbasal nerves with thickening, increased nerve tortuosity and shortened nerve fibre length. Repopulation of keratocytes occurs up to 1 year post procedure. IVCM also correlates corneal nerve status to functional corneal sensitivity. Immediately after CXL, there is reduced nerve density and keratocyte absence due to mechanical removal of the epithelium and CXL effect. Nerve regeneration begins after 1 month, with nerve fibre densities recovering to pre-operative levels between 6 months to 1 year and remains stable up to 5 years. Nerves remain tortuous and nerve densities are reduced. Corneal sensitivity is reduced immediately postoperatively but recovers with nerve regeneration. Our article provides comprehensive review on the use of IVCM imaging in keratoconus patients.

Diagnostic armamentarium of infectious keratitis: A comprehensive review

Infectious keratitis (IK) represents the leading cause of corneal blindness worldwide, particularly in developing countries. A good outcome of IK is contingent upon timely and accurate diagnosis followed by appropriate interventions. Currently, IK is primarily diagnosed on clinical grounds supplemented by microbiological investigations such as microscopic examination with stains, and culture and sensitivity testing. Although this is the most widely accepted practice adopted in most regions, such an approach is challenged by several factors, including indistinguishable clinical features shared among different causative organisms, polymicrobial infection, long diagnostic turnaround time, and variably low culture positivity rate. In this review, we aim to provide a comprehensive overview of the current diagnostic armamentarium of IK, encompassing conventional microbiological investigations, molecular diagnostics (including polymerase chain reaction and mass spectrometry), and imaging modalities (including anterior segment optical coherence tomography and in vivo confocal microscopy). We also highlight the potential roles of emerging technologies such as next-generation sequencing, artificial intelligence-assisted platforms. and tele-medicine in shaping the future diagnostic landscape of IK.

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.

A Review On digital image processing techniques for in-Vivo confocal images of the cornea

This work reviews the scientific literature regarding digital image processing for in vivo confocal microscopy images of the cornea. We present and discuss a selection of prominent techniques designed for semi- and automatic analysis of four areas of the cornea (epithelium, sub-basal nerve plexus, stroma and endothelium). The main context is image enhancement, detection of structures of interest, and quantification of clinical information. We have found that the preprocessing stage lacks of quantitative studies regarding the quality of the enhanced image, or its effects in subsequent steps of the image processing. Threshold values are widely used in the reviewed methods, although generally, they are selected empirically and manually. The image processing results are evaluated in many cases through comparison with gold standards not widely accepted. It is necessary to standardize values to be quantified in terms of sensitivity and specificity of methods. Most of the reviewed studies do not show an estimation of the computational cost of the image processing. We conclude that reliable, automatic, computer-assisted image analysis of the cornea is still an open issue, constituting an interesting and worthwhile area of research.

Clinical Applications of In Vivo Confocal Microscopy in Keratorefractive Surgery

PURPOSE

To review the contribution of in vivo confocal microscopy (IVCM) to the understanding of corneal wound healing following refractive surgery, and its role in the diagnosis and management of complications arising from keratorefractive procedures.

METHODS

Review of the basic science and clinical literature relating to the study of keratorefractive surgical procedures using IVCM.

RESULTS

Extensive research using IVCM has generated a comprehensive understanding of tissue responses after corneal refractive surgery. Epithelial thickness and stromal keratocyte density can be quantified postoperatively and studied longitudinally. Corneal nerve loss and subsequent reinnervation has been characterized and differs significantly between laser refractive techniques. IVCM has also been used to study complications arising from postoperative inflammation (diffuse lamellar keratitis, central toxic keratopathy, ring keratitis, and ectasia), infection (microbial keratitis), and neuropathy (dry eye and neuralgia). This imaging technique can have a critical role in the diagnosis of these complications and subsequent monitoring of treatment response. Manual processing of IVCM images is time-consuming and there may be significant interobserver and intraobserver variability with poor repeatability. However, increasing automation and the use of artificial intelligence is improving the speed and accuracy of image analysis.

CONCLUSIONS

IVCM has historically been confined to a research setting because image capture and subsequent processing was extremely labor intensive. However, advances in both hardware and software capabilities promise to allow the use of IVCM in routine clinical practice. Real-time evaluation of the cornea at a cellular level will be particularly useful in patients with inflammatory, infectious, or neuropathic complications of keratorefractive surgery. [J Refract Surg. 2021;37(7):493-503.].

Laser Doppler holography of the anterior segment for blood flow imaging, eye tracking, and transparency assessment

Laser Doppler holography (LDH) is a full-field blood flow imaging technique able to reveal human retinal and choroidal blood flow with high temporal resolution. We here report on using LDH in the anterior segment of the eye without making changes to the instrument. Blood flow in the bulbar conjunctiva and episclera as well as in corneal neovascularization can be effectively imaged. We additionally demonstrate simultaneous holographic imaging of the anterior and posterior segments by simply adapting the numerical propagation distance to the plane of interest. We used this feature to track the movements of the retina and pupil with high temporal resolution. Finally, we show that the light backscattered by the retina can be used for retro-illumination of the anterior segment. Hence digital holography can reveal opacities caused by absorption or diffusion in the cornea and eye lens.

Imaging of vascular abnormalities in ocular surface disease

The vascular system of the ocular surface plays a central role in infectious, autoimmune, inflammatory, traumatic and neoplastic diseases. The development, application, and monitoring of treatments for vascular abnormalities depends on the in vivo analysis of the ocular surface vasculature. Until recently, ocular surface vascular imaging was confined to biomicroscopic and color photographic assessment, both limited by poor reproducibility and the inability to image lymphatic vasculature in vivo. The evolvement and clinical implementation of innovative imaging modalities including confocal microscopy, intravenous, and optical coherence tomography-based angiography now allows standardized quantitative and functional vascular assessment with potential applicability to automated analysis algorithms and diagnostics.

A New Methodology for the Assessment of Very Low Concentrations of Cells in Serous Body Fluids Based on the Count of Ultrasound Echoes Backscattered From Cells

A methodology for the assessment of cell concentration, in the range 5-100 cells/ [Formula: see text], suitable for in vivo analysis of serous body fluids is presented in this work. This methodology is based on the quantitative analysis of ultrasound images obtained from cell suspensions and considers applicability criteria, such as short analysis times, moderate frequency, and absolute concentration estimation, all necessary to deal with the variability of tissues among different patients. Numerical simulations provided the framework to analyze the impact of echo overlapping and the polydispersion of scatterer sizes on the cell concentration estimation. The cell concentration range that can be analyzed as a function of the transducer and emitted waveform used was also discussed. Experiments were conducted to evaluate the performance of the method using 7- [Formula: see text] and 12- [Formula: see text] polystyrene particles in water suspensions in the 5-100 particles/ [Formula: see text] range. A single scanning focused transducer working at a central frequency of 20 MHz was used to obtain ultrasound images. The method proposed to estimate the concentration proved to be robust for different particle sizes and variations of gain acquisition settings. The effect of tissues placed in the ultrasound path between the probe and the sample was also investigated using 3-mm-thick tissue mimics. Under this situation, the algorithm was robust for the concentration analysis of 12 [Formula: see text] particle suspensions, yet significant deviations were obtained for the smallest particles.

Morphological characterization of the human corneal epithelium by in vivo confocal laser scanning microscopy

Background

Regarding the growing interest and importance of understanding the cellular changes of the cornea in diseases, a quantitative cellular characterization of the epithelium is becoming increasingly important. Towards this, the latest research offers considerable improvements in imaging of the cornea by confocal laser scanning microscopy (CLSM). This study presents a pipeline to generate normative morphological data of epithelial cell layers of healthy human corneas.

Methods

3D in vivo CLSM was performed on the eyes of volunteers (n=25) with a Heidelberg Retina Tomograph II equipped with an in-house modified version of the Rostock Cornea Module implementing two dedicated piezo actuators and a concave contact cap. Image data were acquired with nearly isotropic voxel resolution. After image registration, stacks of en-face sections were used to generate full-thickness volume data sets of the epithelium. Beyond that, an image analysis algorithm quantified en-face sections of epithelial cells regarding the depth-dependent mean of cell density, area, diameter, aggregation (Clark and Evans index of aggregation), neighbor count and polygonality.

Results

Imaging and cell segmentation were successfully performed in all subjects. Thereby intermediated cells were efficiently recognized by the segmentation algorithm while efficiency for superficial and basal cells was reduced. Morphological parameters showed an increased mean cell density, decreased mean cell area and mean diameter from anterior to posterior (5,197.02 to 8,190.39 cells/mm²; 160.51 to 90.29 µm²; 15.9 to 12.3 µm respectively). Aggregation gradually increased from anterior to posterior ranging from 1.45 to 1.53. Average neighbor count increased from 5.50 to a maximum of 5.66 followed by a gradual decrease to 5.45 within the normalized depth from anterior to posterior. Polygonality gradually decreased ranging from 4.93 to 4.64 sides of cells. The neighbor count and polygonality parameters exhibited profound depth-dependent changes.

Conclusions

This in vivo study demonstrates the successful implementation of a CLSM-based imaging pipeline for cellular characterization of the human corneal epithelium. The dedicated hardware in combination with an adapted image registration method to correct the remaining motion-induced image distortions followed by a dedicated algorithm to calculate characteristic quantities of different epithelial cell layers enabled the generation of normative data. Further significant effort is necessary to improve the algorithm for superficial and basal cell segmentation.

Can in vivo confocal microscopy differentiate between sub-types of dry eye disease? A review

Many studies utilised in vivo confocal microscopy (IVCM) to associate variations in corneal structures with dry eye disease (DED). However, DED is an umbrella term that covers various aetiologies and presentations. This review analyses populations by DED aetiology to determine the relationships between IVCM parameters and specific DED sub-types. It focuses on the most commonly examined structures, sub-basal nerves and dendritic cells. Across the literature, most studies found individuals with immune-mediated DED had lower sub-basal nerve fibre number and density than controls, with smaller differences between non-immune DED and controls. However, wide ranges of values reported across studies demonstrate considerable overlap between DED sub-types and controls, rendering these metrics less helpful when diagnosing an individual patient. Dendritic cell density was considerably higher in individuals with immune-mediated DED than in non-immune DED or controls. As such, dendritic cell density may be a better indicator of DED associated with a systemic immune-mediated process.

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.

High Molecular Weight Hyaluronan Promotes Corneal Nerve Growth in Severe Dry Eyes

The purpose of this study was to investigate the effect of high molecular weight hyaluronan (HMWHA) eye drops on subbasal corneal nerves in patients suffering from severe dry eye disease (DED) and to evaluate the damage of subbasal corneal nerves associated with severe DED. Designed as an international, multicenter study, 16 patients with symptoms of at least an Ocular Surface Disease Index (OSDI) score of 33, and corneal fluorescein staining (CFS) of at least Oxford grade 3, were included and randomized into two study arms. The control group continued to use their individual optimum artificial tears over the study period of eight weeks; in the verum group, the artificial tears were substituted by eye drops containing 0.15% HMWHA. At the baseline visit, and after eight weeks, the subbasal nerve plexus of 16 patients were assessed by confocal laser scanning microscopy (CSLM). The images were submitted to a masked reading center for evaluation. Results showed a significant increase of total nerve fiber lengths (CNFL) in the HMWHA group (p = 0.030) when compared to the control group, where the total subbasal CNFL did not significantly change from baseline to week 8. We concluded that in severe DED patients, HMWHA from topically applied eye drops could cross the epithelial barrier and reach the subbasal nerve plexus, where it exercised a trophic effect.

In Vivo Confocal Microscopy Findings in Bowman Layer Transplantation

PURPOSE

To report the in vivo confocal microscopy (IVCM) findings of a case who underwent femtosecond laser-assisted Bowman layer transplantation (BLT).

METHODS

This is a case report.

RESULTS

In a 25-year-old man with previous diagnosis of keratoconus in whom a BLT was performed using the femtosecond laser-assisted technique, IVCM (Confoscan 4; Fortune Technologies, Vigonza, Italy) was performed 3 months after surgery, obtaining a sequence of 4 digitalized images of the total thickness of the cornea, from the epithelium to the endothelium, and then backward. The images were analyzed with the Navis v. 3.5.0. system (NIDEK, Multi-Instrument Diagnostic System, Japan). In the anterior stroma, before arriving to the graft interphase, activated keratocytes could be observed with higher reflectivity. In this first image of the anterior interphase, a homogenous hyporreflective image could be observed. In the interior of the graft, no keratocytes were found and some hyperreflective particles were present. In addition to the anterior, the posterior interphase presented bright particles.

CONCLUSIONS

This is the first report that documents a BLT using IVCM.

Multiwavelength confocal laser scanning microscopy of the cornea

Confocal reflectance microscopy has demonstrated the ability to produce in vivo images of corneal tissue with sufficient cellular resolution to diagnose a broad range of corneal conditions. To investigate the spectral behavior of corneal reflectance imaging, a modified laser ophthalmoscope was used. Imaging was performed in vivo on a human cornea as well as ex vivo on porcine and lamb corneae. Various corneal layers were imaged at the wavelengths 488 nm, 518 nm, and 815 nm and compared regarding image quality and differences in the depicted structures. Besides the wavelength- and depth-dependent scattering background, which impairs the image quality, a varying spectral reflectance of certain structures could be observed. Based on the obtained results, this paper emphasizes the importance of choosing the appropriate light source for corneal imaging. For the examination of the epithelial layers and the endothelium, shorter wavelengths should be preferred. In the remaining layers, longer wavelength light has the advantage of less scattering loss and a potentially higher subject compliance.

Micro-optical coherence tomography for high-resolution morphologic imaging of cellular and nerval corneal micro-structures

We demonstrate the highest resolution (1.5×1.5×1 µm) micrometer optical coherence tomography (µOCT) imaging of the morphologic micro-structure of excised swine and non-human primate corneas. Besides epithelial, stromal, and endothelial cell morphology, this report focuses on investigating the most peripheral corneal nerve fibers, the nerve fibers of the subbasal plexus (SBP). Alterations of SBP nerve density and composition are reportedly linked to major neurologic disorders, such as diabetic neuropathy, potentially indicating earliest onsets of denervation. Here, the fine, hyperreflective, epithelial nerve structures located just above Bowman's membrane, are i) visualized using our µOCT prototype, ii) validated by comparison to fluorescence confocal microscopy (including selective immunohistochemical staining), and iii) segmented using state-of-the-art image processing. Here, we also introduce polarization sensitive (PS) µOCT imaging, demonstrating, to the best of our knowledge, the highest resolution corneal PS-OCT scans reported to date.

In vivo confocal microscopy and trachomatous conjunctival scarring: Predictors for clinical progression

IMPORTANCE

In vivo confocal microscopy (IVCM) provides high-resolution images of the ocular surface and has been validated in trachomatous conjunctival scarring.

BACKGROUND

This study used IVCM to identify parameters associated with clinical scarring progression.

DESIGN

Prospective cohort study.

PARTICIPANTS

A total of 800 participants in Northern Tanzania with trachomatous scarring.

METHODS

Participants underwent clinical examination, photography and IVCM at baseline and 24-months. Clinical progression of scarring was defined by comparing baseline and 24-month photographs. Masked grading of IVCM images was used to identify scarring at both time points. Multivariable logistic regression was used to assess factors associated with clinical progression.

MAIN OUTCOME MEASURES

Risk factors associated with clinical scarring progression.

RESULTS

Clinical and IVCM assessment of 800 participants were performed at baseline, with 617 (77.1%) seen at 24-months. Of these, 438 of 617 (71.0%) had gradable IVCM images at both time points and 342 of 438 (78.1%) of these could be graded as showing definite clinical progression or no progression on image comparison. Clinical progression was found to occur in 79 of 342 (23.1%). After adjusting for age and sex, clinical scarring progression was strongly associated with a high IVCM connective tissue organization score at both baseline (odds ratio [OR] = 1.84 for each increase in scarring category; P = .002) and 24-months (OR = 1.60; P = .02). Dendritiform cells present at 24-months were strongly associated with clinical scarring progression after adjustment (OR = 2.62; P = .03).

CONCLUSIONS AND RELEVANCE

Quantitative IVCM parameters, including connective tissue organization score and the presence of dendritiform cells, are associated with disease progression and may be useful markers in trachoma and other conjunctival fibrotic diseases.

Diabetic Peripheral Neuropathy: Diagnosis and Treatment

BACKGROUND

Diabetic peripheral neuropathy (DPN) is traditionally divided into large and small fibre neuropathy (SFN). Damage to the large fibres can be detected using nerve conduction studies (NCS) and often results in a significant reduction in sensitivity and loss of protective sensation, while damage to the small fibres is hard to reliably detect and can be either asymptomatic, associated with insensitivity to noxious stimuli, or often manifests itself as intractable neuropathic pain.

OBJECTIVE

To describe the recent advances in both detection, grading, and treatment of DPN as well as the accompanying neuropathic pain.

METHODS

A review of relevant, peer-reviewed, English literature from MEDLINE, EMBASE and Cochrane Library between January 1st 1967 and January 1st 2020 was used.

RESULTS

We identified more than three hundred studies on methods for detecting and grading DPN, and more than eighty randomised-controlled trials for treating painful diabetic neuropathy.

CONCLUSION

NCS remains the method of choice for detecting LFN in people with diabetes, while a gold standard for the detection of SFN is yet to be internationally accepted. In the recent years, several methods with huge potential for detecting and grading this condition have become available including skin biopsies and corneal confocal microscopy, which in the future could represent reliable endpoints for clinical studies. While several newer methods for detecting SFN have been developed, no new drugs have been accepted for treating neuropathic pain in people with diabetes. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors and anticonvulsants remain first line treatment, while newer agents targeting the proposed pathophysiology of DPN are being developed.

Development and Assessment of a Simulator for in Vivo Confocal Microscopy in Fungal and Acanthamoeba Keratitis

BACKGROUND AND PURPOSE

In vivo confocal microscopy (IVCM) is a non-invasive imaging technique that allows morphological analysis as a diagnostic approach of the cornea in real time, thus providing a suspected diagnosis of fungal or amoebic keratitis immediately, whereas culture or PCR require several days or even weeks. Since these infections are rare, it is difficult for ophthalmologists to gain the experience necessary to differentiate infection from normal findings or artefacts. The purpose of this project was to establish a simulator, on which physicians could practice as well as acquiring a database of IVCM images of fungal or amoebic keratitis and respective analyses.

PATIENTS AND METHODS

An IVCM simulator was set up with cadaver human corneas, infected with either acanthamoeba, candida or aspergillus. Twenty-one ophthalmologists were trained in IVC microscopy first in a Dry Lab, then practically on the simulator. For evaluation, the participants were asked to fill out a standardized questionnaire, with a pre- and post-course self-assessment.

RESULTS

The self-assessed theoretical and practical skills in differentiating infectious from non-infectious keratitis in IVCM significantly increased (p = 0.0001, p = 0.0002, respectively). The barrier to use this technique decreased (p = 0.0474).

CONCLUSION

A very simple protocol based on a model of ex vivo corneal mycotic and amoebic infections can be used to train novices in the structured approach and diagnostic use of IVCM for corneal infections.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Real-time non-contact cellular imaging and angiography of human cornea and limbus with common-path full-field/SD OCT

In today's clinics, a cell-resolution view of the cornea can be achieved only with a confocal microscope (IVCM) in contact with the eye. Here, we present a common-path full-field/spectral-domain OCT microscope (FF/SD OCT), which enables cell-detail imaging of the entire ocular surface in humans (central and peripheral cornea, limbus, sclera, tear film) without contact and in real-time. Real-time performance is achieved through rapid axial eye tracking and simultaneous defocusing correction. Images contain cells and nerves, which can be quantified over a millimetric field-of-view, beyond the capability of IVCM and conventional OCT. In the limbus, palisades of Vogt, vessels, and blood flow can be resolved with high contrast without contrast agent injection. The fast imaging speed of 275 frames/s (0.6 billion pixels/s) allows direct monitoring of blood flow dynamics, enabling creation of high-resolution velocity maps. Tear flow velocity and evaporation time can be measured without fluorescein administration.

Stromal Nerve Imaging and Tracking Using Micro-Optical Coherence Tomography

Purpose

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

Methods

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

Results

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

Conclusions

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

Translational Relevance

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

Hyaluronic Acid as an Alternative to Autologous Human Serum Eye Drops: Initial Clinical Results with High-Molecular-Weight Hyaluronic Acid Eye Drops

Introduction

Autologous serum eye drops (ASED) are used in the treatment of most severe stages of dry eye. Once introduced, it is currently considered impossible to return to other lubricating eye drops or other commercially available therapeutic regimen.

Materials and Methods

In a randomized study, non-preserved high-molecular-weight hyaluronic acid eye drops were offered as an alternative to 11 patients using autologous serum treatment for at least 3 months. The control group (n = 5) continued their treatment with ASED. The verum group (n = 6) used very-high-molecular-weight hyaluronic eye drops (Comfort Shield®) instead of the ASED.

Results

From four of initially six patients in the verum group that finished the study, 2 (50%) preferred to stay with the very-high-molecular-weight hyaluronic acid eye drops beyond the trial period, the other two returned to the earlier therapy with ASED. The control group continued their treatment as before and finished the study after 8 weeks.

Conclusion

For the first time, artificial eye drops, i.e., high-molecular-weight hyaluronic acid eye drops, offered an acceptable alternative to ASED. Some patients perceived these drops as even better than the patient's own serum. This is the first evidence that optimization of the molecular structure of hyaluronic acid can be used to create eye drops that are perceived to be better than other tested tear substitutes and even patients' own serum. This offers a new treatment perspective for patients with very severe dry eye disease.

Ultrahigh-resolution anterior segment optical coherence tomography for analysis of corneal microarchitecture during wound healing

PURPOSE

To employ ultrahigh-resolution (UHR) optical coherence tomography (OCT) for investigation of the early wound healing process in corneal epithelium.

METHODS

A custom-built UHR-OCT system assessed epithelial healing in human keratoconic cornea after epi-off crosslinking (CXL) procedure and a wound healing model in rabbits with iatrogenic corneal injury. 3D OCT data sets enhanced obtaining epithelial thickness maps and evaluation of reepithelization stage. Accompanying changes in deeper corneal microarchitecture were analysed.

RESULTS

The mean central corneal thickness in 40 eyes with keratoconus at baseline was 482.7 ± 38.2 μm, while mean central epithelial thickness (CET) was 43.8 ± 6.4 μm. At the final visit 20 ± 5 days post-CXL procedure, CET was 35.0 ± 5.8 μm, significantly thinner after reepithelization (p < 0.001). Surgical success was assessed at the final visit through the demarcation line (DL), identified at 43.7 ± 13.5% stromal depth. In rabbits, the mean CET in 20 eyes at baseline was 35.9 ± 2.6 μm. In rabbits that revealed complete wound closure (10/20 eyes) at the last study day at 72 hr, CET was significantly thinner compared to baseline (30.4 ± 2.8 μm versus 35.4 ± 2.9 μm, p = 0.005). An intra-stromal landmark indicating early keratocyte apoptosis was measured at 30.0 ± 5.1% stromal depth. Epithelial thickness maps showed the time-course of corneal healing.

CONCLUSION

Ultrahigh-resolution (UHR)-OCT provided precise assessment of epithelial wound and its healing by 3D-mapping. In addition, microarchitectural changes in the cornea in early phases of epithelial healing were revealed.

In vivo two-photon microscopy of the human eye

Two-photon (2P) microscopy is a powerful tool for imaging and exploring label-free biological tissues at high resolution. Although this type of microscopy has been demonstrated in ex vivo ocular tissues of both humans and animal models, imaging the human eye in vivo has always been challenging. This work presents a novel compact 2P microscope for non-contact imaging of the anterior part of the living human eye. The performance of the instrument was tested and the maximum permissible exposure to protect ocular tissues established. To the best of our knowledge, 2P images of the in vivo human cornea, the sclera and the trabecular meshwork are shown for the very first time. Acquired images are of enough quality to visualize collagen arrangement and morphological features of clinical interest. Future implementations of this technique may constitute a potential tool for early diagnosis of ocular diseases at submicron scale.

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.

Clinically Relevant Immune-Cellular Metrics of Inflammation in Meibomian Gland Dysfunction

Purpose

To determine the reliability and clinical relevance of in vivo confocal microscopy (IVCM)-based immune-cellular metrics of palpebral conjunctival inflammation in meibomian gland dysfunction (MGD).

Methods

Sixteen MGD patients and 13 reference controls included in this cross-sectional, retrospective study, had an ocular surface exam, symptom assessment (Ocular Surface Disease Index questionnaire [OSDI]), and palpebral conjunctival IVCM imaging. Bland-Altman analyses, intraclass correlation coefficient (ICC_a), Lin's concordance correlation coefficient (ρ_c), receiver operating characteristic (ROC) analyses, and correlations were performed. Clinical outcome measures were symptom severity (OSDI scores), tear break-up time (TBUT), and corneal fluorescein staining (CFS grade).

Results

Compared to controls, patients with MGD had variable symptom severity (average OSDI score: 48.3 ± 7.6, P = 0.0008, range: 8.3–85.42), shorter TBUT (6.8 ± 0.9 seconds, P = 0.002), comparable corneal staining (0.31 ± 0.19, P = 0.20), and greater conjunctival inflammation (epithelial immune cells [EIC]: 477.8 ± 54.2 vs. 123.3 ± 17.2 cells/mm², P < 0.0001; intraglandular immune cells [IGIC]: 41.9 ± 3.3% vs. 20.33 ± 7.3%, P < 0.01). Immune-cellular metrics had high inter- and intraobserver agreement (ρ_c: 0.86–0.94; ICC_a and Cronbach's α: 0.85–0.97, P < 0.0001). EIC correlated positively with OSDI (r_s: 0.49, P = 0.03), while both EIC and IGIC correlated inversely with TBUT (r_s: −0.47, −0.45, P < 0.05), and had high accuracy in detecting inflammation (ROC area under the curve [AUC]: 0.97 and 0.89, P ≤ 0.001).

Conclusions

EIC and IGIC are increased in highly symptomatic patients with MGD that have minimal corneal staining, and correlate with symptoms and clinical signs. EIC and IGIC may provide reliable and clinically relevant metrics of inflammation.

In vivo corneal confocal microscopy aided by optical coherence tomography

In vivo corneal confocal microscopy and its operability in scientific as well as in clinical applications is often impaired by the lack of information on imaging plane position and orientation inside the cornea during patient's examination. To overcome this hurdle, we have developed a novel corneal imaging system based on a commercial scanning device and a modified Rostock Cornea Module. The presented preliminary system produces en face images by confocal laser scanning microscopy and sagittal cross-section images by optical coherence tomography simultaneously. This enables imaging guidance during examinations, improved features for diagnostics along with thickness measurements of the cornea as well as corneal substructures from oblique sections.

Efficacy of autologous serum tears for treatment of neuropathic corneal pain

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Cellular resolution corneal imaging with extended imaging range

Current optical coherence tomography (OCT) technology, which is used for imaging the eye's anterior segment, has been established as a clinical gold standard for the diagnosis of corneal diseases. However, the cellular resolution level information that is critical for many clinical applications is still not available. The major technical challenges toward cellular resolution OCT imaging are the limited ranging depth and depth of focus (DOF). In this work, we present a novel ultrahigh resolution OCT system that achieves an isotropic spatial resolution of <2 µm in tissue. The proposed system could approximately double the ranging depth and extend the DOF using the dual-spectrometer design and the forward-model based digital refocusing method, respectively. We demonstrate that the novel system is capable of visualizing the full thickness of the pig cornea over the ranging depth of 3.5 mm and the border of the corneal endothelial cells 8 times Rayleigh range away from the focal plane. This technology has the potential to realize cellular resolution corneal imaging in vivo.

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

PURPOSE

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

DESIGN

Prospective, cross-sectional, controlled study.

METHODS

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

RESULTS

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

CONCLUSION

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

Long-term evaluation of corneal sub-basal nerve recovery after photorefractive keratectomy and influence of pars plana vitrectomy

The corneal sub-basal nerve (SBN) plexus is destroyed during photorefractive keratectomy (PRK) and its recovery is still a matter of debate. In vivo confocal microscopy (IVCM) was used to evaluate SBN plexus in 23 patients at a distance of 10-25 years (mean 15.6 years) from myopic PRK. Because 8 out of the 23 PRK patients underwent pars plana vitrectomy (PPV) for rhegmatogenous retinal detachment, IVCM was also performed on those patients 6 months after PPV. Thirteen patients matched for age and myopia served as controls (non-PRK). SBN plexus was markedly reduced after PRK compared with non-PRK eyes and showed a slow, continuous but incomplete recovery up to the end of our follow-up (range 10-25 years). PRK and non-PRK eyes showed a marked reduction in SBN density 6 months after PPV, thus demonstrating a detrimental effect exerted by PPV on SBN plexus.

[Confocal microscope examination of the corneal nerve plexus as biomarker for systemic diseases : View from the corneal nerve plexus on diabetes mellitus disease]

It is estimated that approximately 50% of patients with diabetes mellitus suffer from polyneuropathy, which is frequently diagnosed too late. Consequently, the question arises whether imaging procedures of the eye, namely optical coherence tomography of the retina and confocal microscopy of the cornea are suitable for the diagnostics and follow-up control of neurodegenerative changes in patients with diabetes mellitus. De Clerck and co-workers could demonstrate this by a systematic review of studies. Of these studies 11 were further evaluated with respect to corneal confocal microscopy. Approximately 15 years after juvenile type 1 diabetes a reduction of corneal nerve fiber length and density was observed, although clinical signs of neuropathy were absent. At this stage an examination seems reasonable. Type 2 diabetes mellitus in the elderly is often associated with a metabolic syndrome and its time of manifestation remains unknown; therefore, corneal confocal microscopy should be implemented at the time of diagnosis of type 2 diabetes. Patients with long disease duration and significant changes in the corneal nerve plexus already showed clinical signs of polyneuropathy and often suffered from proliferative retinopathy. The accessibility of the eye for non-invasive optical modalities should be used more often in the treatment of patients with diabetes mellitus for early identification of patients at risk. Further longitudinal studies are highly necessary.

Cornea and anterior eye assessment with slit lamp biomicroscopy, specular microscopy, confocal microscopy, and ultrasound biomicroscopy

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple, and several devices and technologies show signs that help in identification of different diseases thereby, helping in diagnosis, management, and follow-up of patients. The purpose of this review is to present and update readers on the evaluation of cornea and ocular surface. This first part reviews a description of slit lamp biomicroscopy (SLB), endothelial specular microscopy, confocal microscopy, and ultrasound biomicroscopy examination techniques and the second part describes the corneal topography and tomography, providing up-to-date information on the clinical recommendations of these techniques in eye care practice. Although the SLB is a traditional technique, it is of paramount importance in clinical diagnosis and compulsory when an eye test is conducted in primary or specialist eye care practice. Different techniques allow the early diagnosis of many diseases, especially when clinical signs have not yet become apparent and visible with SLB. These techniques also allow for patient follow-up in several clinical conditions or diseases, facilitating clinical decisions and improving knowledge regarding the corneal anatomy.