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

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

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

In vivo high resolution human corneal imaging using full-field optical coherence tomography

We present the first full-field optical coherence tomography (FFOCT) device capable of in vivo imaging of the human cornea. We obtained images of the epithelial structures, Bowman's layer, sub-basal nerve plexus (SNP), anterior and posterior stromal keratocytes, stromal nerves, Descemet's membrane and endothelial cells with visible nuclei. Images were acquired with a high lateral resolution of 1.7 µm and relatively large field-of-view of 1.26 mm x 1.26 mm - a combination, which, to the best of our knowledge, has not been possible with other in vivo human eye imaging methods. The latter together with a contactless operation, make FFOCT a promising candidate for becoming a new tool in ophthalmic diagnostics.

The corneal subbasal nerve plexus and thickness of the retinal layers in pediatric type 1 diabetes and matched controls

Optical coherence tomography (OCT) of the retina and corneal confocal laser scanning microscopy (CLSM) of the subbasal nerve plexus (SBP) are noninvasive techniques for quantification of the ocular neurodegenerative changes in individuals with type 1 diabetes mellitus (T1DM). In adult T1DM patients these changes are hardly related to T1DM only. Instead, ageing and/or lifestyle associated comorbidities have to be considered as putative confounding variables. Therefore, we investigated pediatric T1DM patients (n = 28; 14.2 ± 2.51 y; duration of disease: 5.39 ± 4.16 y) without clinical signs of diabetic retina disease, neuropathy, vasculopathy or nephropathy and compared our findings with those obtained in healthy controls (n = 46; 14.8 ± 1.89 y). The SBP was characterized by the averaged length, thickness, and tortuosity of nerve fibers as well as the number of branching and connecting points. OCT was used to determine the total thickness of the retina (ALL) and the thickness of each retinal layer. Both methods revealed signs of early neurodegenerative changes, e.g. thinning of distinct retinal layers at the pericentral ring and shortening of corneal nerve fibers that are already present in pediatric T1DM patients. Standardization of instruments and algorithms are urgently required to enable uniform comparison between different groups and define normative values to introduce in the clinical setting.

Corneal profile in primary congenital glaucoma

PURPOSE

To investigate biomechanical and ultrastructural corneal parameters and ocular biometrics in the affected eyes of patients with unilateral primary congenital glaucoma (PCG) as compared to unaffected fellow eyes and age-matched healthy controls.

METHODS

A total of 12 patients with treated unilateral PCG and 10 normal subjects were evaluated. LENSTAR was performed to determine biometric parameters; the ocular response analyser was employed to determine biomechanical properties and slit-scanning confocal microscopy was used for evaluation of corneal ultrastucture.

RESULTS

Axial length was significantly higher and mean keratometry in affected eyes was significantly flatter in affected eyes as compared to fellow eyes and normal controls (p < 0.05), and a negative correlation was present between axial length and mean keratometry (p < 0.05). Mean aqueous depth and anterior chamber depth were increased in affected eyes as compared to fellow eyes and normal controls (p < 0.05). There was no significant difference in central corneal thickness (CCT) among affected eyes, fellow eyes and normal controls. Corneal hysteresis (CH) was significantly reduced in affected eyes (p < 0.05) and corneal resistance factor (CRF) was also reduced in the affected eyes as compared to fellow eyes and normal controls, although not statistically significant. Mean endothelial cell density was reduced in the affected eyes compared to fellow eyes and normal controls (p < 0.05).

CONCLUSION

Corneal biometrics, biomechanical parameters and ultrastructural features are altered in eyes affected with PCG despite clinically normal and clear corneas. These findings should be considered in the preoperative assessment of intraocular or corneal surgery in these patients.

In vivo confocal microscopy detects bilateral changes of corneal immune cells and nerves in unilateral herpes zoster ophthalmicus

PURPOSE

To analyze bilateral corneal immune cell and nerve alterations in patients with unilateral herpes zoster ophthalmicus (HZO) by laser in vivo confocal microscopy (IVCM) and their correlation with corneal sensation and clinical findings.

MATERIALS AND METHODS

This is a prospective, cross-sectional, controlled, single-center study. Twenty-four eyes of 24 HZO patients and their contralateral clinically unaffected eyes and normal controls (n = 24) were included. Laser IVCM (Heidelberg Retina Tomograph/Rostock Cornea Module), corneal esthesiometry (Cochet-Bonnet) were performed. Changes in corneal dendritiform cell (DC) density and morphology, number and length of subbasal nerve fibers and their correlation to corneal sensation, pain, lesion location, disease duration, and number of episodes were analyzed.

RESULTS

HZO-affected and contralateral eyes showed a significant increase in DC influx of the central cornea as compared to controls (147.4 ± 33.9, 120.1 ± 21.2, and 23.0 ± 3.6 cells/mm2; p < 0.0001). In HZO eyes DCs were larger in area (319.4 ± 59.8 μm²; p < 0.001) and number of dendrites (3.5 ± 0.4 n/cell; p = 0.01) as compared to controls (52.2 ± 11.7, and 2.3 ± 0.5). DC density and size showed moderate negative correlation with total nerve length (R = -0.43 and R = -0.57, respectively; all p < 0.001). A higher frequency of nerve beading and activated DCs close to nerve fibers were detected specifically in pain patients.

CONCLUSIONS

Chronic unilateral HZO causes significant bilateral increase in corneal DC density and decrease of the corneal subbasal nerves as compared to controls. Negative correlation was observed for DC density and size to nerve parameters, suggesting interplay between the immune and nervous systems. Patients with chronic pain also showed increased nerve beading and activated DCs.

[Morphometric characterization of the subbasal nerve plexus : Detection and analysis of networks of nerve fibers]

Confocal laser scanning microscopy is a versatile tool in medical research and enables noninvasive in vivo imaging of the corneal subbasal nerve plexus. The aim of this work is to provide a structured overview about the detection and quantification of nerve fibers of the subbasal nerve plexus from images acquired by confocal laser scanning microscopy. Relevant steps are explained and potential factors influencing the quality of the results are pointed out. Information obtained from the quantification of subbasal nerve fiber structure can be potentially used as clinical parameters in the context of diagnostics and therapy control of diabetic neuropathy.

Ultrahigh-resolution OCT imaging of the human cornea

We present imaging of corneal pathologies using optical coherence tomography (OCT) with high resolution. To this end, an ultrahigh-resolution spectral domain OCT (UHR-OCT) system based on a broad bandwidth Ti:sapphire laser is employed. With a central wavelength of 800 nm, the imaging device allows to acquire OCT data at the central, paracentral and peripheral cornea as well as the limbal region with 1.2 µm x 20 µm (axial x lateral) resolution at a rate of 140 000 A-scans/s. Structures of the anterior segment of the eye, not accessible with commercial OCT systems, are visualized. These include corneal nerves, limbal palisades of Vogt as well as several corneal pathologies. Cases such as keratoconus and Fuchs's endothelial dystrophy as well as infectious changes caused by diseases like Acanthamoeba keratitis and scarring after herpetic keratitis are presented. We also demonstrate the applicability of our system to visualize epithelial erosion and intracorneal foreign body after corneal trauma as well as chemical burns. Finally, results after Descemet's membrane endothelial keratoplasty (DMEK) are imaged. These clinical cases show the potential of UHR-OCT to help in clinical decision-making and follow-up. Our results and experience indicate that UHR-OCT of the cornea is a promising technique for the use in clinical practice, but can also help to gain novel insight in the physiology and pathophysiology of the human cornea.

Corneal epithelial cells function as surrogate Schwann cells for their sensory nerves

The eye is innervated by neurons derived from both the central nervous system and peripheral nervous system (PNS). While much is known about retinal neurobiology and phototransduction, less attention has been paid to the innervation of the eye by the PNS and the roles it plays in maintaining a functioning visual system. The ophthalmic branch of the trigeminal ganglion contains somas of neurons that innervate the cornea. These nerves provide sensory functions for the cornea and are referred to as intraepithelial corneal nerves (ICNs) consisting of subbasal nerves and their associated intraepithelial nerve terminals. ICNs project for several millimeters within the corneal epithelium without Schwann cell support. Here, we present evidence for the hypothesis that corneal epithelial cells function as glial cells to support the ICNs. Much of the data supporting this hypothesis is derived from studies of corneal development and the reinnervation of the ICNs in the rodent and rabbit cornea after superficial wounds. Corneal epithelial cells activate in response to injury via mechanisms similar to those induced in Schwann cells during Wallerian Degeneration. Corneal epithelial cells phagocytize distal axon fragments within hours of ICN crush wounds. During aging, the proteins, lipids, and mitochondria within the ICNs become damaged in a process exacerbated by UV light. We propose that ICNs shed their aged and damaged termini and continuously elongate to maintain their density. Available evidence points to new unexpected roles for corneal epithelial cells functioning as surrogate Schwann cells for the ICNs during homeostasis and in response to injury. GLIA 2017;65:851-863.

A rapid decline in corneal small fibers and occurrence of foot ulceration and Charcot foot

We present clinical, neuropathy and corneal nerve morphology data in a participant with type 2 diabetes who developed diabetic foot ulceration, partial amputation and Charcot during a longitudinal observational study. While conventional measures of neuropathy did not deteriorate significantly, corneal nerve parameters showed a rapid reduction prior to the development of foot complications.

Early detection of diabetic neuropathy by investigating CNFL and IENFD in thy1-YFP mice

Small fiber neuropathy is one of the most common and painful long-term complications of diabetes mellitus. Examination of the sub-basal corneal nerve plexus is a promising surrogate marker of diabetic neuropathy. To investigate the efficacy, reliability and reproducibility of in vivo corneal confocal microscopy (IVCCM), we used thy1-YFP mice, which express yellow fluorescence protein (YFP) in nerve fibers. 4 weeks after multiple low-dose injections of streptozotocin, thy1-YFP mice showed manifest diabetes. Subsequent application of insulin-releasing pellets for 8 weeks resulted in a significant reduction of blood glucose concentration and HbA_1c, a significant increase in body weight and no further increase in advanced glycation end products (AGEs). IVCCM, carried out regularly over 12 weeks and analyzed both manually and automatically, revealed a significant loss of corneal nerve fiber length (CNFL) during diabetes manifestation and significant recovery after insulin therapy. Ex vivo analyses of CNFL by YFP-based microscopy confirmed the IVCCM results (with high sensitivity between manual and automated approaches) but demonstrated that the changes were restricted to the central cornea. Peripheral areas, not accessible by IVCCM in mice, remained virtually unaffected. Because parallel assessment of intraepidermal nerve fiber density revealed no changes, we conclude that IVCCM robustly captures early signs of diabetic neuropathy.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Specificity of in vivo confocal cornea microscopy in Acanthamoeba keratitis

PURPOSE

To report on the presence of 4 different structures visualized by confocal microscopy in patients whose clinical presentation suggested infection by Acanthamoeba.

METHODS

Data and charts of 28 consecutive patients were analyzed in a retrospective study. Four types of structures were recognized by confocal microscopy performed with HRT II Rostock Cornea Module: trophozoites, double-walled cysts, signet rings, and bright spots. The 28 patients (mean age 30.8 years, range 17-61 years, 10 male, 18 female) were divided into 4 groups according to the diagnosis established later by microscopic examination of smear, culture, response to therapy, and the course of keratitis. The 4 groups were Acanthamoeba keratitis (AK), Acanthamoeba suspect (AK-suspect), bacterial keratitis (BK), and fungal keratitis (FK).

RESULTS

The rate of patients in AK, AK-suspect, FK, and BK groups where bright spots were found were 100%, 100%, 40%, and 55%, respectively. The sensitivity of presence of bright spots in the in vivo confocal microscopy in Acanthamoeba keratitis was 100% (95% confidence interval [CI] 73.5% to 100.00%) and specificity was 50% (CI 24.7% to 75.4%). When cases where the only signs of Acanthamoeba were bright spots were excluded, and only those cases were counted where any of cysts, trophozoites, or signet rings were also found, the sensitivity was 67% (95% CI 34. 9% to 90.1%) and the specificity was 94% (95% CI 69.8% to 99.8%).

CONCLUSIONS

The relatively high rate of bright spots in non-Acanthamoeba keratitis challenges the assumption that bright spots seen by confocal microscopy are a specific indication of Acanthamoeba keratitis.

[Significance of laser confocal tomography in diagnosis and monitoring of keratoconjunctivitis sicca]

Laser confocal tomography of the cornea enables studying ultrathin sections of corneal layers, which provides additional reliable information on tissue changes in keratoconjunctivitis sicca (KCS).

AIM

To assess the significance of laser confocal tomography of the cornea in the diagnosis and monitoring of KCS.

MATERIAL AND METHODS

We investigated 38 eyes of 30 patients with severe KCS. The patients were divided into two groups. Group 1 (15 patients, 19 eyes) was prescribed cyclosporine А 0.05% instillations 2 times daily, artificial tears, and soft contact lenses. Group 2 (15 patients, 19 eyes) received only instillations of cyclosporine А 0.05% 2 times daily and artificial tears. Besides standard ophthalmic examination, additional tests were performed, namely Schirmer's test, tear break-up time test, fluorescein eye stain test, tear osmolarity test (TearLab System, USA), and Heidelberg retinal tomography of the cornea (HRT, Heidelberg Engineering GmbH, Germany).

RESULTS

HRT findings revealed a 3 times shorter epithelization period and faster recovery of corneal transparency in group 1 as compared to group 2 (1.5 and 4.5 months, respectively). There was also an evident reduction in the number of immune cells in the cornea, most pronounced in group 1 at 3 months, which is indicative of inflammation termination.

CONCLUSION

The use of HRT of the cornea in KCS patients allows real-time cellular level observation of corneal changes, which together with clinical findings and diagnostic tests not only confirms the diagnosis but also determines treatment effectiveness. It has been also found that soft contact lenses accelerate epithelization of the cornea and relieve inflammation of the ocular surface in KCS patients under cyclosporine A 0.05% instillation therapy. Transparency of financial activity: the authors have no financial interest in the submitted materials and methods.

The Effect of Autologous Platelet Lysate Eye Drops: An In Vivo Confocal Microscopy Study

Purpose. To determine the effectiveness of autologous platelet lysate (APL) eye drops in patients with primary Sjögren syndrome (SS) dry eye, refractory to standard therapy, in comparison with patients treated with artificial tears. We focused on the effect of APL on cornea morphology with the in vivo confocal microscopy (IVCM). Methods. Patients were assigned to two groups: group A used autologous platelet lysate QID, and group B used preservative-free artificial tears QID, for 90 days. Ophthalmological assessments included ocular surface disease index (OSDI), best corrected visual acuity (BCVA), Schirmer test, fluorescein score, and breakup time (BUT). A subgroup of patients in group A underwent IVCM: corneal basal epithelium, subbasal nerves, Langerhans cells, anterior stroma activated keratocytes, and reflectivity were evaluated. Results. 60 eyes of 30 patients were enrolled; in group A (n = 20 patients) mean OSDI, fluorescein score, and BUT showed significant improvement compared with group B (n = 10 patients). The IVCM showed a significant increase in basal epithelium cells density and subbasal nerve plexus density and number and a decrease in Langerhans cells density (p < 0.05). Conclusion. APL was found effective in the treatment of SS dry eye. IVCM seems to be a useful tool to visualize cornea morphologic modifications.

Laser Scanning In Vivo Confocal Microscopy of Clear Grafts after Penetrating Keratoplasty

PURPOSE

To evaluate the changes of keratocytes and dendritic cells in the central clear graft by laser scanning in vivo confocal microscopy after penetrating keratoplasty (PK).

METHODS

Thirty adult subjects receiving PK at Shandong Eye Institute and with clear grafts and no sign of immune rejection after surgery were recruited into this study, and 10 healthy adults were controls. The keratocytes and dendritic cells in the central graft were evaluated by laser scanning confocal microscopy, as well as epithelium cells, keratocytes, corneal endothelium cells, and corneal nerves (especially subepithelial plexus nerves).

RESULTS

Median density of subepithelial plexus nerves, keratocyte density in each layer of the stroma, and density of corneal endothelium cells were all lower in clear grafts than in controls. The dendritic cells of five (16.7%) patients were active in Bowman's membrane and stromal membrane of the graft after PK.

CONCLUSIONS

Activated dendritic cells and Langerhans cells could be detected in some of the clear grafts, which indicated that the subclinical stress of immune reaction took part in the chronic injury of the clear graft after PK, even when there was no clinical rejection episode.

Contralateral Clinically Unaffected Eyes of Patients With Unilateral Infectious Keratitis Demonstrate a Sympathetic Immune Response

PURPOSE

To analyze the contralateral unaffected eyes of patients with microbial keratitis (MK) for any immune cell or nerve changes by laser in vivo confocal microscopy (IVCM).

METHODS

A prospective study was performed on 28 patients with MK, including acute bacterial, fungal, and Acanthamoeba keratitis, as well as on their contralateral clinically unaffected eyes and on control groups, which consisted of 28 age-matched normal controls and 15 control contact lens (CL) wearers. Laser IVCM with the Heidelberg Retinal Tomograph 3/Rostock Cornea Module and Cochet-Bonnet esthesiometry of the central cornea were performed. Two masked observers assessed central corneal dendritiform cell density and subbasal corneal nerve parameters.

RESULTS

The contralateral clinically unaffected eyes of patients with MK demonstrated significant diminishment in nerve density (15,603.8 ± 1265.2 vs. 24,102.1 ± 735.6 μm/mm²), total number of nerves (11.9 ± 1.0 vs. 24.9 ± 1.2/frame), number of branches (1.7 ± 0.2 vs. 19.9 ± 1.3/frame), and branch nerve length (5775.2 ± 757.1 vs. 12,715.4 ± 648.4 μm/mm²) (P < 0.001 for all parameters) compared to normal controls and CL wearers. Further, dendritiform cell density in the contralateral unaffected eyes was significantly increased as compared to that in controls (117.5 ± 19.9 vs. 24.2 ± 3.5 cells/mm², P < 0.001).

CONCLUSIONS

We demonstrate a subclinical involvement in the contralateral clinically unaffected eyes in patients with unilateral acute MK. In vivo confocal microscopy reveals not only a diminishment of the subbasal corneal nerves and sensation, but also an increase in dendritiform cell density in the contralateral unaffected eyes of MK patients. These findings show bilateral immune alterations in a clinically unilateral disease.

Age-Related Changes in Murine Corneal Nerves

PURPOSE

The aim of this study is to determine age-related morphological changes in the corneal subbasal nerve plexus (SNP) in two inbred mouse strains.

MATERIALS AND METHODS

The corneal SNP was investigated by in vivo confocal laser scanning microscopy (CLSM) in 0.5-, 1-, 1.5-, and 2-year-old C57BL/6J mice and in 0.5- and 1-year-old BALB/c mice (n = 4 per age category and strain; 10 images per mouse). Fixed corneal samples from C57BL/6J mice were also analyzed after PGP9.5 staining. Nerve fiber density (NFD) was determined using the semi-automated NeuronJ program. In addition, a new custom-designed, fully automated computerized technique based on oriented multiscale matched filtering was tested to objectify and accelerate image analysis.

RESULTS

C57BL/6J mice showed low NFD (11.7 ± 0.5 mm/mm²). Aging from 0.5 to 1, 1.5, and 2 years resulted in significant reductions in subbasal NFD by 34%, 49%, and 66%, respectively. The decline in nerve fibers revealed by in vivo CLSM together with NeuronJ quantification was confirmed by ex vivo immunohistochemical analyses. Subbasal NFD in BALB/c mice (30.0 ± 1.4 mm/mm²) was 3-fold higher than in C57BL/6J mice. Aging from 0.5 to 1 year resulted in a significant 17% reduction in NFD. With the automated approach, NFD of 22.6 ± 2.9 mm/mm² and a 45% reduction during aging was determined from the same images.

CONCLUSIONS

An age-related reduction in subbasal corneal nerve fibers was observed. The differing extent of reduction in the two mouse strains may be accounted for by genetic factors. Automated NFD quantification of corneal nerve fibers in mice appears to be a useful, reliable, objective, and time-saving tool.

An efficient intelligent analysis system for confocal corneal endothelium images

A confocal microscope provides a sequence of images of the corneal layers and structures at different depths from which medical clinicians can extract clinical information on the state of health of the patient's cornea. A hybrid model based on snake and particle swarm optimisation (S-PSO) is proposed in this paper to analyse the confocal endothelium images. The proposed system is able to pre-process images (including quality enhancement and noise reduction), detect cells, measure cell densities and identify abnormalities in the analysed data sets. Three normal corneal data sets acquired using a confocal microscope, and three abnormal confocal endothelium images associated with diseases have been investigated in the proposed system. Promising results are presented and the performance of this system is compared with manual and two morphological based approaches. The average differences between the manual and the automatic cell densities calculated using S-PSO and two other morphological based approaches is 5%, 7% and 13% respectively. The developed system will be deployable as a clinical tool to underpin the expertise of ophthalmologists in analysing confocal corneal images.

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

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

Multimodal and multiplex spectral imaging of rat cornea ex vivo using a white-light laser source

We applied our multimodal nonlinear spectral imaging microscope to the measurement of rat cornea. We successfully obtained multiple nonlinear signals of coherent anti-Stokes Raman scattering (CARS), third-order sum frequency generation (TSFG), and second harmonic generation (SHG). Depending on the nonlinear optical processes, the cornea tissue was visualized with different image contrast mechanism simultaneously. Due to white-light laser excitation, multiplex CARS and TSFG spectra were obtained. Combined multimodal and spectral analysis clearly elucidated the layered structure of rat cornea with molecular structural information. This study indicates that our multimodal nonlinear spectral microscope is a promising bioimaging method for tissue study. Multimodal nonlinear spectral images of rat cornea at corneal epithelium and corneal stroma in the in-plane (XY) direction. With use of the combinational analysis of different nonlinear optical processes, detailed molecular structural information is available without staining or labelling.

New ophthalmologic imaging techniques for detection and monitoring of neurodegenerative changes in diabetes: a systematic review

Optical coherence tomography (OCT) of the retina and around the optic nerve head and corneal confocal microscopy (CCM) are non-invasive and repeatable techniques that can quantify ocular neurodegenerative changes in individuals with diabetes. We systematically reviewed studies of ocular neurodegenerative changes in adults with type 1 or type 2 diabetes and noted changes in the retina, the optic nerve head, and the cornea. Of the 30 studies that met our inclusion criteria, 14 used OCT and 16 used CCM to assess ocular neurodegenerative changes. Even in the absence of diabetic retinopathy, several layers in the retina and the mean retinal nerve fibre layer around the optic nerve head were significantly thinner (-5·36 μm [95% CI -7·13 to -3·58]) in individuals with type 2 diabetes compared with individuals without diabetes. In individuals with type 1 diabetes without retinopathy none of the intraretinal layer thicknesses were significantly reduced compared with individuals without diabetes. In the absence of diabetic polyneuropathy, individuals with type 2 diabetes had a lower nerve density (nerve branch density: -1·10/mm(2) [95% CI -4·22 to 2·02]), nerve fibre density: -5·80/mm(2) [-8·06 to -3·54], and nerve fibre length: -4·00 mm/mm(2) [-5·93 to -2·07]) in the subbasal nerve plexus of the cornea than individuals without diabetes. Individuals with type 1 diabetes without polyneuropathy also had a lower nerve density (nerve branch density: -7·74/mm(2) [95% CI -14·13 to -1·34], nerve fibre density: -2·68/mm(2) [-5·56 to 0·20]), and nerve fibre length: -2·58 mm/mm(2) [-3·94 to -1·21]). Ocular neurodegenerative changes are more evident when diabetic retinopathy or polyneuropathy is present. OCT and CCM are potentially useful, in addition to conventional clinical methods, to assess diabetic neurodegenerative changes. Additional research is needed to determine their incremental benefit and to standardise procedures before the application of OCT and CCM in daily practice.

Two-photon microscopy of a Flt1 peptide-hyaluronate conjugate

AIM

Two-photon microscopy was performed to visualize ocular distribution of Flt1 peptide-hyaluronate (HA) conjugate micelles for eye drop treatment of corneal neovascularization.

MATERIALS & METHODS

Flt1 peptide-HA conjugate micelles were topically administered to the eye for two-photon microscopy and antiangiogenic effect assessment after silver nitrate cauterization.

RESULTS

In vivo two-photon microscopy revealed that Flt1 peptide-HA conjugate micelles were absorbed and remained on the corneal epithelia with an increased residence time, facilitating the corneal delivery of carboxyfluorescein succinimidyl ester (CFSE) as a model drug. Furthermore, repeated eye drops of Flt1 peptide-HA conjugate micelles showed comparable therapeutic effect to the subconjunctival injection on the corneal neovascularization.

DISCUSSION & CONCLUSION

We confirmed the feasibility of Flt1 peptide-HA conjugate micelles for eye drop treatment of corneal neovascularization.

Acanthamoeba keratitis: improving the Scottish diagnostic service for the rapid molecular detection of Acanthamoeba species

Acanthamoeba species are responsible for causing the potentially sight-threatening condition, Acanthamoeba keratitis, which is commonly associated with contact lens use. In this report, we highlight the challenges faced using conventional laboratory identification methods to identify this often under-reported pathogen, and discuss the reasons for introducing the first national service in Scotland for the rapid and sensitive molecular identification of Acanthamoeba species. By comparing culture and molecular testing data from a total of 63 patients (n = 80 samples) throughout Scotland presenting with ocular eye disease, we describe the improvement in detection rates where an additional four positive cases were identified using a molecular assay versus culture. The testing of a further ten patients by confocal imaging is also presented. This report emphasizes the importance of continuing to improve clinical laboratory services to ensure a prompt, correct diagnosis and better prognosis, in addition to raising awareness of this potentially debilitating opportunistic pathogen.

In vivo confocal microscopic analysis of normal human anterior limbal stroma

PURPOSE

To characterize the microarchitecture of anterior limbal stroma in healthy individuals using in vivo confocal microscopy (IVCM) and to correlate it with mesenchymal stem cells (MSCs), a component of the limbal niche.

METHODS

The corneal side of the superior limbus was scanned in 30 eyes of 17 normal subjects beyond the basal epithelium, deep into the stroma using an HRT III laser scanning microscope. The IVCM findings were correlated with the immunohistochemical features of MSCs in the anterior limbal stroma.

RESULTS

Clusters of hyperreflective structures were observed in the anterior limbal stroma, subjacent to the basal epithelium (depth, 50.2 ± 8.7 μm to 98 ± 12.8 μm), but not in the corneal stroma. The structures showed unique morphology compared with epithelial cells, keratocytes, neurons, and dendritic cells. In parallel, confocal analysis of immunostained sections showed clusters of cells, double positive for MSC-specific markers (CD90 and CD105) in the anterior limbal stroma at a depth of 55.3 ± 12.7 μm to 72 ± 37.6 μm. The organization and distribution of the MSC clusters locates them within the hyperreflective region in the anterior limbal stroma.

CONCLUSIONS

The hyperreflective structures, demonstrated for the first time in the human anterior limbal stroma, probably represent an important component of the limbal niche. Our approach of in vivo imaging may pave the way for assessing the limbal stromal health.

Corneal confocal microscopy: Recent progress in the evaluation of diabetic neuropathy

The present brief review discusses recent progress with corneal confocal microscopy for the evaluation of diabetic sensorimotor polyneuropathy. Corneal confocal microscopy is a new, non-invasive and reproducible diagnostic modality, and it can also be easily applied for patient follow up. It enables new perspectives of studying the natural history of diabetic sensorimotor polyneuropathy, severity of nerve fiber pathology and documenting early nerve fiber regeneration after therapeutic intervention. It shows moderate to high sensitivity and specificity for the timely diagnosis of diabetic sensorimotor polyneuropathy. Currently, corneal confocal microscopy is mainly used in specialized centers, but deserves more widespread application for the assessment of diabetic sensorimotor polyneuropathy. Finally, further progress is required in terms of technical improvements for automated nerve fiber quantification and for analysis of larger images.

Autologous Serum Tears for Treatment of Photoallodynia in Patients with Corneal Neuropathy: Efficacy and Evaluation with In Vivo Confocal Microscopy

OBJECTIVE

Patients suffering from corneal neuropathy may present with photoallodynia; i.e., increased light sensitivity, frequently with a normal slit-lamp examination. This study aimed to evaluate the efficacy of autologous serum tears (AST) for treatment of severe photoallodynia in corneal neuropathy and to correlate clinical findings with corneal subbasal nerve alterations by in vivo confocal microscopy (IVCM).

METHODS

Retrospective case control study with 16 patients with neuropathy-induced severe photoallodynia compared to 16 normal controls. Symptom severity, clinical examination and bilateral corneal IVCM scans were recorded.

RESULTS

All patients suffered from extreme photoallodynia (8.8±1.1) with no concurrent ocular surface disease. Subbasal nerves were significantly decreased at baseline in patients compared to controls; total nerve length (9208±1264 vs 24714±1056 μm/mm(2); P<.0001) and total nerve number (9.6±1.4 vs 28.6±2.0; P<.0001), respectively. Morphologically, significantly increased reflectivity (2.9±0.2 vs 1.8±0.1; P<.0001), beading (in 93.7%), and neuromas (in 62.5%) were seen. AST (3.6±2.1 months) resulted in significantly decreased symptom severity (1.6±1.7; P=.02). IVCM demonstrated significantly improved nerve parameters (P<.005), total nerve length (15451±1595 μm/mm(2)), number (13.9±2.1), and reflectivity (1.9±0.1). Beading and neuromas were seen in only 56.2% and 7.6% of patients.

CONCLUSION

Patients with corneal neuropathy-induced photoallodynia show profound alterations in corneal nerves. AST restores nerve topography through nerve regeneration, and this correlated with improvement in patient-reported photoallodynia. The data support the notion that corneal nerve damage results in alterations in afferent trigeminal pathways to produce photoallodynia.

Impact of long-term soft contact lens wear on epithelial flap production and postoperative recovery in laser-assisted subepithelial keratomileusis

PURPOSE

To investigate the impact and postoperative clinical recovery of long-term soft contact lens wear on the epithelial flap made during laser-assisted subepithelial keratomileusis (LASEK).

METHODS

In a prospective study, 371 patients (589 eyes) who underwent LASEK were divided into four groups (G1, G2, G3, G4) according to their length of soft contact lens wear. After the contact lens (CL) was removed 1 week after surgery, various symptoms - uncorrected visual acuity (UCVA), oedema of the corneal epithelium, spherical equivalent (SE) and haze degree - were recorded on day 1, and at 1 and 3 months postoperatively.

RESULTS

There were no significant differences in corneal flap production among the first three groups that wore CLs, but various symptoms and UCVA were all different from the fourth group that did not wear CLs. There were statistically significant differences in oedema of corneal epithelium among the first three groups, and the degree of oedema was positively correlated with the CL wearing time. There were no significant differences in postoperative SE and haze in all four groups.

CONCLUSIONS

Long-term soft CL wear can affect production of the epithelial flap and postoperative recovery, including various symptoms, oedema of the central corneal epithelium and visual acuity. In contrast, there was no effect of long-term CL wear on postoperative mean refractive spherical equivalent (MRSE) and haze.

Correlation between human tear cytokine levels and cellular corneal changes in patients with bacterial keratitis by in vivo confocal microscopy

PURPOSE

We investigated bilateral tear cytokine levels in patients with unilateral bacterial keratitis (BK) as associated with in vivo confocal microscopic (IVCM) alterations in corneal nerves and dendritiform immune cells (DCs).

METHODS

A total of 54 (13 BK, 13 contralateral, 28 healthy controls) tear samples was collected prospectively and analyzed by multiplex microbeads assay. The IVCM of the central cornea was performed on the same day, and assessed for corneal nerve and DC alterations.

RESULTS

Interleukin-1β, IL-6, and IL-8 were significantly elevated only in affected eyes (66.6 ± 26.8, 7174 ± 2430, and 810 ± 315 ρg/mL, respectively; P = 0.04, P < 0.001, and P < 0.001, respectively), compared to healthy controls (13.0 ± 4.0, 171.8 ± 32.1, and 56.5 ± 33.8 ρg/mL). Levels of chemokine ligand 2 (CCL-2), IL-10, and IL-17a were elevated only in contralateral eyes (813 ± 478, 86.7 ± 38.3, and 3350 ± 881 ρg/mL, respectively; P = 0.02, P = 0.01, and P = 0.04, respectively), compared to controls (73.7 ± 25.3, 17.5 ± 4.9, and 1350 ± 337 ρg/mL). Triggering receptor expressed on myeloid cells (TREM)-1 was significantly elevated in affected (551 ± 231 ρg/mL, P = 0.02) and contralateral unaffected (545 ± 298 ρg/mL, P = 0.03) eyes compared to controls (31.3 ± 12.4 ρg/mL). The density of DCs was significantly increased in affected (226.9 ± 37.3 cells/mm(2), P < 0.001) and unaffected (122.3 ± 23.7 cells/mm(2), P < 0.001) eyes compared to controls (22.7 ± 5.9 cells/mm(2)). Sub-basal nerve density significantly decreased in affected (3337 ± 1615 μm/mm(2), P < 0.001) and contralateral (13,230 ± 1635 μm/mm(2), P < 0.001) eyes compared to controls (21,200 ± 545 μm/mm(2)). Levels of IL-1β, IL-6, and IL-8 were significantly correlated with DC density (R = 0.40, R = 0.55, and R = 0.31, all P < 0.02) and nerve density (R = -0.30, R = -0.53, and R = -0.39, all P < 0.01).

CONCLUSIONS

Proinflammatory tear cytokines are elevated bilaterally in patients with unilateral BK, and are correlated strongly with alterations in DCs and nerve density as detected by IVCM.

Ophthalmic imaging

INTRODUCTION OR BACKGROUND

The last two decades have seen a revolution in ophthalmic imaging. In this review we present an overview of the breadth of ophthalmic imaging modalities in use today and describe how the role of ophthalmic imaging has changed from documenting abnormalities visible on clinical examination to the detection of clinically silent abnormalities which can lead to an earlier and more precise diagnosis.

SOURCES OF DATA

This review is based on published literature in the fields of ophthalmic imaging and with focus on most commonly used imaging modalities.

AREAS OF AGREEMENT

New imaging techniques enable non-invasive evaluation of ocular structures at a resolution of a few micrometres. This has led to a re-evaluation of diagnostic criteria for ocular disease, which were previously defined by clinical findings without significant reference to imaging.

AREAS OF CONTROVERSY

Lack of formal training and clinical guidelines regarding use of new imaging techniques in diagnosing and monitoring various ocular conditions. Lack of large normative databases and interchangeability issues between different commercial machines can hinder the detection of disease progression.

GROWING POINTS

Imaging devices are being constantly refined with improved image capture and image analysis tools.

AREAS TIMELY FOR DEVELOPING RESEARCH

Clinical applications of new techniques and devices have yet to be determined using systematic scientific research methods.

Cornea characterization using a combined multiphoton microscopy and optical coherence tomography system

We present a multimodal imaging system which combines multiphoton microscopy and optical coherence tomography to visualize the morphological structures, and to quantify the refractive index (RI) and thickness of cornea. The morphological similarities and differences at different corneal layers across various species are identified. In the piscine and human corneas, the stromata exhibit thin fibers that indicate an overall collagen direction. Human corneas display collagen micro-folds which cause increased light attenuation. In the murine, porcine and bovine corneas, the stromata show interwoven collagen patterns. The Bowman's layer and the Descemet's membrane are also distinguished in some species. The RI and thicknesses are quantified for the epithelium and the stromal layers respectively, where the epithelium is found to have slightly higher RI than the stroma. The average epithelial and stromal RI are, respectively, 1.371 ± 0.016 and 1.360 ± 0.008 for the murine corneas; 1.502 ± 0.057 and 1.335 ± 0.011 for the piscine corneas; 1.433 ± 0.023 and 1.357 ± 0.013 for the human corneas; 1.476 ± 0.091 and 1.343 ± 0.013 for the porcine corneas; and 1.400 ± 0.007 and 1.376 ± 0.003 for the bovine corneas. The multimodal system can potentially provide a comprehensive characterization of the cornea.

Cytokine deposition alters leukocyte morphology and initial recruitment of monocytes and γδT cells after corneal injury

PURPOSE

An in vivo mouse model reproducibly induces recurrent epithelial erosions in wild-type mice spontaneously 2 weeks after a single 1.5-mm corneal debridement wound made with a dulled blade. When 1.5-mm wounds are made by a rotating burr so that the corneal epithelial basement membrane is removed, corneas heal without developing erosions. Here, we characterize differences in cytokine deposition and changes in leukocytes between 0 and 6 hours after dulled-blade and rotating-burr wounding.

METHODS

BALB/c mice were used to study 1.5-mm corneal wounds made using a dulled blade or a rotating burr. Mice were studied immediately after wounding (0 hour) and at 6 hours in vivo and in vitro in organ culture. Corneas, corneal extracts, and collagenase digests from naïve and wounded mice were used for three-dimensional (3D) confocal imaging, cytokine arrays, and flow cytometry.

RESULTS

Confocal imaging showed CD45, a protein derived from leukocytes, accumulates at the wound edge by 3 and 6 hours after wounding in vivo but not in vitro with more CD45 accumulating after dulled-blade compared with rotating-burr wounds. Morphologic changes occurred in CD45+ leukocytes and higher levels for several cytokines were detected in the stromal wound bed within minutes following dulled-blade wounds. Flow cytometry showed significantly more monocytes (CD45+/CD11b+/Ly6C+) and γδT cells (CD45+/GL3+) recruited into the corneas of mice with dulled-blade wounds by 6 hours.

CONCLUSIONS

Differences in cytokine-driven leukocyte responses are seen after dulled-blade debridement compared with rotating-burr injury.

Non-invasive in vivo imaging by confocal laser scanning microscopy of gingival tissues following natural plaque deposition

AIM

Imaging with Confocal Laser Scanning Microscopy (CLSM) generates high-resolution images and may be well suited for basic research in Periodontology and Implant Dentistry. The present study was aimed to explore the in vivo application of CLSM in experimentally induced gingivitis.

MATERIALS AND METHODS

Ten subjects were recruited and were advised to stop any oral hygiene of the upper front teeth for 7 days. The gingival tissues were observed using a Heidelberg Retina Tomograph combined with a Rostock Cornea Module at baseline and day 7. The system used a laser of 670 nm and the contrast was given by backscattering from different tissues. Each examination created 800-1200 images that were descriptively analysed.

RESULTS

After 7 days of abandoned oral hygiene, plaque scores and bleeding frequencies increased. By using CLSM images tooth hard substances, cells and plaque deposits were distinguishable. Increased epithelial cell irregularities, the apical migration of the sulcular epithelium, cellular infiltrates within the sulcus and plaque deposits were observed at day 7.

CONCLUSIONS

The present study showed for the first time that CLSM is suitable for in vivo imaging of the gingival sulcus and adjacent tissues.

Age-related dystrophic changes in corneal endothelium from DNA repair-deficient mice

The corneal endothelium (CE) is a single layer of cells lining the posterior face of the cornea providing metabolic functions essential for maintenance of corneal transparency. Adult CE cells lack regenerative potential, and the number of CE cells decreases throughout life. To determine whether endogenous DNA damage contributes to the age-related spontaneous loss of CE, we characterized CE in Ercc1(-/Δ) mice, which have impaired capacity to repair DNA damage and age prematurely. Eyes from 4.5- to 6-month-old Ercc1(-/Δ) mice, age-matched wild-type (WT) littermates, and old WT mice (24- to 34-month-old) were compared by spectral domain optical coherence tomography and corneal confocal microscopy. Histopathological changes in CE were further identified in paraffin tissue sections, whole-mount immunostaining, and scanning electron and transmission electron microscopy. The CE of old WT mice displayed polymorphism and polymegathism, polyploidy, decreased cell density, increased cell size, increases in Descemet's thickness, and the presence of posterior projections originating from the CE toward the anterior chamber, similar to changes documented for aging human corneas. Similar changes were observed in young adult Ercc1(-/Δ) mice CE, demonstrating spontaneous premature aging of the CE of these DNA repair-deficient mice. CD45(+) immune cells were associated with the posterior surface of CE from Ercc1(-/Δ) mice and the tissue expressed increased IL-1α, Cxcl2, and TNFα, pro-inflammatory proteins associated with senescence-associated secretory phenotype. These data provide strong experimental evidence that DNA damage can promote aging of the CE and that Ercc1(-/Δ) mice offer a rapid and accurate model to study CE pathogenesis and therapy.

In vivo confocal microscopy of the ocular surface: from bench to bedside

In vivo confocal microscopy (IVCM) is an emerging technology that provides minimally invasive, high resolution, steady-state assessment of the ocular surface at the cellular level. Several challenges still remain but, at present, IVCM may be considered a promising technique for clinical diagnosis and management. This mini-review summarizes some key findings in IVCM of the ocular surface, focusing on recent and promising attempts to move "from bench to bedside". IVCM allows prompt diagnosis, disease course follow-up, and management of potentially blinding atypical forms of infectious processes, such as acanthamoeba and fungal keratitis. This technology has improved our knowledge of corneal alterations and some of the processes that affect the visual outcome after lamellar keratoplasty and excimer keratorefractive surgery. In dry eye disease, IVCM has provided new information on the whole-ocular surface morphofunctional unit. It has also improved understanding of pathophysiologic mechanisms and helped in the assessment of prognosis and treatment. IVCM is particularly useful in the study of corneal nerves, enabling description of the morphology, density, and disease- or surgically induced alterations of nerves, particularly the subbasal nerve plexus. In glaucoma, IVCM constitutes an important aid to evaluate filtering blebs, to better understand the conjunctival wound healing process, and to assess corneal changes induced by topical antiglaucoma medications and their preservatives. IVCM has significantly enhanced our understanding of the ocular response to contact lens wear. It has provided new perspectives at a cellular level on a wide range of contact lens complications, revealing findings that were not previously possible to image in the living human eye. The final section of this mini-review provides a focus on advances in confocal microscopy imaging. These include 2D wide-field mapping, 3D reconstruction of the cornea and automated image analysis.

[Imaging and quantification of corneal neovascularization]

Corneal neovascularization is defined as the invasion of vessels into the normally avascular clear corneal stroma, secondary to acute or chronic tissue injury. In addition to decreasing visual acuity, vascularity introduces circulating immune cells, reducing corneal immune privilege and the graft survival of subsequent keratoplasty. Thus, reducing neovascularization has become a recent therapeutic target in order to increase the success of corneal transplantation. Comparing the effects of antiangiogenic drugs assumes that we are able to quantify corneal neovascularization before and after treatment. In the first part of this literature review, we present the various methods to document neovessels (color photos, fluorescein and indocyanine green anterior segment angiography, in vivo confocal microscopy). Next, we report methods to classify and quantify corneal neovascularization.

Characteristic quantities of corneal epithelial structures in confocal laser scanning microscopic volume data sets

PURPOSE

Fully automated quantification of the morphologic features of different epithelial cell layers in healthy human corneas.

METHODS

In vivo confocal laser scanning microscopy was performed on the unilateral eyes of 6 healthy volunteers. Stacks of 160 images (400 × 400 μm) with an interslice distance of 0.4 μm were used to generate full thickness volume data sets of the epithelium. Size and shape factors of basal (BC) and intermediate cell (IC) layers were quantified using appropriate image analysis algorithms. Evaluated parameters include mean area, compactness, solidity, major and minor diameter, and maximum boundary distance.

RESULTS

Mean area of BC and IC demonstrated a linear increase from 80 to 160 μm². A similar trend was noted with major and minor diameter and maximum boundary distance. Major diameters of BC and IC measured between 13.2 and 17.0 μm, whereas minor diameter of these cells measured between 8.6 and 12.4 μm. The maximum boundary distance of BC and IC ranged from 7.0 to 9.1 μm. Compactness of epithelial cells clustered around 1.45 and 1.5, whereas cell solidity measured between 1.0 and 1.03.

CONCLUSION

Several characteristic morphologic quantities can be calculated using this methodology without manual intervention. Our study demonstrated promising results and suggests that this fully automated morphologic quantification can be successfully applied to assess microstructural changes of the epithelium in normal and various corneal disorders.

Corneal confocal microscopy: a new technique for early detection of diabetic neuropathy

Corneal confocal microscopy (CCM) is a noninvasive method for the study of human cornea in vivo. It has increasingly been used to assess the morphology of the sub-basal corneal nerve plexus. CCM has good reproducibility and may contribute to the early diagnosis of diabetic polyneuropathy. It may also be useful to document favorable changes in nerve fiber structure early after therapeutic intervention. Corneal nerve pathology is more pronounced in patients with diabetic polyneuropathy and is associated with its clinical severity. The sensitivity and specificity of CCM for the diagnosis of polyneuropathy is moderate to high. CCM now merits further use in large longitudinal studies to provide more information on the natural history of diabetic neuropathy and effects of treatment. Moreover, there is a need for a larger normative database. Finally, technical progress is expected to enable visualization of larger corneal areas and improve nerve fiber quantification, increasing diagnostic accuracy.

Keeping an eye on decellularized corneas: a review of methods, characterization and applications

The worldwide limited availability of suitable corneal donor tissue has led to the development of alternatives, including keratoprostheses (Kpros) and tissue engineered (TE) constructs. Despite advances in bioscaffold design, there is yet to be a corneal equivalent that effectively mimics both the native tissue ultrastructure and biomechanical properties. Human decellularized corneas (DCs) could offer a safe, sustainable source of corneal tissue, increasing the donor pool and potentially reducing the risk of immune rejection after corneal graft surgery. Appropriate, human-specific, decellularization techniques and high-resolution, non-destructive analysis systems are required to ensure reproducible outputs can be achieved. If robust treatment and characterization processes can be developed, DCs could offer a supplement to the donor corneal pool, alongside superior cell culture systems for pharmacology, toxicology and drug discovery studies.

Changes in the micromorphology of the corneal subbasal nerve plexus in patients after plaque brachytherapy

Background

To quantify the development of radiation neuropathy in corneal subbasal nerve plexus (SNP) after plaque brachytherapy, and the subsequent regeneration of SNP micromorphology and corneal sensation.

Methods

Nine eyes of 9 melanoma patients (ciliary body: 3, iris: 2, conjunctiva: 4) underwent brachytherapy (ruthenium-106 plaque, dose to tumour base: 523 ± 231 Gy). SNP micromorphology was assessed by in-vivo confocal microscopy. Using software developed in–house, pre-irradiation findings were compared with those obtained after 3 days, 1, 4 and 7 months, and related to radiation dose and corneal sensation.

Results

After 3 days nerve fibres were absent from the applicator zone and central cornea, and corneal sensation was abolished. The earliest regenerating fibres were seen at the one-month follow-up. By 4 months SNP structures had increased to one-third of pre-treatment status (based on nerve fibre density and nerve fibre count), and corneal sensation had returned to approximately two-thirds of pre-irradiation values. Regeneration of SNP and corneal sensation was nearly complete 7 months after plaque brachytherapy.

Conclusions

The evaluation of SNP micromorphology and corneal sensation is a reliable and clinically useful method for assessing neuropathy after plaque brachytherapy. Radiation-induced neuropathy of corneal nerves develops quickly and is partly reversible within 7 months. The clinical impact of radiation-induced SNP damage is moderate.