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

Cell therapy in the cornea: The emerging role of microenvironment

The cornea is an ideal testing field for cell therapies. Its highly ordered structure, where specific cell populations are sequestered in different layers, together with its accessibility, has allowed the development of the first stem cell-based therapy approved by the European Medicine Agency. Today, different techniques have been proposed for autologous and allogeneic limbal and non-limbal cell transplantation. Cell replacement has also been attempted in cases of endothelial cell decompensation as it occurs in Fuchs dystrophy: injection of cultivated allogeneic endothelial cells is now in advanced phases of clinical development. Recently, stromal substitutes have been developed with excellent integration capability and transparency. Finally, cell-derived products, such as exosomes obtained from different sources, have been investigated for the treatment of severe corneal diseases with encouraging results. Optimization of the success rate of cell therapies obviously requires high-quality cultured cells/products, but the role of the surrounding microenvironment is equally important to allow engraftment of transplanted cells, to preserve their functions and, ultimately, lead to restoration of tissue integrity and transparency of the cornea.

Focus on limbal stem cell deficiency and limbal cell transplantation

Limbal stem cell deficiency (LSCD) causes severe vision impairment and can lead to blindness, representing one of the most challenging ocular surface disorders. Stem cell deficiency can be congenital or, more often, acquired. The categorization of ocular surface transplantation techniques is crucial to achieving treatment homogeneity and quality of care, according to the anatomic source of the tissue being transplanted, genetic source, autologous or allogenic transplantation (to reflect histocompatibility in the latter group), and cell culture and tissue engineering techniques. The aim of this minireview is to provide a summary of the management of LSCD, from clinical characteristics and therapeutic outcomes to the development of novel therapeutic approaches. The manuscript also briefly summarizes recent findings in the current literature and outlines the future challenges to overcome in the management of the major types of ocular surface failure.

A Review of Contact Lens-Induced Limbal Stem Cell Deficiency

Limbal stem cell deficiency (LSCD) is a pathologic condition caused by the dysfunction and destruction of stem cells, stem cell precursors and limbal cell niche in the corneal epithelium, leading to severe conjunctivalization of the cornea. Etiologies for LSCD span from congenital (aniridia), traumatic (chemical or thermal injuries), autoimmune (Stevens-Johnson syndrome) and iatrogenic disease to contact lens (CL) wear. Of these, CL wear is the least understood and is often a subclinical cause of LSCD. Even with recent advances in LSCD research, limitations persist in establishing the pathogenesis and treatment guidelines for CL-induced LSCD. A literature search was conducted to include original articles containing patients with CL-induced LSCD. This review will critically discuss the complex pathophysiology behind CL-induced LSCD, the underlying risk factors and epidemiology of the disease as well as methods to obtain a diagnosis. Various treatment options will be reviewed based on proposed treatment strategies.

Latent diffusion augmentation enhances deep learning analysis of neuro-morphology in limbal stem cell deficiency

Introduction

Limbal Stem Cell Deficiency (LSCD) is a blinding corneal disease characterized by the loss of function or deficiency in adult stem cells located at the junction between the cornea and the sclera (i.e., the limbus), namely the limbal stem cells (LSCs). Recent advances in in vivo imaging technology have improved disease diagnosis and staging to quantify several biomarkers of in vivo LSC function including epithelial thickness measured by anterior segment optical coherence tomography, and basal epithelial cell density and subbasal nerve plexus by in vivo confocal microscopy. A decrease in central corneal sub-basal nerve density and nerve fiber and branching number has been shown to correlate with the severity of the disease in parallel with increased nerve tortuosity. Yet, image acquisition and manual quantification require a high level of expertise and are time-consuming. Manual quantification presents inevitable interobserver variability.

Methods

The current study employs a novel deep learning approach to classify neuron morphology in various LSCD stages and healthy controls, by integrating images created through latent diffusion augmentation. The proposed model, a residual U-Net, is based in part on the InceptionResNetV2 transfer learning model.

Results

Deep learning was able to determine fiber number, branching, and fiber length with high accuracy (R2 of 0.63, 0.63, and 0.80, respectively). The model trained on images generated through latent diffusion on average outperformed the same model when trained on solely original images. The model was also able to detect LSCD with an AUC of 0.867, which showed slightly higher performance compared to classification using manually assessed metrics.

Discussion

The results suggest that utilizing latent diffusion to supplement training data may be effective in bolstering model performance. The results of the model emphasize the ability as well as the shortcomings of this novel deep learning approach to predict various nerve morphology metrics as well as LSCD disease severity.

A Review of the Diagnosis and Treatment of Limbal Stem Cell Deficiency

Limbal stem cell deficiency (LSCD) can cause significant corneal vascularization and scarring and often results in serious visual morbidity. An early and accurate diagnosis can help prevent the same with a timely and appropriate intervention. This review aims to provide an understanding of the different diagnostic tools and presents an algorithmic approach to the management based on a comprehensive clinical examination. Although the diagnosis of LSCD usually relies on the clinical findings, they can be subjective and non-specific. In such cases, using an investigative modality offers an objective method of confirming the diagnosis. Several diagnostic tools have been described in literature, each having its own advantages and limitations. Impression cytology and in vivo confocal microscopy (IVCM) aid in the diagnosis of LSCD by detecting the presence of goblet cells. With immunohistochemistry, impression cytology can help in confirming the corneal or conjunctival source of epithelium. Both IVCM and anterior segment optical coherence tomography can help supplement the diagnosis of LSCD by characterizing the corneal and limbal epithelial changes. Once the diagnosis is established, one of various surgical techniques can be adopted for the treatment of LSCD. These surgeries aim to provide a new source of corneal epithelial stem cells and help in restoring the stability of the ocular surface. The choice of procedure depends on several factors including the involvement of the ocular adnexa, presence of systemic co-morbidities, status of the fellow eye and the comfort level of the surgeon. In LSCD with wet ocular surfaces, autologous and allogeneic limbal stem cell transplantation is preferred in unilateral and bilateral cases, respectively. Another approach in bilateral LSCD with wet ocular surfaces is the use of an autologous stem cell source of a different epithelial lineage, like oral or nasal mucosa. In eyes with bilateral LSCD with significant adnexal issues, a keratoprosthesis is the only viable option. This review provides an overview on the diagnosis and treatment of LSCD, which will help the clinician choose the best option amongst all the therapeutic modalities currently available and gives a clinical perspective on customizing the treatment for each individual case.

Segmentation methods and morphometry of confocal microscopy imaged corneal epithelial cells

PURPOSE

To develop and explore automated cell identification and segmentation methods for morphometry of confocal microscopy imaged corneal epithelial cells using ImageJ software.

METHODS

In vivo confocal microscopy images of the intermediate (wing) and basal cell layers of the central and peripheral corneas of 20 healthy participants were analysed. The intermediate and basal cell areas obtained using the two new techniques (i.e., manual- and auto- thresholding) were compared with the widely used manual tracing technique. A predefined range of epithelial cell morphometric parameters was used as image descriptors to improve cell identification and segmentation.

RESULTS

The mean intermediate cell area obtained using the manual tracing (central; 120 ± 14 µm², peripheral; 123 ± 15 µm²) was statistically similar (p > 0.05) to the manual thresholding (central; 119 ± 7 µm², peripheral; 119 ± 8) but not with the auto thresholding technique (central; 101 ± 8 µm², peripheral; 101 ± 7 µm²). Bland-Altman limits of agreement for the mean difference (measurement bias) in central and peripheral intermediate cell area determined via manual tracing and manual thresholding techniques were 1 µm² (+25 to - 23 µm²) and 4 µm² (+29.8 to - 21.9 µm²). There were statistically significant differences in basal cell area between the three methods.

CONCLUSION

The manual thresholding technique may be used for automated identification and segmentation of corneal epithelial intermediate cells (central and peripheral) for assessing various morphometric parameters. However, measurement of the corneal epithelial basal cells is less reliable using thresholding techniques.

In Vivo Confocal Microscopy of the Corneal Sub-Basal Nerve plexus in Medically Controlled Glaucoma

The present study investigated the corneal sub-basal nerve plexus (SNP) modifications in glaucoma. Ninety-five glaucomatous patients were enrolled and divided into Group 1 and 2, preserved and preservative-free mono-therapy (30 and 28 patients), and Group 3, multi-therapy (37). Thirty patients with dry eye disease (DED) and 32 healthy subjects (HC) served as controls. In vivo confocal microscopy evaluated the nerve fibers density (CNFD), length (CNFL), thickness (CNFT), branching density (CNBD), and dendritic cell density (DCD). CNFD, CNFL, and CNBD were reduced in Group 3 and DED compared to HC (p < 0.05). CNFL was reduced in Group 3 compared to Group 2 (p < 0.05), and in Group 1 compared to HC (p < 0.001). CNFD, CNBD, and CNFT did not differ between glaucomatous groups. DCD was higher in Group 3 and DED compared to HC and Group 2 (p < 0.01). Group 3 showed worse ocular surface disease index (OSDI) scores compared to Group 1, 2, and HC (p < 0.05). CNFL and DCD correlated with OSDI score in Group 3 (r = −0.658, p < 0.001; r = 0.699, p = 0.002). Medical therapy for glaucoma harms the corneal nerves, especially in multi-therapy regimens. Given the relations with the OSDI score, SNP changes seem features of glaucoma therapy-related OSD and negatively affects the patient's quality of life.

Biomarkers of in vivo limbal stem cell function

PURPOSE

To evaluate in vivo parameters as biomarkers of limbal stem cell function and to establish an objective system that detects and stage limbal stem cell deficiency (LSCD).

METHODS

A total of 126 patients (172 eyes) with LSCD and 67 normal subjects (99 eyes) were included in this observational cross-sectional comparative study. Slit-lamp biomicroscopy, in vivo laser scanning confocal microscopy (IVCM), and anterior segment optical coherence tomography (AS-OCT) were performed to obtain the following: clinical score, cell morphology score, basal cell density (BCD), central corneal epithelial thickness (CET), limbal epithelial thickness (LET), total corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), and tortuosity coefficient. Their potential correlations with the severity of LSCD were investigated, and cutoff values were determined.

RESULTS

An increase clinical score correlated with a decrease in central cornea BCD, limbal BCD, CET, mean LET, maximum LET, CNFL, CNFD, CNBD, and tortuosity coefficient. Regression analyses showed that central cornea BCD, CET and CNFL were the best parameters to differentiate LSCD from normal eyes (Coef = 3.123, 3.379, and 2.223; all p < 0.05). The rank correlation analysis showed a similar outcome between the clinical scores and the central cornea BCD (ρ = 0.79), CET (ρ = 0.82), and CNFL (ρ = 0.71). A comprehensive LSCD grading formula based on a combination of these parameters was established.

CONCLUSIONS

A comprehensive staging system combining clinical presentation, central cornea BCD, CET, and CNFL is established to accurately and objectively diagnose LSCD and stage its severity.

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

Purpose

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

Patients and Methods

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

Results

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

Conclusion

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

Corneal epithelium and limbal region alterations due to glaucoma medications evaluated by anterior segment optic coherence tomography: a case-control study

AIM

To investigate the corneal epithelial and limbal epithelial alterations in patients under topical glaucoma treatment using anterior segment-OCT (AS-OCT) and to determine the changes of the limbal region due to the preservatives and glaucoma drugs, that can progress to limbal stem cell deficiency (LSCD). Limbal thickness was measured by AS-OCT to evaluate limbal cell deficiency.

METHODS

Forty-seven patients using topical medication for glaucoma, and 48 control subjects were enrolled in this matched case-control study. The patients were divided into four groups according to the treatment regimens. Group 1: One-drug regimen, Group 2: Two-drug regimen, Group 3: Three-drug regimen, Group 4: Four-drug regimen For the ocular surface evaluation; tear break-up time with standard fluorescein sodium sterile strip application, Schirmer test-I, Ocular Surface Disease Index Questionnaire, and AS-OCT were performed.

RESULTS

A total of 95 subjects were included: 47 eyes of 47 patients with glaucoma medication and 48 eyes of 48 healthy subjects. There was a statistically significant difference between patients and controls according to BUT, SCH, and OSDI (p < 0.001). The mean central corneal epithelium thickness was 48.5 ± 5.3 in patients and 54.5 ± 5.9 in controls (p < 0.001). The mean central total corneal thickness was 529.2 ± 41.2 in patients and 536 ± 35.3 in controls (p = 0.335). The mean limbal epithelium thickness was 64.1 ± 9.1 in patients and 76 ± 11.5 in controls (p < 0.001).

CONCLUSION

Using at least one glaucoma drug caused limbal area injury, changed ocular surface measurements, and significantly reduced the limbal epithelial thickness where the stem cells reside. The limbal epithelial thickness measurement by AS-OCT seems to be an innovative, non-invasive, and promising technique for detecting and staging corneal damage in topical glaucoma therapy.