Limbal Stem Cell Deficiency-Demography and Underlying Causes

Limbal stem cell therapy

PURPOSE OF REVIEW

To highlight the progress and future direction of limbal stem cell (LSC) therapies for the treatment of limbal stem cell deficiency (LSCD).

RECENT FINDINGS

Direct LSC transplantation have demonstrated good long-term outcomes. Cultivated limbal epithelial transplantation (CLET) has been an alternative to treat severe to total LSCD aiming to improve the safety and efficacy of the LSC transplant. A prospective early-stage uncontrolled clinical trial shows the feasibility and safety of CLET manufactured under xenobiotic free conditions. Other cell sources for repopulating of the corneal epithelium such as mesenchymal stem cells (MSCs) and induced pluripotent stem cells are being investigated. The first clinical trials of using MSCs showed short-term results, but long-term efficacy seems to be disappointing. A better understanding of the niche function and regulation of LSC survival and proliferation will lead to the development of medical therapies to rejuvenate the residual LSCs found in a majority of eyes with LSCD in vivo. Prior efforts have been largely focused on improving LSC transplantation. Additional effort should be placed on improving the accuracy of diagnosis and staging of LSCD, and implementing standardized outcome measures which enable comparison of efficacy of different LSCD treatments for different severity of LSCD. The choice of LSCD treatment will be customized based on the severity of LSCD in the future.

SUMMARY

New approaches for managing different stages of LSCD are being developed. This concise review summarizes the progresses in LSC therapies for LSCD, underlying mechanisms, limitations, and future areas of development.

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.

Severity Classification of Limbal Stem Cell Failure Due to Steven Johnson Syndrome in the Light of the Classification Consensus of Limbal Stem Cell Deficiency

OBJECTIVES

To examine and to understand the limbal stem-cell deficiency (LSCD) because of Steven-Johnson syndrome (SJS) in line with the new classification system for the first time in the literature.

METHODS

Medical records of patients with LSCD because of SJS were reviewed retrospectively. In addition to demographic data and ophthalmologic or systemic findings, anterior segment photographs of the patients were reviewed retrospectively. Limbal stem-cell deficiency severity was graded according to the classification published by the Limbal Stem Cell Working Group.

RESULTS

Twenty-four eyes of 14 patients with eye involvement secondary to SJS were included in the study. The mean age of the patients was 36.09±16.70 (9-58) years and the female-to-male ratio was 11:3. The anterior segment photographs of the patients were evaluated by two independent masked observers. Limbal stem-cell deficiency severity was graded according to the classification published by Deng et al. Corneal opacity was divided into three stages according to the area of involvement. Corneal opacity was classified as Stage I if the central 5 mm region of the cornea was not affected, as Stage II if the central 5 mm region of the cornea was affected, and as Stage III if the entire corneal surface was affected. Limbal involvement was classified as Stage A if it was below 50%, as Stage B if it was between 50% and 100%, and as Stage C if it was 100%.

CONCLUSION

This is the first study in the literature to describe and classify LSCD because of SJS, according to the new LSCD classification. Consistent with the results, LSCD follows a bimodal distribution. Most patients demonstrated severe (Stage III-32.14%) or mild (Stage IA-21.42%) LSCD.

Animal Models for Limbal Stem Cell Deficiency: A Critical Narrative Literature Review

This literature review will provide a critical narrative overview of the highlights and potential pitfalls of the reported animal models for limbal stem cell deficiency (LSCD) and will identify the neglected aspects of this research area. There exists significant heterogeneity in the literature regarding the methodology used to create the model and the predefined duration after the insult when the model is supposedly fully fit for evaluations and/or for testing various therapeutic interventions. The literature is also replete with examples wherein the implementation of a specific model varies significantly across different studies. For example, the concentration of the chemical, as well as its duration and technique of exposure in a chemically induced LSCD model, has a great impact not only on the validity of the model but also on the severity of the complications. Furthermore, while some models induce a full-blown clinical picture of total LSCD, some are hindered by their ability to yield only partial LSCD. Another aspect to consider is the nature of the damage induced by a specific method. As thermal methods cause more stromal scarring, they may be better suited for assessing the anti-fibrotic properties of a particular treatment. On the other hand, since chemical burns cause more neovascularisation, they provide the opportunity to tap into the potential treatments for anti-neovascularisation. The animal species (i.e., rats, mice, rabbits, etc.) is also a crucial factor in the validity of the model and its potential for clinical translation, with each animal having its unique set of advantages and disadvantages. This review will also elaborate on other overlooked aspects, such as the anaesthetic(s) used during experiments, the gender of the animals, care after LSCD induction, and model validation. The review will conclude by providing future perspectives and suggestions for further developments in this rather important area of research.

Wnt activation as a potential therapeutic approach to treat partial limbal stem cell deficiency

Limbal epithelial stem/progenitor cells (LSCs) are adult stem cells located at the limbus, tightly regulated by their niche involving numerous signaling pathways, such as Wnt. Wnt proteins are secreted morphogens that play critical roles in embryonic development, stem cell proliferation, self-renewal, tissue regeneration, and remodeling in adults. It has been shown that a small molecule Wnt mimic could improve LSCs expansion ex vivo. Damage to the LSCs and/or their niche can lead to limbal stem cell deficiency (LSCD), a condition that can cause corneal blindness and is difficult to treat. This study explored if repopulating residual LSCs in partial LSCD through Wnt activation could be a novel therapeutic approach. To mimic LSCD due to a chemical injury, single cultured LSCs were exposed to various concentrations of sodium hydroxide. A progressive loss of the LSCs phenotype was observed: the percentage of p63bright cells and cytokeratin (K)14+ cells decreased while the percentage of K12+ increased. Wnt activation was attained by treating the LSCs with lithium chloride (LiCl) and a small-molecule Wnt mimic, respectively. After 18 h of treatment, LSCs proliferation was increased, and the LSCs phenotype was recovered, while the untreated cells did not proliferate and lost their phenotype. The percentage of p63bright cells was significantly higher in the Wnt mimic-treated cells compared with untreated cells, while the percentage of K12+ cells was significantly lower. These findings suggest that local Wnt activation may rescue LSCs upon alkaline injury.

Clinical and allelic heterogeneity in dystrophic epidermolysis bullosa- lessons from an Indian cohort

BACKGROUND

Dystrophic epidermolysis bullosa (DEB) is due to variation in the COL7A1 gene. The clinical phenotype and severity depends on the type of variation and domain of the affected protein.

OBJECTIVES

To characterize the spectrum of COL7A1 variations in a cohort of DEB patients from India, to correlate these findings with clinical phenotypes and to establish a genotype-phenotype correlation.

METHODS

This was a retrospective, observational study involving patients with DEB diagnosed on the basis of clinical manifestations, Immuno-fluorescence antigen mapping (IFM) and genetic analysis. A genotype-phenotype correlation was attempted and observations were further explained using IFM on skin biopsies and molecular dynamic simulations. Descriptive statistics were performed using SPSS version 20.0 with P values of <0.05 considered significant.

RESULTS

We report 68 unrelated Indian DEB patients classified as RDEB-Intermediate (RDEB-I), RDEB-Severe (RDEB-S) or DDEB based on the EB diagnostic matrix, immunofluorescence antigen mapping and genetic data. Of 68 DEB patients, 59 (86.76%) were inherited in a recessive pattern (RDEB) and 9 (13.24%) in a dominant pattern (DDEB). Limbal stem cell deficiency was seen in four cases of RDEB-S very early in the course of the disease. A total of 88 variants were detected of which 66 were novel. There were no hotspots and recurrent variations were seen in a very small group of patients. We found a high frequency of compound heterozygotes (CH) in RDEB patients born out of non-consanguineous marriage. RDEB patients older than two years who had oral mucosal involvement, and/or deformities, were more likely to have esophageal involvement. Genotype phenotype correlation showed a higher frequency of extracutaneous manifestations and deformities in patients with Premature Termination Codons (PTCs) than in patients with other variations. Molecular simulation studies in patients with missense mutations showed severe phenotype when they were localized in interrupted regions of GLY-X-Y repeats.

CONCLUSION

This large study of DEB patients in South Asia adds to the continually expanding genetic database of this condition. This study has direct implications on management as this group of patients can be screened early and managed appropriately.

Demographic profile and clinical characteristics of patients presenting with acute ocular burns

Purpose

To study and compare the demographic and clinical profile of acute ocular burns (AOB) in children and adults.

Methods

This retrospective case series included 271 children (338 eyes) and 1300 adults (1809 eyes) who presented to two tertiary eye care centers within one month of sustaining AOB. Data regarding demographics, causative agents, severity of injury, visual acuity (VA), and treatment were collected and analyzed.

Results

Males were more commonly affected particularly among adults (81% versus 64%, P < 0.00001). Among children, 79% sustained domestic injuries, whereas 59% of adults had work-place injuries (P < 0.0001). Most cases were due to alkali (38%) and acids (22%). Edible lime (chuna, 32%), superglue (14%), and firecrackers (12%) in children, and chuna (7%), insecticides, lye, superglue (6% each), toilet cleaner (4%) and battery acid (3%) in adults, were the main causative agents. The percentage of cases with Dua grade IV-VI was greater in children (16% versus 9%; P = 0.0001). Amniotic membrane grafting and/or tarsorrhaphy were needed in 36% and 14% of affected eyes in children and adults, respectively (P < 0.00001). The median presenting VA was logMAR 0.5 in children and logMAR 0.3 in adults (P = 0.0001), which improved significantly with treatment in both groups (P < 0.0001), but the final VA in eyes with Dua grade IV-VI burns was poorer in children (logMAR 1.3 versus logMAR 0.8, P = 0.04).

Conclusion

The findings clearly delineate the at-risk groups, causative agents, clinical severity, and treatment outcomes of AOB. Increased awareness and data-driven targeted preventive strategies are needed to reduce the avoidable ocular morbidity in AOB.

The Multifold Etiologies of Limbal Stem Cell Deficiency: A Comprehensive Review on the Etiologies and Additional Treatment Options for Limbal Stem Cell Deficiency

Given the various ocular manifestations of limbal stem cell insufficiency, an awareness of the genetic, acquired, and immunological causes and associated additional treatments of limbal stem cell deficiency (LSCD) is essential for providers. We performed a comprehensive review of the literature on the various etiologies and specific therapies for LSCD. The resources utilized in this review included Medline (PubMed), Embase, and Google Scholar. All English-language articles and case reports published from November 1986 through to October 2022 were reviewed in this study. There were collectively 99 articles on these topics. No other exclusion criteria were applied. Depending on the etiology, ocular manifestations of limbal stem cell deficiency range from dry eye syndrome and redness to more severe outcomes, including corneal ulceration, ocular surface failure, and vision loss. Identifying the source of damage for LSCD is critical in the treatment process, given that therapy may extend beyond the scope of the standard protocol, including artificial tears, refractive surgery, and allogeneic stem cell transplants. This comprehensive review of the literature demonstrates the various genetic, acquired, and immunological causes of LSCD and the spectrum of supplemental therapies available.

Identification of Normal Fornix Depth Dataset Generated with a Validated Fornix Meter in Healthy Turkish Population

PURPOSE

To provide an age and sex-classified reference dataset for normal fornix depth by measuring the lower and upper conjunctival fornix depth (FD) in healthy volunteers.

METHODS

An epidemiological, prospective, cross-sectional study evaluates conjunctival FDs in 301 healthy Turkish volunteers aged 20-83. Fornix measurements were made using a validated fornix depth measurer (FDM).

RESULTS

The mean age was 49.2 ± 19 in males and 48.6 ± 16.2 in females. The mean upper and lower conjunctival FDs were 15.9 (12-21) mm and 10.1 (6-13) mm, respectively. The mean upper and lower FDs were 15.4 (13-20) mm and 9.7 (6-13) mm in females, and 16.3 (12-21) mm and 10.5 (8-13) mm in males, respectively.   .

CONCLUSION

When the normative dataset created in healthy Turkish volunteers, it was observed that both the upper and lower FDs were shallower in females and that they gradually became shallower with age. Accordingly, when an evaluation for conjunctival pathology is to be made, the expected normal FD value for both age and sex should be considered.

Management of limbal stem cell deficiency by amnion-assisted conjunctival epithelial redirection using vacuum-dried amniotic membrane and fibrin glue

PURPOSE

To study the outcome of a modified amnion-assisted conjunctival epithelial redirection (ACER) technique using vacuum-dried amnion (Omnigen) and fibrin glue for managing total limbal stem cell deficiency (LSCD).

METHOD

A retrospective, interventional case series of all patients with total LSCD who underwent limbal stem cell transplant (LSCT) using the modified ACER procedure between 2016 and 2019. The outcome was defined as: (1) success: complete corneal re-epithelialisation without conjunctivalisation; (2) partial success: sub-total corneal re-epithelialisation with partial non-progressive conjunctivalisation sparing the visual axis and (3) failure: conjunctivalisation affecting the visual axis.

RESULTS

Ten patients (six men), with a mean age of 46.2±18.4 years, were included. The mean follow-up was 23.0±13.9 months. Causes of LSCD were chemical eye injury (30%), congenital aniridia-related keratopathy (30%), ocular surface malignancy (20%), Steven-Johnson syndrome (10%) and contact lens overuse (10%). 50% were bilateral. The time from diagnosis to ACER (for acquired causes) was 45.6±44.4 months. 80% of patients achieved a complete/partial success following ACER and 20% of patients required repeat LSCT. Auto-LSCT was associated with a significantly higher chance of success than allo-LSCT (p=0.048). The mean best-corrected-visual-acuity (logMAR) improved significantly from 1.76±0.64 preoperatively to 0.94±0.94 at final follow-up (p=0.009). Omnigen was available off-the-shelf stored at room temperature and its transparency enabled visualisation of the healing epithelium beneath.

CONCLUSION

LSCT using the modified ACER serves as an effective ocular surface reconstruction technique in managing total LSCD and improving vision. Vacuum-dried amnion provides advantages of easy handling, transparency and storage at room temperature.

Profile of biological characterizations and clinical application of corneal stem/progenitor cells

Corneal stem/progenitor cells are typical adult stem/progenitor cells. The human cornea covers the front of the eyeball, which protects the eye from the outside environment while allowing vision. The location and function demand the cornea to maintain its transparency and to continuously renew its epithelial surface by replacing injured or aged cells through a rapid turnover process in which corneal stem/progenitor cells play an important role. Corneal stem/progenitor cells include mainly corneal epithelial stem cells, corneal endothelial cell progenitors and corneal stromal stem cells. Since the discovery of corneal epithelial stem cells (also known as limbal stem cells) in 1971, an increasing number of markers for corneal stem/progenitor cells have been proposed, but there is no consensus regarding the definitive markers for them. Therefore, the identification, isolation and cultivation of these cells remain challenging without a unified approach. In this review, we systematically introduce the profile of biological characterizations, such as anatomy, characteristics, isolation, cultivation and molecular markers, and clinical applications of the three categories of corneal stem/progenitor cells.

Mini-Conjunctival Limbal Autograft (Mini-CLAU) Using Platelet-Rich Plasma Eye Drops (E-PRP): A Case Series

PURPOSE

The purpose of this study was to introduce a new method of limbal stem cell transplantation using autologous platelet-rich plasma (E-PRP) eye drops for unilateral total limbal stem cell deficiency.

METHODS

Patients with total unilateral limbal stem cell deficiency due to chemical burn underwent mini-conjunctival limbal autograft using autologous E-PRP drops. One small limbal block, measuring 2 × 2 mm, was harvested from the patients' contralateral healthy eye and transplanted to the diseased eye. All patients received E-PRP drops until achieving complete corneal epithelialization. Subsequent corneal transplantation was performed in eyes with significant stromal opacification. Corneal buttons obtained during corneal transplantation underwent immunohistochemistry for the evaluation of limbal stem cell markers (ABCG2 and P63). Visual acuity, epithelial healing, corneal clarity, and regression of corneal conjunctivalization/vascularization were evaluated after surgery.

RESULTS

Ten patients with acid (n = 7) or alkali (n = 3) burn were included. The mean follow-up period was 21.7 ± 5.8 months (range, 12-32 months). Corneas were completely reepithelialized within 14.9 ± 3.5 days (range, 11-21 days). Corneal conjunctivalization/vascularization dramatically regressed 1 to 2 months after surgery in all cases, and corneal clarity considerably improved in 7 patients. In the 3 eyes with significant stromal opacification, subsequent optical penetrating keratoplasty was performed. The ocular surface was stable throughout the follow-up period in all eyes. BSCVA improved to 0.60 ± 0.0.32 and 0.46 ± 0.0.25 logMAR in eyes with and without corneal transplantation, respectively, at the final follow-up visit. ABCG2 and P63 markers were detected on corneal buttons after keratoplasty.

CONCLUSIONS

Based on our clinical and laboratory findings, mini-conjunctival limbal autograft using E-PRP can be considered as a promising alternative to ocular surface reconstruction.

Importance of Corneal Angiography in Subclinical Limbitis in a Case of Atopic Keratoconjunctivitis

PURPOSE

The aim of this study was to report corneal angiography features in subclinical limbitis in a patient with atopic keratoconjunctivitis.

METHODS

This is a case report.

RESULTS

A 22-year-old woman with a medical history of atopic keratoconjunctivitis was referred for bilateral corneal neovascularization with scarring. On examination, no signs of active disease were noticed at the slit lamp. Ocular surface angiography detected active corneal limbitis, showing as limbal leakage at fluorescein angiography in the early phase and leakage after indocyanine green angiography in the late phase. The patient was treated with topical corticosteroid. At follow-up, the fluorescein angiography and indocyanine green angiography no longer showed limbal leakage, whereas the slit lamp examination was unchanged.

CONCLUSIONS

Active allergic corneal limbitis may present as subclinical inflammation, with no signs of activity at the slit lamp examination. Therefore, its diagnosis can be challenging without the use of corneal angiography.

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.

SOX2 Is a Univocal Marker for Human Oral Mucosa Epithelium Useful in Post-COMET Patient Characterization

Total bilateral Limbal Stem Cells Deficiency is a pathologic condition of the ocular surface due to loss or impairment of corneal stem cell function, altering homeostasis of the corneal epithelium. Cultivated Oral Mucosa Epithelial Transplantation (COMET) is the only autologous treatment for this pathology. During the follow-up, a proper characterization of the transplanted oral mucosa on the ocular surface supports understanding the regenerative process. The previously proposed markers for oral mucosa identification (e.g., keratins 3 and 13) are co-expressed by corneal and conjunctival epithelia. Here, we propose a new specific marker to distinguish human oral mucosa from the epithelia of the ocular surface. We compared the transcriptome of holoclones (stem cells) from the human oral mucosa, limbal and conjunctival cultures by microarray assay. High expression of SOX2 identified the oral mucosa vs. cornea and conjunctiva, while PAX6 was highly expressed in corneal and conjunctival epithelia. The transcripts were validated by qPCR, and immunological methods identified the related proteins. Finally, the proposed markers were used to analyze a 10-year follow-up aniridic patient treated by COMET. These findings will support the follow-up analysis of COMET treated patients and help to shed light on the mechanism of corneal repair and regeneration.

Allogeneic simple limbal epithelial transplantation for bilateral limbal stem cell deficiency in chronic vernal keratoconjunctivitis: A case report

Introduction and importance

This report describes the management of bilateral limbal stem cell deficiency (LSCD) in vernal keratoconjunctivitis (VKC) with allogeneic simple limbal epithelial transplantation (allo-SLET).

Presentation of case

A 22-year-old female presented with bilateral VKC with total LSCD. A thick fibrotic pannus was present in both eyes, with visual axis involvement in the right eye. The central cornea in the left eye was clear. The patient underwent a cadaveric allo-SLET in the right eye to restore the ocular surface. Systemic immunosuppression with oral cyclosporine was administered following the surgery. The corrected visual acuity with scleral contact lenses (SCL) was 20/20 in both eyes which was maintained until the last follow-up visit, one year after the surgery. No recurrence of LSCD was observed in the right eye and the ocular surface was well epithelialized.

Discussion

Allo-SLET is a simple and efficacious surgical technique for bilateral LSCD. Eyes with VKC have a wet ocular surface, relatively clear corneal stroma, and minimal adnexal involvement. Thus, allo-SLET is the ideal procedure to address LSCD in such cases. The systemic immunosuppression that is given for ensuring graft survival can also help control the underlying allergy. Scleral contact lenses improve the visual acuity and their long-term usage does not affect the functioning of the SLET transplants.

Conclusion

VKC with bilateral LSCD can be successfully managed with allogeneic SLET. Post-operative systemic immunosuppressants are essential to maintain viable grafts. The use of SCL can improve vision and they do not pose any risk to the SLET transplants.

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Bilateral total limbal stem cell deficiency requires allogeneic stem cell transplant.

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Systemic immunosuppression is essential to maintain viable grafts in allo-SLET.

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In ocular allergy, these medications also help control the underlying inflammation.

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Scleral lenses can optimize the visual outcomes after allogeneic SLET.

Management of Symblepharon Prior to Keratoprosthesis in Chronic Ocular Burns: A Sequential Approach

This report describes two cases with stepwise management of chronic ocular burn sequelae with concurrent total limbal stem cell deficiency (LSCD) and advanced symblepharon. Both were mono-ocular patients with the other eye being phthisical. In both cases, a sequential approach was planned, and at the first stage, the symblepharon was released to stabilize the ocular surface and form the fornices. This was followed by a type 1 keratoprosthesis (KPro) after four months of symblepharon release in the first case, and after nine months in the second case. In the first case, after symblepharon release, the resultant bare sclera was addressed with an oral mucous membrane graft (MMG). Over two years of follow-up, there was no evidence of recurrence of the symblepharon. No further surgical interventions were required. In the second case, after symblepharon release, the resultant bare sclera was addressed with a cryopreserved amniotic membrane (AM). Over eight years of follow-up, six episodes of recurrence of the symblepharon were noted over the optic of the KPro, necessitating trimming of the conjunctiva from over the optic. Thus, with these two cases, we would like to emphasize that addressing adnexal pathologies such as a symblepharon with an oral MMG before implanting a KPro, may help prevent further recurrences of symblephara and the need for multiple surgical interventions. The oral mucosa is a better alternative to the conjunctiva as compared to the AM in a mono-ocular patient where conjunctiva cannot be harvested from the contralateral eye.

Case Report: Allogenic Simple Limbal Epithelial Transplantation From a Human Leukocyte Antigen-Matched Living Related Donor to Treat Bilateral Corneal Chemical Burns Post Laser-Assisted in situ Keratomileusis

A 35-year-old woman who had undergone laser-assisted in situ keratomileusis in both eyes experienced bilateral total limbal stem cell deficiency (LSCD) due to chemical burns. Due to bilateral severe LSCD, allogenic simple limbal epithelial transplantation (SLET) from a human leukocyte antigen (HLA)-matched living related donor was the first choice of treatment for her left eye. We report the first case of HLA or ABO matching living related allogenic SLET for permanent restoration of the cornea for bilateral LSCD treatment. Our ABO-HLA-matched living related allogenic SLET alleviation of the systemic immunosuppressant to topical corticosteroids alone. It also came the limitations of prolonged systemic immunosuppressant usage in conjunctival-limbal allografts and keratolimbal allograft.

Observational study of cenegermin for the treatment of limbal stem cell deficiency associated with neurotrophic keratopathy

Background:

Neurotrophic keratopathy (NK) and limbal stem cell deficiency (LSCD) have high morbidity and require aggressive management to prevent permanent vision loss. Cenegermin, a recombinant human nerve growth factor, was approved by the Federal Drug Administration in 2018 for the treatment of NK.

Objectives:

To determine the efficacy and safety of cenegermin in the treatment of LSCD associated with NK.

Design:

Prospective cohort study

Methods:

Patients diagnosed with LSCD and NK who had failed conventional treatment were enrolled in this prospective open-label study. Patients were treated with cenegermin for 8 weeks. The primary objective was to determine whether the area of abnormal epithelium decreased following treatment. Corneal sensation, visual acuity (VA), and LSCD severity were also evaluated.

Results:

Six eyes of 5 patients were included in the study. Cenegermin significantly improved the area of abnormal corneal epithelium in 5 of 6 eyes, measuring 73% of total corneal area at the initial visit and 48% at the final visit ( P = .036). Corneal sensation improved in all patients, Cochet–Bonnet aesthesiometry measured 14.7 and 26.7 mm at the initial and final visit, respectively ( P = .009). VA improved in 4 out of 6 eyes, with mean initial logMAR VA of 1.67 and final logMAR VA of 1.19 ( P = .045). Finally, LSCD grading improved using the Aravena scoring system; however, this difference was not statistically significant ( P = .14). One patient presented with an epithelial defect at baseline, which resolved following treatment. No patient withdrew from the study due to adverse effects.

Conclusions:

Cenegermin effectively improved the cornea epithelium, VA, and corneal sensation in patients with LSCD and NK who had failed prior treatment. Further studies are necessary to better understand the anatomical changes and to confirm our results with a larger randomized control trial.

Registration:

The study was registered at ClinicalTrials.gov with identifier NCT04552730 ( https://clinicaltrials.gov/ct2/show/NCT04552730 ).

OUP accepted manuscript

The corneal epithelium serves to protect the underlying cornea from the external environment and is essential for corneal transparency and optimal visual function. Regeneration of this epithelium is dependent on a population of stem cells residing in the basal layer of the limbus, the junction between the cornea and the sclera. The limbus provides the limbal epithelial stem cells (LESCs) with an optimal microenvironment, the limbal niche, which strictly regulates their proliferation and differentiation. Disturbances to the LESCs and/or their niche can lead to the pathologic condition known as limbal stem cell deficiency (LSCD) whereby the corneal epithelium is not generated effectively. This has deleterious effects on the corneal and visual function, due to impaired healing and secondary corneal opacification. In this concise review, we summarize the characteristics of LESCs and their niche, and present the current and future perspectives in the management of LSCD with an emphasis on restoring the function of the limbal niche.

Clinical, histological and immunohistochemistry characteristics of cornea in the sequelae stage of chronic vernal keratoconjunctivitis

Purpose:

To report the clinical outcomes and histopathological and immunohistochemistry (IHC) features in eyes with the sequelae stage of vernal keratoconjunctivitis (VKC).

Methods:

Investigative study of corneal samples obtained following surgical intervention for vision restoration in four eyes of three patients with VKC. Patient 1 (an 11-year-old boy) had deep anterior lamellar keratoplasty in both eyes, Patient 2 (a 24-year-old male) underwent superficial keratectomy followed by penetrating keratoplasty, and Patient 3 (a 22-year-old male) underwent penetrating keratoplasty. The corneal samples retrieved after surgical intervention were assessed for histology features and immunohistochemistry (IHC) studies.

Results:

The grafts were clear till the follow-up of 2–18 months. Histopathology of all four corneal samples showed epithelial hyperplasia, absent Bowman layer, thick hyalinized stromal lamellae, vascularization, and chronic inflammatory cells such as lymphocytes and plasma cells. IHC showed strong expression of CK 3 in both eyes of Patient 1 and no expression in Patients 2 and 3. The marker for limbal stem cells, ABCG2, was absent in all four samples; however, p63α was expressed strongly in Patients 2 and 3, moderately in the right eye of Patient 1, and marginally expressed in the left eye of Patient 1.

Conclusion:

The eyes in the sequelae stage of VKC (having corneal scarring and 360° hypertrophied limbus) can be managed favorably with keratoplasty and amniotic membrane transplantation without allogenic/cadaveric stem cell transplantation. The expression of transient progenitor cells in the scarred corneas of VKC patients in the sequelae stage suggests that the limbal stem cell dysfunction is more likely partial and self-renewal of limbal stem cells is a plausibility in these eyes.

Corneal epithelial differentiation of human pluripotent stem cells generates ABCB5+ and ∆Np63α+ cells with limbal cell characteristics and high wound healing capacity

Background

Differentiation of functional limbal stem cells (LSCs) from human pluripotent stem cells (hPSCs) is an important objective which can provide novel treatment solutions for patients suffering from limbal stem cell deficiency (LSCD). Yet, further characterization is needed to better evaluate their immunogenicity and regenerative potential before clinical applications.

Methods

Human PSCs were differentiated towards corneal fate and cryopreserved using a clinically applicable protocol. Resulting hPSC-LSC populations were examined at days 10–11 and 24–25 during differentiation as well as at passage 1 post-thaw. Expression of cornea-associated markers including PAX6, ABCG2, ∆Np63α, CK15, CK14, CK12 and ABCB5 as well as human leukocyte antigens (HLAs) was analyzed using immunofluorescence and flow cytometry. Wound healing properties of the post-thaw hPSC-LSCs were assessed via calcium imaging and scratch assay. Human and porcine tissue-derived cultured LSCs were used as controls for marker expression analysis and scratch assays at passage 1.

Results

The day 24–25 and post-thaw hPSC-LSCs displayed a similar marker profile with the tissue-derived LSCs, showing abundant expression of PAX6, ∆Np63α, CK15, CK14 and ABCB5 and low expression of ABCG2. In contrast, day 10–11 hPSC-LSCs had lower expression of ABCB5 and ∆Np63α, but high expression of ABCG2. A small portion of the day 10–11 cells coexpressed ABCG2 and ABCB5. The expression of class I HLAs increased during hPSC-LSCs differentiation and was uniform in post-thaw hPSC-LSCs, however the intensity was lower in comparison to tissue-derived LSCs. The calcium imaging revealed that the post-thaw hPSC-LSCs generated a robust response towards epithelial wound healing signaling mediator ATP. Further, scratch assay revealed that post-thaw hPSC-LSCs had higher wound healing capacity in comparison to tissue-derived LSCs.

Conclusions

Clinically relevant LSC-like cells can be efficiently differentiated from hPSCs. The post-thaw hPSC-LSCs possess functional potency in calcium responses towards injury associated signals and in wound closure. The developmental trajectory observed during hPSC-LSC differentiation, giving rise to ABCG2⁺ population and further to ABCB5⁺ and ∆Np63α⁺ cells with limbal characteristics, indicates hPSC-derived cells can be utilized as a valuable cell source for the treatment of patients afflicted corneal blindness due to LSCD.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02673-3.

Limbal Stem Cell Deficiency: Demographics and Clinical Characteristics of a Large Retrospective Series at a Single Tertiary Referral Center

PURPOSE

The aim of this study was to characterize a large cohort of patients presenting to a single referral center for limbal stem cell deficiency (LSCD).

METHODS

A retrospective chart review of all patients with a clinical diagnosis of LSCD from 2002 to 2015 was performed. Demographics, etiology, previous ocular surgeries, visual acuity, and treatment were assessed.

RESULTS

Seven hundred thirty-eight eyes of 434 patients (51.4% male subjects) were diagnosed with LSCD. The mean presenting age was 42.9 years, 70% presented with bilateral disease, and overall vision was poor. The most common etiologies were congenital aniridia (30.9%), chemical or thermal injuries (20.6%), contact lens (16.8%), Stevens-Johnson syndrome (SJS, 10.4%), and iatrogenic (7.3%). Congenital aniridia had a significantly increased association with glaucoma or ocular hypertension (P < 0.0001). Chemical or thermal injuries (P = 0.0007), SJS (P < 0.0001), and mucous membrane pemphigoid (P < 0.0001) had a significantly increased association with eyelid pathology. The mean logMAR best corrected visual acuity (analysis excluded eyes with light perception and no light perception) at presentation was 1.145 (∼20/280). Keratoplasty performed (before presentation at our center) without first addressing the LSCD was seen in 80 eyes; all keratoplasties failed due to recurrence of the LSCD.

CONCLUSIONS

Patients presenting with LSCD were on average middle aged without sex predominance. LSCD was most commonly bilateral, comprised a wide range of etiologies, and decreased vision substantially. Ocular comorbidities may need to be treated before treating the LSCD surgically. Finally, not addressing the LSCD (primary issue) first can result in keratoplasty failure.

Midterm outcomes of penetrating keratoplasty following allogeneic cultivated limbal epithelial transplantation in patients with bilateral limbal stem cell deficiency

AIM

To evaluate the midterm outcomes of penetrating keratoplasty (PK) following allogeneic cultivated limbal epithelial transplantation (CLET) for bilateral total limbal stem cell deficiency (LSCD).

METHODS

Ten patients (10 eyes) with bilateral LSCD were enrolled in this prospective noncomparative case series study. Each participant underwent PK approximately 6mo after a CLET. Topical tacrolimus, topical and systemic steroids, and oral ciclosporin were administered postoperatively. Best-corrected visual acuity (BCVA), intraocular pressure (IOP), ocular surface grading scores (OSS), corneal graft epithelial rehabilitation, persistent epithelial defect (PED), immunological rejection, and graft survival rate were assessed.

RESULTS

The time interval between PK and allogeneic CLET was 6.90±1.29 (6-10)mo. BCVA improved from 2.46±0.32 logMAR preoperatively to 0.77±0.55 logMAR post-PK (P<0.001). Kaplan-Meier analysis of mean graft survival revealed graft survival rates of 100% at 12 and 24mo and 80.0% at 36mo. PEDs appeared in 5 eyes at different periods post-PK, and graft rejection occurred in 4 eyes. The total OSS decreased from 12.4±4.4 before allogeneic CLET to 1.4±1.51 after PK.

CONCLUSION

A sequential therapy design of PK following allogeneic CLET can maintain a stable ocular surface with improved BCVA despite the relatively high graft rejection rate.

Surgical Management of Unilateral Partial Limbal Stem Cell Deficiency: Conjunctival Autografts versus Simple Limbal Epithelial Transplantation

Purpose

To evaluate the clinical outcomes of conjunctival autograft (CAG) versus simple limbal epithelial transplant (SLET) for management of unilateral partial limbal stem cell deficiency (LSCD).

Methods

This retrospective, comparative, interventional case series evaluated 30 eyes of 30 patients with unilateral partial LSCD. After corneal pannus dissection, 17 patients underwent CAG where graft was harvested from the ipsilateral or contralateral eye, while 13 patients underwent SLET where limbal biopsy was harvested from the contralateral eye. The primary outcome measure was anatomical success in the form of restoration of a completely epithelised, stable, and avascular corneal surface at last follow-up.

Results

Both groups were comparable in terms of age at time of surgery, preoperative best-corrected visual acuity, median duration since injury, number of clock hours of limbus involved, and number of previous surgeries performed. The most common etiology for LSCD was chemical burns in both groups. The median duration of post-operative follow-up was 5.6 months [interquartile range [(IQR): 3.6–15.1] in the CAG group versus 6.2 months (IQR: 4.5–12.2) in the SLET group (p=0.75)]. The anatomical success rates were 86.5 ± 8.9% in the CAG group and 28.3 ± 13.7% in the SLET group at final follow-up visit (p = 0.025). Most failures in both groups occurred within the first 8 months after surgery.

Conclusion

For eyes with unilateral partial LSCD secondary to chemical burns, CAG is a safe and effective method for restoring the corneal epithelium. Limbal transplantation may not be necessary for the treatment of partial LSCD.

Evaluating the clinical translational relevance of animal models for limbal stem cell deficiency: A systematic review

PURPOSE

Animal models are pivotal for elucidating pathophysiological mechanisms and evaluating novel therapies. This systematic review identified studies that developed or adapted animal models of limbal stem cell deficiency (LSCD), assessed their reporting quality, summarized their key characteristics, and established their clinical translational relevance to human disease.

METHODS

The protocol was prospectively registered (PROSPERO CRD42020203937). Searches were conducted in PubMed, Ovid EMBASE and Web of Science in August 2020. Two authors screened citations, extracted data, assessed the reporting quality of eligible studies using the ARRIVE guidelines, and judged the clinical translational relevance of each model using a custom matrix.

RESULTS

105 studies were included. Rabbits were the most common animal species. Overall, 97% of studies recapitulated LSCD to a clinical etiology, however 62% did not provide sufficient methodological detail to enable independent reproduction of the model. Adverse events and/or exclusion of animals were infrequently (20%) reported. Approximately one-quarter of studies did not produce the intended severity of LSCD; 34% provided insufficient information to assess the fidelity of disease induction. Adjunctive diagnostic confirmation of LSCD induction was performed in 13% of studies.

CONCLUSIONS

This is the first systematic review to assess the reporting quality and clinical translational relevance of animal models of LSCD. Models of LSCD have evolved over time, resulting in variable reporting of the characteristics of animals, experimental procedures and adverse events. In most studies, validation of LSCD was made using clinical tests; newer adjunctive techniques would enhance diagnostic validation. As most studies sought to evaluate novel therapies for LSCD, animal models should ideally recapitulate all features of the condition that develop in patients.

Clinical Aspects of Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis With Severe Ocular Complications in India

Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) is a spectrum of rare, severe immunological blistering skin reactions which are triggered by medication intake or infections. The acute phase is characterized by necrolysis of the skin and desquamation of mucosa, primarily oral and ocular, with significant mortality rates. The chronic phase is characterized by multi-organ sequelae with increased rates of morbidity and reduced quality of life for patients who have survived the acute phase. Since the primary goal in the acute phase is saving the life of the patient, ocular involvement is often missed and a significant proportion of patients present to an ophthalmologist with the chronic ocular sequelae. In India, chronic ocular sequelae and low vision are observed in two-thirds of patients who present in the chronic phase of SJS/TEN. In the chronic phase of ocular involvement, there are definite windows of opportunity which if targeted with specific interventions such as scleral lenses and mucous membrane grafts can help reduce the incidence of corneal blindness and improve the quality of life for patients with SJS/TEN. Over the last decade, several studies from India have advanced the understanding of the natural course of ocular involvement in SJS/TEN and the outcomes of timely interventions in the chronic phase of the disease. We present an overview of the epidemiology of ocular complications of SJS/TEN in India, the specific challenges faced in the management of ocular complications in the acute stage and recent advances in management of the chronic ocular complications of the disease.

Referral Patterns of Patients with Limbal Stem Cell Deficiency to a Specialized Tertiary Center in the United Kingdom

INTRODUCTION

Limbal stem cell deficiency (LSCD) is a potentially blinding disease; hence, referral to a specialist service is becoming increasingly common. Our aim was to investigate the referral patterns and associated details.

METHODS

We conducted an audit of 100 consecutive patients with LSCD who were referred to our service from 2011 to 2018. Patient demographics, geographical location, cause of LSCD, coexisting ocular diseases, best corrected visual acuity (BCVA), and extent of LSCD were recorded. The following two subgroups were further analyzed: (1) burns and (2) other causes of LSCD.

RESULTS

Out of the 100 patients (138 eyes), 70% were male, with a mean age of 45 years (SD 19). LSCD was unilateral in 62% of the cases. The most common ocular comorbidity was glaucoma, in 21 patients (33 eyes). Burns were the most frequent cause of referral (61%). The mean BCVA of the involved eye was 1.22 (SD 0.8) LogMAR, and total LSCD was present in 75 eyes (54%). There were statistically significant age, gender and eye-involved differences between the burns group and other causes group, mean 39 (SD 17) and 53 (SD 19) years (p < 0.001); 85% were men versus 48.7%, (p = 0.001); and 82% were unilateral versus 31% (p < 0.001), respectively.

CONCLUSIONS

LSCD was more common in men and usually unilateral. Overall, the main cause of LSCD was burns. There were significant differences between the burns group and other causes of LSCD group in terms of age, gender and unilateral involvement that may help to guide management decisions.

Role of anterior segment optical coherence tomography angiography in the assessment of acute chemical ocular injury: a pilot animal model study

To examine the use of anterior segment-optical coherence tomography angiography (AS-OCTA) in the assessment of limbal ischemia in an animal model chemical ocular injury. We conducted a prospective study using an established chemical ocular injury model in 6 rabbits (12 eyes), dividing the cornea limbus into 4 quadrants. Chemical injury grade was induced based on extent of limbal injury (0 to 360 degrees) and all eyes underwent serial slit-lamp with AS-OCTA imaging up to one month. Main outcome measure was changes in AS-OCTA vessel density (VD) comparing injured and control cornea limbal quadrants within 24 h and at one month. AS-OCTA was able to detect differences in limbal VD reduction comparing injured (3.3 ± 2.4%) and control quadrants (7.6 ± 2.3%; p < 0.001) within 24 h of ocular chemical injury. We also observed that AS-OCTA VD reduction was highly correlated with the number of quadrants injured (r = − 0.89; p < 0.001; 95% CI − 5.65 to − 1.87). Corneal vascularization was detected by AS-OCTA in injured compared to control quadrants (10.1 ± 4.3% vs 7.0 ± 1.2%; p = 0.025) at 1 month. Our animal pilot study suggests that AS-OCTA was able to detect limbal vessel disruption from various severities of acute chemical insult, and in the future, could potentially serve as an adjunct in providing objective grading of acute ocular chemical injury once validated in a clinical trial.

"Doughnut" Amniotic Membrane Transplantation With Penetrating Keratoplasty for Vernal Keratoconjunctivitis With Limbal Stem Cell Disease

PURPOSE

Severe vernal keratoconjunctivitis (VKC) can cause ocular surface disease including partial or complete limbal stem cell deficiency (LSCD), especially in early-onset and severe limbal form of VKC. We report a novel technique of doughnut amniotic membrane transplantation (AMT) along with penetrating keratoplasty (PK) for management of partial LSCD and corneal scarring in a case of severe VKC.

METHODS

Case report.

RESULTS

A 17-year-old boy, with onset of disease at 8 years of age, and development of partial LSCD and corneal scarring over a period of 9 years despite therapy, presented with profound visual loss due to dense bilateral corneal scarring. After the active allergy subsided, he underwent modified AMT (doughnut AMT) with simultaneous PK in his left eye. Histopathology of the excised button revealed conjunctival phenotype and dense corneal scarring up to the posterior stroma. At 1-year follow up, his best spectacle-corrected visual acuity was maintained at 20/30 in the operated eye, the graft was clear, and the ocular surface was stable.

CONCLUSIONS

Severe VKC can cause ocular surface disease including LSCD with corneal scarring, especially in early-onset limbal form of VKC. The modified technique of AMT (doughnut AMT) along with PK can successfully visually rehabilitate and address partial LSCD in such patients.

High-Resolution Optical Coherence Tomography Angiography Characteristics of Limbal Stem Cell Deficiency

This study aimed to identify the anterior segment high-resolution optical coherence tomography (HR-OCT) and HR-OCT angiography (HR-OCTA) features suggestive of limbal stem cell deficiency (LSCD) as confirmed by both impression cytology (IC) and in vivo confocal microscopy (IVCM). This was a single-centre prospective cross-sectional study including 24 eyes of 22 patients with clinical suspicion of LSCD based on peripheral superficial corneal vascularisation and scarring. On IC and IVCM, performed and interpreted by blinded observers, 12 eyes each were diagnosed with and without LSCD. Additionally, 10 eyes of 5 healthy volunteers with no ocular pathology were also imaged. The 136 HR-OCT/A images of these 34 eyes were analysed with respect to 12 imaging parameters; the parameters most suggestive of LSCD were identified and the sensitivity and specificity were calculated. In the LSCD group, the most common aetiology was ocular chemical burns (83%), whereas in the non-LSCD group, the most common aetiology was viral keratitis (67%). Multiple logistic regression analysis revealed that mean epithelial reflectivity, mean stromal reflectivity, and mean superficial vascular density were the parameters that were diagnostic of LSCD on HR-OCT/A (p < 0.0001). A ratio of the mean epithelial reflectivity to stromal reflectivity of >1.29 corresponded with a high sensitivity (91.7%) and specificity (98.75%); while a mean superficial vascular density score of >0.38 corresponded with a sensitivity of 97.9% and specificity of 73.8%. In conclusion, HR-OCT/A as a non-invasive imaging modality could prove to be a useful tool for confirming the diagnosis of LSCD, with potential clinical and research applications.

Histopathological Characteristics of Limbal Stem Cell Deficiency Secondary to Chronic Vernal Keratoconjunctivitis

PURPOSE

To describe the histopathological characteristics of limbal stem cell deficiency (LSCD) due to chronic vernal keratoconjunctivitis (VKC).

METHODS

This retrospective study included 14 eyes of 13 patients who underwent simple limbal epithelial transplantation for total LSCD from 2017 to 2018. The histological characteristics of the excised fibrovascular pannus were compared between 2 groups of 7 eyes, each with LSCD due to VKC and chemical burns (CB). Histological characteristics and type of inflammation were studied using special stains and immunohistochemistry. Fisher exact test was used to detect the statistical significance of the histological differences between both groups.

RESULTS

Epithelial hypertrophy, epithelial downgrowth, and eosinophilic infiltration were noted in all eyes in the VKC group (7/7, 100%). Epithelial hypertrophy was noted in 3 of the 7 (42.8%) eyes in the CB group, whereas epithelial downgrowth and eosinophilic infiltrates were absent. The average chronic inflammatory score of the pannus (5.28) was higher in VKC than in CB (3.85; P = 0.1080). The presence of goblet cells was higher in the CB group (5/7, 1.4%) than in the VKC group (3/4, 2.8%), although not statistically significant. Other histological differences between the groups were not statistically significant.

CONCLUSIONS

The histopathological features of LSCD in VKC reveal some distinctive characteristics. These include the presence of epithelial downgrowth, eosinophilic infiltration, and epithelial solid and cystic implants. Although this information may be used to establish the diagnostic criteria for VKC as the cause of LSCD, further studies are needed to elucidate the reasons behind these unique findings.

Mini-Review: Regenerating the Corneal Epithelium With Simple Limbal Epithelial Transplantation

Simple limbal epithelial transplantation (SLET) is an ingenious, low cost and effective technique of limbal stem cell transplantation (LSCT) that is increasingly being undertaken in practice across the world. Since it was first described a decade ago, the technique has been performed in a variety of cases of limbal stem cell deficiency (LSCD) and has underwent several innovative modifications. Published literature on SLET has progressively increased over time and successful outcomes in various clinical scenarios have been reported. This concise review attempts to present a crisp account of SLET covering the indications and contraindications of performing the procedure; detailed account of pre-operative work up and preparation; surgical technique and its modifications; post-operative course, care and possible complications as well as published outcomes of surgery from across the world. Comparative analysis of various techniques of LSCT have been discussed and common concerns of surgeons practising or those who are planning to start practising SLET have been addressed. The authors hope that the pragmatic insights and pearls given at the end of the review will aid the surgeons in performing this technique to provide maximum benefit to patients suffering from the potentially blinding condition of LSCD.

Chronic cicatrizing conjunctivitis: A review of the differential diagnosis and an algorithmic approach to management

Cicatrizing conjunctivitis constitutes a group of chronic local and systemic disorders that cause conjunctival scarring. A systematic approach is required to sift through the clinical history, examination, and laboratory investigations of patients to arrive at the correct diagnosis of the underlying cause. Establishing the etiology is critical, as the therapeutic approach changes based on the cause of conjunctival inflammation. Effective management of patients with the condition requires knowledge of multiple modalities such as systemic immunosuppressive therapy, use of scleral contact lenses, and surgery for ocular surface and vision improvement. We review the clinical features of this condition and present diagnostic and treatment algorithms to help simplify the complexities in its management. This review attempts to place all the relevant information on chronic cicatrizing conjunctivitis together in one place for the benefit of cornea and ocular surface specialists, general ophthalmologists, and ophthalmology residents.

Surgical Management and Recent Advances in Chemical Injury: A 5-year Review

Purpose: To review the surgical management options in ocular chemical burn, including newer advances.Methods: Online literature search of published articles over last 5 years on surgical management of ocular chemical burn and newer advances were performed on December 30, 2020.Results: Following literature search and screening using adequate filters, 67 review articles on surgical management of ocular chemical burns were retrieved. The review talks about the surgical management options starting from Debridement in acute stage to various visual rehabilitative procedures in the chronic stage. The review also highlights the evolving surgical advances in this field.Conclusion: It is imperative to choose adequate surgical tool wherever applicable; current review discusses the role of each surgical option at different clinical stages in detail.

Therapeutic effect of secretome from TNF-α stimulated mesenchymal stem cells in an experimental model of corneal limbal stem cell deficiency

AIM

To explore the secretome efficacy in tumor necrosis factor (TNF)-α stimulated mouse mesenchymal stem cells (MSCs) in a murine model of corneal limbal alkali injury.

METHODS

Corneal limbal stem cell deficiency (LSCD) was created in the eyes of male C57 mice. Concentrated conditioned medium from TNF-α stimulated MSCs (MSC-CMT) was applied topically for 4wk, with basal medium and conditioned medium from MSCs as controls. Corneal opacification, corneal inflammatory response, and corneal neovascularization (NV) were evaluated. Corneal epithelial cell apoptosis, corneal conjunctivation, and inflammatory cell infiltration were assessed with TUNEL staining, CK3 and Muc-5AC immunostaining, and CD11b immunofluorescence staining, respectively. The effect of TSG-6 was further evaluated by knockdown with short hairpin RNA (shRNA).

RESULTS

Compared to the controls, topical administration of MSC-CMT significantly ameliorated the clinical symptoms of alkali-induced LSCD, with restrained corneal NV, reduced corneal epithelial cell apoptosis, and inhibition of corneal conjunctivation. In addition, MSC-CMT treatment significantly reduced CD11b⁺ inflammatory cell infiltration, and inhibited the expression of pro-inflammatory cytokines (IL-1β, TNF-α and IL-6). Furthermore, the promotion of corneal epithelial reconstruction by MSC-CMT was largely abolished by TSG-6 knockdown.

CONCLUSION

Our study provides evidence that MSC-CMT enhances the alleviation of corneal alkali injuries, partially through TSG-6-mediated anti-inflammatory protective mechanisms. MSC-CMT may serve as a potential strategy for treating corneal disorders.

Medical management and visual rehabilitation of limbal niche dysfunction

Limbal niche dysfunction (LND) has been described as a medically reversible form of limbal stem cell deficiency. The current literature is sparse regarding therapeutic options to improve visual function after stabilization of the disease. A 61-year-old monocular woman with an extensive medical and ocular history presented with long-standing recalcitrant epitheliopathy in both eyes. History and examination findings on presentation led to a diagnosis of LND, and medical therapy was initiated. After 8 months, her ocular surface had improved and corrected distance visual acuity (CDVA) was 20/40. She was fit with a scleral contact lens because of its ability to promote ocular surface healing and improve visual acuity. She maintained symptom resolution and her CDVA improved to 20/20. LND is a distinctive and reversible epitheliopathy that responds favorably to appropriate medical therapy. To the authors' knowledge, this is the first reported case of using the scleral contact lens as an adjunctive visual rehabilitation therapy to complement medical treatment for LND.

Limbal stem cell diseases

The function of limbal stem/progenitor cells (LSCs) is critical to maintain corneal epithelial homeostasis. Many external insults and intrinsic defects can be deleterious to LSCs and their niche microenvironment, resulting in limbal stem cell dysfunction or deficiency (LSCD). Ocular comorbidities, frequent in eyes with LSCD, can exacerbate the dysfunction of residual LSCs, and limit the survival of transplanted LSCs. Clinical presentation and disease evolution vary among different etiologies of LSCD. New ocular imaging modalities and molecular markers are now available to standardize the diagnosis criteria and stage the severity of the disease. Medical therapies may be sufficient to reverse the disease if residual LSCs are present. A stepwise approach should be followed to optimize the ocular surface, eliminate the causative factors and treat comorbid conditions, before considering surgical interventions. Furthermore, surgical options are selected depending on the severity and laterality of the disease. The standardized diagnostic criteria to stage the disease is necessary to objectively evaluate and compare the efficacy of the emerging customized therapies.

Allogeneic simple limbal epithelial transplantation: an appropriate treatment for bilateral stem cell deficiency

A 39-year-old man presented with both eyes limbal stem cell deficiency status post chemical injury. He was managed initially with topical medications to subside the ocular surface inflammation. Over the course of subsequent visits, the fibrovascular pannus over the cornea gradually progressed, leading to further diminution of vision in left eye more than right eye. Since, the ocular surface was wet, the patient committed for lifelong immunosuppression and his brother consented to donate healthy limbal tissue; he underwent living-related allogeneic simple limbal epithelial transplantation in the left eye.

A beginner's guide to mucous membrane grafting for lid margin keratinization: Review of indications, surgical technique and clinical outcomes

The posterior lid margin, where the mucocutaneous junction (MCJ) between the eyelid skin and tarsal conjunctiva is located, plays a critical role in maintaining the homeostasis of the ocular surface. Posterior migration of the MCJ leads to lid-margin keratinization (LMK), which has a domino effect on the delicate balance of the ocular surface microenvironment. This occurs most commonly following Stevens-Johnson syndrome/toxic epidermal necrolysis and is not known to regress spontaneously or with medical therapy. Over time, LMK causes blink-related chronic inflammatory damage to the corneal surface which may have blinding consequences. Lid-margin mucous membrane grafting (MMG) is the only definitive therapy for LMK. Timely MMG can significantly alter the natural course of the disease and not only preserve but even improve vision in affected eyes. Literature searches were conducted on PubMed, using the keywords "mucous membrane grafts," "lid margin keratinization," "Stevens-Johnson syndrome," "toxic epidermal necrolysis," "lid related keratopathy," and "lid wiper epitheliopathy". This review, which is a blend of evidence and experience, attempts to describe the indications, timing, surgical technique, postoperative regimen, and clinical outcomes of MMG for LMK. The review also covers the possible complications and pearls on how they can be effectively managed, including how suboptimal cosmetic outcomes can be avoided. The authors hope that this review will aid ophthalmologists, including cornea and oculoplasty specialists, to learn and perform this vision-saving surgery better, with the aim of helping their patients with chronic ocular surface disorders, relieving their suffering, and improving their quality of life.

Genetic Markers for Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis in the Asian Indian Population: Implications on Prevention

This review attempts to collate all the studies performed in India or comprising a population originating from India and to find out if there is an association between the HLA (human leucocyte antigen) type of individual and development of Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) subsequent to medication use. The authors performed a PubMed search of all articles published in English from 2009 to 2019 for articles that studied HLA type in patients who developed SJS/TEN after intake of a specific drug in the Asian Indian population or in individuals of Asian Indian origin. The selection criteria were satisfied by a total of 11 studies that reported HLA associations with specific drugs, which induced SJS/TEN, mainly anti-epileptic drugs, and cold medicine/non-steroidal anti-inflammatory drugs. These studies involved a small number of patients, and hence, there is limited evidence to conclude if these associations can be extrapolated to a larger population of the same ethnicity. Similar multi-center studies need to be conducted with a larger sample size to confirm these associations. This would have implications in policy making and for understanding the potential of using genetic markers as a screening tool before prescribing a drug to a patient, which might make them susceptible to developing a potentially life-threatening disease such as SJS/TEN. This is possibly the only mode of primary prevention for this potentially fatal severe cutaneous adverse drug reaction.

Single-cell transcriptomics identifies limbal stem cell population and cell types mapping its differentiation trajectory in limbal basal epithelium of human cornea

PURPOSE

This study aimed to uncover novel cell types in heterogenous basal limbus of human cornea for identifying LSC at single cell resolution.

METHODS

Single cells of human limbal basal epithelium were isolated from young donor corneas. Single-cell RNA-Sequencing was performed using 10x Genomics platform, followed by clustering cell types through the graph-based visualization method UMAP and unbiased computational informatic analysis. Tissue RNA in situ hybridization with RNAscope, immunofluorescent staining and multiple functional assays were performed using human corneas and limbal epithelial culture models.

RESULTS

Single-cell transcriptomics of 16,360 limbal basal cells revealed 12 cell clusters belonging to three lineages. A smallest cluster (0.4% of total cells) was identified as LSCs based on their quiescent and undifferentiated states with enriched marker genes for putative epithelial stem cells. TSPAN7 and SOX17 are discovered and validated as new LSC markers based on their exclusive expression pattern and spatial localization in limbal basal epithelium by RNAscope and immunostaining, and functional role in cell growth and tissue regeneration models with RNA interference in cultures. Interestingly, five cell types/states mapping a developmental trajectory of LSC from quiescence to proliferation and differentiation are uncovered by Monocle3 and CytoTRACE pseudotime analysis. The transcription factor networks linking novel signaling pathways are revealed to maintain LSC stemness.

CONCLUSIONS

This human corneal scRNA-Seq identifies the LSC population and uncovers novel cell types mapping the differentiation trajectory in heterogenous limbal basal epithelium. The findings provide insight into LSC concept and lay the foundation for understanding the corneal homeostasis and diseases.

Opening the Soul Window Manually: Limbal Tissue Scaffolds with Electrospun Polycaprolactone/Gelatin Nanocomposites

Restricted by the difficulty in fabricating scaffolds suitable for cell proliferation, the use of ex vivo expanded limbal stem cell (LSC) for LSC transplantation, an effective treatment method for patients with limb stem cell deficiency (LSCD), is hard to be widely used in clinical practice. To tackle these challenges, a novel electrospun polycaprolactone (PCL)/gelatin nanocomposite is proposed to make 3D scaffolds for limbal niche cells (LNC) proliferation in vitro, which is a milestone in the treatment of diseases such as LSCD. PCL and gelatin in different weight ratios are dissolved in a mixed solvent, and then electrospinning and cross-linking are performed to prepare a scaffold for cell proliferation. The characterizations of the nanocomposites indicate that the gelatin content has a significant effect on its micro-morphology, thermal properties, crystallinity, degradation temperature, hydrophilicity, and mechanical properties. P8G2-C (PCL: gelatin = 80: 20, cross-linked), with smooth fibers and homogeneous pores, has better hydrophilicity, mechanical properties, and flexibility, so it can support LNC as cell proliferation assays revealed. This detailed investigation presented here demonstrates the feasibility of using PCL/gelatin nanocomposites electrospun fiber membranes as a limbus tissue engineering scaffold, which undoubtedly provide a new perspective for the development of tissue engineering field.

Lid-Related Keratopathy in Stevens-Johnson Syndrome: Natural Course and Impact of Therapeutic Interventions in Children and Adults

PURPOSE

To compare the long-term visual outcomes of different management strategies in children and adults with Stevens-Johnson Syndrome (SJS)-induced chronic lid-related keratopathy.

DESIGN

Retrospective comparative case series.

METHODS

This study included 705 eyes of 401 patients (81 children and 320 adults) with SJS who presented with chronic lid-related keratopathy between 1990 and 2015. Affected eyes received either conservative therapy [topical medications (n = 363)] or definitive management (n = 342) that included mucous membrane grafting (MMG), prosthetic replacement of the ocular surface ecosystem (PROSE) contact lenses, or both. The primary outcome measure was change in best corrected visual acuity (BCVA) over time. The secondary outcome measure was the odds of developing corneal ulceration or perforation in the first year.

RESULTS

The treatment subgroups were comparable at baseline in terms of BCVA and previous management (P > .10). Over 10 years, children and adults who received conservative therapy lost at least 5 lines of median BCVA and carried a 3 times higher risk of developing corneal ulceration in the first year. Conversely, definitive therapy provided significant benefit by improving median BCVA (P < .0001). In children, MMG was more effective than PROSE (P = .009), whereas PROSE was more effective than MMG in adults (P = .028). However, the combination of MMG followed by PROSE provided the best results in both children and adults (P < .036).

CONCLUSIONS

Both MMG and PROSE changed the natural course and helped in preserving and improving vision in eyes with SJS-induced lid-related keratopathy. Regardless of age, those who received both MMG and PROSE had the best long-term visual outcomes.

Limbal Stem Cell Deficiency Associated With Herpes Keratitis

PURPOSE

To describe the demographic features and clinical characteristics of patients with herpes keratitis (HK) and limbal stem cell deficiency (LSCD) and identify possible factors associated with development of LSCD after HK.

METHODS

In this retrospective case-series study, records of patients with a clinical diagnosis of HK seen at Massachusetts Eye and Ear over a 5-year period were reviewed for evidence of LSCD. Patient demographics, medical history, treatment, and best-corrected visual acuities (BCVAs) were recorded.

RESULTS

We identified 626 patients with HK. Fifty-seven had been diagnosed with LSCD (9.3%). Thirteen percent of patients with herpes zoster keratitis (N= 25) and 7% of patients with herpes simplex keratitis (N= 32) had LSCD (P = 0.01). Keratitis caused by herpes zoster virus [odds ratios (OR), 1.77; 95% confidence interval (CI), 0.97-3.19; P = 0.01], stromal involvement (OR, 2.28; 95% CI, 1.27-4.18; P = 0.02), and the use of topical antihypertensives (OR, 2.28; 95% CI, 1.27-4.18; P = 0.02) were found to be associated with a higher likelihood of developing LSCD. The final logarithm of the minimum angle of resolution (LogMAR) BCVA was significantly lower in patients with LSCD compared with those without LSCD with a mean BCVA of 1.34 ± 1.52 LogMar (∼20/200) as compared to 0.18 ± 0.54 LogMar (∼20/30 ± 20/60) in those patients without LSCD (P = 0.005).

CONCLUSIONS

Our data suggest that HK may be a risk factor for development of LSCD. Patients with HK should be monitored for the development of LSCD to reduce the risk of chronic ocular surface morbidity.

Recent Advances in Stem Cell Therapy for Limbal Stem Cell Deficiency: A Narrative Review

Destruction of the limbus and depletion of limbal stem cells (LSCs), the adult progenitors of the corneal epithelium, leads to limbal stem cell deficiency (LSCD). LSCD is a rare, progressive ocular surface disorder which results in conjunctivalisation and neovascularisation of the corneal surface. Many strategies have been used in the treatment of LSCD, the common goal of which is to regenerate a self-renewing, transparent, and uniform epithelium on the corneal surface. The development of these techniques has frequently resulted from collaboration between stem cell translational scientists and ophthalmologists. Direct transplantation of autologous or allogeneic limbal tissue from a healthy donor eye is regarded by many as the technique of choice. Expansion of harvested LSCs in vitro allows smaller biopsies to be taken from the donor eye and is considered safer and more acceptable to patients. This technique may be utilised in unilateral cases (autologous) or bilateral cases (living related donor). Recently developed, simple limbal epithelial transplant (SLET) can be performed with equally small biopsies but does not require in vitro cell culture facilities. In the case of bilateral LSCD, where autologous limbal tissue is not available, autologous oral mucosa epithelium can be expanded in vitro and transplanted to the diseased eye. Data on long-term outcomes (over 5 years of follow-up) for many of these procedures is needed, and it remains unclear how they produce a self-renewing epithelium without recreating the vital stem cell niche. Bioengineering techniques offer the ability to re-create the physical characteristics of the stem cell niche, while induced pluripotent stem cells offer an unlimited supply of autologous LSCs. In vivo confocal microscopy and anterior segment OCT will complement impression cytology in the diagnosis, staging, and follow-up of LSCD. In this review we analyse recent advances in the pathology, diagnosis, and treatment of LSCD.

Niche regulation of limbal epithelial stem cells: HC-HA/PTX3 as surrogate matrix niche

Homeostasis of the corneal epithelium is ultimately maintained by stem cells that reside in a specialized microenvironment within the corneal limbus termed palisades of Vogt. This limbal niche nourishes, protects, and regulates quiescence, self-renewal, and fate decision of limbal epithelial stem/progenitor cells (LEPCs) toward corneal epithelial differentiation. This review focuses on our current understanding of the mechanism by which limbal (stromal) niche cells (LNCs) regulate the aforementioned functions of LEPCs. Based on our discovery and characterization of a unique extracellular matrix termed HC-HA/PTX3 (Heavy chain (HC1)-hyaluronan (HA)/pentraxin 3 (PTX3) complex, "-" denotes covalent linkage; "/" denotes non-covalent binding) in the birth tissue, i.e., amniotic membrane and umbilical cord, we put forth a new paradigm that HC-HA/PTX3 serves as a surrogate matrix niche by maintaining the in vivo nuclear Pax6+ neural crest progenitor phenotype to support quiescence and self-renewal but prevent corneal fate decision of LEPCs. This new paradigm helps explain how limbal stem cell deficiency (LSCD) develops in aniridia due to Pax6-haplotype deficiency and further explains why transplantation of HC-HA/PTX3-containing amniotic membrane prevents LSCD in acute chemical burns and Stevens Johnson syndrome, augments the success of autologous LEPCs transplantation in patients suffering from partial or total LSCD, and assists ex vivo expansion (engineering) of a graft containing LEPCs. We thus envisage that this new paradigm based on regenerative matrix HC-HA/PTX3 as a surrogate niche can set a new standard for regenerative medicine in and beyond ophthalmology.