The structure and function of the limbal stem cell and the disease states associated with limbal stem cell deficiency

Limbal stem cell deficiency approaches and limbal niche restoration

Approaches to limbal stem cell deficiency remain challenging, especially in bilateral cases, where healthy limbal stem cells are not accessible. While living-related allogeneic and allogeneic limbal stem cell sources have been utilized, their dependence on immunosuppression and its associated side effects pose significant limitations. Mucosal and mesenchymal stem cells have shown potential for differentiation into limbal stem cells and promoting corneal healing, primarily when cultured on the amniotic membrane or fibrin. However, none can fully replicate the original limbus. Innovations in surgical techniques, such as simple oral mucosal transplantation and subconjunctival or intrastromal mesenchymal stem cell injections, are emerging approaches. For successful limbal regeneration, both appropriate cells and suitable scaffolds are essential. Recent studies on decellularized and acellularized limbus models have demonstrated the potential to provide a three-dimensional native structure for cell seeding, retention, and differentiation. Creating a thin, evenly decellularized scaffold is a critical step in ensuring proper corneo-limbal slope formation, facilitating cell migration to the ocular surface. Harvesting the limbus, decellularization, and cell seeding are the three main steps in limbal reconstruction. Recent studies focus on microkeratome-assisted limbal harvesting to create a thin, even, and 360-degree limbal graft. This technique helps form an attached corneo-limbal interface, facilitating limbal stem cell migration. In the second step, acellularization is performed to preserve the extracellular matrix as much as possible, maintaining hemostasis and supporting paracrine interactions. The final steps involve recellularization and transplantation onto the eye. We summarize various limbal decellularization methods, their outcomes, and their potential in limbal reconstruction. More clinical studies are needed to validate this phase of limbal deficiency treatment.

Revitalizing Vision: Eye Drops and Corneal Limbal Stem Cells Survival

In the quest to transform vision care, researchers have been investigating novel methods to boost the efficacy of eye drops and enhance the survival of corneal limbal stem cells. Aimed at rejuvenating vision, these innovations seek to tackle a range of ocular conditions and restore sight to those in need. This article examines the most recent advancements in eye drops and corneal limbal stem cells, highlighting their potential to revolutionize ophthalmology. Findings from various studies indicate that the drive to rejuvenate vision has resulted in significant progress within the field of ophthalmology, especially regarding eye drops and corneal limbal stem cells. By improving the effectiveness of eye drops and increasing the survival rates of CLSCs, researchers are creating pathways for more sustainable and effective treatment options. These advancements offer great hope for patients experiencing various ocular issues, suggesting a future where vision restoration is attainable. As research continues to refine these strategies, we can look forward to an era marked by better visual outcomes and an enhanced quality of life for many individuals around the world.

Allogenic Cultured Limbal Epithelial Transplantation and Cultivated Oral Mucosal Epithelial Transplantation in Limbal Stem Cells Deficiency: A Comparative Study

INTRODUCTION

This study compared the clinical outcomes of allogenic cultured limbal epithelial transplantation (ACLET) and cultivated oral mucosal epithelial transplantation (COMET) in the management of limbal stem cell deficiency (LSCD).

METHODS

Forty-one COMET procedures in 40 eyes and 69 ACLET procedures in 54 eyes were performed in the Corneoplastic Unit of Queen Victoria Hospital, East Grinstead. Data were examined for demographics, indications, ocular surface stability, absence of epithelial defect, ocular surface inflammation, visual outcomes, and intra- and postoperative complications.

RESULTS

Kaplan-Meier analysis showed that patients in the ACLET group with longer follow-up had a significantly higher graft survival rate (81.7%, n = 56) than the COMET group (60.7%, n = 25) and the difference was statistically significant (p = 0.01). In the COMET group, there was no statistically significant improvement in the visual acuity (VA) while in the ACLET group there was statistically significant improvement in the final VA. Elevated intraocular pressure (IOP) developed in 9 eyes (22.0%) in the COMET group and in 18 eyes (26.1%) in the ACLET group; infection developed in 4 eyes (9.8%) in the COMET group and in 10 eyes (14.5%) in the ACLET group; and perforation or melting happened in 4 eyes (9.8%) in the COMET group and in 1 eye (1.4%) in the ACLET group. Postoperative immunosuppression complications were noted in 9 eyes (13.0%) in the ACLET group. No graft rejection was observed in either group.

CONCLUSION

Both ACLET and COMET are effective therapeutic procedures for managing advanced and bilateral cases of LSCD. Although COMET has lower graft survival rate than ACLET, it does not mandate systemic immunosuppression therapy to protect against potential graft rejection.

Classification and treatment approach of chemical burn associated Limbal stem cell deficiency: based on novel global consensus

PURPOSE

To evaluate the severity distribution of chemical burn-induced Limbal stem cell deficiency (LSCD) according to the novel global consensus classification and to compare the treatment approach, before and after the global consensus.

METHODS

Medical records of 127 eyes of 109 patients with LSCD were included. LSCD stages were categorized according to the global consensus classification published by "International LSCD Working Group".

RESULTS

The mean age was 37.5 ± 16.5(6-75). The distribution of LSCD stage according to the global consensus scale was as follows: Stage 1A in 5 eyes(3.9%);Stage 1B in 16 eyes(12.6%);Stage 1C in 4 eyes(3.2%);Stage 2A in 15 eyes(11.8%);Stage 2B in 36 eyes(28.3%);Stage 3 in 51 eyes(40.2%). A total of 88(69.3%) eyes underwent surgery for LSCD. Of these, 80 had surgery prior to the publication of the global consensus (before October 2020), 58(72.5%) had preoperative severe (≥ Stage 2B) LSCD and 22(27.5%) had preoperative early stage (≤ Stage 2A) LSCD. As of October 2020, all 8 eyes that underwent surgery had preoperative severe (≥ Stage 2B) LSCD, as recommended by global consensus.

CONCLUSION

Recently, a global consensus has been established on both the classification and the management of LSCD. This study is one of the first to present small-scale epidemiological data on the severity distribution of LSCD in the light of the global consensus. It was observed that surgery was performed on 27.5% of the eyes that were not recommended for surgery according to this new consensus. With the increasing awareness of this consensus, it might be possible to avoid unnecessary surgical intervention.

Opposing Roles of Blood-Borne Monocytes and Tissue-Resident Macrophages in Limbal Stem Cell Damage after Ocular Injury

Limbal stem cell (LSC) deficiency is a frequent and severe complication after chemical injury to the eye. Previous studies have assumed this is mediated directly by the caustic agent. Here we show that LSC damage occurs through immune cell mediators, even without direct injury to LSCs. In particular, pH elevation in the anterior chamber (AC) causes acute uveal stress, the release of inflammatory cytokines at the basal limbal tissue, and subsequent LSC damage and death. Peripheral C-C chemokine receptor type 2 positive/CX3C motif chemokine receptor 1 negative (CCR2+ CX3CR1-) monocytes are the key mediators of LSC damage through the upregulation of tumor necrosis factor-alpha (TNF-α) at the limbus. In contrast to peripherally derived monocytes, CX3CR1+ CCR2- tissue-resident macrophages have a protective role, and their depletion prior to injury exacerbates LSC loss and increases LSC vulnerability to TNF-α-mediated apoptosis independently of CCR2+ cell infiltration into the tissue. Consistently, repopulation of the tissue by new resident macrophages not only restores the protective M2-like phenotype of macrophages but also suppresses LSC loss after exposure to inflammatory signals. These findings may have clinical implications in patients with LSC loss after chemical burns or due to other inflammatory conditions.

Substance P/neurokinin-1 receptor pathway blockade ameliorates limbal stem cell deficiency by modulating mTOR pathway and preventing cell senescence

Severe ocular surface diseases can lead to limbal stem cell deficiency (LSCD), which is accompanied by defective healing. We aimed to evaluate the role of the substance P (SP)/neurokinin-1 receptor (NK1R) pathway in corneal epithelium wound healing in a pre-clinical model of LSCD. SP ablation or NK1R blockade significantly increased epithelial wound healing (p < 0.001) and corneal transparency (p < 0.001), compared with wild type (WT). In addition, a reduced number of infiltrating goblet and conjunctival cells (p < 0.05) and increased number of epithelial stem cells (p < 0.01), which also expressed NK1R, was observed. The mammalian target of rapamycin (mTOR) pathway was significantly inhibited (p < 0.05) and expression of γH2AX was significantly reduced (p < 0.05) after SP ablation. These results suggest that excessive expression of SP is associated with LSCD and results in accelerated senescence and exhaustion of residual stem cells. Topical treatment with NK1R antagonist ameliorates clinical signs associated with LSCD and could be used as an adjuvant treatment in LSCD.

Lipid Keratopathy: A Review of Pathophysiology, Differential Diagnosis, and Management

Lipid keratopathy is a disease in which fat deposits accumulate in the cornea, leading to opacification and decrease of visual acuity. This condition can be idiopathic without signs of previous corneal disease or secondary to ocular or systemic diseases. Lipid keratopathy is usually associated with abnormal vascularization of the cornea, and the lipid classically deposits adjacent to these vessels. Treatment of this condition usually aims to eliminate or prevent abnormal vessel formation, and several modalities have been described. In this review we summarize the etiology, pathophysiology, and clinical presentation of lipid keratopathy and describe current and emerging treatment regimens.

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.

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.

Short-Term Results Analysis in the Allogenic Transplantation of Limbal Stem Cells Expanded on Amniotic Membrane in Patients with Bilateral Limbal Stem Cell Deficiency

Purpose: The objective of this study was to describe the short-term results of allogenic transplantation of limbal stem cells expanded on amniotic membrane for the ocular surface reconstruction. Methods: Prospective nonrandomized, nonmasked study in a single ophthalmological center. Ten patients with bilateral total limbal stem cell deficiency (LSCD) were included. Expression and presence of ABCB5 and Δp63α in amniotic membrane-cultured limbal epithelial stem cells were analyzed, in relationship with clinical changes after allogenic transplantation. An objective evaluation was performed to determine corneal transparency and superficial vascularization. Results: In a median follow-up time of 11.6 months, 7 patients (70%) were considered as failure compared with the preoperative status. ABCB5 and Δp63α are expressed in similar amount in the limbal epithelial cells expanded in vitro and transplanted in patients with bilateral LSCD. Conclusions: Transplantation of allogenic epithelial limbal cells expanded in amniotic membrane could be considered in patients with LSCD due to burns or congenital etiologies such as aniridia, but its benefit is limited for patients with immunologic diseases.

Synthetic Nanofiber-Reinforced Amniotic Membrane via Interfacial Bonding

Severe damage to the ocular surface can result in limbal stem cell (LSC) deficiency, which contributes to loss of corneal clarity, potential vision loss, chronic pain, photophobia, and keratoplasty failure. Human amniotic membrane (AM) is the most effective substrate for LSC transplantation to treat patients with LSC deficiency. However, the widespread use of the AM in the clinic remains a challenge because of the high cost for preserving freshly prepared AM and the weak mechanical strength of lyophilized AM. Here, we developed a novel composite membrane consisting of an electrospun bioabsorbable polymer fiber mesh bonded to a decellularized AM (dAM) sheet through interfacial conjugation. This membrane engineering approach drastically improved the tensile property and toughness of dAM, preserved similar levels of bioactivities as the dAM itself in supporting LSC attachment, growth, and maintenance, and retained significant anti-inflammatory capacity. These results demonstrate that the lyophilized nanofiber-dAM composite membrane offers superior mechanical properties for easy handling and suturing to the dAM, while presenting biochemical cues and basement membrane structure to facilitate LSC transplantation. This composite membrane exhibits major advantages for clinical applications in treating soft tissue damage and LSC deficiency.

Differentiation of rat adipose-derived mesenchymal stem cells into corneal-like epithelial cells driven by PAX6

Corneal integrity, transparency and vision acuity are maintained by corneal epithelial cells (CECs), which are continuously renewed by corneal limbal stem cells (LSCs). Deficiency of CECs and/or LSCs is associated with numerous ocular diseases. Paired box (PAX)6 is an eye development-associated transcription factor that is necessary for cell fate determination and differentiation of LSCs and CECs. In the present study, the PAX6 gene was introduced into adipose-derived rat mesenchymal stem cells (ADMSCs) to investigate whether PAX6-transfected cells were able to transdifferentiate into corneal-like epithelial cells and to further verify whether the cells were suitable as a cell source for corneal transplantation. The ADMSCs were isolated from the bilateral inguinal region of healthy Sprague Dawley rats. The characteristics of ADMSCs were identified using flow cytometric analysis. After subculture, ADMSCs underwent transfection with recombinant plasmid containing either PAX6-enhanced green fluorescent protein (EGFP) complementary (c)DNA or EGFP cDNA (blank plasmid group), followed by selection with G418 and determination of the transfection efficiency. Subsequently, the morphology of the ADMSCs and the expression profiles of corneal-specific markers CK3/12 and epithelial-specific adhesion protein were determined. E-cadherin was detected using immunofluorescence staining and western blot analysis at 21 days following transfection. An MTT cell proliferation and a colony formation assay were performed to assess the proliferative activity and clonogenicity of PAX6-transfected ADMSCs. Finally, the PAX6-expressing ADMSCs were transplanted onto the cornea of a rabbits with limbal stem cell deficiency (LSCD). At 21 days after transfection, the ADMSCs with PAX6 transfection exhibited a characteristic flagstone-like appearance with assembled corneal-like epithelial cells, and concomitant prominent expression of the corneal-specific markers cytokeratin 3/12 and E-cadherin. Furthermore, the proliferation and colony formation ability of PAX6-overexpressing ADMSCs was significantly retarded. The transplantation experiment indicated that PAX6-reprogramed ADMSCs attached to and replenished the damaged cornea via formation of stratified corneal epithelium. Taken together, these results suggested that conversion of ADMSCs into corneal-like epithelium may be driven by PAX6 transfection, which makes ADMSCs a promising cell candidate for the treatment of LSCD.

Optical Coherence Tomography Imaging of the Palisades of Vogt to Assist Clinical Evaluation and Surgical Planning in a Case of Limbal Stem-Cell Deficiency

PURPOSE

To describe the use of volumetric optical coherence tomography (OCT) imaging to assist evaluation of a patient referred for autologous limbal stem-cell transplant.

METHODS

This is a case report of a 50-year-old patient presenting with unilateral limbal stem-cell deficiency who was referred for autologous limbal stem-cell transplant. The presence of Salzmann nodules in the donor eye raised questions about the efficacy of transplantation, prompting examination of both eyes using volumetric OCT imaging to determine whether there were palisades of Vogt (POV) present. Image volumes were acquired in all clock hours and were compared against those of an age-matched normal subject.

RESULTS

Palisades were found in both eyes, although in both eyes there were fewer palisade ridges, and those that were present were not as distinct as those of the normal subject. The OCT volumes also showed that stromal scarring was present only in the anterior stroma of the intended transplant eye. These findings suggested that the patient may be able to sustain a deep anterior lamellar keratoplasty without an autologous transplant, which would spare any insult to the opposing eye and require less surgery to restore vision in the affected eye. Nine months postsurgical follow-up revealed significant improvement in visual acuity and no scar tissue development.

CONCLUSION

The OCT evaluation of the POV provides detailed information to the clinician that may assist in diagnosis and evaluation of patients before transplantation. Further development of this technique is necessary to make it clinically available.

In-vivo imaging of the palisades of Vogt and the limbal crypts with sub-micrometer axial resolution optical coherence tomography

A research-grade OCT system was used to image in-vivo and without contact with the tissue, the cellular structure and microvasculature of the healthy human corneo-scleral limbus. The OCT system provided 0.95 µm axial and 4 µm (2 µm) lateral resolution in biological tissue depending on the magnification of the imaging objective. Cross-sectional OCT images acquired tangentially from the inferior limbus showed reflective, loop-like features that correspond to the fibrous folds of the palisades of Vogt (POV). The high OCT resolution allowed for visualization of individual cells inside the limbal crypts, capillaries extending from the inside of the POV's fibrous folds and connecting to a lateral grid of micro-vessels located in the connective tissue directly below the POV, as well as reflections from individual red blood cells inside the capillaries. Difference in the reflective properties of the POV was observed among subjects of various pigmentation levels of the POV. Morphological features observed in the high resolution OCT images correlated well with histology. The ability to visualize the limbal morphology and microvasculature in-vivo at cellular level can aid the diagnostics and treatment of limbal stem cell dysfunction and dystrophies.

Concomitant Simple Limbal Epithelial Transplantation After Surgical Excision of Ocular Surface Squamous Neoplasia

PURPOSE

To compare the surgical outcomes of ocular surface squamous neoplasia (OSSN) following wide excisional biopsy with and without primary simple limbal epithelial transplantation (p-SLET).

DESIGN

Nonrandomized clinical study with historical controls.

METHODS

setting: Single-institutional study.

PATIENTS

Eight patients who underwent wide excisional biopsy of OSSN without p-SLET (historical controls) and 7 patients with p-SLET (cases).

INTERVENTION

Wide excisional biopsy, p-SLET.

MAIN OUTCOME MEASURES

Limbal stem cell deficiency (LSCD).

RESULTS

The tumor features of cases vs historical controls, including mean number of limbal clock hours affected by OSSN (6 vs 4; P = .12), mean tumor basal dimension (13 mm vs 8 mm; P = .11), and mean number of clock hours of corneoscleral limbal dissection owing to wide tumor excision (8 vs 7; P = .12), were comparable. The occurrence of partial LSCD in historical controls vs cases was 75% vs 0% (P = .007) at a mean follow-up period of 12 months in both groups. Of these 6 historical controls that developed LSCD, pannus was noted in 1 (13%) and pseudopterygium extending onto the cornea in 5 (63%) patients. The mean number of clock hours of LSCD was 3 (median, 2; range, 2-6) in these historical controls. The mean time interval between surgical excision of OSSN and onset of LSCD was 8 weeks (median, 6 weeks; range, 6-12 weeks).

CONCLUSION

Corneoscleral limbal dissection of ≥6 clock hours during wide excision of OSSN can cause LSCD. Concomitant p-SLET after surgical excision of OSSN prevents LSCD in cases requiring extensive corneoscleral limbal dissection.

Identifying the Palisades of Vogt in Human Ex Vivo Tissue

PURPOSE

The Palisades of Vogt (POV) constitute the corneal epithelial stem cell niche, but identification of this region in ex vivo tissue is difficult. Here we introduce a simple, direct method of identifying the POV in unsectioned, ex vivo human tissue.

METHODS

Twenty-two eyes were studied, four whole and eighteen rims. Orientation of whole eyes was determined and the eyes were marked to maintain their cardinal orientation prior to dissection. Samples were imaged with brightfield, linearly polarized light and transmitted circularly polarized light (CPL), and optical coherence tomography (OCT) volumes were acquired in all twelve clock hrs around the limbus. Five samples were also fluorescently labeled to identify the epithelial basement membrane, and whole mounts were imaged with laser scanning confocal microscopy. Images were compared to confirm that the structures visible with polarized light were POV.

RESULTS

Under CPL the POV presented as amber radial ridges visible in the superior and inferior regions of the tissue. Identification of POV was confirmed by correlating the structures seen under CPL, OCT and laser-scanning confocal microscopy.

CONCLUSIONS

CPL can be used to quickly identify POV regions in donor tissue. This technique can assist in targeted harvesting of stem cell regions for research and tissue for limbal transplant.

Using optical coherence tomography to assess the role of age and region in corneal epithelium and palisades of vogt

Using spectral-domain optical coherence tomography (OCT) to observe the morphology and epithelial thickness (ET) of the palisades of Vogt (POV), and to evaluate the role of age and region on these structures.One hundred twelve eyes of 112 healthy subjects were enrolled and divided into 4 groups: A (0-19), B (20-39), C (40-59), and D (≥60 years old). RTvue-100 OCT was applied on the cornea and the limbus. The morphology of the subepithelial stroma underneath the epithelium of POV was classified into typical and atypical types. Maximum ET of POV was measured manually from OCT images.The positive rate of typical POV in superior, nasal, temporal, and inferior limbus was: Group A: 100%, 69.2%, 65.4%, 100%; Group B: 100%, 73.5%, 61.8%, 94.1%; Group C: 95.8%, 41.7%, 37.5%, 83.3%; Group D: 67.9%, 0%, 3.6%, 25%, showing a significant decreasing tendency with age. The maximum ET of POV in superior, nasal, temporal, and inferior limbus was: Group A: 103.5 ± 10.1 um, 89.2 ± 9.7 um, 87.9 ± 13.6 um, 104.7 ± 14.1 um; Group B: 111.4 ± 15.8 um, 85.3 ± 9.9 um, 88.2 ± 8.6 um, 112.6 ± 19.7 um; Group C: 116.4 ± 16.4 um, 82.8 ± 11.6 um, 87.0 ± 11.6 um, 120.0 ± 25.6 um; Group D: 96.3 ± 17.9 um, 73.8 ± 15.9 um, 79.2 ± 16.7 um, 87.4 ± 18.5 um. Age-dependent change was observed. In general, the maximum ET of POV in superior/inferior quadrants was thicker than the other 2 quadrants.Spectral-domain OCT is a useful tool to observe the limbal microstructure and provide invaluable information. Aging and anatomic regions had significant effects on the microstructure of these areas.

Stability of limbal stem cell deficiency after mechanical and thermal injuries in mice

We studied the reproducibility and stability of limbal stem cell deficiency (LSCD) in mice following controlled injuries to the corneal and limbal epithelia. In one method, corneal and limbal epithelia were entirely removed with a 0.5 mm metal burr. In the other, limbus to limbus epithelial removal with the burr was followed by thermal injury to the limbus. These two methods were compared with a previously published one. Unwounded corneas were used as control. The corneas were examined monthly for three months by slit lamp with fluorescein staining. Immunofluorescence staining for cytokeratin 12 and 8 on corneal wholemount and cross sections were performed to determine the phenotype of the epithelium. Mechanical shaving of the epithelium, with or without thermal injury, resulted in a reproducible state of LSCD marked by superficial neovascularization, reduce of keratin 12 expression and presence of goblet cells on the cornea. The phenotype was stable in 100% of the eyes up to at least three months. Thermal injury produced a more severe phenotype with more significant stromal opacification. These corneal injury models may be useful for studying the mechanisms leading to limbal stem cell deficiency.

Epithelial Thinning in Limbal Stem Cell Deficiency

PURPOSE

To investigate the epithelial thickness in the cornea and limbus in limbal stem cell deficiency (LSCD) by using in vivo laser scanning confocal microscopy.

DESIGN

Cross-sectional comparative study.

METHODS

Confocal images of 48 eyes of 35 patients with LSCD collected by the Heidelberg Retina Tomograph III Rostock Corneal Module Confocal Microscope from 2010 to 2014 were analyzed. Volume Z-scans of the central cornea and the superior, nasal, inferior, and temporal limbus were included in the analysis. Eleven normal eyes served as control. Epithelial thickness in all locations was measured by 2 independent observers.

RESULTS

The mean epithelial layer thickness was 48.6 ± 2.3 μm in the central cornea and 63.7 ± 11.3 μm in the limbus in the control. Compared with the epithelial thickness in normal control, the epithelial thickness in LSCD patients was reduced by an average of 20.2% in the central cornea and 38.5% in the limbus (all P < .05). The mean corneal epithelial thickness in patients with LSCD reduced 7.6%, 20.8%, and 61.3% in the early, intermediate, and late stage, respectively, compared to the control. In the limbus, the overall epithelial thickness decreased 30.0%, 39.7%, and 62.8% in the early, intermediate, and late stage of LSCD, respectively (all P < .05). Epithelial thinning correlated with the severity of LSCD in both cornea and limbus. In eyes with sectoral LSCD, a similar degree of epithelial thinning was also detected in the clinically unaffected limbal regions.

CONCLUSIONS

Both corneal and limbal epithelia become progressively thinner in LSCD. Epithelial thickness could be used as a diagnostic measure of LSCD.

Ultra high-resolution anterior segment optical coherence tomography in the diagnosis and management of ocular surface squamous neoplasia

The development of optical coherence tomography (OCT) technology has helped to usher in a new era of in vivo diagnostic imaging of the eye. The utilization of OCT for imaging of the anterior segment and ocular surface has evolved from time-domain devices to spectral-domain devices with greater penetrance and resolution, providing novel images of anterior segment pathology to assist in diagnosis and management of disease. Ocular surface squamous neoplasia (OSSN) is one such pathology that has proven demonstrable by certain anterior segment OCT machines, specifically the newer devices capable of performing ultra high-resolution OCT (UHR-OCT). Distinctive features of OSSN on high resolution OCT allow for diagnosis and differentiation from other ocular surface pathologies. Subtle findings on these images help to characterize the OSSN lesions beyond what is apparent with the clinical examination, providing guidance for clinical management. The purpose of this review is to examine the published literature on the utilization of UHR-OCT for the diagnosis and management of OSSN, as well as to report novel uses of this technology and potential directions for its future development.

Canine herpesvirus-1 ocular diseases of mature dogs

Canine herpesvirus-1 (CHV-1) is an alphaherpesvirus with a host range restricted to canids. Latent CHV-1 infection is endemic in domestic dog populations worldwide. The role of CHV-1 in severe systemic neonatal infections and as an aetiology of infectious infertility and abortion has been appreciated for decades; however, ocular diseases of mature dogs conclusively associated with CHV-1 infection were only recently described. Clinically, CHV-1 infection may produce a diverse range of adnexal and ocular surface lesions in mature dogs, including blepharitis, conjunctivitis, ulcerative keratitis, and nonulcerative keratitis. These conditions can develop during primary or recurrent ocular CHV-1 infection. Recurrent CHV-1 infections associated with reactivation of latent virus may be observed during a variety of situations and in association with numerous different viral reactivation stimuli, including the administration of immunosuppressive pharmaceuticals. The understanding of CHV-1 pathophysiology and ocular infections in mature dogs has expanded rapidly during the past few years, but much remains to be elucidated. As the number of dogs living with chronic immunomodulatory systemic diseases and receiving immunosuppressive therapeutics continues to grow, the clinical importance of CHV-1 ocular infections is also likely to increase.

Optical coherence tomography as a rapid, accurate, noncontact method of visualizing the palisades of Vogt

PURPOSE

This study explored the efficacy of optical coherence tomography (OCT) as a high-resolution, noncontact method for imaging the palisades of Vogt by correlating OCT and confocal microscopy images.

METHODS

Human limbal rims were acquired and imaged with OCT and confocal microscopy. The area of the epithelial basement membrane in each of these sets was digitally reconstructed, and the models were compared.

RESULTS

OCT identified the palisades within the limbus and exhibited excellent structural correlation with immunostained tissue imaged by confocal microscopy.

CONCLUSIONS

OCT successfully identified the limbal palisades of Vogt that constitute the corneal epithelial stem cell niche. These findings offer the exciting potential to characterize the architecture of the palisades in vivo, to harvest stem cells for transplantation more accurately, to track palisade structure for better diagnosis, follow-up and staging of treatment, and to assess and intervene in the progression of stem cell depletion by monitoring changes in the structure of the palisades.

Tissue-regenerating, vision-restoring corneal epithelial stem cells

The cornea, the most anterior segment of the eye, provides us with exquisite vision. Unlike other vital tissues, it is poorly protected from the environment and is thus reliant on a self-renewal program to preserve integrity. This function is reserved for corneal epithelial stem cells located in the basal layer of the limbus, a narrow transition zone that segregates the peripheral cornea from the adjacent conjunctiva. Under physiological conditions, these cells replenish the corneal epithelium when mature or traumatized cells are lost. However, when the limbus is extensively damaged, stem cell activity is compromised, resulting in a condition known as limbal stem cell deficiency (LSCD). This disease is characterized by corneal neovascularization and persistent epithelial defects which impair vision. Over the past 20 years a myriad of treatment options have been developed for LSCD, most of which incorporate stem cell transplantation. Due to the disadvantages associated with the use of allogeneic and xenogeneic material, researchers are currently focusing on refining techniques involving autologous limbal tissue transplantation and are delving into the possibility that stem cells found in other organs can provide an alternative source of corneal epithelium. Determining where donor stem cells reside on the recipient's ocular surface and how long they remain viable will provide further insights into improving current therapeutic options for patients with LSCD.

Limbal stem cell disease: management with scleral lenses

BACKGROUND

Limbal stem cell deficiency (LSCD) results from damage to or destruction of corneal stem cells.

METHODS

A retrospective review of clinical records of a patient with LSCD describes the use of scleral lenses in disease management.

RESULTS

A patient presented with a one-year history of clinically diagnosed LSCD, which was worsening despite aggressive topical and systemic medical therapy. The condition resolved rapidly with initiation of scleral lens wear. The integrity of the ocular surface was maintained for 18 months even after the cessation of lens wear.

CONCLUSION

Scleral lenses might allow some patients with LSCD to delay or avoid more aggressive surgical intervention.

Midterm outcomes of autologous cultivated limbal stem cell transplantation with or without penetrating keratoplasty

PURPOSE

To report the midterm outcomes of autologous limbal stem cell transplantation cultivated on amniotic membrane (AM) with or without subsequent penetrating keratoplasty (PKP) in patients with total unilateral limbal stem cell deficiency (LSCD).

METHODS

Eight eyes of 8 consecutive patients with unilateral total LSCD underwent autologous limbal stem cell transplantation cultivated on AM. Four eyes underwent subsequent optical PKP. Main outcome measures were corneal vascularization and transparency.

RESULTS

The patients were followed for 34.0 +/- 13.5 months (6-48 months). Seven cases had a stable corneal epithelium with marked decrease in opacification and vascularization. Progressive sectorial conjunctivalization was evident in all cases with subsequent PKP at the last follow-up. Primary failure was observed in one case because of exposure.

CONCLUSIONS

Transplantation of autologous stem cells cultivated on AM with or without subsequent PKP seems to be an effective way for visual rehabilitation in total LSCD. More work with more cases and longer follow-up are needed to optimize this procedure to provide and maintain an adequate supply of limbal stem cells in these patients.

Dyskeratosis congenita and limbal stem cell deficiency

In light of the latest developments in the field of molecular hematology, we herein discuss the reported cases that have presented dyskeratosis congenita as one of the inherited stem cell diseases causing limbal stem cell deficiency.

Limbal stem cell deficiency in chronic and delayed-onset mustard gas keratopathy

PURPOSE

To evaluate limbal stem cell deficiency (LSCD) using impression cytology in patients with chronic and delayed-onset mustard gas keratopathy (MGK).

DESIGN

Prospective observational case series.

PARTICIPANTS

Thirty-five eyes of 18 patients (all male) with MGK were included.

METHODS

A consecutive series of patients with MGK underwent impression cytology. Finding of goblet cells on the corneal side of specimens was considered as LSCD. Severity of corneal clinical manifestation was graded as mild, moderate, and severe in each quadrant. Relation between impression cytology findings and clinical grading was evaluated.

MAIN OUTCOME MEASURES

Impression cytology findings and clinical grading.

RESULTS

There was LSCD in at least 1 quadrant of cornea in all 35 eyes (100% of cases). No differences were found between impression cytology findings (positive vs. negative for corneal goblet cells) among different quadrants (P = 0.378). Clinical grading was the same between nasal and temporal quadrants (P = 0.266) and between superior and inferior quadrants (P = 0.263). By combining superior and inferior quadrants (vertical zone) and nasal and temporal quadrants (horizontal zone), corneal clinical grading was more severe in horizontal versus vertical zones (P<0.001). There was no relation between LSCD and corneal clinical severity (P = 0.893).

CONCLUSIONS

A varying degree of LSCD was demonstrated in all patients with chronic or delayed-onset MGK using impression cytology. Corneal clinical manifestations are more severe in nasal and temporal quadrants. There was no relation between impression cytology findings (positive vs. negative for goblet cells) and corneal clinical grading. Other factors, such as perilimbal conjunctival ischemia, may play a role.