Ultrastructural analysis of explanted CyPass microstents and correlation with clinical findings.

PURPOSE: The purpose of this study was to obtain insight into cellular processes after CyPass microstent implantation into the supraciliary space. With this knowledge, we expected to find some reason for surgical failure. METHODS: Nine CyPass microstents of 8 patients with primary open-angle glaucoma (n = 1), pseudoexfoliation glaucoma (n = 5), uveitic glaucoma (n = 1), and posttraumatic open-angle glaucoma (n = 1) were explanted due to recurrence of IOP elevation, corneal decompensation, or persistent hypotony. The explants were processed for light and transmission electron microscopy. RESULTS: Fibrotic material, consisting of collagen fibrils, microfibrils, pseudoexfoliation fibrils produced by activated fibroblasts, was detected in the stent lumen of 4/5 pseudoexfoliation glaucoma patients and also in posttraumatic open-angle glaucoma. Fibrotic material was also present on the outer surface and within fenestrations of the majority of stents. Complete absence of fibrotic reaction was noticed in 3 of 9 microstents. CONCLUSION: Although MIGS is known to be less invasive than conventional surgery, implants placed in the suprachoroidal space may be adversely affected by a fibrotic tissue reaction resulting in implant failure. Understanding mechanisms and risk factors leading to fibrotic scarring following antiglaucomatous surgery may help to develop novel strategies that improve surgical outcome.

Imbalances in protein homeostasis caused by mutant desmin.

AIMS: We investigated newly generated immortalized heterozygous and homozygous R349P desmin knock-in myoblasts in conjunction with the corresponding desminopathy mice as models for desminopathies to analyse major protein quality control processes in response to the presence of R349P mutant desmin. METHODS: We used hetero- and homozygous R349P desmin knock-in mice for analyses and for crossbreeding with p53 knock-out mice to generate immortalized R349P desmin knock-in skeletal muscle myoblasts and myotubes. Skeletal muscle sections and cultured muscle cells were investigated by indirect immunofluorescence microscopy, proteasomal activity measurements and immunoblotting addressing autophagy rate, chaperone-assisted selective autophagy and heat shock protein levels. Muscle sections were further analysed by transmission and immunogold electron microscopy. RESULTS: We demonstrate that mutant desmin (i) increases proteasomal activity, (ii) stimulates macroautophagy, (iii) dysregulates the chaperone assisted selective autophagy and (iv) elevates the protein levels of αB-crystallin and Hsp27. Both αB-crystallin and Hsp27 as well as Hsp90 displayed translocation patterns from Z-discs as well as Z-I junctions, respectively, to the level of sarcomeric I-bands in dominant and recessive desminopathies. CONCLUSIONS: Our findings demonstrate that the presence of R349P mutant desmin causes a general imbalance in skeletal muscle protein homeostasis via aberrant activity of all major protein quality control systems. The augmented activity of these systems and the subcellular shift of essential heat shock proteins may deleteriously contribute to the previously observed increased turnover of desmin itself and desmin-binding partners, which triggers progressive dysfunction of the extrasarcomeric cytoskeleton and the myofibrillar apparatus in the course of the development of desminopathies.

Recurrence of paraproteinemic keratopathy after penetrating keratoplasty and its assessment with confocal microscopy.

PURPOSE: To report on a case of recurrence of paraproteinemic keratopathy (PPK) associated with monoclonal gammopathy after bilateral penetrating keratoplasty. OBSERVATIONS: Penetrating keratoplasty was performed on both eyes of a 45-year-old man due to bilateral progressive corneal stromal clouding. Recurrence of the corneal stromal opacities accompanied by a decrease in visual acuity was observed on slit-lamp examination already two years after penetrating keratoplasty. Confocal laser scanning microscopy (CLSM) of the corneal grafts performed three years after penetrating keratoplasty showed bilateral morphological changes identical to that found in the patient's corneas prior to penetrating keratoplasty. A hematological work-up revealed monoclonal gammopathy of type IgG kappa. The histochemical examination of the explanted corneas confirmed the diagnosis of PPK. CONCLUSIONS AND IMPORTANCE: Paraproteinemic keratopathy is an underdiagnosed ophthalmological condition, which may be associated with potentially life-threatening hematologic disorders. A hematological workup should be performed in patients with corneal opacities of uncertain etiology. Penetrating keratoplasty should be performed with caution in patients with monoclonal gammopathy due to the possibility of a very fast recurrence of PPK in the corneal graft. This is the first presentation of the recurrence of flake-like PPK after penetrating keratoplasty assessed with CLSM.

[Basic research in ophthalmology in Germany and its international context]. / Grundlagenforschung in der Augenheilkunde in Deutschland im internationalen Kontext.

BACKGROUND: Experimental basic research provides the foundations for the elucidation of pathophysiological mechanisms of diseases and the development of novel diagnostic and therapeutic strategies for ophthalmological diseases. The objective of this contribution is to provide an overview of the international interconnection of basic research in ophthalmology in Germany. METHODS: The international context of ophthalmological research conducted in Germany is presented by means of personal experiences and data published by the German Ophthalmological Society (DOG), the German Research Foundation (DFG) and the European Union (EU). Due to the lack of organized databases this article lays no claim to completeness. RESULTS: Basic research in ophthalmology in Germany is mainly conducted in university eye departments and is mainly related to the etiology, pathophysiology and therapy development for various ophthalmic diseases. It is primarily funded by the DFG, the Federal Ministry of Education and Research (BMBF) and the EU plays an increasingly important role. Thus, ophthalmological research is integrated into numerous European research networks and beyond that into many international interconnections and relationships. CONCLUSION: In Germany, both clinical and basic research in ophthalmology is integrated into many international networks and is only functionally viable in an international context; however, given the increasing impact of ophthalmological research in Asian countries, future strategies require a continued focus on career development, research infrastructure, working environment and international cooperation.

[The emerging technology of tissue engineering : Focus on stem cell niche]. / Zukunftstechnologie Tissue-Engineering : Fokus auf die Stammzellnische.

Limbal stem cells reside in a highly specialized complex microenvironment that is known as the stem cell niche, an anatomically protected region at the bottom of the Palisades of Vogt, where the stem cells are located and where their quiescence, proliferation and differentiation are maintained in balance. Besides the epithelial stem and progenitor cell clusters, the limbal niche comprises several types of supporting niche cells and a specific extracellular matrix mediating biochemical and biophysical signals. Stem cell-based tissue engineering aims to mimic the native stem cell niche and to present appropriate microenvironmental cues in a controlled and reproducible fashion in order to maintain stem cell function within the graft. Current therapeutic approaches for ex vivo expansion of limbal stem cells only take advantage of surrogate niches. However, new insights into the molecular composition of the limbal niche and innovative biosynthetic scaffolds have stimulated novel strategies for niche-driven stem cell cultivation. Promising experimental approaches include collagen-based organotypic coculture systems of limbal epithelial stem cells with their niche cells and biomimetic hydrogel platforms prefunctionalized with appropriate biomolecular and biophysical signals. Future translation of these novel regenerative strategies into clinical application is expected to improve long-term outcomes of limbal stem cell transplantation for ocular surface reconstruction.

Whole exome sequencing reveals a novel de novo FOXC1 mutation in a patient with unrecognized Axenfeld-Rieger syndrome and glaucoma.

We report the identification of a novel mutation in the fork-head box C1 (FOXC1) gene which occurred de novo in an Italian patient with unrecognized Axenfeld-Rieger syndrome. He was previously diagnosed as having late recognized primary congenital glaucoma at the age of 14 years and was subsequently subjected to multiple surgical interventions due to uncontrolled intraocular pressure and progressive visual field loss. After exclusion of mutations in CYP1B1 and MYOC, trio-whole-exome sequencing revealed de novo in frame deletion in the coding region of the FOXC1 gene (c.407_409delGTC, p.V137del) leading to a deletion of the evolutionary conserved amino acid Valine at position 137 of the protein. Molecular modeling predicted that Val137 deletion impairs FOXC1 DNA-binding capacity and transcriptional activation. Since loss-of-function mutations in FOXC1 are associated with Axenfeld-Rieger syndrome, the genetic findings in combination with re-evaluation of the patient's clinical data resulted in a corrected diagnosis of Axenfeld-Rieger syndrome with developmental glaucoma. We therefore suggest that in addition to CYP1B1 and MYOC, FOXC1 should be included in the genetic analysis of cases with unclear glaucomatous phenotypes to ensure proper diagnosis, adequate treatment and appropriate genetic counseling.

[Structural alterations during the course of glaucoma disease]. / Strukturelle Veränderungen im Verlauf der Glaukomerkrankung.

BACKGROUND: Structural changes in the course of glaucoma disease affect the trabecular meshwork and ciliary body in addition to the optic disc as the primary site of glaucoma damage. OBJECTIVES: Latest results from experimental studies, animal models and measurements in human eyes are presented and discussed. RESULTS: The presenting scenario is complex with age, biochemical and mechanical stress factors leading to subsequent, irreversible tissue change in the trabecular meshwork and cribriform plate of the optic nerve, resulting in neuronal tissue loss. CONCLUSION: Knowledge of these changes will be the key for future glaucoma therapies.

Peripheral hypertrophic subepithelial corneal degeneration presenting with bilateral nasal and temporal corneal changes.

PURPOSE: To characterise the history, clinical and histopathological features of patients with bilateral nasal and temporal peripheral hypertrophic subepithelial corneal degeneration in a German population. METHODS: A detailed ophthalmological and dermatological history and clinical findings were recorded of nine patients with bilateral simultaneous nasal and temporal peripheral corneal degeneration from two centers in Germany. Excised tissues were studied by histopathology, immunohistochemistry, and transmission electron microscopy. RESULTS: Foreign body sensation and need of artificial tear substitutes were the only symptoms reported regularly. Schirmer's and Jones-test were normal in all, but fluorescein break-up time of >10 s was found in five eyes of four patients. Best corrected visual acuity was reduced only under glare conditions. Corneal topography revealed irregular astigmatism in 13 of 14 eyes. Follow-up median time was 35 months. Most cases were stable within the follow-up period. Light and electron microscopy revealed the findings of superficial vascularised corneal hypertrophic scars, oxytatlan fibers, and discontinued Bowmans layer. CONCLUSION: In this series of German patients with peripheral hypertrophic subepithelial corneal degeneration, the changes were predominantly located in the palpebral aperture and often present in both eyes. No associated surface disease could be established in this study. Light and transmission electron microscopy showed histological features that are similar to Salzmann's corneal changes without any inflammation. We hypothesise that light exposure and a localised limbal insufficiency could be involved in the pathogenesis.

[Corneal endothelial cell density and its correlation with the severity of pseudoexfoliation]. / Hornhautendothelzelldichte in Abhängigkeit vom Schweregrad der Pseudoexfoliation.

INTRODUCTION: Pseudoexfoliation (PEX) syndrome is a common, age-related disease which is associated with the multifocal deposition of fibrillar PEX material in intra- and extraocular tissues. Subsequently among others second chronic open-angle glaucoma and corneal endothelial cell loss occurs. The present study analysed whether there is a correlation between the stage of the PEX process and corneal endothelial cell density (cECD), regardless of the non-existence or proof of secondary glaucoma. MATERIALS AND METHODS: One eye of 109 Caucasian subjects (mean age 71.7 years) was examined by slit-lamp microscopy and classified based on visible PEX deposits on the lens (mild and severe) and presence of glaucoma in 4 study groups. The control groups were healthy subjects and patients with primary open angle glaucoma (POAG). The cECD was measured with the endothelial cell mirror microscope (SeaEagle). RESULTS: All study groups and the POAG group showed a significant cECD reduction compared to the healthy control group: POAG: 6.0 %; PEX syndrome: mild 5.5 % and severe 11.0 %, PEX glaucoma: mild 7.7 % and severe 12.3 %. Further the cECD was significantly lower compared to the POAG group in severe PEX syndrome by 5.4 % and in severe PEX glaucoma by 6.8 %. cECD significantly decreased with increasing PEX stage independently of the presence of glaucoma. These differences remained statistically significant after Bonferroni-Holm correction. The analysis of the entire group of test subjects showed only a weak correlation between mean intraocular pressure and mean cECD. CONCLUSION: The results of this study showed a decreasing cECD with increasing PEX stage, regardless of whether glaucoma is present or not. The influence of the PEX process appears to be more pronounced than the influence of intraocular pressure.

[Limbal stem cells and their niche: implications for bioengineered tissue constructs]. / Limbusstammzellen und ihre nische: bedeutung für biotechnologischen gewebeersatz.

Regeneration and repair of corneal epithelium rely on a reservoir of unipotent progenitor cells, which is situated within the basal epithelial layer at the corneoscleral limbus. If these cells are lost, corneal surface integrity is disturbed, which may lead to a painful loss of vision. Since the late 1990s cultivated grafts of limbal epithelium are being used therapeutically. Limbal epithelial cells are obtained from the fellow eye or from an allogeneic donor, propagated in culture on different types of carriers, and subsequently transplanted. This process entails removal of progenitor cells from their natural environment. However, surrounding cells and extracellular matrix are widely believed to provide important stimuli for stem cell maintenance and for correct differentiation. Therefore, new approaches aim at providing this so-called stem cell niche ex vivo and following transplantation. Niche factors can also drive transdifferentiation of alternative progenitor cell types towards a corneal phenotype. This permits the use of autologous cells in cases of bilateral limbal stem cell insufficiency. Several biosynthetic substrates have been devised for culture, transdifferentiation and transplantation of donor cells. This work intends to provide an overview of constructs that are currently available and to some extent clinically employed. In addition, a summary is given of novel concepts which aim at integrating putative niche factors into the stem cell carriers to replicate the stem cell niche.

[New pathogenetic insights into pseudoexfoliation syndrome/glaucoma. Therapeutically relevant?]. / Neue pathogenetische Erkenntnisse zum Pseudoexfoliations-Syndrom/Glaukom. Therapeutisch relevant?

Pseudoexfoliation (PEX) syndrome is a genetically determined, generalized disease of the extracellular matrix leading to the progressive deposition of an abnormal fibrillar material in various intraocular and extraocular tissues including the trabecular meshwork. It thus represents the most common identifiable cause of open-angle glaucoma and a leading cause of blindness worldwide. The PEX-specific fibrotic matrix process, a stress-induced elastosis, is characterized by an excessive production and abnormal cross-linking of elastic microfibrils into fibrillar PEX aggregates. Co-modulating factors triggering this fibrotic process include elevated concentrations of fibrogenic growth factors, such as TGF-ß1, reduced activity of proteolytic enzymes, subtle inflammatory processes and various external stress factors, such as oxidative stress. Genetic studies identified a highly significant association between several polymorphisms in the LOXL1 (lysyl oxidase-like 1) gene with both PEX syndrome and PEX glaucoma. As these LOXL1 risk variants were found to occur in almost 100% of PEX patients throughout all geographical populations worldwide, LOXL1 appears to represent a principal risk factor for manifestation of the PEX phenotype. LOXL1 is a pivotal cross-linking enzyme in extracellular matrix metabolism and seems to be specifically required for elastic fiber formation and stabilization. The available data suggest that LOXL1 enzyme function and expression are dysregulated in PEX tissues and thereby play a central role in glaucoma development. On the one hand, increased expression of LOXL1 and elastic fiber components contributes to the formation of abnormally cross-linked PEX aggregates in the outflow pathways leading to increased outflow resistance and intraocular pressure. On the other hand, reduced expression and inadequate tissue levels of LOXL1 may lead to degenerative tissue alterations, particularly in the lamina cribrosa adversely affecting the biomechanical properties of this critical tissue. This PEX-specific elastinopathy of the lamina cribrosa rendering PEX eyes more vulnerable to pressure-induced optic nerve damage may constitute an independent risk factor for glaucoma development. The findings may have direct consequences for the clinical management of PEX patients underlining the need for an exact diagnosis, a strict IOP-reducing therapy and a close and regular follow-up.

[PEX syndrome. Clinical diagnosis and systemic manifestations]. / Pseudoexfoliationssyndrom. Klinische Diagnose und systemische Manifestationen.

As a result of demographic changes pseudoexfoliation (PEX) syndrome, an age-related systemic disorder of the extracellular matrix, will become an increasingly important issue in clinical practice. Apart from its well-known association with cataract and glaucoma, PEX syndrome predisposes to a broad spectrum of spontaneous and surgical ocular complications due to characteristic alterations of all anterior segment tissues. In view of the high risk of glaucoma development and potential complications during cataract surgery, an accurate and early diagnosis of PEX syndrome is of considerable clinical relevance. Since the characteristic central PEX deposits are lacking in up to 50 % of patients, a reliable diagnosis requires pupillary dilation. Early stages of the disease may be recognized on the basis of subtle alterations of the lens surface in addition to poor pupillary dilation and pigment-related signs including pigment dispersion and peripupillary atrophy. Any asymmetric clinical signs, e.g., regarding pupil width, pigmentation, cataract and intraocular pressure, should alert the ophthalmologist to the potential presence of PEX syndrome. Although the description of PEX syndrome as a systemic disorder of the extracellular matrix associated with the deposition of PEX material in the skin, blood vessel walls and various organ systems dates back to the early 1990s, a causal relationship between the abnormal material deposits and systemic diseases has not yet been clearly established. A growing number of smaller studies have found suggestive evidence for associations between PEX syndrome and cardiovascular/cerebrovascular diseases. The current evidence, however, is ambiguous and requires further investigation through multicenter or population-based, prospective, randomized clinical studies.

[Oxidative stress and pseudoexfoliation glaucoma]. / Oxidativer Stress beim Pseudoexfoliationsglaukom.

Pseudoexfoliation (PEX) glaucoma is the most common identifiable cause of open-angle glaucoma worldwide, comprising the majority of glaucoma in some countries. The underlying disorder, PEX syndrome, is a generalised, genetically determined, elastotic process of the extracellular matrix characterised by the excessive production and progressive accumulation of a fibrillar material in various tissues including the outflow pathways. Increasing evidence suggests that the oxidative-antioxidative balance is disturbed in patients with PEX syndrome/glaucoma, both in the anterior segment and throughout the body, and that the resulting oxidative stress constitutes a major mechanism involved in the pathophysiology of this fibrotic process. Significantly reduced levels of antioxidants, such as ascorbic acid, glutathione, trace elements, antioxidative enzymes, and total antioxidative capacity in aqueous humor and serum suggest a faulty antioxidative defense system in PEX patients. The down-regulation of antioxidative enzymes in anterior segment tissues also indicates an inadequate cytoprotection against oxidative stress. Concomitantly, levels of oxidants such as hydrogen peroxide or nitric oxide, and oxidative stress markers, including lipid peroxidation products, degradation products of oxidated and methylated proteins, advanced glycation end products, and homocysteine are significantly increased in aqueous humor, tissues, and serum. The available data suggest that chronic oxidative stress in combination with weakened cytoprotective and repair strategies affects the abnormal matrix metabolism by induction of a persistent pro-inflammatory state and activation of the profibrotic growth factor TGF-beta1. Oxidative stress, therefore, appears to represent a modifiable risk factor in the management of patients with PEX syndrome/glaucoma.

[Nodular fasciitis of the eyelid and anterior orbit in children: case report and review of the literature]. / Noduläre Fasziitis im Kindesalter im Bereich des Lids und der vorderen Orbita: Kasuistik und Literaturübersicht.

An 8-year-old boy presented with a 6-week history of a rapidly progressive erythematous swelling of the right upper eyelid. Ultrasonography and magnetic resonance imaging revealed a subcutaneous nodular mass of the right upper eyelid medially with extension into the anterior orbit. The clinical differential diagnosis included rhabdomyosarcoma. A transcutaneous excisional biopsy was performed, and histopathologic examination confirmed the diagnosis of nodular fasciitis. Five years after surgery, there is no evidence of local recurrence, and the result is aesthetically satisfactory.

Effect of latanoprost and timolol on the histopathology of the human conjunctiva.

AIM: To investigate the effect of timolol and latanoprost on the extracellular matrix organisation, inflammatory infiltration, and expression of matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) in the human conjunctiva. METHODS: Conjunctival biopsies were obtained from the inferior fornix during routine cataract surgery from 20 patients with primary open-angle glaucoma, who had received a monotherapy either with timolol or latanoprost, and from 10 non-glaucomatous patients. Specimens were investigated by light microscopy, immunohistochemistry using antibodies against MMP-1,-3, TIMP-2,-3 and CD 68 antibodies and by quantitative transmission electron microscopy. RESULTS: The number of collagen fibres was significantly decreased in latanoprost-treated conjunctival specimens compared with timolol-treated eyes (p<0.01) but showed no difference to controls. Amorphous material was increased in both treated groups compared with controls (p<0.001) but was less in latanoprost-treated specimens compared with timolol-treated eyes (p<0.001). Optically clear spaces, probably containing glycosaminoglycans, were significantly reduced in both treated groups-with less of a reduction in latanoprost-compared with timolol-treated eyes (p<0.001). A marked upregulation of MMP-1 and MMP-3 and moderately increased staining for TIMP-2 and TIMP-3 was found in epithelial cells and subepithelial stromal cells of latanoprost-treated eyes. A moderate infiltration with macrophages and inflammatory cells was observed in timolol-treated eyes. CONCLUSIONS: Latanoprost-treated conjunctival specimens showed a decreased stromal collagen density and a less pronounced inflammatory infiltration. The upregulation of MMP-1 and MMP-3 in latanoprost-treated eyes might explain the reduced extracellular matrix accumulation in the conjunctival stroma. Therefore, latanoprost therapy might have a more favourable effect on the outcome of glaucoma filtering surgery.

Increased homocysteine levels in tear fluid of patients with primary open-angle glaucoma.

AIMS: We assessed homocysteine (Hcy) levels in tear fluid and plasma of patients with primary open-angle glaucoma (POAG). We determined the association between Hcy levels, dry eye syndrome and B vitamin status. METHODS: This prospective case-control study included 36 patients with POAG and 36 controls. Hcy concentrations were measured by high-performance liquid chromatography. RESULTS: Patients with POAG had significantly higher mean Hcy levels both in tear fluid (205 +/- 84 nmol/l; p < 0.001, t test) and in plasma (13.43 +/- 3.53 micromol/l; p = 0.001, t test) than control subjects (130 +/- 53 nmol/l and 10.50 +/- 3.33 micromol/l, respectively). Hcy in tear fluid was significantly correlated with plasma Hcy in POAG patients (r = 0.459; p = 0.005, Pearson's correlation), but not in controls (r = 0.068; p = 0.695). POAG patients with dry eye disease had significantly higher Hcy levels both in tear fluid and plasma than POAG patients without dry eye disease. There was no association between Hcy levels and B vitamin status in subjects with POAG. CONCLUSIONS: The study suggests increased Hcy levels in tear fluid and plasma of patients with POAG. Elevated Hcy levels might be a risk factor for POAG and dry eye syndrome in subjects with glaucoma.

Characterization of extracellular matrix components in the limbal epithelial stem cell compartment.

A specialized microenvironment or niche, which regulates maintenance, self-renewal, activation, and proliferation of stem cells by external signals, is one of the key prerequisites for stem cell function. However, the parameters determining the limbal stem cell niche are not yet defined. In order to characterize the role of basement membrane (BM) and extracellular matrix components in the generation of a microenvironmental niche for limbal stem and progenitor cells, we extensively analyzed the topographical variations of the BM zone of human ocular surface epithelia using immunohistochemistry and a large panel of antibodies to most of the presently described intrinsic and associated BM components. Apart from BM components uniformly expressed throughout all ocular surface epithelia (e.g. type IV collagen alpha5 and alpha6 chains, collagen types VII, XV, XVII, and XVIII, laminin-111, laminin-332, laminin chains alpha3, beta3,and gamma2, fibronectin, matrilin-2 and -4, and perlecan), the BM of the limbal epithelium shared many similarities with that of the conjunctival epithelium, including positive labelling for type IV collagen alpha1 and alpha2 chains, laminin alpha5, beta2, and gamma1 chains, nidogen-1 and -2, and thrombospondin-4, whereas type IV collagen alpha3, type V collagen, fibrillin-1 and -2, thrombospondin-1, and endostatin were present in the corneal BM, but lacking or more weakly expressed in the limbal and conjunctival BMs. As compared to both the corneal and conjunctival BMs, the limbal BM showed a markedly increased immunoreactivity for laminin alpha1, alpha2, beta1 chains, and agrin, and a specific but patchy immunoreactivity for laminin gamma3 chain, BM40/SPARC, and tenascin-C, which co-localized with ABCG2/p63/K19-positive and K3/Cx43/desmoglein/integrin-alpha2-negative cell clusters comprising putative stem and early progenitor cells in the basal epithelium of the limbal palisades. Components that were particularly expressed in the corneal-limbal transition zone included type XVI collagen, fibulin-2, tenascin-C/R, vitronectin, bamacan, chondroitin sulfate, and versican, all of which co-localized with vimentin-positive cell clusters comprising putative late progenitor cells in the basal epithelium. This pronounced heterogeneity of the BM in the limbal area, both in the region of limbal palisades and the corneal-limbal transition zone, appears to be involved in providing unique microenvironments for corneal epithelial stem and late progenitor cells. Identification of specific niche parameters might not only help to understand limbal stem cell regulation, but also to improve their selective enrichment and in vitro expansion for therapeutic strategies.