Figure 1 - uploaded by Aboulghassem Shahdadfar
Content may be subject to copyright.
Anatomy of the cornea. (a) Section of the anterior part of the eye; (b) Section of the cornea illustrating six layers; (c) In vivo confocal microscopy image of the corneal endothelium. Courtesy of Geir A. Qvale.
Source publication
Corneal endothelium is a single layer of specialized cells that lines the posterior surface of cornea and maintains corneal hydration and corneal transparency essential for vision. Currently, transplantation is the only therapeutic option for diseases affecting the corneal endothelium. Transplantation of corneal endothelium, called endothelial kera...
Context in source publication
Context 1
... cornea is the transparent anterior part of the eye that transmits and focuses light onto the retina. From anterior to posterior (Figure 1), the cornea is composed of the corneal epithelium (50 μm thick), the Bowman's membrane (12 μm), the stroma (480-500 μm), the Descemet's membrane (8-10 μm), and the endothelium (5 μm) [1]. Recently, a new layer of the cornea, Dua's layer, was also described [2]. ...
Similar publications
Corneal endothelial cells (CECs) are essential for maintaining corneal stromal hydration and ensuring its transparency, which is necessary for normal vision. Dysfunction of CECs leads to stromal decompensation, loss of transparency and corneal blindness. Corneal endothelium has low proliferative potential compared to surface epithelial cells leadin...
The corneal endothelium is a simple layer of epithelial cells strategically positioned at the posterior surface of the cornea. As the anatomic and physiologic boundary between the nutrient-rich aqueous humor and the avascular collag-enous stroma, the endothelium plays essential roles in tissue nourishment and transparency by balancing the influx an...
Citations
... It is also one of the most extremely innervated and sensitive tissues in the body, it is known that the density of nerve endings of corneal tissue about 300-400 times greater compared to the skin. Due to numerous nerve density in the cornea, the corneal diseases may be painful [7][8][9][10][11]. The cornea is composed of cellular and acellular components. ...
... However, a new cornea layer, Dua's layer, has been also described recently. Each of these layers has its own role in order to maintain normal visual function [2,3,[9][10][11]. In this paper, we reviewed the development, structure, function and physiological features of corneal epithelium, Bowman layer, corneal stroma, Dua's layer, Descemet's membrane and corneal endothelium from a new perspective. ...
... However, a new cornea layer, Dua's layer, has been also described recently. Each of these layers has its own role in order to maintain normal visual function [2,3,[9][10][11]. ...
The cornea has important functions such as protecting the structures within the globe, contributing to the refractive power of the eye, and focusing the light rays on the retina with minimum scattering. Although the neurobiological complexity of the retina and the dynamic movement of the lens are absent in the cornea, it is one of the most critical components of the perfect visual system, thanks to its transparency. In order to provide sustainable transparency in the cornea, which is very important for visual function, it is possible with the intense metabolic activity in the cornea and the perfect operation of the balanced ion liquid pump. The cornea provides excellent vision thanks to the structure and functions necessary for its unique function to continue regularly. This review focuses on cornea and tear film structure and physiology.
... Despite of the great advances in the clinical scenario, corneal transplantation still faces several unmet challenges, such as donor shortage and rejection, that limit the overall viability and urges the seek of alternative solutions [3,6]. Taking into account that the most damaged and vulnerable tissue is the endothelium, there is a need to find alternative solutions such as the development of an in vitro tissue construct for corneal endothelium regeneration. ...
Corneal endothelium defects are one of the leading causes of blindness worldwide. Actual treatment is transplantation, which requires the use of human cadaveric donors, but it faces several problems such as, global shortage of donors. Therefore, new alternatives are being developed and, among them, cell therapy has gained interest in the last years due to its promising results in tissue regeneration. Nevertheless, the direct administration of cells may sometimes have limited success due to the immune response, hence requiring the combination with extracellular mimicking materials. In this review, we present different methods to obtain corneal endothelial cells (CEC) from diverse cell sources such as pluripotent or multipotent stem cells. Moreover, we discuss different substrates in order to allow a correct implantation as a cell sheet and to promote an enhanced cell behavior. For this reason, natural or synthetic matrixes that mimic native environment have been developed. These matrixes have been optimized in terms of their physicochemical properties such as stiffness, topography, composition and transparency. To further enhance the matrixes properties, these can be tuned by incorporating certain molecules that can be delivered in a sustained manner in order to enhance biological behavior. Finally, we elucidate future directions for corneal endothelial regeneration, such as 3D printing, in order to obtain patient specific substrates.
... The cornea is composed of six layers: the epithelium and its basement membrane, Bowman layer, the stroma, Dua's layer, Descemet membrane, and the endothelium. Besides three main cell types, epithelial cells, stromal keratocytes, and endothelial cells, the cornea is endowed with a heterogeneous population of accessory cells involved in its homeostasis [1,2]. Central corneal thickness (CCT) measurement plays a major role in diagnostic and therapeutic approaches to corneal pathology and has an important impact on intraocular pressure readings. ...
Central corneal thickness measurement plays a crucial role in the assessment and treatment of glaucoma and several corneal diseases in addition to its importance in refractive surgery management. There are various methods for central corneal thickness measurement, which differ in their operating principles and technology beside the difference in their advantages and limitation. This study aims to compare central corneal thickness (CCT) values of healthy eyes measured by two common devices: ultrasound pachymetry (UP) and non-contact specular microscopy (NCSM) and to determine the average difference between the two measurements. The study was conducted in the ophthalmology outpatient clinic in Imam Al-Sadiq Hospital- Hilla city and included 99 healthy individuals (198 eyes) of both genders. Results indicated that NCSM tends to give thinner CCT values compared to UP while providing quicker, safer and more comfortable evaluation for corneal thickness in addition to corneal endothelial cell density.
... 14,15 The vision gradually decreases at a critical density of 500 cell/mm 2 , due to swelling which can ultimately lead to blindness. 13 Fuchs' endothelial corneal dystrophy (FECD) is the commonest disorder of the corneal endothelium. Several hallmarks characterized and reported including an accelerated decline of endothelial function due to the low density of corneal endothelial cells (CECs). ...
Human corneal endothelium (HCE) is a single layer of hexagonal cells that lines the posterior surface of the cornea. It forms the barrier that separates the aqueous humor from the rest of the corneal layers (stroma and epithelium layer). This layer plays a fundamental role in maintaining the hydration and transparency of the cornea, which in turn ensures a clear vision. In vivo, human corneal endothelial cells (HCECs) are generally believed to be nonproliferating. In many cases, due to their nonproliferative nature, any damage to these cells can lead to further issues with Descemet’s membrane (DM), stroma and epithelium which may ultimately lead to hazy vision and blindness. Endothelial keratoplasties such as Descemet’s stripping automated endothelial keratoplasty (DSAEK) and Descemet’s membrane endothelial keratoplasty (DEK) are the standard surgeries routinely used to restore vision following endothelial failure. Basically, these two similar surgical techniques involve the replacement of the diseased endothelial layer in the center of the cornea by a healthy layer taken from a donor cornea. Globally, eye banks are facing an increased demand to provide corneas that have suitable features for transplantation. Consequently, it can be stated that there is a significant shortage of corneal grafting tissue; for every 70 corneas required, only 1 is available. Nowadays, eye banks face long waiting lists due to shortage of donors, seriously aggravated when compared with previous years, due to the global COVID-19 pandemic. Thus, there is an urgent need to find alternative and more sustainable sources for treating endothelial diseases, such as utilizing bioengineering to use of biomaterials as a remedy. The current review focuses on the use of biomaterials to repair the corneal endothelium. A range of biomaterials have been considered based on their promising results and outstanding features, including previous studies and their key findings in the context of each biomaterial.
... The substrate composition and topography have a crucial impact on the success of CEC culture because they stimulate the attachment, migration, proliferation, and overall function of the cultured CECs [17,61]. Due to the poor adherence of CECs to uncoated culture dishes, various biological, biosynthetic, or synthetic substrates for CEC expansion have been tested up to now, as reviewed elsewhere [62][63][64] (Table 1). The ideal substrate should mimic the composition (collagens 4-6, 8, 18, fibronectin, laminin, thrombospondin) and topography of DM [64,65], therefore helping to maintain the CEC phenotype and function and promoting CE regeneration after injury [66]. ...
... Due to the poor adherence of CECs to uncoated culture dishes, various biological, biosynthetic, or synthetic substrates for CEC expansion have been tested up to now, as reviewed elsewhere [62][63][64] (Table 1). The ideal substrate should mimic the composition (collagens 4-6, 8, 18, fibronectin, laminin, thrombospondin) and topography of DM [64,65], therefore helping to maintain the CEC phenotype and function and promoting CE regeneration after injury [66]. It was shown that a replacement of the DM alone can be sufficient to induce the regeneration of host CECs in vivo [67]. ...
... The disadvantage is that the substrate must meet specific characteristics, such as structural regularity and reproducibility, biocompatibility, and biodegradability (if it is intended only as a cell carrier), or similarity to DM (if it is to be maintained and possibly replace the DM following Tx). A suitable substrate should also support the function of CECs [64]. ...
The corneal endothelium plays a key role in maintaining corneal transparency. Its dysfunction is currently treated with penetrating or lamellar keratoplasty. Advanced cell therapy methods seek to address the persistent global deficiency of donor corneas by enabling the renewal of the endothelial monolayer with tissue-engineered grafts. This review provides an overview of recently published literature on the preparation of endothelial grafts for transplantation derived from cadaveric corneas that have developed over the last decade (2010–2021). Factors such as the most suitable donor parameters, culture substrates and media, endothelial graft storage conditions, and transplantation methods are discussed. Despite efforts to utilize alternative cellular sources, such as induced pluripotent cells, cadaveric corneas appear to be the best source of cells for graft preparation to date. However, native endothelial cells have a limited natural proliferative capacity, and they often undergo rapid phenotype changes in ex vivo culture. This is the main reason why no culture protocol for a clinical-grade endothelial graft prepared from cadaveric corneas has been standardized so far. Currently, the most established ex vivo culture protocol involves the peel-and-digest method of cell isolation and cell culture by the dual media method, including the repeated alternation of high and low mitogenic conditions. Culture media are enriched by additional substances, such as signaling pathway (Rho-associated protein kinase, TGF-β, etc.) inhibitors, to stimulate proliferation and inhibit unwanted morphological changes, particularly the endothelial-to-mesenchymal transition. To date, this promising approach has led to the development of endothelial grafts for the first in-human clinical trial in Japan. In addition to the lack of a standard culture protocol, endothelial-specific markers are still missing to confirm the endothelial phenotype in a graft ready for clinical use. Because the corneal endothelium appears to comprise phenotypically heterogeneous populations of cells, the genomic and proteomic expression of recently proposed endothelial-specific markers, such as Cadherin-2, CD166, or SLC4A11, must be confirmed by additional studies. The preparation of endothelial grafts is still challenging today, but advances in tissue engineering and surgery over the past decade hold promise for the successful treatment of endothelial dysfunctions in more patients worldwide.
... Scaffold-based strategy is based on transplanting cultivated corneal endothelium on a vector plate in a similar procedure to EK [35,63]. Okumura et al. and Koizumi et al. [53,63] and other researchers [64][65][66] have cultivated CEC on specific substrates. Examples of substrates are amniotic membrane [67], DM, human anterior lens capsule [68,69], and bioengineered matrices composed of compressed collagen [70], gelatin [71,72], silk-fibroin, and a combination of biopolymers. ...
The treatment of corneal endothelial dysfunction has experienced a revolutionary change in the past decades with the emergence of endothelial keratoplasty techniques: descemet stripping automated endothelial keratoplasty (DSAEK) and descemet membrane endothelial keratoplasty (DMEK). Recently, new treatments such as cultivated endothelial cell therapy, Rho-kinase inhibitors (ROCK inhibitors), bioengineered grafts, and gene therapy have been described. These techniques represent new lines of treatment for endothelial dysfunction. Their advantages are to help address the shortage of quality endothelial tissue, decrease the complications associated with tissue rejection, and reduce the burden of postoperative care following transplantation. Although further randomized clinical trials are required to validate these findings and prove the long-term efficacy of the treatments, the positive outcomes in preliminary clinical studies are a stepping stone to a promising future. Our aim is to review the latest available alternatives and advancements to endothelial corneal transplant.
... The cornea is a transparent avascular tissue forming the anterior part of the eye. 1 It plays a critical role in transmitting and focusing incoming light onto the retina (Figure 1(a)). 2 It consists of five layers with the corneal endothelium (CE) being the posterior monolayer ( Figure 1(b)). 3 Viability of the CE is crucial for maintaining corneal transparency 4 which is preserved through dynamic regulation of corneal hydration between a "leaky" barrier and active ionic pumps on the corneal endothelial cells (CECs). ...
... [36][37][38][39] As highlighted in a review, a number of studies have shown that PIPAAm supports important structures such as the Na + /K + -ATPase pump and morphology of CECs with the presence of microvilli and cellular interconnections. 2 Rabbit models have been used to assess cell functionality after culture on PIPAAm. [37][38][39] The cell layers were retrieved from the PIPAAm surfaces and transferred to gelatin disc carriers for transplantation into the rabbit anterior chamber. ...
... There have been challenges associated with this approach, most notably being able to provide the specialized environment required for favorable expansion followed by maintenance of an endothelial phenotype as well as production of a robust endothelial tissue which can be handled without difficulty for transplantation. 2 Steps have been made to combat this, including the use of different types of biomaterials, with the aim of mimicking some of the features of DM as a base or scaffold to cultivate the hCEC monolayer. These approaches have been trialed in in vivo animal models but, so far, not in humans. ...
The corneal endothelium is the posterior monolayer of cells that are responsible for maintaining overall transparency of the avascular corneal tissue via pump function. These cells are non-regenerative in vivo and therefore, approximately 40% of corneal transplants undertaken worldwide are a result of damage or dysfunction of endothelial cells. The number of available corneal donor tissues is limited worldwide, hence, cultivation of human corneal endothelial cells (hCECs) in vitro has been attempted in order to produce tissue engineered corneal endothelial grafts. Researchers have attempted to recreate the current gold standard treatment of replacing the endothelial layer with accompanying Descemet’s membrane or a small portion of stroma as support with tissue engineering strategies using various substrates of both biologically derived and synthetic origin. Here we review the potential biomaterials that are currently in development to support the transplantation of a cultured monolayer of hCECs.
... As the corneal endothelium lacks the capability of regeneration, the loss of corneal endothelium will be compensated for by the expansion and migration of neighboring cells. The damage caused to endothelial cells can lead to corneal stromal hydration and vision loss, which can only be reversed by corneal transplantation [17]. However, this could impose a heavy burden on patients both financially and psychologically. ...
Abstract Background This research was conducted with the aim to determine the effect of diabetes mellitus on corneal endothelial cells. Methods The terms: (“diabetes mellitus” or “diabetes” or “diabetic”) and (“corneal endothelium” or “cornea” or “Corneas”) searched in Pubmed, Embase, Cochrane, and Web of science until August 2019. The included types of studies contained observational studies. The standard mean difference (SMD) which was deemed as main size effects for continuous data was calculated by means and standard deviations. The data on corneal endothelial cell density (ECD), mean cell area (MCA), cell area variation coefficient (CV) and percentage of hexagonal cells (HEX) included in the study were collected and analyzed using stata15.1. Results The final 16 cross-sectional studies and 2 case-control studies were included for the meta-analysis. Meta-analysis revealed that diabetes mellitus could reduce ECD (SMD = − 0.352, 95% CI -0.538, − 0.166) and the HEX (SMD = − 0.145, 95% CI -0.217, − 0.074), in addition to increasing CV (SMD = 0.195, 95% CI 0.123, 0.268). Nevertheless, there was no statistically significant differences observed when combining MCA (SMD = 0.078, 95% CI -0.022, 0.178). In subgroup analysis, Type 2 diabetes patients owned less corneal ECD (P
... Thus, cellular therapy is considered an emerging field of research since it provides, theoretically, an unlimited source of endothelial corneal tissues while limiting immune rejection. Based on the abundant literature on cell and tissue engineering, cell therapy has the potential to replace deficient tissues of the cornea using autologous or heterologous cells (Navaratnam et al., 2015;Proulx and Brunette, 2012;Wagoner et al., 2018). ...
... The main issue here is to determine the best marker of CEnCs. Indeed, markers such as ZO-1, Na + /K + -ATPase are present on CEnCs, but are also found on other cell populations, making them unsuitable for CEnCs isolation (Navaratnam et al., 2015). Similarly, an anti-mouse Flk1 antibody combined with an anti-mouse VE-cadherin may also be useful for CEnCs isolation but these markers are also found in all cells of endothelial origin (Chatterjee et al., 2016). ...
... The main problem is that in vitro produced tissues are very thin and thus difficult to manipulate without damaging them during in vivo implantation into the recipient. According to literature, a lot of carriers could be used for cornea grafting such as amniotic membrane (Ishino et al., 2004), natural polymers (collagen 1 and 4, laminin, fibronectin, gelatin, association of laminin and chondroitin sulfate, combination of fibronectin collagen and albumin (Navaratnam et al., 2015)), anterior crystalline lens capsule (LC) (Van den Bogerd et al., 2018b), silk fibroin Fig. 2. Evaluation of iPSC therapy strategies to treat corneal endothelium dysfunction. The first common step is to isolate iPSCs. ...
The cornea is a multi-layered structure which allows fine refraction and provides both resistance to external insults and adequate transparency. The corneal endothelium ensures stromal hydration, failure of which, such as in Fuchs endothelial corneal dystrophy, after trauma or in aging, may lead to loss of corneal transparency and induce blindness. Currently, no efficient therapeutic alternatives exist except for corneal grafting. Thus corneal tissue engineering represents a valuable alternative approach, which may overcome cornea donor shortage. Several studies describe protocols to isolate, differentiate, and cultivate corneal endothelial cells (CEnCs) in vitro. Two main in vitro strategies can be described: expansion of eye-native cell populations, such as CEnCs, or the production and expansion of CEnCs from non-eye native cell populations, such as induced Pluripotent Stem Cells (iPSC). The challenge with these cells is to obtain a monolayer of CEnCs on a biocompatible carrier, with a specific morphology (flat hexagonal cells), and with specific functions such as programmed cell cycle arrest. Another issue for this cell culture methodology is to define the adapted protocol (media, trophic factors, timeframe) that can mimic physiological development. Additionally, contamination by other cell types still represents a huge problem. Thus, purification methods, such as Fluorescence Activated Cell Sorting (FACS), Magnetic Ativated Cell Sorting (MACS) or Sedimentation Field Flow Fractionation (SdFFF) are useful. Animal models are also crucial to provide a translational approach for these therapies, integrating macro- and microenvironment influences, systemic hormonal or immune responses, and exogenous interactions. Non-eye native cell graft protocols are constantly improving both in efficacy and safety, with the aim of being the most suitable candidate for corneal therapies in future routine practice. The aim of this work is to review these different aspects with a special focus on issues facing CEnC culture in vitro, and to highlight animal graft models adapted to screen the efficacy of these different protocols.
... However, a dormant population of replicationcompetent endothelial progenitor cells has been identified (Amano et al. 2006). A number of different cell sources and substrates have been used in an attempt to activate the dormant endothelial progenitor cells for expansion, including amniotic membrane, decellularized cornea, and different collagen types (Levis et al. 2015;Navaratnam et al. 2015). Approaches to activate the dormant endothelial progenitor cells also include the use of Rho-associated kinase (ROCK) inhibitor Y-27632 (Koizumi et al. 2014). ...
