Amniotic membrane in ophthalmology: indications and limitations. Eye (Lond). 2009;23:1954-1961. [PMID: 19169225 DOI: 10.1038/eye.2008.410]

Advancements in Understanding and Managing Radiation Cystitis: A Comprehensive Review

PURPOSE OF REVIEW

This manuscript aims to provide a comprehensive overview of the pathophysiology, risk factors, prevention strategies, and management options for radiation cystitis.

RECENT FINDINGS

Recent studies have shed light on the pathophysiology of radiation cystitis, highlighting the role of inflammation, fibrosis, and vascular damage. Emerging preventive measures like stem cell therapy offer promise, alongside novel treatments such as amniotic bladder therapy and hyperbaric oxygen therapy. This review outlines the latest research on radiation cystitis, covering its pathophysiology, risk factors, prevention, and management. Major findings include insights into the mechanisms of RC development, promising preventive and therapeutic approaches, and the importance of standardized treatment pathways. Future research should focus on identifying genetic risk factors, improving treatment efficacy, and enhancing patient outcomes. This review offers valuable insights for clinicians and researchers, guiding future investigations into radiation cystitis management.

Cell therapy in the cornea: The emerging role of microenvironment

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

Amniotic Membrane Transplantation in the Management of Corneal Ulceration Following Infectious Keratitis

PURPOSE

To report on the outcomes of amniotic membrane transplantation (AMT) for corneal ulceration following infectious keratitis.

METHOD

In this retrospective cohort study of 654 patients with culture-proven infectious keratitis from 8 hospitals in Galicia (Spain), a total of 43 eyes of 43 patients (6.6%) underwent AMT for postinfectious corneal ulceration. The indications for AMT were sterile persistent epithelial defects, severe corneal thinning or perforation.

RESULTS

AMT was successful in 62.8% of cases, with 37.2% requiring an additional surgery. Median time to healing was 40.0 days (IQR 24.2-101.7 days) and final BCVA was lower than baseline (p = 0.001). Ulcers were large (>3 mm) in 55.8% of cases. Previous herpetic keratitis and topical steroid use were more common in patients who received AMT (p < 0.001). 49 microorganisms (43 bacteria and 6 fungi) were isolated.

CONCLUSIONS

AMT is a therapeutic option for complications following infectious keratitis, which present with a sterile persistent epithelial defect, significant corneal thinning or perforation.

The landscape of clinical trials in corneal regeneration: A systematic review of tissue engineering approaches in corneal disease

The limited availability of a healthy donor cornea and the incidence of allograft failure led researchers to seek other corneal substitutes via tissue engineering. Exploring the trend of clinical trials of the cornea with the vision of tissue engineering provides an opportunity to reveal future potential corneal substitutes. The results of this clinical trial are beneficial for future study designs to overcome the limitations of current therapeutic approaches. In this study, registered clinical trials of bio-based approaches were reviewed for corneal regeneration on March 22, 2024. Among the 3955 registered trials for the cornea, 392 trials were included in this study, which categorized in three main bio-based scaffolds, stem cells, and bioactive macromolecules. In addition to the acellular cornea and human amniotic membrane, several bio-based materials have been introduced as corneal substrates such as collagen, fibrin, and agarose. However, some synthetic materials have been introduced in recent studies to improve the desired properties of bio-based scaffolds for corneal substitutes. Nevertheless, new insights into corneal regenerative medicine have recently emerged from cell sheets with autologous and allogeneic cell sources. In addition, the future perspective of corneal regeneration is described through a literature review of recent experimental models.

Combined superficial keratectomy, alcohol delamination and amniotic membrane patch with fibrin glue in Salzmann nodular degeneration

PURPOSE

To describe the outcomes of five Salzmann's Nodular Degeneration (SND) cases treated with a combination of alcohol delamination, superficial keratectomy and amniotic membrane patch with fibrin glue.

METHODS

Five patients affected by SND with significant discomfort and decreased visual acuity were evaluated with refraction, best corrected visual acuity, Break-up time test, corneal topography, Anterior Segment of Optical Coherence Tomography and images of anterior segment with a full slit lamp examination. All the patients underwent alcohol delamination of the corneal epithelium followed by superficial keratectomy to remove the subepithelial nodules. A patch of amniotic membrane was applied to all of them with a ring shape and a banana shape in two patients due to the location of the disease. A bandage contact lens was inserted. The patch was kept in place for 14 days. Another bandage contact lens was inserted for 21 days until the corneal epithelium had completely healed.

RESULTS

The surgical procedure was successful in removing the nodules in all patients. Vision was restored in all cases with a significant regularization of the corneal surface and reduction of ocular discomfort. After a 12-month follow-up, none of the patients showed recurrence of the disease.

CONCLUSIONS

Combining alcohol delamination with superficial keratectomy and amniotic membrane patch with fibrin glue is an effective procedure for the management of SND to regularize the corneal surface and avoid the recurrence of subsequent nodules. This report is the first description of the outcomes of SND cases treated with a combination of the aforementioned techniques.

The combined effect of epidermal growth factor and keratinocyte growth factor delivered by hyaluronic acid hydrogel on corneal wound healing

This study strategically incorporates epidermal growth factor (EGF) and keratinocyte growth factor (KGF) within a hyaluronic acid (HA) hydrogel to enhance corneal wound healing. The controlled release of EGF and KGF from the HA hydrogel is engineered to promote the regeneration of both the epithelial and stromal layers. Specifically, EGF plays a pivotal role in the regeneration of the epithelial layer, while KGF exhibits efficacy in the regeneration of the stromal layer. The combination of these growth factors facilitates efficient regeneration of each layer and demonstrates the capability to modulate each other's regenerative effects. The interplay between EGF and KGF provides an understanding of their cooperative influence on the dynamics of corneal wound healing. The results of this study contribute to the development of advanced strategies for corneal wound management and offer insights into the complex process of corneal regeneration.

A Biosynthetic Alternative to Human Amniotic Membrane for Use in Ocular Surface Surgery

Purpose

The biosynthetic Symatix membrane (SM) was developed to replace fresh human amniotic membrane (hAM) in ocular surgical applications. The purpose of this study was to test the biocompatibility of the SM with human limbus-derived epithelial cells with regard to their physical and biological properties.

Methods

Different physical properties of SM were tested ex vivo by simulation on human corneas. In vitro, primary limbal epithelial cells from limbal explants were used to test biological properties such as cell migration, proliferation, metabolic activity, and limbal epithelial cell markers on the SM, hAM, and freeze-dried amniotic membrane (FDAM).

Results

The surgical handleability of the SM was equivalent to that of the hAM. Ultrastructural and histological studies demonstrated that epithelial cells on the SM had the typical tightly apposed, polygonal, corneal epithelial cell morphology. The epithelial cells were well stratified on the SM, unlike on the hAM and FDAM. Rapid wound healing occurred on the SM within 3 days. Immunofluorescence studies showed positive expression of CK-19, Col-1, laminin, ZO-1, FN, and p-63 on the SM, plastic, and FDAM compared to positive expression of ZO-1, Col-1, laminin, FN, and p63 and negative expression of CK-19 in the hAM.

Conclusions

These results indicate that the SM is a better substrate for limbal epithelial cell migration, proliferation, and tight junction formation. Altogether, the SM can provide a suitable alternative to the hAM for surgical application in sight-restoring operations.

Translational Relevance

The hAM, currently widely used in ocular surface surgery, has numerous variations and limitations. The biocompatibility of corneal epithelial cells with the SM demonstrated in this study suggests that it can be a viable substitute for the hAM.

Harnessing Human Placental Membrane-Derived Bioinks: Characterization and Applications in Bioprinting and Vasculogenesis

Bioprinting applications in the clinical field generate great interest, but developing suitable biomaterial inks for medical settings is a challenge. Placental tissues offer a promising solution due to their abundance, stability, and status as medical waste. They contain basement membrane components, have a clinical history, and support angiogenesis. This study formulates bioinks from two placental tissues, amnion (AM) and chorion (CHO), and compares their unique extracellular matrix (ECM) and growth factor compositions. Rheological properties of the bioinks are evaluated for bioprinting and maturation of human endothelial cells. Both AM and Cho-derived bioinks sustained human endothelial cell viability, proliferation, and maturation, promoting optimal vasculogenesis. These bioinks derived from human sources have significant potential for tissue engineering applications, particularly in supporting vasculogenesis. This research contributes to the advancement of tissue engineering and regenerative medicine, bringing everyone closer to clinically viable bioprinting solutions using placental tissues as valuable biomaterials.

A Review of Current Uses of Amniotic Membrane Transplantation in Ophthalmic Plastic and Reconstructive Surgery

PURPOSE

To review and summarize the existing literature on the clinical applications of amniotic membrane transplantation (AMT) in ophthalmic plastic and reconstructive surgery.

METHODS

A literature review was conducted on the PubMed database using the following search terms: "amniotic membrane" and "eyelid" or "orbit" or "fornix" or "socket" or "lacrimal".

RESULTS

In total 516 articles resulted from the search, of which 62 were included. Numerous cases and case series have been published on the use of amniotic membrane transplantation for ocular surface reconstruction, eyelid and forniceal reconstruction, and cicatricial eyelid abnormalities. Surgical methods of securing the graft vary. Few comparative studies exist; some show a similar or improved result when compared to oral mucous membrane grafting for certain indications.

CONCLUSIONS

Amniotic membrane transplantation can be a useful tool for the oculoplastic surgeon when faced with a case requiring reconstruction of the posterior lamellae, particularly in patients without other graft donor sites available, and uses of AMT continue to expand. Additional studies directly comparing AMT to other reconstructive techniques would be helpful in choosing between the available surgical techniques and standardizing best practices.

Injectable hydrogels derived from marine polysaccharides as cell carriers for large corneal epithelial defects

Injectable hydrogels have been employed for sutureless repair of corneal epithelial defects, which can perfectly fit the defect sites and minimize the associated discomfort. However, numerous hydrogels are ineffective in treating large corneal epithelial defects and still suffer from poor biocompatibility or weak applicability when used as cell carriers. Herein, hydroxypropyl chitin/carboxymethyl chitosan (HPCT/CMCS) temperature-sensitive hydrogels are fabricated, and their physicochemical properties and suitability for corneal epithelial repair are investigated. The results demonstrate that HPCT/CMCS hydrogels have excellent temperature sensitivity between 20 and 25 °C and a transparency of over 80 %. Besides, HPCT/CMCS hydrogels can promote cell proliferation and facilitate cell migration of primary rabbit corneal epithelial cells (CEpCs). A rabbit large corneal epithelial defect model (6 mm) is established, and CEpCs are transplanted into defect sites by HPCT/CMCS hydrogels. The results suggest that HPCT/CMCS/CEpCs significantly enhance the repair of large corneal epithelial defects with a healing rate of 99.6 % on day 8, while reducing inflammatory responses and scarring formation. Furthermore, HPCT/CMCS/CEpCs can contribute to the reconstruction of damaged tissues and the recovery of functional capacities. Overall, HPCT/CMCS hydrogels may be a feasible corneal cell carrier material and can provide an alternative approach to large corneal epithelial defects.

New developments in the management of persistent corneal epithelial defects

A persistent epithelial defect (PED) is a corneal epithelial defect that failed to heal after 2weeks. It is a condition that carries much morbidity, and our understanding of PED remains poor, with current treatment methods often having unsatisfactory outcomes. With PEDs becoming more prevalent, more efforts are required to establish reliable treatment modalities. Our reviews describe the causes of PEDs and the different approaches developed to manage them, as well as their associated limitations. Emphasis is placed on understanding various advances in the development of new treatment modalities. We have also described a case of a woman with a background of graft-versus-host disease on long-term topical corticosteroids who developed complicated PED involving both eyes. The current approach to managing PEDs generally involves exclusion of an active infection, followed by treatment modalities that aim to encourage corneal epithelial healing. Success rates, however, remain far from desirable, as treatment remains challenging due to multiple underlying etiologies. In summary, advances in the development of new therapies may be able to facilitate progress in the understanding and treatment of PED.

Future directions in managing aniridia-associated keratopathy

Congenital aniridia is a panocular disorder that is typically characterized by iris hypoplasia and aniridia-associated keratopathy (AAK). AAK results in the progressive loss of corneal transparency and thereby loss of vision. Currently, there is no approved therapy to delay or prevent its progression, and clinical management is challenging because of phenotypic variability and high risk of complications after interventions; however, new insights into the molecular pathogenesis of AAK may help improve its management. Here, we review the current understanding about the pathogenesis and management of AAK. We highlight the biological mechanisms involved in AAK development with the aim to develop future treatment options, including surgical, pharmacological, cell therapies, and gene therapies.

Decellularized Porcine Conjunctiva in Treating Severe Symblepharon

This prospective study aimed to evaluate the effectiveness of decellularized porcine conjunctiva (DPC) in the management of severe symblepharon. Sixteen patients with severe symblepharon were enrolled in this study. After symblepharon lysis and Mitomycin C (MMC) application, tarsus defects were covered with residual autologous conjunctiva (AC), autologous oral mucosa (AOM), or DPC throughout the fornix, and DPC was used for all the exposed sclera. The outcomes were classified as complete success, partial success, or failure. Six symblepharon patients had chemical burns and ten had thermal burns. Tarsus defects were covered with DPC, AC, and AOM in two, three, and eleven cases, respectively. After an average follow-up of 20.0 ± 6 months, the anatomical outcomes observed were complete successes in twelve (three with AC+DPC, four with AC+AOM+DPC, and five with AOM+DPC) (75%) cases, partial successes in three (one with AOM+DPC and two with DPC+DPC) (18.75%) cases, and failure in one (with AOM+DPC) (6.25%) case. Before surgery, the depth of the narrowest part of the conjunctival sac was 0.59 ± 0.76 mm (range, 0-2 mm), tear fluid quantity (Schirmer II tests) was 12.5 ± 2.26 mm (range, 10-16 mm), and the distance of the eye rotation toward the opposite direction of the symblepharon was 3.75 ± 1.39 mm (range, 2-7 mm). The fornix depths increased to 7.53 ± 1.64 mm (range, 3-9 mm), eye movement was significantly improved, and the distance of eye movement reaching 6.56 ± 1.24 mm (range, 4-8 mm) 1 month after the operation; the postoperative Schirmer II test (12.06 ± 2.90 mm, range, 6-17 mm) was similar to that before surgery. Goblet cells were finally found in fifteen patients by conjunctival impression cytology in the transplantation area of DPC, except for one patient who failed. DPC could be considered an alternative for ocular surface reconstruction of severe symblepharon. Covering tarsal defects with autologous mucosa is necessary for extensive reconstruction of the ocular surface.

New Promising Therapeutic Approach for Refractory Corneal Epithelial Defects

The purpose of this case report is to describe a case of continuous wear of a gas-permeable mini-scleral contact lens with a fluid reservoir of autologous serum (AS) combined with AS drops as a successful empirical and accessible alternative therapeutic option for refractory persistent epithelial defects in a patient with severe neurotrophic keratopathy (NK) due to severe dry eye disease and chronic contact lens wear. A 61-year-old Caucasian female with bilateral NK presented a history of multiple episodes of bilateral persistent epithelial defects, having already been submitted to three tectonic-penetrating keratoplasties in her left eye (OS). In May 2017, the patient developed de novo refractory central neurotrophic ulcers in both eyes (OU), unresponsive to conventional treatment with preservative-free lubricants, topical antibiotics, topical anti-inflammatory agents, and oral doxycycline. By March 2018, after initiating hourly AS eyedrops, the ulcer in her right eye (OD) improved to a smaller ulcer, while her OS presented complete graft re-epithelialization. In May 2018, her OD neurotrophic ulcer was complicated with fungal and subsequent bacterial secondary infection. Eventually, a therapeutic penetrant keratoplasty was required for her OD. Subsequently, her OD graft developed a de novo 6x6mm central persistent epithelial defect unresponsive to all the aforementioned therapeutic strategies. After months of unsuccessful treatment, a new therapeutic option was experimented with: a gas-permeable mini-scleral contact lens in combination with AS eyedrops. After two weeks of this treatment regimen, the corneal epithelium eventually started to regenerate, and four weeks later, the cornea was completely re-epithelized. To date, there are no signs of recurrence of the corneal epithelial defect/ulcer.

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

PURPOSE

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

METHOD

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

RESULTS

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

CONCLUSION

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

Development of a new plasma rich in growth factors membrane with improved optical properties

PURPOSE

The aim of the present work was to develop a fibrin membrane using plasma rich in growth factors (PRGF) technology with improved optical properties to be used for the treatment of ocular surface diseases.

BASIC PROCEDURES

Blood was drawn from three healthy donors, and the volume of PRGF obtained from each donor was divided into two main groups: i) PRGF or ii) platelet-poor plasma (PPP). Each membrane was then used pure or diluted to 90 %, 80 %, 70 %, 60 % and 50 %. The transparency of each of the different membranes was evaluated. The degradation and morphological characterization of each membrane was also performed. Finally, a stability study of the different fibrin membranes was performed.

MAIN FINDINGS

The transmittance test showed that the fibrin membrane with the best optical characteristics was obtained after removal of platelets and dilution of fibrin to 50 % (50 % PPP). No significant differences (p > 0.05) were observed between the different membranes in the fibrin degradation test. The stability test showed that the membrane at 50 % PPP retains its optical and physical characteristics after storage at - 20 °C for 1 month compared to storage at 4 °C.

PRINCIPAL CONCLUSIONS

The present study describes the development and characterization of a new fibrin membrane with improved optical characteristics while maintaining mechanical and biological characteristics. The physical and mechanical properties of the newly developed membrane are preserved after storage for at least 1 month at - 20 °C.

Detection of Limbal Stem Cells Adhered to Melt Electrospun Silk Fibroin and Gelatin-Modified Polylactic Acid Scaffolds

Limbal stem cells (LSCs) are of paramount importance in corneal epithelial tissue repair. The cornea becomes opaque in case of limbal stem cell deficiency (LSCD), which may cause serious damage to the ocular visual function. There are many techniques to restore damaged epithelium, one of which is the transplantation of healthy cultured LSCs, usually onto a human amniotic membrane or onto bio-based engineered scaffolds in recent years. In this study, melt electrospun polylactic acid (PLA) was modified by silk fibroin or gelatin and further cultured with LSCs originating from three different donors. In terms of physicochemical properties, both modifications slightly increased PLA scaffold porosity (with a significantly larger pore area for the PLA/gelatin) and improved the scaffolds' swelling percentage, as well as their biodegradation rate. In terms of the scaffold application function, the aim was to detect/visualize whether LSCs adhered to the scaffolds and to further determine cell viability (total number), as well as to observe p63 and CK3 expressions in the LSCs. LSCs were attached to the surface of microfibers, showing flattened conformations or 3D spheres in the formation of colonies or agglomerations, respectively. All scaffolds showed the ability to bind the cells onto the surface of individual microfibers (PLA and PLA/gelatin), or in between the microfibers (PLA/silk fibroin), with the latter showing the most intense red fluorescence of the stained cells. All scaffolds proved to be biocompatible, while the PLA/silk fibroin scaffolds showed the highest 98% viability of 2.9 × 10⁶ LSCs, with more than 98% of p63 and less than 20% of CK3 expressions in the LSCs, thus confirming the support of their growth, proliferation and corneal epithelial differentiation. The results show the potential of these bio-engineered scaffolds to be used as an alternative clinical approach.

Keratin films for ocular surface reconstruction: Wound healing in an in-vivo model

The most commonly used tissue substitute for ocular surface reconstruction is human amniotic membrane (AM). Because of its low biomechanical strength and intransparency there is a need to search for alternatives of consistent quality. This study, further explored the biocompatibility of Keratin Film (KF) and its ability to sustain corneal epithelial wound healing. In three equal groups of 5 New Zeeland white rabbits a 4 mm superficial keratectomy was created in the right eye. Five eyes received a KF, five a human AM graft and the remaining five no implant. All eyes were treated with ofloxacin and dexamethasone eye drops and followed up for 10 days. Corneal fluorescein staining, vascularization, and transparency were assessed using slit lamp biomicroscopy according to a standardized grading score during and at the end of follow-up. The corneal-scleral-button was excised and processed for histology. After 10 days all eyes which had received a KF showed complete epithelial healing and no signs of neovascularization. In the AM group 1 eye showed a persistent epithelial defect at day 10 and 2 eyes showed neovascularization at day 7 resolving at day 10. Transparency improved progressively both in the KF group as well as in the AM group towards the end of the follow. Histology showed a multilayer epithelium firmly adherent to the KF with no evidence of keratocyte migration or inflammatory reaction in the corneal stroma. In this study on rabbit eyes KF better supported corneal epithelial wound healing than amniotic membrane.

The developments in amniotic membrane transplantation in glaucoma and vitreoretinal procedures

The main reasons why Amniotic Membrane (AM) is transplanted in Ophthalmology are: to provide a substrate for cellular growth and to provide tectonic support or as a biological bandage and barrier that protects the wound to facilitate an environment for wound healing. The application of AM is well-documented in corneal disorders of various aetiologies [1], however, research within the field has highlighted how it can be used in conjunctival disorders and most recently, in glaucoma and vitreoretinal procedures. This review explores the preservation modalities of AM and summarises the current literature regarding AM transplantation in Glaucoma and Vitreoretinal conditions. AM transplantation in conjunction with trabeculectomy was reported to be used in two different surgical techniques. They differ in relation to the position of the implant: below the scleral flap or over the entire exposed sclera. The results of these studies suggest that AM transplant is a safe procedure that helps in the improvement of the intraocular pressure when associated with trabeculectomies. Moreover, it enhances trabeculectomies success rates when used along with mitomycin C [2]. The use of AM is also described for managing leaking blebs. It is mentioned to be a suitable alternative to conjunctival advancement. Regarding AM transplantation in glaucoma shunt or valve surgeries, the current literature is relatively limited. However, AM has been described as a good tectonic support for shunt procedures [3]. Successful results are described in the literature for surgical treatments using AM plug for vitreoretinal procedures. In particular macular hole closure and rhegmatogenous retinal detachment. In conclusion, AM transplant is a very promising and versatile adjutant therapy. However, further studies are also required for a better understanding and refinement of surgical techniques.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

Restrictive Strabismus Developing after Conjunctivodacryocystorhinostomy

Purpose: To report a case of diplopia caused by restrictive strabismus developing after conjunctivodacryocystorhinostomy (CDCR).Case summary: A 61-year-old female presented with persistent epiphora after failure to repair ipsilateral canalicular lacerations of the left eye caused by trauma occurred 25 years ago. CDCR was performed and the epiphora improved. Four months later, the patient presented with diplopia on the left gaze. An abduction limitation of -4 and a supraduction limitation of -3 were observed in the left eye. Therefore, Jones tube removal was performed 5 months after CDCR surgery. Two weeks later, as the limitations persisted, adhesiolysis of the conjunctiva and an amniotic membrane transplantation (AMT) were performed. This exposed a subconjunctival adhesion at the inferonasal conjunctiva; histopathological examination revealed fibrotic tissues. Three months later, the adhesions recurred and the patient was transferred to another hospital. Conjunctival adhesiolysis, AMT, and a 6.5 mm recession of medial rectus (MR) muscle were performed. One week later, exotropia occurred in the primary position, and the MR muscle of the left eye was advanced by 2 mm. Nine months after the final surgery, the primary gaze was orthotropia. The diplopia within the central 20° of visual field had disappeared. However, a levoelevation limitation of -1.5 remained in the left eye.Conclusions: CDCR is the only treatment method for patients with occlusion of both the upper and lower proximal lacrimal canaliculi. However, rare complications such as restrictive strabismus with diplopia may occur. As preventing adhesion is difficult, sufficient patient notice is required prior to surgery.

Induction of Corneal Epithelial Differentiation of Induced Pluripotent and Orbital Fat-Derived Stem Cells Seeded on Decellularized Human Corneas

Up to 40% of donor corneas are deemed unsuitable for transplantation, aggravating the shortage of graft tissue. In most cases, the corneal extracellular matrix is intact. Therefore, their decellularization followed by repopulation with autologous cells may constitute an efficient alternative to reduce the amount of discarded tissue and the risk of immune rejection after transplantation. Although induced pluripotent (hiPSCs) and orbital fat-derived stem cells (OFSCs) hold great promise for corneal epithelial (CE) reconstruction, no study to date has evaluated the capacity of decellularized corneas (DCs) to support the attachment and differentiation of these cells into CE-like cells. Here, we recellularize DCs with hiPSCs and OFSCs and evaluate their differentiation potential into CE-like cells using animal serum-free culture conditions. Cell viability and adhesion on DCs were assessed by calcein-AM staining and scanning electron microscopy. Cell differentiation was evaluated by RT-qPCR and immunofluorescence analyses. DCs successfully supported the adhesion and survival of hiPSCs and OFSCs. The OFSCs cultured under differentiation conditions could not express the CE markers, TP63, KRT3, PAX6, and KRT12, while the hiPSCs gave rise to cells expressing high levels of these markers. RT-qPCR data suggested that the DCs provided an inductive environment for CE differentiation of hiPSCs, supporting the expression of PAX6 and KRT12 without the need for any soluble induction factors. Our results open the avenue for future studies regarding the in vivo effects of DCs as carriers for autologous cell transplantation for ocular surface reconstruction.

Cryopreservation in a Standard Freezer: −28 °C as Alternative Storage Temperature for Amniotic Membrane Transplantation

Human amniotic membrane (hAM) is usually stored at −80 °C. However, in many regions, cryopreservation at −80 °C is not feasible, making hAM unavailable. Therefore, the possibility of cryopreservation at −28 °C (household freezer) was investigated. hAMs (n = 8) were stored at −80 °C or −28 °C for a mean time of 8.2 months. hAM thickness, epithelial integrity and basement membrane were assessed histologically. The collagen content, concentration of hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF) were determined. Elastic modulus and tensile strength were measured. The mean thickness of hAM stored at −28 °C was 33.1 ± 21.6 µm (range 9.7–74.9); thickness at −80 °C was 30.8 ± 14.7 µm (range 13.1–50.7; p = 0.72). Mean collagen content, epithelial cell number and integrity score showed no significant difference between samples stored at −28 °C or −80 °C. Basement membrane proteins were well preserved in both groups. Mean tensile strength and elastic modulus were not significantly different. Concentration of bFGF at −28 °C was 1063.2 ± 680.3 pg/g (range 369.2–2534.2), and 1312.1 ± 778.2 pg/g (range 496.2–2442.7) at −80 °C (p = 0.11). HGF was 5322.0 ± 2729.3 pg/g (range 603.3–9149.8) at −28 °C, and 11338.5 ± 6121.8 pg/g (range 4143.5 to 19806.7) at −80 °C (p = 0.02). No microbiological contamination was detected in any sample. The cryopreservation of hAM at −28 °C has no overt disadvantages compared to −80 °C; the essential characteristics of hAM are preserved. This temperature could be used in an alternative storage method whenever storage at −80 °C is unavailable.

OUP accepted manuscript

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

Placenta Donation - The Expectant Mother's View

The placenta has been used in different facets of medicine however some low-income countries are yet to apply these uses for different reasons. A cross-sectional study of 150 expectant mothers attending antenatal clinic was conducted to determine the willingness to donate the placenta. Analysis was conducted using Statistical Package for the Social Sciences version 20 with a level of significance set at P ≤ .05. The mean age of the participants was 32.3 (SD±5.0) years. Almost all (98.7%) were married while 89.3% had tertiary-level education. The majority (82.7%) knew there was no connection between the placenta and baby after delivery; however, only 12.0% knew about placenta donation and 10.0% were willing to donate the placenta at delivery. About three quarters (74.0%) were unwilling to promote the donation of the placenta, most (55.0%) believed that the placenta was used for rituals, while some (19.0%) thought placenta donation would affect the child's future. Participants' occupation, 'knowledge about placenta donation and its uses' and willingness to promote donation were all significantly associated with their willingness to donate (P < .05). Willingness to donate the placenta at delivery was low in this study. Participants' occupation and their knowledge were some factors influencing willingness to donate the placenta for medical use.

Biomolecular evaluation of cryopreserved amniotic membranes for ophthalmological use by ELISA and RT-PCR at one and eighteen months

PURPOSE

To study the presence of certain proteins - EGF (epidermal growth factor), KGF (keratinocyte growth factor), IL-10 (interleukin 10), HGF (hepatocyte growth factor), Alpha2-macroglobulin and IL-1RA (interleukin 1 receptor antagonist) in cryopreserved amniotic membranes at 1 and 18 months and, as a secondary objective, to detect mRNA corresponding to KGF, IL-1Ra, Alpha2-macroglobulin, Fas Ligand, TGF beta (transforming growth factor beta) and Lumican by RT-PCR in membranes preserved at 1 and 18 months.

MATERIAL AND METHODS

Four samples of amniotic membrane were divided into 2 groups: the first group (N=2) cryopreserved for 1 month and the second group (N=2) cryopreserved for 18 months, in order to be studied by RT-PCR and ELISA.

RESULTS

RT-PCR detected KGF, IL-1Ra, Alpha2-macroglobulin, Fas Ligand, and Lumican. Of these, FAS Ligand mRNA was found in samples preserved for 1and 18 months. KGF, Lumican, and alpha2-microglobulin mRNA were found only at 1 month, and IL-1Ra mRNA was absent in both sample groups. RT-PCR for TGF-beta was inconclusive. ELISA was performed for detection and quantification of 6 proteins (EGF, KGF, IL-10, HGF, Alpha2-macroglobulin and IL-1Ra) in both amniotic membrane groups. All 6 proteins were found in all samples, with a lower concentration at 18 months compared to 1 month of preservation.

CONCLUSION

This study shows that membranes cryopreserved in 50% glycerol for 18 months do retain the proteins necessary for regeneration of the corneal surface, giving these membranes their biochemical properties.

Transformation of electrospun Keratin/PVA nanofiber membranes into multilayered 3D Scaffolds: Physiochemical studies and corneal implant applications

In this study, we engineered an electrospun keratin/polyvinyl alcohol (PVA) nanofiber membrane with a three-dimensional (3D) fiber network. Both keratin and PVA are known as biocompatible materials, and the 3D assembly of these two led to a transparent membrane with superior mechanical properties. The as-prepared three-dimensionally assembled keratin/PVA nanofiber (3D keratin/PVA NFs) membrane was characterized by state-of-the-art techniques and used as a corneal implant in rabbit eyes. The transparency, mechanical properties, and biocompatibility of the electrospun keratin/PVA NFs were highly enhanced after 3D modification which is mainly attributed to its unique three-dimensional morphology. The performance of 3D keratin/PVA NFs membrane was compared with horse amniotic membrane (AM), and the results obtained from the clinical and histological evaluations showed that it could be considered as an alternative material to the AM. Furthermore, this study provides an emerging approach for converting a two-dimensional electrospun nanofiber membrane to three-dimensional fiber networks that resemble the structure of the extracellular matrix (ECM).

Experimental evaluation of safety and efficacy of plasma-treated poly-ε-caprolactone membrane as a substitute for human amniotic membrane in treating corneal epithelial defects in rabbit eyes

Purpose:

To evaluate biocompatibility and safety of plasma-treated poly-ε-caprolactone (pPCL) membrane compared to the human amniotic membrane in the healing of corneal epithelial defects in an experimental model.

Methods:

This is a prospective, randomized animal study including 12 rabbits. Circular epithelial injury measuring 6 mm in diameter was induced over the central cornea of one eye in twelve rabbits. The rabbits were randomized into two groups; in group A, the defect was covered with human amniotic membrane, while in group B, an artificial membrane made of bio-polymer plasma-treated poly-ε-caprolactone was grafted. Six rabbits were euthanized after 1 month and the other six after 3 months and the corneal epithelium was evaluated histopathologically and with immunohistochemistry.

Results:

Light microscopy of the corneal tissue performed after 1 month and 3 months demonstrated similar findings with no significant complications in either group. Immunohistochemistry with anti-CK-3 antibody showed characteristic corneal phenotype in the healed epithelium. In eyes grafted with pPCL membrane, epithelial healing as estimated by a decrease in size of the defect was significantly better than the group treated with the human amniotic membrane at all time periods monitored (P < 0.05), except day 1 (P = 0.83). The percentage reduction in the size of the epithelial defect was also significantly more in the pPCL membrane group as compared to the human amniotic membrane at all time periods (P < 0.05 at all observations) post-implantation except day 1 (P = 0.73).

Conclusion:

Plasma-treated poly-ε-caprolactone membrane is safe, biocompatible, and effective in the healing of corneal epithelial defects in rabbits.

Determining the efficacy of the bovine amniotic membrane homogenate during the healing process in rabbits' ex vivo corneas

OBJECTIVE

To evaluate the efficacy of bovine amniotic membrane homogenate (BAMH) on wounded ex vivo rabbit corneas.

PROCEDURE

Eighteen corneas obtained from normal rabbit eyes were wounded equally using a 6 mm trephine and cultured into an air-liquid interface model. Corneas were treated with phosphate-buffered saline (PBS) (n = 6, control group), 0.2% ethylenediaminetetraacetic acid (EDTA; n = 6), or BAMH (n = 6). All treatments were applied topically 6 times/day. Each cornea was macrophotographed daily with and without fluorescein stain to assess epithelialization and haziness. After 7 days, corneal transparency was evaluated, and the tissues prepared for histologic analysis of viability, and total and epithelial thickness.

RESULTS

The mean epithelialization time was 6.2 ± 0.82 days for the control group, 6.2 ± 0.75 days for the EDTA-treated group, and 5.1 ± 0.40 days for the BAMH-treated group, demonstrating a significant difference between the BAMH and the other groups. The corneas that received EDTA had better transparency compared with the other groups. Histologically, all corneas had adequate morphology and architecture after healing. Analysis of corneal and epithelial thickness revealed no significant difference among groups.

CONCLUSION

Bovine amniotic membrane homogenate is an effective and promising treatment for stromal and epithelial ulcers.

Progress in the use of plasma rich in growth factors in ophthalmology: from ocular surface to ocular fundus

Introduction: The use of blood derivatives and especially Plasma rich in growth factors (PRGF), for regenerative purposes has been a common trend along the last decades in the field of oral surgery, dermatology, orthopedics, and more recently in ophthalmology.Areas covered: PRGF is a type of platelet-rich plasma that is being explored for the treatment of ocular injuries. The present review article highlights 50 ophthalmology-related publications about the application of PRGF in the treatment of acute and chronic pathologies in ophthalmology as well as most relevant challenges and future prospects.Expert opinion: PRGF technology provides a wide range of formulations that can be used therapeutically in many different acute and chronic ocular pathologies. In addition to eye drops enriched with autologous growth factors, PRGF enables the preparation of both immunologically safe and fibrin-based formulations. Recent advances in the field have promoted PRGF storage for 12 months under freezing conditions, its daily use for 7 days at room temperature and the freeze-dried formulation. The thermally treated immunosafe formulation has shown promising clinical results for the treatment of several diseases such as Sjögren syndrome, graft versus host disease or cicatrizing conjunctivitis. In addition, several fibrin formulations have been preclinically evaluated and clinically incorporated as an adjuvant to ocular surface or glaucoma surgeries, dermal fat graft procedures, limbal stem cell expansion and retinal surgeries. The present review explores the latest scientific and clinical data, current challenges, and main prospects of this technology for the treatment of several ocular injuries.

The eggshell membrane: A potential biomaterial for corneal wound healing

The eggshell membrane (ESM) is an abundant resource with innate complex structure and composition provided by nature. With at least 60 million tonnes of hen eggs produced globally per annum, utilisation of this waste resource is highly attractive in positively impacting sustainability worldwide. Given the morphology and mechanical properties of this membrane, it has great potential as a biomaterials for wound dressing. However, to date, no studies have demonstrated nor reported this application. As such, the objective of this investigation was to identify and optimise a reproducible extraction protocol of the ESM and to assess the physical, chemical, mechanical and biological properties of the substrate with a view to use as a wound dressing. ESM samples were isolated by either manual peeling (ESM-strip) or via extraction using acetic acid [ESM-A0.5] or ethylenediaminetetraacetic acid, EDTA [ESM-E0.9]. Energy dispersive X-ray spectroscopy (EDS) confirmed that there were no traces of calcium residues from the extraction process. Fourier transform infrared (FTIR) spectroscopy revealed that the extraction method (acetic acid and EDTA) did not alter the chemical structures of the ESM and also clarified the composition of the fibrous proteins of the ESM. Scanning electron microscopy (SEM) analyses revealed a three-layer composite structure of the ESM: an inner layer as continuous, dense and non-fibrous (limiting membrane), a middle layer with a network of fibres (inner shell membrane) and the outer layer (outer shell membrane) of larger fibres. Material properties including optical transparency, porosity, fluid absorption/uptake, thermal stability, mechanical profiling of the ESM samples were performed and demonstrated suitable profiles for translational applications. Biological in vitro studies using SV40 immortalised corneal epithelial cells (ihCEC) and corneal mesenchymal stromal cells (C-MSC) demonstrated excellent biocompatibility. Taken together, these results document the development of a novel sustainable biomaterial that may be used for ophthalmic wounds and/or other biomedical therapies.

Bibliometric analysis and mapping knowledge domain of pterygium: 2000-2019

AIM

To track the knowledge structure, topics in focus, and trends in emerging research in pterygium in the past 20y.

METHODS

Base on the Web of Science Core Collection (WoSCC), studies related to pterygium in the past 20y from 2000-2019 have been included. With the help of VOSviewer software, a knowledge map was constructed and the distribution of countries, institutions, journals, and authors in the field of pterygium noted. Meanwhile, using co-citation analysis of references and co-occurrence analysis of keywords, we identified basis and hotspots, thereby obtaining an overview of this field.

RESULTS

The search retrieved 1516 publications from WoSCC on pterygium published between 2000 and 2019. In the past two decades, the annual number of publications is on the rise and fluctuated a little. Most productive institutions are from Singapore but the most prolific and active country is the United States. Journal Cornea published the most articles and Coroneo MT contributed the most publications on pterygium. From co-occurrence analysis, the keywords formed 3 clusters: 1) surgical therapeutic techniques and adjuvant of pterygium, 2) occurrence process and pathogenesis of pterygium, and 3) epidemiology, and etiology of pterygium formation. These three clusters were consistent with the clustering in co-citation analysis, in which Cluster 1 contained the most references (74 publications, 47.74%), Cluster 2 contained 53 publications, accounting for 34.19%, and Cluster 3 focused on epidemiology with 18.06% of total 155 co-citation publications.

CONCLUSION

This study demonstrates that the research of pterygium is gradually attracting the attention of scholars and researchers. The interaction between authors, institutions, and countries is lack of. Even though, the research hotspot, distribution, and research status in pterygium in this study could provide valuable information for scholars and researchers.

Biological tissues and components, and synthetic substrates for conjunctival cell transplantation

The conjunctiva is the largest component of the ocular surface. It can be damaged by various pathological processes leading to scarring, loss of tissue and dysfunction. Depending on the amount of damage, restoration of function may require a conjunctival graft. Numerous studies have investigated biological and synthetic substrates in the search for optimal conditions for the ex vivo culture of conjunctival epithelial cells that can be used as tissue grafts for transplantation. These substrates have advantages and disadvantages that are specific to the characteristics of each material; the development of an improved material remains a priority. This review is the second of a two-part review in The Ocular Surface. In the first review, the structure and function of the conjunctiva was evaluated with a focus on the extracellular matrix and the basement membrane, and biological and mechanical characteristics of the ideal substrate with recommendations for further studies. In this review the types of biological and synthetic substrates used for conjunctival transplantation are discussed including substrates based on the extracellular matrix. .

Applications of Human Amniotic Membrane for Tissue Engineering

An important component of tissue engineering (TE) is the supporting matrix upon which cells and tissues grow, also known as the scaffold. Scaffolds must easily integrate with host tissue and provide an excellent environment for cell growth and differentiation. Human amniotic membrane (hAM) is considered as a surgical waste without ethical issue, so it is a highly abundant, cost-effective, and readily available biomaterial. It has biocompatibility, low immunogenicity, adequate mechanical properties (permeability, stability, elasticity, flexibility, resorbability), and good cell adhesion. It exerts anti-inflammatory, antifibrotic, and antimutagenic properties and pain-relieving effects. It is also a source of growth factors, cytokines, and hAM cells with stem cell properties. This important source for scaffolding material has been widely studied and used in various areas of tissue repair: corneal repair, chronic wound treatment, genital reconstruction, tendon repair, microvascular reconstruction, nerve repair, and intraoral reconstruction. Depending on the targeted application, hAM has been used as a simple scaffold or seeded with various types of cells that are able to grow and differentiate. Thus, this natural biomaterial offers a wide range of applications in TE applications. Here, we review hAM properties as a biocompatible and degradable scaffold. Its use strategies (i.e., alone or combined with cells, cell seeding) and its degradation rate are also presented.

Fibrin-Plasma Rich in Growth Factors Membrane for the Treatment of a Rabbit Alkali-Burn Lesion

The purpose of this work is to describe the use of Fibrin-Plasma Rich in Growth Factors (PRGF) membranes for the treatment of a rabbit alkali-burn lesion. For this purpose, an alkali-burn lesion was induced in 15 rabbits. A week later, clinical events were evaluated and rabbits were divided into five treatment groups: rabbits treated with medical treatment, with a fibrin-PRGF membrane cultured with autologous or heterologous rabbit Limbal Epithelial Progenitor Cells (LEPCs), with a fibrin-PRGF membrane in a Simple Limbal Epithelial Transplantation and with a fibrin-PRGF membrane without cultured LEPCs. After 40 days of follow-up, corneas were subjected to histochemical examination and immunostaining against corneal or conjunctival markers. Seven days after alkali-burn lesion, it was observed that rabbits showed opaque cornea, new blood vessels across the limbus penetrating the cornea and epithelial defects. At the end of the follow-up period, an improvement of the clinical parameters analyzed was observed in transplanted rabbits. However, only rabbits transplanted with cultured LEPCs were positive for corneal markers. Otherwise, rabbits in the other three groups showed positive staining against conjunctival markers. In conclusion, fibrin-PRGF membrane improved the chemically induced lesions. Nonetheless, only fibrin-PRGF membranes cultured with rabbit LEPCs were able to restore the corneal surface.

Long-term outcome of cultivated oral mucosal epithelial transplantation for fornix reconstruction in chronic cicatrising diseases

BACKGROUND/AIMS

To investigate the long-term outcomes of cultivated oral mucosal epithelial transplantation (COMET) for fornix reconstruction in eyes with chronic cicatrising disease.

METHODS

This retrospective cohort study involved 16 eyes of 15 patients who underwent COMET for symblepharon release and fornix reconstruction between June 2002 and December 2008. The mean postoperative follow-up period was 102.1±46.0 months (range: 32-183 months). The treated cicatrising disorders included ocular cicatricial pemphigoid (OCP, five eyes), thermal/chemical injury (three eyes) and other chronic diseases (seven eyes; including recurrent pterygium (two eyes), Stevens-Johnson syndrome (one eye) and graft-versus-host disease (one eye)). Ocular-surface appearance was evaluated before surgery, at 1, 4, 12 and 24 weeks postoperative, and then annually based on the previously reported scoring system. Main outcome measures included overall and disease-specific fornix-reconstruction success probabilities analysed by the Kaplan-Meier survival curve. Symblepharon/fornix-shortening recurrence at 24 weeks postoperative, and its relationship to long-term surgical success was also examined.

RESULTS

At 5 years postoperative, the mean±SD overall fornix-reconstruction success probability was 79.6%±10.7%, and success probability for thermal/chemical injury and OCP was 100% and 53.3%±24.8%, respectively (p=0.53, log-rank test). The 3-year success probability was significantly higher in the no-disease-recurrence group at 24 weeks postoperative (13 eyes) than in the disease-recurrence group (three eyes) (100% and 33.3%±27.2%, respectively) (p=0.0073, log-rank test).

CONCLUSION

COMET was found to be safe and effective for symblepharon release and long-term fornix reconstruction in eyes with chronic cicatrisation. Although the 5-year success probability differed depend on the underlying disease, ocular-surface appearance at 24 weeks postoperative is a factor for predicting long-term outcome.

Oxygen Permeability of Silk Fibroin Hydrogels and Their Use as Materials for Contact Lenses: A Purposeful Analysis

Fibroin is a fibrous protein that can be conveniently isolated from the silk cocoons produced by the larvae of Bombyx mori silk moth. In its form as a hydrogel, Bombyx mori silk fibroin (BMSF) has been employed in a variety of biomedical applications. When used as substrates for biomaterial-cells constructs in tissue engineering, the oxygen transport characteristics of the BMSF membranes have proved so far to be adequate. However, over the past three decades the BMSF hydrogels have been proposed episodically as materials for the manufacture of contact lenses, an application that depends on substantially elevated oxygen permeability. This review will show that the literature published on the oxygen permeability of BMSF is both limited and controversial. Additionally, there is no evidence that contact lenses made from BMSF have ever reached commercialization. The existing literature is discussed critically, leading to the conclusion that BMSF hydrogels are unsuitable as materials for contact lenses, while also attempting to explain the scarcity of data regarding the oxygen permeability of BMSF. To the author’s knowledge, this review covers all publications related to the topic.

Use of autologous plasma rich in growth factors fibrin membrane in the surgical management of ocular surface diseases

PURPOSE

To evaluate the safety and efficacy of the surgical use of autologous plasma rich in growth factors fibrin membrane (mPRGF) in improving corneal wound healing and regeneration in a variety of complex ocular surface defects.

METHODS

Chart review on 15 eyes of 14 included patients undergoing ocular surface intervention using intraoperative mPRGF at the Bascom Palmer Eye Institute and at the Instituto Oftalmológico Fernández-Vega was performed. Patients were grouped based on type of intervention or condition (penetrating keratoplasty, superficial keratectomy, neurotrophic or persistent corneal ulcers, and corneal perforation). Patients were followed for an average of 11 ± 5 months. Main outcomes measured were mPRGF dissolving time, best-corrected visual acuity, and evidence of any persistent epithelial defects, rejections, or complications.

RESULTS

All 15 eyes underwent successful placement of mPRGF. Average dissolving time for fibrin membrane was 21 ± 3 days. mPRGF resulted in total healing of the corneal defects in 13/15 (86.7%) of the treated eyes and partial healing in 2/15 (13.3%) eyes in which persistent epithelial defects were noted on follow-up. Visual acuity improvement was seen in 9/15 (60%) of the cases.

CONCLUSION

The use of autologous mPRGF in the healing and regeneration of the ocular surface is a secure and efficacious surgical option. Our data demonstrate that PRGF fibrin membrane should be contemplated as an important tool to optimize ocular surface regeneration in complex cases.

Nano-Scale Modifications of Amniotic Membrane Induced by UV and Antibiotic Treatment: Histological, AFM and FTIR Spectroscopy Evidence

The efficiency of amniotic membrane (AM) transplantation in different types of ocular surface disorders is due to its outstanding properties such as antifibrotic, antibacterial, anti-inflammatory and antiangiogenic, working as a versatile scaffold to promote corneal tissue epithelialization. A proper preparation, preservation and clinical application are crucial for the best outcomes in the treatment of different severe ocular disorders, taking into account its fragility. In this context, by combining high-sensitivity tools such as atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy with histological and immunohistochemical examination, we aimed to investigate the ultrastructural modifications of the amniotic membrane (AM) upon UV exposure and/or antibiotic treatment, with relevance for clinical applications in ocular surface surgery. From the morphological point of view, we noticed a loss of cuboidal cells in the basal membrane, accompanied by the splitting of collagen fibers upon UV and/or gentamicin treatment, while structural alteration of proteins was evidenced by the FTIR quantitative analysis of the secondary structure. A decrease in α-helix and β-sheet content, accompanied by increased content in less ordered structures (turns, random and side chains), was noticed after all the treatments. At the nano-scale, AFM details showed modifications of collagen fibrils in terms of their thickness and network compaction upon gentamicin and/or UV treatment. The enzymatic digestion assay demonstrated that UV exposure significantly reduces the degradation rate of the AM, while gentamicin treatment promotes an accelerated enzymatic digestion upon UV exposure. In order to highlight the clinical impact of the research, a clinical case is presented showing the relevance of amniotic membrane transplantation in pterygium surgery.

Potential of mesenchymal stem cells as topical immunomodulatory cell therapies for ocular surface inflammatory disorders

Ocular surface inflammatory disorders (OSIDs) are a group of highly prevalent, heterogeneous diseases that display a variety of aetiologies and symptoms and are risk factors for serious complications, including ocular and cornea impairment. Corneal inflammation is a common factor of all OSIDs, regardless of their cause or symptoms. Current medications include over-the-counter lubricating eye drops, corticosteroids, and ciclosporin, which either do not treat the corneal inflammation or have been associated with multiple side effects leading to alternative treatments being sought. Regenerative medicine cell therapies, particularly mesenchymal stem cells (MSCs), have shown great promise for immunosuppression and disease amelioration across multiple tissues, including the cornea. However, for successful development and clinical translation of MSC therapy for OSIDs, significant problems must be addressed. This review aims to highlight considerations, including whether the source of MSC isolation impacts the efficacy and safety of the therapy, in addition to assessing the feasibility of MSC topical application to the cornea and ocular surface through analysis of potential scaffolds and cell carriers for application to the eye. The literature contains limited data assessing MSCs incorporated into scaffolds for corneal administration, thus here we highlight the necessity of further investigations to truly exploit the potential of an MSC-based cell therapy for the treatment of OSIDs.

Insights on the Human Amniotic Membrane in Clinical Practice with a Focus on the New Applications in Retinal Surgery

Recently, the use of the human amniotic membrane (hAM) has been extended to treat retinal disorders such as refractory macular holes, retinal breaks and dry and wet age-related macular degeneration. Not only the hAM has proved to be an excellent tool for repairing retinal tissue, but it has also shown a promising regeneration potential. This review aims to highlight the novel use of the hAM in treating retinal diseases. Although the hAM has been used in the ocular anterior segment reconstruction for more than 60 years, in the last 2 years, we have found in literature articles showing the use of the hAM in the retinal surgery field with interesting results in terms of tissue healing and photoreceptor regeneration.

Development and optimization of a personalized fibrin membrane derived from the plasma rich in growth factors technology

PURPOSE

To develop and characterize a new type of plasma rich in growth factors (PRGF) membrane for patients in which immune system is involved in the disease etiology.

METHODS

Blood from three healthy donors was collected to obtain the different fibrin membranes by PRGF technology. PRGF obtained volumes were activated and divided into two groups: PRGF membrane (mPRGF) obtained after incubation at 37 °C for 30 min (control); and is-mPRGF: mPRGF obtained after incubation for 30 min at 56 °C. The concentration of several growth factors, proteins, immunoglobulin E and the complement activity was determined in the different mPRGF. The proliferative potential of heat-inactivated mPRGF were assayed on keratocytes (HK) and conjunctival fibroblasts (HConF). In addition, morphological and physical features of the inactivated mPRGF were evaluated in contrast to the control mPRGF.

RESULTS

Heat-inactivation of the mPRGF preserves the content of most of the growth factors involved in the ocular wound healing while reducing drastically the content of IgE and the complement activity. The heat-inactivated mPRGF conserve the morphological and physical characteristics of the fibrin meshwork in comparison with the control mPRGF. Furthermore, no significant differences were found in the biological activity of the control mPRGF regarding the heat-inactivated mPRGF (is-mPRGF) in any of both ocular cell types evaluated.

CONCLUSIONS

The heat-inactivation of the PRGF membranes (is-mPRGF) reduces drastically the content of IgE and complement activity while preserving the content of most of the proteins and morphogens involved in ocular wound healing. Furthermore, the morphological and physical features of the immunosafe mPRGF were also preserved after heat-inactivation.

Amniotic Membrane Patch Graft in Management of Double Chamber after Deep Anterior Lamellar Keratoplasty

Purpose

To describe a novel technique of amniotic membrane (AM) patch graft in the management of double chamber treatment after big-bubble deep anterior lamellar keratoplasty (DALK).

Case Report

A 35-year-old male patient with advanced keratoconus underwent big-bubble DALK. Manual lamellar dissection was done due to failed big-bubble. First-day postoperative double chamber was detected. Air bubbling and SF6 injection were tried without any success. Double chamber resolved by fixation of AM transplantation patch graft (1 × 1 mm) over the Descemet's membrane perforation with fibrin glue.

Conclusion

Amniotic membrane patch graft can be used in the management of double chamber after DALK not responsive to intracameral gas injection.

Update review on five top clinical applications of human amniotic membrane in regenerative medicine

Due to the increasing number of studies performed in the field of regenerative medicine during the last two decades, more analytic studies are still needed to clarify the future prospect of this area of science. The main aim of this research was to review the clinical applications of human Amniotic membrane in the field of regenerative medicine critically. Furthermore, in the light of increasing numbers of available products derived from amniotic membrane, we aimed look in depth to see whether regenerative medicine research strategies have a place in the clinical setting. More specifically, in the present study, we attempted to provide insight on developing the new indication for more research and in the next step, for market leaders companies to expand cost-effectiveness of new derived AM products. 20 companies or distributers have offered some commercial products in this field. Survey on more than 90 clinical trials in last five years showed dermatology (and more specific wound healing), orthopedic, and ophthalmology are heavily biased toward multibillion dollar industry. Moreover, urology and dentistry with fewer numbers of clinical data in comparison with the above-mentioned areas, currently are in the path of translation (especially dentistry). In addition, otolaryngology and oncology with the lowest number showed more potential of research thorough understanding the properties that will help guiding the use of AM-derived products in these two areas in future. More than 50% of clinical studies were done or are developing in USA, which have the biggest share in market products. Subsequently, China, Egypt, India, Iran, and Germany with the ongoing clinical trials in different phases may have more approved products in near future.

Diabetic keratopathy: Insights and challenges

Ocular complications from diabetes mellitus are common. Diabetic keratopathy, the most frequent clinical condition affecting the human cornea, is a potentially sight-threatening condition caused mostly by epithelial disturbances that are of clinical and research attention because of their severity. Diabetic keratopathy exhibits several clinical manifestations, including persistent corneal epithelial erosion, superficial punctate keratopathy, delayed epithelial regeneration, and decreased corneal sensitivity, that may lead to compromised visual acuity or permanent vision loss. The limited amount of clinical studies makes it difficult to fully understand the pathobiology of diabetic keratopathy. Effective therapeutic approaches are elusive. We summarize the clinical manifestations of diabetic keratopathy and discuss available treatments and up-to-date research studies in an attempt to provide a thorough overview of the disorder.

Decellularized porcine conjunctiva as an alternative substrate for tissue-engineered epithelialized conjunctiva

PURPOSE

The long-term success of visual rehabilitation in patients with severe conjunctival scarring is reliant on the reconstruction of the conjunctiva with a suitable substitute. The purpose of this study is the development and investigation of a re-epithelialized conjunctival substitute based on porcine decellularized conjunctiva (PDC).

METHODS

PDC was re-epithelialized either with pre-expanded human conjunctival epithelial cells (PDC + HCEC) or with a human conjunctival explant placed directly on PDC (PDC + HCEx). Histology and immunohistochemistry were performed to evaluate epithelial thickness, proliferation (Ki67), apoptosis (Caspase 3), goblet cells (MUC5AC), and progenitor cells (CK15, ΔNp63, ABCG2). The superior construct (PDC + HCEx) was transplanted into a conjunctival defect of a rabbit (n = 6). Lissamine green staining verified the epithelialization in vivo. Orbital tissue was exenterated on day 10 and processed for histological and immunohistochemical analysis to examine the engrafted PDC + HCEx. A human-specific antibody was used to detect the transplanted cells.

RESULTS

From day-14 in vitro onward, a significantly thicker epithelium and greater number of cells expressing Ki67, CK15, ΔNp63, and ABCG2 were noted for PDC + HCEx versus PDC + HCEC. MUC5AC-positive cells were found only in PDC + HCEx. The PDC + HCEx-grafted rabbit conjunctivas were lissamine-negative during the evaluation period, indicating epithelial integrity. Engrafted PDC + HCEx showed preserved progenitor cell properties and an increased number of goblet cells comparable to those of native conjunctiva.

CONCLUSION

Placing and culturing a human conjunctival explant directly on PDC (PDC + HCEx) enables the generation of a stable, stratified, goblet cell-rich construct that could provide a promising alternative conjunctival substitute for patients with extensive conjunctival stem and goblet cell loss.

Current clinical application of sclera and amniotic membrane for ocular tissue bio-replacement

To report the current clinical applications and trends of scleral and amniotic membrane use in ophthalmology. Review of annual reports from the Catalan Transplant Organization (OCATT), on scleral patch and amniotic membrane eye indications in Catalonia region (Spain) over a 6-year period from 2013 to 2018. A total of 874 scleral and 1665 amniotic membranes patches were implanted, from January 2013 to December 2018. The most frequent indication over the 6-year period for scleral patch was glaucoma surgery (77.5%), eyelid reconstruction (5.2%) and corneal or scleral ulcer (5%). Regarding amniotic membrane, corneal ulcer (26.9%), conjunctival reconstruction (23.8%) and corneal epithelial defect (22.7%) were the most common indications. During the study period, an increasing trend was found on sclera patches for eyelid reconstruction (p = 0.0032) and amniotic membrane for inflammation management (p = 0.0198). Glaucoma surgery and corneal ulcers have represented the top indications for scleral patch and amniotic membrane use, over the period, respectively. A significant trend has also been found towards eyelid reconstruction using scleral patches and amniotic membrane for anterior segment inflammation management. This evolving scenario in tissue use for ocular surgery has to be taken into consideration, especially regarding eye banks facing current and futures changes in tissue preservation, storage and indications.

Epithelial basement membrane of human decellularized cornea as a suitable substrate for differentiation of embryonic stem cells into corneal epithelial-like cells

The ability to decellularize and recellularize the corneas deemed unsuitable for transplantation may increase the number of available grafts. Decellularized corneas (DCs) may provide a natural microenvironment for cell adhesion and differentiation. Despite this, no study to date has evaluated their efficacy as a substrate for the induction of stem cell differentiation into corneal cells. The present study aimed to compare the efficiency of NaCl and NaCl plus nucleases methods to decellularize whole human corneas, and to investigate the effect of epithelial basement membrane (EBM) of whole DCs on the ability of human embryonic stem cells (hESCs) to differentiate into corneal epithelial-like cells when cultured in animal serum-free differentiation medium. As laminin is the major component of EBM, we also investigated its effect on hESCs differentiation. The decellularization efficiency and integrity of the extracellular matrix (ECM) obtained were investigated by histology, electron microscopy, DNA quantification, immunofluorescence, and nuclear staining. The ability of hESCs to differentiate into corneal epithelial-like cells when seeded on the EBM of DCs or laminin-coated wells was evaluated by immunofluorescence and RT-qPCR analyses. NaCl treatment alone, without nucleases, was insufficient to remove cellular components, while NaCl plus nucleases treatment resulted in efficient decellularization and preservation of the ECM. Unlike cells induced to differentiate on laminin, hESCs differentiated on DCs expressed high levels of corneal epithelial-specific markers, keratin 3 and keratin 12. It was demonstrated for the first time that the decellularized matrices had a positive effect on the differentiation of hESCs towards corneal epithelial-like cells. Such a strategy supports the potential applications of human DCs and hESCs in corneal epithelium tissue engineering.