Implantation of an Artificial Endothelial Layer for Treatment of Chronic Corneal Edema

Emerging alternatives to keratoplasty for corneal endothelial cell dysfunction

PURPOSE OF REVIEW

While effective for treating endothelial dysfunction, keratoplasty has shortcomings including limited access to donor tissue for much of the world. Thus, alternative strategies are under development. This review explores the main advancements achieved in this field during 2022-2023.

RECENT FINDINGS

Recent publications further support the validity of intracameral cultivated allogeneic endothelial cell injection and Descemet stripping only, while emphasizing the benefits of adjunctive Rho-associated kinase inhibitor (ROCKi) therapy. New donor-independent artificial implants, such as EndoArt, show favorable results. Multiple pharmacologic agents, especially ROCKi, show promise as monotherapies, yet none are currently approved for human treatment. Multiple regenerative and genetic therapies are being investigated but all are still in preclinical stages.

SUMMARY

A plethora of innovative alternatives to keratoplasty for endothelial disease is in development. Among these, surgical methods are still the mainstay of treatment and closest to clinical application, though further studies to establish their benefits over keratoplasty are needed. Albeit promising, pharmacologic, regenerative, and genetic approaches require validation and are farther from clinical application.

Early Outcomes of an Artificial Endothelial Replacement Membrane Implantation After Failed Repeat Endothelial Keratoplasty

PURPOSE

The purpose of this study was to report the outcomes of a novel artificial endothelial replacement membrane implant for treating corneal edema after failed repeat endothelial keratoplasty (EK).

DESIGN

This was a retrospective interventional case series.

METHODS

Patients with chronic corneal edema underwent removal of the EK graft and implantation of an artificial endothelial replacement membrane (EndoArt, EyeYon Medical, Israel) several months after 2 or more Descemet stripping endothelial keratoplasty procedures. The implant was secured to the posterior corneal surface using an air-gas bubble. Outcome measures included corrected distance visual acuity (logMAR), central corneal thickness, device-related complications, and ocular discomfort.

RESULTS

Five eyes of 5 patients underwent EndoArt implantation. Six months after surgery, the synthetic endothelial replacement membrane was well-centered and adherent to the posterior corneal surface, with improvement in central corneal transparency in all patients. Corrected distance visual acuity increased from mean 1.26 ± 0.25 (logMAR) preoperatively to 0.74 ± 0.44 (logMAR) postoperatively ( P = 0.06). Central corneal thickness significantly decreased from a mean of 805 ± 135 μm (excluding the EK graft) preoperatively to 588 ± 60 μm (excluding the EndoArt) postoperatively ( P = 0.015). No severe device-related complications developed after surgery, although most patients required more than 1 air-gas bubble injection to achieve complete implant adhesion. All patients experienced preoperative reduction in subjective ocular pain.

CONCLUSIONS

Synthetic endothelial replacement membrane implantation improves central corneal transparency and visual acuity in patients with failed EK and guarded prognosis for repeat keratoplasty. No significant implant-related adverse events occurred after surgery.

Potential of an Amphiphilic Artificial Corneal Endothelial Layer as a Replacement Option for Damaged Corneal Endothelium

Bullous keratopathy, a condition severely impacting vision and potentially leading to corneal blindness, necessitates corneal transplantation. However, the shortage of donor corneas and complex surgical procedures drive the exploration of tissue-engineered corneal endothelial layers. This study develops a transparent, amphiphilic, and cell-free membrane for corneal endothelial replacement. The membrane, securely attached to the posterior surface of the cornea, is created by mixing hydroxyethyl methacrylate (HEMA) and ethylene glycol dimethylacrylate (EGDMA) in a 10:1 ratio. A 50 µL volume is used to obtain a 60 µm hydrophobic membrane on both sides, with one side treated with a polyvinylpyrrolidone (PVP) solution. The resulting membrane is transparent, foldable, biocompatible, amphiphilic, and easily handled. When exposed to 20% sulfur hexafluoride (SF6), the hydrophilic side of the membrane adheres tightly to the corneal Descemet's membrane, preventing water absorption into the corneal stroma, and thus treating bullous keratopathy. Histological test confirms its effectiveness, showing normal corneal structure and low inflammation when implanted in rabbits for up to 100 d. This study showcases the potential of this membrane as a viable option for corneal endothelial replacement, offering a novel approach to address donor tissue scarcity in corneal transplantation.

Exploring single-cell RNA sequencing as a decision-making tool in the clinical management of Fuchs' endothelial corneal dystrophy

Single-cell RNA sequencing (scRNA-seq) has enabled the identification of novel gene signatures and cell heterogeneity in numerous tissues and diseases. Here we review the use of this technology for Fuchs' Endothelial Corneal Dystrophy (FECD). FECD is the most common indication for corneal endothelial transplantation worldwide. FECD is challenging to manage because it is genetically heterogenous, can be autosomal dominant or sporadic, and progress at different rates. Single-cell RNA sequencing has enabled the discovery of several FECD subtypes, each with associated gene signatures, and cell heterogeneity. Current FECD treatments are mainly surgical, with various Rho kinase (ROCK) inhibitors used to promote endothelial cell metabolism and proliferation following surgery. A range of emerging therapies for FECD including cell therapies, gene therapies, tissue engineered scaffolds, and pharmaceuticals are in preclinical and clinical trials. Unlike conventional disease management methods based on clinical presentations and family history, targeting FECD using scRNA-seq based precision-medicine has the potential to pinpoint the disease subtypes, mechanisms, stages, severities, and help clinicians in making the best decision for surgeries and the applications of therapeutics. In this review, we first discuss the feasibility and potential of using scRNA-seq in clinical diagnostics for FECD, highlight advances from the latest clinical treatments and emerging therapies for FECD, integrate scRNA-seq results and clinical notes from our FECD patients and discuss the potential of applying alternative therapies to manage these cases clinically.

How Would Nature See Our Corneal Triumphs? The LXXIX Edward Jackson Lecture

PURPOSE

To describe discrepancies between clinical observation and current teachings in corneal endothelial disease, particularly in Fuchs endothelial dystrophy and its potential association with primary open angle glaucoma.

DESIGN

Perspective.

METHODS

A perspective is presented on Fuchs dystrophy, a disorder that commonly presents with a compromised endothelium but minimal stromal edema, indicating that the corneal imbibition pressure is relatively "too high."

RESULTS

The discrepancy between the relative lack of stromal edema in the absence of an endothelial cell layer cannot be explained by the current theories involving a circulatory pumping mechanism over the endothelial cell layer, but may point to the following: (1) secondary involvement of the corneal endothelium in Fuchs dystrophy; (2) separate hydration systems for maintaining the imbibition pressure (vertical static hydration) and corneal nutrition (horizontal dynamic hydration); (3) the cornea as net contributor of aqueous humor; (4) a close relationship between the corneal imbibition and intraocular pressure, with potentially a shared regulatory system; and (5) a potential steroid-type hormone dependency of this regulatory system.

CONCLUSIONS

Clinical observation shows that the stromal imbibition pressure is "too high" in Fuchs endothelial dystrophy, indicating that it may not primarily be an endothelial disease, but a type of "corneal glaucoma."

Artificial Endothelial Layer Implantation After Multiple Failed Keratoplasties

PURPOSE

Presenting the first case of noncellular corneal endothelial substitute after multiple failed penetrating keratoplasty (PK) and lamellar endothelial keratoplasty.

METHODS

Our case presented with pseudophakic bullous keratopathy after a history of 2 rejected PKs and 1 rejected Descemet stripping automated endothelial keratoplasty. We implanted an artificial endothelial layer.

RESULTS

The implant remained fully attached for a follow-up period of 12 months, and central corneal thickness decreased significantly. The patient reported improvement in her subjective vision, although ocular comorbidities limited the visual potential.

CONCLUSIONS

This new device could serve as an alternative to lamellar endothelial corneal transplantation in cases where tissue rejection has occurred and is highly likely to recur. The technique is simple, and the deswelling effect on the cornea persisted, although the visual results require further validation in patients with a higher visual potential.

Effect of Anterior Chamber Air on Central Corneal Thickness in Human Donor Eyes

PURPOSE

The purpose of this study was to describe the effects of intracameral air on corneal edema.

METHODS

A laboratory investigation was performed on human donor corneas. Baseline pachymetry measurements through anterior segment optical coherence tomography and endothelial cell density were obtained for all corneas. Each pair of corneas was separated and randomly assigned to undergo air injection or Optisol-GS into a BIONIKO artificial anterior chamber for 5 minutes at physiologic intraocular pressure confirmed by digital palpation. Photographs were obtained immediately on connection of the cornea to the artificial anterior chamber and on completion of the 5 minutes of treatment, with anterior chamber air being exchanged for Optisol-GS. Pretreatment and posttreatment photographs were obtained. Immediately after treatment, pachymetry was again obtained on all corneas. Pachymetry data underwent statistical analysis.

RESULTS

Corneal pachymetry improved from 690.5 ± 126.6 to 576.1 ± 87.2 μm, yielding a 114.4 ± 50.4 μm improvement of pachymetry in the group with air injected into the anterior chamber. This was a significant improvement of pachymetry when compared with the group with Optisol-GS injected into the anterior chamber, which showed an improvement from 662.3 ± 126.5 to 613.5 ± 108.0 μm, yielding an improvement of 48.8 ± 34.3 μm.

CONCLUSIONS

Injection of air into the anterior chamber leads to a significant decrease in corneal pachymetry. We thereby propose that injecting air intracamerally is an effective intraoperative intervention when visualization is negatively affected by corneal edema.

Development of Thermoplastic Polyurethane Films for the Replacement of Corneal Endothelial Function of Transparency Maintenance

Endothelial keratoplasty is the main surgical procedure for treating corneal endothelial dysfunction (CED), which is limited by the global shortage of donor corneas. Herein, we developed and evaluated the modified thermoplastic polyurethane (M-TPU) films with gelatin-glycidyl methacrylate to replace the corneal endothelial function and maintain corneal transparency. The films displayed comparable light transmission characteristics with normal corneas and clinically favorable mechanical properties for surgical manipulation. After surface modification, the hydrophilicity and biocompatibility of M-TPU films were significantly improved. In the rabbit CED model, the M-TPU implants exhibited firm adhesion to the exposed stromal surface. The rabbit corneal transparency and thickness could be restored completely within 1 week of M-TPU film implantation. There was no significant inflammatory reaction and immune rejection during the follow-up of 1 month. Proteomic analysis suggested that the complement inhibition, the increase of mineral absorption, and the decrease of P53 apoptosis signaling pathway and lysine degradation might be beneficial in maintaining the corneal transparency. Overall, our study demonstrated the potential of M-TPU films as artificial implants for the replacement of corneal endothelial function to restore corneal thickness and transparency.

Pull-through insertion of EndoArt for complex eyes

Purpose

To report an alternative technique to implant the EndoArt using a pull-through insertion. This technique is helpful in complex eyes, especially in eyes with unstable iris lens diaphragm.

Observation

We present a case of advanced pseudophakic bullous keratopathy with aniridia, previous vitrectomy, and tube implants in which the initial attempt to implant the EndoArt failed, and the device was lost to the vitreous cavity. An alternative surgical technique, a pull-through insertion, was used to implant a second device successfully. The patient was followed over a period of 1 year. Corneal edema gradually improved over time, and all epithelial bullae resolved. The central corneal thickness (CCT) decreased from 911um to 691 μm.

Conclusion and Importance

EndoArt is a treatment for endothelial failure in complex eyes. In addition, the pull-through insertion technique can help improve control over the implant in very complicated eyes.

Ex vivo cultivated retinal pigment epithelial cell transplantation for the treatment of rabbit corneal endothelial dysfunction

OBJECTIVE

Stem cell therapy is a promising strategy for the treatment of corneal endothelial dysfunction, and the need to find functional alternative seed cells of corneal endothelial cells (CECs) is urgent. Here, we determined the feasibility of using the retinal pigment epithelium (RPE) as an equivalent substitute for the treatment of corneal endothelial dysfunction.

METHODS

RPE cells and CECs in situ were obtained from healthy New Zealand male rabbits, and the similarities and differences between them were analyzed by electron microscopy, immunofluorescent staining, and quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). Rabbit primary RPE cells and CECs were isolated and cultivated ex vivo, and Na+/K+-ATPase activity and cellular permeability were detected at passage 2. The injection of cultivated rabbit primary RPE cells, CECs and human embryonic stem cell (hESC)-derived RPE cells was performed on rabbits with corneal endothelial dysfunction. Then, the therapeutic effects were evaluated by corneal transparency, central corneal thickness, enzyme linked immunosorbent assay (ELISA), qRT-PCR and immunofluorescent staining.

RESULTS

The rabbit RPE cells were similar in form to CECs in situ and ex vivo, showing a larger regular hexagonal shape and a lower cell density, with numerous tightly formed cell junctions and hemidesmosomes. Moreover, RPE cells presented a stronger barrier and ionic pumping capacity than CECs. When intracamerally injected into the rabbits, the transplanted primary RPE cells could dissolve corneal edema and decrease corneal thickness, with effects similar to those of CECs. In addition, the transplantation of hESC-derived RPE cells exhibited a similar therapeutic effect and restored corneal transparency and thickness within seven days. qRT-PCR results showed that the expressions of CEC markers, like CD200 and S100A4, increased, and the RPE markers OTX2, BEST1 and MITF significantly decreased in the transplanted RPE cells. Furthermore, we have demonstrated that rabbits transplanted with hESC-derived RPE cells maintained normal corneal thickness and exhibited slight pigmentation in the central cornea one month after surgery. Immunostaining results showed that the HuNu-positive transplanted cells survived and expressed ZO1, ATP1A1 and MITF.

CONCLUSION

RPE cells and CECs showed high structural and functional similarities in barrier and pump characteristics. Intracameral injection of primary RPE cells and hESC-derived RPE cells can effectively restore rabbit corneal clarity and thickness and maintain normal corneal function. This study is the first to report the effectiveness of RPE cells for corneal endothelial dysfunction, suggesting the feasibility of hESC-derived RPE cells as an equivalent substitute for CECs.

Corneal Oedema: Aetiology, Diagnostic Testing, and Treatment

Corneal oedema results from an underlying pathology, which can be diverse in origin, and may be mechanical, dystrophic, or inflammatory, and affect any layer of the cornea. Diagnostic tools such as Scheimpflug imaging and anterior segment optical coherence tomography have standardised quantification of corneal oedema and have become important aids in clinical practice. Timely diagnosis and treatment are key to preventing irreversible damage to the corneal ultrastructure, such as anterior corneal fibrosis or endothelial cell damage. The oedema usually resolves quickly when the underlying cause has been addressed. Symptomatic treatment using hyperosmolar agents has failed to show any benefits in oedema resolution or improvement in visual acuity compared to placebo. In contrast, rho-associated protein kinase (ROCK) inhibitors offer a promising option for medical treatment in cases of endothelial dysfunction, but their safety and efficacy must be further validated in large scale clinical trials. Until then, endothelial or penetrating keratoplasties remain the mainstay treatment where structural changes to the cornea have occurred.