Modeling inherited retinal diseases using human induced pluripotent stem cell derived photoreceptor cells and retinal pigment epithelial cells.

Since the discovery of induced pluripotent stem cell (iPSC) technology, there have been many attempts to create cellular models of inherited retinal diseases (IRDs) for investigation of pathogenic processes to facilitate target discovery and validation activities. Consistency remains key in determining the utility of these findings. Despite the importance of consistency, quality control metrics are still not widely used. In this review, a toolkit for harnessing iPSC technology to generate photoreceptor, retinal pigment epithelial cell, and organoid disease models is provided. Considerations while developing iPSC-derived IRD models such as iPSC origin, reprogramming methods, quality control metrics, control strategies, and differentiation protocols are discussed. Various iPSC IRD models are dissected and the scientific hurdles of iPSC-based disease modeling are discussed to provide an overview of current methods and future directions in this field.

Dysfunctional Autophagy, Proteostasis, and Mitochondria as a Prelude to Age-Related Macular Degeneration.

Retinal pigment epithelial (RPE) cell dysfunction is a key driving force of AMD. RPE cells form a metabolic interface between photoreceptors and choriocapillaris, performing essential functions for retinal homeostasis. Through their multiple functions, RPE cells are constantly exposed to oxidative stress, which leads to the accumulation of damaged proteins, lipids, nucleic acids, and cellular organelles, including mitochondria. As miniature chemical engines of the cell, self-replicating mitochondria are heavily implicated in the aging process through a variety of mechanisms. In the eye, mitochondrial dysfunction is strongly associated with several diseases, including age-related macular degeneration (AMD), which is a leading cause of irreversible vision loss in millions of people globally. Aged mitochondria exhibit decreased rates of oxidative phosphorylation, increased reactive oxygen species (ROS) generation, and increased numbers of mitochondrial DNA mutations. Mitochondrial bioenergetics and autophagy decline during aging because of insufficient free radical scavenger systems, the impairment of DNA repair mechanisms, and reductions in mitochondrial turnover. Recent research has uncovered a much more complex role of mitochondrial function and cytosolic protein translation and proteostasis in AMD pathogenesis. The coupling of autophagy and mitochondrial apoptosis modulates the proteostasis and aging processes. This review aims to summarise and provide a perspective on (i) the current evidence of autophagy, proteostasis, and mitochondrial dysfunction in dry AMD; (ii) current in vitro and in vivo disease models relevant to assessing mitochondrial dysfunction in AMD, and their utility in drug screening; and (iii) ongoing clinical trials targeting mitochondrial dysfunction for AMD therapeutics.

Impact of Microplastics on the Ocular Surface.

Plastics are synthetic materials made from organic polymers that are ubiquitous in daily living and are especially important in the healthcare setting. However, recent advances have revealed the pervasive nature of microplastics, which are formed by degradation of existing plastic products. Although the impact on human health has yet to be fully characterised, there is increasing evidence that microplastics can trigger inflammatory damage, microbial dysbiosis, and oxidative stress in humans. Although there are limited studies investigating their effect on the ocular surface, studies of microplastics on other organs provide some insights. The prevalence of plastic waste has also triggered public outcry, culminating in the development of legislation aimed at reducing microplastics in commercial products. We present a review outlining the possible sources of microplastics leading to ocular exposure, and analyse the possible mechanisms of ocular surface damage. Finally, we examine the utility and consequences of current legislation surrounding microplastic regulation.

Treat and extend regimen for diabetic macular oedema-a systematic review and meta-analysis.

PURPOSE: Various treatment regimens are currently practiced in the treatment of CI-DMO (centre-involving diabetic macular oedema). In recent years, there has been a growing body of evidence supporting a treat and extend (T&E) regimen for DMO which offers the promise of comparable visual and anatomical outcomes while reducing injection burden. This meta-analysis was hence performed to evaluate the aforementioned outcomes in the treatment of DMO. Ten studies met the inclusion criteria. METHODS: A search of PubMed, MEDLINE, Current Contents, and Cochrane Central Register of Controlled Trials (CENTRAL) databases was performed. We employed the terms 'treat AND extend AND (diabetic AND macular AND edema OR oedema)' to ensure a comprehensive search. The search workflow adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. RESULTS: The pooled analysis of the mean number of injections in 1 year for T&E-aflibercept (AFL), T&E-ranibizumab (RBZ) and collectively was 9.1 (95% CI: 7.63-10.63), 10.0 (95% CI: 9.55-10.47) and 9.6 (95% CI: 8.62-10.49), respectively. Improvements in vision at 1 year for T&E-AFL, T&E-RBZ and collectively were 6.26 (95% CI: 3.24-9.29), 7.14 (95% CI: 4.76-9.52) and 7.08 (95% CI: 5.32-8.84) letters, respectively. The improvements in central subfield thickness at 1 year for T&E-AFL, T&E-RBZ and collectively were 131.94 (95% CI: 100.29-163.60), 108.64 (95% CI: 82.82-134.46) and 121.32 (95% CI: 102.89-139.75) microns, respectively. CONCLUSION: The meta-analysis of T&E for DMO did not show a clear advantage in reducing the number of injections compared to landmark clinical trials with pro-re-nata (PRN) treatment regimens in the first year of treatment with limited gains in visual and anatomical outcomes. However, the T&E approach offers the potential for fewer patient visits, thereby reducing treatment burden. Longer term studies on T&E with a standardised protocol would be required to assess the longevity of the vision gain in the first year despite a likely reduced treatment burden compared to the PRN trials.

Polymeric biomaterials in the treatment of posterior segment diseases.

Polymeric biomaterials are biological or synthetic substances which can be engineered to interact with biological systems for the diagnosis or treatment of diseases. These biomaterials have immense potential for treating eyes diseases, particularly the retina-a site of many inherited and acquired diseases. Polymeric biomaterials can be engineered to function both as an endotamponade agent and to prevent intraocular scarring in retinal detachment repair surgeries. They can also be designed as a drug delivery platform for treatment of retinal diseases. Finally, they can be used as scaffolds for cellular products and provide non-viral gene delivery solutions to the retina. This perspective article explains the role of polymeric biomaterials in the treatment of retinal conditions by highlighting recent advances being translated to clinical practice. The article will also identify potential hurdles to clinical translation as future research directions in the field.

Developing Non-Human Primate Models of Inherited Retinal Diseases.

Inherited retinal diseases (IRDs) represent a genetically and clinically heterogenous group of diseases that can eventually lead to blindness. Advances in sequencing technologies have resulted in better molecular characterization and genotype-phenotype correlation of IRDs. This has fueled research into therapeutic development over the recent years. Animal models are required for pre-clinical efficacy assessment. Non-human primates (NHP) are ideal due to the anatomical and genetic similarities shared with humans. However, developing NHP disease to recapitulate the disease phenotype for specific IRDs may be challenging from both technical and cost perspectives. This review discusses the currently available NHP IRD models and the methods used for development, with a particular focus on gene-editing technologies.

Endothelial cell loss associated with minimally invasive glaucoma surgery.

PURPOSE OF REVIEW: Minimally invasive glaucoma surgery (MIGS) represents a safer, albeit moderately effective surgical option for intraocular pressure control. However, the CyPass Micro-Stent (Alcon Laboratories) was withdrawn from the market in 2018 as the COMPASS-XT study demonstrated greater cornea endothelial cell (CEC) loss in patients who received the CyPass Micro-Stent with phacoemulsification compared with phacoemulsification alone. This led to the increased attention on MIGS-associated CEC loss and thus, this review will summarise the recent, available evidence on MIGS-associated CEC loss. RECENT FINDINGS: Prospective clinical trials and retrospective observational studies published between 2011 and 2021 reported a wide range of 12 month CEC loss from 'insignificant', and up to 14.6%, for phacoemulsification combined with various MIGS procedures. Recent clinical trials over the same time period reported CEC loss of 12.8-15.2% associated with phacoemulsification alone. SUMMARY: Apart from the CyPass Micro-Stent clinical trial, no other studies on combined phacoemulsification with MIGS that is 'phaco-plus' procedures have reported a higher short-term CEC loss compared with phacoemulsification alone. However, studies that specifically examine postprocedural CEC loss following phacoemulsification compared to 'phaco-plus' procedures over a longer follow-up period are required.

Antiangiogenic Nanomicelles for the Topical Delivery of Aflibercept to Treat Retinal Neovascular Disease.

The traditional intravitreal injection delivery of antivascular endothelial growth factor (anti-VEGF) to the posterior segment of the eye for treatment of retinal diseases is invasive and associated with sight-threatening complications. To avoid such complications, there has been significant interest in developing polymers for topical drug delivery to the retina. This study reports a nanomicelle drug delivery system made of a copolymer EPC (nEPCs), which is capable of delivering aflibercept to the posterior segment topically through corneal-scleral routes. EPC is composed of poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and polycaprolactone (PCL) segments. In this study, aflibercept-loaded nEPCs (nEPCs + A) are capable of penetrating the cornea in ex vivo porcine eye models and deliver a clinically significant amount of aflibercept to the retina in laser-induced choroidal neovascularization (CNV) murine models, causing CNV regression. nEPCs + A also demonstrate biocompatibility in vitro and in vivo. Interestingly, this study also suggests that nEPCs have intrinsic antiangiogenic properties. The ability to deliver anti-VEGF drugs and the intrinsic antiangiogenic properties of nEPCs may result in synergistic effects, which can be harnessed for effective therapeutics. nEPCs may be a promising topical anti-VEGF delivery platform for the treatment of retinal diseases.

Retinal Pigment Epithelium Transplantation in a Non-human Primate Model for Degenerative Retinal Diseases.

Retinal pigment epithelial (RPE) transplantation holds great promise for the treatment of inherited and acquired retinal degenerative diseases. These conditions include retinitis pigmentosa (RP) and advanced forms of age-related macular degeneration (AMD), such as geographic atrophy (GA). Together, these disorders represent a significant proportion of currently untreatable blindness globally. These unmet medical needs have generated heightened academic interest in developing methods of RPE replacement. Among the animal models commonly utilized for preclinical testing of therapeutics, the non-human primate (NHP) is the only animal model that has a macula. As it shares this anatomical similarity with the human eye, the NHP eye is an important and appropriate preclinical animal model for the development of advanced therapy medicinal products (ATMPs) such as RPE cell therapy. This manuscript describes a method for the submacular transplantation of an RPE monolayer, cultured on a polyethylene terephthalate (PET) cell carrier, underneath the macula onto a surgically created RPE wound in immunosuppressed NHPs. The fovea-the central avascular portion of the macula-is the site of the greatest mechanical weakness during the transplantation. Foveal trauma will occur if the initial subretinal fluid injection generates an excessive force on the retina. Hence, slow injection under perfluorocarbon liquid (PFCL) vitreous tamponade is recommended with a dual-bore subretinal injection cannula at low intraocular pressure (IOP) settings to create a retinal bleb. Pretreatment with an intravitreal plasminogen injection to release parafoveal RPE-photoreceptor adhesions is also advised. These combined strategies can reduce the likelihood of foveal tears when compared to conventional techniques. The NHP is a key animal model in the preclinical phase of RPE cell therapy development. This protocol addresses the technical challenges associated with the delivery of RPE cellular therapy in the NHP eye.

Surgical Transplantation of Human RPE Stem Cell-Derived RPE Monolayers into Non-Human Primates with Immunosuppression.

Recent trials of retinal pigment epithelium (RPE) transplantation for the treatment of disorders such as age-related macular degeneration have been promising. However, limitations of existing strategies include the uncertain survival of RPE cells delivered by cell suspension and the inherent risk of uncontrolled cell proliferation in the vitreous cavity. Human RPE stem cell-derived RPE (hRPESC-RPE) transplantation can rescue vision in a rat model of retinal dystrophy and survive in the rabbit retina for at least 1 month. The present study placed hRPESC-RPE monolayers under the macula of a non-human primate model for 3 months. The transplant was able to recover in vivo and maintained healthy photoreceptors. Importantly, there was no evidence that subretinally transplanted monolayers underwent an epithelial-mesenchymal transition. Neither gliosis in adjacent retina nor epiretinal membranes were observed. These findings suggest that hRPESC-RPE monolayers are safe and may be a useful source for RPE cell replacement therapy.

A Pilot Study on MicroRNA Profile in Tear Fluid to Predict Response to Anti-VEGF Treatments for Diabetic Macular Edema.

(1) Background: Intravitreal anti-vascular endothelial growth factor (anti-VEGF) is an established treatment for center-involving diabetic macular edema (ci-DME). However, the clinical response is heterogeneous. This study investigated miRNAs as a biomarker to predict treatment response to anti-VEGF in DME. (2) Methods: Tear fluid, aqueous, and blood were collected from patients with treatment-naïve DME for miRNA expression profiling with quantitative polymerase chain reaction. Differentially expressed miRNAs between good and poor responders were identified from tear fluid. Bioinformatics analysis with the miEAA tool, miRTarBase Annotations, Gene Ontology categories, KEGG, and miRWalk pathways identified interactions between enriched miRNAs and biological pathways. (3) Results: Of 24 participants, 28 eyes received bevacizumab (15 eyes) or aflibercept (13 eyes). Tear fluid had the most detectable miRNA species (N = 315), followed by serum (N = 309), then aqueous humor (N = 134). MiRNAs that correlated with change in macular thickness were miR-214-3p, miR-320d, and hsa-miR-874-3p in good responders; and miR-98-5p, miR-196b-5p, and miR-454-3p in poor responders. VEGF-related pathways and the angiogenin-PRI complex were enriched in good responders, while transforming growth factor-ß and insulin-like growth factor pathways were enriched in poor responders. (4) Conclusions: We reported a panel of novel miRNAs that provide insight into biological pathways in DME. Validation in larger independent cohorts is needed to determine the predictive performance of these miRNA candidate biomarkers.

Correction: Use of biomaterials for sustained delivery for anti-VEGF to treat retinal diseases.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Can the Coronavirus Disease 2019 (COVID-19) Affect the Eyes? A Review of Coronaviruses and Ocular Implications in Humans and Animals.

In December 2019, a novel coronavirus (CoV) epidemic, caused by the severe acute respiratory syndrome coronavirus - 2 (SARS-CoV-2) emerged from China. This virus causes the coronavirus disease 2019 (COVID-19). Since then, there have been anecdotal reports of ocular infection. The ocular implications of human CoV infections have not been widely studied. However, CoVs have been known to cause various ocular infections in animals. Clinical entities such as conjunctivitis, anterior uveitis, retinitis, and optic neuritis have been documented in feline and murine models. In this article, the current evidence suggesting possible human CoV infection of ocular tissue is reviewed. The review article will also highlight animal CoVs and their associated ocular infections. We hope that this article will serve as a start for further research into the ocular implications of human CoV infections.