Retinal pigment epithelium translocation and central visual function in age related macular degeneration: preliminary results

Electronic retinal prosthesis for severe loss of vision in geographic atrophy in age-related macular degeneration: First-in-human use

BACKGROUND

To date there are yet no available approved therapies for Geographic Atrophy (GA) secondary to age-related macular degeneration (AMD).

METHODS

Single site, non-randomized safety and efficacy study presenting the preliminary results in a cohort of five late stage AMD (GA) patients successfully implanted with the Argus II Retinal Prosthesis System (Second Sight Medical Products Inc., Sylmar, CA, USA). Extensive fundus imaging including retinal photographs from which the GA area was measured. A combination of custom and traditional tests designed for very low vision subjects assessed visual function in study subjects. A Functional Low-Vision Observer Rated Assessment was carried out to evaluate the impact of the system on the subject's daily life. In addition, a study to evaluate structural characteristics of the visual cortex of the brain was performed in one subject using magnetic resonance imaging.

RESULTS

Seven device-related adverse events were reported, four of which were classed as serious adverse events. Retinal detachment was reported in three patients and was successfully treated within 12 months of onset. Testing showed an improvement in visual function in three of five patients with the system turned on. Magnetic resonance imaging assessed in one patient after implantation indicates a selective increase in cortical myelin and thickness in visual brain regions 1 year post implantation.

CONCLUSIONS

Epiretinal prostheses can successfully be implanted in those affected by GA secondary to late-stage AMD and can elicit visual percepts by electrical stimulation of residual neuroretinal elements and improve basic visual function in those affected.

Stem cell therapies for retinal diseases: from bench to bedside

As the human retina has no regenerative ability, stem cell interventions represent potential therapies for various blinding retinal diseases. This type of therapy has been extensively studied in the human eyes through decades of preclinical studies. The safety profiles shown in clinical trials thus far have indicated that these strategies should be further explored. There are still challenges with regard to cell source, cell delivery, immuno-related adverse events and long-term maintenance of the therapeutic effects. Retinal stem cell therapy is likely to be most successful with a combination of multiple technologies, such as gene therapy. The purpose of this review is to present a synthetical and systematic coverage of stem cell therapies that target retinal diseases from bench to bedside, intending to appeal to both junior specialists and the broader community of clinical investigators alike. This review will only focus on therapies that have already been studied in clinical trials. This review summarizes key concepts, highlights the main studies in human patients and discusses the current challenges and potential methods to reduce safety concerns while enhancing the therapeutic effects.

Clinical Trials in Retinal Dystrophies

Research development is burgeoning for genetic and cellular therapy for retinal dystrophies. These dystrophies are the focus of many research efforts due to the unique biology and accessibility of the eye, the transformative advances in ocular imaging technology that allows for in vivo monitoring, and the potential benefit people would gain from success in the field – the gift of renewed sight. Progress in the field has revealed the immense complexity of retinal dystrophies and the challenges faced by researchers in the development of this technology. This study reviews the current trials and advancements in genetic and cellular therapy in the treatment of retinal dystrophies and also discusses the current and potential future challenges.

Retinal pigment epithelium transplantation: concepts, challenges, and future prospects

The retinal pigment epithelium (RPE) is a single layer of cells that supports the light-sensitive photoreceptor cells that are essential for retinal function. Age-related macular degeneration (AMD) is a leading cause of visual impairment, and the primary pathogenic mechanism is thought to arise in the RPE layer. RPE cell structure and function are well understood, the cells are readily sustainable in laboratory culture and, unlike other cell types within the retina, RPE cells do not require synaptic connections to perform their role. These factors, together with the relative ease of outer retinal imaging, make RPE cells an attractive target for cell transplantation compared with other cell types in the retina or central nervous system. Seminal experiments in rats with an inherited RPE dystrophy have demonstrated that RPE transplantation can prevent photoreceptor loss and maintain visual function. This review provides an update on the progress made so far on RPE transplantation in human eyes, outlines potential sources of donor cells, and describes the technical and surgical challenges faced by the transplanting surgeon. Recent advances in the understanding of pluripotent stem cells, combined with novel surgical instrumentation, hold considerable promise, and support the concept of RPE transplantation as a regenerative strategy in AMD.

Regenerating Retinal Pigment Epithelial Cells to Cure Blindness: A Road Towards Personalized Artificial Tissue

Retinal pigment epithelium (RPE) is a polarized monolayer tissue that functions to support the health and integrity of retinal photoreceptors (PRs). RPE atrophy has been linked to pathogenesis of age-related macular degeneration (AMD), a leading cause of blindness in elderly in the USA. RPE atrophy in AMD leads to the PR cell death and vision loss. It is thought that replacing diseased RPE with healthy RPE tissue can prevent PR cell death. Retinal surgical innovations have provided proof-of-principle data that autologous RPE tissue can replace diseased macular RPE and provide visual rescue in AMD patients. Current efforts are focused on developing an in vitro tissue using natural and synthetic scaffolds to generate a polarized functional RPE monolayer. In the future, these tissue-engineering approaches combined with pluripotent stem cell technology will lead to the development of personalized and "off-the-shelf" cell therapies for AMD patients. This review summarizes the historical development and ongoing efforts in surgical and in vitro tissue engineering techniques to develop a three-dimensional therapeutic native RPE tissue substitute.

25th RCOphth Congress, President's Session paper: 25 years of progress in vitreoretinal surgery

Over the past 25 years, vitreoretinal surgery has undergone considerable change in technology, techniques, and professional organisation. Many conditions that were considered untreatable in 1988 are now treated routinely by vitreoretinal surgeons. Over the same period, vitreoretinal surgery has become a separate subspecialty with its own scientific meetings and professional organisation. This article describes a noncomprehensive selection of some of the highlights of the past 25 years, including the establishment and growth of BEAVRS (British and Eire Association of Vitreoretinal Surgeons), the revolution in the management of macular holes, the development of submacular surgery, and the introduction of sutureless vitrectomy.

A pedicled autologous choroid RPE patch: a technique to preserve perfusion

The aim of the study is to report a technique of a pedicled autologous choroid retinal pigment epithelium (RPE) patch that aims to preserve perfusion of the transplanted tissue. A case report of a patient with sudden vision deterioration due to submacular hemorrhage in age-related macular degeneration. The surgery involved a 180-degree peripheral retinectomy and the creation of a pedicled graft instead of an isolated one. Outcome measures included preoperative and postoperative visual acuity and optical coherence tomography scans at 1, 3, 6, 12 months and patch vascularization on postoperative indocyanine green angiography. Postoperatively the patch was positioned under the fovea with an intact pedicle. Indocyanine green angiography showed perfusion through the pedicle and patch vasculature on the third postoperative day. Best corrected visual acuity improved from 0.5/50 to 5/50 at 1 month and remained stable over 1 year follow-up. No choroidal neovascularization recurrence was observed. This case report demonstrates the feasibility of a pedicled RPE-choroid graft that is an alternative to a free isolated graft. Our modification of patch surgery, by demonstrating early perfusion, offers an advantage, similar to macular translocation, when photoreceptors are embedded in RPE and choroid with blood circulation immediately after the surgery.

A free retinal pigment epithelium-choroid graft in patients with exudative age-related macular degeneration: results up to 7 years

PURPOSE

To report and analyze long-term best-corrected visual acuity (BCVA) outcomes following a free autologous retinal pigment epithelium (RPE)-choroid graft translocation in patients with exudative age-related macular degeneration (AMD).

DESIGN

Prospective cohort study.

METHODS

SETTING

Institutional.

STUDY POPULATION

One hundred and thirty consecutive patients (133 eyes) with AMD underwent RPE-choroid graft translocation between October 2001 and February 2006. All patients had a subfoveal choroidal neovascular membrane with or without hemorrhage and/or an RPE tear. All were either ineligible for or nonresponsive to photodynamic therapy, the standard treatment at the time of surgery.

OBSERVATION PROCEDURES

Data collection included preoperative and postoperative visual acuity measurements, fundus photography, fluorescein and indocyanine green angiography, and microperimetry.

MAIN OUTCOME MEASURES

Postoperative BCVA.

RESULTS

The mean preoperative BCVA was 20/250. Four years after surgery, 15% of the eyes had a BCVA of >20/200, and 5% had a BCVA of ≥20/40. One patient achieved a BCVA of 20/32, which was maintained at 7 years after surgery. Complications consisted of proliferative vitreoretinopathy (n = 13), recurrent neovascularization (n = 13), and hypotony (n = 2).

CONCLUSIONS

RPE-choroid graft transplantation may maintain macular function for up to 7 years after surgery, with relatively low complication and recurrence rates. Retinal sensitivity, BCVA data, and fixation on the graft suggest that the graft, rather than simply the removal of submacular hemorrhage and/or choroidal neovascular membrane, was responsible for the preservation of macular function. This surgery may be an alternative for patients with AMD who cannot undergo other standard treatment.

Subretinal transplantation of forebrain progenitor cells in nonhuman primates: survival and intact retinal function

PURPOSE

Cell-based therapy rescues retinal structure and function in rodent models of retinal disease, but translation to clinical practice will require more information about the consequences of transplantation in an eye closely resembling the human eye. The authors explored donor cell behavior using human cortical neural progenitor cells (hNPC(ctx)) introduced into the subretinal space of normal rhesus macaques.

METHODS

hNPC(ctx) transduced with green fluorescent protein (hNPC(ctx)-GFP) were delivered bilaterally into the subretinal space of six normal adult rhesus macaques under conditions paralleling those of the human operating room. Outcome measures included clinical parameters of surgical success, multifocal electroretinogram (mfERG), and histopathologic analyses performed between 3 and 39 days after engraftment. To test the effects of GFP transduction on cell bioactivity, hNPC(ctx)-GFP from the same batch were also injected into Royal College of Surgeons (RCS) rats and compared with nonlabeled hNPC(ctx).

RESULTS

Studies using RCS rats indicated that GFP transduction did not alter the ability of the cells to rescue vision. After cells were introduced into the monkey subretinal space by a pars plana transvitreal approach, the resultant detachment was rapidly resolved, and retinal function showed little or no disturbance in mfERG recordings. Retinal structure was unaffected and no signs of inflammation or rejection were seen. Donor cells survived as a single layer in the subretinal space, and no cells migrated into the inner retina.

CONCLUSIONS

Human neural progenitor cells can be introduced into a primate eye without complication using an approach that would be suitable for extrapolation to human patients.

Histological evidence for revascularisation of an autologous retinal pigment epithelium--choroid graft in the pig

BACKGROUND

Translocation of a free autologous graft consisting of retinal pigment epithelium (RPE), Bruch's membrane, choriocapillaris and choroid in patients with exudative age-related macular degeneration is currently being evaluated in clinical practice. Angiographic studies in these patients suggest that their grafts become revascularised.

AIM

To investigate the histological evidence of revascularisation of the graft in a porcine model.

METHODS

In 11 pigs (11 eyes), an RPE-choroid graft was translocated from the mid-periphery to an intact or an intentionally damaged RPE and Bruch's membrane at the recipient site. The eyes were enucleated 1 week or 3 months after surgery. Tissue sections were evaluated using immunohistochemistry.

RESULTS

Bridging vessels between recipient layer and graft were identified from 1 week to 3 months after surgery. This reconnection occurred regardless of whether the Bruch's membrane of the recipient site was left intact or intentionally damaged at the time of transplantation. The vasculature of the graft appeared open and perfused. Vessels with transcapillary pillars and conglomerates of small new vessels were present in the graft.

CONCLUSIONS

This study showed histological evidence for revascularisation by angiogenesis of a free autologous RPE-choroid graft.