Light localization with low-contrast targets in a patient implanted with a suprachoroidal-transretinal stimulation retinal prosthesis

Stargardt disease and progress in therapeutic strategies

Background: Stargardt disease (STGD1) is an autosomal recessive retinal dystrophy due to mutations in ABCA4, characterized by subretinal deposition of lipofuscin-like substances and bilateral centrifugal vision loss. Despite the tremendous progress made in the understanding of STGD1, there are no approved treatments to date. This review examines the challenges in the development of an effective STGD1 therapy.Materials and Methods: A literature review was performed through to June 2021 summarizing the spectrum of retinal phenotypes in STGD1, the molecular biology of ABCA4 protein, the in vivo and in vitro models used to investigate the mechanisms of ABCA4 mutations and current clinical trials.Results: STGD1 phenotypic variability remains an challenge for clinical trial design and patient selection. Pre-clinical development of therapeutic options has been limited by the lack of animal models reflecting the diverse phenotypic spectrum of STDG1. Patient-derived cell lines have facilitated the characterization of splice mutations but the clinical presentation is not always predicted by the effect of specific mutations on retinoid metabolism in cellular models. Current therapies primarily aim to delay vision loss whilst strategies to restore vision are less well developed.Conclusions: STGD1 therapy development can be accelerated by a deeper understanding of genotype-phenotype correlations.

Retinal Implantation of Electronic Vision Prostheses to Treat Retinitis Pigmentosa: A Systematic Review

Purpose

Retinitis pigmentosa (RP) is a hereditary disease causing photoreceptor degeneration and permanent vision loss. Retinal implantation of a stimulating electrode array is a new treatment for RP, but quantification of its efficacy is the subject of ongoing work. This review evaluates vision-related outcomes resulting from retinal implantation in participants with RP.

Methods

We searched MEDLINE and Embase for journal articles published since January 1, 2015. We selected articles describing studies of implanted participants that reported the postimplantation measurement of vision. We extracted study information including design, participants’ residual vision, comparators, and assessed outcomes. To assess the risk of bias, we used signaling questions and a target trial.

Results

Our search returned 425 abstracts. We reviewed the full text of 34 articles. We judged all studies to be at high risk of bias owing to the study design or experimental conduct. Regarding design, studies lacked the measures that typical clinical trials take to protect against bias (e.g., control groups and masking). Regarding experimental conduct, outcome measures were rarely comparable before and after implantation, and psychophysical methods were prone to bias (subjective, not forced choice, methods). The most common comparison found was between postimplantation visual function with the device powered off versus on. This comparison is at high risk of bias.

Conclusions

There is a need for high-quality evidence of efficacy of retinal implantation to treat RP.

Translational Relevance

For patients and clinicians to make informed choices about RP treatment, visual function restored by retinal implantation must be properly quantified and reported.

Testing of Newly Developed Wide-Field Dual-Array Suprachoroidal-Transretinal Stimulation Prosthesis in Dogs

Purpose

This study was conducted to investigate the feasibility of a newly developed wide-field dual-array suprachoroidal–transretinal stimulation (STS) prosthesis in dogs and to examine its biocompatibility and stability over a 4-month period.

Methods

Three types of STS dual arrays were designed and tested. The STS dual-array was implanted into a scleral pocket of the left eye of six healthy beagle dogs. Ophthalmic examinations, fundus photography, fluorescein angiography (FA), electroretinography (ERG), and functional testing of this system were conducted postoperatively. The dogs were euthanatized at the end of the experiment, and their eyes were enucleated and histologically examined.

Results

All prostheses were successfully implanted without complications, and no serious adverse event occurred during the postoperative period. Fundus photographs and FA showed no serious damage in the retina surrounding the arrays. The ERGs recorded from the implanted eyes showed no significant differences from those from control eyes. Histological evaluations demonstrated good preservation of the retina over the array. However, system failure occurred in 50% of the dogs owing to dog-specific habits.

Conclusions

Implantation of this prosthesis system in dogs is feasible and can be performed without significant damage to the eye. The biocompatibility and stability of the array were good during the observation period, but the low durability of the system against dogs (not humans) is an issue to be resolved in the future.

Translational Relevance

This study suggests that this wide-field dual-array prosthesis might widen the visual field and might be useful for patients with retinitis pigmentosa.

Retinal Prosthetic Approaches to Enhance Visual Perception for Blind Patients

Retinal prostheses are implantable devices that aim to restore the vision of blind patients suffering from retinal degeneration, mainly by artificially stimulating the remaining retinal neurons. Some retinal prostheses have successfully reached the stage of clinical trials; however, these devices can only restore vision partially and remain insufficient to enable patients to conduct everyday life independently. The visual acuity of the artificial vision is limited by various factors from both engineering and physiological perspectives. To overcome those issues and further enhance the visual resolution of retinal prostheses, a variety of retinal prosthetic approaches have been proposed, based on optimization of the geometries of electrode arrays and stimulation pulse parameters. Other retinal stimulation modalities such as optics, ultrasound, and magnetics have also been utilized to address the limitations in conventional electrical stimulation. Although none of these approaches have been clinically proven to fully restore the function of a degenerated retina, the extensive efforts made in this field have demonstrated a series of encouraging findings for the next generation of retinal prostheses, and these could potentially enhance the visual acuity of retinal prostheses. In this article, a comprehensive and up-to-date overview of retinal prosthetic strategies is provided, with a specific focus on a quantitative assessment of visual acuity results from various retinal stimulation technologies. The aim is to highlight future directions toward high-resolution retinal prostheses.

Advances in retinal prosthesis systems

Retinal prosthesis systems have undergone significant advances in the past quarter century, resulting in the development of several different novel surgical and engineering approaches. Encouraging results have demonstrated partial visual restoration, with improvement in both coarse objective function and performance of everyday tasks. To date, four systems have received marketing approval for use in Europe or the United States, with numerous others undergoing preclinical and clinical evaluation, reflecting the established safety profile of these devices for chronic implantation. This progress represents the first notion that the field of visual restorative medicine could offer blind patients a hope of real and measurable benefit. However, there are numerous complex engineering and biophysical obstacles still to be overcome, to reconcile the gap that remains between artificial and natural vision. Current developments in the form of enhanced image processing algorithms and data transfer approaches, combined with emerging nanofabrication and conductive polymerization techniques, herald an exciting and innovative future for retinal prosthetics. This review provides an update of retinal prosthetic systems currently undergoing development and clinical trials while also addressing future challenges in the field, such as the assessment of functional outcomes in ultra-low vision and strategies for tackling existing hardware and software constraints.