Five-Year Safety and Performance Results from the Argus II Retinal Prosthesis System Clinical Trial

MRI safety and devices: An update and expert consensus

The use of magnetic resonance imaging (MRI) is increasing globally, and MRI safety issues regarding medical devices, which are constantly being developed or upgraded, represent an ongoing challenge for MRI personnel. To assist the MRI community, a panel of 10 radiologists with expertise in MRI safety from nine high-volume academic centers formed, with the objective of providing clarity on some of the MRI safety issues for the 10 most frequently questioned devices. Ten device categories were identified. The panel reviewed the literature, including key MRI safety issues regarding screening and adverse event reports, in addition to the manufacturer's Instructions For Use. Using a Delphi-inspired method, 36 practical recommendations were generated with 100% consensus that can aid the clinical MRI community. Level of Evidence: 5 Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2020;51:657-674.

Molecular Therapies for Inherited Retinal Diseases-Current Standing, Opportunities and Challenges

Inherited retinal diseases (IRDs) are both genetically and clinically highly heterogeneous and have long been considered incurable. Following the successful development of a gene augmentation therapy for biallelic RPE65-associated IRD, this view has changed. As a result, many different therapeutic approaches are currently being developed, in particular a large variety of molecular therapies. These are depending on the severity of the retinal degeneration, knowledge of the pathophysiological mechanism underlying each subtype of IRD, and the therapeutic target molecule. DNA therapies include approaches such as gene augmentation therapy, genome editing and optogenetics. For some genetic subtypes of IRD, RNA therapies and compound therapies have also shown considerable therapeutic potential. In this review, we summarize the current state-of-the-art of various therapeutic approaches, including the pros and cons of each strategy, and outline the future challenges that lie ahead in the combat against IRDs.

Trade-Off Between Field-of-View and Resolution in the Thermal-Integrated Argus II System

Purpose

To investigate the effect of a wider field-of-view (FOV) of a retinal prosthesis on the users' performance in locating objects.

Methods

One female and four male subjects who were blind due to end-stage retinitis pigmentosa and had been implanted with the Argus II retinal prosthesis participated (aged 63.4 ± 15.4). Thermal imaging was captured by an external sensor and converted to electrical stimulation to the retina. Subjects were asked to localize and to reach for heat-emitting objects using two different FOV mappings: a normal 1:1 mapping (no zoom) that provided 18° × 11° FOV and a 3:1 mapping (zoom out) that provided 49° × 35° FOV. Their accuracy and response time were recorded.

Results

Subjects were less accurate and took longer to complete the tasks with zoom out compared to no zoom. Localization accuracy decreased from 83% (95% confidence interval, 75%, 90%) with no zoom to 76% (67%, 83%) with zoom out (P = 0.07). Reaching accuracy differed between the two mappings only in one subject. Response time increased by 43% for the localization task (24%, 66%; P < 0.001) and by 20% for the reaching task (0%, 45%; P = 0.055).

Conclusions

Argus II wearers can efficiently find heat-emitting objects with the default 18° × 11° FOV of the current Argus II. For spatial localization, a higher spatial resolution may be preferred over a wider FOV.

Translational Relevance

Understanding the trade-off between FOV and spatial resolution in retinal prosthesis users can guide device optimization.

One-Year Safety and Performance Assessment of the Argus II Retinal Prosthesis: A Postapproval Study

Importance

The Argus II Retinal Prosthesis System is indicated for patients with vision loss due to severe to profound outer retinal degeneration, a group with few treatment options.

Objectives

To collect postapproval safety and visual function data for the Argus II.

Design, Setting, and Participants

Multicenter, postapproval clinical trial conducted at 9 sites in Germany and Italy. Data were collected from December 2, 2011, to September 30, 2017, and patients were followed-up for 12 months or longer. Patients were 25 years or older with severe to profound outer retinal degeneration, some residual light perception or the ability of the retina to respond to electrical stimulation, and a history of useful form vision and were already planning to undergo Argus II implantation.

Main Outcomes and Measures

The primary end point of this study was the nature and rate of adverse events. Secondary end points included 3 visual function tests: square localization (SL), direction of motion, and grating visual acuity (GVA).

Results

Forty-seven patients were followed for 12 months or longer after implant. Mean (SD) age was 56 (12) years, 37 (79%) had retinitis pigmentosa, and 27 (57%) were male. Through the first 12 months postimplantation, 23 patients (49%) experienced 51 nonserious adverse events and 12 (26%) experienced 13 serious adverse events (SAEs), 9 of which were judged to be related to the Argus II, and 4 of which were judged to be related to the procedure. The most common SAE was conjunctival erosion, reported in 4 patients. No significance testing was done for group analysis for the SL or direction-of-motion tests. When averaged across the group, patients' accuracy on the SL test, but not on the direction-of-motion test, appeared better when the Argus II was on than when it was switched off. For GVA, more patients at each point in time achieved the 2.9 GVA cutoff in the implanted eye when the Argus II was on compared with it switched off.

Conclusions and Relevance

Safety and visual function outcomes in this clinical practice setting cohort of patients with Argus II implants were consistent with previously reported results. Longer follow-up of these patients and data from additional patients are required to better outline the risks and benefits of this approach to addressing blindness secondary to severe-to-profound outer retinal degeneration.

Trial Registration

ClinicalTrials.gov identifier: NCT01490827.

Emerging Encapsulation Technologies for Long-Term Reliability of Microfabricated Implantable Devices

The development of reliable long-term encapsulation technologies for implantable biomedical devices is of paramount importance for the safe and stable operation of implants in the body over a period of several decades. Conventional technologies based on titanium or ceramic packaging, however, are not suitable for encapsulating microfabricated devices due to their limited scalability, incompatibility with microfabrication processes, and difficulties with miniaturization. A variety of emerging materials have been proposed for encapsulation of microfabricated implants, including thin-film inorganic coatings of Al2O3, HfO2, SiO2, SiC, and diamond, as well as organic polymers of polyimide, parylene, liquid crystal polymer, silicone elastomer, SU-8, and cyclic olefin copolymer. While none of these materials have yet been proven to be as hermetic as conventional metal packages nor widely used in regulatory approved devices for chronic implantation, a number of studies have demonstrated promising outcomes on their long-term encapsulation performance through a multitude of fabrication and testing methodologies. The present review article aims to provide a comprehensive, up-to-date overview of the long-term encapsulation performance of these emerging materials with a specific focus on publications that have quantitatively estimated the lifetime of encapsulation technologies in aqueous environments.

A bionic eye: performance of the Argus II retinal prosthesis in low-vision and social rehabilitation of patients with end-stage retinitis pigmentosa

The death of outer retinal layers occurring in retinitis pigmentosa causes severe visual impairment and often leads to total blindness. Inner retinal layers are spared, though, which provides a possibility of inducing visual perception by direct electrical stimulation of intact retinal cells. This article presents clinical outcomes of two patients who were the first in Russia to have received the Argus II Retinal Prosthesis System. Both implantations were successful. No complications were reported throughout the entire follow-up period. Upon completing 3 rehabilitation sessions, the patients were able to navigate indoors and outdoors, locate small high-contrast objects, discern contours of large objects and people’s silhouettes.

First implantation of retinal prosthesis in a patient with high myopia after surgery and rehabilitation program in Taiwan

The implantation of the Argus II retinal prosthesis system in a 54-year-old woman with retinitis pigmentosa who presented with an eye of long axial length at 26.82 mm was successful. Postoperative examination revealed a gap of 700 µm between the electrode array and the retina, which caused decreased visual perception. A modified strategy with quad and quinary electrode stimulation was introduced to generate higher perceptual thresholds. The patient experienced visual functional changes during the first half of the year after surgery, although no remarkable difference was observed in terms of implant-retina distance. Fibrosis around the tack developed and extended between the gap with the retina elevated from the tack toward the center array, 8 months after the surgery. Schisis of the retina developed and filled the gap, resulting in decreased threshold, and the strategy was then shifted back to single electrode stimulation mode. Rehabilitation program is an evolving process that depends on the distance between the array and the retina in the eye with staphyloma. This study first showed the implantation in a patient with high myopia who presented with long axial length after surgery and rehabilitation program in Taiwan.

A model of ganglion axon pathways accounts for percepts elicited by retinal implants

Degenerative retinal diseases such as retinitis pigmentosa and macular degeneration cause irreversible vision loss in more than 10 million people worldwide. Retinal prostheses, now implanted in over 250 patients worldwide, electrically stimulate surviving cells in order to evoke neuronal responses that are interpreted by the brain as visual percepts ('phosphenes'). However, instead of seeing focal spots of light, current implant users perceive highly distorted phosphenes that vary in shape both across subjects and electrodes. We characterized these distortions by asking users of the Argus retinal prosthesis system (Second Sight Medical Products Inc.) to draw electrically elicited percepts on a touchscreen. Using ophthalmic fundus imaging and computational modeling, we show that elicited percepts can be accurately predicted by the topographic organization of optic nerve fiber bundles in each subject's retina, successfully replicating visual percepts ranging from 'blobs' to oriented 'streaks' and 'wedges' depending on the retinal location of the stimulating electrode. This provides the first evidence that activation of passing axon fibers accounts for the rich repertoire of phosphene shape commonly reported in psychophysical experiments, which can severely distort the quality of the generated visual experience. Overall our findings argue for more detailed modeling of biological detail across neural engineering applications.

Contemporary approaches to visual prostheses

Visual prostheses serve to restore visual function following acquired blindness. Acquired blindness (as opposed to congenital blindness) has many causes, including diseases such as retinitis pigmentosa, glaucoma, and macular degeneration, or trauma such as caused by automobile accident or blast damage from explosions. Many of the blindness-causing diseases target the retina or other ocular structure. Often, despite the loss of sensitivity to light, the remainder of the visual pathway is still functional, enabling electrical devices to deliver effective and meaningful visual information to the brain via arrays of electrodes. These arrays can be placed in any part of the early visual pathway, such as the retina, optic nerve, lateral geniculate nucleus, or visual cortex. A camera or other imaging source is used to drive electrical stimulation of remaining healthy cells or structures to create artificial vision and provide restoration of function. In this review, each approach to visual prostheses is described, including advantages and disadvantages as well as assessments of the current state of the art. Most of the work to-date has been targeting stimulation of (a) the retina, with three devices approved for general use and two more in clinical testing; (b) the lateral geniculate nucleus, with efforts still in the pre-clinical stage; and (c) the cortex, with three devices in clinical testing and none currently approved for general use despite the longest history of investigation of the three major approaches. Each class of device has different medical indications, and different levels of invasiveness required for implantation. All contemporary devices deliver relatively poor vision. There has been remarkable progress since the first proof-of-concept demonstration that used stimulation of the primary visual cortex, with the field exploring all viable options for restoration of function. Much of the progress has been recent, driven by advances in microelectronics and biocompatibility. With three devices currently approved for general use in various parts of the world, and a handful of additional devices well along in the pipeline toward approval, prospects for wide deployment of a device-based therapy to treat acquired blindness are good.

Histopathologic Assessment of Optic Nerves and Retina From a Patient With Chronically Implanted Argus II Retinal Prosthesis System

Purpose

To characterize histologic changes in the optic nerve and the retina of an end-stage retinitis pigmentosa (RP) patient after long-term implantation with the Argus II retinal prosthesis system.

Methods

Serial cross sections from the patient's both eyes were collected postmortem 6 years after implantation. Optic nerve from both eyes were morphometrically analyzed and compared. Retina underneath and outside the array was analyzed and compared with corresponding regions in the fellow eye.

Results

Although the optic nerve of the implant eye demonstrated significantly more overall atrophy than the fellow eye (P < 0.01), the temporal quadrant that retinotopically corresponded to the location of the array did not show additional damage. The total neuron count of the macular area was not significantly different between the two eyes, but the tack locations and their adjacent areas showed significantly fewer neurons than other perimacular areas. There was an increased expression of glial fibrillary acidic protein (GFAP) throughout the retina in the implant eye versus the fellow eye, but there was no significant difference in the cellular retinaldehyde-binding protein (CRALBP) expression. Except for the revision tack site, no significant increase of inflammatory reaction was detected in the implant eye.

Conclusion

Long-term implantation and electrical stimulation with an Argus II retinal prosthesis system did not result in significant tissue damage that could be detected by a morphometric analysis.

Translational Relevance

This study supports the long-term safety of the Argus II device and encourages further development of bioelectronics devices at the retina-machine interface.

In Vivo Photovoltaic Performance of a Silicon Nanowire Photodiode-Based Retinal Prosthesis

Purpose

For more than 20 years, there has been an international, multidisciplinary effort to develop retinal prostheses to restore functional vision to patients blinded by retinal degeneration. We developed a novel subretinal prosthesis with 1512 optically addressed silicon nanowire photodiodes, which transduce incident light into an electrical stimulation of the remaining retinal circuitry. This study was conducted to evaluate the efficacy of optically driving the subretinal prosthesis to produce visual cortex activation via electrical stimulation of the retina.

Methods

We measured electrically evoked potential responses (EEPs) in rabbit visual cortex in response to illumination of the subretinal nanowire prosthesis with pulsed 852-nm infrared (IR) light. We compared the EEP responses to visually evoked potential responses (VEPs) to pulsed 532-nm visible light (positive control) and pulsed 852-nm IR light (negative control).

Results

Activating the devices with IR light produced EEP responses with a significantly higher trough-to-peak amplitude (54.17 ± 33.4 μV) than IR light alone (24.07 ± 22.1 μV) or background cortical activity (23.22 ± 17.2 μV). EEP latencies were significantly faster than focal VEP latencies. Focal VEPs produced significantly higher amplitudes (94.88 ± 43.3 μV) than EEPs. We also demonstrated how an electrode placed on the cornea can be used as a noninvasive method to monitor the function of the implant.

Conclusions

These results show that subretinal electrical stimulation with nanowire electrodes can elicit EEPs in the visual cortex, providing evidence for the viability of a subretinal nanowire prosthetic approach for vision restoration.

Feasibility of Intraocular Projection for Treatment of Intractable Corneal Opacity

Despite many decades of research and development, corneal opacity remains a leading cause of reversible blindness worldwide. Corneal transplantation and keratoprosthesis can restore corneal clarity, but both have well-known limitations. High-resolution electronic microdisplays may offer an alternative to traditional methods of treating corneal disease using an intraocular implant to project imagery onto the retina, obviating the need for a clear cornea. In this study, we review previous work and recent technologic developments relevant to the development of such an intraocular projection system.

Electrophysiological evaluation of a chronically implanted electrode for suprachoroidal transretinal stimulation in rabbit eyes

In this study, we aimed to determine the electrophysiological efficacy, safety, and electrical stability of a chronically implanted electrode for suprachoroidal transretinal stimulation (STS) in rabbit eyes. A platinum microelectrode was implanted into the scleral pocket of rabbit eyes (n = 5) and followed-up for 6 months. To evaluate the electrophysiological efficacy, electrically evoked potentials (EEPs) were measured every month after implantation. To evaluate safety, fundus examinations, fluorescein angiograms, electroretinograms (ERGs), and visually evoked potentials (VEPs) were measured before and every month after the implantation. At the end of the experiment, histological examination of retinal tissue beneath the site of the electrode was performed. To evaluate electrical stability, the resistance of the circuit was measured every month after implantation. EEPs could be elicited from the STS electrodes at all testing times. The mean threshold current to evoke EEPs was 186.4 ± 47.0 µA at 6 months after implantation. There was no significant change in the threshold over the follow-up period. The resistance of the circuit was significantly increased at 1 months after implantation, with no further increase at 6 months. There was no statistically significant change in the relative amplitudes and implicit times of a- and b-waves of ERGs and VEPs. No intraocular infection, inflammation, or vitreoretinal proliferation was observed in any eye. Histological examination revealed no retinal damage beneath the electrode. We conclude that chronically implanted electrodes for STS appear to be effective, safe, and electrically stable.

Psychosocial assessment of potential retinal prosthesis trial participants

BACKGROUND

As the field of retinal prostheses advances, volunteers are required for device trials, and optimal participant recruitment is vital for intervention success. The aims of this study were: (i) to select tests that assess the psychosocial aspects of visual impairment and develop a psychosocial assessment protocol for persons who may be eligible for participation in retinal prostheses trials; (ii) to investigate correlations between these tests; and (iii) to determine associations between psychosocial factors and a person's interest in participating in a retinal prosthesis (bionic eye) trial.

METHODS

Cross-sectional study of 72 adults with advanced retinal degeneration. Questionnaire assessments included personality, cognitive ability, social-support, self-efficacy, coping, optimism, depression, and quality of life (Impact of Vision Impairment Profile ([IVI], and Vision and Quality of Life Index [VisQoL]). Level of interest in a retinal prosthesis was also evaluated.

RESULTS

All questionnaires were completed without floor or ceiling effects and with minimal respondent burden. Depression correlated with decreased quality of life (rho = -0.37 and 0.40, p < 0.001 for IVI and VisQoL, respectively). Together, depression, gender and vision-specific coping explained 35.2 per cent of variance in IVI quality of life (p < 0.001). Forty-nine per cent of participants were interested in a retinal prosthesis now and 77 per cent in the future. Although the personality trait of 'openness' was somewhat predictive of interest in retinal prostheses (odds ratio 0.78, 95% CI 0.62-0.97), neither severity of vision impairment nor any of the psychosocial measures were strong predictors.

CONCLUSIONS

Several existing psychosocial questionnaires can be used for patients with advanced retinal degeneration and may be useful in exploring suitability for a retinal prosthesis or evaluating outcomes. However, the questionnaires used in this study were not good predictors of whether or not a person might be interested in a retinal prosthesis.

Active photonic sensing for super-resolved reading performance in simulated prosthetic vision

In this work, we study the enhancement of simulated prosthetic reading performance through "active photonic sensing" in normally sighted subjects. Three sensing paradigms were implemented: active sensing, in which the subject actively scanned the presented words using the computer mouse, with an option to control text size; passive scanning produced by software-initiated horizontal movements of words; and no scanning. Our findings reveal a 30% increase in word recognition rate with active scanning as compared to no or passive scanning and up to 14-fold increase with zooming. These results highlight the importance of a patient interactive interface and shed light on techniques that can greatly enhance prosthetic vision quality.

Assessment of Postoperative Morphologic Retinal Changes by Optical Coherence Tomography in Recipients of an Electronic Retinal Prosthesis Implant

Importance

The postoperative retinal changes at the interface between an implant electrode array and the retina and whether these anatomic changes have an association with the patient visual performance are unknown.

Objective

To report morphologic changes in recipients of an Argus II Retinal Prosthesis.

Design, Setting, and Participants

This consecutive, noncomparative case series study included a retrospective review of the preoperative and postoperative optical coherence tomography of 33 eyes among 33 individuals who underwent Argus II Retinal Prosthesis System implantation between October 28, 2011, and June 8, 2017, at 2 different centers, by the same surgeon (S.R.). Thirteen patients received an implant at Azienda Ospedaliero Universitaria Pisana, Pisa, Italy, between October 28, 2011, and October 27, 2014, and 20 patients underwent surgery at Azienda Ospedaliera Universitaria Careggi, Florence, Italy, between December 20, 2014, and June 8, 2017. Patients were excluded if they did not reach the 6-month follow-up.

Main Outcomes and Measures

All patients were evaluated before surgery, during the first postoperative day, and at 1, 3, 6, 12, and 24 months (subsequently once a year, except for patient-related adverse events), with a comprehensive ophthalmic examination, retinal fundus photography, spectral-domain optical coherence tomography, and visual function tests to evaluate the stability or improvement of their visual performance.

Results

Of the 20 patients included in the analysis, all were of white race/ethnicity, 12 (60%) were male, and the mean (SD) age was 57.4 (11.6) years. Optical coherence tomography revealed the development of a fibrosislike hyperreflective tissue limited at the interface between the array and retina in 10 eyes (50%). In 9 of 10 patients (90%), fibrosis evolved and progressed to retinal schisis. Despite the development of the fibrosis and schisis, there was no deterioration in the patient's visual performance evaluated prospectively with visual function tests (square localization and direction of motion).

Conclusions and Relevance

Optical coherence tomography may be used to observe the retinal anatomic changes in patients with an Argus II Prothesis. This analysis revealed the development of a fibrosislike hyperreflective tissue limited at the interface between array and retina that progressed to retinal schisis but with no deterioration in the patients' visual performance.

Argus II Retinal Prosthesis Implantation in a Patient With a History Of Strabismus Surgery:A Surgical Technique

BACKGROUND AND OBJECTIVE

The authors describe a modified surgical technique for Argus II retinal prosthesis implantation.

PATIENTS AND METHODS

The modified surgical technique was performed in a 43-year-old male with retinitis pigmentosa (RP) who underwent strabismus surgery in that eye at age 8.

RESULTS

During Argus II implantation, the lateral rectus (LR) was noted to be 10 mm posterior to its original insertion due to prior strabismus surgery. The authors placed three 5-0 nylon mattress sutures at the expected location of the LR to support the external portion of the prosthesis, specifically the coil. The band was then passed through the mattress sutures, underneath the inferior, and medial recti with temporal placement of the coil.

CONCLUSION

Placement of three mattress sutures allowed proper positioning of the device and enabled fixation of the suture tabs, thus minimizing the risk of postoperative conjunctival erosion and device exposure. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:116-119.].

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.

Brain Machine Interfaces for Vision Restoration: The Current State of Cortical Visual Prosthetics

Loss of vision alters the day to day life of blind individuals and may impose a significant burden on their family and the economy. Cortical visual prosthetics have been shown to have the potential of restoring a useful degree of vision via stimulation of primary visual cortex. Due to current advances in electrode design and wireless power and data transmission, development of these prosthetics has gained momentum in the past few years and multiple sites around the world are currently developing and testing their designs. In this review, we briefly outline the visual prosthetic approaches and describe the history of cortical visual prosthetics. Next, we focus on the state of the art of cortical visual prosthesis by briefly explaining the design of current devices that are either under development or in the clinical testing phase. Lastly, we shed light on the challenges of each design and provide some potential solutions.

Contrast sensitivity deficits in patients with mutation-proven inherited retinal degenerations

BACKGROUND

Patients with retinal diseases frequently complain of poor visual function even when visual acuity is relatively unaffected. This clinical finding has been attributed to deficits in contrast sensitivity (CS). The purpose of our study was to evaluate the CS in patients with clinical and genetic diagnosis of inherited retinal degeneration (IRD) and relatively preserved visual acuity.

METHODS

Seventeen patients (30 eyes) with IRD and visual acuity of 20/40 or better, and 18 controls (18 eyes) without any ocular condition underwent slit lamp examination, visual acuity testing via standard Snellen chart testing, CS testing via the Quick Contrast Sensitivity Function (QCSF), and Spectral Domain Optical Coherence Tomography (SD-OCT). CS were measured at 1.0, 1.5, 3.0, 6.0, 12.0, and 18.0 cycles per degree (cpd). T tests with general estimated equations were used to compare CS between groups. Wald chi square followed by pairwise comparisons was used to compare CS between multiple groups.

RESULTS

We included 12 patients with rod-cone dystrophy (RCD), 3 patients with Stargardt disease (STGD) and 2 patients with Best disease. Patients with IRD had significantly worse CS than controls (p < 0.001) in all spatial frequencies. Patients with STGD had more marked deficits in CS than patients with Best disease (p < 0.001) and RCD (p < 0.001) despite having similar visual acuities.

CONCLUSION

Patients with IRD, especially patients with STGD with relatively preserved visual acuity have marked deficits in CS when measured across a range of spatial frequencies. We recommend that clinical trials for STGD incorporate CS measured over a range of spatial frequencies as a secondary clinical endpoint for monitoring visual function. CS may provide an explanation for complaints of visual dysfunction when visual acuity is not significantly altered.

Long-term recording reliability of liquid crystal polymer µECoG arrays

OBJECTIVE

The clinical use of microsignals recorded over broad cortical regions is largely limited by the chronic reliability of the implanted interfaces.

APPROACH

We evaluated the chronic reliability of novel 61-channel micro-electrocorticographic (µECoG) arrays in rats chronically implanted for over one year and using accelerated aging. Devices were encapsulated with polyimide (PI) or liquid crystal polymer (LCP), and fabricated using commercial manufacturing processes. In vitro failure modes and predicted lifetimes were determined from accelerated soak testing. Successful designs were implanted epidurally over the rodent auditory cortex. Trends in baseline signal level, evoked responses and decoding performance were reported for over one year of implantation.

MAIN RESULTS

Devices fabricated with LCP consistently had longer in vitro lifetimes than PI encapsulation. Our accelerated aging results predicted device integrity beyond 3.4 years. Five implanted arrays showed stable performance over the entire implantation period (247-435 d). Our regression analysis showed that impedance predicted signal quality and information content only in the first 31 d of recordings and had little predictive value in the chronic phase (>31 d). In the chronic phase, site impedances slightly decreased yet decoding performance became statistically uncorrelated with impedance. We also employed an improved statistical model of spatial variation to measure sensitivity to locally varying fields, which is typically concealed in standard signal power calculations.

SIGNIFICANCE

These findings show that µECoG arrays can reliably perform in chronic applications in vivo for over one year, which facilitates the development of a high-density, clinically viable interface.

Neural Prosthetics:A Review of Empirical vs. Systems Engineering Strategies

Implantable electrical interfaces with the nervous system were first enabled by cardiac pacemaker technology over 50 years ago and have since diverged into almost all of the physiological functions controlled by the nervous system. There have been a few major clinical and commercial successes, many contentious claims, and some outright failures. These tend to be reviewed within each clinical subspecialty, obscuring the many commonalities of neural control, biophysics, interface materials, electronic technologies, and medical device regulation that they share. This review cites a selection of foundational and recent journal articles and reviews for all major applications of neural prosthetic interfaces in clinical use, trials, or development. The hard-won knowledge and experience across all of these fields can now be amalgamated and distilled into more systematic processes for development of clinical products instead of the often empirical (trial and error) approaches to date. These include a frank assessment of a specific clinical problem, the state of its underlying science, the identification of feasible targets, the availability of suitable technologies, and the path to regulatory and reimbursement approval. Increasing commercial interest and investment facilitates this systematic approach, but it also motivates projects and products whose claims are dubious.

Improvement in reading performance through training with simulated thalamic visual prostheses

Simulations of artificial vision are used to provide the researcher an opportunity to explore different aspects of visual prosthesis device design by observing subject performance on various tasks viewed through the simulation. Such studies typically use normal, sighted subjects to measure performance at a given point in time. Relatively few studies examine performance changes longitudinally to quantitatively assess the benefits from a training plan that would be akin to post-implantation rehabilitation. Here, we had six normal, sighted subjects use a standard reading task with daily practice over eight weeks to understand the effects of an intensive training schedule on adaptation to artificial sight. Subjects read 40 MNREAD-style sentences per session, with a new set each session, that were presented at five font sizes (logMAR 1.0–1.4) and through three center-weighted phosphene patterns (2,000, 1,000, 500 phosphenes). We found that subjects improved their reading accuracy across sessions, and that the training lead to an increase of reading speed that was equivalent to a doubling of available phosphenes. Most importantly, the hardest condition, while initially illegible, supported functional reading after training. Consistent with experience-driven neuroplastic changes, gaps in the training schedule lead to transient decreases in reading speed, but, surprisingly, not reading accuracy. Our findings contribute to our larger project of developing a thalamic visual prosthesis and to post-implant rehabilitation strategies.

Retinotopic Responses in the Visual Cortex Elicited by Epiretinal Electrical Stimulation in Normal and Retinal Degenerate Rats

Purpose

Electronic retinal prostheses restore vision in people with outer retinal degeneration by electrically stimulating the inner retina. We characterized visual cortex electrophysiologic response elicited by electrical stimulation of retina in normally sighted and retinal degenerate rats.

Methods

Nine normally sighted Long Evans and 11 S334ter line 3 retinal degenerate (rd) rats were used to map cortical responses elicited by epiretinal electrical stimulation in four quadrants of the retina. Six normal and six rd rats were used to compare the dendritic spine density of neurons in the visual cortex.

Results

The rd rats required higher stimulus amplitudes to elicit responses in the visual cortex. The cortical electrically evoked responses (EERs) for both healthy and rd rats show a dose-response characteristic with respect to the stimulus amplitude. The EER maps in healthy rats show retinotopic organization. For rd rats, cortical retinotopy is not well preserved. The neurons in the visual cortex of rd rats show a 10% higher dendritic spine density than in the healthy rats.

Conclusions

Cortical activity maps, produced when epiretinal stimulation is applied to quadrants of the retina, exhibit retinotopy in normal but not rd rats. This is likely due to a combination of degeneration of the retina and increased stimulus thresholds in rd, which broadens the activated area of the retina.

Translational Relevance

Loss of retinotopy is evident in rd rats. If a similar loss of retinotopy is present in humans, retinal prostheses design must include flexibility to account for patient specific variability.

Age-related macular degeneration

Age-related macular degeneration is a leading cause of visual impairment and severe vision loss. Clinically, it is classified as early-stage (medium-sized drusen and retinal pigmentary changes) to late-stage (neovascular and atrophic). Age-related macular degeneration is a multifactorial disorder, with dysregulation in the complement, lipid, angiogenic, inflammatory, and extracellular matrix pathways implicated in its pathogenesis. More than 50 genetic susceptibility loci have been identified, of which the most important are in the CFH and ARMS2 genes. The major non-genetic risk factors are smoking and low dietary intake of antioxidants (zinc and carotenoids). Progression from early-stage to late-stage disease can be slowed with high-dose zinc and antioxidant vitamin supplements. Intravitreal anti-vascular endothelial growth factor therapy (eg, ranibizumab, aflibercept, or bevacizumab) is highly effective at treating neovascular age-related macular degeneration, and has markedly decreased the prevalence of visual impairment in populations worldwide. Currently, no proven therapies for atrophic disease are available, but several agents are being investigated in clinical trials. Future progress is likely to be from improved efforts in prevention and risk-factor modification, personalised medicine targeting specific pathways, newer anti-vascular endothelial growth factor agents or other agents, and regenerative therapies.

Leveraging Zebrafish to Study Retinal Degenerations

Retinal degenerations are a heterogeneous group of diseases characterized by death of photoreceptors and progressive loss of vision. Retinal degenerations are a major cause of blindness in developed countries (Bourne et al., 2017; De Bode, 2017) and currently have no cure. In this review, we will briefly review the latest advances in therapies for retinal degenerations, highlighting the current barriers to study and develop therapies that promote photoreceptor regeneration in mammals. In light of these barriers, we present zebrafish as a powerful model to study photoreceptor regeneration and their integration into retinal circuits after regeneration. We outline why zebrafish is well suited for these analyses and summarize the powerful tools available in zebrafish that could be used to further uncover the mechanisms underlying photoreceptor regeneration and rewiring. In particular, we highlight that it is critical to understand how rewiring occurs after regeneration and how it differs from development. Insights derived from photoreceptor regeneration and rewiring in zebrafish may provide leverage to develop therapeutic targets to treat retinal degenerations.

The Argus-II Retinal Prosthesis Implantation; From the Global to Local Successful Experience

Over the past few years, visual prostheses (namely, Argus II retinal implant) and gene therapy have obtained FDA approval in treating blindness resulting from retinitis pigmentosa. Compared to gene therapy; Argus II is less costly with a demonstrated favorable outcome, though the vision is yet artificial. To obtain better results, expectation counseling and preoperative retinal assessment are critical. The global experience with Argus II has enrolled no more than 300 cases so far. The first Argus II retinal prosthesis in Iran was successfully implanted in Shiraz (October 2017). To date, Argus II artificial retina is implanted in four patients in Iran. Beside successful surgery and post-operative care, rehabilitation efforts with validated outcome measures including visual rehabilitation together with neurovisual, visuo-constructive and cognitive rehabilitation/empowerment approaches are expected to boost the functional outcome. A multidisciplinary approach within a cross-functional team would optimize strategies toward better patient outcomes. As such, establishing a collaborative network will foster organized research efforts to better define outcome assessment and rehabilitation strategies. This technology report paper has been an attempt to provide an overview of Argus-II retinal implant global experience as well as the clinical outcome of the so far cases in Iran. Insights from this report were communicated during the first “Brain Engineering and Computational Neuroscience Conference,” 31 January-2 February 2018 in Tehran.

Quantitative progression of retinitis pigmentosa by optical coherence tomography angiography

Optical coherence tomography angiography (OCT-A) is a non-invasive alternative to fluorescein angiography that allows for the study of the retinal and choroidal vasculatures. In this retrospective cohort study of 28 patients with retinitis pigmentosa (RP), we used OCT-A to quantify changes in perfusion density, foveal avascular zone (FAZ) area, and choriocapillaris blood flow over time and correlated these variables with ellipsoid zone (EZ) line width and best-corrected visual acuity (BCVA). Perfusion density decreased by 2.42 ± 0.62% per year at the superior capillary plexus (SCP) (P = 0.001) and 2.41 ± 0.76% per year at the deep capillary plexus (DCP) (P = 0.004). FAZ area increased by 0.078 ± 0.021 mm² per year (P = 0.001) at the SCP and 0.152 ± 0.039 mm² per year (P = 0.001) at the DCP. No changes were observed in the choriocapillaris blood flow. EZ line width had the strongest correlation to perfusion density at the SCP (r = 0.660 and 0.635, first and second visit, respectively, P = 0.001), while BCVA most strongly correlated with FAZ area at the SCP (r = 0.679 and 0.548, P = 0.001 and 0.003). Our results suggest that OCT-A is a useful tool for monitoring RP disease progression and may be used to measure retinal vascular parameters as outcomes in clinical trials.

Printable Graphene Oxide Micropatterns for a Bio-Subretinal Chip

Recently, implantable artificial subretinal chips using electronic components have replaced photoreceptors to serve as the most feasible treatment for retinal diseases. As such a chip that is meant to be implanted and used for very long periods, growing retinal cells on it to improve the electrical stimulation efficiency and attraction of neuronal elements remains a challenge. Here, an inkjet printing technology is employed to create graphene oxide (GO) micropatterns onto microelectrodes of a photovoltaic-powered implantable retinal chip. These GO micropatterns allow human retinal pigment epithelium (RPE) cells to specially attach and grow in each microelectrode. In addition, the cell proliferation, viability, and tight junction of RPE cells are improved during culturing. The development of a simple surface-coating technology would pave the way for the development of the first fully integrated and encapsulated retinal prostheses with biocompatible on-chip microelectrodes for long-term implantation, which could be effectively applied in retina tissue engineering and therapy.

Retinal Anatomy and Electrode Array Position in Retinitis Pigmentosa Patients After Argus II Implantation: An International Study

PURPOSE

To assess the retinal anatomy and array position in Argus II retinal prosthesis recipients.

DESIGN

Prospective, noncomparative cohort study.

METHODS

Setting: International multicenter study.

PATIENTS

Argus II recipients enrolled in the Post-Market Surveillance Studies.

PROCEDURES

Spectral-domain optical coherence tomography images collected for the Surveillance Studies (NCT01860092 and NCT01490827) were reviewed. Baseline and postoperative macular thickness, electrode-retina distance (gap), optic disc-array overlap, and preretinal membrane presence were recorded at 1, 3, 6, and 12 months.

MAIN OUTCOME MEASURES

Axial retinal thickness and axial gap along the array's long axis (a line between the tack and handle); maximal retinal thickness and maximal gap along a B-scan near the tack, midline, and handle.

RESULTS

Thirty-three patients from 16 surgical sites in the United States and Germany were included. Mean axial retinal thickness increased from month 1 through month 12 at each location, but reached statistical significance only at the array midline (P = .007). The rate of maximal thickness increase was highest near the array midline (slope = 6.02, P = .004), compared to the tack (slope = 3.60, P < .001) or the handle (slope = 1.93, P = .368). The mean axial and maximal gaps decreased over the study period, and the mean maximal gap size decrease was significant at midline (P = .032). Optic disc-array overlap was seen in the minority of patients. Preretinal membranes were common before and after implantation.

CONCLUSIONS

Progressive macular thickening under the array was common and corresponded to decreased electrode-retina gap over time. By month 12, the array was completely apposed to the macula in approximately half of the eyes.

A head mounted device stimulator for optogenetic retinal prosthesis

Objective. Our main objective is to demonstrate that compact high radiance gallium nitride displays can be used with conventional virtual reality optics to stimulate an optogenetic retina. Hence, we aim to introduce a non-invasive approach to restore vision for people with conditions such as retinitis pigmentosa where there is a remaining viable communication link between the retina and the visual cortex. Approach. We design and implement the headset using a high-density µLED matrix, Raspberry Pi, microcontroller from NXP and virtual reality lens. Then, a test platform is developed to evaluate the performance of the headset and the optical system. Furthermore, image simplification algorithms are used to simplify the scene to be sent to the retina. Moreover, in vivo evaluation of the genetically modified retina response at different light intensity is discussed to prove the reliability of the proposed system. Main results. We demonstrate that in keeping with regulatory guidance, the headset displays need to limit their luminance to 90 kcd m⁻². We demonstrate an optical system with 5.75% efficiency which allows for 0.16 mW mm⁻² irradiance on the retina within the regulatory guidance, but which is capable of an average peak irradiance of 1.35 mW mm⁻². As this is lower than the commonly accepted threshold for channelrhodopsin-2, we demonstrate efficacy through an optical model of an eye onto a biological retina. Significance. We demonstrate a fully functional 8100-pixel headset system including software/hardware which can operate on a standard consumer battery for periods exceeding a 24 h recharge cycle. The headset is capable of delivering enough light to stimulate the genetically modified retina cells and also keeping the amount of light below the regulation threshold for safety.

Investigation of Surgical Techniques for Optimization of Long-Term Outcomes of LCP-Based Retinal Prosthesis Implantation

Purpose

To investigate reproducible surgical techniques to optimize the long-term safety of liquid crystal polymer (LCP)-based retinal prosthesis implantation.

Methods

An LCP-based retinal prosthesis is fabricated monolithically on a single-body LCP substrate with all components, including the package and electrode array. We implanted the electrode array into the suprachoroidal space and anchored the package and transition part to the sclera in rabbits (n = 11). The safety profile was assessed upon the completion of the surgery and postoperatively.

Results

The surgical procedures for implantation of the entire system were easily performed in nine eyes (81.8%) without any intraoperative complications. In the other two eyes (18.2%), surgical complications related to electrode insertion, including optic nerve damage and retinal tear, arose. In 10 eyes (90.9%), the devices were well tolerated for at least 3 months. However, in most eyes (nine; 81.8%), two complications began to appear after 3 months, postoperatively, including conjunctival erosion or dehiscence over the package or transition part. The electrode arrays were maintained safely in the suprachoroidal space after surgery without any complications, regardless of the status of the extraocular components in all cases except two intraoperative complications.

Conclusions

We established safe and reproducible surgical techniques for implantation of our LCP-based retinal prosthesis into the suprachoroidal space. Although issues related to surgical technique or device configuration were identified, further technical solutions would improve the long-term safety of device implantation.

Translational Relevance

This study presents successful implantation of LCP-based retinal prosthesis. The technical solutions will permit an optimization of surgical techniques.

Development of visual Neuroprostheses: trends and challenges

Visual prostheses are implantable medical devices that are able to provide some degree of vision to individuals who are blind. This research field is a challenging subject in both ophthalmology and basic science that has progressed to a point where there are already several commercially available devices. However, at present, these devices are only able to restore a very limited vision, with relatively low spatial resolution. Furthermore, there are still many other open scientific and technical challenges that need to be solved to achieve the therapeutic benefits envisioned by these new technologies. This paper provides a brief overview of significant developments in this field and introduces some of the technical and biological challenges that still need to be overcome to optimize their therapeutic success, including long-term viability and biocompatibility of stimulating electrodes, the selection of appropriate patients for each artificial vision approach, a better understanding of brain plasticity and the development of rehabilitative strategies specifically tailored for each patient.

Responsive Neural Activities in the Primary Visual Cortex of Retina-Degenerated Rats

To study the responsive neural activities in the primary visual cortex (V1) of retinal degeneration (RD) models, experiments involving the wild-type (WT) and RD rats were conducted. The neural responses in the V1 were recorded extracellularly, while a visual stimulus with varied light intensity was given to the subjects. First, the firing rate and its relationship with light intensity were compared between the WT and RD groups. Second, the mutual information (MI) between the visual stimulus and neural response was determined for every isolated unit to quantify the amount and efficiency of information transmission in the V1 for both the control and experimental groups. Third, the local field potential (LFP) signal was characterized and its power used to compute the MI and further evaluate the function change in the RD model regarding information transmission. Analysis of spiking activity showed that the RD group exhibited a relatively decreased firing rate, information amount and efficiency compared with the control group. However, the information transmission performance of the RD model was similar to that of the WT group in the context of LFP activity. Therefore, for the RD rats, the early stage of the visual system was impaired, while the later stage of the visual system, V1, was able to capture the information about the visual stimulus, especially at the population level. Thus, this pathway could be used to restore visual ability, such as by visual prostheses.

Progress in artificial vision through suprachoroidal retinal implants

Retinal implants have proven their ability to restore visual sensation to people with degenerative retinopathy, characterized by photoreceptor cell death and the retina's inability to sense light. Retinal bionics operate by electrically stimulating the surviving neurons in the retina, thus triggering the transfer of visual sensory information to the brain. Suprachoroidal implants were first investigated in Australia in the 1950s. In this approach, the neuromodulation hardware is positioned between the sclera and the choroid, thus providing significant surgical and safety benefits for patients, with the potential to maintain residual vision combined with the artificial input from the device. Here we review the latest advances and state of the art devices for suprachoroidal prostheses, highlight future technologies and discuss challenges and perspectives towards improved rehabilitation of vision.

Argus II retinal prosthesis system: a review of patient selection criteria, surgical considerations, and post-operative outcomes

Retinitis pigmentosa (RP) is a group of heterogeneous inherited retinal degenerative disorders characterized by progressive rod and cone dysfunction and ensuing photoreceptor loss. Many patients suffer from legal blindness by their 40s or 50s. Artificial vision is considered once patients have lost all vision to the point of bare light perception or no light perception. The Argus II retinal prosthesis system is one such artificial vision device approved for patients with RP. This review focuses on the factors important for patient selection. Careful pre-operative screening, counseling, and management of patient expectations are critical for the successful implantation and visual rehabilitation of patients with the Argus II device.

Word recognition: re-thinking prosthetic vision evaluation

OBJECTIVE

Evaluations of vision prostheses and sensory substitution devices have frequently relied on repeated training and then testing with the same small set of items. These multiple forced-choice tasks produced above chance performance in blind users, but it is unclear if the observed performance represents restoration of vision that transfers to novel, untrained items.

APPROACH

Here, we tested the generalizability of the forced-choice paradigm on discrimination of low-resolution word images. Extensive visual training was conducted with the same 10 words used in previous BrainPort tongue stimulation studies. The performance on these 10 words and an additional 50 words was measured before and after the training sessions.

MAIN RESULTS

The results revealed minimal performance improvement with the untrained words, demonstrating instead pattern discrimination limited mostly to the trained words.

SIGNIFICANCE

These findings highlight the need to reconsider current evaluation practices, in particular, the use of forced-choice paradigms with a few highly trained items. While appropriate for measuring the performance thresholds in acuity or contrast sensitivity of a functioning visual system, performance on such tasks cannot be taken to indicate restored spatial pattern vision.

Restoring vision

Restoring vision to the blind by retinal repair has been a dream of medicine for centuries, and the first successful procedures have recently been performed. Although we are still far from the restoration of high-resolution vision, step-by-step developments are overcoming crucial bottlenecks in therapy development and have enabled the restoration of some visual function in patients with specific blindness-causing diseases. Here, we discuss the current state of vision restoration and the problems related to retinal repair. We describe new model systems and translational technologies, as well as the clinical conditions in which new methods may help to combat blindness.

Visual Evoked Potential Recovery by Subretinal Implantation of Photoelectric Dye-Coupled Thin Film Retinal Prosthesis in Monkey Eyes With Macular Degeneration

Retinal prosthesis or artificial retina is a promising modality of treatment for outer retinal degeneration, caused by primary and secondary loss of photoreceptor cells, in hereditary retinal dystrophy and age‐related macular degeneration, respectively. Okayama University‐type retinal prosthesis (OUReP) is a photoelectric dye‐coupled polyethylene film which generates electric potential in response to light and stimulates nearby neurons. The dye‐coupled films were implanted by vitreous surgery in the subretinal space of monkey eyes with macular degeneration which had been induced by cobalt chloride injection from the scleral side. A pilot 1‐month observation study involved 6 monkeys and a pivotal 6‐month observation study involved 8 monkeys. Of 8 monkeys in 6‐month group, 3 monkeys underwent dye‐coupled film removal at 5 months and were observed further for 1 month. The amplitude of visual evoked potential which had been reduced by macular degeneration did recover at 1 month after film implantation and maintained the level at 6 months. Optical coherence tomography showed no retinal detachment, and full‐field electroretinograms maintained a‐wave and b‐wave amplitudes, indicative of no retinal toxicity. Pathological examinations after 6‐month implantation showed structural integrity of the inner retinal layer in close apposition to dye‐coupled films. The implanted films which were removed by vitrectomy 5 months later showed light‐evoked surface electric potentials by scanning Kelvin probe measurement. The photoelectric dye‐coupled film (OUReP), which serves as a light‐receiver and a displacement current generator in the subretinal space of the eye, has a potential for recovering vision in diseases with photoreceptor cell loss, such as retinitis pigmentosa and age‐related macular degeneration.

Non-syndromic retinitis pigmentosa

Retinitis pigmentosa (RP) encompasses a group of inherited retinal dystrophies characterized by the primary degeneration of rod and cone photoreceptors. RP is a leading cause of visual disability, with a worldwide prevalence of 1:4000. Although the majority of RP cases are non-syndromic, 20-30% of patients with RP also have an associated non-ocular condition. RP typically manifests with night blindness in adolescence, followed by concentric visual field loss, reflecting the principal dysfunction of rod photoreceptors; central vision loss occurs later in life due to cone dysfunction. Photoreceptor function measured with an electroretinogram is markedly reduced or even absent. Optical coherence tomography (OCT) and fundus autofluorescence (FAF) imaging show a progressive loss of outer retinal layers and altered lipofuscin distribution in a characteristic pattern. Over the past three decades, a vast number of disease-causing variants in more than 80 genes have been associated with non-syndromic RP. The wide heterogeneity of RP makes it challenging to describe the clinical findings and pathogenesis. In this review, we provide a comprehensive overview of the clinical characteristics of RP specific to genetically defined patient subsets. We supply a unique atlas with color fundus photographs of most RP subtypes, and we discuss the relevant considerations with respect to differential diagnoses. In addition, we discuss the genes involved in the pathogenesis of RP, as well as the retinal processes that are affected by pathogenic mutations in these genes. Finally, we review management strategies for patients with RP, including counseling, visual rehabilitation, and current and emerging therapeutic options.