The Argus II Retinal Prosthesis: 12-month outcomes from a single-study center

A virtual patient simulation modeling the neural and perceptual effects of human visual cortical stimulation, from pulse trains to percepts

The field of cortical sight restoration prostheses is making rapid progress with three clinical trials of visual cortical prostheses underway. However, as yet, we have only limited insight into the perceptual experiences produced by these implants. Here we describe a computational model or 'virtual patient', based on the neurophysiological architecture of V1, which successfully predicts the perceptual experience of participants across a wide range of previously published human cortical stimulation studies describing the location, size, brightness and spatiotemporal shape of electrically induced percepts in humans. Our simulations suggest that, in the foreseeable future the perceptual quality of cortical prosthetic devices is likely to be limited by the neurophysiological organization of visual cortex, rather than engineering constraints.

Current Assistive Devices Usage and Recommendations for a Future Artificial Vision Prosthesis among Patients with Severe Visual Impairment Due to Inherited Retinal Diseases

Patients with inherited retinal diseases (IRDs) utilize various adaptive techniques and devices designed to assist them with activities of daily living (ADLs). The purpose of this study was to assess the assistive devices used by patients with IRDs, the difficulties they face despite these devices, and their recommendations for a future visual prosthesis. In collaboration with blind patients, an online survey was developed and administered to adults with IRDs and visual acuities of 20/400 to no light perception in the better-seeing eye. We analyzed data from 121 survey respondents (aged 18 to >80 years). Five respondents were Argus II prosthesis recipients. The most commonly used aids were cellular phones/tablets for reading (63.6%) as well as a sighted guide (75.0%) and a cane (71.4%) for mobility. Despite current assistive devices, participants reported continued difficulty with ADLs. Improved navigation, reading, and facial recognition were ranked the most desirable features for future visual prostheses. Argus II recipients suggested technology with improved ability to recognize objects and obstacles, detect movement, and cut out busy backgrounds. These insights are valuable in shaping the design of future prosthetic devices tailored to the needs of IRD patients.

Pulse trains to percepts: A virtual patient describing the perceptual effects of human visual cortical stimulation

The field of cortical sight restoration prostheses is making rapid progress with three clinical trials of visual cortical prostheses underway. However, as yet, we have only limited insight into the perceptual experiences produced by these implants. Here we describe a computational model or 'virtual patient', based on the neurophysiological architecture of V1, which successfully predicts the perceptual experience of participants across a wide range of previously published cortical stimulation studies describing the location, size, brightness and spatiotemporal shape of electrically induced percepts in humans. Our simulations suggest that, in the foreseeable future the perceptual quality of cortical prosthetic devices is likely to be limited by the neurophysiological organization of visual cortex, rather than engineering constraints.

Object recognition and localization enhancement in visual prostheses: a real-time mixed reality simulation

Blindness is a main threat that affects the daily life activities of any human. Visual prostheses have been introduced to provide artificial vision to the blind with the aim of allowing them to restore confidence and independence. In this article, we propose an approach that involves four image enhancement techniques to facilitate object recognition and localization for visual prostheses users. These techniques are clip art representation of the objects, edge sharpening, corner enhancement and electrode dropout handling. The proposed techniques are tested in a real-time mixed reality simulation environment that mimics vision perceived by visual prostheses users. Twelve experiments were conducted to measure the performance of the participants in object recognition and localization. The experiments involved single objects, multiple objects and navigation. To evaluate the performance of the participants in objects recognition, we measure their recognition time, recognition accuracy and confidence level. For object localization, two metrics were used to measure the performance of the participants which are the grasping attempt time and the grasping accuracy. The results demonstrate that using all enhancement techniques simultaneously gives higher accuracy, higher confidence level and less time for recognizing and grasping objects in comparison to not applying the enhancement techniques or applying pair-wise combinations of them. Visual prostheses could benefit from the proposed approach to provide users with an enhanced perception.

Clinical Progress and Optimization of Information Processing in Artificial Visual Prostheses

Visual prostheses, used to assist in restoring functional vision to the visually impaired, convert captured external images into corresponding electrical stimulation patterns that are stimulated by implanted microelectrodes to induce phosphenes and eventually visual perception. Detecting and providing useful visual information to the prosthesis wearer under limited artificial vision has been an important concern in the field of visual prosthesis. Along with the development of prosthetic device design and stimulus encoding methods, researchers have explored the possibility of the application of computer vision by simulating visual perception under prosthetic vision. Effective image processing in computer vision is performed to optimize artificial visual information and improve the ability to restore various important visual functions in implant recipients, allowing them to better achieve their daily demands. This paper first reviews the recent clinical implantation of different types of visual prostheses, summarizes the artificial visual perception of implant recipients, and especially focuses on its irregularities, such as dropout and distorted phosphenes. Then, the important aspects of computer vision in the optimization of visual information processing are reviewed, and the possibilities and shortcomings of these solutions are discussed. Ultimately, the development direction and emphasis issues for improving the performance of visual prosthesis devices are summarized.

Factors affecting two-point discrimination in Argus II patients

Two of the main obstacles to the development of epiretinal prosthesis technology are electrodes that require current amplitudes above safety limits to reliably elicit percepts, and a failure to consistently elicit pattern vision. Here, we explored the causes of high current amplitude thresholds and poor spatial resolution within the Argus II epiretinal implant. We measured current amplitude thresholds and two-point discrimination (the ability to determine whether one or two electrodes had been stimulated) in 3 blind participants implanted with Argus II devices. Our data and simulations show that axonal stimulation, lift and retinal damage all play a role in reducing performance in the Argus 2, by either limiting sensitivity and/or reducing spatial resolution. Understanding the relative role of these various factors will be critical for developing and surgically implanting devices that can successfully subserve pattern vision.

Learning to see again: Perceptual learning of simulated abnormal on- off-cell population responses in sighted individuals

Many forms of artificial sight recovery, such as electronic implants and optogenetic proteins, generally cause simultaneous, rather than complementary firing of on- and off-center retinal cells. Here, using virtual patients—sighted individuals viewing distorted input—we examine whether plasticity might compensate for abnormal neuronal population responses. Five participants were dichoptically presented with a combination of original and contrast-reversed images. Each image (I) and its contrast-reverse (Iʹ) was filtered using a radial checkerboard (F) in Fourier space and its inverse (Fʹ). [I * F′] + [Iʹ * F] was presented to one eye, and [I * F] + [Iʹ * F′] was presented to the other, such that regions of the image that produced on-center responses in one eye produced off-center responses in the other eye, and vice versa. Participants continuously improved in a naturalistic object discrimination task over 20 one-hour sessions. Pre-training and post-training tests suggest that performance improvements were due to two learning processes: learning to recognize objects with reduced visual information and learning to suppress contrast-reversed image information in a non–eye-selective manner. These results suggest that, with training, it may be possible to adapt to the unnatural on- and off-cell population responses produced by electronic and optogenetic sight recovery technologies.

Argus II retinal prosthesis for retinitis pigmentosa in the Middle East: The 2015 Pan-American Association of Ophthalmology Gradle Lecture

BACKGROUND

To describe the outcomes of patients with retinitis pigmentosa (RP) who received the Argus II Retinal Prosthesis System.

METHODS

This retrospective, interventional case series evaluated 10 consecutive patients who received the Argus II retinal implant and underwent visual function tests with the system on and system off. The main outcome measures were safety (the number, seriousness, and relatedness of adverse events), and visual function measured by computer-based objective tests, including square localization (SL) and direction of motion (DOM). Secondary measures included functional vision performance, including orientation and mobility (O&M) tasks.

RESULTS

There were no intraoperative complications and all prostheses remained implanted at the end of follow up. The mean patient age was 41.3 years; mean duration of the implant in vivo was 2.1 years. One patient had a suture exposure over the coil suture tab and over the inferior case suture tab at 2 years postoperatively, which was managed successfully. One patient developed mild vitreous hemorrhage that resolved spontaneously. One patient developed high intraocular pressure postoperatively due to a tight scleral band (SB) that was managed successfully. Patients performed significantly better with the Argus II system on than off on all tasks.

CONCLUSION

Patients who received the Argus II had a safety profile out to 4 years post-implantation that was markedly better than that observed in the pre-approval phase of the Argus II. In this population of RP patients, the Argus II retinal prosthesis provided useful visual function over several years that likely translates into improved quality of life.

TRIAL REGISTRATION

clinicaltrials.gov identifier, NCT00407602.

ANATOMICAL CHANGES BETWEEN ARGUS II RETINAL PROSTHESIS AND INNER RETINAL LAYERS DETECTED BY SPECTRAL DOMAIN OPTICAL COHERENCE TOMOGRAPHY IN FIRST YEAR: A CASE REPORT

PURPOSE

To report and describe the anatomical changes detected by spectral domain optical coherence tomography between an Argus II retinal prosthesis and the inner retinal layers during 1-year follow-up.

METHODS AND RESULTS

A patient presented with epiretinal fibrosis 12 months after implant of an Argus II epiretinal prosthesis. One month after uneventful surgery in March 2016, an evident hyporeflective space was detected between the epiretinal prosthesis and the inner retinal surface by spectral domain optical coherence tomography. An epiretinal hyperreflective band was noticed during follow-up and 1 year after surgery. Spectral domain optical coherence tomography showed close contact of the band with the array, which greatly increased the electrical threshold of stimulation for most of the electrodes. Some electrodes were no longer functioning. No changes in visual performance were detected.

CONCLUSION

Argus II epiretinal prosthesis implant may be complicated by the formation of a hyperreflective epiretinal band, detectable by spectral domain optical coherence tomography. The band may alter prosthesis function; to date, the patient did not scored any decrease in visual function.

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.

Safety, effectiveness, and cost-effectiveness of Argus II in patients with retinitis pigmentosa: a systematic review

AIM

To assess the effectiveness, safety, and cost-effectiveness of the Argus II in treatment of the retinitis pigmentosa (RP) patients.

METHODS

The ProQuest, Web of Science, EMBASE, MEDLINE (via PubMed) were searched using combinations of the keywords of Argus, safety, effectiveness, bionic eye, retinal prosthesis, and RP through March 2018. The retrieved records were screened and then assessed for eligibility.

RESULTS

Totally 926 records were retrieved from the searched databases and finally 12 studies included. The RP patients showed improvements in visual function after receiving the prosthesis, compared to the time before the prosthesis or the time it was off. This was measured by square localization, direction of motion, and grating visual acuity tests. No major adverse effect was reported for the Argus II prosthesis itself and/or the surgery to implement it, but the most frequently reported items were hypotony, and conjunctival dehiscence. The incremental cost-effectiveness ratio (ICER) was calculated to be €14603 per quality-adjusted life year (QALY) in UK and $207 616 per QALY in Canada.

CONCLUSION

The available evidence shows that the Argus II prosthesis in RP patients is effective in improvement of their visual function. Some minor adverse effects are reported for the prosthesis. The cost-effectiveness studies show that the technology is cost-effective only at high levels of willingness-to-pay.

What do blind people "see" with retinal prostheses? Observations and qualitative reports of epiretinal implant users

INTRODUCTION

Retinal implants have now been approved and commercially available for certain clinical populations for over 5 years, with hundreds of individuals implanted, scores of them closely followed in research trials. Despite these numbers, however, few data are available that would help us answer basic questions regarding the nature and outcomes of artificial vision: what do recipients see when the device is turned on for the first time, and how does that change over time?

METHODS

Semi-structured interviews and observations were undertaken at two sites in France and the UK with 16 recipients who had received either the Argus II or IRIS II devices. Data were collected at various time points in the process that implant recipients went through in receiving and learning to use the device, including initial evaluation, implantation, initial activation and systems fitting, re-education and finally post-education. These data were supplemented with data from interviews conducted with vision rehabilitation specialists at the clinical sites and clinical researchers at the device manufacturers (Second Sight and Pixium Vision). Observational and interview data were transcribed, coded and analyzed using an approach guided by Interpretative Phenomenological Analysis (IPA).

RESULTS

Implant recipients described the perceptual experience produced by their epiretinal implants as fundamentally, qualitatively different than natural vision. All used terms that invoked electrical stimuli to describe the appearance of their percepts, yet the characteristics used to describe the percepts varied significantly between recipients. Artificial vision for these recipients was a highly specific, learned skill-set that combined particular bodily techniques, associative learning and deductive reasoning in order to build a "lexicon of flashes"-a distinct perceptual vocabulary that they then used to decompose, recompose and interpret their surroundings. The percept did not transform over time; rather, the recipient became better at interpreting the signals they received, using cognitive techniques. The process of using the device never ceased to be cognitively fatiguing, and did not come without risk or cost to the recipient. In exchange, recipients received hope and purpose through participation, as well as a new kind of sensory signal that may not have afforded practical or functional use in daily life but, for some, provided a kind of "contemplative perception" that recipients tailored to individualized activities.

CONCLUSION

Attending to the qualitative reports of implant recipients regarding the experience of artificial vision provides valuable information not captured by extant clinical outcome measures.

One-Year Anatomical and Functional Outcomes of the Argus II Implantation in Korean Patients with Late-Stage Retinitis Pigmentosa: A Prospective Case Series Study

PURPOSE

To report the anatomical and functional outcomes of Argus II retinal prosthesis implantation in Korean patients.

METHODS

We included 5 consecutive patients with end-stage retinitis pigmentosa (RP) who underwent Argus II retinal prosthesis implantation and were followed for at least 12 months. The transcorneal electrical evoked response was utilized for patient selection. We used intraoperative optical coherence tomography (OCT) for optimal placement of the array and provided specialized vision rehabilitation training. A morphological evaluation using SD-OCT and a functional evaluation using computer-based visual function tests, a letter-reading ability test, and the Functional Low-Vision Observer Rated Assessment (FLORA) were conducted.

RESULTS

Postoperatively, the array was completely apposed to the retinal surface in all eyes, except for one eye which had a preexisting macular concavity. Fibrosis-like tissues of ≥50-μm thickness developed at the interface in 2 eyes. All of the patients showed improvement in computer-based visual function tests and could read ETDRS letters at a distance of 50 cm. Three patients could read Korean words. FLORA was improved in all patients, mainly in tasks of visual mobility, daily activities, and social interactions.

CONCLUSIONS

Along with good anatomical outcomes and specialized rehabilitation practices, recipients of the Argus II implant showed profound improvements in functional vision and mobility.

Effect of the electrode array-retina gap distance on visual function in patients with the Argus II retinal prosthesis

Background

Post-implantation visual outcomes in patients with the Argus II Retinal Prosthesis is dependent on a multitude of factors including the positioning of the electrode array on the retina. The purpose of this study is to determine whether the average electrode array-retina gap distance correlates with objective visual function outcomes and sensitivity detection thresholds in patients implanted with the Argus II Retinal Prosthesis.

Methods

Five patients with implantation of the Argus II Retinal Prosthesis were enrolled in this single-institution retrospective study. Patient demographics were collected from medical records. Visual function data (Square Localization [SL] and Direction of Motion [DOM]) and Optical Coherence Tomography (Cirrus HD-OCT) images were extracted retrospectively from the Argus II Retinal Prosthesis Post-Approval study. Visual function tests were performed with the device OFF and ON at each study visit. Electrode array-retina gap distances were measured at each of the array’s 60 electrodes using the Cirrus HD-OCT software in both the nasotemporal and superoinferior planes. Data was obtained at baseline, and post-operative month 1, month 3, month 6, and year 1. Sensitivity detection thresholds were obtained at the initial programming visit and each reprogramming session.

Results

Three patients performed significantly better in SL visual function testing with the device ON. Patients that worsened in visual function testing with the device ON in both SL and DOM testing had a statistically significant decrease in performance. The electrode array-retina gap distance was found to effect performance in SL testing in a patient-dependent manner. No effect was found between the electrode-array gap distance and DOM testing or sensitivity detection threshold.

Conclusion

Our results demonstrate that the electrode array-retina gap distance may affect visual function outcomes in SL testing in certain patients with the Argus II Retinal Prosthesis, and the direction and magnitude of this effect is likely patient-dependent. Furthermore, complete apposition between the electrode array and retina may not always be necessary to achieve optimal visual outcomes.

Hemispherical Microelectrode Array for Ex Vivo Retinal Neural Recording

To investigate the neuronal visual encoding process in the retina, researchers have performed in vitro and ex vivo electrophysiological experiments using animal retinal tissues. The microelectrode array (MEA) has become a key component in retinal experiments because it enables simultaneous neural recording from a population of retinal neurons. However, in most retinal experiments, it is inevitable that the retinal tissue is flattened on the planar MEA, becoming deformed from the original hemispherical shape. During the tissue deforming process, the retina is subjected to mechanical stress, which can induce abnormal physiological conditions. To overcome this problem, in this study, we propose a hemispherical MEA with a curvature that allows retinal tissues to adhere closely to electrodes without tissue deformation. The electrode array is fabricated by stretching a thin, flexible polydimethylsiloxane (PDMS) electrode layer onto a hemispherical substrate. To form micro patterns of electrodes, laser processing is employed instead of conventional thin-film microfabrication processes. The feasibility for neural recording from retinal tissues using this array is shown by conducting ex vivo retinal experiments. We anticipate that the proposed techniques for hemispherical MEAs can be utilized not only for ex vivo retinal studies but also for various flexible electronics.

A Three-Dimensional Microelectrode Array to Generate Virtual Electrodes for Epiretinal Prosthesis Based on a Modeling Study

Despite many advances in the development of retinal prostheses, clinical reports show that current retinal prosthesis subjects can only perceive prosthetic vision with poor visual acuity. A possible approach for improving visual acuity is to produce virtual electrodes (VEs) through electric field modulation. Generating controllable and localized VEs is a crucial factor in effectively improving the perceptive resolution of the retinal prostheses. In this paper, we aimed to design a microelectrode array (MEA) that can produce converged and controllable VEs by current steering stimulation strategies. Through computational modeling, we designed a three-dimensional concentric ring–disc MEA and evaluated its performance with different stimulation strategies. Our simulation results showed that electrode–retina distance (ERD) and inter-electrode distance (IED) can dramatically affect the distribution of electric field. Also the converged VEs could be produced when the parameters of the three-dimensional MEA were appropriately set. VE sites can be controlled by manipulating the proportion of current on each adjacent electrode in a current steering group (CSG). In addition, spatial localization of electrical stimulation can be greatly improved under quasi-monopolar (QMP) stimulation. This study may provide support for future application of VEs in epiretinal prosthesis for potentially increasing the visual acuity of prosthetic vision.

Computer-Assisted Immersive Visual Rehabilitation in Argus II Retinal Prosthesis Recipients

PURPOSE

The field of retinal prostheses is expanding. However, the best approach to training and assessing the functional benefit of postoperative vision has not been established. The purpose of this single-center prospective interventional case series was to evaluate the feasibility and effectiveness of using the Computer Assisted Rehabilitation Environment (CAREN) system as a visual rehabilitation tool in Argus II patients.

DESIGN

Single-center prospective interventional case series (clinicaltrials.gov identifier, NCT03444961).

PARTICIPANTS

Four Argus II recipients (3 men and 1 woman).

METHODS

Eight visual rehabilitation sessions using the CAREN system (twice weekly for 4 weeks).

MAIN OUTCOME MEASURES

Baseline and postintervention assessments consisted of visual function, mobility, and balance tests.

RESULTS

All patients successfully completed training on the CAREN system. While the Argus II device was active, walking speed increased from baseline to immediately after the intervention on flat and undulating surfaces and while localizing objects by 20%, 10%, and 18%, respectively. An improved ability to complete the timed up and go test successfully was observed.

CONCLUSIONS

Novel methods of visual rehabilitation for retinal prostheses recipients, such the CAREN system, are feasible and may result in improved ability to use the Argus II while performing functional tasks. Immersive technology may provide a solution for the standardization of effective rehabilitation approaches to augment retinal prosthesis performance. Heterogeneity of results indicates that a larger sample size would be beneficial.

Retinal Prostheses and Artificial Vision

In outer retinal degenerative diseases such as retinitis pigmentosa, choroideremia, and geographic atrophy, 30% of the ganglion cell layer in the macula remains intact. With subretinal and epiretinal prostheses, these inner retinal cells are stimulated with controlled electrical current by either a microphotodiode placed in the subretinal area or a microelectrode array tacked to the epiretinal region. As the patient learns to interpret the resulting phosphene patterns created in the brain through special rehabilitation exercises, their orientation, mobility, and quality of life increase. Implants that stimulate the lateral geniculate nucleus or visual cortex are currently being studied for diseases in which the ganglion cells and optic nerve are completely destroyed.

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.

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.

Photochemistry of Organic Retinal Prostheses

Organic devices are attracting considerable attention as prostheses for the recovery of retinal light sensitivity lost to retinal degenerative disease. The biotic/abiotic interface created when light-sensitive polymers and living tissues are placed in contact allows excitation of a response in blind laboratory rats exposed to visual stimuli. Although polymer retinal prostheses have proved to be efficient, their working mechanism is far from being fully understood. In this review article, we discuss the results of the studies conducted on these kinds of polymer devices and compare them with the data found in the literature for inorganic retinal prostheses, where the working mechanisms are better comprehended. This comparison, which tries to set some reference values and figures of merit, is intended for use as a starting point to determine the direction for further investigation.

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.

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.

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.

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

PURPOSE

To evaluate the improvement in targeted reaching movements toward targets of various contrasts in a patient implanted with a suprachoroidal-transretinal stimulation (STS) retinal prosthesis.

METHODS

An STS retinal prosthesis was implanted in the right eye of a 42-year-old man with advanced Stargardt disease (visual acuity: right eye, light perception; left eye, hand motion). In localization tests during the 1-year follow-up period, the patient attempted to touch the center of a white square target (visual angle, 10°; contrast, 96, 85, or 74%) displayed at a random position on a monitor. The distance between the touched point and the center of the target (the absolute deviation) was averaged over 20 trials with the STS system on or off.

RESULTS

With the left eye occluded, the absolute deviation was not consistently lower with the system on than off for high-contrast (96%) targets, but was consistently lower with the system on for low-contrast (74%) targets. With both eyes open, the absolute deviation was consistently lower with the system on than off for 85%-contrast targets. With the system on and 96%-contrast targets, we detected a shorter response time while covering the right eye, which was being implanted with the STS, compared to covering the left eye (2.41 ± 2.52 vs 8.45 ± 3.78 s, p < 0.01).

CONCLUSIONS

Performance of a reaching movement improved in a patient with an STS retinal prosthesis implanted in an eye with residual natural vision. Patients with a retinal prosthesis may be able to improve their visual performance by using both artificial vision and their residual natural vision.

CLINICAL TRIAL REGISTRATION

Beginning date of the trial: Feb. 20, 2014 Date of registration: Jan. 4, 2014 Trial registration number: UMIN000012754 Registration site: UMIN Clinical Trials Registry (UMIN-CTR) http://www.umin.ac.jp/ctr/index.htm.

Multimodal Imaging Including Optical Coherence Tomography Angiography of a Patient With Argus II Retinal Prosthesis One Year After Implantation

A 58-year-old man with end-stage retinitis pigmentosa (RP) and visual acuity of light perception in both eyes received simultaneous phacoemulsification with intraocular lens implantation and implantation of the Argus II Retinal Prosthesis System (Second Sight Medical Products, Sylmar, CA) to his right eye 1 year ago. He accomplished the fitting and rehabilitation sessions, and no extraocular or intraocular complications were encountered perioperatively, postoperatively, or during the follow-up. The patient used the prosthesis actively for 2.5 to 3 hours per day. In this report, the authors compare the multimodal imaging findings including optical coherence tomography angiography of the chronic electrically stimulated retinal prosthesis implanted eye with the fellow eye. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:55-59.].

Flexible microelectrode array for retinal prosthesis

fMEA (flexible microelectrode array) is one of the key implantable components for neural stimulating and recording. For its specific implanted environment, it should be designed and fabricated to meet following requirements such as biocompatibility, high-resolution, flexible and low impedance to ensure safety and long-term effective stimulation. Here we proposed a high resolution (1025-channel) fMEA for artificial retina. The adhesion between its substrate polyimide (PI) and metal was enhanced by using plasma treatment. The stimulation spots were electroplated with Pt-gray, which significantly reduced the electrochemical impedance from 110 kμ to 16 kμ at 1 kHz, and also provided larger charge storage capacity up to 83.2 mC/cm². It shows a promising application for neural stimulation and recording.

Learning to see again: biological constraints on cortical plasticity and the implications for sight restoration technologies

The 'bionic eye'-so long a dream of the future-is finally becoming a reality with retinal prostheses available to patients in both the US and Europe. However, clinical experience with these implants has made it apparent that the visual information provided by these devices differs substantially from normal sight. Consequently, the ability of patients to learn to make use of this abnormal retinal input plays a critical role in whether or not some functional vision is successfully regained. The goal of the present review is to summarize the vast basic science literature on developmental and adult cortical plasticity with an emphasis on how this literature might relate to the field of prosthetic vision. We begin with describing the distortion and information loss likely to be experienced by visual prosthesis users. We then define cortical plasticity and perceptual learning, and describe what is known, and what is unknown, about visual plasticity across the hierarchy of brain regions involved in visual processing, and across different stages of life. We close by discussing what is known about brain plasticity in sight restoration patients and discuss biological mechanisms that might eventually be harnessed to improve visual learning in these patients.

[Visual prostheses]

Sensory neuroprostheses for restoration of vision are a technical approach for treatment of previously untreatable blindness. These systems consist of a technical sensor such as a camera and an implanted multi-electrode array within the visual system. The image information from the sensor is processed with specially designed integrated circuits in such a way that the stimulation pulses can be determined and presented to the implanted multi-electrode matrix. Energy supply and the transfer of the stimulus pulse information is realized either via direct cable connections within the site of the implant or by telemetric inductive links. Currently, two retinal implant systems are approved in the European Union (EU) to be used in blind patients with retinitis pigmentosa. With both systems basic visual functions can be restored. The complication rate is relatively low given the complexity of the surgical procedure. Other systems are still under development but approval studies by several manufacturers and consortia are already in preparation.

Visual BOLD Response in Late Blind Subjects with Argus II Retinal Prosthesis

Retinal prosthesis technologies require that the visual system downstream of the retinal circuitry be capable of transmitting and elaborating visual signals. We studied the capability of plastic remodeling in late blind subjects implanted with the Argus II Retinal Prosthesis with psychophysics and functional MRI (fMRI). After surgery, six out of seven retinitis pigmentosa (RP) blind subjects were able to detect high-contrast stimuli using the prosthetic implant. However, direction discrimination to contrast modulated stimuli remained at chance level in all of them. No subject showed any improvement of contrast sensitivity in either eye when not using the Argus II. Before the implant, the Blood Oxygenation Level Dependent (BOLD) activity in V1 and the lateral geniculate nucleus (LGN) was very weak or absent. Surprisingly, after prolonged use of Argus II, BOLD responses to visual input were enhanced. This is, to our knowledge, the first study tracking the neural changes of visual areas in patients after retinal implant, revealing a capacity to respond to restored visual input even after years of deprivation.

The potential of the second sight system bionic eye implant for partial sight restoration

INTRODUCTION

Second Sight System bionic eye implant, a commercially available visual prosthesis developed by Second Sight Medical Products, has been implanted in over 125 patients with outer retinal dystrophies such as retinitis pigmentosa. The system has gained regulatory approval in both the USA and Europe, and aims to restore vision by electrical stimulation of the nerve cells of the inner retina.

AREAS COVERED

In this review, we present the safety profile of this implant from the international clinical trial and discuss the nature and levels of improvement in visual function achieved by patients implanted with the system. Expert commentary: Future developments for the system will be explored following the discussion of the current usefulness of the device, its limitation as and the areas in which further development is necessary.

Worldwide Argus II implantation: recommendations to optimize patient outcomes

Background

A position paper based on the collective experiences of Argus II Retinal Prosthesis System investigators to review strategies to optimize outcomes in patients with retinitis pigmentosa undergoing retinal prosthesis implantation.

Methods

Retinal surgeons, device programmers, and rehabilitation specialists from Europe, Canada, Middle East, and the United States were convened to the first international Argus II Investigator Meeting held in Ann Arbor, MI in March 2015. The recommendations from the collective experiences were collected. Factors associated with successful outcomes were determined.

Results

Factors leading to successful outcomes begin with appropriate patient selection, expectation counseling, and preoperative retinal assessment. Challenges to surgical implantation include presence of staphyloma and inadequate Tenon’s capsule or conjunctiva. Modified surgical technique may reduce risks of complications such as hypotony and conjunctival erosion. Rehabilitation efforts and correlation with validated outcome measures following implantation are critical.

Conclusions

Bringing together Argus II investigators allowed the identification of strategies to optimize patient outcomes. Establishing an on-line collaborative network will foster coordinated research efforts to advance outcome assessment and rehabilitation strategies.

Retinal remodeling in human retinitis pigmentosa

Retinitis Pigmentosa (RP) in the human is a progressive, currently irreversible neural degenerative disease usually caused by gene defects that disrupt the function or architecture of the photoreceptors. While RP can initially be a disease of photoreceptors, there is increasing evidence that the inner retina becomes progressively disorganized as the outer retina degenerates. These alterations have been extensively described in animal models, but remodeling in humans has not been as well characterized. This study, using computational molecular phenotyping (CMP) seeks to advance our understanding of the retinal remodeling process in humans. We describe cone mediated preservation of overall topology, retinal reprogramming in the earliest stages of the disease in retinal bipolar cells, and alterations in both small molecule and protein signatures of neurons and glia. Furthermore, while Müller glia appear to be some of the last cells left in the degenerate retina, they are also one of the first cell classes in the neural retina to respond to stress which may reveal mechanisms related to remodeling and cell death in other retinal cell classes. Also fundamentally important is the finding that retinal network topologies are altered. Our results suggest interventions that presume substantial preservation of the neural retina will likely fail in late stages of the disease. Even early intervention offers no guarantee that the interventions will be immune to progressive remodeling. Fundamental work in the biology and mechanisms of disease progression are needed to support vision rescue strategies.

Argus II retinal prosthesis system: An update

This review focuses on a description of the Argus II retinal prosthesis system (Argus II; Second Sight Medical Products, Sylmar, CA) that was approved for humanitarian use by the FDA in 2013 in patients with retinitis pigmentosa with bare or no light perception vision. The article describes the components of Argus II, the studies on the implant, and future directions.

False reaching movements in localization test and effect of auditory feedback in simulated ultra-low vision subjects and patients with retinitis pigmentosa

PURPOSE

To determine the accuracy of reaching movements with localization tests in subjects with simulated ultra-low vision, and to examine the effectiveness of auditory feedback training in improving the accuracy of the reaching movements.

METHODS

Twenty-one subjects with simulated ultra-low vision and three patients with advanced retinitis pigmentosa (RP) were studied with the localization tester. The localization tester had white square targets with a visual angle of 10° that were projected randomly on a computer monitor screen. The subjects or RP patients were instructed to touch the center of the target. Each subject was tested 20 trials. The distance from the center of the target to the point where subjects touched, the deviation, was calculated automatically by the computer. We also examined the effect of auditory feedback on improving the accuracy of reaching movements.

RESULTS

The average angle of deviation in the subjects was not significantly correlated with visual acuity. The points touched by subjects with simulated low vision were located downward and horizontally toward the hand they used. They were condensed around the barycenter of the touched points (paired t tests; *p = 0.037). The touched points of the patients also deviated downward and condensed around the barycenter. The deviations decreased significantly with auditory feedback when trained over 100 trials.

CONCLUSIONS

The subjects with simulated ultra-low vision and the advanced RP patients had false orientations against the position of localized target systematically. An auditory feedback system may help to correct the false orientations for reaching movements in patients with very low vision.

Argus II retinal prosthesis malrotation and repositioning with intraoperative optical coherence tomography in a posterior staphyloma

Introduction

The Argus II retinal prosthesis may improve visual function in patients with severe vision loss from retinitis pigmentosa. Optimal centration of the electrode array over the macula is important to achieve optimal visual results. Argus tack malrotation is a novel entity that may be encountered during placement, especially in patients with posterior staphyloma.

Methods

Retrospective case review.

Results

During tacking of the electronics array a clockwise rotation occurred resulting in malposition. We hypothesize this was secondary to undue rotation or posterior pressure applied during tack insertion in conjunction with placement over a previously unrecognized posterior staphyloma. Intraoperative optical coherence tomography, because of the cross-sectional images provided, was helpful in visualizing the distance between the electronics array and the retina, which was difficult to assess using the surgical microscope alone. Repositioning was achieved by adjusting the tack without removal. The patient experienced an improvement in vision as a result of the surgery.

Conclusion

Malrotation may occur when tacking the Argus II prosthesis, and the presence of a posterior staphyloma may increase this risk. It is important to differentiate malrotation from tack misplacement – the former may be addressed with array unrotation or partial tack withdrawal and the latter may require tack removal and reinsertion. Also, intraoperative optical coherence tomography may be helpful in characterizing electronics array position during surgery.

Using the rd1 mouse to understand functional and anatomical retinal remodelling and treatment implications in retinitis pigmentosa: A review

Retinitis Pigmentosa (RP) reflects a range of inherited retinal disorders which involve photoreceptor degeneration and retinal pigmented epithelium dysfunction. Despite the multitude of genetic mutations being associated with the RP phenotype, the clinical and functional manifestations of the disease remain the same: nyctalopia, visual field constriction (tunnel vision), photopsias and pigment proliferation. In this review, we describe the typical clinical phenotype of human RP and review the anatomical and functional remodelling which occurs in RP determined from studies in the rd/rd (rd1) mouse. We also review studies that report a slowing down or show an acceleration of retinal degeneration and finally we provide insights on the impact retinal remodelling may have in vision restoration strategies.

Prenatal Exposure to Curcumin Protects Rod Photoreceptors in a Transgenic Pro23His Swine Model of Retinitis Pigmentosa

PURPOSE

Rhodopsin localization and rod photoreceptor (PR) morphology is altered in embryonic transgenic (Tg) Pro23His (P23H) miniswine. At birth, the Tg P23H swine retina lacks rod driven signaling. Curcumin, a neuroprotective food additive, has been shown to rescue Tg P23H rat rod PRs and promote normal trafficking of rhodopsin. We tested the hypothesis that prenatal exposure to curcumin would prevent PR morphological changes in Tg P23H miniswine retinae.

METHODS

A domestic sow was inseminated with semen from a Tg P23H miniswine founder. Her daily diet was supplemented with curcumin (100 mg/Kg body weight) from embryonic (E) day 80 to E112. The same diet without curcumin was fed to a second inseminated control sow. At E112, 2 days before parturition, both sows were euthanized. Their embryos were harvested, genotyped, and their eyes enucleated and prepared for morphological evaluation.

RESULTS

In all pigs, we measured mean outer retinal thickness, localization of rhodopsin, and rod PR morphology. Curcumin-treated Tg P23H swine embryonic retinas were similar to WT. Untreated Tg P23H embryonic retinas show significant degenerative effects; their outer retina was thinner, rod PR morphology was abnormal, and rhodopsin was mislocalized to the outer nuclear layer (ONL).

CONCLUSIONS

These data support a role for curcumin as a neuroprotective agent that prevents/delays morphological abnormalities associated with rod PR degeneration in this Tg P23H swine model of retinitis pigmentosa (RP).

TRANSLATIONAL RELEVANCE

Curcumin, a Food and Drug Administration-approved dietary supplement, may arrest/delay PR degeneration if ingested by individuals at risk for developing RP.

Vision Science: Can Rhodopsin Cure Blindness?

Outer retinal degeneration is the leading cause of blindness in the developed world. A new study now demonstrates that ectopic expression of human rhodopsin in the inner retina, mediated by viral gene therapy, can restore light sensitivity and some vision to mice blind from outer retinal degeneration.