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

Noninvasive Ultrasound Retinal Stimulation for Vision Restoration at High Spatiotemporal Resolution

Objective. Retinal degeneration involving progressive deterioration and loss of function of photoreceptors is a major cause of permanent vision loss worldwide. Strategies to treat these incurable conditions incorporate retinal prostheses via electrically stimulating surviving retinal neurons with implanted devices in the eye, optogenetic therapy, and sonogenetic therapy. Existing challenges of these strategies include invasive manner, complex implantation surgeries, and risky gene therapy. Methods and Results. Here, we show that direct ultrasound stimulation on the retina can evoke neuron activities from the visual centers including the superior colliculus and the primary visual cortex (V1), in either normal-sighted or retinal degenerated blind rats in vivo. The neuron activities induced by the customized spherically focused 3.1 MHz ultrasound transducer have shown both good spatial resolution of 250 μm and temporal resolution of 5 Hz in the rat visual centers. An additional customized 4.4 MHz helical transducer was further implemented to generate a static stimulation pattern of letter forms. Conclusion. Our findings demonstrate that ultrasound stimulation of the retina in vivo is a safe and effective approach with high spatiotemporal resolution, indicating a promising future of ultrasound stimulation as a novel and noninvasive visual prosthesis for translational applications in blind patients.

Selective Activation of Retinal Ganglion Cell Subtypes Through Targeted Electrical Stimulation Parameters

To restore vision to the low vision, epiretinal implants have been developed to electrically stimulate the healthy retinal ganglion cells (RGCs) in the degenerate retina. Given the diversity of retinal ganglion cells as well as the difference in their visual function, selective activation of RGCs subtypes can significantly improve the quality of the restored vision. Our recent results demonstrated that with the proper modulation of the current amplitude, small D1-bistratified cells with the contribution to blue/yellow color opponent pathway can be selectively activated at high frequency (200 Hz). The computational results correlated with the clinical findings revealing the blue sensation of 5/7 subjects with epiretinal implants at high frequency. Here we further explored the impacts of alterations in pulse duration and interphase gap on the response of RGCs at high frequency. We used the developed RGCs, A2-monostratified and D1-bistratified, and examined their response to a range of pulse durations (0.1−1.2 ms) and interphase gaps (0−1 ms). We found that the use of short pulse durations with no interphase gap at high frequency increases the differential response of RGCs, offering better opportunities for selective activation of D1 cells. The presence of the interphase gap has shown to reduce the overall differential response of RGCs. We also explored how the low density of calcium channels enhances the responsiveness of RGCs at high frequency.

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.

The First Epiretinal Implant for Hereditary Blindness in the Asia-Pacific Region

In February 2013, the Argus® II Retinal Prosthesis System (Second Sight Medical Products, Inc., Sylmar, CA, US) became the first "bionic eye" approved by the FDA to restore useful vision in patients previously blinded by end-stage retinitis pigmentosa, a hereditary, progressive degeneration of the outer retinal photoreceptor cells. The system captures and converts an external optical input into an electrical signal that activates an epiretinal electrode array on the inner surface of the retina. This signal bypasses dysfunctional photoreceptors and directly stimulates the functional inner retina, thus transmitting information to the visual cortex and creating artificial vision. This article describes the first implantation of the Argus II Retinal Prosthesis System in the Asia-Pacific region, which occurred in a deaf and blind 72-year-old Japanese American woman with Usher syndrome. At 57 months after her operation, the patient uses the device daily to perform visual tasks, and the microelectrode array remains in the proper position on the macula. This case demonstrates the long-term safety and efficacy of the Argus II epiretinal implant, which allowed a functionally blind patient to gain meaningful vision.

Detecting Progression of Retinitis Pigmentosa Using the Binomial Pointwise Linear Regression Method

Purpose

A method of evaluating central visual field (VF) progression in eyes with retinitis pigmentosa (RP) has still to be established. We previously reported the potential merit of applying a binomial test to pointwise linear regression (binomial PLR) in glaucoma progression. In the current study, we investigated the usefulness of binomial PLR in eyes with RP.

Methods

A series of 10 VFs (VF 1–10, Humphrey field analyzer, 10-2 test) from 196 eyes of 103 patients with RP were collected retrospectively. The PLR was performed by regressing the total deviation of all test points with the complete series of 10 VFs. The accuracy (positive predictive value, negative predictive value, and false-positive rate) and the time required to detect VF progression with shorter VF series (from VF 1–5 to VF 1–9) were compared across the binomial PLR, a permutation analysis of PLR (PoPLR), and a mean deviation (MD) trend analysis.

Results

In evaluating VF progression, the binomial PLR was comparable with the PoPLR and MD trend analyses in its positive predictive value (0.55 to 0.95), negative predictive value (0.67 to 0.92), and false-positive rate (0.01 to 0.05). The binomial PLR required significantly less time to detect VF progression (5.0 ± 2.0 years) than the PoPLR and MD trend analyses (P < 0.01, P < 0.001, respectively).

Conclusions

The application of a binomial PLR achieved reliable and earlier detection of central VF progression in eyes with RP.

Translational Relevance

A binomial PLR was useful in assessing VF progression in RP.

Improved performance and safety from Argus II retinal prosthesis post-approval study in France

PURPOSE

To evaluate the post-approval long-term outcomes of the Argus II Retinal Prosthesis, with a specific focus on its functional visual benefit in patients' daily activities.

METHODS

Eighteen patients with bare light perception due to end-stage retinitis pigmentosa were included in a French prospective, multicentre, single-arm study and followed for 2 years. Visual benefit in patients' daily activities was monitored through the use of the Functional Low-vision Observer Rated Assessment (FLORA), and the final score at 2 years was the primary effectiveness outcome. Standardized visual assessments were also performed. Device- or procedure-related adverse events were recorded.

RESULTS

Seventeen subjects completed the study. Positive impacts of the Argus II system on functional vision and well-being were demonstrated for over 70% of subjects on the FLORA. Among the daily activities/tasks tested, finding doorways was one of the most statistically significantly improved tasks (p < 0.001), along with estimating the size of an obstacle (p < 0.001), visually locating a place setting on a dining table (p < 0.001) and visually locating people in a non-crowded setting (p < 0.001). Visual function was improved on most standardized tests. Only two device- or procedure-related serious adverse events were observed (one vitreous haemorrhage and one endophthalmitis, both resolved with treatment). No explantation was required.

CONCLUSION

This first report of a completed post-approval study of Argus II with a two-year follow-up demonstrates the safety and effectiveness of the Argus II System in a real-world cohort of patients and further highlights its real functional benefit in implanted patients' daily activities.

Assessing Vision Quality in Retinal Prosthesis Implantees through Deep Learning: Current Progress and Improvements by Optimizing Hardware Design Parameters and Rehabilitation

Retinal prosthesis (RP) is used to partially restore vision in patients with degenerative retinal diseases. Assessing the quality of RP-acquired (i.e., prosthetic) vision is needed to evaluate RP impact and prospects. Spatial distortions caused by electrical stimulation of the retina in RP, and the low number of electrodes, have limited the prosthetic vision: patients mostly localize shapes and shadows rather than recognizing objects. We simulate prosthetic vision and evaluate vision on image classification tasks, varying critical hardware parameters: total number and size of electrodes. We also simulate rehabilitation by re-training our models on prosthetic vision images. We find that electrode size has little impact on vision while at least 400 electrodes are needed to sufficiently restore vision (more than 65% classification accuracy on a complex visual task after rehabilitation). Argus II, a currently available implant, produces a low-resolution vision leading to low accuracy (21.3% score after rehabilitation) in complex vision tasks. Rehabilitation produces significant improvements (accuracy improvement of up to 30% on complex tasks, depending on the number of electrodes) in the attained vision, boosting our expectations for RP interventions and motivating the establishment of rehabilitation procedures for RP implantees.

Microelectrode Array With Integrated Pneumatic Channels for Dynamic Control of Electrode Position in Retinal Implants

Retinal prostheses are biomedical devices that directly utilize electrical stimulation to create an artificial vision to help patients with retinal diseases such as retinitis pigmentosa. A major challenge in the microelectrode array (MEA) design for retinal prosthesis is to have a close topographical fit on the retinal surface. The local retinal topography can cause the electrodes in certain areas to have gaps up to several hundred micrometers from the retinal surface, resulting in impaired, or totally lost electrode functions in specific areas of the MEA. In this manuscript, an MEA with dynamically controlled electrode positions was proposed to reduce the electrode-retina distance and eliminate areas with poor contact after implantation. The MEA prototype had a polydimethylsiloxane and polyimide hybrid flexible substrate with gold interconnect lines and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate electrodes. Ring shaped counter electrodes were placed around the main electrodes to measure the distance between the electrode and the model retinal surface in real time. The results showed that this MEA design could reduce electrode-retina distance up to [Formula: see text] with 200 kPa pressure. Meanwhile, the impedance between the main and counter electrodes increased with smaller electrode-model retinal surface distance. Thus, the change of electrode-counter electrode impedance could be used to measure the separation gap and to confirm successful electrode contact without the need of optical coherence tomography scan. The amplitude of the stimulation signal on the model retinal surface with originally poor contact could be significantly improved after pressure was applied to reduce the gap.

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.

Assessing Photoreceptor Status in Retinal Dystrophies: From High-Resolution Imaging to Functional Vision

Purpose

To describe the value of integrating phenotype/genotype data, disease staging, and evaluation of functional vision in patient-centered management of retinal dystrophies.

Methods

(1) Cross-sectional structure-function and retrospective longitudinal studies to assess the correlations between standard fundus autofluorescence (FAF), optical coherence tomography, visual acuity (VA), and perimetry (visual field [VF]) examinations to evaluate photoreceptor functional loss in a cohort of patients with rod-cone dystrophy (RCD); (2) flood-illumination adaptive optics (FIAO) imaging focusing on photoreceptor misalignment and orientation of outer segments; and (3) evaluation of the impact of visual impairment in daily life activities, based on functional (visual and mobility) vision assessment in a naturalistic environment in visually impaired subjects with RCD and subjects treated with Luxturna^Ⓡ for RPE65-related Leber congenital amaurosis before and after therapy.

Results

The results of the cross-sectional transversal study showed that (1) VA and macular sensitivity were weakly correlated with the structural variables; and (2) functional impairment (VF) was correlated with reduction of anatomical markers of photoreceptor structure and increased width of autofluorescent ring. The dimensions of the ring of increased FAF evolved faster. Other criteria that differed among groups were the lengths of the ellipsoid zone, the external limiting membrane, and the foveal thickness. FIAO revealed a variety of phenotypes: paradoxical visibility of foveal cones; heterogeneous brightness of cones; dim, inner segment–like, and RPE-like mosaic. Directional illumination by varying orientation of incident light (Stiles-Crawford effect) and the amount of side illumination (gaze-dependent imaging) affected photoreceptor visibility. Mobility assessment under different lighting conditions showed correlation with VF, VA, contrast sensitivity (CS), and dark adaptation, with different predictive values depending on mobility study paradigms and illumination level. At high illumination level (235 lux), VF was a predictor for all mobility performance models. Under low illumination (1 and 2 lux), VF was the most significant predictor of mobility performance variables, while CS best explained the number of collisions and segments. In subjects treated with Luxturna^Ⓡ, a very favorable impact on travel speed and reduction in the number of collisions, especially at low luminance, was observable 6 months following injection, in both children and adults.

Conclusions

Our results suggest the benefit of development and implementation of quantitative and reproducible tools to evaluate the status of photoreceptors and the impact of both visual impairment and novel therapies in real-life conditions. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

EPIRETINAL FIBROSIS REMOVAL IN AN ARGUS II-IMPLANTED EYE: Histological Characteristics and Functional Results

PURPOSE

1) To investigate morphologic and histochemical characteristics of an epiretinal fibrosis removed in an Argus II-implanted eye; 2) to evaluate the Argus II function before and after the fibrosis removal, and 3) to compare morphologic and functional data.

METHODS

Fibrosis, which developed between the Argus II prosthesis and the retina two years after implant, was surgically removed. Its morphologic and histochemical characteristics were evaluated both in light and transmission electron microscopy, with special stains and immunohistochemistry. The Argus II function was evaluated during the follow-up before surgical removal and 1 month later.

RESULTS

Fibrosis was successfully removed. It was composed of a fibrotic tissue with spindle cells arranged in nodular aggregates with a symmetric distribution, mixed with an inflammatory infiltrate. Extra- and intracellular, irregular, small iron particles were found and confirmed ultrastructural characterization with degenerative cellular changes. The repositioned Argus II restored, and its function was partially nearly to normal values 1 month after surgery.

CONCLUSION

Fibrosis can develop between the Argus II and the retina with increasing reduced function. Morphologic characteristics of the removed fibrosis suggested a pathogenesis based on an inflammatory process involved in a foreign body reaction with progressing connective tissue deposition leading to sclerosis. Adequate clinical follow-up is critical to successful removal of the fibrosis with reactivation of the Argus II function.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Translational Relevance

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

First Human Results With the 256 Channel Intelligent Micro Implant Eye (IMIE 256)

Purpose

To report on the safety and efficacy of the 256-channel Intelligent Micro Implant Eye epiretinal prosthesis system (IMIE 256).

Methods

The IMIE 256 implants were implanted in the right eyes of five subjects with end-stage retinitis pigmentosa. Following implantation, the subjects underwent visual rehabilitation training for 90 days, and their visual performance was evaluated using the grating visual acuity test, Tumbling E visual acuity test, direction of motion, square localization, and orientation and mobility test. To evaluate the safety of the IMIE 256, all adverse events were recorded.

Results

Subjects performed significantly better on all evaluations with the IMIE 256 system on as compared with the performance at baseline or with the system off. There was a steady improvement in performance at each observation interval, indicating that the training and/or practice helped the subjects use the IMIE 256. There were two serious adverse events—electrode array movement and low intraocular pressure in one subject, which resolved with surgery. There were no other adverse events observed except those expected in the course of postoperative healing.

Conclusions

These results show an improved safety and efficacy profile compared with that of the Argus II implant. Further clinical trials are needed to confirm these results in a larger number of subjects and over longer durations.

Translational Relevance

To our knowledge, this study reports the first in-human data from a high-density (256 electrodes) epiretinal implant to restore sight to a subset of blind patients.

A Second-Generation (44-Channel) Suprachoroidal Retinal Prosthesis: Interim Clinical Trial Results

Purpose

To report the initial safety and efficacy results of a second-generation (44-channel) suprachoroidal retinal prosthesis at 56 weeks after device activation.

Methods

Four subjects, with advanced retinitis pigmentosa and bare-light perception only, enrolled in a phase II trial (NCT03406416). A 44-channel electrode array was implanted in a suprachoroidal pocket. Device stability, efficacy, and adverse events were investigated at 12-week intervals.

Results

All four subjects were implanted successfully and there were no device-related serious adverse events. Color fundus photography indicated a mild postoperative subretinal hemorrhage in two recipients, which cleared spontaneously within 2 weeks. Optical coherence tomography confirmed device stability and position under the macula. Screen-based localization accuracy was significantly better for all subjects with device on versus device off. Two subjects were significantly better with the device on in a motion discrimination task at 7, 15, and 30°/s and in a spatial discrimination task at 0.033 cycles per degree. All subjects were more accurate with the device on than device off at walking toward a target on a modified door task, localizing and touching tabletop objects, and detecting obstacles in an obstacle avoidance task. A positive effect of the implant on subjects' daily lives was confirmed by an orientation and mobility assessor and subject self-report.

Conclusions

These interim study data demonstrate that the suprachoroidal prosthesis is safe and provides significant improvements in functional vision, activities of daily living, and observer-rated quality of life.

Translational Relevance

A suprachoroidal prosthesis can provide clinically useful artificial vision while maintaining a safe surgical profile.

A Review on Mesenchymal Stem Cells for Treatment of Retinal Diseases

Mesenchymal Stem Cells (MSCs) have been studied extensively for the treatment of several retinal diseases. The therapeutic potential of MSCs lies in its ability to differentiate into multiple lineages and secretome enriched with immunomodulatory, anti-angiogenic and neurotrophic factors. Several studies have reported the role of MSCs in repair and regeneration of the damaged retina where the secreted factors from MSCs prevent retinal degeneration, improve retinal morphology and function. MSCs also donate mitochondria to rescue the function of retinal cells and exosomes secreted by MSCs were found to have anti-apoptotic and anti-inflammatory effects. Based on several promising results obtained from the preclinical studies, several clinical trials were initiated to explore the potential advantages of MSCs for the treatment of retinal diseases. This review summarizes the various properties of MSCs that help to repair and restore the damaged retinal cells and its potential for the treatment of retinal degenerative diseases.

Stem Cell Therapy for Retinal Degeneration: The Evidence to Date

There is a rise in the number of people who have vision loss due to retinal diseases, and conventional therapies for treating retinal degeneration fail to repair and regenerate the damaged retina. Several studies in animal models and human trials have explored the use of stem cells to repair the retinal tissue to improve visual acuity. In addition to the treatment of age-related macular degeneration (AMD) and diabetic retinopathy (DR), stem cell therapies were used to treat genetic diseases such as retinitis pigmentosa (RP) and Stargardt’s disease, characterized by gradual loss of photoreceptor cells in the retina. Transplantation of retinal pigment epithelial (RPE) cells derived from embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have shown promising results in improving retinal function in various preclinical models of retinal degeneration and clinical studies without any severe side effects. Mesenchymal stem cells (MSCs) were utilized to treat optic neuropathy, RP, DR, and glaucoma with positive clinical outcomes. This review summarizes the preclinical and clinical evidence of stem cell therapy and current limitations in utilizing stem cells for retinal degeneration.

Functional Dynamics of Deafferented Early Visual Cortex in Glaucoma

In advanced retinitis pigmentosa with retinal lesions, the lesion projection zone (LPZ) in the early visual cortex can be driven during visual tasks, while it remains unresponsive during passive viewing. We tested whether this finding translates to advanced glaucoma, a major cause of acquired blindness. During visual stimulation, 3T fMRI scans were acquired for participants with advanced glaucoma (n = 4; age range: 51–72) and compared to two reference groups, i.e., advanced retinitis pigmentosa (n = 3; age range: 46–78) and age-matched healthy controls with simulated defects (n = 7). The participants viewed grating patterns drifting in 8 directions (12 s) alternating with uniform gray (12 s), either during passive viewing (PV), i.e., central fixation, or during a one-back task (OBT), i.e., reports of succeeding identical motion directions. As another reference, a fixation-dot task condition was included. Only in glaucoma and retinitis pigmentosa but not in controls, fMRI-responses in the lesion projection zone (LPZ) of V1 shifted from negative for PV to positive for OBT (p = 0.024 and p = 0.012, respectively). In glaucoma, these effects also reached significance in V3 (p = 0.006), while in V2 there was a non-significant trend (p = 0.069). The general absence of positive responses in the LPZ during PV underscores the lack of early visual cortex bottom-up plasticity for acquired visual field defects in humans. Trends in our exploratory analysis suggesting the task-dependent LPZ responses to be inversely related to visual field loss, indicate the benefit of patient stratification strategies in future studies with greater sample sizes. We conclude that top-down mechanisms associated with task-elicited demands rather than visual cortex remapping appear to shape LPZ responses not only in retinitis pigmentosa, but also in glaucoma. These insights are of critical importance for the development of schemes for treatment and rehabilitation in glaucoma and beyond.

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.

Glow in the dark: Using a heat-sensitive camera for blind individuals with prosthetic vision

To date, retinal implants are the only available treatment for blind individuals with retinal degenerations such as retinitis pigmentosa. Argus II is the only visual implant with FDA approval, with more than 300 users worldwide. Argus II stimulation is based on a grayscale image coming from a head-mounted visible-light camera. Normally, the 11°×19° field of view of the Argus II user is full of objects that may elicit similar phosphenes. The prosthesis cannot meaningfully convey so much visual information, and the percept is reduced to an ambiguous impression of light. This study is aimed at investigating the efficacy of simplifying the video input in real-time using a heat-sensitive camera. Data were acquired from four Argus II users in 5 stationary tasks with either hot objects or human targets as stimuli. All tasks were of m-alternative forced choice design where precisely one of the m≥2 response alternatives was defined to be "correct" by the experimenter. To compare performance with heat-sensitive and normal cameras across all tasks, regardless of m, we used an extension of signal detection theory to latent variables, estimating person ability and item difficulty in d' units. Results demonstrate that subject performance was significantly better across all tasks with the thermal camera compared to the regular Argus II camera. The future addition of thermal imaging to devices with very poor spatial resolution may have significant real-life benefits for orientation, personal safety, and social interactions, thereby improving quality of life.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Translational Relevance

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

The Burden of X-Linked Retinitis Pigmentosa on Patients and Society: A Narrative Literature Review

X-linked retinitis pigmentosa (XLRP) is a severe form of retinitis pigmentosa (RP), a rare, inherited retinal degenerative disorder, that causes blindness. The aim of this literature review was to identify what is currently known about the burden of XLRP. Literature databases were searched for articles describing the clinical, humanistic, or economic burden of XLRP or RP in the US, Japan, France, Germany, Italy, Spain, and the UK, published in English between 2014 and 2019; gray literature and cited references were reviewed. Literature describing XLRP is limited as this is an ultra-rare condition; findings relating to burden of RP have been reported with interpretation of how burden differs for XLRP. In XLRP, night blindness usually presents in the first decade of life, followed by loss of peripheral and then central vision; legal blindness is reported at a median of 45 years in affected males (vs median 70 years for RP). There is limited evidence of humanistic or economic burden specific to XLRP; one study identified greater vision-related activity limitations in patients with XLRP compared with the wider RP population. Qualitative studies describe increased humanistic burden for people living with RP; difficulty undertaking everyday tasks (driving, hobbies, reading), psychosocial burden and barriers to work and career. People described the emotional impact of dealing with progression of RP, ongoing social and physical challenges, and the impact of RP on relationships. The economic burden of RP is associated with lost productivity, greater healthcare costs and increasing requirement for formal and informal care. In summary, XLRP remains an untreatable condition that can impact people from childhood. The humanistic burden of RP has been shown to increase as the disease progresses; hence, in XLRP the earlier onset and earlier progression to blindness during prime working years may mean a comparatively greater lifetime burden of disease.

Precise temporal control of interferential neural stimulation via phase modulation

OBJECTIVE

Noninvasive neural stimulation via temporally interferential (TI) electrical field is currently an area of interest as a noninvasive method of brain stimulation. The major limitation of TI stimulation is the difficulty of precise temporal control of the stimulation, due to the nature of the sinusoidal envelope generated by the interference. The purpose of this study was to investigate the possibility of improving interferential stimulation by introducing precise temporal control using phase modulation.

METHODS

In conventional TI, a sinusoidal current is applied to two electrode pairs with slightly different frequencies, to cause interference. In this paper we describe phase modulation interference (PMI). Instead of shifting frequency, the phase of a sinusoidal wave was partially modulated, causing a transient increase or decrease of the envelope. The spatial distribution of envelope modulation amplitude by TI and PMI was visualized using both electromagnetic simulation and actual measurement using tissue phantom.

RESULTS

The measured voltage transient in the tissue phantom produce a precise, temporally controlled pulse-like envelope using PMI. The spatial distributions of the amplitude of the envelope modulation by TI and PMI did not differ significantly, and were consistent with electromagnetic simulation.

CONCLUSION

PMI allows precise temporal control of interferential stimulation, thus increasing the practical utility of interferential stimulation.

SIGNIFICANCE

PMI improves interferential stimulation, allowing more temporally precise stimulation to neural tissue located distantly from the stimulating electrodes.

Discrimination of simple objects decoded from the output of retinal ganglion cells upon sinusoidal electrical stimulation

Objective. Most neuroprosthetic implants employ pulsatile square-wave electrical stimuli, which are significantly different from physiological inter-neuronal communication. In case of retinal neuroprosthetics, which use a certain type of pulsatile stimuli, reliable object and contrast discrimination by implanted blind patients remained challenging. Here we investigated to what extent simple objects can be discriminated from the output of retinal ganglion cells (RGCs) upon sinusoidal stimulation.Approach. Spatially confined objects were formed by different combinations of 1024 stimulating microelectrodes. The RGC activity in theex vivoretina of photoreceptor-degenerated mouse, of healthy mouse or of primate was recorded simultaneously using an interleaved recording microelectrode array implemented in a CMOS-based chip.Main results. We report that application of sinusoidal electrical stimuli (40 Hz) in epiretinal configuration instantaneously and reliably modulates the RGC activity in spatially confined areas at low stimulation threshold charge densities (40 nC mm^-2). Classification of overlapping but spatially displaced objects (1° separation) was achieved by distinct spiking activity of selected RGCs. A classifier (regularized logistic regression) discriminated spatially displaced objects (size: 5.5° or 3.5°) with high accuracy (90% or 62%). Stimulation with low artificial contrast (10%) encoded by different stimulus amplitudes generated RGC activity, which was classified with an accuracy of 80% for large objects (5.5°).Significance. We conclude that time-continuous smooth-wave stimulation provides robust, localized neuronal activation in photoreceptor-degenerated retina, which may enable future artificial vision at high temporal, spatial and contrast resolution.

Early and late stage gene therapy interventions for inherited retinal degenerations

Inherited and age-related retinal degeneration is the hallmark of a large group of heterogeneous diseases and is the main cause of untreatable blindness today. Genetic factors play a major pathogenic role in retinal degenerations for both monogenic diseases (such as retinitis pigmentosa) and complex diseases with established genetic risk factors (such as age-related macular degeneration). Progress in genotyping techniques and back of the eye imaging are completing our understanding of these diseases and their manifestations in patient populations suffering from retinal degenerations. It is clear that whatever the genetic cause, the majority of vision loss in retinal diseases results from the loss of photoreceptor function. The timing and circumstances surrounding the loss of photoreceptor function determine the adequate therapeutic approach to use for each patient. Among such approaches, gene therapy is rapidly becoming a therapeutic reality applicable in the clinic. This massive move from laboratory work towards clinical application has been propelled by the advances in our understanding of disease genetics and mechanisms, gene delivery vectors, gene editing systems, and compensatory strategies for loss of photoreceptor function. Here, we provide an overview of existing modalities of retinal gene therapy and their relevance based on the needs of patient populations suffering from inherited retinal degenerations.

Assessment of optogenetically-driven strategies for prosthetic restoration of cortical vision in large-scale neural simulation of V1

The neural encoding of visual features in primary visual cortex (V1) is well understood, with strong correlates to low-level perception, making V1 a strong candidate for vision restoration through neuroprosthetics. However, the functional relevance of neural dynamics evoked through external stimulation directly imposed at the cortical level is poorly understood. Furthermore, protocols for designing cortical stimulation patterns that would induce a naturalistic perception of the encoded stimuli have not yet been established. Here, we demonstrate a proof of concept by solving these issues through a computational model, combining (1) a large-scale spiking neural network model of cat V1 and (2) a virtual prosthetic system transcoding the visual input into tailored light-stimulation patterns which drive in situ the optogenetically modified cortical tissue. Using such virtual experiments, we design a protocol for translating simple Fourier contrasted stimuli (gratings) into activation patterns of the optogenetic matrix stimulator. We then quantify the relationship between spatial configuration of the imposed light pattern and the induced cortical activity. Our simulations in the absence of visual drive (simulated blindness) show that optogenetic stimulation with a spatial resolution as low as 100 [Formula: see text]m, and light intensity as weak as [Formula: see text] photons/s/cm[Formula: see text] is sufficient to evoke activity patterns in V1 close to those evoked by normal vision.

Modelling the visual response to an OUReP retinal prosthesis with photoelectric dye coupled to polyethylene film

Objective.Retinal prostheses have been developed to restore vision in blind patients suffering from diseases like retinitis pigmentosa.Approach.A new type of retinal prosthesis called the Okayama University-type retinal prosthesis (OUReP) was developed by chemically coupling photoelectric dyes to a polyethylene film surface. The prosthesis works by passively generating an electric potential when stimulated by light. However, the neurophysiological mechanism of how OUReP stimulates the degenerated retina is unknown.Main results.Here, we explore how the OUReP affects retinal tissues using a finite element model to solve for the potential inside the tissue and an active Hodgkin-Huxley model based on rat vision to predict the corresponding retinal bipolar response.Significance.We show that the OUReP is likely capable of eliciting responses in retinal bipolar cells necessary to generate vision under most ambient conditions.

Inducing lateralized phosphenes over the occipital lobe using transcranial magnetic stimulation to navigate a virtual environment

Electrical stimulation involving visual areas of the brain produces artificial light percepts called phosphenes. These visual percepts have been extensively investigated in previous studies involving intracortical microsimulation (ICMS) and serve as the basis for developing a visual prosthesis for the blind. Although advances have been achieved, many challenges still remain with implementing a functional ICMS for visual rehabilitation purposes. Transcranial magnetic stimulation (TMS) over the primary occipital lobe offers an alternative method to produce phosphenes non-invasively. A main challenge facing blind individuals involves navigation. Within the scientific community, methods to evaluate the ability of a visual prosthesis to facilitate in navigation has been neglected. In this study, we investigate the effectiveness of evoking lateralized phosphenes to navigate a computer simulated virtual environment. More importantly, we demonstrate how virtual environments along with the development of a visual prosthesis share a mutual relationship benefiting both patients and researchers. Using two TMS devices, a pair of 40mm figure-of-eight coils were placed over each occipital hemisphere resulting in lateralized phosphene perception. Participants were tasked with making a series of left and right turns using peripheral devices depending on the visual hemifield in which a phosphene is present. If a participant was able to accurately perceive all ten phosphenes, the simulated target is able to advance and fully exit the virtual environment. Our findings demonstrate that participants can interpret lateralized phosphenes while highlighting the integration of computer based virtual environments to evaluate the capability of a visual prosthesis during navigation.

Intravitreal quantum dots for retinitis pigmentosa: a first-in-human safety study

Background: Studies indicate that electrical stimulation of retinitis pigmentosa (RP) retina is beneficial. Quantum dots (QDs) can convert light to electrical stimulus and therefore may have therapeutic potential for RP. Methods: This was an open-label, fellow eye-controlled, first-in-human safety study. Five adults with end-stage (arm A) and 15 with severe (arm B) RP received one or two intravitreal injections of 0.2 or 2μM cadmium/selenium 655 Alt QDs. Results: No adverse events were attributed to QDs. In arm A, median best corrected visual acuity was unchanged. In arm B, mean best corrected visual acuity improved from 6/398 to 6/177, versus 6/147 to 6/144 in the fellow eye. Conclusion: Intravitreal QDs can be safely administered to patients with RP. Vision appears to benefit and further validating studies are justified.

Advances in Neuroscience, Not Devices, Will Determine the Effectiveness of Visual Prostheses

Background: Innovations in engineering and neuroscience have enabled the development of sophisticated visual prosthetic devices. In clinical trials, these devices have provided visual acuities as high as 20/460, enabled coarse navigation, and even allowed for reading of short words. However, long-term commercial viability arguably rests on attaining even better vision and more definitive improvements in tasks of daily living and quality of life. Purpose: Here we review technological and biological obstacles in the implementation of visual prosthetics. Conclusions: Research in the visual prosthetic field has tackled significant technical challenges, including biocompatibility, signal spread through neural tissue, and inadvertent activation of passing axons; however, significant gaps in knowledge remain in the realm of neuroscience, including the neural code of vision and visual plasticity. We assert that further optimization of prosthetic devices alone will not provide markedly improved visual outcomes without significant advances in our understanding of neuroscience.

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.

Color and cellular selectivity of retinal ganglion cell subtypes through frequency modulation of electrical stimulation

Epiretinal prostheses aim at electrically stimulating the inner most surviving retinal cells-retinal ganglion cells (RGCs)-to restore partial sight to the blind. Recent tests in patients with epiretinal implants have revealed that electrical stimulation of the retina results in the percept of color of the elicited phosphenes, which depends on the frequency of stimulation. This paper presents computational results that are predictive of this finding and further support our understanding of the mechanisms of color encoding in electrical stimulation of retina, which could prove pivotal for the design of advanced retinal prosthetics that elicit both percept and color. This provides, for the first time, a directly applicable "amplitude-frequency" stimulation strategy to "encode color" in future retinal prosthetics through a predictive computational tool to selectively target small bistratified cells, which have been shown to contribute to "blue-yellow" color opponency in the retinal circuitry. The presented results are validated with experimental data reported in the literature and correlated with findings in blind patients with a retinal prosthetic implant collected by our group.

Novel Graphene Electrode for Retinal Implants: An in vivo Biocompatibility Study

Evaluating biocompatibility is a core essential step to introducing a new material as a candidate for brain-machine interfaces. Foreign body reactions often result in glial scars that can impede the performance of the interface. Having a high conductivity and large electrochemical window, graphene is a candidate material for electrical stimulation with retinal prosthesis. In this study, non-functional devices consisting of chemical vapor deposition (CVD) graphene embedded onto polyimide/SU-8 substrates were fabricated for a biocompatibility study. The devices were implanted beneath the retina of blind P23H rats. Implants were monitored by optical coherence tomography (OCT) and eye fundus which indicated a high stability in vivo up to 3 months before histology studies were done. Microglial reconstruction through confocal imaging illustrates that the presence of graphene on polyimide reduced the number of microglial cells in the retina compared to polyimide alone, thereby indicating a high biocompatibility. This study highlights an interesting approach to assess material biocompatibility in a tissue model of central nervous system, the retina, which is easily accessed optically and surgically.

Development of highly durable retinal prosthesis using photoelectric dyes coupled to polyethylene film and quantitative in vitro evaluation of its durability

Retinal prostheses have been developed to restore vision in blind patients suffering from such diseases as retinitis pigmentosa. In our previous studies, we developed a retinal prosthesis called dye-coupled film by chemical coupling of photoelectric dyes, which absorb light and then generate electrical potential, with a polyethylene film surface. The dye-coupled film is nontoxic, and we recovered the vision of a monkey with macular degeneration. The amount of dye on the dye-coupled film, however, decreased to one-third after five months in the monkey's eye. The photoelectric dye consists of a cation with photoresponsivity and a bromide ion (Br^-). Therefore, an anion-exchange reaction could be applied to the dye-coupled film to improve its durability. In this study, the anion-exchange reaction was conducted using bis(trifluoromethanesulfonyl)imide ion (TFSI^-), which has lower nucleophilicity than Br^-. First, the long-term durability was examined without using animal subjects and in a short period. Subsequently, an elemental analysis was performed to confirm the exchange between Br^-and TFSI^-, and chemical properties, such as photoresponsivity and durability, before and after the anion exchange, were evaluated. It was quantitatively confirmed that the long-term durability of dye-coupled films can be evaluated in an in vitro environment and in a short period of one-thirtieth by utilizing a saline solution at 60°C, compared with an in vivo environment. In addition, the durability of the dye-coupled film with TFSI^-was improved to 270%-320% compared with that of the dye-coupled film with Br^-.

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.

Multisensory perception in Argus II retinal prosthesis patients: Leveraging auditory-visual mappings to enhance prosthesis outcomes

Crossmodal mappings associate features (such as spatial location) between audition and vision, thereby aiding sensory binding and perceptual accuracy. Previously, it has been unclear whether patients with artificial vision will develop crossmodal mappings despite the low spatial and temporal resolution of their visual perception (particularly in light of the remodeling of the retina and visual cortex that takes place during decades of vision loss). To address this question, we studied crossmodal mappings psychophysically in Retinitis Pigmentosa patients with partial visual restoration by means of Argus II retinal prostheses, which incorporate an electrode array implanted on the retinal surface that stimulates still-viable ganglion cells with a video stream from a head-mounted camera. We found that Argus II patients (N = 10) exhibit significant crossmodal mappings between auditory location and visual location, and between auditory pitch and visual elevation, equivalent to those of age-matched sighted controls (N = 10). Furthermore, Argus II patients (N = 6) were able to use crossmodal mappings to locate a visual target more quickly with auditory cueing than without. Overall, restored artificial vision was shown to interact with audition via crossmodal mappings, which implies that the reorganization during blindness and the limitations of artificial vision did not prevent the relearning of crossmodal mappings. In particular, cueing based on crossmodal mappings was shown to improve visual search with a retinal prosthesis. This result represents a key first step toward leveraging crossmodal interactions for improved patient visual functionality.

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.

Clinical Perspective: Treating RPE65-Associated Retinal Dystrophy

Until recently, there was no approved treatment for a retinal degenerative disease. Subretinal injection of a recombinant adeno-associated virus (AAV) delivering the normal copy of the human RPE65 cDNA led to reversal of blindness first in animal models and then in humans. This led to the first US Food and Drug Administration (FDA)-approved gene therapy product for a genetic disease, voretigene neparvovec-rzyl (Luxturna). Luxturna was then approved by the European Medicines Association and is now available in the US through Spark Therapeutics and worldwide through Novartis. Not only has treatment with Luxturna changed the lives of people previously destined to live a life of blindness, but it has fueled interest in developing additional gene therapy reagents targeting numerous other genetic forms of inherited retinal disease. This review describes many of the considerations for administration of Luxturna and describes how lessons from experience with Luxturna could lead to additional gene-based treatments of blindness.

Optogenetic therapy: high spatiotemporal resolution and pattern discrimination compatible with vision restoration in non-human primates

Vision restoration is an ideal medical application for optogenetics, because the eye provides direct optical access to the retina for stimulation. Optogenetic therapy could be used for diseases involving photoreceptor degeneration, such as retinitis pigmentosa or age-related macular degeneration. We describe here the selection, in non-human primates, of a specific optogenetic construct currently tested in a clinical trial. We used the microbial opsin ChrimsonR, and showed that the AAV2.7m8 vector had a higher transfection efficiency than AAV2 in retinal ganglion cells (RGCs) and that ChrimsonR fused to tdTomato (ChR-tdT) was expressed more efficiently than ChrimsonR. Light at 600 nm activated RGCs transfected with AAV2.7m8 ChR-tdT, from an irradiance of 10¹⁵ photons.cm⁻².s⁻¹. Vector doses of 5 × 10¹⁰ and 5 × 10¹¹ vg/eye transfected up to 7000 RGCs/mm² in the perifovea, with no significant immune reaction. We recorded RGC responses from a stimulus duration of 1 ms upwards. When using the recorded activity to decode stimulus information, we obtained an estimated visual acuity of 20/249, above the level of legal blindness (20/400). These results lay the groundwork for the ongoing clinical trial with the AAV2.7m8 - ChR-tdT vector for vision restoration in patients with retinitis pigmentosa.

Gauvain et al demonstrate that optogenetic therapy using the AAV2.7m8- ChR-tdT construct can partially restore vision in non-human primates to levels above those considered legally-blind. This study enables the identification of the most suitable construct for ongoing clinical trials attempting vision restoration in patients with retinitis pigmentosa.

Effects of the Argus II Retinal Prosthesis System on the Quality of Life of Patients With Ultra-Low Vision Due to Retinitis Pigmentosa: Protocol for a Single-Arm, Mixed Methods Study

Background

Retinitis pigmentosa is an incurable, degenerative retinal condition causing progressive sight loss, significantly affecting patients’ quality of life. The Argus II Retinal Prosthesis is a surgically implanted medical device that delivers electrical stimulation to the retina. It is intended to produce a form of artificial vision for blind people with severe-to-profound retinitis pigmentosa by stimulating the remaining viable retinal cells to induce visual perception. This study has been initiated by National Health Service England’s Commissioning through Evaluation program and funded through the National Institute of Health Research of the United Kingdom.

Objective

The aim of this study was to assess the effect of the Argus II device on patient’s daily activities and quality of life.

Methods

This protocol is a prospective, single-arm, open-label, mixed methods study on 10 consecutive participants receiving the Argus II device. The patient representatives played an integral role in the design of this study. Eligibility criteria include ultra-low vision in both eyes as a result of end-stage retinitis pigmentosa and a willingness and capacity to complete the postimplantation rehabilitation program. Participants will be interviewed by independent researchers at baseline and 12 months later by using a semistructured, in-depth approach, alongside validated questionnaires (Impact of Vision Impairment-Very Low Vision, 5-level EuroQoL-5 dimensions scale, EuroQoL-visual analog scale, and Hospital Anxiety and Depression Scale) and a bespoke device-related questionnaire, which includes questions about users’ experiences with the procedure, the device, and rehabilitation. The effect of the device on patients’ functional vision and activities of daily living will be assessed by vision rehabilitation specialists using a set of tests measured on an ordinal scale (eg, ability to locate objects and avoid obstacles). Clinical outcomes include full-field stimulus light threshold, square localization, direction of motion, grating visual acuity, Landolt-C, procedural success, and adverse events. Qualitative and quantitative outcomes will be linked in a single database to enable individual participant measures to be considered in toto, comparing baseline to the final review.

Results

This study was approved by the local ethics committee on April 24, 2019 (London-Camberwell St. Giles Research Ethics Committee, reference 19/LO/0429). It has also been approved by the Health Research Authority and Health and Care Research Wales. At the time of protocol writing, Argus II was available for use in the United Kingdom; however, the manufacturer recently withdrew the Argus II device from sale in the United Kingdom. Therefore, the study is not going ahead at this time.

Conclusions

The mixed methods approach provides a rich and in-depth assessment of the effect of the device on participants’ quality of life. Despite the work not going ahead, the publication of this publicly funded protocol is important for researchers planning similar work.

International Registered Report Identifier (IRRID)

PRR1-10.2196/17436

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.

How is flexible electronics advancing neuroscience research?

Innovative neurotechnology must be leveraged to experimentally answer the multitude of pressing questions in modern neuroscience. Driven by the desire to address the existing neuroscience problems with newly engineered tools, we discuss in this review the benefits of flexible electronics for neuroscience studies. We first introduce the concept and define the properties of flexible and stretchable electronics. We then categorize the four dimensions where flexible electronics meets the demands of modern neuroscience: chronic stability, interfacing multiple structures, multi-modal compatibility, and neuron-type-specific recording. Specifically, with the bending stiffness now approaching that of neural tissue, implanted flexible electronic devices produce little shear motion, minimizing chronic immune responses and enabling recording and stimulation for months, and even years. The unique mechanical properties of flexible electronics also allow for intimate conformation to the brain, the spinal cord, peripheral nerves, and the retina. Moreover, flexible electronics enables optogenetic stimulation, microfluidic drug delivery, and neural activity imaging during electrical stimulation and recording. Finally, flexible electronics can enable neuron-type identification through analysis of high-fidelity recorded action potentials facilitated by its seamless integration with the neural circuitry. We argue that flexible electronics will play an increasingly important role in neuroscience studies and neurological therapies via the fabrication of neuromorphic devices on flexible substrates and the development of enhanced methods of neuronal interpenetration.

CHOROIDEREMIA: Retinal Degeneration With an Unmet Need

PURPOSE

Choroideremia is an incurable, X-linked, recessive retinal dystrophy caused by loss of function mutations in the CHM gene. It is estimated to affect approximately 1 in 50,000 male patients. It is characterized by progressive degeneration of the retinal pigment epithelium, choroid, and photoreceptors, resulting in visual impairment and blindness. There is an unmet need in choroideremia, because currently, there are no approved treatments available for patients with the disease.

METHODS

We review the patient journey, societal impact, and emerging treatments for patients with choroideremia.

RESULTS

Its relative rarity and similarities with other retinal diseases in early years mean that diagnosis of choroideremia can often be delayed. Furthermore, its impact on affected individuals, and wider society, is also likely underestimated. AAV2-mediated gene therapy is an investigational treatment that aims to replace the faulty CHM gene. Early-phase studies reported potentially important visual acuity gains and maintenance of vision in some patients, and a large Phase 3 program is now underway.

CONCLUSION

Choroideremia is a disease with a significant unmet need. Interventions that can treat progression of the disease and improve visual and functional outcomes have the potential to reduce health care costs and enhance patient quality of life.

[Vision restoration: science fiction or reality?]

Visual prostheses aim at restoring useful vision to patients who have become blind. This useful vision should enable them to regain autonomy in society for navigation, face recognition or reading. Two retinal prostheses have already obtained market authorization for patients affected by retinal dystrophies while a new device is in clinical trials for patients affected by age-related macular degeneration. Various prostheses, in particular cortical prostheses, are currently in clinical trials for optic neuropathies (glaucoma). Optogenetic therapy, an alternative strategy, has now reached the stage of clinical trials at the retinal level while moving forward at the cortical level. Other innovating strategies have obtained proofs of concepts in rodents but require a further validation in large animals prior to their evaluation on patients. Restoring vision should therefore become a reality for many patients even if this vision will not be as extensive and perfect as natural vision.

Blockade of Retinal Oscillations by Benzodiazepines Improves Efficiency of Electrical Stimulation in the Mouse Model of RP, rd10

Purpose

In RP, photoreceptors degenerate. Retinal prostheses are considered a suitable strategy to restore vision. In animal models of RP, a pathologic rhythmic activity seems to compromise the efficiency of retinal ganglion cell stimulation by an electrical prosthesis. We, therefore, strove to eliminate this pathologic activity.

Methods

Electrophysiologic recordings of local field potentials and spike activity of retinal ganglion cells were obtained in vitro from retinae of wild-type and rd10 mice using multielectrode arrays. Retinae were stimulated electrically.

Results

The efficiency of electrical stimulation was lower in rd10 retina than in wild-type retina and this was highly correlated with the presence of oscillations in retinal activity. Glycine and GABA, as well as the benzodiazepines diazepam, lorazepam, and flunitrazepam, abolished retinal oscillations and, most important, increased the efficiency of electrical stimulation to values similar to those in wild-type retina.

Conclusions

Treatment of patients with these benzodiazepines may offer a way to improve the performance of retinal implants in cases with poor implant proficiency. This study may open the way to a therapy that supports electrical stimulation by prostheses with pharmacologic treatment.

Highest reported visual acuity after electronic retinal implantation

PURPOSE

To report the highest attained visual acuity with an electronic retinal implant for the treatment of advanced retinal degeneration following a novel intensive period of visual training.

METHODS

A case study as part of the prospective, international, multi-centre, interventional clinical trial (ClinicalTrials.gov NCT02720640 and NCT01024803) of patients with the Retina Implant Alpha AMS (Retina Implant AG, Reutlingen, Germany) for advanced retinal degeneration. A patient with subretinal device implanted into worse-seeing eye with no useful perception of light vision secondary to USH2A retinal degeneration underwent intensive period of visual training.

RESULTS

The device remains functional with no safety concerns at 3 years postsurgical implantation, and following visual training, the patient achieved the highest visual acuity so far with an electronic retinal device, with real, digitally unenhanced, reading vision of 0.04 decimal (equivalent to 1.39 LogMAR and 20/500 or 6/150 Snellen). In addition, perception as well as partial identification of obstacles and evaluation of distances was possible in both daylight and night-time settings.

CONCLUSIONS

Retinal implants are currently the only available therapy option for advanced retinal degeneration. Visual rehabilitation postimplantation has potential to maximize visual percepts. The novel concept of intensive visual training presented herein shows what is achievable with electronic retinal implants and has implications for other therapeutic options, such as optogenetics, that aim to stimulate remaining inner retinal cells in advanced retinal degeneration.

Prosthetic Visual Performance Using a Disparity-Based Distance-Filtering System

PURPOSE

At present, Argus II is the only retinal prosthesis approved by the US Food and Drug Administration that induces visual percepts in people who are blind from end-stage outer retinal degenerations such as retinitis pigmentosa. It has been shown to work well in sparse, high-contrast settings, but in daily practice visual performance with the device is likely to be hampered by the cognitive load presented by a cluttered real-world environment. In this study, we investigated the effect of a stereo-disparity-based distance-filtering system on four experienced Argus II users for a range of tasks: object localization, depth discrimination, orientation and size discrimination, and people detection and direction of motion.

METHODS

Functional vision was assessed in a semicontrolled setup using unfiltered (normal camera) and distance-filtered (stereo camera) imagery. All tasks were forced choice designs and an extension of signal detection theory to latent (unobservable) variables was used to analyze the data, allowing estimation of person ability (person measures) and task difficulty (item measures) on the same axis.

RESULTS

All subjects performed better with the distance filter compared with the unfiltered image (P  < 0.001 on all tasks except localization).

CONCLUSIONS

Our results show that depth filtering using a disparity-based algorithm has significant benefits for people with Argus II implants.

TRANSLATIONAL RELEVANCE

The improvement in functional vision with the distance filter found in this study may have an important impact on vision rehabilitation and quality of life for people with visual prostheses and ultra low vision.