Matthew A. Petoe

Objective. To evaluate the effectiveness of a novel depth-based vision processing (VP) method, local background enclosure (LBE), in comparison to the comprehensive VP method, Lanczos2 (L2), in suprachoroidal retinal prosthesis implant recipients during navigational tasks in laboratory and real-world settings. Approach. Four participants were acclimatized to both VP methods. Participants were asked to detect and navigate past five of eight possible obstacles in a white corridor across 20–30 trials. Randomized obstacles included black or white mannequins, black or white overhanging boxes, black or white bins and black or white stationary boxes. The same four participants underwent trials at three different real-word urban locations using both VP methods (randomized order). They were tasked with navigating a complex, dynamic pre-determined scene while detecting, verbally identifying, and avoiding obstacles in their path. Main results. The indoor obstacle course showed that the LBE method (63.6 ± 10.7%, mean ± SD) performed significantly better than L2 (48.5 ± 11.2%), for detection of obstacles (p < 0.001, Mack–Skillings). The real-world assessment showed that of the objects detected, 50.2% (138/275) were correctly identified using LBE and 41.7% (138/331) using L2, corresponding to a risk difference of 8 percentage points, p = 0.081). Significance. Real world outcomes can be improved using an enhanced VP algorithm, providing depth-based visual cues (#NCT05158049).

Background: To assess the safety and stability profile of the suprachoroidal retinal prosthesis (ScRP) in participants with retinitis pigmentosa (RP) for 2 years from implantation. Methods: Four participants, with advanced RP and bare‐light perception vision were enrolled in a prospective, single arm unmasked interventional clinical trial and unilaterally implanted with a 44‐channel ScRP (NCT03406416). Electrical stimulation commenced in the psychophysics laboratory prior to use in local environments. Outcome measures included serious adverse events, adverse events, implant stability and implant functionality to assess the safety and stability profile over 2.0–2.7 years. Results: Surgical procedures took 204–260 min and were uncomplicated. Postoperative recovery was uneventful. Imaging confirmed the device position under the macula and the absence of retinal trauma. There were no serious adverse events and the adverse events that occurred were mild. All electrodes were functional at surgery completion, and only 3% electrodes lost functionality by study end. There was minor array movement (translational and rotational) within the first 10–15 weeks only. The electrode to retina distance increased as expected with fibrous capsule development, but plateaued in three of four participants within 12 months. Retinal and choroidal thicknesses were consistent with the underlying retinal dystrophic disease. Conclusions: The ScRP can be safely implanted in the suprachoroidal space and has minimal long‐term impacts on the eye, with no SAEs and only slight array movement seen over 2.0–2.7 years. Hence, the findings indicate approach feasibility and further multicentre studies are warranted.

Objective. This study investigated software methods for removing stimulation artefacts in recordings undertaken during deep brain stimulation (DBS). We aimed to evaluate artefact attenuation using sample recordings of evoked resonant neural activity (ERNA), as well as a synthetic ground-truth waveform that emulated observed ERNA characteristics. Approach. The synthetic waveform and eight raw DBS recordings were processed by fourteen algorithms spanning the following categories: signal modification, signal decomposition, and template subtraction. For the synthetic waveform, performance was quantified by comparing each reconstructed signal against the ground-truth waveform. For DBS recordings, performance was contrasted amongst each other. The stimulation artefact was quantified by its amplitude and subsequent decay to baseline by the time to first zero-crossing. Each reconstructed ERNA signal was characterised by peak-to-peak-amplitude, root-mean-square amplitude, latency, and number of zero-crossings. Main results. None of the methods performed overall as well as the Backward Filter. Signal decomposition techniques were able to attenuate stimulation artefact albeit with unacceptable ERNA distortion. Significance. Upon evaluation of common software methods for DBS artefact attenuation, we advocate the use of the Backward Filter for reducing such artefacts while reconstructing ERNA.

Purpose: To report the long-term observations of the electrode–tissue interface and perceptual stability in humans after chronic stimulation with a 44-channel suprachoroidal retinal implant. Methods: Four subjects (S1–4) with end-stage retinitis pigmentosa received the implant unilaterally (NCT03406416). Electrode impedances, electrode–retina distance (measured using optical coherence tomography imaging), and perceptual thresholds were monitored up to 181 weeks after implantation as the subjects used the prosthesis in the laboratory and in daily life. Stimulation charge density was limited to 32 µC/cm² per phase. Results: Electrode impedances were stable longitudinally. The electrode–retina distances increased after surgery and then stabilized, and were well-described by an asymptotic exponential model. The stabilization of electrode–retina distances was variable between subjects, stabilizing after 45 weeks for S1, 63 weeks for S2, and 24 weeks for S3 (linear regression; P_gradient > 0.05). For S4, a statistically significant increase in electrode–retina distance persisted (P < 0.05), but by the study end point the rate of increase was clinically insignificant (exponential model: 0.33 µm/wk). Perceptual electrical thresholds were stable in one subject, decreased over time in two subjects (linear model; P < 0.05), and increased slightly in one subject but remained within the predefined charge limits (P = 0.02). Conclusions: Chronic stimulation with the suprachoroidal retinal prosthesis over 3 years resulted in stable impedances, small individual changes in perceptual electrical thresholds, and no clinically significant increase in electrode–retina distances after a period of settling after surgery. Translational Relevance: Chronic stimulation with the 44-channel suprachoroidal retinal implant with a charge density of up to 32 µC/cm² per phase is suitable for long-term use in humans.

Purpose: In a clinical trial (NCT03406416) of a second-generation (44-channel) suprachoroidal retinal prosthesis implanted in subjects with late-stage retinitis pigmentosa (RP), we assessed performance in real-world functional visual tasks and emotional well-being. Methods: The Functional Low-Vision Observer Rated Assessment (FLORA) and Impact of Vision Impairment–Very Low Vision (IVI-VLV) instruments were administered to four subjects before implantation and after device fitting. The FLORA contains 13 self-reported and 35 observer-reported items ranked for ease of conducting task (impossible-easy, central tendency given as mode). The IVI-VLV instrument quantified the impact of low vision on daily activities and emotional well-being. Results: Three subjects completed the FLORA for two years after device fitting; the fourth subject ceased participation in the FLORA after fitting for reasons unrelated to the device. For all subjects at each post-fitting visit, the mode ease of task with device ON was better or equal to device OFF. Ease of task improved over the first six months with device ON, then remained stable. Subjects reported improvements in mobility, functional vision, and quality of life with device ON. The IVI-VLV suggested self-assessed vision-related quality of life was not impacted by device implantation or usage. Conclusions: Subjects demonstrated sustained improved ease of task scores with device ON compared to OFF, indicating the device has a positive impact in the real-world setting. Translational Relevance: Our suprachoroidal retinal prosthesis shows potential utility in everyday life, by enabling an increased environmental awareness and improving access to sensory information for people with end-stage RP.

Objective: The positioning of the external camera in current designs of retinal prostheses may affect the egocentric spatial frame of reference and lead to pointing and localisation errors. The present simulated prosthetic vision (SPV) study investigated the immediate effects of four camera positions: (i) centre-mounted (CM), (ii) head-mounted (HM), (iii) left-mounted (LM), (iv) right-mounted (RM) on egocentric localisation. Approach: Fifteen sighted participants performed a pointing task while viewing the stimulus through a simulation of Bionic Vision Technologies’ 44-channel retinal prosthesis. Pointing responses were recorded immediately after exposure to different camera positions and prior to adaptation. The direction and magnitude of pointing errors and associated head movement behaviour were analysed using linear mixed effects analysis. Main results: Our results showed lower errors for medial camera positions (CM and HM) and overall improved accuracy and precision for CM position. Head orientation was found to largely influence the direction of pointing. There was a high positive correlation between direction of head orientation and direction of pointing with CM and HM camera positions, suggesting medial camera positions facilitated intuitive head orientation cues that are important for reliable egocentric direction estimation. Significance: The empirical evidence derived from the present SPV study offers practical guidance to reduce the effect on spatial dissociation of camera position in localisation tasks and inform design of future prosthetic vision devices and improve rehabilitation approaches.

Translational research in vision prosthetics, gene therapy, optogenetics, stem cell and other forms of transplantation, and sensory substitution is creating new therapeutic options for patients with neural forms of blindness. The technical challenges faced by each of these disciplines differ considerably, but they all face the same challenge of how to assess vision in patients with ultra-low vision (ULV), who will be the earliest subjects to receive new therapies. Historically, there were few tests to assess vision in ULV patients. In the 1990s, the field of visual prosthetics expanded rapidly, and this activity led to a heightened need to develop better tests to quantify end points for clinical studies. Each group tended to develop novel tests, which made it difficult to compare outcomes across groups. The common lack of validation of the tests and the variable use of controls added to the challenge of interpreting the outcomes of these clinical studies. In 2014, at the bi-annual International “Eye and the Chip” meeting of experts in the field of visual prosthetics, a group of interested leaders agreed to work cooperatively to develop the International Harmonization of Outcomes and Vision Endpoints in Vision Restoration Trials (HOVER) Taskforce. Under this banner, more than 80 specialists across seven topic areas joined an effort to formulate guidelines for performing and reporting psychophysical tests in humans who participate in clinical trials for visual restoration. This document provides the complete version of the consensus opinions from the HOVER taskforce, which, together with its rules of governance, will be posted on the website of the Henry Ford Department of Ophthalmology (www.artificialvision.org). Research groups or companies that choose to follow these guidelines are encouraged to include a specific statement to that effect in their communications to the public. The Executive Committee of the HOVER Taskforce will maintain a list of all human psychophysical research in the relevant fields of research on the same website to provide an overview of methods and outcomes of all clinical work being performed in an attempt to restore vision to the blind. This website will also specify which scientific publications contain the statement of certification. The website will be updated every 2 years and continue to exist as a living document of worldwide efforts to restore vision to the blind. The HOVER consensus document has been written by over 80 of the world's experts in vision restoration and low vision and provides recommendations on the measurement and reporting of patient outcomes in vision restoration trials.