Reflections on the Safety and Stability of the Second‐Generation Suprachoroidal Retinal Prosthesis: Response

We were pleased to hear in the letter from Ying Wei and Zhenggao Xie 1 that they found our study 2 titled ‘A second-generation (44-channel) suprachoroidal retinal prosthesis: Surgical stability and safety during a 2-year clinical trial’ comprehensive and transparent in reporting outcomes. On the request for real-time impedance monitoring, our device already automatically bypasses failing electrodes in two ways: by a daily impedance check and a real-time compliance voltage check. Hence, these design features ensure the device remains functional. We report that over the 2.0–2.7 years of the trial only 3% (5 electrodes across 4 participants) of electrodes became non-functional, indicating very high robustness 2. For further information about impedance measures in the trial, please refer to our paper Titchener et al. 3, which shows how impedances were stable longitudinally from daily measures (Figure 1). Second, we strongly agree with the comment that our observation of the choroidal effusion event in one participant at 2.5 months post-surgery highlights the need for clear postoperative monitoring protocols in patients receiving a retinal prosthesis in the real-world setting. In our trial we performed multi-modal high-resolution retinal imaging (colour fundus photos, optical coherence tomography, near-infrared) weekly for 27 weeks post-surgery and during the fitting and training period, then every 12 weeks thereafter 2, 4. In the case of our participant with the choroidal effusion, there were no patient-reported symptoms, indicating the importance of follow-up to check for haemorrhage, effusion and device stability. We support the proposal by Wei and Xie 1 that surgeons implanting these devices should closely monitor the retina post-surgery. We suggest multi-modal retinal imaging at a minimum of every 1–2 weeks for the first 8 weeks, then every 3–6 months for the first 12 months after surgery. Finally, we agree that the headaches and photopsia symptoms after heavy device use are not ideal. However, we would like to emphasise that the acclimatisation process was structured and gradual, with the first 16 weeks post-switch-on devoted to fitting and training, as outlined in our papers Petoe et al. 4 and Karapanos et al. 5. The first few days involved single and paired electrode studies to determine thresholds. Training in use of the camera (with greater activity levels) occurred during the second half of the training period. The participants were very keen to start using the camera but were only allowed to take the device home after surgeon approval, the camera training was complete, and the orientation and mobility specialist had completed device-specific navigation training with the participant in their home environment (device take home range: 20–27 weeks post-switch-on across 4 participants) 5. We always used personalised stimulus parameters for each participant at each session, informed by their real-time feedback of discomfort and psychophysical measurements such as visual thresholds. We also collected feedback at monthly intervals via a phone call to keep track of discomfort/headaches during device use at home, and participants were advised to call us immediately if they experienced any change to their vision. In the real-world setting, personalised rehabilitation training needs to be provided by trained personnel to optimise outcomes and ensure discomfort is minimised. In summary, we agree with the points in the letter raised by Wei and Xie 1 and are very supportive of protocols such as those we have outlined to support the safe use of retinal prostheses in the real-world setting. We hope to expand our clinical validation of the suprachoroidal retinal prosthesis through a pivotal multi-centre trial. This work was supported by the National Health and Medical Research Council (NHMRC) Grant 1082358 (P.J.A.; Canberra, ACT, Australia) and Bionic Vision Technologies Pty Ltd. (Australia). The Bionics Institute and the Centre for Eye Research Australia wish to acknowledge the support of the Victorian Government through its Operational Infrastructure Support Program (VIC, Australia), and for generous support from the estate of the late Dr. Brian Entwisle. The Sponsor and/or funding organisations had no role in the design or conduct of this research. P.J.A., D.A.X.N., J.V., C.E.W., M.A.P. hold patents in relation to this work. P.J.A., M.K., E.K.B., S.A.T., J.K., D.A.X.N., C.D.L., M.A.P., C.J.A. received financial support for the work from Bionic Vision Technologies. M.K., E.B., M.P., C.J.A. received travel funding from Bionic Vision Technologies to present this work at an international conference in 2019. J.Y., R.J.B., M.B.M. report nothing to disclose. Writing Group Members: Penelope J Allen, Maria Kolic, Elizabeth K. Baglin, Samuel A. Titchener, Jessica Kvansakul, David AX Nayagam, Jonathan Yeoh, Robert J Briggs, Joel Villalobos, Christopher E. Williams, Myra B. McGuinness, Chi D Luu, Matthew A. Petoe and Carla J. Abbott. Study Group Members: Lauren N Ayton; Nick Barnes; Peter J. Blamey; Owen Burns; Robert G Buttery; Daniel WK Chiu; Rosie CH Dawkins; Stephanie B. Epp; Dean Johnson; Lewis Karapanos; William Kentler; Hugh J. McDermott; Ceara McGowan; Rodney E. Millard; Peter M. Seligman; Robert K. Shepherd; Nicholas C. Sinclair; Mohit N. Shivdasani; Patrick C. Thien; Ross Thomas; Janine G. Walker; Kiera A. Young. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions. Data S1: Supporting Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.