Article
44-channel suprachoroidal retinal prosthesis clinical trial: interim device status update 1 year post-implantation
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Published: | December 10, 2019 |
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Purpose: To evaluate the functionality and mechano-electrical stability of our suprachoroidal retinal prosthesis (SRP) in clinical trial participants.
Methods: 4 patients were implanted with a generation-2 SRP (Feb-Aug, 2018; ClinicalTrials.gov:NCT03406416). The implant had 44 platinum electrodes of 1mm diameter and 2 large return electrodes, embedded within a silicone substrate. This array was surgically positioned, suprachoroidally, with its stimulator package located on the ipsilateral skull. A patch affixed the implant to the temporal sclera beneath the lateral rectus muscle and a grommet stabilised the cable at the orbit. Impedances were measured intraoperatively and at follow-up visits to evaluate the implant’s electrical status and its effect on surrounding tissue. Impedances were calculated from voltage measurements in response to monopolar current controlled biphasic pulses (75µA, 25µs/phase). Array stability was assessed with optical coherence tomography (OCT). From 8 weeks post-implantation, electrodes were utilised with a range of stimulation parameters remaining within 250nC/phase/electrode.
Results: Intraoperatively 100% electrodes were operational; median impedances were 3.5kΩ (mean=3.5; SE=0.04; range=2.2-6.0). At switch-on, median impedance had risen to 5.9kΩ (mean=5.8; SE=0.05; range=3.2-8.1) in all participants and held steady thereafter. After a year of implantation, 98% electrodes remained <10kΩ. Electrode utilisation was weakly associated with short term decreases in impedances. There were no clear threshold trends. The array remained generally stable in the suprachoroidal space after an initial settling period. There was an average increase of 64-98µm in electrode to retina distance, as expected for fibrous tissue encapsulation.
Conclusion: The 44-channel SRP remains functional and stable after a year of implantation. Likewise, mechanical fixation and local tissue reaction are consistent with previous preclinical and clinical findings.
Acknowledgements and Funding: ARC Special Research Initiative in Bionic Vision Science and Technology grant to Bionic Vision Australia; NHMRC grant 1082358 to CIA PJA. NHMRC grant 1120664 to CIA CEW. The Centre for Eye Research Australia and the Bionics Institute wish to acknowledge the support of the Victorian Government through its Operational Infrastructure Support Program. DN, MP, ST, MK, EB, CA, CL, JK, WK, OB, PS, CW, PA receive(d) funding support from Bionic Vision Technologies.