Abstract
Purpose :
The Intracortical Visual Prosthesis (ICVP), a recently developed cortical implant, stimulates modular wireless floating microelectrode arrays (WFMAs) with the aim to restore vision. The purpose of this study was to investigate the stability of the ICVP system in the recipient by monitoring the thresholds of an electrode subset designated as sentinel electrodes.
Methods :
Each WFMA comprises 16 electrodes. Sentinel electrodes include one single low and one pair of high threshold electrodes from WFMAs with any single electrode threshold lower than the safe amplitude limit (60 µA), and one quad per WFMA for other WFMAs. Sentinel electrode thresholds were measured in 9 sessions from May to August 2022. Each session was either conducted in the morning or afternoon after the electrode analyzer test, and a single session usually comprised one or three threshold tests. Stimuli were 200 Hz pulse trains with 400 ms duration and a cathodic phase duration of 200 µs. Except for morning-afternoon comparisons, all threshold tests were performed at the start of the day to avoid adaptation by repeated stimulation. Data were analyzed using the Wilcoxon sign-rank test with Bonferroni-Holm correction for multiple comparisons.
Results :
Cross session analysis showed only 14 out 36 possible session pairs had a significant difference (p < 0.05). Therefore, 61.1% of session pairs had stable thresholds across sessions. There are 27 unique sentinel electrodes, of which 15 were tested on all sessions with slopes ranging from -0.3 to 0.2; only one slope, for a quad with thresholds around 10 uA, went down significanly over the test period (slope -0.06+-0.02 uV/day). This significant decrease in threshold is of no concern: Electrode properties were monitored through reverse telemetry and showed no changes. Within the second and third sessions, data were measured in both morning and afternoon. Statistical analysis showed that on average, afternoon thresholds are increased by 24%, presumably due to adaptation during the test day.
Conclusions :
Based on the stable thresholds of sentinel electrodes, we conclude that the first human-implanted ICVP system does not show signs of systematic sensitivity changes over a period of months. Although thresholds increased after repeated stimulation, they came back down before the next testing day.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.