Oculomotor Responses to Dynamic Stimuli in a 44-Channel Suprachoroidal Retinal Prosthesis

Abstract

Purpose To investigate oculomotor behavior in response to dynamic stimuli in retinal implant recipients. Methods Three suprachoroidal retinal implant recipients performed a four-alternative forced-choice motion discrimination task over six sessions longitudinally. Stimuli were a single white bar (“moving bar”) or a series of white bars (“moving grating”) sweeping left, right, up, or down across a 42″ monitor. Performance was compared with normal video processing and scrambled video processing (randomized image-to-electrode mapping to disrupt spatiotemporal structure). Eye and head movement was monitored throughout the task. Results Two subjects had diminished performance with scrambling, suggesting retinotopic discrimination was used in the normal condition and made smooth pursuit eye movements congruent to the moving bar stimulus direction. These two subjects also made stimulus-related eye movements resembling optokinetic reflex (OKR) for moving grating stimuli, but the movement was incongruent with stimulus direction. The third subject was less adept at the task, appeared primarily reliant on head position cues (head movements were congruent to stimulus direction), and did not exhibit retinotopic discrimination and associated eye movements. Conclusions Our observation of smooth pursuit indicates residual functionality of cortical direction-selective circuits and implies a more naturalistic perception of motion than expected. A distorted OKR implies improper functionality of retinal direction-selective circuits, possibly due to retinal remodeling or the non-selective nature of the electrical stimulation. Translational Relevance Retinal implant users can make naturalistic eye movements in response to moving stimuli, highlighting the potential for eye tracker feedback to improve perceptual localization and image stabilization in camera-based visual prostheses.

A Second-Generation (44-Channel) Suprachoroidal Retinal Prosthesis: Long-Term Observation of the Electrode–Tissue Interface

“…Although enlarging the electrodes is generally expected to lead to a decreased spatial resolution, the second-generation device still provided significant improvement in visual function tasks (including a grating acuity task) and activities of daily living. 16 – 18 …”

“…This study presents data from four adult human subjects (S1–S4) who participated in the clinical trial of a 44-channel suprachoroidal retinal implant (NCT03406416) between 2018 and 2021. 16 – 18 The subjects were profoundly blind (bare light perception only) from end-stage retinitis pigmentosa and had the suprachoroidal retinal prosthesis implanted unilaterally in 2018 ( Table 1 ). Device fitting commenced 8 weeks postoperatively, followed by training in laboratory and real-world environments and a minimum of 2 years of regular outcome measure assessments.…”

“…Device fitting commenced 8 weeks postoperatively, followed by training in laboratory and real-world environments and a minimum of 2 years of regular outcome measure assessments. 16 – 18 During this time the subjects used the prosthesis unsupervised in their daily lives and regularly visited the laboratory for training, functional vision assessment, and OCT imaging. Table 1 summarizes the subject demographics and the length of observation for each subject.…”

“…All four subjects perceived phosphenes in response to electrical stimulation with the implant, and the prosthesis provided functional vision improvements and meaningful assistance in activities of daily living. 16 – 18 For these practical benefits to be sustained in the long term, it is important that chronic stimulation with the implant does not lead to a loss of device functionality owing to changes in the electrode–tissue interface.…”

Functional Vision in the Real-World Environment With a Second-Generation (44-Channel) Suprachoroidal Retinal Prosthesis

“…Subjects then attended the laboratory for visual rehabilitation with the research team (weeks 1–16) receiving training on phosphene interpretation, 8 effective head-scanning, 25 and using the camera in laboratory-based tasks. 13 , 26 Head-scanning skills and eye-head-camera position awareness were developed by discussing the purpose and position of the camera, explaining how to perform environment scanning methodically, and practicing interacting with high-contrast objects and obstacles. 25 The post-fitting baseline FLORA assessments at week 17 were conducted after initial training was complete but before any O&M training.…”