Browsing by Author "Kentler, William"

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    Oculomotor Responses to Dynamic Stimuli in a 44-Channel Suprachoroidal Retinal Prosthesis
    (tvst, 2020-12) Titchener, Samuel; Kvansakul, Jessica; Shivdasani, Mohit; Nayagam, David; Epp, Stephanie; Williams, Chris; Barnes, Nick; Kentler, William; Kolic, Maria; Balin, Elizabeth; Ayton, Lauren; Abbott, Carla; Luu, Chi; Allen, Penelope; Petoe, Matthew
    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.
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    A Second-Generation (44-Channel) Suprachoroidal Retinal Prosthesis: Long-Term Observation of the Electrode–Tissue Interface
    (Translational Vision Science & Technology, 2022-06) Titchener, Samuel; Nayagam, David; Kvansakul, Jessica; Kolic, Maria; Baglin, Elizabeth; Abbott, Carla; McGuinness, Myra; Ayton, Lauren; Luu, Chi; Greenstein, Steven; Kentler, William; Shivdasani, Mohit; Allen, Penelope; Petoe, Matthew
    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; Pgradient > 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.