Browsing by Author "Epp, Stephanie"

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    A Flexible Wireless System for Preclinical Evaluation of Retinal Prosthesis
    (MYU KK, 2018-01) Thien, Patrick; Millard, Rodney; Epp, Stephanie; Nayagam, David
    In this paper, we present a novel stimulation controller and monitoring system for evaluating the safety and efficacy of implantable neuroprosthetic devices in a preclinical setting. It features a programmable controller designed to be worn in a custom backpack by freely moving feline subjects. A custom controller powered two, modified, 22-channel clinical stimulators simultaneously. The controller and stimulators together weighed 140 g and measured 85 × 70 × 35 mm3. Power was supplied from a 3350 mAh lithium-ion battery. A Bluetooth-enabled laptop-PC base station managed up to six systems and allowed the remote adjustment of the stimulation amplitude and automated collection of stimulator telemetry data. The initial application was for the chronic safety testing of a 44-channel retinal prosthesis. Thirteen feline subjects were implanted with a suprachoroidal electrode array, which was then stimulated or monitored continuously for an average of 54.5 d. Batteries were changed twice weekly and electrode impedances were recorded hourly. This allowed broken electrodes and other issues to be quickly identified and addressed. The ability to remotely control the stimulation amplitude minimised the amount of subject handling that was required, likely reducing subject stress. Existing preclinical evaluation systems are either designed for short-term experiments and have many features but limited battery life, or for long-term static stimulation and are long-lived, but with restricted stimulation parameters and channel counts. Here, we have described a system designed to improve the chronic safety testing of electrode arrays. While it was used here with a suprachoroidal retinal implant, it could be readily adapted for other preclinical models requiring continuous, deterministic stimulation over a prolonged period.
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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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    Safety Studies for a 44-Channel Suprachoroidal Retinal Prosthesis: A Chronic Passive Study
    (IOVS, 2018-03) Abbott, Carla; Nayagam, David; Luu, Chi; Epp, Stephanie; Williams, Richard; Salinas-LaRosa, Cesar; Villalobos, Joel; McGowan, Ceara; Shivdasani, Mohit; Burns, Owen; Leavens, Jason; Yeoh, Jonathon; Brandli, Alice; Thien, Patrick; Zhou, Jenny; Feng, Helen; Williams, Chris; Shepherd, Robert; Allen, Penelope
    Abstract Purpose: Following successful clinical outcomes of the prototype suprachoroidal retinal prosthesis, Bionic Vision Australia has developed an upgraded 44-channel suprachoroidal retinal prosthesis to provide a wider field of view and more phosphenes. The aim was to evaluate the preclinical passive safety characteristics of the upgraded electrode array. Methods: Ten normal-sighted felines were unilaterally implanted with an array containing platinum electrodes (44 stimulating and 2 returns) on a silicone carrier near the area centralis. Clinical assessments (color fundus photos, optical coherence tomography, full-field electroretinography, intraocular pressure) were performed under anesthesia prior to surgery, and longitudinally for up to 20 weeks. Histopathology grading of fibrosis and inflammation was performed in two animals at 13 to 15 weeks. Results: Eight animals showed safe electrode array insertion (good retinal health) and good conformability of the array to the retinal curvature. Eight animals demonstrated good mechanical stability of the array with only minor (<2 disc diameters) lateral movement. Four cases of surgical or stability complications occurred due to (1) bulged choroid during surgery, (2) hemorrhage from a systemic bleeding disorder, (3) infection, and (4) partial erosion of thin posterior sclera. There was no change in retinal structure or function (other than that seen at surgery) at endpoint. Histopathology showed a mild foreign body response. Electrodes were intact on electrode array removal. Conclusions: The 44-channel suprachoroidal electrode array has an acceptable passive safety profile to proceed to clinical trial. The safety profile is expected to improve in human studies, as the complications seen are specific to imitations (anatomic differences) with the feline model.