Browsing by Author "Barnes, Nick"

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    Determining the Contribution of Retinotopic Discrimination to Localization Performance With a Suprachoroidal Retinal Prosthesis
    (IOVS, 2017-06) Petoe, Matthew; McCarthy, Chris; Shivdasani, Mohit; Sinclair, Nicholas; Scott, Adele; Ayton, Lauren; Barnes, Nick; Bionic Vision Australia Consortium
    Purpose: With a retinal prosthesis connected to a head-mounted camera, subjects can perform low vision tasks using a combination of electrode discrimination and head-directed localization. The objective of the present study was to investigate the contribution of retinotopic electrode discrimination (perception corresponding to the arrangement of the implanted electrodes with respect to their position beneath the retina) to visual performance for three recipients of a 24-channel suprachoroidal retinal implant. Proficiency in retinotopic discrimination may allow good performance with smaller head movements, and identification of this ability would be useful for targeted rehabilitation. Methods: Three participants with retinitis pigmentosa performed localization and grating acuity assessments using a suprachoroidal retinal prosthesis. We compared retinotopic and nonretinotopic electrode mapping and hypothesized that participants with measurable acuity in a normal retinotopic condition would be negatively impacted by the nonretinotopic condition. We also expected that participants without measurable acuity would preferentially use head movement over retinotopic information. Results: Only one participant was able to complete the grating acuity task. In the localization task, this participant exhibited significantly greater head movements and significantly lower localization scores when using the nonretinotopic electrode mapping. There was no significant difference in localization performance or head movement for the remaining two subjects when comparing retinotopic to nonretinotopic electrode mapping. Conclusions: Successful discrimination of retinotopic information is possible with a suprachoroidal retinal prosthesis. Head movement behavior during a localization task can be modified using a nonretinotopic mapping. Behavioral comparisons using retinotopic and nonretinotopic electrode mapping may be able to highlight deficiencies in retinotopic discrimination, with a view to address these deficiencies in a rehabilitation environment. (ClinicalTrials.gov number, NCT01603576).
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    Identification of Characters and Localization of Images Using Direct Multiple-Electrode Stimulation With a Suprachoroidal Retinal Prosthesis
    (IOVS, 2017-08) Shivdasani, Mohit; Sinclair, Nicholas; Gillespie, Lisa; Petoe, Matthew; Titchener, Samuel; Fallon, James; Perera, Thushara; Pardinas-Diaz, Darien; Barnes, Nick; Blamey, Peter; Bionic Vision Australia Consortium
    Purpose: Retinal prostheses provide vision to blind patients by eliciting phosphenes through electrical stimulation. This study explored whether character identification and image localization could be achieved through direct multiple-electrode stimulation with a suprachoroidal retinal prosthesis. Methods: Two of three retinitis pigmentosa patients implanted with a suprachoroidal electrode array were tested on three psychophysical tasks. Electrode patterns were stimulated to elicit perception of simple characters, following which percept localization was tested using either static or dynamic images. Eye tracking was used to assess the association between accuracy and eye movements. Results: In the character identification task, accuracy ranged from 2.7% to 93.3%, depending on the patient and character. In the static image localization task, accuracy decreased from near perfect to <20% with decreasing contrast (patient 1). Patient 2 scored up to 70% at 100% contrast. In the dynamic image localization task, patient 1 recognized the trajectory of the image up to speeds of 64 deg/s, whereas patient 2 scored just above chance. The degree of eye movement in both patients was related to accuracy and, to some extent, stimulus direction. Conclusions: The ability to identify characters and localize percepts demonstrates the capacity of the suprachoroidal device to provide meaningful information to blind patients. The variation in scores across all tasks highlights the importance of using spatial cues from phosphenes, which becomes more difficult at low contrast. The use of spatial information from multiple electrodes and eye-movement compensation is expected to improve performance outcomes during real-world prosthesis use in a camera-based system. (ClinicalTrials.gov number, NCT01603576.).
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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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    An update on retinal prostheses
    (Elsevier B.V., 2019-12) Ayton, Lauren; Barnes, Nick; Dagnelie, Gislin; Fujikado, Takashi; Goetz, Georges; Hornig, Ralf; Jones, Bryan; Muqit, Mahiul; Rathbun, Daniel; Stingl, Katarina; Weiland, James; Petoe, Matthew
    Retinal prostheses are designed to restore a basic sense of sight to people with profound vision loss. They require a relatively intact posterior visual pathway (optic nerve, lateral geniculate nucleus and visual cortex). Retinal implants are options for people with severe stages of retinal degenerative disease such as retinitis pigmentosa and age-related macular degeneration. There have now been three regulatory-approved retinal prostheses. Over five hundred patients have been implanted globally over the past 15 years. Devices generally provide an improved ability to localize high-contrast objects, navigate, and perform basic orientation tasks. Adverse events have included conjunctival erosion, retinal detachment, loss of light perception, and the need for revision surgery, but are rare. There are also specific device risks, including overstimulation (which could cause damage to the retina) or delamination of implanted components, but these are very unlikely. Current challenges include how to improve visual acuity, enlarge the field-of-view, and reduce a complex visual scene to its most salient components through image processing. This review encompasses the work of over 40 individual research groups who have built devices, developed stimulation strategies, or investigated the basic physiology underpinning retinal prostheses. Current technologies are summarized, along with future challenges that face the field.
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    Vision function testing for a suprachoroidal retinal prosthesis: effects of image filtering
    (IOP Publishing, 2016-04) Barnes, Nick; Scott, Adele; Lieby, Paulette; Petoe, Matthew; McCarthy, Chris; Stacey, Ashley; Ayton, Lauren; Sinclair, Nicholas; Shivdasani, Mohit; Lovell, Nigel; McDermott, Hugh; Walker, Janine; BVA Consortium
    OBJECTIVE: One strategy to improve the effectiveness of prosthetic vision devices is to process incoming images to ensure that key information can be perceived by the user. This paper presents the first comprehensive results of vision function testing for a suprachoroidal retinal prosthetic device utilizing of 20 stimulating electrodes. Further, we investigate whether using image filtering can improve results on a light localization task for implanted participants compared to minimal vision processing. No controlled implanted participant studies have yet investigated whether vision processing methods that are not task-specific can lead to improved results. APPROACH: Three participants with profound vision loss from retinitis pigmentosa were implanted with a suprachoroidal retinal prosthesis. All three completed multiple trials of a light localization test, and one participant completed multiple trials of acuity tests. The visual representations used were: Lanczos2 (a high quality Nyquist bandlimited downsampling filter); minimal vision processing (MVP); wide view regional averaging filtering (WV); scrambled; and, system off. MAIN RESULTS: Using Lanczos2, all three participants successfully completed a light localization task and obtained a significantly higher percentage of correct responses than using MVP ([Formula: see text]) or with system off ([Formula: see text]). Further, in a preliminary result using Lanczos2, one participant successfully completed grating acuity and Landolt C tasks, and showed significantly better performance ([Formula: see text]) compared to WV, scrambled and system off on the grating acuity task. SIGNIFICANCE: Participants successfully completed vision tasks using a 20 electrode suprachoroidal retinal prosthesis. Vision processing with a Nyquist bandlimited image filter has shown an advantage for a light localization task. This result suggests that this and targeted, more advanced vision processing schemes may become important components of retinal prostheses to enhance performance. ClinicalTrials.gov Identifier: NCT01503576.