December 2022
Volume 22, Issue 14
Open Access
Vision Sciences Society Annual Meeting Abstract  |   December 2022
Factors affecting two-point discrimination thresholds in Argus II patients
Author Affiliations & Notes
  • Ezgi Yucel
    Department of Psychology, University of Washington, USA
  • Michael Beyeler
    Department of Computer Science, UC Santa Barbara, Santa Barbara, USA
  • Roksana Sadeghi
    Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD, USA
  • Arathy Kartha
    Department of Ophthalmology, Johns Hopkins School of Medicine, Baltimore, MD, USA
  • Gislin Dagnelie
    Department of Ophthalmology, Johns Hopkins School of Medicine, Baltimore, MD, USA
  • Ariel Rokem
    Department of Psychology, University of Washington, USA
  • Ione Fine
    Department of Psychology, University of Washington, USA
  • Footnotes
    Acknowledgements  UW Institute of Neuroengineering (UWIN), NIH
Journal of Vision December 2022, Vol.22, 3754. doi:https://doi.org/10.1167/jov.22.14.3754
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      Ezgi Yucel, Michael Beyeler, Roksana Sadeghi, Arathy Kartha, Gislin Dagnelie, Ariel Rokem, Ione Fine; Factors affecting two-point discrimination thresholds in Argus II patients. Journal of Vision 2022;22(14):3754. https://doi.org/10.1167/jov.22.14.3754.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Introduction: Retinal prostheses electrically stimulate remaining non-photoreceptor cells to generate phosphenes that can provide some functional vision. However, a major obstacle to the development of retinal prostheses has been the failure to consistently elicit pattern vision in patients. Here, we tried to determine the main contributors to the poor spatial resolution of Argus II devices, a 60-electrode epiretinal implant developed by Second Sight Medical Products, Inc. Methods: We measured two-point discrimination performance (the ability to determine whether one or two electrodes had been stimulated) in 3 blind participants implanted with the Argus II. We identified three factors that might predict two-point discrimination performance (1) current amplitude required to reach threshold, (2) physical distance between the electrodes, and (3) position of the two electrodes with respect to ganglion cell axon bundle trajectories. Results and Conclusions: The probability of the stimulation of two electrodes merging into a single percept was high when threshold currents were high, the physical separation between electrodes was small, or when electrodes were close to the same axon bundle. Although axonal stimulation plays a role, the primary contribution to the poor two-point discrimination of Argus II patients is primarily current spread, resulting from the high current amplitudes required to exceed detection threshold. Simulations demonstrate that these high thresholds stem from retinal damage, but also seem to be partly due to the electrode arrays not being flush to the retinal surface, offering a target for future developments.

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