Axonal stimulation affects the linear summation of single-point perception in three Argus II users.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Ophthalmology

Background:

• Retinal implants use electrical stimulation to create phosphenes, or perceived light flashes.
• Single-electrode phosphene characteristics are understood but not fully explored for paired-electrode stimulation.
• Understanding paired-electrode stimulation is crucial for advancing retinal prosthesis design.

Purpose of the Study:

• To investigate phosphene shape and number elicited by paired-electrode stimulation in Argus II Retinal Prosthesis users.
• To correlate phosphene perception with stimulus parameters and neuroanatomical factors.
• To determine if paired-electrode phosphene perception follows principles of linear summation.

Main Methods:

• Retrospective analysis of 3548 phosphene drawings from three blind participants with Argus II implants.
• Phosphene shape (area, perimeter, axis lengths) and number were correlated with single-electrode parameters.
• Statistical analysis included linear regression and partial correlation, examining stimulus amplitude and neuroanatomical distances (electrode-retina, electrode-fovea, between-axon, along-axon).

Main Results:

• Paired-electrode phosphene shape was predictable by the sum of individual single-electrode phosphene shapes (p < .001).
• Stimulus amplitude and electrode-fovea distance were primary predictors of paired-electrode phosphene shape (p < .05).
• Increased between-axon distance correlated with a higher number of elicited phosphenes in two participants (p < .05).

Conclusions:

• Phosphene perception from paired electrodes can be modeled as a linear summation of single-electrode perceptions.
• The influence of between-axon distance on phosphene count supports the axon map model for epiretinal stimulation.
• Findings provide insights for optimizing retinal prosthesis design and improving visual restoration.