Abstract
Purpose :
The shape of phosphenes elicited by single-electrode stimulation of epiretinal prostheses has been shown to depend on stimulus parameters and the retinal location of the stimulating electrode. The purpose of this study was to investigate whether these parameters could also predict phosphene appearance elicited by paired-electrode stimulation.
Methods :
We retrospectively analyzed 4402 phosphene drawings of three blind subjects implanted with an Argus II Retinal Prosthesis. Phosphene shape, characterized by four descriptors (area, perimeter, major/minor axis length), was first averaged across trials and normalized per subject, then correlated with stimulus parameters (amplitude) and neuroanatomical parameters (electrode-retina distance, electrode-fovea distance). Statistical analyses were conducted using simple and multiple linear regression.
Results :
Multiple regression revealed that stimulus amplitude predicted paired-electrode phosphene area (β=.360, p=.013) and minor axis length (β=.166, p=.026) and that electrode-retina distance (i.e., stimulating electrodes’ average distance to the retinal surface) predicted area (β=.934, p<.001), perimeter (β=.122, p=.003), and minor axis length (β=.451, p<.001). Interestingly, electrode-fovea distance (i.e., stimulating electrodes’ average retinal eccentricity) predicted perimeter (β=.158, p<.001) and major axis length (β=.170, p<.001). Moreover, a simple regression revealed that each paired-electrode shape descriptor could be predicted by the sum of the two corresponding single-electrode shape descriptors (p<.001).
Conclusions :
The shape of phosphenes elicited by paired-electrode stimulation was well predicted by the shape of their corresponding single-electrode phosphenes. We also identified electrode-fovea distance as a significant predictor of paired-electrode phosphene shape. Overall, these results demonstrate that two-point perception can be expressed as the linear summation of single-point perception. Future studies should assess if this linearity can be extended to more complex phosphene patterns.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.