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Heval Benav, Robert Wilke, Alfred Stett, Eberhart Zrenner; A model for temporal features of visual sensations evoked by a subretinal electrode array for restoration of vision. Journal of Vision 2008;8(6):370. doi: https://doi.org/10.1167/8.6.370.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Subretinal microphotodiode-arrays (MPDAs) have the potential to restore vision in patients suffering from degenerative retinal diseases such as Retinitis Pigmentosa. Experiments with patients taking part in clinical studies revealed the feasibility of electrically evoking visual sensations (phosphenes). Here we present results delivered by a model which reproduces implant-evoked activity distributions of retinal ganglion cells (RGC), considering activity spread in the retinal network as well as frequency dependent RGC-adaptation. Methods: Input to the model was a movie-file representing two parallel rotating white bars. Width of the bars was 20x100 pixels with 20 pixels distance on a 100x100 pixels black background. Parameters for timing were set such that the output allowed recognizing form, number, speed and orientation of input stimuli. Retinal activity parameters from previous experiments were regarded in order to quantify spread of network activation in the retina and amplitude of RGC-activity. RGC-activity furthermore underwent frequency dependent adaptation. Results: RGC activity patterns conveyed a satisfactory motion picture quality in this model when electrodes were activated with sufficiently high frequencies between 5Hz and 10Hz, assuming an input frame rate of 10–20 frames per second. High stimulation frequencies allowed continuous evaluation of position and speed of the stimuli, however visual sensations faded quickly within only few seconds after onset of the movie. RGC activity was not subject to adaptation if the stimulation frequency remained below 2Hz. Therefore slowly moving objects still were recognizable at low stimulation frequencies, but movement speed of the rotating bar - stimulus could no longer be realistically estimated. Conclusions: Simulation of realistic approximations to visual sensations as evoked by subretinal MPDAs is subject to a number of assumptions made during model development. However model outputs sufficiently reproduced critical attributes of input stimuli. Also, disappearance of the sensations was in principal agreement with reports from clinical study patients carrying the subretinal MPDA.
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