This Basic Experimental Studies Involving Humans (BESH) study investigates phosphene perception and performance factors in blind participants implanted with the Argus II retinal prosthesis system. Using paired-electrode stimulation, we analyze how phosphene shape and number are influenced by neuroanatomical factors, stimulus parameters, and spatial offsets. Additionally, we examine the causes of high current thresholds and limited spatial resolution, which impede pattern vision in Argus II devices. This research aims to provide insights for optimizing stimulation strategies and improving retinal prosthesis design.

This study focuses on two experiments involving blind participants implanted with the Argus II retinal prosthesis:

Experiment 1: Paired-Electrode Phosphene Perception The study retrospectively analyzes 3548 phosphene drawings made by three participants. We investigate the impact of single- and paired-electrode stimulation on phosphene shape (area, perimeter, major/minor axis length) and the number of perceived phosphenes. Neuroanatomical parameters, including electrode-retina distance, electrode-fovea distance, and electrode-electrode distance (both along-axon and between-axon), are correlated with these outcomes. Statistical analyses include linear regression and partial correlation to examine the relationship between stimulation parameters and phosphene perception.

Experiment 2: Performance Factors in Argus II Prostheses This study explores the factors contributing to high current amplitude thresholds and poor spatial resolution in three participants. We measure current amplitude thresholds and two-point discrimination (the ability to distinguish stimulation on one versus two electrodes). Data from psychophysical experiments and simulations are analyzed to identify the roles of axonal stimulation, electrode lift, and retinal damage in limiting device performance.

These experiments aim to advance the understanding of epiretinal stimulation and inform the development of future retinal prostheses with improved spatial resolution and sensitivity.

Inclusion criteria:

• Subject must be at least 25 years of age;
• Subject has been implanted with the Argus II system;
• Subject's eye has healed from surgery and the surgeon has cleared the subject for programming;
• Subject has the cognitive and communication ability to participate in the study (i.e., follow spoken directions, perform tests, and give feedback);
• Subject is willing to conduct psychophysics testing up to 4-6 hours per day of testing on 3-5 consecutive days;
• Subject is capable of understanding patient information materials and giving written informed consent;
• Subject is able to walk unassisted.

Exclusion criteria:

• Subject is unwilling or unable to travel to testing facility for at least 3 days of testing within a one-week timeframe;
• Sighted controls: Subject has a history of motion sickness or flicker vertigo
• Subject does not speak English;
• Subject has language or hearing impairment

Deidentified data will be available from the investigative team, following initial publication of the results

Spring 2023 onward

Any researchers with a legitimate reason for wishing to re-analyze the data or compare them to study data collected in similar experiments

1 day