Retinitis Pigmentosa
Conditions
Brief summary
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.
Detailed description
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.
Interventions
DEVICEArgus II
Participants used the Argus II retinal prosthesis system in both experiments to perform visual perception tasks.
Sponsors
Johns Hopkins University
University of Michigan
National Eye Institute (NEI)
University of California, Santa Barbara
Study design
Allocation
NA
Intervention model
SINGLE_GROUP
Primary purpose
BASIC_SCIENCE
Masking
NONE
Eligibility
Sex/Gender
ALL
Age
18 Years to No maximum
Healthy volunteers
Yes
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
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Number of Phosphenes Perceived | during single-session testing | Number of phosphenes perceived in response to paired-electrode stimulation across 5 spatial distances and 7 temporal interpulse delays. Phosphenes are brief sensations of light or visual flashes that occur in the absence of an external light source. A response is counted as a phosphene if the participant reports any visual sensation consistent with a flash of light. |
Countries
United States
Participant flow
Participants by arm
| Arm | Count |
|---|---|
| Argus II Users Blind individuals previously implanted with the Argus II retinal prosthesis system participated in two experiments. The first experiment tested phosphene perception by varying the spatial offsets and temporal delays between pairs of electrodes. The second experiment tested the effect of gamification on circle localization and motion discrimination tasks.
Argus II: Participants used the Argus II retinal prosthesis system in both experiments to perform visual perception tasks.
Gamification: Participants performed gamified versions of circle localization and motion discrimination tasks designed to improve engagement and task performance. | 6 |
| Total | 6 |
Baseline characteristics
| Characteristic | Argus II Users |
|---|---|
| Age, Categorical <=18 years | 0 Participants |
| Age, Categorical >=65 years | 3 Participants |
| Age, Categorical Between 18 and 65 years | 3 Participants |
| Race (NIH/OMB) American Indian or Alaska Native | 0 Participants |
| Race (NIH/OMB) Asian | 0 Participants |
| Race (NIH/OMB) Black or African American | 0 Participants |
| Race (NIH/OMB) More than one race | 0 Participants |
| Race (NIH/OMB) Native Hawaiian or Other Pacific Islander | 0 Participants |
| Race (NIH/OMB) Unknown or Not Reported | 0 Participants |
| Race (NIH/OMB) White | 6 Participants |
| Region of Enrollment United States | 6 participants |
| Sex: Female, Male Female | 1 Participants |
| Sex: Female, Male Male | 5 Participants |
Adverse events
| Event type | EG000 affected / at risk |
|---|---|
| deaths Total, all-cause mortality | 0 / 6 |
| other Total, other adverse events | 0 / 6 |
| serious Total, serious adverse events | 0 / 6 |
Outcome results
Primary
Number of Phosphenes Perceived
Number of phosphenes perceived in response to paired-electrode stimulation across 5 spatial distances and 7 temporal interpulse delays. Phosphenes are brief sensations of light or visual flashes that occur in the absence of an external light source. A response is counted as a phosphene if the participant reports any visual sensation consistent with a flash of light.
Time frame: during single-session testing
Population: Data were collected in 6 participants ranging in age from 45 to 88 years old. One participant was female. All identified as white, non-hispanic.
| Arm | Measure | Group | Value (MEAN) | Dispersion |
|---|---|---|---|---|
| Argus II Users | Number of Phosphenes Perceived | Delay 0 | 1.09 number of phosphenes | Standard Deviation 0.91 |
| Argus II Users | Number of Phosphenes Perceived | Delay 4ms | 1.43 number of phosphenes | Standard Deviation 0.555 |
| Argus II Users | Number of Phosphenes Perceived | Delay 12ms | 1.46 number of phosphenes | Standard Deviation 0.538 |
| Argus II Users | Number of Phosphenes Perceived | Delay 29ms | 1.41 number of phosphenes | Standard Deviation 0.57 |
| Argus II Users | Number of Phosphenes Perceived | Delay 50ms | 1.48 number of phosphenes | Standard Deviation 0.511 |
| Argus II Users | Number of Phosphenes Perceived | Delay 178ms | 1.37 number of phosphenes | Standard Deviation 0.544 |
| Argus II Users | Number of Phosphenes Perceived | Delay 419ms | 1.36 number of phosphenes | Standard Deviation 0.639 |
| Argus II Users | Number of Phosphenes Perceived | Distance (808 - 1834um) | 1.24 number of phosphenes | Standard Deviation 0.642 |
| Argus II Users | Number of Phosphenes Perceived | Distance (1835 - 2856um) | 1.44 number of phosphenes | Standard Deviation 0.685 |
| Argus II Users | Number of Phosphenes Perceived | Distance (2857 - 3877um) | 1.31 number of phosphenes | Standard Deviation 0.622 |
| Argus II Users | Number of Phosphenes Perceived | Distance (3878 - 4898um) | 1.41 number of phosphenes | Standard Deviation 0.663 |
| Argus II Users | Number of Phosphenes Perceived | Distance (4899 - 5920um) | 1.45 number of phosphenes | Standard Deviation 0.631 |
Comparison: The model tested whether stimulation delay ('abs\_delay'), retinal distance ('dist\_ret'), and their interaction ('abs\_delay:dist\_ret') affect the number of elicited phosphenes ('num\_phosphenes').p-value: 0.002Mixed Models Analysis