This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for The Perceptual Experience of Argus II Users (NCT05285618), a na na study. The primary outcome is Number of Phosphenes Perceived.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT05285618 |
| Phase | NA |
| Condition | Retinitis Pigmentosa |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 6 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of California, Santa Barbara |
| Results posted | Yes |
2. Clinical Question
Population
The study collected data from 6 blind participants with retinitis pigmentosa who had Argus II retinal prostheses. Participants ranged in age from 45 to 88 years; one was female, and all identified as white, non-hispanic. These characteristics describe the people in this study, not necessarily all Argus II users.
Intervention
The device listed is Argus II. During single-session testing, paired electrodes were stimulated to examine perceptual responses. The study description focuses on how phosphene shape and number may relate to neuroanatomical factors, stimulation parameters, and spatial offsets. The registry record does not report a treatment regimen or a clinical-care intervention.
Comparator
This is a single-group study, with allocation recorded as NA and masking recorded as none. The registry record does not report a separate control group or a like-for-like comparator. The study therefore describes responses among Argus II users rather than a contrast between randomized treatment groups.
Primary question
The primary outcome is the number of phosphenes perceived in response to paired-electrode stimulation across 5 spatial distances and 7 temporal interpulse delays. A phosphene is defined as a brief sensation of light or visual flash without an external light source; a response counts when a participant reports a visual sensation consistent with a flash. The registry record does not report the observed outcome values.
3. Trial Design
The registry identifies NCT05285618 as a completed Basic Experimental Studies Involving Humans study titled “The Perceptual Experience of Argus II Users.” Its official title is “Predicting the Perceptual Experience of Argus II Retinal Prosthesis System Users.” The sponsor is the University of California, Santa Barbara. The recorded study start was 2022-01-11, and the primary completion date was 2023-08-31.
The design is listed as single group. Allocation is recorded as NA, and masking as none; phase is also listed as NA. Enrollment was 6. The listed intervention is the Argus II device, and the condition is retinitis pigmentosa. The study description characterizes the work as an investigation of perception and performance factors in blind people implanted with the device, using paired-electrode stimulation.
The registry does not describe a randomized comparison, and it does not report a separate control arm. Consequently, the design supports description of responses within the enrolled group, not an estimate of a between-group treatment contrast. The arm description is truncated in the registry record, so further details beyond its stated focus are not reported in the registry record.
The study description also says that the investigators examine high current thresholds and limited spatial resolution as factors that impede pattern vision in Argus II devices. That statement describes the study’s research aims; it is not a numerical finding. Protocol details, including the recruitment process and the precise testing sequence, are not reported in the registry record.
4. Participant Flow and Accounting
The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.
Overall Study
| Stage | Argus II Users |
|---|---|
| STARTED | 6 |
| COMPLETED | 6 |
| NOT COMPLETED | 0 |
Analysis population for the primary outcome, as defined in the registry: 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.
5. Baseline Characteristics
The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.
| Characteristic | Unit | Argus II Users |
|---|---|---|
| Participants analysed | 6 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 3 |
| Age, Categorical: >=65 years | Participants | 3 |
| Sex: Female, Male: Female | Participants | 1 |
| Sex: Female, Male: Male | Participants | 5 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 |
| Race (NIH/OMB): Asian | Participants | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 |
| Race (NIH/OMB): White | Participants | 6 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 |
| Region of Enrollment: United States | participants | 6 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Phosphenes Perceived, measured over during single-session testing.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | number of phosphenes |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is the number of phosphenes perceived during single-session testing. A phosphene is a brief sensation of light or a visual flash that occurs without an external light source. For this endpoint, a response is counted when the participant reports any visual sensation consistent with a flash of light.
The registry describes paired-electrode stimulation across 5 spatial distances and 7 temporal interpulse delays. Counting reported phosphenes provides a way to describe how often perceptual flashes are experienced under these stimulation conditions. The measure is relevant to the study’s stated interest in phosphene perception and the factors that may influence the perceptual experience of Argus II users.
The endpoint is recorded as a continuous measure summarized by a mean and standard deviation, even though its underlying observations are counts. The registry record does not report the mean, standard deviation, participant-level values, or results for particular distances or delays. It also does not report whether the endpoint was aggregated across conditions or analyzed separately for each condition.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record defines the primary outcome and reports that data were collected in 6 participants, but it does not report numerical results for the number of phosphenes perceived. In particular, a mean and standard deviation are not reported in the registry record. Without those values, the magnitude and variability of the observed responses cannot be described from the record. There is also no reported estimate of a difference between conditions, and the single-group design has no separate comparator for such a contrast.
The outcome concerns participants’ reported visual sensations during paired-electrode stimulation. It is not, by itself, a direct measure of everyday visual function, pattern recognition, or overall device performance. The study description connects the work to phosphene shape, number, spatial resolution, and current thresholds, but the primary endpoint named in the record is the number of phosphenes perceived. The record does not give numerical findings for the other factors mentioned in the study aims.
Although the registry lists 1 primary outcome measure and 1 analysis, the numerical analysis results are not reported in the registry record. A p-value, confidence interval, or other estimate of precision for the primary outcome is not reported. A confidence interval, as a general statistical concept, expresses uncertainty around an estimate; it cannot be interpreted for this outcome without a reported estimate and interval.
The participant count and study design matter when considering how broadly any findings could apply. The study includes 6 participants, and it does not include a randomized control group. Even if descriptive results were available, this design would principally characterize the enrolled participants’ responses under the tested conditions. It would not establish that any observed pattern was caused by a particular device feature or would occur in a different group.
The registry’s listed status is completed, but completion does not supply the missing outcome values. The appropriate interpretation is therefore limited: the record describes what was measured and in whom, while leaving the numerical primary findings and their precision unreported.
9. Statistical Methods Explained
The primary measure is the number of phosphenes perceived, and the registry specifies a mean with standard deviation as its summary. A mean describes the average of the observations included in a calculation. The standard deviation describes how spread out those observations are around their mean. These summaries answer different questions: the mean conveys the central level of the measured response, while the standard deviation conveys variability within the observations being summarized.
The record calls the endpoint continuous, although phosphene counts are counts. As a general statistical point, count outcomes can have distributions that differ from the symmetric distributions often assumed by simple continuous-outcome methods. They may be concentrated at lower values, skewed, or more variable than a simple model expects. Over-dispersion means that the observed variability is greater than a model’s assumed variability; if present, it can make standard errors and inferential conclusions from an unsuitable model misleading. The registry record does not report a distributional assessment or a model addressing over-dispersion, so it is not possible to determine how these issues were handled.
The endpoint arises from testing at 5 spatial distances and 7 temporal interpulse delays. These conditions describe dimensions of the stimulation protocol, but the analysis strategy for combining or separating observations across them is not reported in the registry record. As a general statistical consideration, repeated observations from the same participant are usually related rather than independent. An analysis that treats related measurements as independent can misstate uncertainty. The registry record does not report whether the analysis accounted for within-participant dependence, nor does it describe the unit of analysis.
A standard deviation alone would not show how precisely the mean is estimated. A standard error or confidence interval can express uncertainty in an estimate, but neither is reported for the primary outcome in the registry record. A confidence interval is generally interpreted as a range of values compatible with the data and the statistical procedure used; its width reflects precision. No interval is available to assess for this outcome, and no p-value is reported. Thus, the registry description supports explanation of the planned summary form, not an inferential conclusion about the observed response.
The registry’s planning assumptions describe an illustration based on the observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated proportion of the observed effect. These are planning assumptions, not evidence that the completed study itself had two arms: its design is listed as single group. The resulting planning quantities are not reported in the registry record. Such calculations are illustrations for hypothetical design choices, not observed power and not evidence about the study’s results.
In general, a sample-size calculation depends on the effect a future study aims to detect, the outcome’s variability, the error rate used for testing, and the planned design. Changing an assumed effect changes the planning requirement. An illustration derived from an observed effect should therefore not be treated as proof that the original study was adequately powered, especially when the actual design and analysis details are not described. The registry record does not report a protocol-based sample-size justification for this study.
Further analysis details are not reported in the registry record. These include the exact statistical model, any covariates, the treatment of outliers, the handling of repeated responses, and the method used to form the reported mean and standard deviation. Without those details or the numerical results, readers cannot independently assess the analysis choices or quantify the precision of the primary outcome.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 1 primary outcome measure and 1 analysis. The outcome description nevertheless spans responses across 5 spatial distances and 7 temporal interpulse delays. The record does not say whether those conditions were analyzed as a combined endpoint, as separate estimates, or through additional comparisons. It does not report a multiplicity adjustment or explain how the risk of false-positive findings across possible comparisons was addressed.
Multiplicity is a general concern when several hypotheses or contrasts are tested: the chance of obtaining at least one apparently notable result can increase as the number of tests grows. Whether that concern applies to a particular analysis depends on which tests were actually conducted and how they were interpreted. The registry description does not identify those tests, so no conclusion about multiplicity control can be drawn.
Missing-data methods are not reported in the registry record. The record does not state whether all enrolled participants contributed to the primary analysis, how incomplete responses were handled, or whether any observations were excluded. It also does not describe an analysis population, such as a defined set of participants or measurements used for the endpoint.
The registry does not report an interim analysis plan, a prespecified statistical analysis plan, or methods for handling missing observations. These details should not be inferred from the completed status or the listed number of analyses. Their absence limits assessment of how the analysis was planned and whether the reported analysis followed that plan.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Argus II Users | 0 | 6 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Argus II Users | 0 of 6 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Argus II Users | 0 of 6 |
The adverse-event record lists 6 participants at risk for serious adverse events and 0 affected. For other adverse events, it lists 6 at risk and 0 affected. Deaths are listed as 0, and no serious adverse-event terms are listed.
These entries describe what is recorded in the registry, not a detailed account of event monitoring. A zero affected count means that the registry reports no participants in the listed group as affected for that category; it should not be expanded into a claim that no symptoms or events of any kind occurred. The record does not provide event narratives, severity details for non-serious events, or information about how events were collected and assessed.
The safety figures also do not compare Argus II users with a control group. The study is single group, and the adverse-event record lists only the Argus II Users group. These counts therefore describe the registry’s entries for that group and do not estimate a comparative safety effect. Additional safety-monitoring methods are not reported in the registry record.
12. What the Result Does, and Does Not, Mean
The study addresses a perceptual question: how many phosphenes participants report during paired-electrode stimulation under varying spatial and temporal conditions. Its focus is experimental and concerns the perceptual experience of people who use the Argus II retinal prosthesis system. The registry describes an interest in factors related to phosphene shape and number, as well as high current thresholds and limited spatial resolution.
The record does not report numerical results for the primary outcome. It therefore does not show the average number of phosphenes, how variable responses were, or how responses differed across the tested conditions. No estimate of precision or inferential result is reported. The study’s stated research aims should not be mistaken for findings.
The design also sets limits on what the study could establish. It is a single-group study with no reported comparator, so it cannot provide a randomized between-group contrast. The endpoint captures a participant-reported visual sensation during testing. It does not, by definition, measure all aspects of vision or establish how responses relate to everyday tasks.
As a general interpretation principle, an observed association between stimulation conditions and reported perceptions would not alone establish the cause of that pattern. Further information about the analysis and numerical results would be needed to assess the evidence. The registry record does not report those details, so the defensible conclusion is about the research question and measurement approach, not the direction or size of any effect.
13. Why This Trial Matters Statistically
This study is statistically distinctive because its main endpoint is a count of reported perceptual experiences collected under multiple stimulation conditions. It makes clear that a clinical-device study can focus on a basic experimental question rather than a conventional comparison of treatment outcomes. The registry describes responses to paired-electrode stimulation and frames the work around phosphene perception and factors that may influence it.
The measurement definition is important. Counting a response when a participant reports any visual sensation consistent with a flash gives an operational rule for the primary endpoint. At the same time, it makes the outcome dependent on reported perception. Statistical interpretation depends not only on the endpoint label but also on how observations were gathered, grouped, and analyzed; those procedural and analytical details are not fully reported in the registry record.
The design also illustrates why study structure matters when reading results. A single-group study can describe the enrolled participants and their responses, but it does not provide a randomized control comparison. Repeated conditions within participants raise general questions about dependence among observations and the appropriate expression of uncertainty. The registry does not report how those analysis issues were addressed.
Finally, the absence of numerical outcome results is consequential for statistical interpretation. The registry identifies the measure and its intended summary, but not the estimate or its variability. Readers can understand the question being asked, but cannot assess the magnitude, precision, or pattern of the primary outcome from the registry record.
14. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The enrolled group was small, with 6 participants, and the study has no separate comparator. Its findings, if reported elsewhere, would need to be interpreted in light of that design rather than as a randomized estimate of a difference between groups. The registry record does not report recruitment details that would help assess how participants entered the study.
The recorded participant characteristics are limited: ages ranged from 45 to 88 years, one participant was female, and all identified as white, non-hispanic. These details describe the enrolled group. They do not establish how representative the group is of other people with retinitis pigmentosa or other Argus II users.
The endpoint is a participant-reported count of visual sensations during single-session testing. A response is counted when it is consistent with a flash of light, which gives the measure a clear stated definition but does not make it a comprehensive measure of vision or daily function. The registry does not report how responses were elicited, whether repeatability was assessed, or how measurements across conditions were combined.
Most importantly for interpretation, the registry record does not report the numerical primary outcome or its standard deviation. It also does not report a confidence interval, p-value, missing-data handling, analysis population, or detailed statistical model. These omissions prevent assessment of the observed magnitude, precision, and analysis choices. Further protocol and analysis details are not reported in the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: The Perceptual Experience of Argus II Users — NCT05285618.
- Registry record last updated 2025-01-01; status last verified 2024-12.
- Results first posted 2025-01-01.
- Data retrieved from ClinicalTrials.gov on 2026-11-09.
- Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.
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18. Record Summary
NCT05285618 is a completed, single-group Basic Experimental Studies Involving Humans study sponsored by the University of California, Santa Barbara. The record lists 6 participants with retinitis pigmentosa who use Argus II. Data were collected during single-session paired-electrode testing across 5 spatial distances and 7 temporal interpulse delays.
The primary outcome is the number of phosphenes perceived, summarized as a mean with standard deviation. The registry defines a counted response as a participant-reported visual sensation consistent with a flash of light. It lists 1 primary outcome measure and 1 analysis, but numerical outcome results and their precision are not reported in the registry record.
The study has no reported control group. The adverse-event record lists 0 of 6 affected for serious adverse events, 0 of 6 affected for other adverse events, and 0 deaths. These figures describe the registry entries and do not provide a comparative safety estimate.