Trial of L-DOPA as a Treatment to Improve Vision in Albinism: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Trial of L-DOPA as a Treatment to Improve Vision in Albinism (NCT01176435), a randomized phase 2 study. The primary outcome is Improved Vision.

2. Clinical Question

The rationale in the record is that L-DOPA might increase melanin pigment production in the retina, and that increased melanin had previously been associated with improved vision. This is the trial’s stated hypothesis and rationale, not a result of this trial. The primary measure is visual acuity, described as the smallest letters a person can read on a standardized chart or card. The posted arm results are means on the logMAR scale with 95% confidence intervals.

The clinical comparison of interest is whether visual acuity differed among people assigned to either L-DOPA dose and those assigned to placebo. However, the registry record gives arm-level means rather than a reported contrast, significance test, or model-based estimate. The results therefore describe the recorded values, but do not by themselves establish the size or statistical uncertainty of a treatment-versus-placebo effect.

3. Trial Design

This is a phase 2, randomized, double-masked, parallel-group trial sponsored by the University of Minnesota. The registry record gives a start date of 2010-09, a primary completion date of 2014-12, and a status of completed. Enrollment is reported as 45. The primary outcome results list 15 participants in each of the two L-DOPA groups and 15 in the placebo group.

The intervention groups received oral solution three times a day: 0.76 mg/kg L-DOPA or 0.51 mg/kg L-DOPA. The comparator group received placebo solution on the same stated schedule. Randomization means assignment was intended to occur by chance, while double masking indicates that the trial is recorded as masked at two levels. The record does not identify which roles were masked or provide details about how randomization and masking were implemented.

A parallel design assigns participants to a group and compares groups over the trial, rather than crossing each participant through multiple treatments. The registry record identifies the design as parallel, but does not report the allocation ratio or describe the sequence-generation and concealment procedures. The outcome results show the listed group counts; details of the analysis population are not reported.

The primary outcome is titled Improved Vision and is recorded as mean binocular best-corrected visual acuity in logMAR, with a 95% confidence interval, at 20 weeks. The record does not state whether this measure is an endpoint value, a change from baseline, or another summary. A sample-size justification, protocol-level statistical plan, and detailed follow-up schedule are not reported in the registry record. The completed status means the trial is recorded as completed; it does not supply additional information about the conduct or interpretation of the analysis.

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

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.

6. Primary Endpoint

The registry lists the primary outcome as Improved Vision, measured over 20 weeks.

The primary endpoint is binocular best-corrected visual acuity, reported as a mean on the logMAR scale with a 95% confidence interval at 20 weeks. The record describes visual acuity as the smallest letters a person can read on a standardized Snellen chart or a card held at a specified distance, with special charts used at shorter distances. It gives a range from 20/10 vision, described as best, to 20/200 vision, described as worst.

Visual acuity is relevant to the stated question because the trial aims to evaluate whether vision can be improved in individuals with albinism. As general measurement context, lower logMAR values generally correspond to better visual acuity. The posted results, however, are arm means at the stated timeframe; the registry record does not say that they represent change from baseline. That distinction matters: an endpoint value and a change score answer different questions, and the record does not identify which interpretation applies beyond its description of the measure and timeframe.

A mean provides a group-level summary, while a confidence interval conveys uncertainty around that estimate under the method used to calculate it. The record gives no further details about the calculation method. It also does not post a contrast between each dose and placebo. Consequently, these endpoint summaries describe the recorded group values but are not, on their own, estimates of how much vision changed because of treatment.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The design is recorded as randomized, double-masked, and parallel. In general, random assignment can help make treatment groups comparable in expectation, and masking can reduce the influence of treatment expectations on care or measurement. These design features do not guarantee that all sources of bias are avoided. The registry record does not explain how the assignment sequence was generated, whether allocation was concealed, which people were masked, or whether masking was maintained.

A parallel-group trial compares outcomes across groups assigned to different interventions. This trial includes two L-DOPA dose groups and a placebo group. A comparison of each dose with placebo would address a different contrast from a direct comparison of the two doses. The registry record posts arm-level summaries but no numerical contrasts. Without those contrasts and their uncertainty, the means cannot answer how large a difference between groups is supported by the data.

The primary measure is continuous: it is summarized as a mean logMAR value. For a continuous outcome, a mean conveys the average value within a group, while a measure of dispersion or a confidence interval conveys information about variability or uncertainty. The registry record identifies the displayed uncertainty as a 95% confidence interval but does not report a standard deviation or other dispersion measure. A confidence interval is not a description of the range of participant measurements. It concerns uncertainty in an estimate, as defined by the calculation procedure.

In general, the width of a confidence interval depends on factors such as the amount of information in the data and the variability of the outcome, as well as the statistical method. A narrower interval generally indicates greater precision for the estimate under that method; a wider interval indicates less precision. The posted intervals allow readers to see uncertainty around each arm mean, but the record does not state the assumptions or calculation used. They do not directly provide uncertainty for a treatment-versus-placebo contrast.

A formal comparative analysis would ordinarily specify the outcome being compared, the groups or contrasts of interest, the analysis population, and the statistical model or test. The registry record lists zero analyses and does not report a model, test, p-value, covariate adjustment, or estimate of a group difference. It also does not say whether the analysis followed randomized assignment or was restricted to participants with observed outcomes. Those details are not reported in the registry record, so they should not be inferred from the design label or the arm summaries.

Multiplicity is relevant because there are two dose groups and a placebo group, creating more than one possible treatment comparison. In general, testing multiple hypotheses can increase the chance of obtaining at least one apparently notable result by chance if no adjustment or prespecified strategy is used. An analysis plan may address this through a hierarchy of questions, adjusted tests, or another approach. The registry record does not report which comparisons were prespecified or how multiplicity was handled. No conclusion about an adjustment can be drawn from the arm means alone.

The record’s sample-size assumptions describe planning illustrations based on the observed effect, not the trial’s own design. They specify 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 fraction of the observed effect. These assumptions describe an illustrative calculation, not an observed-power analysis and not evidence that the trial was designed using those assumptions. The registry record does not report the trial’s sample-size justification. Any sample-size results associated with such assumptions should be read as planning illustrations rather than as a measure of the probability that the completed trial detected an effect.

For a continuous endpoint, a planning calculation depends on assumptions about the effect of interest and outcome variability, among other choices. The registry record does not post a dispersion estimate for the endpoint or explain the choice of the observed effect used in the illustration. The calculation therefore cannot be treated as a replacement for the trial’s own design rationale. Nor does an illustrative number of participants required for a hypothetical comparison tell readers whether the observed trial result is statistically significant.

The primary timeframe is 20 weeks. A timeframe indicates when the outcome is summarized, but does not by itself establish whether the measurement is a change score or a value at that visit. The endpoint is described as a mean and confidence interval, without a baseline result or a definition of the analysis value. This limits the interpretation of the reported means and the ability to connect them to change over time.

Finally, a reported group mean cannot show the distribution of individual responses. Participants may vary substantially even when group means are close, and the mean does not identify how many people improved, worsened, or remained unchanged. No individual-level data or responder definition is reported in the registry record. Statistical interpretation should therefore stay at the level of the published summaries and avoid conclusions about individual outcomes.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome measure and no posted secondary outcome measures. It lists zero analyses. These entries establish what is posted in the record, but do not show whether additional analyses were conducted elsewhere or whether other outcomes were collected but not posted.

With two dose groups and a placebo group, there are multiple possible comparisons. In general, multiplicity matters when several hypotheses are tested because the chance of a chance-positive finding can increase across a set of tests. The registry record does not report a prespecified comparison hierarchy, a multiplicity adjustment, or another strategy for handling multiple comparisons. The absence of that information is not evidence that no strategy was used; it means the strategy is not reported in the registry record.

Missing-data procedures are also not reported. The record does not describe how missing visual acuity measurements were handled, whether participants with missing measurements were included in any analysis, or whether sensitivity analyses assessed the impact of missing outcomes. The group results list 15 participants in each arm, but the record does not explain whether these are all randomized participants, all participants with an observed endpoint, or another analysis set.

The analysis population is not reported in the registry record. There is no stated intention-to-treat, per-protocol, or other population definition, and no account of exclusions from analysis. The record also does not provide baseline outcome values or a missingness summary. These gaps prevent assessment of whether missing data or analysis-population choices could affect the reported means. They also make it impossible to determine from the registry record whether the analysis followed the randomization or how robust the result was to different assumptions.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry record reports zero serious adverse events among 15 participants at risk in each of the 0.76 mg/kg L-DOPA, 0.51 mg/kg L-DOPA, and placebo groups. No serious adverse-event terms are listed. The record separately reports other adverse events affecting 11 participants in the 0.76 mg/kg L-DOPA group, 7 in the 0.51 mg/kg L-DOPA group, and 5 in the placebo group, with 15 participants at risk in each group.

These are counts by group, not comparative safety estimates. The registry record does not provide a formal statistical comparison, event descriptions for the other adverse events, or details about severity and timing. It also does not report how adverse events were defined, collected, or attributed. A zero count for reported serious adverse events means none are recorded in these results; it does not establish that the treatment has no serious risks. Deaths are not reported in the registry record.

12. What the Result Does, and Does Not, Mean

The result establishes that the registry record contains mean binocular best-corrected visual acuity values and 95% confidence intervals for the two L-DOPA groups and the placebo group at 20 weeks. The means are 0.67 for 0.76 mg/kg L-DOPA, 0.55 for 0.51 mg/kg L-DOPA, and 0.53 for placebo. The record does not give a formal estimate comparing either L-DOPA group with placebo.

These summaries do not establish that L-DOPA improved vision, nor do they establish that it did not. A group mean at one timeframe is not necessarily a measure of change, and the registry record does not clarify whether these values are endpoint values or changes from baseline. It also does not post baseline measurements, an analysis of change, or a comparative test. Without these details, the reported values cannot establish how visual acuity changed during the trial or whether any change differed by assigned group.

The confidence intervals describe uncertainty around the arm means, but they are not confidence intervals for treatment effects. A treatment-effect estimate would require a specified comparison and an estimate of its uncertainty. The record does not post either. The overlap among the arm intervals is not a substitute for a direct test of group differences, and the absence of a reported p-value should not be interpreted as evidence that groups were the same.

The trial’s proposed biological rationale is that L-DOPA might increase retinal melanin pigment production, with increased melanin previously associated with improved vision. That rationale explains why visual acuity was of interest, but the posted primary endpoint does not measure the proposed pigment change. The record does not report a result about the mechanism.

The appropriate reading is therefore limited to the posted descriptive outcome and safety counts. The completed status and randomized design provide trial context, but do not fill gaps in the analysis report. Conclusions about treatment effects, the precision of a between-group effect, or individual participants’ responses are not supported by the registry record alone.

13. Why This Trial Matters Statistically

This trial illustrates the distinction between an arm-level summary and a comparative treatment-effect estimate. A randomized design poses a question about differences between assigned groups, but the registry record posts means and confidence intervals for each group without a reported contrast. Readers can see the group summaries, yet cannot assess the size or precision of a treatment-versus-placebo difference from those summaries alone.

The record also highlights why endpoint definitions matter. The stated primary measure is mean binocular best-corrected visual acuity at 20 weeks, but it does not clarify whether the values are endpoint measurements or changes from baseline. Those alternatives answer different questions. Clear reporting of the estimand, analysis population, baseline handling, and comparison would help readers understand what the numbers represent.

The two active doses create an additional statistical question: whether each dose is compared with placebo, whether the doses are compared with each other, and how those comparisons are organized. Multiplicity planning and reporting help readers distinguish primary hypotheses from exploratory comparisons. The registry record does not describe such a strategy, nor does it post analyses for the listed outcome.

Finally, the confidence intervals make uncertainty visible for the group means, while also showing why uncertainty around the treatment contrast is important. Statistical interpretation requires more than comparing point estimates. This record is a useful example of the value of complete reporting: numerical outcomes, an explicit comparative analysis, and a transparent account of missing data and analysis choices are all needed to evaluate a trial’s central question.

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 registry record does not report baseline visual acuity values or clarify whether the posted means are endpoint measurements or changes from baseline. This limits interpretation of the primary results as improvement or change over time. The record also does not provide a direct estimate comparing either L-DOPA dose with placebo, a p-value, or a model-based analysis.

Details needed to assess the conduct of the trial are not reported, including eligibility criteria, the randomization procedure, allocation concealment, and which roles were masked. The record does not describe the analysis population, exclusions, missing visual acuity measurements, or methods used to handle missing data. It also does not state how the confidence intervals were calculated or provide a measure of outcome dispersion other than the intervals.

The handling of multiple possible comparisons is not reported, and no analyses are posted for the primary outcome. The registry record does not give the trial’s sample-size justification or a detailed statistical plan. Adverse-event definitions, event descriptions for the other adverse events, and death counts are also not reported in the registry record. These omissions constrain assessment of both efficacy-related outcomes and safety summaries; they should not be filled in by assumption.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Trial of L-DOPA as a Treatment to Improve Vision in Albinism — NCT01176435.
• Registry record last updated 2018-05-02; status last verified 2018-04.
• Results first posted 2018-05-02.
• 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.

18. Record Summary

The registry record describes a completed, randomized, double-masked, parallel phase 2 trial sponsored by the University of Minnesota. It lists enrollment of 45, a start date of 2010-09, and a primary completion date of 2014-12. The trial evaluated oral L-DOPA solution taken three times a day at 0.76 mg/kg and 0.51 mg/kg, against placebo solution taken on the same schedule.

The primary outcome was mean binocular best-corrected visual acuity in logMAR at 20 weeks, with 95% confidence intervals. Results are posted for 15 participants in each group. The registry record does not report a formal between-group analysis, an analysis population, missing-data methods, or a multiplicity strategy. It lists no posted secondary outcomes and zero analyses. Serious adverse events are reported as zero in each group; deaths are not reported in the registry record.