OCT Screening for Diabetic Macular Edema at Primary Diabetes Care Visits: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for OCT Screening for Diabetic Macular Edema at Primary Diabetes Care Visits (NCT01875783), a na na study. The primary outcome is Rates of Retina Care Referral for Patients With Diabetic Macular Edema.

2. Clinical Question

In practical terms, the study was designed to examine whether imaging within a diabetes-care setting could identify people for referral to retina specialists. Its stated rationale is that identifying DME or an inadequate scan could facilitate specialist evaluation. That rationale is a study hypothesis, not a result. The record does not establish whether referral rates changed relative to usual care, because it does not describe a comparison group or report a referral result.

3. Trial Design

The registry describes a completed, single-group study of OCT imaging at non-ophthalmic diabetes-care visits. Enrollment is listed as 385. The study start date is 2014-03-17, and primary completion is listed as 2015-05-14. The phase is recorded as NA, and allocation is also recorded as NA. The intervention is OCT imaging, classified as a device.

All study participants were to undergo OCT imaging. The arm description states that participants would be referred to a retina specialist for further standard-care evaluation and management if DME was identified or if scan quality was insufficient to evaluate macular status. This means the referral pathway could be triggered by either a clinical finding or an inability to assess the scan. The record does not give further operational details about the algorithm or how scan quality was determined.

Masking is listed as DOUBLE, but the registry record does not report which people were masked or how masking was implemented. It also does not report a randomization procedure. With a single group and no described control condition, the study record does not provide a randomized comparison of referral approaches. Observed referrals, even if reported, would describe this study pathway; they would not by themselves quantify what would have happened under a different pathway.

The sponsor is Joslin Diabetes Center, and the status is COMPLETED. The registry lists a primary outcome and secondary outcomes concerning referral and retinal treatment for people with DME, including treatment over 1 year. The record does not provide results for these outcomes. Nor does it report a detailed protocol for follow-up, outcome ascertainment, or the statistical analysis. Those design details should not be inferred from the study title or stated hypothesis.

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 Rates of Retina Care Referral for Patients With Diabetic Macular Edema, measured over Baseline visit.

The primary endpoint is titled “Rates of Retina Care Referral for Patients With Diabetic Macular Edema.” It concerns participants referred to a retina specialist for evaluation and management of DME after OCT imaging and use of the OCT-guided referral algorithm. Its stated time frame is the baseline visit. The registry describes the measure as a percentage of participants referred, while its parameter description identifies a count of participants.

These descriptions point to a binary participant-level outcome: a participant either had a referral recorded for the endpoint or did not. General: a percentage for a binary outcome requires a numerator, the number meeting the outcome definition, and a denominator, the number eligible for assessment under the stated definition. Neither the observed referral count nor the denominator for this endpoint is reported in the registry record, and the percentage is not reported.

The endpoint is relevant to the study’s stated question because the intervention is intended to connect OCT findings at a diabetes-care visit with referral to a retina specialist. However, the arm description says referral could also follow a scan that was not adequate to evaluate macular status. The record does not report how referrals prompted by insufficient scan quality were handled in the primary endpoint, or how the analysis distinguished them from referrals prompted by identified DME.

General: a referral endpoint measures a care-process outcome, not whether a retinal condition improved or whether treatment was received. The secondary outcomes listed in the record address retinal referral and treatment, but their observed values are not reported. The primary endpoint therefore indicates what the study set out to measure; the registry record does not show the measured result.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

General: a binary outcome records whether each participant meets a defined condition. For this study’s primary outcome, the condition is referral to a retina specialist for evaluation and management of DME after OCT imaging and the referral algorithm. A count of participants with the event can be expressed as a proportion or percentage only when the eligible denominator is specified. The record describes a percentage but does not report the count, denominator or result. It also does not report how participants with missing or unassessable endpoint information were treated in the analysis.

What does a confidence interval describe?

General: a confidence interval expresses statistical uncertainty around an estimated quantity, such as a proportion or a difference between groups. A narrow interval indicates greater precision under the chosen method, while a wide interval indicates less precision. An interval does not resolve limitations in the design, make an unreported outcome available, or establish that an association is causal. The registry record does not report a primary-outcome estimate or confidence interval, so no assessment of its precision is possible.

What can a single-group result establish?

General: a result from one group can describe the outcome observed under that group’s study pathway. It does not directly estimate what would have happened to the same participants under a different pathway. A concurrent comparator can help distinguish an intervention-related difference from other explanations, provided the design and analysis support that comparison. This registry record describes a single-group study, lists allocation as NA, and does not describe a control group. It therefore does not document a like-for-like comparison of OCT-guided referral against another approach.

The primary endpoint is measured at the baseline visit. The record’s intervention description states that referral could follow identification of DME or inadequate scan quality. General: clear outcome definitions matter because different triggers can lead to the same recorded event. If the analysis combines referrals prompted by different triggers, the resulting proportion describes the combined pathway unless the triggers are also reported separately. The registry record does not report whether such separate outcome summaries were made.

Why does over-dispersion matter?

General: over-dispersion occurs when the observed variability in data is greater than a statistical model expects. If it is ignored, standard errors may be too small and confidence intervals or tests may overstate precision. It is especially relevant when the data structure or outcome variation does not fit a model’s assumptions. The record identifies a participant-count endpoint, but it does not report a statistical model, a dispersion estimate, or an analysis that would allow over-dispersion to be assessed. No claim about over-dispersion can therefore be made for this study.

How should planning assumptions be read?

The registry record includes a description of planning illustrations based on an observed effect. It describes two-sided significance level 0.05, equal allocation between two arms, a normal approximation, and an effect to detect expressed as a stated fraction of the observed effect. It distinguishes participant counts per arm for non-time-to-event outcomes from total event counts for time-to-event outcomes. These are described as planning assumptions, not as a report of how this single-group study was designed or analyzed. The record does not report the trial’s own sample-size justification.

General: power is a design-stage probability, under specified assumptions, of detecting an effect of a chosen size using a specified test. Planning calculations depend on assumptions about the effect, variability, allocation and analysis. A planning illustration does not show the power actually achieved after data collection. It also does not establish that an effect was observed. No numerical planning result is reported in the registry record, and the observed primary effect needed to interpret an effect-based illustration is not reported there.

General: a p-value summarizes how compatible the observed data are with a specified null model, under the assumptions of the test. It is not the probability that the null hypothesis is true, nor a measure of clinical importance. The registry record lists 0 analyses and does not report a primary-outcome p-value or test. There is consequently no reported test result to interpret.

The masking entry is DOUBLE, but the people masked and procedures are not reported in the registry record. The analysis method, covariate adjustments, confidence-interval method and handling of repeated or incomplete observations are also not reported. These omissions limit the ability to assess whether a particular statistical model was appropriate. They should not be filled in by assuming common practice; the method used is not established by the outcome description alone.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Retina Specialist Care")
n      <- c(385)
events <- c(44)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Retina Specialist Care  385  44  11.4  8.4  15.0  8.6  15.0  8.6  15.0

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists four outcome measures and names secondary outcomes concerning retinal referral for people with DME, retinal treatment for people with DME, and retinal treatment over 1 year for people with DME. It identifies a primary referral outcome at the baseline visit. The observed values for the primary and secondary outcomes are not reported in the registry record. The record also lists 0 analyses.

General: when a study evaluates multiple outcomes or performs multiple statistical tests, the chance of at least one apparently notable result can increase. Statistical plans may address this through a prespecified hierarchy, adjustment, or another approach. The registry record does not report a multiplicity procedure, a hierarchy among the secondary outcomes, or the statistical tests used. It is not possible to determine how multiple outcomes were handled.

The record does not report the amount or pattern of missing outcome data, or how missing observations were handled. It also does not report an analysis population definition, such as which enrolled participants were included in each outcome analysis. Enrollment of 385 alone does not establish the denominator for the primary endpoint, because the number with DME, the number referred, and the number with assessable outcome information are not reported.

General: missingness can affect an estimate when the availability of outcome data is related to participants’ characteristics or outcomes. The direction and extent of any resulting bias depend on the missing-data process and the analysis assumptions. Without counts and a stated handling method, those issues cannot be evaluated for this study. The registry record also does not report whether any sensitivity analyses were performed.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

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

The adverse-event record lists the OCT Imaging group with 385 at risk for serious adverse events and 0 affected. It separately lists 385 at risk for other adverse events and 0 affected, as well as 0 deaths. These are recorded counts, not estimates of comparative risk: the study record describes a single group and does not provide a control group for safety comparison.

The record does not state the observation period for these adverse-event counts or provide a list of serious adverse-event terms. It also does not report event definitions, collection procedures, or whether the counts refer to participants with events or event episodes beyond the labels shown. The absence of reported event counts should therefore be read narrowly as the registry’s recorded figures, not as evidence that no events occurred under every possible definition or observation period.

General: safety counts depend on who was followed, for how long, and how events were defined and collected. Without those details, a count cannot be interpreted as a complete description of safety. A zero in a reported count also does not establish zero underlying risk; rare events or events outside the reporting window may not be represented. The registry record does not provide enough detail to quantify such uncertainty or to compare safety with another care approach.

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

The record describes an approach in which OCT imaging was performed during primary diabetes-care visits and an OCT-guided algorithm could lead to retina-specialist referral. The primary question is whether participants with DME were referred for evaluation and management at the baseline visit. The record establishes the intended question and pathway, but it does not report the observed referral count, denominator or percentage.

Because the study is single-group and no control group is described, the record does not establish how referral under this pathway compares with referral under another approach. A referral result, if available, would describe what happened in the study group. It would not by itself show that OCT imaging caused an increase in referrals. The record also does not report outcomes that would establish whether referral led to retinal treatment or a change in vision.

The study hypothesis proposes that OCT imaging and an automated referral algorithm could help identify people at risk for vision loss from DME and facilitate more timely specialist evaluation and treatment. This is the stated rationale, not an observed finding. The registry’s listed secondary outcomes include referral and retinal treatment, including treatment over 1 year, but their results are not reported in the registry record.

General: a statistically precise estimate can still be limited by the design and outcome definition, while an imprecise estimate may leave substantial uncertainty about the underlying rate. In this record, the absence of the primary estimate means neither the rate nor its precision can be judged. The absence of a comparator also limits conclusions about relative effects. These are distinct limitations: reporting a precise single-group percentage would not, by itself, resolve the comparative question.

The appropriate reading is therefore descriptive and cautious. The registry documents a completed study, its intervention and a referral-focused primary outcome. It does not provide enough outcome information to determine the observed referral rate, the treatment experience, or whether the proposed pathway changed care relative to an alternative.

14. Why This Trial Matters Statistically

This study raises a statistical question about a care pathway rather than only an imaging result. Its stated primary outcome is referral to a retina specialist after OCT imaging and an OCT-guided algorithm. Referral is a binary participant-level event in the endpoint description, but its interpretation depends on defining who is eligible for the denominator and which referral triggers count. The arm description includes both identified DME and scan quality insufficient for assessment as reasons for referral, while the primary outcome is framed around patients with DME. The registry record does not explain how those situations were separated in the endpoint analysis.

The single-group design is also important. A referral proportion can describe the pathway’s observed use, but without a concurrent comparator it does not directly estimate the difference from another screening or referral approach. This distinction matters because the study hypothesis concerns increased rates of retina-specialist care. A claim about an increase requires a credible reference condition, not just a count within the intervention group.

General: process outcomes can be meaningful for understanding how a care pathway operates, but they are not interchangeable with downstream outcomes. Referral, specialist evaluation, treatment and vision outcomes address different stages. The registry lists several referral and treatment outcomes, yet does not report their results. Keeping these measures distinct avoids treating a referral as proof of treatment or benefit.

The record also illustrates why statistical interpretation relies on complete reporting: an outcome estimate, its denominator, uncertainty, analysis method and handling of missing data all affect what can be concluded. Here, the endpoint is defined, but its observed estimate and associated analysis are not reported. The study is therefore relevant as a description of a screening-and-referral question, while its statistical evidence about the resulting referral rate cannot be assessed from the registry record.

15. 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 main limitation for interpreting the primary outcome is that its observed result is not reported in the registry record. The referral count, denominator and percentage are unavailable, as is a confidence interval or test result. Enrollment of 385 does not identify how many participants had DME or how many contributed to the primary endpoint.

The single-group design and absence of a described control condition limit comparative interpretation. Allocation is listed as NA, and the record does not describe a randomized comparison. A result from the OCT Imaging group could describe referrals under that pathway, but could not establish the difference from an alternative pathway using this record alone.

The referral pathway includes more than one trigger: identified DME or scan quality insufficient to evaluate macular status. The record does not report how these triggers were classified or whether referrals for inadequate scans were distinguished from referrals for DME in the primary outcome. This matters because the primary endpoint is framed as referral for patients with DME, while the arm description includes referrals arising from scan quality.

Further limitations arise from missing methodological details. The people masked, algorithm implementation, outcome-assessment procedures, statistical analysis, missing-data handling and analysis populations are not reported in the registry record. The record also does not report a sample-size justification for the trial, multiplicity handling, or the observation period and event definitions for adverse-event counts. These details cannot be inferred from the study title, status or intervention description.

Finally, the primary outcome is a referral measure at the baseline visit. The record does not report whether referral led to specialist evaluation or treatment, or whether any vision-related outcomes were measured and observed. The study’s stated rationale should therefore not be mistaken for evidence about those downstream outcomes.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: OCT Screening for Diabetic Macular Edema at Primary Diabetes Care Visits — NCT01875783.
• Registry record last updated 2017-12-22; status last verified 2017-11.
• Results first posted 2017-09-20.
• 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.

19. Record Summary

NCT01875783 is a completed, single-group study titled “OCT Screening for Diabetic Macular Edema at Primary Diabetes Care Visits.” It lists OCT imaging as the intervention and enrollment of 385. The record gives a start date of 2014-03-17 and primary completion date of 2015-05-14. Allocation and phase are listed as NA; masking is listed as DOUBLE.

The primary outcome concerns retina-care referral for participants with DME after OCT imaging and an OCT-guided referral algorithm, at the baseline visit. The intervention description also specifies referral when scan quality is insufficient to evaluate macular status. The registry record does not report the primary outcome result, its denominator, or the statistical analysis. Secondary outcomes concern retinal referral and treatment, but their results are not reported.

The adverse-event record lists 0 serious events, 0 other events and 0 deaths in the OCT Imaging group. The observation period and further event details are not reported. Overall, the registry record describes the study pathway and questions but does not provide outcome estimates needed to assess the observed referral rate or make comparative conclusions.