Optimizing the Ocular Surface Prior to Cataract Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Optimizing the Ocular Surface Prior to Cataract Surgery (NCT02766907), a non-randomized na study. The primary outcome is Change in Intraocular Lens Calculation.

2. Clinical Question

The clinical rationale in the registry is to optimize ocular-surface integrity and intraocular lens calculation before cataract surgery in people with epithelial basement membrane dystrophy. The study compares a prospective group receiving the membrane after debridement with a retrospective review of debridement without the membrane. The question is therefore about the measured change associated with the prospective treatment approach relative to historical experience, not a randomized estimate of a causal treatment effect.

The primary endpoint is a continuous measure expressed in diopters. The registry identifies the endpoint as a mean change, with standard deviation specified as its dispersion measure, and gives the assessment interval as baseline to 1 month. It does not report the numerical change in either group, a between-group contrast, or uncertainty around any estimate. Consequently, the clinical question is identifiable, but the posted registry results do not establish the size, direction, or precision of the observed difference.

The record describes a study of 20 participants and lists 10 people at risk in each group for the adverse-event summaries. The precise primary-endpoint analysis population, eligibility criteria, and handling of participants without endpoint measurements are not reported in the registry record. Those omissions matter when interpreting any comparison, particularly because the groups were assembled using different designs.

3. Trial Design

This was a completed, prospective study registered as NCT02766907, with a single-group model and non-randomized allocation. The intervention was cryopreserved amniotic membrane after debridement. The study arm is described as prospective, while the control arm is a retrospective review of debridement without the membrane. Thus, despite the registry’s single-group model label, the record describes a historical comparison rather than a concurrent randomized control group.

The registry lists enrollment of 20, with the study beginning in 2016-03 and primary completion in 2017-01. The record lists the phase as NA and masking as none. BioTissue Holdings, Inc is identified as the sponsor. The condition is corneal dystrophy, epithelial basement membrane. The study’s stated purpose is to evaluate the intervention for optimizing ocular-surface integrity and intraocular lens calculation before cataract surgery.

These design details shape what the comparison can show. Random assignment is not reported; instead, treatment status is linked to prospective study participation, whereas the comparison group comes from retrospective review. Differences between groups could therefore reflect factors other than the membrane, including differences in participant characteristics, clinical practice, measurement, or record availability. The registry record does not report methods used to make the groups comparable or to adjust for potential confounding.

The record does not report the protocol’s sample-size justification, detailed eligibility criteria, recruitment approach, planned statistical model, interim analyses, or analysis populations. It also does not report a masking procedure. The prospective nature of the intervention arm may define when data were collected for that group, but it does not by itself make the comparison randomized or eliminate differences in how the two groups were assembled. The design should therefore be read as a small, non-randomized prospective intervention group compared with historical control information, with the limits that this entails for causal interpretation.

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 Change in Intraocular Lens Calculation, measured over Change from Baseline to 1 month.

The primary endpoint is change in intraocular lens calculation, measured in diopters and assessed by corneal topography. The registry specifies change from baseline to 1 month and describes the summary as a mean with standard deviation. This is a continuous outcome: its numerical value can vary across a range rather than being limited to event categories.

The endpoint is relevant to the stated purpose because the study seeks to optimize ocular-surface integrity and intraocular lens calculation before cataract surgery. Corneal topography provides the assessment named in the record. The measure is intended to capture whether the calculation changes over the stated interval after the ocular-surface procedure. The registry does not give a threshold for a change considered important, nor does it describe how the calculation was derived beyond naming corneal topography as the assessment method.

Interpretation would ordinarily require the mean change for each group, a clearly defined between-group contrast, and an estimate of uncertainty. A mean alone describes the central tendency, while the standard deviation describes variation among observations; neither is a substitute for a confidence interval around the treatment contrast. The registry record does not report the primary endpoint values, standard deviations, confidence interval, or statistical test. It therefore does not permit an assessment of the size or precision of the observed change.

The endpoint is specified over baseline to 1 month, but the record does not report the number of participants with measurements at each time point or how missing measurements were handled. Those details affect how representative the endpoint estimate would be of the enrolled group. The stated endpoint and timeframe are clear enough to identify the intended measurement, but not enough to reconstruct or evaluate its analysis.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary endpoint summarized as a mean, with standard deviation as the measure of dispersion. A mean represents the average observed value in a group. A standard deviation describes how spread out individual observations are around that average; it does not directly quantify uncertainty in a difference between groups. The endpoint is the change in intraocular lens calculation from baseline to 1 month, assessed by corneal topography.

What does a continuous-outcome comparison estimate?

In general, a comparison of continuous outcomes can focus on the average value in each group or on a contrast between those averages. For a change outcome, the analysis must also make clear whether it compares changes from baseline or compares follow-up values while accounting for baseline. These approaches can answer related but not identical questions. The registry record does not report the specific statistical model or the exact contrast used for the primary endpoint. Nor does it post the group summaries needed to interpret an estimate.

A confidence interval is a way to communicate uncertainty around an estimated quantity. In general, it describes values that are reasonably compatible with the observed data under the analysis assumptions. It is useful to consider both the interval’s location and its width: location speaks to the range and direction of possible effects, while width reflects precision. A p-value, when reported, addresses compatibility of the data with a specified null hypothesis under a statistical model; it does not measure the size or clinical importance of an effect. The registry record does not report a confidence interval or p-value for the primary endpoint.

Why does the comparison design matter?

Non-randomized comparisons can be affected by confounding. In general, confounding occurs when characteristics associated with both the group a participant enters and the outcome influence the observed comparison. Random allocation is one way to reduce systematic differences between groups, but the record lists non-randomized allocation. The study arm was prospective and the control arm was a retrospective review. That difference can introduce concerns beyond participant characteristics, including differences in documentation, timing, measurement practice, or availability of records. The registry record does not report adjustment methods, matching procedures, or other steps used to address these concerns.

The single-group model label should be read alongside the arm descriptions. The record identifies a prospective study arm receiving the membrane and a retrospective control review of debridement without it. This means the comparison is not described as a randomized, concurrent trial. A retrospective control may provide context, but it does not automatically represent the counterfactual outcome for participants in the prospective group. Any causal interpretation would require assumptions about comparability and measurement that are not documented in the registry record.

What does dispersion tell the reader?

For continuous outcomes, the standard deviation describes variation among individual observations. In general, greater variability can make an estimated mean contrast less precise, particularly when the number of observations is limited. Standard deviation and standard error have different meanings: the former describes participant-level spread, while the latter describes uncertainty in an estimated mean. The registry specifies standard deviation as the dispersion measure but does not post its value for the endpoint. No standard error or confidence interval is reported either.

Over-dispersion is principally a concern for count data when observed variability exceeds what a chosen count model expects. In general, the remedy is to use a model or uncertainty estimate that allows for the extra variation. That concept does not directly define the analysis of this continuous mean endpoint, and the registry record does not report a count-outcome analysis for the primary question. More broadly, selecting an analysis requires matching the model to the outcome’s measurement scale and distribution; the record does not provide enough detail to assess that selection.

How should planning calculations be distinguished from trial findings?

A sample-size calculation is a planning exercise, not an observed result. The registry describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation; the intended effect is expressed as a stated fraction of the observed effect. Such calculations ask how many participants per arm might be required under specified assumptions. They do not show that the trial had that power after completion, and they are not a substitute for the observed effect estimate or its confidence interval. The registry record does not report the trial’s own sample-size justification. No numerical planning estimate is available in the registry record.

More generally, power is a property of a design and a specified effect under assumptions. It is not a measure of whether a result is true, and retrospective power calculations based on an observed estimate do not resolve uncertainty better than the confidence interval around that estimate. Since the endpoint estimate and its uncertainty are not reported, the posted record does not support quantitative interpretation of the primary outcome or an assessment of its precision.

What information would make the analysis assessable?

For the primary outcome, an interpretable statistical report would identify the number of participants analyzed in each group, the group summaries, the between-group estimate, and its uncertainty. It would also describe how baseline values were used, how missing measurements were handled, and whether any adjustment was made for differences between the prospective and retrospective groups. These details are not reported in the registry record. Their absence limits reproducibility and makes it impossible to judge whether the analysis adequately reflects the intended comparison.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Study", "Control")
n   <- c(9, 9)
m   <- c(1.56, 0.94)
sp  <- c(1.6, 0.7)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Study  9  1.560  1.600  0.330  2.790
CARM  Control  9  0.940  0.700  0.402  1.478

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and zero analyses. It does not report a multiplicity plan, a hierarchy of outcomes, or a method for controlling the risk of false-positive findings across multiple statistical tests. In general, multiplicity arises when several outcomes or comparisons are tested; interpreting each test without accounting for the others can make chance findings more likely across the set. The number of listed outcomes alone does not establish which analyses were performed or whether adjustment was needed. No primary endpoint test result is reported.

The record does not specify how missing primary endpoint data were handled. It does not give the number with baseline and 1-month measurements, reasons for missingness, or a missing-data method. In general, complete-case analysis uses participants with the required measurements, while other approaches may use modeling or imputation assumptions. Each approach relies on assumptions, and the consequences depend on why data are missing. No particular approach can be attributed to this study from the registry record.

Analysis populations are also not defined. The record does not say whether the primary endpoint analysis included all enrolled participants, only those who received the intervention, or a subset with complete measurements. This matters because the denominator determines which participants contribute to the reported estimate. The adverse-event group counts do not establish the primary endpoint denominators.

The prospective intervention arm and retrospective control may also differ in data completeness or measurement procedures. The registry does not report methods to evaluate or address those possibilities. Without the analysis population, missingness information, and a statistical plan, readers cannot determine how these issues were handled or how robust the results might be. In addition, the primary endpoint result is not reported, preventing assessment of any planned or performed multiplicity adjustments.

12. 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.

The registry’s adverse-event summaries list 10 participants at risk in the Study group and 10 in the Control group. For each group, the reported count affected by serious adverse events is 0, and the count affected by other adverse events is also 0. These are the posted counts for the groups and categories specified in the record.

A zero reported count means that no affected participants are listed in that category in the registry summary. It should not be read as proof that an event is impossible or that no event could occur outside the period or scope captured by the record. The registry record does not provide further detail about how adverse events were collected, the observation period for safety reporting, or the definition used for the “other” category. It also does not report deaths; the death entries are not reported in the registry record.

The group counts should be interpreted descriptively. The study was non-randomized, and the control group was based on retrospective review, so the safety summaries do not constitute a randomized comparative safety assessment. The record gives no statistical comparison of adverse-event rates and does not report confidence intervals for these counts. These summaries describe what is recorded, not a precise estimate of the likelihood of harm.

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

The registry record establishes that a prospective study evaluated cryopreserved amniotic membrane after debridement for epithelial basement membrane dystrophy, with the stated aim of optimizing ocular-surface integrity and intraocular lens calculation before cataract surgery. It also identifies the primary endpoint as change in intraocular lens calculation from baseline to 1 month, assessed by corneal topography. Those details define the clinical question and the measurement approach.

The record does not report the primary endpoint results. It therefore does not show the observed mean change, the comparison between the prospective study arm and the retrospective control, or the uncertainty around any difference. No conclusion about whether the values changed, in which direction they changed, or how precisely any contrast was estimated can be drawn from the posted registry results. Completion of the study and the presence of a defined endpoint are not substitutes for outcome results.

Even if a numerical contrast were available, the design would require cautious interpretation. The allocation was non-randomized, and the control group was a retrospective review. Those features leave open the possibility that differences between groups, data collection, or clinical practice contributed to an observed contrast. The record does not describe adjustment methods that would clarify how such differences were addressed.

The reported adverse-event counts are zero for serious and other adverse events in both groups, with 10 at risk in each group. These counts are limited registry summaries and do not establish that risk is absent. Details about safety ascertainment and observation are not reported.

Overall, the registry supports an account of the study’s design, intended endpoint, and recorded adverse-event counts. It does not support a claim that the intervention changed the endpoint by a particular amount or that the two approaches were equivalent. The primary effect, its precision, missing-data handling, and analysis population are not reported in the registry record.

14. Why This Trial Matters Statistically

This study is statistically notable because its clinical question is framed around a continuous measurement intended to inform intraocular lens calculation before cataract surgery, while its comparison combines prospective intervention data with retrospective control data. Such a design makes the distinction between a measured association and a causal effect especially important. The analysis must account for the way participants entered each group and how outcomes were collected if a group contrast is to be interpreted as more than a descriptive comparison.

The registry record also illustrates why a clearly named endpoint is not enough to evaluate a result. It specifies the measure, unit, summary type, assessment method, and timeframe, but does not report the numerical endpoint findings. Without the estimate and its uncertainty, readers cannot judge the size or precision of the observed change. A study’s aim, completion status, or planned assessment cannot substitute for those statistics.

Small studies often have limited capacity to estimate effects precisely, but the record does not provide endpoint denominators or results from which to quantify precision in this case. In general, the appropriate focus is the estimated effect and its confidence interval rather than a binary interpretation of statistical significance. Here, neither is available in the registry record.

The adverse-event summaries offer another statistical lesson: zero recorded events in a group is a count, not proof of zero risk. Interpretation depends on the number observed, the period of observation, and the way events were collected. The record provides group counts at risk but does not give the additional detail needed to characterize those aspects.

Finally, planning calculations and observed results answer different questions. Planning assumptions can illustrate sample requirements under a specified effect and model, but they do not establish what was observed or how certain the result is. The registry record does not report the trial’s own sample-size justification or the primary result. Separating design information, observed evidence, and uncertainty is therefore central to reading this study accurately.

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 interpretation is that the registry record does not report the primary outcome results. No group means, standard deviations, between-group estimate, confidence interval, or test result are posted. The record therefore cannot support a quantitative assessment of the endpoint or its precision.

The comparison is non-randomized, with a prospective study arm and a retrospective control group. Historical controls can differ from prospective participants in characteristics, care, documentation, and outcome measurement. The registry record does not report matching, adjustment, or other methods intended to address those differences. This limits causal interpretation even if a contrast were available.

The registry does not report detailed eligibility criteria, the primary-endpoint analysis population, the number of participants with measurements at each time point, or the handling of missing data. It also does not provide the protocol’s sample-size justification or the statistical plan. These omissions prevent assessment of whether the endpoint analysis followed a prespecified approach and whether the analyzed participants represent the enrolled group.

The record lists two outcome measures but no analyses. It does not report how multiplicity was considered or how endpoints were prioritized for inference. The adverse-event summaries show zero affected participants for the listed categories in both groups, but the record lacks details about event definitions, ascertainment, and observation duration. Deaths are not reported in the registry record.

The registry identifies enrollment of 20 and completion dates, but those details do not resolve the missing outcome information. In particular, enrollment does not establish that all participants contributed endpoint data. The available information is sufficient to describe the study’s intended question and broad design, but not to establish the size, direction, or reliability of its primary finding.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Optimizing the Ocular Surface Prior to Cataract Surgery — NCT02766907.
• Registry record last updated 2019-03-19; status last verified 2019-03.
• Results first posted 2019-03-05.
• 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

NCT02766907 describes a completed, non-randomized, prospective study of cryopreserved amniotic membrane after debridement for epithelial basement membrane dystrophy. The comparator is a retrospective review of debridement without the membrane. The registry lists enrollment of 20, a single-group model, no masking, and phase NA. The study began in 2016-03 and primary completion was 2017-01.

The primary endpoint is mean change in intraocular lens calculation, in diopters, assessed by corneal topography from baseline to 1 month. The registry record does not report the endpoint results, analysis details, analysis populations, or missing-data methods. Serious and other adverse-event counts are 0 in each group, with 10 at risk per group; deaths are not reported in the registry record.

The record defines the intended clinical question and broad design, but does not provide the numerical primary outcome evidence needed to assess effect size or precision. The prospective-versus-retrospective comparison also limits causal interpretation.