Modified Instrumentation for Surgery to Correct Trichiasis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Modified Instrumentation for Surgery to Correct Trichiasis (NCT00886015), a randomized na study. The primary outcome is Number of Eyelids With Presence of Recurrent Trichiasis.

2. Clinical Question

This question focuses on recurrence after surgery, rather than on the occurrence of trichiasis before surgery or on a general measure of eye health. The endpoint is expressed as a number of eyelids with recurrence. That framing matters: eyelids are the measurement units for the outcome, while enrollment is recorded for the trial as a whole. The record does not provide enough detail to reconstruct the full relationship between enrollment, assigned treatment, follow-up, and the endpoint analysis in both groups.

Random allocation means the study was designed to assign participants or units to the two procedures by chance. In general, random allocation can help make groups comparable at the start of a trial, but it does not by itself establish the size or precision of any outcome difference. Those judgments require the reported outcome data and an appropriate analysis. Neither a primary outcome comparison nor its uncertainty is reported in the registry record.

3. Trial Design

The registry describes a completed, randomized, single-masked, parallel-group trial sponsored by Johns Hopkins University. The study is titled “Modified Instrumentation for Surgery to Correct Trichiasis,” and its official title identifies it as a PRET clinical trial evaluating modified instrumentation for trichiasis surgery. The condition listed is trachoma. The registry records an enrollment of 1927 and lists the phase as not applicable.

In the parallel design, the two treatment groups receive different surgical approaches: the TT Clamp group receives surgery using the clamp, while the Standard BLTR Technique group receives standard bilamellar tarsal rotation surgery. Random allocation is reported, but the allocation method, sequence generation, concealment procedures, and allocation ratio are not reported in the registry record. The record says masking was single, but it does not identify who was masked or describe how masking was maintained. It therefore does not support a more specific account of masking.

The record gives a study start of 2009-05 and a primary completion date of 2012-01, and lists the status as completed. The primary endpoint has a two-year timeframe. Those dates and the endpoint timeframe describe the study record; they do not establish when each participant entered follow-up or whether all participants reached the endpoint assessment. Recruitment details, study sites, the number assigned to each group, and the extent of follow-up by group are not reported in the registry record.

The primary outcome is framed at the eyelid level, while the registry enrollment is a trial-level figure. One detail about the TT Clamp analysis is explicit: 1671 eyes were initially assigned to that group, and one participant’s two eyelids were excluded from the analysis because the participant died before follow-up. The record does not give equivalent detail for the standard-technique group or a complete account of all analysis populations.

The study also lists secondary outcomes concerning eyelid contour abnormality and trachomatous trichiasis severity. The registry records six outcome measures and eight analyses, but these counts do not specify the complete analysis plan, the order of all comparisons, or which analyses were prespecified. Those details 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.

Before assignment: 963 individuals assigned to Trachomatous Trichiasis (TT) clamp, 6 did not participate. 3 refused surgery, 2 ineligible because of lower eyelid trichiasis only, 1 participant did not present for surgery. 964 individuals assigned to Standard, 4 did not participate. 2 refused surgery, 2 ineligible because of lower eyelid trichiasis only.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Of the 1671 eyes initially assigned to TT Clamp, 1 participant (2 eyelids) was excluded from TT Clamp analysis because participant died before follow-up.

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.

Population: 1927 participants were originally enrolled. 10 participants did not undergo surgery for the following reasons: refused surgery (5), ineligible because of lower eyelid trichiasis only (4), or surgery was delayed and patient did not attend (1). The final total number of participants was 1917.

6. Primary Endpoint

The registry lists the primary outcome as Number of Eyelids With Presence of Recurrent Trichiasis, measured over 2 years.

The primary endpoint is the number of eyelids with recurrent trichiasis at two years. The registry defines trichiasis for this measure as one or more eyelashes touching the globe in primary position. It is therefore a count of eyelids meeting a specified clinical description at the follow-up assessment, not a continuous measure of symptom severity or a time-to-event measure.

Recurrence is relevant to a comparison of surgical procedures because the study’s stated objective is to compare outcomes after TT clamp surgery and standard BLTR surgery. Counting eyelids with the defined finding provides a way to describe whether trichiasis is present again after the operation. The endpoint’s value depends on how recurrence was assessed and on which eyelids were included in the analysis. Assessment procedures beyond the stated definition, rules for classifying borderline findings, and details of assessor training are not reported in the registry record.

A count alone is not sufficient to compare groups fairly if the numbers of eyelids assessed differ. Interpretation also requires the number assessed in each group, information about missing follow-up, and a clear analysis population. The record identifies an exclusion from the TT Clamp analysis after a participant died before follow-up, but does not report a full accounting of assessed and unassessed eyelids in both groups.

The primary endpoint results themselves are not reported in the registry record. No group-specific recurrence counts, treatment-effect estimate, confidence interval, or statistical test for this endpoint is available in the record. Consequently, the endpoint definition can be described, but the observed comparison and its precision cannot be interpreted from the registry information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies random allocation and a parallel-group design, but does not report the full statistical methods used for the primary outcome. The concepts below are general explanations of issues relevant to a comparison of eyelid counts; they should not be read as a description of methods confirmed for this trial.

What does a count endpoint represent?

A count records how many units meet a stated condition. In this trial, the primary measure is the number of eyelids with recurrent trichiasis, with recurrence defined as one or more eyelashes touching the globe in primary position. A count is different from a rate, a proportion, or a time-to-event outcome. A proportion would require a denominator—the number of eyelids assessed or included in each group. A rate would also require a defined amount of observation time. The registry names the endpoint as a number of eyelids and gives a two-year timeframe, but does not report group-specific outcome counts or the full denominators used in the primary analysis.

Why is the unit of analysis important?

The outcome is recorded for eyelids, but participants may contribute more than one eyelid. In general, two measurements from the same person can be correlated because they share characteristics and circumstances. If an analysis assumes that every eyelid is independent when some are related, the estimated uncertainty may be too small. Statistical approaches can account for clustering, for example by modeling participant-level grouping or by using methods that allow correlated observations. Which approach is suitable depends on the design and data. The registry record does not say which eyelids contributed to the analysis in each group or whether the analysis accounted for within-participant correlation.

The record notes that one participant’s two eyelids were excluded from the TT Clamp analysis because the participant died before follow-up. This illustrates why the analysis unit and the participant-level follow-up history both matter. It does not reveal how many other eyelids were observed, whether any endpoint data were missing for other reasons, or how such data were handled. Those details are not reported in the registry record.

What do an effect estimate and its uncertainty add?

A group count describes the number meeting the endpoint, but it cannot alone establish the size of a difference between groups. An analysis may express a comparison as a difference in counts, a difference in proportions, a ratio, or another measure. These approaches answer different questions and may require different assumptions. The appropriate measure also depends on the denominators, follow-up, and statistical model. The registry record does not report the primary comparison measure or its estimate, so no particular effect measure can be attributed to this trial.

A confidence interval is a general way of expressing the uncertainty around an estimated effect. Its width reflects the information in the data as well as the assumptions of the method. A narrow interval indicates greater precision for the estimated contrast under those assumptions; a wide interval indicates less precision. An interval’s interpretation also depends on the effect scale and whether the model is appropriate. No confidence interval for recurrent trichiasis is reported in the registry record.

A hypothesis test, in general, evaluates how compatible the observed data are with a specified null hypothesis under a statistical model. A p-value is not the probability that the null hypothesis is true, and it does not quantify the size or clinical importance of an effect. A small p-value alone does not establish importance, while a larger p-value does not establish equivalence. The registry record does not report a primary-outcome p-value or identify the test used.

Why can count data require special care?

Count outcomes often have distributions that differ from a normal distribution, particularly when counts are low, highly variable, or contain many zero values. General methods for count data can model the expected count while allowing for features such as unequal observation time or extra variability. Over-dispersion occurs when the variation in counts exceeds what a simpler model expects; ignoring it can make uncertainty appear smaller than it is. These are general statistical considerations, not evidence that any particular distribution or model was used in this trial. The registry does not describe the distribution of the endpoint data or the model used.

For a count of eyelids meeting a condition, group size and the number of eyelids actually assessed are essential context. Counts can differ because of different numbers assessed, different outcome frequency, or both. A comparison of proportions or another standardized measure may be more interpretable than raw counts when denominators differ, but the chosen analysis must match the design and available data. The registry record does not report the denominators for the primary outcome comparison in both groups.

What does randomization contribute?

In general, random allocation aims to balance prognostic characteristics between groups on average, reducing confounding by factors measured or unmeasured at baseline. It does not guarantee that groups will be identical, particularly in a particular trial, and it cannot correct for biased outcome measurement or differential loss to follow-up. The registry states that allocation was randomized, but does not report the randomization procedure, concealment, or baseline characteristics. It also does not identify who was masked under the single-masked design. These missing details limit assessment of how the design was implemented.

Finally, planning calculations and outcome analysis answer different questions. A sample-size calculation is a planning exercise based on assumptions about an effect, variability, significance level, and allocation. It is not an observed result and is not a measure of the evidence produced by the trial. The record describes planning illustrations based on fractions of an observed effect and specifies general assumptions, but those illustrations do not replace the outcome data or the trial’s own design rationale. The registry does not report a sample-size justification or the complete statistical analysis plan.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists secondary outcomes on eyelid contour abnormality and trachomatous trichiasis severity. It also records six outcome measures and eight analyses. These entries indicate that the trial record includes more than the primary endpoint, but they do not disclose the complete set of planned comparisons, their hierarchy, or which analyses were designated as confirmatory.

When a study examines multiple outcomes or conducts multiple statistical tests, the chance of finding at least one apparently notable result can increase. General approaches to this issue include defining a primary outcome in advance, specifying a testing hierarchy, or adjusting interpretation or inference for multiple comparisons. The registry record does not report whether any such approach was used. The count of outcomes and analyses alone does not establish how multiplicity was handled.

Missing outcome data can also affect interpretation. The registry reports that one participant’s two eyelids were excluded from the TT Clamp analysis because the participant died before follow-up. It does not provide a complete account of missingness, follow-up completion, or exclusions across both groups. It also does not state whether the primary analysis used an intention-to-treat approach, a per-protocol population, or another definition. The reasons and methods for handling any other missing data are not reported in the registry record.

In general, excluding participants or measurement units after randomization can weaken the protection that random allocation provides, especially if exclusion is related to prognosis or differs between groups. That is a methodological concern to assess, not proof that bias occurred in this trial. Without a full accounting of assigned, followed, and analyzed units, the extent and possible consequences of missingness cannot be evaluated from the registry record.

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’s adverse-event figures list 0 serious affected participants in the Standard Instrumentation group, with 960 at risk, and 0 in the TT Clamp group, with 957 at risk. For the other affected category, the listed figures are 15 of 960 for Standard Instrumentation and 12 of 957 for TT Clamp. These are reported as counts; they should not be interpreted as rates or compared after converting them into percentages.

The record does not provide the definitions or event terms underlying the other affected category, the observation period for these figures, or a detailed account of how events were collected. It lists no top serious-event terms. Death counts in the adverse-event entry are not reported in the registry record. The separate note about a participant who died before follow-up concerns exclusion of two eyelids from the TT Clamp primary analysis; it does not supply a full mortality account or explain the cause of death.

These safety counts are descriptive and do not establish that the groups had equivalent safety profiles. A meaningful safety comparison would depend on event definitions, follow-up, exposure, completeness of reporting, and statistical uncertainty. Those details are not reported in the registry record.

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

The registry record documents a randomized comparison of surgery using the TT clamp with standard BLTR technique for trachomatous trichiasis. It defines the primary outcome as the number of eyelids with recurrent trichiasis at two years, using a stated clinical definition. It also reports several secondary outcome topics and adverse-event counts. These elements clarify what the trial set out to examine and some of the information recorded.

However, the primary outcome counts by group are not reported in the registry record. There is no reported treatment-effect estimate, confidence interval, or primary-outcome test result. It is therefore not possible from this record to state the direction or size of the observed recurrence comparison, how precisely it was estimated, or whether the data were compatible with a range of possible effects. No claim that one procedure was better, worse, or equivalent to the other follows from the information reported.

The distinction between absence of a reported result and evidence of no difference is important. A result that is not reported cannot be treated as a null finding. Equivalence or non-inferiority would require a suitable design, a prespecified margin, and an analysis that addresses that question; such details are not reported in the registry record. Likewise, the mere presence of a randomized design does not reveal the outcome findings.

The endpoint is counted in eyelids, and the record describes exclusion of two eyelids from the TT Clamp analysis after a participant died before follow-up. Without complete information on denominators, follow-up, analysis populations, and any handling of dependence between eyelids from the same participant, the primary analysis cannot be reconstructed or fully assessed. These are limitations in what the registry reports, not evidence that the trial necessarily used an inappropriate method.

The serious adverse-event figures list no serious affected participants in either group, alongside counts in an unspecified other affected category. Those entries are also limited by absent definitions and follow-up details. They do not establish a comprehensive comparison of safety. The most supportable conclusion is that the registry gives the design and endpoint description, but not enough outcome information to interpret the principal efficacy comparison or make a firm comparative safety assessment.

13. Why This Trial Matters Statistically

This trial raises several important statistical issues because its primary endpoint is a count of eyelids rather than a simple participant-level outcome. The distinction between the unit randomized, the unit followed, and the unit analyzed is central to interpreting a comparison. If a participant can contribute more than one eyelid, observations within that participant may be related. Statistical methods and uncertainty estimates should reflect the structure of the data when relevant. The registry describes an exclusion involving both eyelids of one participant, but does not explain the full unit-of-analysis approach.

The endpoint also illustrates why a count should not be interpreted without its denominator. A group with more eyelids assessed can have a larger raw count even if the underlying proportion meeting the endpoint is similar. Conversely, a count alone cannot show whether the groups differ in recurrence frequency when the number assessed is unknown. Group-specific denominators and transparent follow-up accounting are therefore essential to a clinically interpretable comparison.

Randomization is an important design feature, but its value is best understood alongside outcome reporting and analysis details. The record identifies random allocation and single masking, yet does not describe the allocation procedure, who was masked, or the primary analysis method. These omissions prevent readers from assessing all safeguards against bias and from reproducing the statistical comparison.

The record’s missing primary outcome results are especially consequential. Without group counts and an estimate with uncertainty, readers cannot distinguish a clearly estimated difference from an imprecise one, or either from a result that is simply not reported. This is not a minor reporting detail: it prevents statistical assessment of the trial’s central question. The listed secondary outcomes and safety counts add context, but they do not substitute for the primary endpoint results.

Finally, the presence of multiple outcomes makes transparent specification of the analysis plan important. The record lists several outcomes and analyses but does not explain the handling of multiple comparisons. Together, these features make the trial useful for illustrating how design, outcome definition, analysis unit, follow-up, and complete reporting must align for a randomized comparison to be interpretable.

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.

Several trial-specific details needed to assess the primary comparison are not reported in the registry record. These include the primary outcome counts in each group, the denominators used for those counts, the treatment-effect estimate, its uncertainty, and the statistical test or model. Consequently, the principal result cannot be reconstructed from the record.

The record defines the endpoint in eyelids but does not describe whether both eyelids could contribute for participants generally, whether outcomes were correlated within a participant in the analysis, or what methods addressed that possibility. It gives one exclusion detail for the TT Clamp analysis—one participant’s two eyelids were excluded because the participant died before follow-up—but does not provide a complete account of follow-up or analysis exclusions in both groups. The cause of death and broader mortality information are not reported in the registry record.

Important design and measurement details are also absent. The registry does not report the randomization procedure, concealment, the identity of the masked party, detailed outcome-assessment procedures, study locations, or further eligibility criteria. It does not provide the full statistical analysis plan, explain the selection of the analysis population, or describe handling of missing data and multiple outcomes. These gaps limit evaluation of bias, reproducibility, and the assumptions behind any comparison.

The adverse-event entry has limited context: definitions, event terms for the other affected category, follow-up duration, and death counts are not reported in the registry record. The listed counts therefore support only a narrow descriptive account. These reporting limitations do not demonstrate that the trial had methodological flaws; they specify what cannot be assessed from the registry information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Modified Instrumentation for Surgery to Correct Trichiasis — NCT00886015.
• Registry record last updated 2017-05-19; status last verified 2017-04.
• Results first posted 2017-05-19.
• 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 describes a completed randomized, single-masked, parallel-group trial sponsored by Johns Hopkins University. It compares trichiasis surgery using the TT clamp with standard BLTR technique. The listed condition is trachoma, and enrollment is 1927. The record gives a study start of 2009-05 and a primary completion date of 2012-01.

The primary endpoint is the number of eyelids with recurrent trichiasis at two years, defined as one or more eyelashes touching the globe in primary position. The registry notes that one participant’s two eyelids were excluded from the TT Clamp analysis because the participant died before follow-up. Secondary outcomes concern eyelid contour abnormality and trachomatous trichiasis severity.

The primary outcome results and statistical comparison are not reported in the registry record. The adverse-event entry lists 0 serious affected participants in each group and other affected counts of 15 for Standard Instrumentation and 12 for TT Clamp. Further details needed to interpret these figures are not reported.