Study of the Cell Response in the Tear Film After Overnight Contact Lens Wear: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of the Cell Response in the Tear Film After Overnight Contact Lens Wear (NCT01379768), a non-randomized na study. The primary outcome is Leukocyte Population.

2. Clinical Question

3. Trial Design

This completed study examined white blood cells collected from tear samples after sleep. Its stated purpose was to count and analyze those cells in contact lens wearers and compare the findings with those from people who did not wear contact lenses. The registry lists an enrollment of 65 and records the study as non-randomized, single-masked, and parallel. The phase is listed as not applicable.

Participants in the Lotrafilcon A group wore the lenses daily for 1 week, then wore a replacement pair overnight for 8 hours. After a 12-hour washout period, a new pair was dispensed for 4 weeks of daily wear, followed by another 8 hours of overnight wear. The Lotrafilcon B group followed the same schedule with that lens material. The no-lens group did not wear contact lenses during the study and had an 8-hour sleep assessment at 1 week and another 4 weeks later.

The primary endpoint is identified as the leukocyte population at Week 5. The registry describes collecting a tear sample after 8 hours of sleep using an ocular surface cell collection apparatus, then identifying leukocyte types including neutrophils, monocytes, and lymphocytes. The listed primary reporting population includes participants who completed the study per protocol.

Non-randomized allocation means that assignment was not reported as random. Differences between groups could therefore reflect group characteristics or other factors as well as lens wear. The record does not report how allocation occurred, whether masking applied to participants, assessors, or both, or whether the groups were adjusted for baseline differences.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: This reporting group includes all participants who completed the study per protocol.

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 Leukocyte Population, measured over Week 5.

The primary endpoint is the mean total leukocyte population in a tear sample collected at Week 5 after 8 hours of sleep. Leukocytes are white blood cells. The endpoint description identifies neutrophils, monocytes, and lymphocytes among the cell types examined, and says that the total amount of leukocytes for contact lens wearers and non-lens wearers is presented.

A count of cells in a tear sample can be used to describe the cellular response observed at the ocular surface after sleep. Comparing the mean count across the lens-wear and no-lens groups addresses whether the measured leukocyte population differs between those conditions. The registry describes a possible difference as potentially indicating a different immune response; it does not establish that a difference, if present, would be caused by lens wear.

The endpoint is specified as a mean with standard deviation, which describes the group average and the spread of individual observations around it. However, the registry record does not report the group means, standard deviations, or a numerical comparison for this primary endpoint. It is therefore not possible to describe the direction, size, or precision of the observed group differences from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary outcome as a continuous measure summarized by a mean and standard deviation. The information recorded does not identify the statistical test, model, confidence-interval method, or adjustment strategy used to compare groups. The following concepts are general explanations of how such data can be interpreted; they are not claims about methods used in this study.

What does a mean describe?

In general, a mean is the arithmetic average of the observed measurements in a group. For a cell-count endpoint, it gives a summary of the group’s measured leukocyte counts. A mean is easy to compare across groups, but it does not show the full distribution of individual measurements. If a small number of observations are unusually high or low, they can influence the mean.

The standard deviation describes how dispersed observations are around the mean. A smaller standard deviation indicates that measurements are more closely clustered around the average; a larger standard deviation indicates greater spread. It is a description of variation among observations, not a direct measure of how precisely the group mean has been estimated. Precision also depends on the number of observations included, and the number contributing to the primary outcome is not reported in the registry record.

What would a group comparison show?

In general, an unadjusted comparison contrasts the observed outcome summaries between groups without accounting for other participant characteristics. An adjusted comparison uses a statistical model to account for selected characteristics, but its interpretation depends on which factors were measured, how they were modeled, and whether the assumptions are reasonable. The registry record does not report whether the comparison was unadjusted or adjusted, or which comparison method was used.

A confidence interval, in general, expresses uncertainty around an estimated effect. Its endpoints describe a range of values compatible with the data under the method’s assumptions. A narrow interval indicates greater precision than a wide interval. The interval does not guarantee that the true effect lies within it, and it does not remove bias from non-randomized allocation. No confidence interval for the primary outcome is reported in the registry record.

A p-value, in general, summarizes how unusual data at least as incompatible with a specified null hypothesis would be if that hypothesis and the analysis assumptions were correct. It is not the probability that the null hypothesis is true, nor does it measure the size or clinical importance of a difference. The registry record does not report a p-value or a hypothesis test for the primary endpoint.

Why does allocation matter?

Random allocation is generally used to reduce systematic differences between comparison groups at the start of a study. This record describes allocation as non-randomized. As a result, any comparison may be affected by differences between groups in characteristics related to leukocyte counts. Statistical adjustment can address measured factors under suitable assumptions, but it cannot automatically resolve differences that were not measured or were modeled inadequately. The record does not describe an adjustment plan.

What does over-dispersion mean for count data?

General statistical note: count measurements can have more variability than some simple probability models allow. This is called over-dispersion. If present, it can make standard errors too small when a model fails to account for that extra variation, which can make uncertainty appear lower than it is. Whether over-dispersion is relevant depends on the observed data and the chosen model. The registry record gives no distributional information or model details, so it is not possible to say whether over-dispersion was assessed or how it was handled.

The primary outcome is summarized as a mean and standard deviation, but the record does not establish that the data followed a normal distribution or that a normal-theory method was used. The suitability of a method depends on the outcome distribution, group sizes, and analysis assumptions. These details, and diagnostics used to assess assumptions, are not reported in the registry record.

How should planning illustrations be read?

Any sample-size illustration based on the observed effect is a planning exercise, not a description of the trial’s achieved power. The stated illustration assumptions are a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect defined as a stated fraction of the observed effect. These assumptions do not establish the study’s original sample-size rationale. The registry record does not report that rationale, and the illustration does not substitute for the missing endpoint estimates or uncertainty intervals.

For a continuous endpoint, a planning calculation generally depends on the effect size to detect, variability, significance level, desired power, and allocation assumptions. Results are sensitive to those choices. Since the primary outcome values and their variability are not reported in the registry record, an illustration tied to the observed effect should not be mistaken for independent evidence about the effect or for observed power.

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("Lotrafilcon A", "Lotrafilcon B", "No Lens Wear")
n   <- c(20, 19, 20)
m   <- c(583187, 420345, 738140)
sp  <- c(832636, 355940, 609853)
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  Lotrafilcon A  20  583187.000  832636.000  193501.357  972872.643
CARM  Lotrafilcon B  19  420345.000  355940.000  248787.412  591902.588
CARM  No Lens Wear  20  738140.000  609853.000  452720.010  1023559.990

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 6 outcome measures and 0 analyses. It does not report a statistical analysis plan describing which outcomes were primary for inference, how secondary outcomes were to be tested, or whether any adjustment for multiple comparisons was planned. The primary outcome is identified as the leukocyte population at Week 5, but the broader set of outcome measures can create multiplicity concerns if several outcomes or comparisons are tested and interpreted together.

In general, when many hypotheses are examined, the chance of obtaining at least one apparently unusual result can increase. A prespecified testing hierarchy or a multiplicity adjustment can help control that issue, but the appropriate approach depends on the scientific question and analysis plan. Whether any such approach was used is not reported in the registry record. No inference about multiplicity control can be drawn from the count of outcome measures alone.

The primary reporting population is described as participants who completed the study per protocol. The record does not report how many participants completed the study, how many contributed a Week 5 tear sample, or how many had usable leukocyte measurements. It does not describe missing observations, reasons for missingness, exclusions, or imputation. The extent to which missing data could affect the estimates therefore cannot be assessed.

A per-protocol population can differ from the group originally enrolled if participants do not complete the protocol or are excluded from analysis. General statistical concern: if inclusion depends on participant characteristics related to the outcome, estimates among completers may not represent the full enrolled population. The record does not report enough information to assess this possibility.

Although the record specifies a primary reporting population, it does not state whether an intention-to-treat analysis or other analysis population was used. The handling of deviations from the assigned regimen and the rationale for any exclusions are not reported in the registry record.

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 5% reporting threshold.

The adverse-event figures record no serious adverse events in the Lotrafilcon A group among 23 participants at risk, no serious adverse events in the Lotrafilcon B group among 22 participants at risk, and no serious adverse events in the no-lens group among 20 participants at risk. The record also lists no other adverse events in the corresponding groups. Death counts are not reported in the registry record.

These are recorded event counts, not proof that the risk of an event is absent. A zero count can occur even when an event is possible, particularly when the amount of observation is limited. Counts also do not describe event timing, duration, severity beyond the serious-event classification, relatedness assessments, or participant-level follow-up in detail.

The registry record does not provide a narrative account of safety monitoring or explain how adverse events were defined and collected. It is therefore best to read the figures as the adverse events recorded in the registry, rather than as a comprehensive characterization of safety. The figures do not resolve the missing primary leukocyte results or establish a comparison of the overall safety profiles of the groups.

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

The registry record establishes that the study was designed to compare tear-film leukocyte populations after sleep in contact lens wearers and people who did not wear lenses. It describes the lens-wear schedules, the no-lens comparator, the Week 5 primary outcome, and the per-protocol reporting population. These details clarify the intended comparison and the biological measurement being summarized.

What the record does not establish is the observed result. Numerical group means and standard deviations, an estimated contrast, uncertainty intervals, and a statistical test are not reported. The direction and size of any difference cannot be stated, and the precision of an estimate cannot be evaluated. It is not possible from the registry record to conclude that the groups differed or did not differ in leukocyte counts.

The non-randomized allocation also matters. A difference between groups, if numerical results were available, could reflect differences in participant characteristics or other factors rather than lens wear alone. The record does not describe an adjustment strategy that would support a stronger causal interpretation.

The endpoint is a measure of cells collected from tears after sleep. It does not, by itself, establish the cause of any observed cellular response or the clinical importance of a difference. The endpoint description suggests that a difference could indicate a different immune response, but that interpretation would require the actual results and relevant context. The record does not report results for the individual leukocyte types named in the outcome description.

The safety counts record no serious or other adverse events in the listed groups, but a zero count is not evidence that an event is impossible. Death counts are not reported in the registry record. Overall, the record conveys the study question and design, while leaving the primary numerical result and its uncertainty unavailable.

14. Why This Trial Matters Statistically

This study is statistically informative as an example of how a clearly defined biological endpoint and a comparison design still require numerical results for interpretation. The record specifies what was measured: the mean total leukocyte population in a tear sample after sleep, at Week 5. It also identifies the dispersion summary as a standard deviation and names the per-protocol group as the primary reporting population. Those definitions matter because they make the intended outcome and analysis population more specific than a broad statement about eye response.

At the same time, the absence of endpoint estimates illustrates why an outcome label is not a result. Without group summaries or an estimated contrast, readers cannot assess the observed magnitude, direction, or precision. A statistical test result alone would not be enough to judge practical importance, but no test result is reported either. The missing estimates prevent both descriptive and inferential interpretation.

The design provides a second statistical lesson. Non-randomized allocation can leave comparisons vulnerable to confounding. A carefully defined endpoint cannot, by itself, make groups exchangeable. Interpretation would depend on the allocation process, measured baseline characteristics, and analysis choices, none of which are described in enough detail in the registry record to assess.

The record also names multiple outcome measures but does not report an analysis plan or multiplicity strategy. This highlights the importance of distinguishing a prespecified primary question from a broader set of measurements, and of reporting how multiple comparisons were handled. Finally, safety counts and sample-size planning illustrations answer different questions from an endpoint estimate: neither supplies the missing comparison of leukocyte counts or its uncertainty.

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 principal limitation for interpreting this record is that numerical results for the primary endpoint are not reported. Group means and standard deviations, the between-group comparison, and an uncertainty interval are absent. As a result, the observed leukocyte counts and their precision cannot be described.

Allocation is non-randomized. The record does not explain how participants entered the groups, whether groups differed at baseline, or whether a statistical method was used to adjust for such differences. This limits causal interpretation and leaves potential confounding unresolved.

The primary endpoint is defined for the per-protocol completer population, but the number contributing to the endpoint and the handling of missing data are not reported. The record does not state how protocol deviations, incomplete follow-up, or unusable tear samples were treated. It is therefore not possible to assess selection into the analysis population or the effect of missing observations.

The registry describes identification of neutrophils, monocytes, and lymphocytes, but does not report numerical results for the total leukocyte count or those cell types. It also does not provide statistical methods, model assumptions, adjustment choices, or a multiplicity plan. The count of outcome measures is recorded, but the inferential strategy across them is not.

Finally, the adverse-event counts have no accompanying narrative on ascertainment, follow-up, or event relatedness, and death counts are not reported in the registry record. The non-randomized design and missing endpoint results mean that the record supports a description of the intended study, but not a quantitative conclusion about the primary comparison.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Study of the Cell Response in the Tear Film After Overnight Contact Lens Wear — NCT01379768.
• Registry record last updated 2013-03-08; status last verified 2013-03.
• Results first posted 2013-03-08.
• 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

The completed study examined leukocytes in tear samples after sleep among contact lens wearers and participants who did not wear lenses. It was recorded as non-randomized, single-masked, and parallel, with enrollment of 65. The lens groups followed daily-wear and overnight-wear schedules, while the comparator group did not wear lenses.

The primary endpoint was the mean leukocyte population at Week 5, measured after 8 hours of sleep. The primary reporting population was described as participants who completed the study per protocol. Numerical results for this endpoint, including group summaries and a statistical comparison, are not reported in the registry record. The registry lists 6 outcome measures and 0 analyses. Adverse-event counts are recorded as zero for serious and other events in each listed group; death counts are not reported.