Ophthalmic Compatibility During Seven Days of Continuous Wear of Silicone Hydrogel Lenses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Ophthalmic Compatibility During Seven Days of Continuous Wear of Silicone Hydrogel Lenses (NCT00934102), a randomized na study. The primary outcome is Front Surface Lens Deposits.

2. Clinical Question

In statistical terms, the endpoint is a continuous summary of a graded observation. The question is about the group means and the uncertainty around differences between those means, rather than about the percentage of participants who crossed a specified threshold. The posted comparisons are unadjusted recalculations from the arm summaries. They can describe the estimates and their precision, but they do not establish that the lenses are equivalent or that a clinically meaningful difference is absent.

3. Trial Design

The registry describes a randomized, double-masked, parallel study of three silicone hydrogel contact lenses. It lists CIBA VISION as sponsor, a planned enrollment of 57, and a completed status. The study purpose was to assess ophthalmic compatibility during overnight use of three lenses for six nights. The registry dates the study start to 2009-08 and primary completion to 2009-09.

The listed devices are Narafilcon A, Lotrafilcon A, and Galyfilcon A. Each arm description identifies a spherical silicone hydrogel lens randomly assigned to one eye and worn on an extended-wear basis. The parallel model indicates that the registry presents the study as parallel rather than as a crossover design. The record does not explain whether assignment was at the participant or eye level, how the other eye was managed, or whether a participant could contribute data to more than one lens group. Those details are not reported in the registry record.

The primary endpoint is reported at Period 2, Day 6. The outcome population is per protocol, limited to participants who completed all study visits. The posted arm summaries each contain 15 participants. This is not the same figure as the overall enrollment, and the registry does not provide a participant flow that reconciles enrollment with the endpoint populations. The record lists one outcome measure and zero analyses.

The registry does not report the trial's original sample-size justification, the assumptions used in its design, a prespecified hypothesis-testing plan, or details of the masking procedures. It also does not describe randomization procedures beyond identifying allocation as randomized. These gaps matter when interpreting design features: the labels establish the broad structure, but they do not supply the operational details needed to assess how allocation, masking, or analysis were implemented.

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: Of the 57 subjects screened for the study, 11 did not start Period 1 due to personal reasons (7) and non-suitability (4). Period 1 established Day One measurements in order to monitor changes during Period 2.

Period 1, One Night of Wear

Reasons for not completing this period:

Period 2, 7 Days/6 Nights of Wear

Analysis population for the primary outcome, as defined in the registry: Per Protocol. Only the data from participants who completed all study visits were analyzed.

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 Front Surface Lens Deposits, measured over Period 2, Day 6.

The primary endpoint is Front Surface Lens Deposits, measured in units on a scale, with the mean and standard deviation reported for each lens group. An investigator assessed protein and lipid deposits on the contact lens surface using a biomicroscope, which magnifies the appearance of the lens on the wearer's eye. Grades range from 0, meaning none, to 4, meaning severe. The reported time point is Period 2, Day 6.

This endpoint is used to summarize the degree of visible surface deposits during lens wear. The grade retains more information than a simple yes-or-no indicator of whether deposits were present: the scale distinguishes levels from none through severe. Reporting a group mean gives a compact summary of the central tendency, while the standard deviation describes the spread of individual grades around that mean.

There are limits to that summary. A mean treats the numeric distances between scale grades as meaningful for averaging, although the underlying assessment is an ordered grading scale. The registry does not provide information about assessor training, repeatability, or how discrepancies between assessments were handled. It also does not post results at other time points or a distribution of grades by category. As a result, the posted mean and standard deviation describe the endpoint in the form reported, but do not show the full pattern of individual observations.

7. Results Posted in the Registry

• Narafilcon A: mean 0.78 versus 0.68 on control; difference 0.10 (95% CI -0.28 to 0.48), standardized effect d = 0.19; z-test p = 0.608.
• Galyfilcon A: mean 0.77 versus 0.68 on control; difference 0.09 (95% CI -0.27 to 0.45), standardized effect d = 0.18; z-test p = 0.620.

8. Statistical Interpretation

9. Statistical Methods Explained

The posted endpoint is a continuous summary: the registry reports a mean and standard deviation for each lens group. The reported comparisons use differences between group means. The statistical interpretation depends on what these summaries capture, on the uncertainty around the estimated differences, and on the population included in the analysis.

What does a mean difference describe?

A mean difference is the mean in one group minus the mean in the reference group. Here, the reference is Lotrafilcon A. The Narafilcon A comparison has an estimated difference of 0.1, and the Galyfilcon A comparison has an estimated difference of 0.09. Both estimates are positive, meaning that the posted means for those groups are above the Lotrafilcon A mean. A difference in means summarizes the average contrast; it does not say that every participant in one group had a higher grade than every participant in another group.

The outcome is an investigator-assigned grade on an ordered scale from 0 to 4. Averaging such grades is a familiar way to summarize group results, but it compresses the underlying observations into a single number. Two groups can have similar means while having different distributions, and the means do not show how many observations were at each grade. No grade-frequency distribution is posted.

What do standard deviations add?

A standard deviation describes variation among the observations within a group. The standard deviations are 0.35 for Lotrafilcon A, 0.67 for Narafilcon A, and 0.61 for Galyfilcon A. The larger values for the latter groups indicate more spread around their group means in the posted summaries. Standard deviation is not the same as uncertainty in the estimated mean. Uncertainty in a mean or in a mean difference also depends on how many observations contribute to that estimate.

General statistical context: when observations vary more, a study generally needs more information to estimate a group contrast precisely. Unequal variability between groups can also make simple comparisons less straightforward. Here, the posted calculations use group summaries and report unadjusted comparisons; the registry record does not provide a detailed model specification or describe checks of statistical assumptions.

How should the confidence intervals be read?

A confidence interval gives a range of values compatible with the data under the calculation's assumptions. It represents uncertainty about the estimated mean difference, rather than a range containing a stated proportion of individual participant grades. Both posted intervals extend below and above zero. Zero corresponds to no difference in group means, so the intervals include that possibility as well as possible differences in either direction. Their breadth indicates that the estimates are not highly precise.

A confidence interval is not a guarantee that the true value lies within its endpoints, and it does not assign a probability to a particular value after the data have been observed. Its interpretation relies on the model and sampling assumptions used for the calculation. The registry does not report the original analysis procedure, and the posted comparison statistics are unadjusted recalculations from the arm summaries.

What do the p-values say?

The unadjusted p-values are 0.608 for Narafilcon A versus Lotrafilcon A and 0.62 for Galyfilcon A versus Lotrafilcon A. In general, a p-value measures how unusual data at least as incompatible with a null hypothesis would be if that hypothesis and the calculation's assumptions held. It is not the probability that the null hypothesis is true. These values do not provide evidence that the mean grades are identical, and they cannot determine whether a difference would matter in practice.

The comparisons are unadjusted. The registry record does not state whether the trial's original analysis accounted for multiple comparisons or whether these comparisons were prespecified. Without that information, the posted p-values should be viewed as descriptive support for the displayed comparisons, not as a complete account of the trial's inferential plan.

What does the analysis population mean?

The endpoint population is described as per protocol and includes only participants who completed all study visits. This definition means that the displayed summaries are not explicitly based on everyone enrolled. The record gives 57 as enrollment and reports 15 participants per arm in the endpoint summaries, but it does not provide a flow diagram or explain the path from enrollment to these analysis groups. The effect of excluding participants who did not complete all visits cannot be assessed from the posted information.

General statistical context: excluding participants after randomization can affect the comparability achieved by random assignment, particularly if completion is related to outcomes or group assignment. That possibility does not establish that bias occurred. The registry does not report reasons for noncompletion or results under a different analysis population, so the robustness of the per-protocol findings cannot be assessed.

10. Confidence Intervals and Precision

The confidence intervals around both mean differences extend from below zero to above zero. This means the posted summaries are compatible with no mean difference and with differences in either direction, under the assumptions used for the unadjusted calculations. The point estimates are 0.1 for Narafilcon A compared with Lotrafilcon A and 0.09 for Galyfilcon A compared with Lotrafilcon A. The intervals are wider than the point estimates, so the point estimates alone should not be treated as precise estimates of the underlying contrasts.

Precision is limited by the number of participants contributing to each arm summary: 15 per arm. The standard deviations also show that observations vary within groups, particularly for Narafilcon A and Galyfilcon A relative to Lotrafilcon A. Together, group size and variability influence how tightly an estimated difference can be pinned down. The posted summaries do not show the individual grades, so it is not possible to inspect whether the uncertainty is driven by a few observations or by broader variation.

A confidence interval that includes zero is not proof of no effect or of equivalence. To support equivalence, an analysis would need a prespecified range of differences considered acceptably small and an interval narrow enough to address that range. Such a margin and analysis are not reported in the registry record. The data therefore support a cautious statement about uncertainty, rather than a conclusion that the three lenses have matching deposit grades.

The interval calculations are presented as unadjusted comparisons. The record does not provide details of any adjustment for multiple comparisons or other covariates, nor does it post a separate analysis output. Precision should consequently be understood as the precision of these posted summary-based comparisons, not necessarily of a more fully specified analysis.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size display is a planning illustration based on the observed mean difference, not the trial's original enrollment design. The figures are participants per arm, not total events. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect targeted in each row is the stated fraction of the observed effect.

The 80% power column gives the number of participants per arm indicated by those assumptions to have an 80% chance of detecting the selected effect if that effect is the true one and the assumptions hold. The 90% column gives the corresponding planning count for a 90% chance. These are prospective planning interpretations, not descriptions of what the completed study achieved. This is not observed power.

The table presents separate planning comparisons for Narafilcon A versus Lotrafilcon A and Galyfilcon A versus Lotrafilcon A. For each, it considers planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The displayed counts rise as the target effect becomes smaller: smaller effects are harder to distinguish from random variation and need more participants under the same assumptions. Higher desired power also entails larger planning counts.

The curve is a visual companion to the table: it helps show how the planning requirement changes as the effect being targeted changes. Neither display is a record of the number enrolled or analyzed in this trial. The trial's original sample-size justification and design assumptions are not reported in the registry record, so the illustrative counts should not be used to infer what the investigators planned or whether the trial met that plan.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 0.100; pooled standard deviation σ = 0.535.
2. n = 2 × (1.96 + 0.842)² × 0.535² / 0.100² = 448.5, rounded up to 449 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 0.1                      # observed difference in means
sigma <- 0.534509120595711                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(934102)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 449 (80% power), 601 (90% power)
 75% of observed effect: n per arm = 798 (80% power), 1,068 (90% power)
 50% of observed effect: n per arm = 1,794 (80% power), 2,402 (90% power)
power.t.test: 449.4 
Simulated power at n = 449 per arm: 0.799 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and zero analyses. It reports a primary endpoint and two comparisons against Lotrafilcon A, but it does not report a statistical analysis plan describing which contrasts were prespecified or how multiple comparisons were handled. The displayed p-values are unadjusted. If multiple contrasts are considered, the chance of at least one false-positive finding can change; adjustment methods are one way to address that issue. The record does not indicate whether any such method was used in the trial's own analysis.

The primary endpoint is based on a per-protocol population, defined as participants who completed all study visits. The record does not provide the number enrolled who failed to complete visits, reasons for noncompletion, or a participant flow by arm. It also does not say how missing endpoint observations were handled. There is no posted alternative analysis using all randomized participants, and no sensitivity analysis is listed. The effect of missing data or per-protocol exclusions therefore cannot be evaluated from the registry results.

The primary endpoint summaries report 15 participants in each arm, while overall enrollment is 57. The registry does not explain the relationship between those figures or reconcile enrollment with the analyzed endpoint groups. Although the arm descriptions say a lens was assigned to one eye, the record does not clarify the unit of allocation and analysis or how the other eye contributed, if at all. This limits assessment of whether observations were independent and whether the analysis appropriately reflected the study structure.

The record also does not report covariate adjustment, handling of repeated assessments, an interim analysis plan, or a prespecified threshold for a meaningful difference. These omissions do not show that the trial lacked such procedures; they mean those details are not reported in the registry record. The available interpretation is consequently limited to the posted per-protocol arm summaries and unadjusted recalculations.

14. 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 serious adverse event figures list 30 participants at risk in each lens group and 0 participants affected by serious adverse events in each group. The figures for other adverse events likewise list 30 at risk and 0 affected for each group. No serious adverse event terms are listed. Death counts are not available in the posted figures.

These entries should be read as counts within the registry's adverse-event reporting fields, not as a guarantee that no event of any kind occurred during the study. The record does not provide event narratives, severity categories beyond the serious-versus-other distinction, or further detail about how events were collected. It also does not explain why the adverse-event denominators differ from the 15 participants per arm in the primary endpoint summaries.

Zero affected participants in these fields is a descriptive finding in the posted safety record. It does not establish that the risks are identical across lenses or that an event could not occur. The study's reported enrollment and analysis populations are limited, and the registry does not provide additional safety analyses to broaden what can be concluded.

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

The posted endpoint results show mean front-surface deposit grades of 0.68 for Lotrafilcon A, 0.78 for Narafilcon A, and 0.77 for Galyfilcon A at Period 2, Day 6. The reported unadjusted mean differences versus Lotrafilcon A are 0.1 for Narafilcon A and 0.09 for Galyfilcon A. Both confidence intervals include zero, and both unadjusted p-values are relatively large. In this dataset, the comparisons do not provide strong evidence of a difference in mean deposit grade.

That statement is narrower than saying the lenses are equivalent or that they have the same performance. A failure to find strong evidence of a difference is not proof of sameness. The registry does not report a prespecified equivalence margin, and the confidence intervals allow for differences in either direction. The posted results also concern one endpoint at one stated time point, not every aspect of ophthalmic compatibility or every possible outcome of lens wear.

The endpoint itself is an investigator grade of protein and lipid deposits on the lens surface. Group means do not show each participant's grade or the proportions at each scale value. The analysis is per protocol and includes only participants who completed all study visits; the registry does not provide enough information to determine how the excluded participants might affect interpretation.

Finally, the record's safety entries report no participants affected by serious or other adverse events in the listed groups, but the entries are limited to those fields and denominators. They should not be expanded into claims about all possible harms. The most defensible reading is descriptive: the reported means are close, the unadjusted comparisons are uncertain, and the registry lacks details needed to draw broader conclusions.

16. Why This Trial Matters Statistically

This trial is statistically interesting because it combines a graded endpoint with small per-arm analysis groups and comparisons among three lens types. A mean difference offers a simple summary, but it can hide the distribution of ordered grades. The posted standard deviations make clear that participant-level results vary within groups, and the groups do not have identical spreads.

The comparison estimates are close to zero, but their confidence intervals extend to both sides of zero. That contrast between a small point estimate and substantial uncertainty is central to interpretation. A result that is not statistically significant does not by itself establish that groups are equivalent. The registry does not provide a clinical or statistical equivalence margin, so the available evidence cannot answer an equivalence question.

The endpoint's per-protocol population also matters. The registry reports overall enrollment of 57 and 15 participants per arm in the endpoint summaries, without explaining the relationship. Because the primary endpoint only includes participants who completed all visits, readers cannot assess from the posted record whether completion differed by group or whether the analyzed groups retained the balance created by randomization.

Finally, the comparison statistics are unadjusted recalculations, while the record lists no analysis outputs. The absence of details on the prespecified analysis and multiplicity handling makes it important to distinguish these descriptive comparisons from a complete account of the trial's statistical plan. This example illustrates why estimates, uncertainty, analysis populations, and missing methodological detail all matter alongside p-values.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry describes a one-eye lens assignment but does not clarify the unit of randomization and analysis, how the other eye was treated, or whether any participant contributed observations to more than one group. Those details are relevant to understanding the study structure and the independence of the observations. The record calls the model parallel, but does not provide enough operational detail to resolve these questions.

The endpoint summaries are per protocol and include 15 participants in each arm, while enrollment is listed as 57. No participant flow, completion counts by group, reasons for withdrawal, or missing-data methods are reported. The available summaries therefore cannot show how exclusions affected the analyzed populations. The adverse-event figures use 30 participants at risk per group, and the registry does not explain how those denominators relate to the endpoint counts.

The outcome is an investigator-assessed grade on an ordered 0-to-4 scale. The record does not describe assessor training, assessment reliability, or whether assessments were independently reviewed. It also does not post grade distributions, so the mean and standard deviation cannot reveal the number of participants at each level or the shape of the data within groups.

Only the primary endpoint at Period 2, Day 6 is described in the posted results. The registry does not report other time-point results, a detailed analysis plan, multiplicity handling, a sample-size justification, or an equivalence margin. These are limits of the available record, not proof that the study did not collect or consider such information.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Ophthalmic Compatibility During Seven Days of Continuous Wear of Silicone Hydrogel Lenses — NCT00934102.
• Registry record last updated 2012-07-10; status last verified 2010-11.
• Results first posted 2010-12-01.
• 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.

21. Record Summary

The registry record describes a completed, randomized, double-masked, parallel study sponsored by CIBA VISION, with enrollment of 57 and a focus on overnight wear of three silicone hydrogel lenses for six nights. The primary endpoint is investigator-assessed front-surface lens deposits at Period 2, Day 6, reported as a mean and standard deviation for the per-protocol population.

The posted means were 0.68 for Lotrafilcon A, 0.78 for Narafilcon A, and 0.77 for Galyfilcon A. Unadjusted recalculations show small positive mean differences versus Lotrafilcon A, with confidence intervals that include zero. The record lists zero analyses and does not report the trial's original sample-size justification or detailed statistical plan. Interpretation is therefore limited to the posted summaries, the specified analysis population, and the uncertainty in the recalculated comparisons.