Performance of Two Toric Silicone Hydrogel Contact Lenses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Performance of Two Toric Silicone Hydrogel Contact Lenses (NCT03578926), a randomized na study. The primary outcome is Lens Centration.

2. Clinical Question

The broader study question was how the two toric lenses performed following two weeks of wear. Wearing time and comfortable wearing time were listed as secondary outcomes at two weeks. Because the primary endpoint is specified at baseline while the secondary outcomes are specified after two weeks, they address different aspects and timepoints of the study. The registry record does not report a primary inferential analysis or a detailed explanation of how the baseline centration measure was intended to distinguish the lenses. The available summaries therefore describe recorded counts and wear-time measures, rather than establishing a complete comparison of every aspect of lens performance.

3. Trial Design

This was a completed, randomized, double-masked, crossover study of two toric silicone hydrogel contact lenses. A total enrollment of 45 is listed. The two randomized sequences switched lenses after two weeks: one sequence used fanfilcon A first and senofilcon A second, while the other used senofilcon A first and fanfilcon A second. Each sequence description specifies bilateral lens wear. The registry record gives study dates from 2018-06-18 to primary completion on 2018-10-08.

A crossover design means participants can contribute observations under both devices, in different periods. This can make within-participant comparisons useful because each person may serve as their own reference. However, interpretation depends on details such as period effects, sequence effects, how outcomes from each period were analyzed, and whether any carryover was considered. Those details are not reported in the registry record. It is therefore not possible to determine from the posted summaries whether the analysis used the paired structure of the study or adjusted for period and sequence.

The outcome summaries list 44 participants for each lens. These counts do not explain the difference between the enrollment figure and the outcome counts, nor do they establish how many participants completed both periods. Participant flow, reasons for any missing observations, and analysis-population definitions are not reported in the registry record. The record also does not report the masking procedures or which people involved in the study were masked.

The study lists eight outcome measures, including wearing time and comfortable wearing time as secondary outcomes. Two secondary outcome summaries are posted, each with 44 participants per lens-period. No reported analyses are listed for those outcomes, and no formal primary analysis is reported in the registry record. The sponsor is CooperVision, Inc. The phase is listed as not applicable. The record identifies the study as prospective and states that it evaluated clinical performance after two weeks of wear.

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.

First Intervention

Second Intervention

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: A total of 45 subjects were enrolled. One participant was ineligible for the study due to an unacceptable lens fit at the first visit. A total of 44 subjects were dispensed and completed all study visits.

6. Primary Endpoint

The registry lists the primary outcome as Lens Centration, measured over Baseline.

The primary endpoint is lens centration at baseline. Centration describes the position of a contact lens on the eye. The registry description identifies three categories: optimum, acceptable decentration, and unacceptable decentration. The measure is intended to capture whether the lens is positioned centrally or is displaced to a degree considered acceptable or unacceptable.

In general, a positioning measure can be relevant to device performance because the position of a toric lens is one observable aspect of how it sits on the eye. That general rationale does not tell us what level of centration is desirable for an individual, nor does it determine whether a difference between devices would matter clinically. The registry record does not report a threshold for a meaningful difference, category-specific results, or a detailed rationale for selecting this endpoint as primary.

The posted summaries characterize the endpoint as a participant count and list 44 for each lens. They do not provide the number of participants in each centration category. Consequently, the equal overall counts cannot be interpreted as evidence that the two devices had the same distribution across optimum, acceptable, and unacceptable positions. The endpoint is also marked as measured at baseline, whereas the study description focuses on performance after two weeks of wear. The registry record does not clarify the relationship between that baseline timing and the stated two-week study objective.

7. Results Posted in the Registry

• Senofilcon A: 100.0% (44/44) versus 100.0% (44/44) on control; risk difference 0.0 percentage points (95% CI 0.0 to 0.0), risk ratio 1.00 (1.00–1.00); unadjusted two-proportion z-test p = n/a.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Wearing Time

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Senofilcon A - 2 Weeks: mean 11.60 versus 12.20 on control; difference -0.60 (95% CI -1.85 to 0.65), standardized effect d = -0.20; z-test p = 0.348.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Senofilcon A - 2 Weeks and the control. The interval gives the range of effects that remain compatible with the data.

Comfortable Wearing Time

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Senofilcon A - 2 Weeks: mean 9.00 versus 10.00 on control; difference -1.00 (95% CI -2.30 to 0.30), standardized effect d = -0.32; z-test p = 0.130.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Senofilcon A - 2 Weeks and the control. The interval gives the range of effects that remain compatible with the data.

The two posted secondary outcomes both concern daily use after two weeks: total wearing time and comfortable wearing time. Their summaries point in the same direction in the sense that the Senofilcon A means are lower than the Fanfilcon A means, but both recalculated intervals include zero. This broad pattern is not a substitute for examining each outcome's uncertainty, nor does a shared direction establish a reliable difference. The outcomes are related in subject matter, but comfortable wearing time is not interchangeable with total wearing time.

The primary endpoint addresses a different measurement: lens centration at baseline. Its posted count comparison does not provide category-level results, so it cannot be used to explain or validate the secondary wear-time pattern. The primary and secondary outcomes also refer to different timepoints in the registry record. They should therefore be considered as distinct pieces of descriptive evidence rather than as a single confirmatory chain of findings.

The secondary p-values are unadjusted recalculations, and no reported analyses are listed. When multiple outcomes are considered, the chance of finding an apparently notable result can increase if each is examined separately without a prespecified plan or adjustment. This is a general statistical concern; the registry record does not report whether a multiplicity procedure was planned. The unadjusted secondary results consequently carry less confirmatory weight than a clearly specified primary analysis would. Their value is descriptive: they indicate what the posted summaries suggest, while leaving the uncertainty and analysis limitations visible.

Neither a pattern across outcomes nor a lack of a clear statistical distinction proves that the lenses have the same performance. The record does not report a protocol-defined hierarchy among secondary endpoints, a clinically important threshold, or an adjustment strategy. The secondary outcomes are best treated as exploratory evidence that may inform questions for a more completely reported analysis, rather than as decisive confirmation of a treatment difference.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Wearing Time
• Comfortable Wearing Time

9. Statistical Interpretation

10. Statistical Methods Explained

Statistical methods help distinguish an observed estimate from the uncertainty around it. A mean is the arithmetic average of measurements, while a standard deviation describes how much individual observations vary around that average. For wearing time, the registry record reports a mean and standard deviation for each lens after two weeks. These summarize the observed hours/day; they do not describe every participant's experience or the range of possible values.

What does a mean difference represent?

The recalculated mean difference compares the two posted group means, with the Senofilcon A value minus the Fanfilcon A value. A negative estimate means the posted mean was lower for Senofilcon A. The difference is an unadjusted calculation from summary statistics, not a trial-reported model estimate. In a crossover study, each participant may have observations under both lenses. A paired analysis can use the within-person relationship between those observations. The posted calculations do not establish whether that relationship, period, or treatment order was incorporated. A recalculation that ignores such design details may not represent the trial's intended analysis.

How should a confidence interval be read?

In general, a confidence interval gives a range of values compatible with the data and the method used to calculate it. A narrower interval indicates greater precision under that method; a wider interval indicates less precision. For both secondary mean differences, the posted intervals include zero, the value corresponding to no difference in the calculated direction. This means the summaries do not rule out no difference under the recalculation. It does not prove that the lenses have identical outcomes, and the interval does not quantify clinical importance unless a meaningful-difference threshold is also specified. No such threshold is reported in the registry record.

What does an unadjusted p-value say?

In general, a p-value measures how unusual data at least as incompatible with a specified null model would be if that model were true, under the assumptions of the analysis. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The posted secondary p-values are unadjusted recalculations. The record does not identify a prespecified significance threshold for the secondary analyses. They should not be treated as reported sponsor analyses: the analyses list is empty.

Why does over-dispersion matter?

General explanation: for count outcomes, a simple statistical model may assume that variability is determined by the mean. Over-dispersion occurs when the observed variability is larger than that assumption allows. If it is ignored, standard errors can be too small and intervals can be too narrow. This trial's primary outcome is recorded as a participant count, not as a repeated event rate, and the registry record supplies no dispersion estimate or model. The count summary does not support an over-dispersion assessment.

What do the sample-size illustrations mean?

The posted planning illustrations are not the trial's design justification and are not observed power. They use the observed secondary effects, a two-sided significance level of 0.05, equal allocation, and a normal approximation. They illustrate participants per arm for 80% or 90% power if a stated fraction of the observed effect were to be detected. For example, using 100% of the observed wearing-time effect gives an illustration of 393 participants per arm for 80% power; using 100% of the observed comfortable-wearing-time effect gives 152 participants per arm for 80% power. These are planning calculations based on observed effects, not a claim that the trial had those numbers or that its design was justified by them. The registry record does not report its own sample-size justification, design assumptions, or planned power.

More generally, power is a design concept: it describes the probability that a specified analysis would detect a particular effect under stated assumptions. It cannot be inferred as a retrospective property from a non-significant result. The planning illustrations are sensitive to the size of the assumed effect and the variability used. Since they are based on observed effects, which are uncertain, they should not be treated as reliable predictions of a future study's results. No adjustment for crossover correlation is identified in the planning assumptions.

The registry record identifies randomization, masking, and crossover as design features, but does not describe the statistical analysis plan. The comparison calculations consequently have a narrower role: they help express the posted summary values and their unadjusted uncertainty, while leaving the planned inferential approach unknown.

11. Confidence Intervals and Precision

Precision concerns how tightly a statistical estimate is determined by the observed data and the assumptions used in its calculation. The primary comparison is listed as a risk difference of 0.0, with a confidence interval from 0.0 to 0.0. However, the arm summaries provide only an overall participant count for each lens, not the number in each centration category. The apparently exact interval therefore cannot resolve the missing category information or support a detailed interpretation of the primary endpoint.

The secondary mean-difference intervals are more informative about uncertainty in the recalculated comparisons: each includes zero. This is compatible with no difference as well as with differences in either direction within the interval. The registry record's summary means and standard deviations describe variation, but the crossover structure complicates precision. The uncertainty of a paired comparison depends on how each participant's measurements under the two lenses relate to one another. That within-person covariance is not reported, and the recalculations do not establish that it was used. Thus, the displayed uncertainty should be understood as applying to the unadjusted recalculation, not necessarily to a fully specified crossover analysis.

Confidence intervals also do not determine whether an effect is clinically meaningful. The registry record does not provide a threshold for an important change in hours/day or for a meaningful difference in centration. Nor does it report a prespecified equivalence margin. The summaries therefore cannot establish equivalence merely because the intervals include zero. The available precision is constrained by the sample counts, the variability in the observations, and the analysis assumptions; details needed to assess those factors fully are not reported in the registry record.

12. Multiplicity, Missing Data and Analysis Populations

The registry record identifies one primary outcome and two secondary outcome summaries, but does not report a multiplicity plan. Multiplicity matters when several outcomes or comparisons are examined: without a prespecified strategy, the chance of at least one apparently unusual result can be greater than for a single test. This is a general concern, not evidence that an error occurred in this study. The secondary p-values are unadjusted recalculations, and the record does not describe any correction, hierarchy, or other approach to multiple testing.

Information about missing data is also limited. Enrollment is listed as 45, while the outcome summaries list 44 participants for each lens. The registry record does not explain this difference, give reasons for missing observations, or report how missing values were handled. In a crossover design, it is important to know whether participants contributed data for both periods and how incomplete sequences were treated. Those details are not reported in the registry record, so the completeness of the paired comparisons cannot be assessed.

The record does not define an intention-to-treat, per-protocol, or other analysis population. It also does not identify a prespecified statistical analysis plan, the primary comparison model, or how period and treatment sequence were considered. Randomization and double masking are listed, but further procedural detail is not reported in the registry record. These omissions limit assessment of the analysis and the potential effects of missingness or design structure. They should not be filled in by assumption.

13. Safety Results

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

Deaths

Other (non-serious) adverse events

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

The safety summaries list 44 participants at risk for serious adverse events in each lens group, with 0 affected in each group. Deaths are listed as 0 in both groups. The record also reports 44 at risk for other adverse events in each group, with 0 affected in either group. No serious adverse-event terms are listed.

These figures describe the events captured in the registry record for the stated at-risk groups. A zero count means no events were reported in these summaries; it does not establish that an event is impossible or that the devices have identical safety profiles. The record does not provide further detail about event collection, follow-up completeness, or how safety was analyzed in the crossover periods. The counts should therefore be read as a limited description of the posted safety data, not as a comprehensive characterization of risk.

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

The posted results describe a randomized crossover comparison of two toric silicone hydrogel lenses, with baseline centration counts and secondary summaries of wearing time and comfortable wearing time after two weeks. The secondary group means and unadjusted recalculations provide estimates of the observed differences and their uncertainty. Both secondary confidence intervals include zero, so the posted recalculations do not establish a clear difference in those averages. The primary count comparison is equal as reported, but the category breakdown needed to understand centration is absent.

These results do not establish that the lenses are equivalent. Equivalence requires a defined margin and an analysis designed to assess whether the plausible difference lies within that margin; neither is reported in the registry record. Nor do the results establish that one lens is superior or that a numerical difference is clinically important. Statistical uncertainty and clinical importance are distinct questions, and no meaningful-difference threshold is reported for these outcomes.

The crossover design has the potential to support within-participant comparisons, but the posted recalculations are not documented as accounting for pairing, period, or sequence. Without the analysis plan and data needed to assess those features, the secondary calculations should not be interpreted as definitive trial analyses. The registry record also does not explain the enrollment-to-outcome count difference or specify analysis populations.

Accordingly, the results are most useful as a description of the recorded summaries and their limitations. They do not support medical advice or a decision about which device an individual should use. Broader conclusions would require a complete analysis with clearly reported methods, category-level primary results, and sufficient information about participant flow and missing data.

15. Why This Trial Matters Statistically

This study illustrates why design and analysis details matter even when a trial has straightforward group summaries. In a crossover study, participants can receive both devices, which creates a natural opportunity to compare measurements within the same person. But an analysis that treats the observations as unrelated can fail to use that structure or misstate its uncertainty. The posted recalculations are unadjusted, and the registry record does not say how the crossover features were handled in the trial's planned analysis.

It also illustrates the difference between an endpoint label and an interpretable result. Lens centration is defined using three categories, yet the posted primary summaries report only an overall participant count for each lens. Without category-specific values, the count comparison cannot describe the distribution of lens positions. Clear reporting of the actual endpoint values is essential to understanding what a result means.

The secondary outcomes show why estimates, intervals, and analysis plans should be read together. An observed difference is not itself proof of a reproducible effect, and an interval that includes zero is not proof of equivalence. Unadjusted recalculations can be useful for orientation, but they do not replace a prespecified analysis that reflects the randomized crossover design and addresses multiple outcomes.

Finally, planning calculations based on observed effects are illustrations, not a retrospective justification for the study size. They show how assumed effect size and variability influence sample-size planning, while leaving the trial's own design rationale unknown. This distinction helps prevent a planning number from being mistaken for evidence about what the completed study could reliably detect.

16. 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 limitations are specific to interpreting this record. The primary endpoint is described as a three-category measure of lens position, but the posted arm summaries contain only participant counts and no distribution among the categories. The endpoint is marked as baseline even though the study description focuses on performance after two weeks, and the relationship between these timings is not explained.

The study is a crossover, yet the record does not report a trial analysis that accounts for within-participant comparisons, period, or treatment sequence. The recalculated secondary comparisons use posted summary statistics and are unadjusted; they should not be confused with a reported sponsor analysis. No reported analyses are listed. It is also not possible to determine how many participants completed both periods or how incomplete observations were handled.

Enrollment is 45, while each lens outcome summary lists 44 participants. The reason for this difference, participant flow, and analysis-population definitions are not reported in the registry record. The record does not give category-level primary results, a clinically meaningful threshold, an equivalence margin, a multiplicity plan, or the trial's sample-size justification. Further information about masking procedures and safety-event collection is also not reported.

These limitations restrict conclusions about both the size and the practical meaning of any difference. They do not show that the study was conducted improperly; they identify information unavailable in the registry record that is needed for a fuller statistical assessment.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: Performance of Two Toric Silicone Hydrogel Contact Lenses — NCT03578926.
• Registry record last updated 2019-12-10; status last verified 2019-11.
• Results first posted 2019-12-10.
• 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.

20. Record Summary

The registry record identifies NCT03578926 as a completed, randomized, double-masked crossover study of fanfilcon A and senofilcon A toric contact lenses in participants with astigmatism. Enrollment was 45. Participants were assigned to one of two sequences, with each lens worn bilaterally for two weeks before switching. The primary outcome was lens centration at baseline; wearing time and comfortable wearing time were listed as secondary outcomes at two weeks.

Outcome summaries list 44 participants per lens. The primary summaries report equal counts but do not give the distribution across centration categories. Secondary means are posted for both wear-time measures, with unadjusted recalculations whose confidence intervals include zero. The registry record does not report a primary inferential analysis, a multiplicity plan, a detailed crossover analysis method, or an explanation of the difference between enrollment and outcome counts. Serious adverse events, other adverse events, and deaths are reported as zero in the posted summaries.