Clinical Performance of Hydrogel vs. Silicone Hydrogel Contact Lenses: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Performance of Hydrogel vs. Silicone Hydrogel Contact Lenses (NCT02131402), a randomized na study. The primary outcome is Participant's Subjective Rating for Lens Handling - Enfilcon A / Omafilcon A.

2. Clinical Question

3. Trial Design

The registry identifies this as a randomized, double-masked, parallel study, with phase listed as not applicable. It is titled a non-dispensing fitting study comparing clinical performance of hydrogel and silicone hydrogel sphere-design contact lenses. The stated aim includes subjective comfort, lens handling, lens fitting characteristics, and visual acuity. The listed condition is myopia, and enrollment is recorded as 60.

The arm descriptions say that a participant wears a pair of lenses, with a test lens in one eye and a control lens in the other eye. After approximately 1 hour, both lenses are removed and another pair is inserted; this is repeated for three pairs. The descriptions name Enfilcon A paired with Omafilcon A, Ocufilcon D, or Methafilcon A. These within-participant, paired-eye details appear alongside the registry’s parallel-model classification. The record does not explain how those details relate to the parallel classification, so the allocation and analysis structure should not be inferred beyond what is stated.

The posted primary endpoint concerns the Enfilcon A and Omafilcon A comparison, rated after 1 hour of wear at removal of Pair #1. The results give n=60 for each lens rating. The record identifies CooperVision, Inc. as sponsor and lists the study as completed. Start and primary-completion dates are both recorded as 2014-05. The registry lists 33 outcome measures, but no secondary results are posted. Further protocol details, including participant eligibility, the randomization procedure, masking procedures, and any planned analysis population, 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: There were 60 subjects enrolled and fitted with the study lenses. All sixty subjects completed the trial (i.e. no discontinuations).

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Participant's Subjective Rating for Lens Handling - Enfilcon A / Omafilcon A, measured over 1 hour post settling.

The primary endpoint is a participant’s subjective rating of lens handling for Enfilcon A compared with Omafilcon A. The rating was collected by questionnaire after 1 hour of lens wear, at removal of the first pair. The scale runs from 0, described as very difficult, to 100, described as very easy. A higher rating therefore represents a more favorable assessment of ease of handling on this particular scale.

Subjective handling ratings are useful because the endpoint captures participants’ own experience of removing or managing the lenses, rather than an instrument-measured property. It is one aspect of clinical performance and is distinct from comfort, fitting characteristics, and visual acuity, which are also named in the study aim. The registry does not report a threshold for a meaningful rating difference, nor does it explain how questionnaire responses were developed or validated.

The endpoint is described as a mean with standard deviation, making it a continuous measure for the reported comparison. The result is specific to the first-pair assessment at lens removal after the stated wear period. It does not, by itself, summarize the other lens pairs, other outcomes, or longer-term performance. Those broader results are not reported in the registry record.

7. Results Posted in the Registry

• Omafilcon A: mean 84.00 versus 97.00 on control; difference -13.00 (95% CI -18.52 to -7.48), standardized effect d = -0.84; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

What is being compared? The endpoint is continuous: each participant’s questionnaire response is a numerical rating on the stated handling scale. The reported summaries are means and standard deviations. A mean describes the average rating in a group; a standard deviation describes how dispersed individual ratings are around that average. These summaries address different features of the data and should be interpreted together.

The comparison is expressed as a mean difference. For the posted contrast, the estimate is -13.0 units, with Omafilcon A as the compared lens and Enfilcon A as the reference. The direction matters: a negative estimate means the average rating for Omafilcon A was lower than the average for Enfilcon A under this subtraction order. The group means are 84.0 and 97.0, respectively. The comparison is an unadjusted result in the registry record; the analysis methods behind it are not reported in the registry record.

What does a confidence interval describe? A confidence interval gives a range of values compatible with the estimate under the statistical model used to construct it. The 95% interval for this mean difference is -18.52 to -7.484. In general, a confidence interval is useful for judging precision because it displays uncertainty around an estimate, not just a single point. Its interpretation depends on the model and design assumptions being appropriate. The registry does not provide enough information to establish all of those assumptions, including how the paired-eye arrangement was handled analytically.

What does the p-value mean? The unadjusted p-value is <0.001. In general, a p-value describes the compatibility of the observed data, or results more extreme, with a specified null model. It is not the probability that the null hypothesis is correct, nor is it a measure of effect size or clinical importance. Because it is identified as unadjusted, it does not reflect any correction for multiple comparisons. Whether such a correction was planned or used is not reported in the registry record.

Why does variation matter? Ratings differ from person to person. The posted standard deviations are 8.2 for Enfilcon A and 20.2 for Omafilcon A. When outcomes are more variable, an estimate can be less precise for a given amount of information. If data are more dispersed than a model assumes, standard errors and confidence intervals based on that model may not accurately reflect uncertainty. This is a general statistical concern; the record does not report diagnostics or an alternative variance model.

What is the design complication? The registry labels the study randomized and parallel, while the arm descriptions state that a test lens and control lens are worn in opposite eyes and that lens pairs are changed after approximately 1 hour. Paired measurements from the same participant are generally statistically related. In general, a paired analysis accounts for that relationship, whereas treating paired observations as independent can affect uncertainty estimates. The record does not specify the analysis model or explain how the stated parallel classification corresponds to the paired-eye procedure. Therefore, the reported result can be described, but its handling of within-participant dependence cannot be verified from the registry record.

What can be said about the planned analysis? The record lists the outcome as a mean with standard deviation and supplies a comparison estimate, confidence interval, and unadjusted p-value. It does not report a detailed statistical analysis plan, model specification, handling of missing values, or analysis population. It also lists 33 outcome measures but posts no secondary results. Without those details, it is not possible to determine whether the primary comparison was selected in advance as reported, how other outcomes were analyzed, or whether additional analyses took place.

Planning calculations based on the observed effect are separate from the trial’s original design assumptions. The registry record’s planning assumptions specify a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The assumed effect to detect is expressed as a fraction of the observed effect. These are planning illustrations, not evidence about the study’s actual design or analysis. The trial’s own sample-size justification and original design assumptions are not reported in the registry record.

10. Confidence Intervals and Precision

The point estimate for the mean difference is -13.0 units, and the 95% confidence interval extends from -18.52 to -7.484. This interval communicates uncertainty about the average contrast under the model used for the reported comparison. Because the entire interval is below zero, the posted result is compatible with a lower mean rating for Omafilcon A than for Enfilcon A. It does not give a range for individual participants’ ratings, and it does not establish the practical importance of any value in the interval.

Precision is also informed by the variability in the ratings. The standard deviation is 8.2 for Enfilcon A and 20.2 for Omafilcon A, so responses were more dispersed in the Omafilcon A group. The reported sample size for each lens rating is 60. These figures help contextualize the estimate, but the registry record does not state whether the uncertainty calculation accounted for the paired-eye structure described in the arm descriptions.

In general, confidence intervals rely on the analysis model and its assumptions. Their width reflects statistical uncertainty as modeled; it does not incorporate every possible source of uncertainty, such as missing outcomes, measurement limitations, or design ambiguities. The record does not report details needed to assess those issues fully. The confidence interval and p-value should therefore be interpreted as the posted statistical comparison, rather than as a complete measure of all uncertainty around the study’s findings.

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 planning values are participants per arm, not total events. They illustrate sample sizes for detecting specified fractions of the observed effect under the stated planning assumptions. For planning for 100% of the observed effect, the figures are 23 participants per arm for 80% power and 30 participants per arm for 90% power. For planning for 75% of the observed effect, they are 40 participants per arm for 80% power and 53 participants per arm for 90% power. For planning for 50% of the observed effect, they are 89 participants per arm for 80% power and 119 participants per arm for 90% power.

In plain terms, the 80% power column gives the estimated number of participants per arm for a design intended to have an 80% chance of detecting the specified effect if that effect is real and the planning assumptions hold. The 90% power column describes the corresponding planning target for a 90% chance. The calculations use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each target effect is the stated fraction of the observed effect.

Smaller effects require more participants under these assumptions, as the planning figures illustrate. These are planning illustrations derived from the observed effect, not the trial’s own design justification, which is not reported in the registry record. This is not observed power.

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 = -13.000; pooled standard deviation σ = 15.416.
2. n = 2 × (1.96 + 0.842)² × 15.416² / -13.000² = 22.1, rounded up to 23 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 <- -13                      # observed difference in means
sigma <- 15.4155765380345                     # 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(2131402)
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 = 23 (80% power), 30 (90% power)
 75% of observed effect: n per arm = 40 (80% power), 53 (90% power)
 50% of observed effect: n per arm = 89 (80% power), 119 (90% power)
power.t.test: 23.1 
Simulated power at n = 23 per arm: 0.797 (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 33 outcome measures, while the posted primary result concerns lens handling for Enfilcon A and Omafilcon A. No secondary results are posted, and the record lists zero analyses. This does not establish that no other analyses were conducted; it describes what is available in the registry record.

When multiple outcomes or comparisons are tested, the chance of obtaining at least one apparently unusual result can increase. In general, multiplicity methods are used to control or describe that issue. The posted p-value is unadjusted. Whether a multiplicity strategy was specified, whether other comparisons were included in a family of tests, or how outcome selection was handled is not reported in the registry record. Accordingly, the p-value should be read as an unadjusted result for the stated comparison, not as evidence that all possible testing has been accounted for.

The registry record also does not report missing-data counts, reasons for missingness, imputation methods, or sensitivity analyses. It does not identify the analysis population, such as whether results used all randomized participants or a defined subset. The listed n=60 for each lens rating gives the reported group sample sizes but does not resolve whether every randomized participant contributed a usable endpoint or how any missing rating was treated.

The study descriptions also raise an analysis question: the registry classifies the design as parallel, while its arm descriptions describe paired lenses worn in opposite eyes and successive pairs. In general, paired outcomes may be correlated within a participant, and analyses can account for this dependence. The statistical model and its treatment of that structure are not reported in the registry record. These omissions prevent a complete assessment of multiplicity, missingness, and the analysis population, and they should be kept in mind when interpreting the posted estimate.

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 entries list 60 at risk and zero affected for each of the three described pairings: Enfilcon A / Omafilcon A, Enfilcon A / Ocufilcon D, and Enfilcon A / Methafilcon A. The other adverse event entries likewise list 60 at risk and zero affected for each pairing. These are the registry’s recorded counts for the displayed safety categories.

A zero count in a registry entry means that no affected participants are recorded for that category in that group; it does not prove that an event is impossible or establish safety beyond the observation and reporting represented in the record. The record does not provide further detail on event collection, follow-up, or how adverse events were assessed. Death counts are not reported in the registry record. No serious adverse event terms are listed. These entries should be read as reported safety information, not as a comprehensive account of all possible harms or as a treatment recommendation.

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

The posted primary result describes average subjective handling ratings at lens removal after 1 hour of wear for the first pair. Enfilcon A has a mean rating of 97.0, and Omafilcon A has a mean rating of 84.0, on a scale where higher values indicate easier handling. The estimated mean difference for Omafilcon A relative to Enfilcon A is -13.0 units, with a 95% confidence interval from -18.52 to -7.484 and an unadjusted p-value of <0.001.

Those statistics characterize the reported group averages and the uncertainty calculated for that comparison. They do not say that every participant rated Enfilcon A more favorably, and the group standard deviations show that individual ratings varied. The result concerns one subjective endpoint at a specified short-term assessment point. It does not answer every question included in the study aim, such as comfort, fitting characteristics, visual acuity, or the other lens pair comparisons, because those results are not posted.

The record also does not report a threshold for a difference that participants or clinicians would regard as important. Statistical evidence of a difference and practical importance are distinct questions. Nor does the record establish durability over longer use, results in populations beyond the enrolled study participants, or the reason for the rating contrast.

Important interpretive details remain unavailable, including the handling of the paired-eye design in the statistical analysis, missing-data methods, analysis populations, and any multiplicity plan. The result should therefore be read as the registry’s reported comparison with the stated limitations, not as a complete evaluation of lens performance or a basis for medical advice.

16. Why This Trial Matters Statistically

This trial illustrates why a numerical outcome needs to be interpreted in relation to what was measured. A handling questionnaire captures a participant-reported experience, whereas fitting characteristics and visual acuity are different outcomes. The posted primary result addresses only the handling rating for the specified lens comparison and assessment time. Keeping that endpoint distinct prevents an average rating from being treated as a summary of every aspect of clinical performance.

The record also illustrates the value of reporting both group summaries and a contrast with uncertainty. The means give the average ratings, the standard deviations describe variation, and the confidence interval conveys uncertainty around the mean difference under the reported analysis. A p-value alone would not convey the magnitude or precision of the estimated contrast. Even with these statistics, interpretation depends on the design and analysis being aligned.

Here, the registry’s parallel classification appears alongside arm descriptions involving paired lenses in opposite eyes and repeated pairs. That makes the unreported statistical handling of within-participant dependence particularly relevant. The record also lists many outcome measures while posting no secondary results, making transparency about endpoint selection and multiplicity important for a complete interpretation.

Finally, planning illustrations based on an observed effect can help readers understand how assumptions about effect size and target power relate to sample-size requirements. They cannot substitute for the study’s original design rationale. The registry record does not report that rationale. Together, these issues show why estimates, uncertainty, design details, and reporting completeness all matter in clinical-trial statistics.

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 record leaves several trial-specific limitations unresolved. It lists myopia as the condition but does not report participant age, detailed eligibility criteria, baseline characteristics, or the representativeness of the enrolled population. The recorded enrollment is 60, but the record does not provide a sample-size justification or the trial’s original design assumptions.

Although the design is classified as randomized, double-masked, and parallel, the arm descriptions state that participants wear a test lens in one eye and a control lens in the other, then change lens pairs after approximately 1 hour. The record does not explain how these procedures correspond to the parallel-model designation or how the paired-eye observations were analyzed. Details of randomization and masking procedures are also not reported in the registry record.

The primary result is limited to a subjective handling questionnaire at lens removal for the first pair after the stated wear period. Questionnaire validation, the interpretation of the scale, a threshold for meaningful difference, and results for the other named outcomes are not reported. The registry lists 33 outcome measures but posts no secondary results.

Further limitations include unreported missing-data handling, analysis populations, statistical model details, and multiplicity procedures. Safety entries report zero affected participants for serious and other adverse event categories, but the record does not describe event ascertainment or follow-up in detail. Death counts are not reported in the registry record. These reporting gaps constrain assessment of the result’s generalizability, robustness, and completeness.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Clinical Performance of Hydrogel vs. Silicone Hydrogel Contact Lenses — NCT02131402.
• Registry record last updated 2017-04-04; status last verified 2017-03.
• Results first posted 2016-07-22.
• 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 study of contact lens performance in myopia, with an enrollment of 60. It is titled a non-dispensing fitting study comparing hydrogel and silicone hydrogel sphere-design contact lenses. The arm descriptions involve Enfilcon A paired with Omafilcon A, Ocufilcon D, or Methafilcon A.

The posted primary endpoint is a subjective lens-handling rating after 1 hour of wear at removal of the first pair. For Enfilcon A and Omafilcon A, the means are 97.0 and 84.0, respectively. The mean difference for Omafilcon A relative to Enfilcon A is -13.0, with a 95% confidence interval from -18.52 to -7.484 and an unadjusted p-value of <0.001. No secondary results are posted.

The registry lists zero affected participants in the serious and other adverse event categories for each described pairing; death counts are not reported in the registry record. Analysis details, missing-data methods, and the trial’s original sample-size rationale are not reported.