This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Comparative Performance of PureVision, Acuvue Oasys and O2Optix (NCT00640341), a randomized phase 4 study. The primary outcome is Any Slit Lamp Finding > Grade 2.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00640341 |
| Phase | Phase 4 |
| Condition | Myopia |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 510 |
| Arms in the primary outcome | 3 |
| Lead sponsor | Bausch & Lomb Incorporated |
| Results posted | Yes |
2. Clinical Question
Population
People with myopia were enrolled. The registry lists 510 participants and identifies the primary-outcome population as all dispensed eyes. The reported outcome is measured in eyes, so the participant enrollment and eye-level outcome counts describe different units.
Intervention
One group received the PureVision contact lens for daily wear. The registry identifies this as a device intervention.
Comparator
Two other groups received Acuvue Oasys or O2Optix contact lenses, also for daily wear. The study used a randomized, parallel design with three lens groups.
Primary question
Across follow-up visits during the one-month study period, how many dispensed eyes in each group had any slit-lamp finding greater than grade 2? The posted counts are 2.0 for PureVision, 5.0 for Acuvue Oasys and 10.0 for O2Optix. The registry record does not post a formal statistical comparison of these counts.
3. Trial Design
The registry record describes a randomized, single-masked, parallel-group phase 4 study of three contact lenses: PureVision, Acuvue Oasys and O2Optix. The study objective was to evaluate lens performance during daily wear. The listed condition is myopia, and the enrollment is 510 participants. The sponsor is Bausch & Lomb Incorporated.
The study began in 2008-02, and primary completion was recorded in 2008-04. Its status is completed. The primary endpoint timeframe is all follow-up visits over the one-month study period. Three outcome measures are listed, but no secondary outcome results are posted in the registry record.
Randomization supports a planned comparison of the assigned groups, while the parallel design means the groups are listed as separate study arms. The record does not identify who was masked, how the randomization sequence was generated, whether allocation was concealed, or the intended allocation ratio. The posted arm counts for the primary outcome are 162.0 for PureVision, 169.0 for Acuvue Oasys and 168.0 for O2Optix. These are reported as eye counts, consistent with the outcome unit; they should not be read as participant counts.
The registry record does not report the study's detailed protocol, a sample-size justification, or a prespecified statistical analysis plan. Nor does it give the reasons for selecting the one-month timeframe or describe procedures for fitting, replacing or discontinuing lenses. These details cannot be inferred from the design labels alone.
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: 510 subjects (1020 eyes) were enrolled (all were dispensed). 477 subjects (954 eyes) completed the study. 10 subjects were ineligible at baseline and 23 were discontinued during the study.
Overall Study
| Stage | PureVision | Acuvue Oasys | O2Optix |
|---|---|---|---|
| STARTED | 170 | 170 | 170 |
| Eligible Participants at Baseline | 165 | 167 | 168 |
| COMPLETED | 149 | 165 | 163 |
| NOT COMPLETED | 21 | 5 | 7 |
Reasons for not completing this period:
| Reason | PureVision | Acuvue Oasys | O2Optix |
|---|---|---|---|
| Adverse Event | 0 | 0 | 1 |
| Positive Slit Lamp Findings | 0 | 0 | 1 |
| Study Related Symptoms/Complaints | 2 | 1 | 2 |
| Inability to Maintain Wearing Schedule | 1 | 1 | 0 |
| Failure to Follow Subject Instructions | 1 | 0 | 0 |
| Lost to Follow-up | 2 | 0 | 0 |
| Withdrawal by Subject | 4 | 0 | 1 |
| Unacceptable Lens Movement | 1 | 0 | 0 |
| Poor fit/Uncomfortable | 4 | 0 | 0 |
| Ineligable at Baseline | 5 | 3 | 2 |
| Adverse event and positive slit lamp | 1 | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: All dispensed eyes
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.
| Characteristic | Unit | PureVision | Acuvue Oasys | O2Optix | Total |
|---|---|---|---|---|---|
| Participants analysed | 165 | 167 | 168 | 500 | |
| Age, Customized: Age 18 to 65 years | Participants | 165 | 167 | 168 | 500 |
| Sex: Female, Male: Female | Participants | 125 | 127 | 124 | 376 |
| Sex: Female, Male: Male | Participants | 40 | 40 | 44 | 124 |
| Region of Enrollment: United States | Participants | 165 | 167 | 168 | 500 |
6. Primary Endpoint
The registry lists the primary outcome as Any Slit Lamp Finding > Grade 2, measured over Over all follow-up visits for the 1 month study period.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | Eyes |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is titled “Any Slit Lamp Finding > Grade 2.” It counts eyes with any finding above grade 2 over all follow-up visits during the one-month study period. The record states that all dispensed eyes are included in the outcome population, and the unit is eyes. The grading scale runs from 0 to 4, with 0 defined as no findings and 4 as severe findings.
The listed findings include epithelial edema, epithelial microcysts, corneal staining, limbal and bulbar injection, conjunctival abnormalities, corneal neovascularization and infiltrates. The endpoint therefore records whether an eye had a qualifying finding, rather than reporting a separate count for each finding or a continuous average grade.
In general, a threshold-based endpoint can make a particular level of finding easier to summarize across groups. It also compresses information: eyes with different findings or grades above the threshold may contribute alike to the count, while the endpoint does not describe lesser findings. The registry record does not explain why grade 2 was selected as the threshold or how repeated observations across visits were combined. Its reported group values are 2.0, 5.0 and 10.0 eyes for PureVision, Acuvue Oasys and O2Optix, respectively.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary-outcome values are 2.0 eyes for PureVision, 5.0 for Acuvue Oasys and 10.0 for O2Optix. Each value refers to eyes with any slit-lamp finding greater than grade 2 during follow-up, as defined by the registry. The arm counts listed alongside the outcome are 162.0, 169.0 and 168.0 eyes, respectively. These descriptive figures identify the observed counts; they do not by themselves establish whether differences between groups are statistically distinguishable or clinically important.
No formal analysis entries are posted, and no p-values, confidence intervals, adjusted estimates or pairwise comparison results appear in the registry record. Consequently, the precision of each count and the uncertainty around differences between lenses cannot be assessed from the posted endpoint results. The values should not be treated as evidence of a statistically significant ranking.
The outcome is a count of eyes meeting a threshold, not a rate per visit or a count of participants. The endpoint population is described as all dispensed eyes, while the safety records list 340 at-risk participants in each group. The registry does not explain the relationship between those different denominators. They should not be substituted for one another or used to reconstruct unreported rates.
The record reports a randomized design, but randomization does not eliminate the need to consider analysis details. For an eye-level outcome, the statistical method may need to account for two eyes belonging to the same participant if both eyes were included. The record does not say whether participants contributed one or both eyes, nor does it report a method for handling within-participant dependence. It also does not describe missing-outcome handling or the analysis population beyond “all dispensed eyes.”
In general, confidence intervals express the uncertainty around an estimated quantity, and a formal comparison helps distinguish the observed pattern from variation that could arise by chance. Neither is posted for this primary endpoint. The numerical pattern is therefore descriptive: the registry lists fewer qualifying eyes in the PureVision group than in the other two groups, but the record does not provide the inferential evidence needed to quantify how reliably the groups differ.
9. Statistical Methods Explained
What kind of outcome is this?
The primary outcome is a count: the number of eyes with any slit-lamp finding above a threshold. It is not a continuous measurement such as an average grade, and it is not a time-to-event outcome. The registry labels the outcome type as “count other,” indicating that the result is not reduced to one two-arm comparison. That matters because the study has three groups and a single reported count for each, rather than one result that captures every possible comparison.
In general, a count outcome can be analyzed by comparing group counts or by modeling counts with an appropriate distribution. The choice depends on details such as the observation period, how counts were generated, and whether variation is greater than a simple model expects. Here the endpoint is defined as whether an eye had any qualifying finding over follow-up, so the reported group value is an eye count, not a count of repeated findings. The registry does not post a statistical model or explain how visit-level observations were combined.
Why does the endpoint unit matter?
The unit is eyes. The registry separately reports enrollment in participants and the primary result in eyes. In general, measurements from two eyes of one person may be related rather than independent. If both eyes contributed, an analysis that treats every eye as unrelated could understate uncertainty. The registry does not report whether both eyes were included for any participant or whether an analysis accounted for possible within-person dependence, so the suitability of any particular model cannot be assessed.
The outcome population is identified as all dispensed eyes. That description does not, by itself, specify how missing observations, discontinued lens wear, or eyes without complete follow-up were handled. Those procedures are not reported in the registry record.
What do the posted results support?
The results support a descriptive statement about the recorded counts: 2.0 eyes in the PureVision group, 5.0 in the Acuvue Oasys group and 10.0 in the O2Optix group met the endpoint definition. The corresponding listed arm counts are 162.0, 169.0 and 168.0 eyes. The registry has no posted analysis entries for this outcome, and it gives no standard errors, confidence intervals, p-values or adjusted comparisons. It is therefore not possible to use the registry results to quantify sampling uncertainty or assess formal evidence for a difference.
In general, a confidence interval gives a range of values that are compatible with an estimate under the assumptions of the analysis. A p-value measures how unusual the observed data would be under a specified null model; it does not express the probability that the null hypothesis is true. Neither type of inferential result is posted for the primary endpoint. The counts alone should not be treated as a substitute for either.
What can a planning calculation mean?
In general, a sample-size calculation describes a hypothetical design intended to detect an effect under stated assumptions. A calculation that uses an effect observed in a completed trial is a planning illustration, not an estimate of the trial's observed power. It does not establish that the original trial was adequately sized, and it does not replace uncertainty estimates for the posted results. The registry record does not report the trial's own sample-size justification or a statistical plan from which its intended power or analysis choices could be evaluated.
For count outcomes, over-dispersion is a general concern when the observed variability exceeds what a simple count model assumes. A model that ignores over-dispersion may produce uncertainty estimates that are too small. Whether over-dispersion was assessed or relevant to the analysis cannot be determined because no model or analysis results are posted. Likewise, no adjustment method for the three-arm structure is reported. Without such information, the posted numbers remain outcome counts rather than estimates from a documented comparative model.
10. Multiplicity, Missing Data and Analysis Populations
The study has three lens groups, which creates more than one possible group comparison. The registry does not report which pairwise or overall comparisons were planned, whether one comparison was primary, or whether any multiplicity adjustment was intended. No analysis entries or comparison-specific results are posted. As a result, the record does not show how the risk of false-positive findings across multiple comparisons was addressed. The three outcome measures listed in the record are not accompanied by posted secondary outcome results.
The primary outcome population is described as all dispensed eyes. Beyond that statement, the registry does not report an intention-to-treat definition, a per-protocol population, or another analysis-population rule. The handling of missing endpoint observations, withdrawals, nonadherence or incomplete follow-up is not reported in the registry record. The record also does not state whether the endpoint was analyzed at the eye or participant level in a statistical model, although its unit and reported values are eyes.
In general, missing-data methods matter when the likelihood of an unobserved outcome could differ across people or groups. Excluding incomplete observations, imputing them, or using a model that accommodates incomplete data can lead to different estimates, depending on assumptions. No such method or assumption is described for this study, so the posted counts cannot be interpreted as adjusted for missingness.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| PureVision | 0 | 340 | 0.0% |
| Acuvue Oasys | 0 | 340 | 0.0% |
| O2Optix | 0 | 340 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| PureVision | 0 of 340 |
| Acuvue Oasys | 0 of 340 |
| O2Optix | 0 of 340 |
The registry lists 340 participants at risk in each of the three groups for serious adverse events. It reports 0 affected in the PureVision group, 0 in the Acuvue Oasys group and 0 in the O2Optix group. For other adverse events, the record also lists 340 at risk in each group and 0 affected in each group. These are the posted registry figures, not estimates adjusted for follow-up duration or other factors.
The record does not identify any serious adverse-event terms, and the death field has no posted value; deaths are therefore not reported in the registry record. A zero affected count means that the registry reports no affected participants in that category. It does not provide an estimate of how frequently events might occur outside the recorded study or establish that an event is impossible.
The safety denominators differ from the eye counts listed for the primary endpoint. The registry does not explain the relationship between these populations, so the safety figures should not be used as denominators for the eye-level outcome. The adverse-event reporting period and the detailed method for collecting or coding events are not reported in the registry record.
12. What the Result Does, and Does Not, Mean
The primary outcome offers a straightforward description of how many eyes in each group had at least one slit-lamp finding greater than grade 2 over the one-month study period. The record lists 2.0 eyes for PureVision, 5.0 for Acuvue Oasys and 10.0 for O2Optix. This is a numerical pattern in the posted counts, not a formal estimate of the relative effect of one lens compared with another.
The endpoint does not describe every aspect of lens performance. It combines several kinds of slit-lamp findings under one threshold, and it does not report separate results for each finding or the grades below the threshold. It also does not provide a measure of how frequently findings occurred at individual visits. The choice to focus on findings above grade 2 may be useful for a defined outcome, but the rationale for that cutoff is not reported.
The record does not include uncertainty intervals, statistical tests or adjusted comparisons for the primary endpoint. Accordingly, it cannot establish from the posted counts alone whether the observed group pattern is unlikely to reflect random variation. Nor does it provide information to determine whether any difference is practically important. No treatment recommendation follows from these registry figures.
The study's randomized, parallel design is relevant context, but the record lacks key analytical details, including the method for handling eyes within participants, missing data and multiple comparisons. The endpoint results should therefore be read as descriptive registry outcomes, with limitations in how precisely and comparatively they can be interpreted.
13. Why This Trial Matters Statistically
This study illustrates why the unit of analysis should be read alongside the outcome. Enrollment is reported in participants, while the primary endpoint counts eyes. Those are not interchangeable units, and an eye-level endpoint can raise questions about whether paired eyes from the same participant were included and how any dependence was handled. The registry does not answer those questions.
It also illustrates the distinction between a numerical ordering and a statistical comparison. The endpoint counts differ across the three lens groups, but no inferential analysis is posted. Without uncertainty estimates or a documented comparison, the numbers describe the recorded outcomes rather than the precision of a treatment contrast.
The outcome definition adds another useful statistical lesson: thresholding a graded measure creates a count of eyes meeting a criterion, while discarding detail about the specific finding and the degree above that criterion. That can make a measure easier to summarize, but interpretation depends on the threshold and on how observations across visits are combined. Those details are not fully described in the registry record.
Finally, three groups make multiplicity and comparison planning relevant. The record does not identify a planned contrast or a multiplicity strategy. These omissions limit what can be concluded from the posted results, even though randomization and a clearly named primary endpoint give useful information about the study's basic structure.
14. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The primary result is reported as a count of eyes, but the registry does not state whether each participant contributed one eye or more than one. It also does not report whether any statistical analysis accounted for possible correlation between eyes from the same participant. This leaves uncertainty about the appropriate analysis unit and the precision that a comparative analysis would produce.
The endpoint covers all follow-up visits over the one-month study period, yet the registry does not explain how observations across visits were combined or how repeated findings in the same eye were handled. The outcome includes several kinds of slit-lamp findings, but no separate counts by finding or grade are posted. The reason for selecting the greater-than-grade-2 threshold is not reported.
The registry gives no analysis entries for the primary endpoint, no confidence intervals or p-values, and no documented method for comparing the three groups. It also does not report missing-data procedures, adherence information, withdrawals, or a detailed analysis population beyond all dispensed eyes. The rationale for the sample size and the prespecified statistical plan are not reported in the registry record.
The record labels the trial single-masked but does not identify who was masked or describe the masking procedure. It also does not report allocation concealment or the randomization method. Safety figures use a denominator of 340 at risk in each group, distinct from the eye counts for the primary endpoint, and the relationship between those denominators is not explained. These omissions restrict interpretation of both comparative precision and the completeness of the reported outcome context.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Comparative Performance of PureVision, Acuvue Oasys and O2Optix — NCT00640341.
- Registry record last updated 2011-12-12; status last verified 2011-12.
- Results first posted 2011-03-31.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
NCT00640341 is a completed, randomized, single-masked, parallel-group phase 4 study of PureVision, Acuvue Oasys and O2Optix contact lenses for daily wear in people with myopia. Enrollment was 510 participants. The study began in 2008-02, with primary completion in 2008-04.
The primary endpoint counted eyes with any slit-lamp finding greater than grade 2 across follow-up visits during the one-month study period. The registry lists 2.0 eyes for PureVision, 5.0 for Acuvue Oasys and 10.0 for O2Optix. No formal analysis entries, inferential comparisons or secondary outcome results are posted. Serious and other adverse-event figures list 0 affected in each group; deaths are not reported in the registry record.