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 A Prospective, Multi-Center Evaluation of Corneal Flap Creation Using Cheetah Femtosecond Laser System and Cheetah Patient Interface (NCT03789669), a randomized na study. The primary outcome is Stromal Bed Surface Quality.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03789669 |
| Phase | NA |
| Condition | Refractive Error |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 200 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Johnson & Johnson Surgical Vision, Inc. |
| Results posted | Yes |
2. Clinical Question
Population
The study concerns people with refractive error undergoing LASIK flap creation. The registry describes both eyes of each subject as treated in the bilateral design. It also records 3 unilateral subjects, who were excluded from the primary endpoint analysis because that evaluation required both eyes to be treated. The record does not report further eligibility details in the registry record for this analysis.
Intervention
The intervention is the Cheetah femtosecond laser system with a Cheetah patient interface. The registry describes evaluating flap quality and optimizing Cheetah settings. Its arm descriptions mention different Cheetah laser and patient-interface configurations, so the exact configuration represented by each arm is not consistently clear in the record.
Comparator
The listed commercial comparator is the IntraLase iFS femtosecond laser and patient interface. The primary endpoint description grades stromal-bed surface quality relative to an IntraLase iFS flap. However, the registry’s arm descriptions include conflicting descriptions of which Cheetah component was used in each eye, so the detailed device contrast cannot be resolved from the record.
Primary question
The primary question is how many participants in the bilateral group met the stated stromal-bed surface-quality threshold of 3 or higher on a scale of 1-5. The registry reports 175 for this outcome among 197 bilateral participants. The endpoint description calls the result a number of participants, while its unit is listed as eyes; that distinction should be kept in mind when interpreting the count.
3. Trial Design
The registry identifies NCT03789669 as a prospective, randomized, open-label comparative device study. It records the design model as parallel and masking as none. The trial is marked completed, with enrollment of 200. The recorded condition is refractive error, and the stated purpose is to evaluate flap quality and optimize Cheetah settings.
The intervention list names the IntraLase iFS femtosecond laser and patient interface and the Cheetah femtosecond laser with Cheetah patient interface. The arm descriptions say that both eyes of each subject would be treated, with a device used on each eye. This suggests a within-participant contrast in the described procedure, but it does not align neatly with the registry’s parallel-model classification. In addition, the two arm descriptions do not give a consistent account of which Cheetah laser and patient-interface configuration was assigned to each eye. The exact allocation procedure and the intended analysis of any within-participant comparison are not reported in the registry record.
The primary endpoint evaluation required both eyes to be treated. The record states that 3 unilaterally treated subjects were excluded from that evaluation. The posted primary outcome has a bilateral group of 197 and a unilateral group with no analyzable primary endpoint. This makes the bilateral group the relevant group for reading the reported primary result; the unilateral row should not be read as evidence of an unsuccessful outcome.
The study started on 2018-12-19, reached primary completion on 2023-03-31, and is marked completed. The registry records the phase as NA, which is consistent with the listing being a device evaluation rather than a drug-phase study. Details such as site count, enrollment targets by group, the recruitment process, and any protocol amendments 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: A total of 200 subjects were enrolled in the study. 45 subjects were consented but not treated in the study. 3 subjects were one-eye treated with ELITA; and 197 subjects were treated bilateral (one eye treated with ELITA, one eye treated with controlled system iFS). 3 unilaterally treated subjects were excluded from the analysis. A score of 4 or 5: study eye was better than the control eye. A score of 3: equal performance. A score of 1 or 2: study eye was worse than the control eye.
Overall Study
| Stage | Unilateral | Bilateral |
|---|---|---|
| STARTED | 3 | 197 |
| COMPLETED | 0 | 197 |
| NOT COMPLETED | 3 | 0 |
Analysis population for the primary outcome, as defined in the registry: 3 unilaterally treated subjects were excluded from the analysis. There is only one arm analyzed for primary outcome measure. The primary endpoint evaluations require both eyes to be treated.
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: 3 unilaterally treated subjects were excluded in analysis as they were not applicable.
| Characteristic | Unit | Unilateral | Bilateral | Total |
|---|---|---|---|---|
| Participants analysed | 3 | 197 | 200 | |
| Age, Customized: >=50 years old | Participants | 0 | 0 | 0 |
| Age, Customized: 40-49 years old | Participants | 0 | 3 | 3 |
| Age, Customized: 30-39 years old | Participants | 1 | 53 | 54 |
| Age, Customized: <30 years old | Participants | 2 | 141 | 143 |
| Sex: Female, Male: Female | Participants | 2 | 95 | 97 |
| Sex: Female, Male: Male | Participants | 1 | 102 | 103 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 0 | 0 | 0 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 3 | 197 | 200 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 3 | 197 | 200 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): White | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
6. Primary Endpoint
The registry lists the primary outcome as Stromal Bed Surface Quality, measured over At the Operative visit, one time visit.
| Element | Registry entry |
|---|---|
| Result type | Count Of Units |
| Measure of spread | not applicable |
| Unit | Eyes |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is stromal-bed surface quality at the operative visit, described as a one-time visit. The surface is graded on a scale of 1-5 relative to an IntraLase iFS flap, and the posted outcome is the number of participants with a score of 3 or higher. The recorded result for the bilateral group is 175 among 197 participants. The registry also gives the unit as eyes, although the endpoint description says number of participants. The record does not clarify this difference in wording.
A threshold-based endpoint turns a graded assessment into a count: the count includes observations meeting the stated cutoff, rather than preserving every score across the scale. This can make a clinical or procedural criterion easier to report, but it removes information about how far scores lie above or below the threshold. A count alone also does not show the distribution of scores, the consistency of grading between assessors, or the magnitude of any difference between devices.
The endpoint is relevant to the stated aim of evaluating the quality of a surgically created flap surface. It is a procedural quality measure, not a direct measure of refractive outcome, vision, or long-term patient experience. The registry does not report additional details about the grading procedure, assessor training, assessor independence, or validation of the scale. Those details matter when interpreting a subjective or ordinal rating, particularly in an open-label study.
Because the primary evaluation required both eyes to be treated, 3 unilateral subjects were excluded. The posted count should therefore be read in the context of the bilateral group, rather than as a result for all 200 enrolled participants. The record does not provide a more detailed account of the excluded subjects or any sensitivity analysis including them.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry reports that 175 participants in the bilateral group met the primary surface-quality threshold, with 197 participants in that group. This is a descriptive count for the endpoint as recorded. It does not by itself provide an estimate of the difference between Cheetah and iFS, nor does it establish how the outcome was distributed between the two eyes or between device assignments.
That limitation matters because the endpoint is described in relation to an iFS flap, while the record also describes both eyes of each participant being treated with different devices. A comparative result would ordinarily need to specify which eye or device contributed each score, how paired observations were handled, and what comparison estimate was prespecified. Those details and an analysis of the comparative effect are not reported in the registry record. The registry lists no analyses, and it does not post a secondary outcome result in the registry record for this analysis.
The reported count is not accompanied by an uncertainty interval, a test statistic, or a p-value. Consequently, the precision of the result cannot be assessed from the count alone. A confidence interval, in general, describes the range of values compatible with the observed data under a stated statistical model. Without such an interval, readers cannot distinguish a relatively precise estimate from one with substantial sampling uncertainty. No interval should be inferred from the count in the absence of a reported analysis.
The endpoint’s unit is listed as eyes, whereas the description frames the threshold result as a number of participants. This ambiguity affects what the denominator and count mean. The registry’s bilateral group contains 197 participants and its primary value is 175, but the record does not clarify whether the outcome count is participant-based or eye-based in the final analysis. The safest reading is to report the posted result and retain the registry’s wording, rather than convert it into a rate or assume a particular eye-level denominator.
The result is also conditioned on bilateral treatment. The 3 unilateral subjects were excluded because the endpoint evaluation required both eyes to be treated. This exclusion is explained in the registry, but the record does not report whether those subjects differed from the bilateral group or whether their exclusion could affect interpretation. The outcome should not be generalized automatically to the unilateral group.
These points do not negate the descriptive information. They define what can be concluded from it: the registry posts a threshold count for the bilateral group, but does not report enough statistical detail to establish the size, precision, or statistical significance of a device contrast. The record’s randomized designation does not fill that gap. Randomization describes assignment, not the analysis or the uncertainty around an outcome.
9. Statistical Methods Explained
General: statistical methods connect the observed data to a clearly defined question. A useful report identifies the unit being analyzed, the comparison being estimated, the analysis population, and the method used to quantify uncertainty. The registry record supplies a primary outcome count, but does not report an analysis method or a comparative estimate. The interpretation therefore remains descriptive.
What does a threshold count show?
General: when a graded measure is summarized as the number meeting a cutoff, the result answers a specific classification question: how many observations reached or exceeded that cutoff? It does not show the full pattern of underlying scores. Two sets of scores can have the same threshold count but different distributions among observations below or above the cutoff. The posted surface-quality outcome uses a score threshold of 3 or higher on a scale of 1-5. The registry reports 175 for the bilateral group of 197, but it does not post the underlying score distribution.
The distinction between an observation and a participant is important. Each subject had both eyes treated according to the arm descriptions, and the endpoint unit is recorded as eyes. Yet the outcome description says number of participants. If two eyes from one participant contribute data, the observations may be statistically related: they share features of the same person and procedure. General: treating related eyes as if they were independent can make uncertainty estimates too narrow. A paired or clustered analysis can account for within-participant dependence, but the registry record does not report whether such an approach was used.
What would a device comparison require?
General: a comparison needs a defined outcome for each treatment condition and a method that matches the design. If each participant receives both devices, the analysis can use the within-participant pairing, provided the outcome is measured and assigned to each eye in a consistent way. If participants are assigned to separate parallel groups, the analysis instead compares outcomes across groups. The registry labels the study randomized and parallel, while its descriptions say both eyes are treated and refer to different devices by eye. Because those descriptions are not fully consistent, the actual unit of randomization and the intended comparison cannot be established from the registry record.
The record does not state whether the primary analysis used a paired method, a model accounting for two eyes per participant, an unpaired comparison, or another procedure. It also does not specify covariate adjustment, handling of ties in the ordinal scale, or whether the threshold count was the only analysis of the score. These are not details that can be reconstructed from the outcome count. General: analysis choices should follow the design and be prespecified, rather than selected after looking at the observed results.
How should uncertainty be understood?
General: a point estimate, such as a count or proportion, describes the observed data; an interval estimate expresses uncertainty about the value that might be expected in a broader population under a stated model. A hypothesis test addresses a different question and depends on a specified null hypothesis and testing procedure. Neither an interval nor a test can be recovered reliably from an isolated count when the outcome unit, design structure, and analysis population are unclear.
No confidence interval, standard error, p-value, or test result is reported for the primary endpoint in the registry entries. The record also lists no analyses. Therefore, it is not possible to assess whether the observed result is statistically compatible with a range of comparative effects or whether a prespecified threshold for statistical evidence was met. The absence of reported inferential statistics is not evidence of no difference; it means that the registry record does not provide that inferential result.
What does the planning information mean?
General: a sample-size calculation is a planning exercise based on assumptions about the effect to detect, variability, significance level, allocation, and analysis method. It is not a measure of the probability that a completed study has found a true effect. The registry’s planning description refers to a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect defined as a stated fraction of an observed effect. These are described as planning assumptions, not as the trial’s own design justification. The record does not report the study’s sample-size rationale or a protocol-based justification for its enrollment.
Planning illustrations derived from an observed effect are conditional on that observed effect and the calculation assumptions. They should not be described as observed power or treated as proof that an analysis is conclusive. The registry entries do not identify a specific planning result to interpret, so no required sample size can be stated for this trial. The record also does not report whether any interim analyses were planned or performed.
General: over-dispersion matters when a count varies more than a simple model assumes. In such settings, a model that understates variability can produce overly narrow intervals and overly optimistic tests. The endpoint is a threshold count, but the registry record does not report a count model, a dispersion assessment, or an inferential analysis. It would be inappropriate to assume that over-dispersion was present or that any particular correction was used.
Overall, the available statistical information supports a precise description of the posted count and its recorded group, but not a reconstruction of the comparative analysis. The randomization label, device descriptions, and count do not identify the model, handling of paired eyes, or uncertainty calculation. Those elements are necessary for a complete statistical interpretation and are not reported in the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry entries available for this analysis list one primary outcome measure and no secondary outcome results. They also list no analyses. The record does not report whether the study tested multiple versions of the surface-quality endpoint, made interim comparisons, or used a multiplicity adjustment. Without an analysis plan, it is not possible to determine which statistical tests were planned or how any family of tests was defined.
General: multiplicity arises when several hypotheses or outcomes are evaluated. Repeated testing can increase the chance of a seemingly notable result arising by chance, so protocols may define a primary endpoint, testing order, or adjustment method. This is a general consideration, not a statement that multiple testing occurred in this study. The registry record does not report a statistical plan or interim-analysis details.
The primary endpoint description explains that 3 unilateral subjects were excluded because both eyes were required for the evaluation. The bilateral group contains 197 participants. The record does not report additional exclusions, missing endpoint values within the bilateral group, reasons for any missing measurements, or an imputation procedure. It also does not state whether every randomized participant was included in an intention-to-treat analysis or whether the primary evaluation used another analysis population.
General: missing data can affect interpretation when the probability of missingness is related to treatment or outcome. A complete-case analysis, imputation, or sensitivity analysis may address different assumptions, but no approach can be attributed to this study without a report. The stated exclusion of unilateral participants is a design-related eligibility condition for the primary evaluation, not enough information to infer how other missing data were handled.
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 |
|---|---|---|---|
| Unilateral | 0 | 3 | 0.0% |
| Bilateral | 0 | 197 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Unilateral | 0 of 3 |
| Bilateral | 0 of 197 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0.15% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Unilateral | 3 of 3 |
| Bilateral | 2 of 197 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Unilateral | Bilateral |
|---|---|---|---|
| Other | Surgical and medical procedures | 2 of 3 | 1 of 197 |
| Miscreated Flap | Surgical and medical procedures | 1 of 3 | 0 of 197 |
| Epithelium in the interface with a loss of 2 or more lines of BSCVA (>10 ETDRS letters) | Surgical and medical procedures | 0 of 3 | 1 of 197 |
The registry reports serious adverse event figures separately for unilateral and bilateral groups. In the unilateral group, 3 were at risk of serious adverse events and 0 were affected; 3 were at risk of other adverse events and 3 were affected. In the bilateral group, 197 were at risk of serious adverse events and 0 were affected; 197 were at risk of other adverse events and 2 were affected. Deaths are recorded as 0 in both groups. No serious adverse event terms are listed.
These are registry counts, not a comparative safety analysis. The groups differ in size and treatment context, and the record does not report a statistical comparison, event timing, severity grading for the other adverse events, or a detailed account of event types. The count of participants affected does not reveal how many separate events occurred if a participant could have had more than one event. The registry also does not report the relationship of events to a device in the registry record for this analysis.
Zero affected participants for serious adverse events means that the registry posts no serious adverse events in either group; it does not establish that the risk is absent. General: when no events are observed, uncertainty remains about the frequency that could occur in a wider population. The adverse-event counts should therefore be read as the observed registry record, not as proof of safety or as evidence for a device comparison.
12. What the Result Does, and Does Not, Mean
The primary result gives a count of participants recorded as meeting a specified stromal-bed surface-quality threshold in the bilateral group. It is useful as a description of the posted endpoint, and it reflects the study’s focus on flap creation quality. The registry reports 175 for the outcome among 197 bilateral participants. The result is tied to the endpoint definition and the eligible bilateral group.
It does not, by itself, quantify a difference between the Cheetah system and the commercial iFS system. The record does not post a comparative estimate, uncertainty interval, or statistical test. It also does not explain how scores from the two eyes were combined or whether eye-level results were analyzed in a way that accounts for their relationship within a participant. The randomized designation cannot substitute for these missing analysis details.
The count is not a complete account of surface-quality scores. The threshold approach groups scores according to whether they meet the stated cutoff and does not disclose the distribution across the full scale. The unit wording is also ambiguous: the endpoint description refers to participants, while the unit is listed as eyes. That ambiguity limits how confidently the count can be interpreted beyond its registry wording.
The result is not a measure of visual acuity, refractive correction, long-term outcomes, or patient-reported experience. Those outcomes are not reported in the registry record for this analysis. Nor does the result establish how the devices perform in populations or circumstances outside the study’s recorded design. Details about eligibility, follow-up beyond the operative visit, and the analysis population are not reported in the registry record.
The appropriate conclusion is narrow: the completed study has a posted threshold count for its bilateral group, alongside limited information about the comparison and statistical analysis. The result can be described, but the registry record does not support a conclusion about the size or precision of a treatment contrast. Absence of a reported comparative analysis should not be mistaken for evidence of equivalence or of no difference.
13. Why This Trial Matters Statistically
This study raises an important statistical issue for device evaluations in which both eyes of a participant may receive different procedures. The design description determines whether the natural comparison is between participants or within participants. When eyes from the same person are both included, they are generally not independent observations. The analysis needs to reflect the unit of assignment and the relationship between eyes, or uncertainty may be misrepresented. The registry’s parallel-model label and bilateral, eye-specific descriptions make the design details especially important to clarify.
The endpoint also illustrates the interpretive cost of thresholding an ordinal score. A count above a cutoff can be easy to communicate, but it conceals the full score distribution and depends on the choice and application of the threshold. In a procedural evaluation, the grading process and the agreement of assessors are relevant to understanding the reliability of the observed count. Those details are not reported in the registry record.
Finally, a randomized designation alone is not a complete statistical account. Readers also need to know which participants and eyes entered the primary analysis, how the comparison was performed, and how uncertainty was quantified. The posted result is descriptive, but the record does not report a comparative effect estimate or inferential analysis. These distinctions matter when evaluating what a completed trial can establish from its registry results.
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.
Several limitations are specific to the information recorded for this trial. The registry describes a randomized, parallel study, but its arm descriptions state that both eyes of each participant were treated and assign devices by eye. The two arm descriptions are also inconsistent about the Cheetah laser and patient-interface configuration. As a result, the exact device contrast and allocation structure cannot be resolved from the registry record.
The primary endpoint is described as a count of participants, while its unit is listed as eyes. The record does not clarify whether each participant or each eye contributed to the posted result, or how the two-eye data were handled. It also does not report the distribution of the 1-5 surface-quality scores, grading reliability, assessor procedures, or comparative estimates with uncertainty.
The record states that 3 unilateral subjects were excluded from the primary evaluation because both eyes were required. It does not report further details on missing endpoint data, other exclusions, or sensitivity analyses. The registry lists no analyses and does not report the statistical analysis plan, sample-size justification, or interim-analysis procedures. These omissions limit evaluation of the result’s precision, robustness, and relationship to any prespecified analysis.
The study is open-label, with masking recorded as none. The registry does not report whether outcome assessors were masked or how the potentially subjective grading process was standardized. The primary endpoint is measured at the operative visit; longer-term outcomes are not reported in the registry record for this analysis. These limitations concern what can be established from the registry record and should not be filled in by assumption.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Prospective, Multi-Center Evaluation of Corneal Flap Creation Using Cheetah Femtosecond Laser System and Cheetah Patient Interface — NCT03789669.
- Registry record last updated 2025-05-31; status last verified 2025-05.
- Results first posted 2025-05-31.
- 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.
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18. Record Summary
NCT03789669 is a completed prospective, randomized, open-label comparative device study of corneal flap creation in refractive error. The registry lists an enrollment of 200, a parallel model, and no masking. The interventions are the Cheetah femtosecond laser system with a Cheetah patient interface and the IntraLase iFS femtosecond laser and patient interface.
The primary endpoint is stromal-bed surface quality at the operative visit, using a 1-5 scale relative to an iFS flap and reporting the count meeting a score of 3 or higher. The registry posts 175 for the bilateral group of 197. It states that 3 unilateral subjects were excluded from the primary evaluation. The endpoint’s participant-versus-eye unit wording is unclear.
The record reports no serious adverse events in either group and records other adverse events in both groups. It does not report a comparative effect estimate, uncertainty interval, p-value, or analysis method. The conflicting descriptions of the treatment configuration, design, and analysis population limit further interpretation.