A Prospective, Contralateral, Eye to Eye Comparison of SMILE Surgery to LASIK Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Prospective, Contralateral, Eye to Eye Comparison of SMILE Surgery to LASIK Surgery (NCT03067077), a randomized na study. The primary outcome is Percentage of Participant Eyes With an Uncorrected Visual Acuity of 20/20 or Better.

2. Clinical Question

This is a within-participant clinical question because each participant is described as receiving both procedures, one in each eye. That structure can make the comparison informative by accounting for characteristics shared by the person, but it also means that outcomes from the two eyes of the same participant are related rather than independent. Statistical methods for a comparison should respect that pairing.

The registry records randomized allocation, but the method of randomization and whether assignment to a particular procedure was randomized by eye are not reported in the registry record. The precise clinical question is therefore clear at the level of treatments and outcome, while important details about assignment and the planned statistical comparison remain unreported.

3. Trial Design

The study is titled as a prospective contralateral, eye-to-eye comparison of SMILE surgery and LASIK surgery. Its official title describes a prospective, randomized comparison of SMILE surgery with wavefront-guided LASIK surgery. The brief summary says each subject undergoes SMILE in one eye and LASIK in the other to correct myopia. Thus, the treatment comparison is described as within-participant, with each person contributing an eye to each treatment group.

The registry records the allocation as randomized, masking as none, and the model as parallel. The parallel model label sits alongside a contralateral description in which each participant receives both procedures. The record does not explain how those classifications were reconciled or give details of sequence generation, allocation concealment, or assignment of procedures to eyes. The trial is marked completed. The sponsor is Stanford University, and the listed phase is NA.

Enrollment is reported as 44. The primary endpoint population is described as participants who completed 12 month follow-up, with 37 eyes reported in each treatment group. The primary endpoint timeframe is one year. The record does not explain why the endpoint population counts differ from enrollment or report reasons for incomplete follow-up.

The registry lists patient satisfaction and several other secondary outcomes, including visual acuity loss, aberrometry, corneal sensation, dry eye symptoms, astigmatism, anterior segment imaging, and predictability. The record does not report a protocol rationale for the enrollment target, a sample-size justification, details of any interim analyses, or a full statistical analysis plan. Those omissions limit what can be inferred about how the design and analysis were planned.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Participants who completed 12 month follow-up

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 Percentage of Participant Eyes With an Uncorrected Visual Acuity of 20/20 or Better, measured over One year.

The primary endpoint is the percentage of participant eyes with uncorrected visual acuity of 20/20 or better at one year. Visual acuity is assessed using an ETDRS testing lane, according to the endpoint description. The outcome concerns vision without correction and is recorded at the eye level, rather than as a single result for each participant. The stated population is participants who completed 12 month follow-up.

A threshold outcome such as 20/20 or better is used to describe the proportion of eyes reaching a specified visual-acuity level. It is easy to interpret as a clinical milestone, but it does not show how far above or below the threshold each eye’s result lies. Eyes with different acuity measurements can fall into the same category, and an eye just short of the threshold is grouped with eyes that are further from it.

General statistical context: reporting a percentage describes the observed frequency in the analyzed group. A comparison between treatments also needs to account for how the outcomes were collected and how precisely the percentages are estimated. Because the two eyes from each participant are linked by the contralateral design, the eye-level observations are paired. The registry reports group percentages but does not report a confidence interval or formal comparative analysis for the primary endpoint. Consequently, the reported values describe the posted groups but do not, by themselves, quantify the uncertainty in the treatment contrast.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a percentage describe?

A percentage for a threshold endpoint describes how much of the analyzed group met that threshold. In this study, the threshold is uncorrected visual acuity of 20/20 or better, and the unit is participant eyes. The reported percentages are 94.0% for SMILE and 83.0% for wavefront-guided LASIK. They summarize the observed results among the eyes included in the stated 12 month follow-up population. They do not describe every possible visual-acuity result, nor do they convey how close an individual eye was to the cutoff.

General statistical context: a percentage is an estimate of an underlying rate. Its precision depends on the amount and structure of the data, not just on the percentage itself. A confidence interval gives a range of values that are reasonably compatible with the data under a specified statistical model. It helps distinguish a precise estimate from one with substantial uncertainty. No confidence interval for the primary percentages or their comparison is reported in the registry record.

Why does the contralateral design matter?

Each participant is described as receiving SMILE in one eye and LASIK in the other. The outcomes are therefore paired: each SMILE eye has a corresponding LASIK eye from the same person. General statistical context: paired methods use the within-person relationship between outcomes. This can account for common factors shared by the two eyes and may provide a more appropriate estimate of treatment contrast than an analysis that treats each eye as unrelated to every other eye.

Randomized allocation is recorded, but the registry does not report the randomization procedure or specify how treatment assignment to eyes was implemented. It also does not report the method used for the primary analysis. The posted group percentages alone do not show whether the pairing was incorporated. Participant-level data or a reported paired estimate would be needed to assess that directly.

What can be concluded from the reported primary values?

The values describe the percentage meeting the threshold in each treatment group. A formal comparison would ordinarily estimate a contrast and its uncertainty, using a method appropriate to the paired design and endpoint. That analysis is not reported for the primary outcome. No primary confidence interval or p-value is given, so the precision of the contrast cannot be assessed from the registry results. The difference between the group percentages should not be recalculated from the posted values; the registry does not provide a primary comparative estimate.

General statistical context: a p-value addresses how compatible observed data are with a particular null model, given assumptions. It is not the probability that the null hypothesis is true, and it does not measure clinical importance. A confidence interval addresses estimation and precision, though it also depends on model assumptions. Neither kind of result can be inferred from two descriptive percentages alone.

How should planning illustrations be read?

The registry’s stated planning assumptions describe illustrations based on the observed effect, a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The effect to detect is defined as a stated fraction of the observed effect. Such calculations are planning illustrations, not observed power and not results from participants in this trial. They depend on assumptions about the effect and analysis that may not hold in a future study.

General statistical context: a sample-size calculation asks how much information a planned study would need to target a chosen level of precision or detection under specified assumptions. It does not show that the completed study had a particular probability of finding an effect, and it does not replace the analysis of observed outcomes. No sample-size justification for the trial’s original design is reported in the registry record.

What remains unclear about the analysis?

The registry does not report the primary analysis method, how missing endpoint data were handled, or whether the analysis population followed a prespecified rule. The endpoint is defined for participants who completed 12 month follow-up, but reasons for noncompletion and the handling of missing eye measurements are not reported in the registry record. These details matter because analyses limited to observed follow-up can be affected if missingness is related to outcomes or treatment.

The record does not report whether covariate adjustment was used, whether there were interim analyses, or what multiplicity procedure was planned. Those omissions do not invalidate the descriptive values, but they constrain interpretation of the study’s inferential evidence. The results should therefore be separated into what is explicitly reported—the group percentages and endpoint definition—and what is unavailable, including a paired treatment-effect estimate and its precision.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies a primary endpoint and lists multiple secondary outcomes. It does not report a statistical analysis plan describing how those outcomes were prioritized beyond the primary designation, whether secondary hypotheses were prespecified, or how multiplicity was handled. It is therefore not possible to determine from the registry record whether the inferential results were adjusted for testing several outcomes or should be viewed as exploratory.

General statistical context: testing multiple hypotheses can increase the chance of at least one result appearing unusual under a set of null hypotheses. Multiplicity procedures can control that risk, but they may also affect the precision or power of individual comparisons. A clear analysis plan helps readers distinguish confirmatory analyses from exploratory ones. In its absence, secondary results generally warrant more cautious interpretation than a prespecified primary analysis.

The primary endpoint population is described as participants who completed 12 month follow-up. The registry reports 37 eyes in each group for that endpoint, while enrollment is reported as 44. Reasons for the difference are not reported in the registry record. There is no account of missed visits, unavailable measurements, withdrawal, or other sources of missing data, and no description of imputation or sensitivity analyses. It is consequently unclear how missing endpoint information may have affected the reported percentages.

The record does not describe the analysis population beyond the completion criterion in the primary outcome definition. It does not state whether all randomized participants were analyzed according to initial assignment, whether exclusions were made, or how the paired eye structure was handled. The registry records randomized allocation, but details of the allocation process and the analysis population are not reported.

These gaps do not change the values that are posted, but they limit assessment of potential bias and the strength of inferential claims. A fuller interpretation would require information on the analysis plan, missing-data handling, outcome-specific denominators, and multiplicity strategy. Those details are not reported in the registry record.

11. 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.

Most frequent non-serious adverse event terms

The registry reports serious adverse events for 44 participants at risk in each treatment group, with zero serious events in both the SMILE and wavefront-guided LASIK groups. Deaths are reported as zero in both groups. For other adverse events, the record reports one event in the SMILE group and zero in the wavefront-guided LASIK group, with 44 at risk in each group.

These are registry counts over the reported safety population. The record does not provide further detail about the non-serious event, its nature, timing, severity, or relationship to a procedure. The figures should not be interpreted as establishing that no other harms occurred, or that the procedures have equivalent safety profiles. They describe the events recorded in this registry entry and the denominators stated for the safety outcomes.

General statistical context: absence of a recorded event does not show that the underlying risk is zero. Safety estimates can be imprecise when event counts are low, and interpretation depends on follow-up duration, event definitions, ascertainment, and attribution procedures. Those details are not reported in the registry record. The serious-event counts are therefore descriptive rather than a complete comparative safety analysis.

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

The results describe a randomized, contralateral comparison of SMILE and wavefront-guided LASIK for myopia. For the primary endpoint, the registry reports the percentage of eyes reaching uncorrected visual acuity of 20/20 or better at one year. The reported percentage is higher in the SMILE group than in the wavefront-guided LASIK group. This is a descriptive pattern in the posted outcome values, not a complete estimate of the comparative effect.

The record does not report a confidence interval or formal comparative analysis for the primary endpoint. Therefore, the precision of the apparent difference is not available, and the data as posted do not establish superiority, equivalence, or noninferiority. Those conclusions require an appropriate analysis and, for equivalence or noninferiority, prespecified margins and methods; such information is not reported in the registry record.

The endpoint measures whether an eye crosses a visual-acuity threshold. It does not capture the full distribution of acuity, all aspects of visual function, patient experience, or every possible adverse outcome. The registry lists additional outcomes, but their results are not comprehensively available in the record. The primary endpoint also applies to participants who completed 12 month follow-up, and the record does not explain missing follow-up or its handling.

General statistical context: statistical evidence is most informative when estimates are considered with uncertainty, study design, measurement definitions, and analysis assumptions. The contralateral structure makes paired analysis important. Without the paired primary estimate and its uncertainty, the posted percentages cannot show how consistent the within-person comparisons were or how much sampling uncertainty surrounds the treatment contrast.

The findings do not support medical advice for an individual. They are registry-level results for the studied population and endpoint. They should be interpreted as descriptive evidence with important limits in the reported analysis, rather than as a definitive statement about the relative merits of either procedure.

13. Why This Trial Matters Statistically

This trial is statistically notable for its contralateral structure. Each participant is described as receiving a different procedure in each eye, which makes the comparison naturally paired. Pairing can be useful because characteristics shared by the participant may affect both eyes. At the same time, that structure requires analysis methods that recognize the link between eyes. The registry’s classification of the model as parallel does not explain how the within-participant design was represented in the analysis.

The primary endpoint is also expressed as a percentage of eyes meeting a threshold. This is straightforward to communicate, but it compresses visual acuity into a binary category. It does not show the distribution of measurements around the cutoff, and group percentages alone do not reveal whether outcomes tended to differ consistently within participants. A paired estimate and its confidence interval would have helped readers understand both the direction and precision of the contrast.

The registry reports descriptive primary values without a formal comparative analysis. That distinction matters: a group result is not equivalent to an inferential treatment comparison. The absence of a reported confidence interval or p-value means that readers cannot assess the primary contrast’s statistical uncertainty from the registry record.

The record also illustrates the importance of transparent reporting beyond the headline endpoint. Information about missing follow-up, the analysis population, multiplicity, and the statistical plan is not reported. Without those details, readers must limit interpretation to the observed values and avoid treating secondary findings as confirmatory. The trial’s value for statistical learning lies in showing why design, outcome definition, paired analysis, and reporting completeness all matter when interpreting a clinical comparison.

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 most important limitation for interpreting the primary result is the absence of a reported comparative estimate and confidence interval. The group percentages describe the observed endpoint values but do not quantify the uncertainty in their contrast. The registry also does not report a primary p-value or analysis method.

The within-participant design creates paired eye data, but the analysis approach is not described. The registry records a parallel model while the study summary describes treatment in both eyes of each participant. The record does not explain that classification or state whether the statistical analysis accounted for the correlation between paired eye outcomes.

The primary endpoint is restricted to participants who completed 12 month follow-up. The record does not report why some enrolled participants are not represented in the endpoint denominators, how missing measurements were handled, or whether sensitivity analyses were performed. The analysis population and any exclusions are not otherwise described.

The registry lists numerous secondary outcomes, but most outcome-specific numerical results and analyses are not reported in the registry record. It also does not report a multiplicity strategy, a detailed statistical analysis plan, interim-analysis information, or the rationale for the enrollment target. These gaps limit assessment of whether analyses were prespecified and how secondary findings should be weighted.

The safety record provides event counts but not detailed descriptions of the non-serious event, event attribution, or fuller ascertainment methods. Finally, the results concern the outcomes and follow-up described in this registry entry; the record does not provide additional information about broader populations or longer-term outcomes.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Prospective, Contralateral, Eye to Eye Comparison of SMILE Surgery to LASIK Surgery — NCT03067077.
• Registry record last updated 2022-02-02; status last verified 2022-01.
• Results first posted 2022-02-02.
• 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.

18. Record Summary

The registry record describes a completed randomized comparison of SMILE and wavefront-guided LASIK for myopia. The study is described as prospective and contralateral, with one procedure performed in each eye of a participant. Masking is listed as none, and the model is recorded as parallel. Enrollment is 44, and the sponsor is Stanford University.

The primary endpoint is the percentage of participant eyes with uncorrected visual acuity of 20/20 or better at one year, among participants who completed 12 month follow-up. The record reports 94.0% for SMILE and 83.0% for wavefront-guided LASIK, with 37 eyes in each group. A formal comparative analysis and confidence interval for this endpoint are not reported in the registry record.

Patient satisfaction is listed among the secondary outcomes, along with visual acuity, optical, corneal, symptom, imaging, and predictability measures. The safety counts report zero serious adverse events and deaths in both groups, with one other adverse event reported for SMILE and zero for wavefront-guided LASIK. Further analysis and outcome details are limited in the registry record.