Topo-guided LASIK and Photorefractive Keratectomy vs Wavefront LASIK and Photorefractive Keratectomy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Topo-guided LASIK and Photorefractive Keratectomy vs Wavefront LASIK and Photorefractive Keratectomy (NCT03075176), a randomized na study. The primary outcome is Change in Uncorrected Visual Acuity From Baseline to Month 12.

2. Clinical Question

The comparison was designed within participants: each participant received the two correction approaches in different eyes, with the eye assigned to each approach randomly chosen. The procedure type was not randomized in the description; participants who chose LASIK received the two LASIK approaches, while those who chose PRK received the two PRK approaches. This distinction matters because the intended comparison is between correction approaches within the same surgery type, rather than a direct comparison of LASIK with PRK.

The registry also lists change in contrast sensitivity from baseline to month 3 as a secondary outcome. It reports three outcome measures, but the record does not reduce the primary outcome to a single comparison. No analyzed primary or secondary results are reported. The clinical question therefore remains unanswered by the posted outcome data: the record gives neither an estimate of the difference in visual-acuity change nor its precision.

3. Trial Design

The registry describes a randomized, single-masked, parallel-design study sponsored by the University of Utah. It lists enrollment as 39 and gives the study status as terminated. The recorded study start was 2017-02-13, and the primary completion date was 2019-08-12. The phase is listed as NA.

Although the registry classifies the design as parallel, the arm descriptions specify a paired-eye arrangement: each participant received wavefront-optimized treatment in one eye and topography-guided treatment in the other. The eye assigned to each approach was randomly chosen. In this design, each participant can serve as a within-person comparator, which can account for characteristics shared by that participant. The record does not describe the masking procedure or identify who was masked.

Participants chose whether to undergo LASIK or PRK. Within the chosen procedure, the two eyes were assigned different correction approaches. The registry lists four interventions: wavefront-optimized LASIK, topography-guided LASIK, wavefront-optimized PRK, and topography-guided PRK. Its arm descriptions show that the comparison was between approaches within LASIK or within PRK, not between procedure types.

The registry states that the twelve-month primary outcome was not collected for any participants. It also states that bias in who qualified for the study made it apparent that statistically valid results would not be obtained. The record does not explain the nature of that bias, how it was identified, or when the termination decision was made. It reports zero analyses. Although three outcome measures are listed, detailed results sufficient for an effect estimate are not reported.

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: 39 participants were randomized, one participant withdrew, 38 completed wavefront surgery on one eye and topoguided surgery on the other eye. A total of 76 eyes were treated.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Twelve month data was not collected for any participants. Because of the bias in who qualified for the study it became apparent we would not get any statistically valid results.

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 Change in Uncorrected Visual Acuity From Baseline to Month 12, measured over 12 months.

The primary endpoint is change in uncorrected visual acuity from baseline to month 12. Uncorrected visual acuity concerns vision assessed without corrective lenses; measuring change compares the follow-up assessment with the preoperative baseline. Such a change measure is intended to describe how vision differs over time after treatment, rather than reporting only a single follow-up value. In general, change from baseline can help account for differences in starting measurements, although interpretation depends on the measurement scale and the analysis used.

The registry says visual acuity was to be tested preoperatively through month 12, but the endpoint unit, parameter type, and dispersion measure are not reported in the registry record. Most importantly, the registry states that no participant had month 12 data collected. There is therefore no posted month 12 change estimate, comparison between correction approaches, or measure of uncertainty for this primary endpoint. The stated outcome describes the intended question, not an observed result.

Change in contrast sensitivity from baseline to month 3 is listed as a secondary outcome. The posted record does not include a result for that outcome either. Without outcome measurements and an analysis, the endpoint definition alone cannot establish the direction or size of any difference between the approaches.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does random assignment mean in this study?

Random assignment means that a chance process determines which eye receives which correction approach. The registry says the eye assignment was randomly chosen. In general, random assignment can reduce systematic differences between comparison conditions, so that the assigned treatment is less likely to be selected according to a participant's or clinician's expectations. Here, the randomization described applies to the eye receiving each approach. The registry does not describe the sequence-generation method, concealment, or any implementation details, so these cannot be assessed from the record.

The procedure type was selected by participants: they chose LASIK or PRK. Thus, random assignment of the approach to the eye does not mean that participants were randomized between LASIK and PRK. Comparisons across those procedure groups could be affected by differences associated with who selected each procedure. The posted record does not report analyses that separate or adjust for such differences.

Why is the paired-eye structure important?

Each participant received both correction approaches, one in each eye. This makes the intended treatment comparison paired within a participant. In general, measurements from two eyes of the same person may be correlated because the eyes share personal characteristics. An analysis that accounts for pairing can distinguish within-participant differences from variation between participants. Treating paired eye observations as independent would generally fail to represent that dependence appropriately.

The record does not state how the primary outcome would have been analyzed, whether the paired structure was explicitly incorporated, or whether outcomes would have been evaluated separately for LASIK and PRK. There are no reported analyses to clarify these points. No statistical method should therefore be attributed to the study on the basis of the posted record.

What does a confidence interval ordinarily communicate?

In general, a confidence interval expresses the uncertainty around an estimated effect under a specified statistical method. A narrower interval indicates greater precision under that method, while a wider interval indicates more uncertainty. It does not correct for bias in participant selection, missing outcome data, or an unsuitable analysis. The registry record reports no interval for the primary endpoint because the month 12 outcome was not collected and no analysis is reported.

What can a p-value answer?

In general, a p-value describes how compatible observed data are with a specified null model, conditional on the analysis assumptions. It is not the probability that the null hypothesis is true, and it does not describe the size or clinical importance of an effect. The record gives no p-value for the primary comparison. Statistical significance therefore cannot be assessed from the posted results.

Why do missing outcomes matter?

When the primary endpoint is not observed, an effect estimate cannot be formed from that endpoint without additional assumptions or other data. Methods for missing data can sometimes use partial observations, but their validity depends on why measurements are missing and on the assumptions made. Here, the registry states that no twelve-month data were collected for any participants. It does not report a missing-data method, intermediate primary-outcome measurements, or assumptions used to estimate unobserved values. No imputed month 12 result is reported.

What can the sample-size illustrations establish?

Any planning illustration based on an observed effect is distinct from an observed trial result. Such an illustration depends on assumptions about the effect to detect, significance level, allocation, and statistical approximation. It does not show the achieved power of a completed study. The registry record does not report the trial's own sample-size justification or a statistical plan, and it supplies no observed primary effect from which to evaluate precision. The reason the trial was terminated, as recorded, was concern about bias in who qualified, not a reported sample-size calculation.

More generally, the design and outcome definitions describe what investigators intended to compare; they do not substitute for outcome measurements and an analysis. Since the record reports no analyses and no month 12 observations, standard inferential quantities for the primary comparison are unavailable.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome of change in uncorrected visual acuity from baseline to month 12 and a secondary outcome of change in contrast sensitivity from baseline to month 3. It also reports three outcome measures in total. The record does not give enough detail to identify all outcome measures, any multiple time-point comparisons, or a hierarchy for interpreting them. A statistical plan describing how multiple outcomes or comparisons would be handled is not reported in the registry record.

Multiplicity arises when several outcomes, time points, or comparisons are tested. In general, conducting many tests without an appropriate plan can increase the chance of a chance-positive finding. Possible approaches include designating a primary outcome in advance or adjusting inference across a defined family of tests. The record does not state whether such an approach was planned. Since no analyses are reported, there are no posted results from which to assess multiplicity or its effect on conclusions.

For missing data, the registry explicitly states that no month 12 data were collected for any participants. It does not report a method for handling missing primary outcomes or any estimates based on imputation. The record also does not explain whether earlier visual-acuity measurements were available, or whether data collection stopped before or after those assessments. The endpoint-specific absence should not be generalized to other outcomes without further information.

The record does not describe an intention-to-treat population, a per-protocol population, or another analysis population. It does not give participant flow or explain exclusions from analyses. With zero analyses reported, it is not possible to determine which participants or eye measurements would have been included in an efficacy analysis. The reason recorded for termination—bias in who qualified—also raises a concern about selection, but the details and statistical consequences are not reported.

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.

The registry lists serious adverse events, other adverse events, and deaths for each of the four treatment groups. It reports zero affected participants in each listed category for every group. The corresponding at-risk counts are 18 for each LASIK group and 20 for each PRK group. These figures describe what is recorded in the registry; they are not a comparison adjusted for exposure or follow-up.

Zero reported events should be interpreted narrowly. It means that the registry lists no affected participants for these categories in the groups shown. It does not establish that no events could occur, and it does not quantify risk beyond the recorded experience. The record does not specify the adverse-event observation window, provide event terms, or explain ascertainment in enough detail to assess how events were captured. No serious adverse-event terms are listed.

The listed safety counts do not resolve the primary visual-acuity question. The registry reports that no month 12 primary-outcome data were collected, and no analyses are reported. Safety and efficacy are distinct outcome domains; zero recorded adverse events cannot be used as evidence of a visual-acuity benefit or equivalence.

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

The registry record documents an intended comparison of topography-guided and wavefront-optimized correction, with each participant receiving one approach in each eye. It also identifies the planned primary outcome and gives a reason the study did not produce statistically valid results: bias in who qualified for the study. That reason is stated by the registry, but its nature and impact are not described in detail.

The record does not establish whether the correction approaches produce different changes in uncorrected visual acuity. No month 12 outcome data were collected, and no analysis or effect estimate is reported. It is therefore not possible to conclude from this record that one approach is superior, inferior, or equivalent to the other. A lack of reported statistical evidence is not evidence of no difference.

The paired-eye design is a feature of the planned comparison, but design alone cannot supply a result. To interpret a treatment contrast, readers would need observed measurements, a suitable analysis accounting for paired eyes, and an estimate of uncertainty. Those results are not reported. The registry also does not report results for the listed month 3 contrast-sensitivity outcome.

The reported zero adverse-event counts have a limited meaning: no affected participants are listed for the event categories shown in the registry. They do not establish the absence of all possible harms, and they do not answer the efficacy question. The registry does not describe the event observation period or provide further event details.

Accordingly, the record is informative about the trial's design, intended endpoint, termination status, and missing primary outcome, but it does not provide evidence that can support a comparative efficacy estimate. Conclusions about the relative visual outcomes or precision of the treatments would require data and analyses that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically notable because the intended comparison used different approaches in the two eyes of each participant. In general, a paired design can control for characteristics shared by both eyes of a participant and can make within-person contrasts informative. It also requires an analysis that recognizes the relationship between paired measurements. The registry provides the design description but no analysis with which to assess how that structure would have been handled.

The record also illustrates the distinction between randomization within a comparison and selection into a broader treatment group. Assignment of the correction approach to each eye was randomized, while participants chose LASIK or PRK. The randomization therefore addresses which eye received which approach, as described, but does not randomize the choice between the two surgery types. This distinction matters if results are interpreted across procedure groups.

Most importantly, statistical design cannot overcome the absence of the primary endpoint. The registry reports that month 12 data were not collected for any participants and that bias in who qualified made statistically valid results unattainable. Without observed outcomes and an analysis, there is no treatment-effect estimate or precision measure to interpret. The case underscores that a planned comparison, random assignment, and outcome definitions do not by themselves produce evidence about an endpoint.

The registry's safety counts are also a reminder that event summaries and efficacy analyses answer different questions. Zero recorded adverse events in the listed groups do not fill the gap in visual-acuity results. The record is therefore useful for understanding what comparison was intended and why the posted evidence is incomplete, rather than for estimating comparative treatment effects.

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 limitation is the absence of the planned month 12 endpoint: the registry states that no twelve-month data were collected for any participants. No primary-outcome estimate, uncertainty interval, or inferential result is reported. The record also reports zero analyses, so there is no statistical result with which to evaluate the stated comparison.

The registry attributes the inability to obtain statistically valid results to bias in who qualified for the study. It does not explain the eligibility process, describe the bias, or report how it might have affected the enrolled participants or the intended comparison. That limits assessment of both the reason for termination and the potential generalizability of any findings; in this case, no primary findings are posted to evaluate.

Participants selected LASIK or PRK, while the eye assigned to each correction approach was randomized. This means procedure type was not randomized according to the arm descriptions. Any interpretation comparing the procedure types would therefore need to account for possible differences between those who selected each procedure. No such analysis is reported.

The record does not detail masking, the statistical analysis plan, sample-size justification, handling of missing data, analysis populations, or the full set of outcome measures. It lists month 3 contrast sensitivity as a secondary outcome but gives no result. It also does not specify the adverse-event observation window or provide further safety detail. These omissions constrain interpretation independently of the unavailable primary endpoint.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Topo-guided LASIK and Photorefractive Keratectomy vs Wavefront LASIK and Photorefractive Keratectomy — NCT03075176.
• Registry record last updated 2023-07-17; status last verified 2023-06.
• Results first posted 2023-07-17.
• 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 describes a randomized, single-masked study comparing topography-guided with wavefront-optimized LASIK or PRK. Participants chose LASIK or PRK, and the correction approach was randomly assigned between their eyes. The record lists enrollment as 39, status as terminated, sponsor as the University of Utah, and phase as NA.

The primary outcome was change in uncorrected visual acuity from baseline to month 12. The registry states that no month 12 data were collected for any participants and that bias in who qualified meant statistically valid results would not be obtained. It reports zero analyses. Change in contrast sensitivity from baseline to month 3 is listed as a secondary outcome, with no result reported. The record lists zero serious and other adverse events and zero deaths in each treatment group.