Micropulse Laser Trabeculoplasty (MLT) Versus Selective Laser Trabeculoplasty (SLT) for Treatment of Open Angle Glaucoma: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Micropulse Laser Trabeculoplasty (MLT) Versus Selective Laser Trabeculoplasty (SLT) for Treatment of Open Angle Glaucoma (NCT01956942), a randomized na study. The primary outcome is Intraocular Pressure Reduction.

2. Clinical Question

The primary endpoint is a continuous measure: percentage change in intraocular pressure. The posted means are 17.01 for MLT and 14.29 for SLT. The reported comparison is a mean difference of -2.72 for SLT relative to MLT. In this direction, a negative value indicates that the posted mean percentage reduction was lower in the SLT arm.

The question is comparative, not whether either laser changed pressure relative to a separate untreated group. The registry record describes both interventions as standard of care for open-angle glaucoma, but it does not give a no-treatment comparison. The posted outcome therefore addresses the difference between the randomized arms on the specified measure and timeframe; it does not by itself establish the effect of either procedure compared with no procedure.

3. Trial Design

The record describes a randomized, parallel-group study with no masking. It lists open-angle glaucoma as the condition and the two device interventions as MLT and SLT. The study status is completed. The title identifies the comparison as a Phase IV study, while the phase field in the registry record is listed as NA.

Enrollment is reported as 81. The primary outcome results list 38 participants for MLT and 31 for SLT. These arm-specific outcome counts do not, by themselves, explain how all enrolled participants were handled in the analysis. Reasons for any difference between enrollment and the numbers represented in the primary outcome are not reported in the registry record.

The start is recorded as 2013-08 and primary completion as 2017-07. The record describes the MLT and SLT settings and says treatment covered the entire 360 degrees of the trabecular meshwork. The arm descriptions are cut off after mentioning pretreatment, so further details of pretreatment or other treatment procedures are not reported in the registry record.

The primary outcome is mean intraocular pressure reduction, expressed as percentage change, within 6 weeks to 3 months after the laser procedure was completed. The record also lists a secondary outcome concerning pain and inflammation measured by a pain scale after laser treatment. Four outcome measures are noted, but only one secondary outcome is posted in the record. The record lists no posted analyses. It does not report further details of randomization procedures, allocation concealment, masking of outcome assessment, or the timing of assessments within the stated primary-outcome window.

Randomization can support a fair comparison when allocation and follow-up are implemented as intended, but the presence of randomization alone does not establish that all potential sources of bias were prevented. With no masking, participants and treating personnel were not masked according to the registry field. Whether outcome assessors were masked is 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.

Overall Study

5. Baseline Characteristics

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

6. Primary Endpoint

The registry lists the primary outcome as Intraocular Pressure Reduction, measured over within 6 weeks to 3 months after the laser procedure is completed.

The primary endpoint is intraocular pressure reduction, reported as mean percentage change. Intraocular pressure is the pressure inside the eye; the registry uses its change as a measure for comparing the two laser procedures in people with open-angle glaucoma. The stated assessment window is within 6 weeks to 3 months after the laser procedure is completed.

A percentage-change outcome expresses change relative to a reference value rather than as an absolute pressure-unit change. That can make changes more comparable across people whose starting measurements differ, although the registry record does not specify the exact formula, reference measurement, or handling of multiple measurements within the stated timeframe. Those details are not reported in the registry record.

The endpoint is continuous, and the registry reports each arm’s mean and standard error. A mean gives a measure of the group’s central result. The standard error describes the estimated precision of that mean, rather than the spread of individual participants’ measurements. The posted means are 17.01 for MLT and 14.29 for SLT.

Using a continuous endpoint allows the comparison to retain information about the magnitude of measured change instead of classifying participants only into categories. The endpoint answers a specific question about pressure reduction during the stated follow-up window. It does not, on its own, describe pain, inflammation, longer-term outcomes, or every aspect of safety and tolerability. The record lists pain and inflammation as a secondary outcome but does not provide that result in the posted outcomes summarized for this comparison.

7. Results Posted in the Registry

• Selective Laser Trabeculoplasty (SLT): mean 14.29 versus 17.01 on control; difference -2.72 (95% CI -5.49 to 0.05), standardized effect d = -0.46; z-test p = 0.054.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous, and the registry reports a mean for each arm. A mean is the arithmetic average of the measured values within an analyzed group. It describes the group’s center, but it does not show how widely individual results varied. The registry lists standard error as the measure of dispersion. Standard error quantifies uncertainty in an estimated mean; it is not the same as the standard deviation, which describes variation among individual observations.

The reported arm means are 17.01 for MLT and 14.29 for SLT. The comparison is expressed as SLT relative to MLT: its estimate is -2.72. This direction matters. A negative estimate means the posted SLT mean is lower than the posted MLT mean for the measure as reported. Because the endpoint is percentage change, the difference is in the reported percentage-change scale; it is not an absolute change in intraocular pressure units.

The registry also reports a confidence interval from -5.492 to 0.052 and an unadjusted p-value of 0.054. A confidence interval gives a range of values compatible with the observed data under the statistical method and its assumptions. It conveys uncertainty about the mean difference, not a range containing a stated percentage of individual participants’ outcomes. This interval includes zero, so the posted analysis does not exclude a zero mean difference at the interval’s confidence level. The confidence level itself is not reported in the registry record.

A p-value is calculated under a null hypothesis and a statistical model. In general, it represents how often results at least as incompatible with that null hypothesis would be expected if the null model and its assumptions were true. It does not measure the size or practical importance of an effect, and it is not the chance that the null hypothesis is true. The registry identifies the reported value as unadjusted; further details about the test, covariate adjustment, or analysis model are not reported in the registry record.

Why consider the mean difference and its interval together?

The estimate describes the observed size and direction of the arm contrast, while the interval communicates uncertainty around that estimate. A small p-value alone would not say how large the difference is, and a point estimate alone would not show how precisely it is estimated. In this trial, the estimated difference is negative in the SLT-relative-to-MLT direction, but the interval reaches slightly above zero. The interval and p-value therefore call for a qualified interpretation rather than a simple claim based only on which arm’s mean is larger.

What does the standard error tell the reader?

In general, the standard error is affected by both the variability of the measurements and the amount of information contributing to the mean. Smaller standard errors indicate more precise estimates of a mean, all else being equal. They do not mean that individual measurements are tightly clustered. The registry gives a standard error of 1.0 for each posted arm mean, but does not provide the standard deviations for the outcome. The comparison also reports a pooled standard deviation of 5.905, which is used in the posted standardized-effect calculation and planning illustration.

Why can over-dispersion matter?

General statistical explanation: over-dispersion occurs when observed variation is greater than a model assumes. It matters because a model that understates variability can make standard errors too small and uncertainty intervals too narrow. The primary endpoint is continuous and the registry does not report a count model or an over-dispersion analysis. Whether any particular distributional concern was assessed is not reported in the registry record; over-dispersion should not be inferred from the posted mean comparison alone.

What can randomization contribute?

General statistical explanation: random allocation aims to make the treatment groups comparable, on average, with respect to measured and unmeasured factors at assignment. It does not guarantee exact balance in a particular trial, nor does it address losses to follow-up or outcome measurement after assignment. The record identifies the study as randomized but does not describe the sequence-generation or allocation-concealment methods. It also lists masking as none, without specifying whether outcome assessors were masked.

What cannot be checked from the posted analysis?

The registry lists no posted analyses. It does not give the statistical analysis plan, define the analysis population, describe missing-data methods, or say whether the result was adjusted for baseline values or other variables. It also does not explain the exact percentage-change calculation or how measurements in the assessment window were selected. These omissions limit independent assessment of how closely the displayed comparison follows the intended analysis. They do not establish that the methods were inappropriate; they mean those details are not reported in the registry record.

10. Confidence Intervals and Precision

The reported mean difference is -2.72 for SLT relative to MLT, with a confidence interval from -5.492 to 0.052. This interval is the main direct summary of precision for the arm comparison: it shows that the point estimate is uncertain over a range that includes both a negative difference and values close to zero or slightly positive. The interval does not establish that every value in the range is equally plausible, nor does it describe individual participants’ outcomes.

Because zero lies within the interval, the posted estimate does not rule out no difference in the population mean under the interval’s method and assumptions. The upper end is close to zero, while the lower end allows a larger negative difference in the stated direction. In context, the direction is important: negative values mean a lower reported mean percentage change in SLT than in MLT. The interval’s confidence level and construction method are not reported in the registry record, so those details cannot be independently characterized from this record.

The standard error reported for each arm mean is 1.0. Standard errors address precision of the mean estimates, not the range of participant-level responses. The registry does not report standard deviations for the arm-level outcome. It does report a pooled standard deviation of 5.905 alongside the comparison and planning information.

Precision depends on the variability of the outcome and the amount of information contributing to the analysis. The outcome counts are 38 for MLT and 31 for SLT. The record does not explain why these counts differ from the enrollment figure, whether all randomized participants had outcome data, or how missing observations were handled. These reporting gaps matter when judging the basis of the uncertainty estimate. The interval is best read as the uncertainty reported for the posted comparison, not as a complete account of uncertainty about all outcomes or longer-term differences.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning display gives illustrative participant counts per arm, not total event counts. The calculation assumptions stated for it are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effects considered are stated fractions of the observed effect. The original trial’s own sample-size assumptions and justification are not reported in the registry record.

The 80% power column indicates the illustrated number of participants per arm for a design with an 80% chance of detecting the specified effect under the planning assumptions, if that effect and the model assumptions were correct. The 90% power column gives the corresponding planning count for 90% power. These figures are design illustrations, not outcomes observed in the trial. They are not observed power.

The display includes planning for 100% of the observed effect, planning for 75% of the observed effect, and planning for 50% of the observed effect. For the observed effect, it lists 74 participants per arm for 80% power and 100 for 90% power. For planning for 75% of the observed effect, it lists 132 per arm for 80% power and 177 for 90% power. For planning for 50% of the observed effect, it lists 296 per arm for 80% power and 397 for 90% power.

The pattern illustrates a general principle: smaller effects are harder to distinguish from random variation and therefore require more participants for the same target power, under otherwise unchanged assumptions. These calculations use the observed effect as their starting point, so they should not be read as the trial’s original target or as proof that the study had a particular power for its observed result.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -2.720; pooled standard deviation σ = 5.905.
2. n = 2 × (1.96 + 0.842)² × 5.905² / -2.720² = 74.0, rounded up to 74 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -2.72                      # observed difference in means
sigma <- 5.90471605090296                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1956942)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 74 (80% power), 100 (90% power)
 75% of observed effect: n per arm = 132 (80% power), 177 (90% power)
 50% of observed effect: n per arm = 296 (80% power), 397 (90% power)
power.t.test: 74.9 
Simulated power at n = 74 per arm: 0.789 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when a study tests multiple outcomes, time points, groups, or analyses. When many hypotheses are tested, the chance of obtaining at least one apparently notable result can increase unless the analysis plan accounts for that multiplicity. General statistical practice may use a prespecified primary outcome or adjustment methods to address this issue. The registry identifies intraocular pressure reduction as the primary outcome and lists a secondary pain-and-inflammation outcome. It does not report whether or how multiplicity was addressed.

The record notes four outcome measures but posts one secondary outcome. It lists no posted analyses. The number of outcomes alone does not show how many statistical tests were performed, whether multiple time points were analyzed, or whether any adjustment was planned. Those details are not reported in the registry record. The p-value for the primary comparison is identified as unadjusted, and no adjusted result is posted.

Missing-data handling is also not described. The primary outcome lists 38 participants for MLT and 31 for SLT, while enrollment is 81. The registry does not explain the relationship between enrollment and the analyzed outcome counts, give reasons for unavailable outcomes, or describe imputation or other missing-data methods. It is therefore not possible to determine from the record whether the posted estimates use all randomized participants, only participants with observed outcomes, or another analysis population.

The record does not identify an intention-to-treat, per-protocol, or safety population for the primary outcome. Nor does it report whether participants were analyzed according to assigned intervention regardless of treatment received. These analysis-population details can affect interpretation in a randomized trial and are not reported in the registry record.

These omissions do not prove that multiplicity or missing data were mishandled. They limit what can be assessed from the registry record. A complete appraisal would require the analysis plan and fuller reporting of outcomes, populations, and methods, none of which is reported in the registry record.

14. 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 serious adverse-event figures list 0 affected participants in the MLT arm, with 38 at risk, and 0 in the SLT arm, with 31 at risk. The registry also lists 0 other adverse events in each arm and 0 deaths in each arm. These are the counts recorded in the adverse-event categories for the groups shown.

Zero recorded events does not establish that the interventions have no risks. Rare events may not be observed in a study, and the record does not provide further details about event definitions, collection methods, severity grading, or the period used for adverse-event reporting. It also does not report whether all participants were monitored in the same way.

The listed secondary outcome concerns pain and inflammation after the laser procedures, but a corresponding result is not posted in the record. The adverse-event counts should not be treated as a substitute for that outcome. They also do not describe unreported symptoms or experiences. The record supports a narrow statement about the reported event counts, not a comprehensive assessment of safety or tolerability.

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

The posted primary outcome shows a higher mean percentage reduction in intraocular pressure for MLT than for SLT in the recorded arm results: 17.01 compared with 14.29. The comparison estimate, expressed as SLT relative to MLT, is -2.72. This describes the direction and size of the observed mean contrast on the registry’s percentage-change scale.

The confidence interval, from -5.492 to 0.052, includes zero, and the unadjusted p-value is 0.054. The data therefore do not provide a precise estimate that excludes no mean difference under the reported comparison. The result is compatible with a range of possible differences, including values close to no difference. It should not be reduced to a claim that one treatment definitively outperformed the other.

The result is limited to the primary endpoint and the timeframe within 6 weeks to 3 months after the procedure. It does not establish what the comparison would be over longer follow-up. Nor does it answer every question about safety, tolerability, or pain and inflammation. The registry lists pain and inflammation as a secondary outcome but does not post its result in the record.

The posted outcomes cannot establish whether the observed difference is clinically important because the registry does not report a threshold for clinical importance. Statistical uncertainty and clinical importance are related but distinct questions: an estimate can be uncertain even when its possible values would matter, and a precisely estimated difference may still be small in practical terms. The record does not provide enough information to resolve that question.

These findings also do not compare either laser with no procedure. The registry describes both as standard of care for open-angle glaucoma, and the randomized comparison is between MLT and SLT. The record’s safety entries list no serious or other adverse events and no deaths in either arm, but those counts cannot establish the absence of all possible harms. Overall, the posted result is a short-term, registry-reported comparison of mean percentage change, with uncertainty and reporting gaps that should remain part of its interpretation.

16. Why This Trial Matters Statistically

This trial is statistically informative because it compares two active procedures using a randomized, parallel-group design and reports a continuous primary outcome. The mean difference provides a direct estimate of the contrast on the percentage-change scale, while the confidence interval shows the uncertainty around that estimate. Reading both helps avoid treating the larger arm mean as a complete answer on its own.

The result also illustrates why direction and precision matter. The reported means favor a larger average percentage reduction in MLT, but the comparison interval reaches across zero. The p-value is 0.054. Together, these statistics describe an observed difference whose direction is clear in the posted sample but whose population magnitude is not precisely determined by the registry comparison.

Sample-size planning offers another useful statistical lesson. The planning illustrations show that designs targeting smaller fractions of the observed effect call for more participants per arm, given the listed assumptions. Such calculations can help readers understand how effect size, power targets, and sample size relate in general. They do not recover the original design rationale, which is not reported in the registry record, and they are not evidence of observed power.

The record also shows the limits of registry-level interpretation. It gives outcome means, standard errors, a comparison interval, a p-value, and adverse-event counts, but does not report the analysis population, missing-data methods, detailed analysis plan, or a multiplicity approach. These omissions affect how fully the numerical result can be evaluated, without by themselves proving that the underlying analysis was flawed.

For biostatisticians and clinical researchers, the key point is to keep the estimate, uncertainty, endpoint, timeframe, and reporting limitations together. A comparison is more informative when the reader can distinguish what was observed from what remains uncertain and what the registry does not report.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record leaves several trial-specific details unavailable. The primary outcome is described as percentage change within 6 weeks to 3 months, but the exact calculation, reference measurement, and method for choosing among measurements in that window are not reported. The record also does not provide baseline intraocular pressure values, limiting assessment of the groups’ starting measurements and the interpretation of a relative-change endpoint.

The arm counts for the primary outcome are 38 for MLT and 31 for SLT, while enrollment is 81. The record does not explain this difference, describe participant flow, state why outcomes may be unavailable, or specify how missing observations were handled. It does not identify the primary-outcome analysis population or say whether participants were analyzed according to randomized assignment.

Although randomization is reported, sequence generation and allocation concealment are not described. Masking is listed as none; whether outcome assessors were masked is not reported. The statistical analysis plan, model details, confidence level, and any adjustment for baseline measurements or other covariates are also not reported in the registry record.

The record lists four outcome measures and one posted secondary outcome, but no posted analyses. The pain-and-inflammation outcome has no result in the posted record, and the adverse-event information does not give detailed event definitions or reporting periods. The stated follow-up window for the primary outcome is relatively specific, but longer-term outcome results are not reported in the registry record.

Finally, no threshold for a clinically important difference or original sample-size justification is reported. The displayed planning calculations are illustrations based on the observed effect, not evidence of the assumptions used to design the trial. These limitations constrain conclusions from the registry results; they do not independently establish whether unreported procedures or analyses were conducted.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Micropulse Laser Trabeculoplasty (MLT) Versus Selective Laser Trabeculoplasty (SLT) for Treatment of Open Angle Glaucoma — NCT01956942.
• Registry record last updated 2023-06-13; status last verified 2023-05.
• Results first posted 2023-06-13.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

The registry describes a completed randomized, unmasked, parallel-group comparison of Micropulse Laser Trabeculoplasty and Selective Laser Trabeculoplasty for open-angle glaucoma. The record lists enrollment as 81 and identifies intraocular pressure reduction as the primary outcome, measured as mean percentage change within 6 weeks to 3 months after the procedure.

The posted primary outcome means are 17.01 for MLT and 14.29 for SLT. The mean difference for SLT relative to MLT is -2.72, with a confidence interval from -5.492 to 0.052 and an unadjusted p-value of 0.054. The interval includes zero, so the estimate does not exclude no mean difference.

The adverse-event record lists zero serious events, zero other adverse events, and zero deaths in both arms. The registry does not post the pain-and-inflammation result or further details of the analysis population, missing-data handling, or statistical plan. The planning display is illustrative and uses the observed effect; the trial’s original sample-size assumptions are not reported in the registry record.