Corneal Nerves Function and Structure: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Corneal Nerves Function and Structure (NCT04222660), a non-randomized na study. The primary outcome is Cornea Sensitivity.

2. Clinical Question

The study has two stated aims. Its first phase concerns whether changes in blinking and squinting after a hyperosmotic solution could help identify early peripheral neuropathy. The primary endpoint is the ratio of time with eyelids closed to time with eyelids open during a recording after saline and Muro 128. Its second phase is described as preliminary work examining whether fish oil treatment is associated with changes in corneal nerve density and sensitivity in people with diabetic neuropathy.

These are research questions, not reported conclusions. The registry record does not report numerical primary outcome results or an estimated treatment effect. It also does not report a result establishing whether the sensitivity measure distinguishes the listed groups, or whether corneal nerve density or sensitivity changed during treatment.

3. Trial Design

The registry identifies this as a completed, non-randomized study with no masking and a single-group model. Enrollment is listed as 44. The study start is 2021-06-21 and primary completion is 2023-06-05. The phase is listed as NA. These administrative details describe the record but do not supply outcome estimates.

The group descriptions cover people with type 2 diabetes with neuropathy, people with type 2 diabetes without neuropathy, and healthy age-matched controls without symptoms of diabetes. Neuropathy status was to be determined from clinical records and evaluation. Since assignment was not randomized, differences between groups may reflect underlying differences in their characteristics as well as neuropathy status. The registry does not describe a method for adjusting for such differences.

The brief summary describes a first phase focused on corneal sensitivity after saline and a hyperosmotic solution, and a second phase involving preliminary investigation of fish oil treatment. The listed dietary supplement is Blackmores Omega Daily (4 1g capsules per day). The record does not report treatment duration, adherence, or whether every participant received the supplement. It is therefore not possible to infer a treatment schedule or a treatment comparison from the intervention listing alone.

The primary sensitivity examination is described as occurring once per patient, immediately after consent or later if requested. Each participant received saline followed by Muro 128 after a 5 minute recovery/washout period. This sequence makes each participant’s responses to the two solutions potentially informative as a within-person contrast, but the analysis plan for that contrast is not reported in the registry record. The record also does not describe how participants were recruited or how many were assigned to each group beyond the figures in the safety listing.

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: The reviewer is correct. Due to the pandemic the course of this study was dramatically changed. Initially there was going to be 2 separate protocols the first to measure cornea sensitivity using a hyperosmotic solution in 3 groups control, and diabetes with or without neuropathy. The second protocol was to be treatment with fish oil to determine whether improvement occurs. Because of COVID we were able to complete only protocol 1 and it was done in only control and diabetes neuropathy subjects.

Overall Study

Analysis population for the primary outcome, as defined in the registry: primary outcome

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 Cornea Sensitivity, measured over Examination of the response to saline and Muro 128 is preformed once in each patient immediately following their consent or if they request at a later more convenient time..

The primary endpoint is cornea sensitivity, expressed as the time ratio of eyelids closed versus open. The description measures eyelid closure over a 150 second recording after applying isotonic saline (0.9% NaCl) and then Muro 128, a hyperosmotic 5% NaCl solution. The response is assessed from recordings made using a multi-camera video platform. Saline is designated as the baseline response and Muro as the stimulant response.

The measure is intended to capture a behavioral response to corneal stimulation. The study summary motivates it as a possible way to detect changes in sensitivity associated with peripheral neuropathy. This is a proposed use, not evidence that the measure has diagnostic accuracy or clinical utility. No sensitivity values, group summaries, effect estimates, confidence intervals, or statistical tests for this endpoint are reported in the registry record.

As a ratio, the endpoint relates time with the eyelids closed to time with them open rather than reporting either duration alone. In general, interpretation of a ratio depends on how its numerator and denominator vary, and on whether the denominator can become very small. The record does not report participant-level distributions or details about handling unusual recordings. It also does not report a threshold for interpreting a response as abnormal.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean and standard deviation describe?

The primary outcome is classified as a continuous measure summarized using a mean and standard deviation. In general, a mean describes the central value of a set of observations, while a standard deviation describes how dispersed individual observations are around that mean. Together they can give a useful overview when the distribution is reasonably represented by its center and spread. They do not, by themselves, show how precisely a group mean has been estimated. Precision is commonly conveyed with a confidence interval, but no confidence interval for this endpoint is reported in the registry record.

For a ratio outcome, the distribution matters. In general, ratios can be skewed when some values are much larger than others, and a small denominator can make a ratio unstable. A mean and standard deviation may not fully convey such features. The registry record does not report a distribution plot, median, range, transformation, or other diagnostic information for the eyelid-closure ratio. It is therefore not possible to assess from the record whether the stated summary adequately describes the observed values.

How should the two solution responses be understood?

Every participant’s procedure is described as saline followed by Muro 128, with a recovery/washout interval between applications. In general, when two measurements are taken from the same person, their values may be correlated. A paired analysis can account for that within-person relationship, while treating measurements as independent can misstate uncertainty. The sequence and repeated measurement make this distinction relevant, but the registry record does not report which analysis was used for the primary outcome.

The fixed order also matters for interpretation. In general, a response after the second application could reflect the solution as well as time, order, or incomplete recovery from the first application. A washout period is part of the stated procedure, but its presence alone does not establish that order effects were eliminated. The record does not report a randomized solution order or an analysis addressing order effects.

Why do non-randomized groups limit causal interpretation?

Random assignment is a method for balancing, on average, both measured and unmeasured characteristics between treatment groups. This study is identified as non-randomized, so that protection against systematic group differences is not established. In general, comparisons among people with and without neuropathy may reflect differences in health or other characteristics alongside neuropathy. Comparisons involving a supplement may likewise be influenced by who received it, how treatment was selected, and other differences between participants. The registry record does not report adjustment methods or enough analytic detail to evaluate these issues.

The groups also serve different descriptive purposes: people with type 2 diabetes are categorized by neuropathy status, and healthy age-matched controls are included. Such groups can help frame measurements, but they are not automatically interchangeable controls for every question. The record expressly indicates that the listed arms are not a like-for-like control comparison. Any interpretation should keep the study’s non-randomized structure in view.

What can a confidence interval and p-value contribute?

In general, a confidence interval describes a range of values compatible with the data and the assumptions of an analysis, and helps communicate estimation uncertainty. A p-value measures how incompatible the observed data are with a specified statistical null model, under the assumptions used. Neither statistic alone establishes clinical importance, measurement validity, or causation. For the primary endpoint, the registry does not report an estimate, confidence interval, or p-value, so these aspects of the evidence cannot be evaluated.

How should the planning illustration be read?

The record describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It states that the effect to detect is a stated fraction of the observed effect, and that non-time-to-event entries are participants per arm. These are assumptions for planning illustrations, not observed trial results and not observed power. The registry does not report its own design justification or enough numerical information in this record to reproduce a planning estimate. A planning illustration also does not establish that the enrolled study had a particular probability of detecting an effect.

In general, planning calculations depend on the target effect, outcome variability, allocation, and analysis assumptions. If an effect estimate from a small or exploratory study is used as the planning basis, the resulting illustration may be sensitive to uncertainty in that estimate. The record does not report a protocol-level sample-size justification, so the planning illustration should not be taken as evidence about the study’s original design rationale.

What role can over-dispersion play?

Over-dispersion is a general statistical issue in which observed variability is greater than a model assumes. If a model understates variation, standard errors may be too small and intervals too narrow. The primary measure is a continuous ratio, and the registry does not report a fitted model or evidence of over-dispersion. This concept is relevant only as a general reminder that model assumptions should match the data; it is not a reported finding about this study.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Type 2 Diabetes With Neuropathy", "Normal Subjects, Aged Match With no Symptoms of Di")
n   <- c(28, 16)
m   <- c(0.177, 0.293)
sp  <- c(0.073, 0.036)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Type 2 Diabetes With Neuropathy  28  0.177  0.073  0.149  0.205
CARM  Normal Subjects, Aged Match With no Symptoms of Di  16  0.293  0.036  0.274  0.312

11. Multiplicity, Missing Data and Analysis Populations

The registry lists nine outcome measures and nine analyses. It does not report a multiplicity plan, such as identifying a hierarchy of outcomes, adjusting significance thresholds, or distinguishing confirmatory from exploratory tests. When many outcomes or analyses are examined, general statistical practice recognizes that the chance of at least one apparently notable result can increase. How much that issue applies depends on the analysis structure and the questions being tested, which are not detailed in the registry record.

The primary endpoint is identified as cornea sensitivity, while the secondary outcomes cover sensory tests, screening instruments, reflexes, visual acuity, questionnaires, and nerve conduction velocity. The record does not provide analysis-specific results or clarify whether each listed measure was analyzed in all groups or at particular time points. No conclusion about multiplicity-adjusted evidence can be drawn from the listing alone.

Missing-data handling is not reported in the registry record. There is no description of the amount or pattern of missing outcome data, exclusions, imputation, or sensitivity analyses. The record also does not define an analysis population, such as all enrolled participants, participants completing an examination, or participants meeting another analysis criterion. Enrollment is listed as 44, but this does not establish how many contributed data to a given outcome.

These omissions matter because estimates can depend on who has usable measurements and how missing observations are handled. In general, missingness related to health status or measured response can affect both the estimated effect and its uncertainty. Without participant flow and analysis-population details, readers cannot assess whether the reported analysis, if any, represents all enrolled participants or a selected subset.

12. 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 adverse-event listing reports zero serious events and zero deaths for both displayed groups. For Type 2 Diabetes With Neuropathy, 28 participants are listed as at risk for serious events and 28 as at risk for other events; zero are listed as affected in either category. For Normal Subjects, Aged Match With no Symptoms of Diabetes, 16 are listed as at risk for serious events and 28 as at risk for other events; zero are listed as affected in either category. No serious adverse-event terms are listed.

The different at-risk counts in the normal-subject group are recorded as stated and are not reconciled in the registry entry. They should not be silently treated as one common denominator. The adverse-event record does not display a Type 2 diabetes without neuropathy group in this listing, so no safety figure for that group can be inferred from these entries.

Zero recorded events means that none are listed for the stated groups and categories in this record. In general, an observed zero does not prove that an event cannot occur, particularly when the number of participants and the observation period are limited. The registry does not report event collection methods or additional details needed to assess the completeness of safety reporting. These figures describe reporting in the record; they are not a basis for medical advice.

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

The record is useful for understanding the study’s measurement concept: eyelid behavior after saline and a hyperosmotic solution is intended to represent corneal sensitivity, with an interest in diabetic neuropathy. It also makes clear that the broader research program included a preliminary fish oil investigation. This describes the questions and procedures, not what the data ultimately showed.

The record does not report numerical findings for the primary endpoint or the secondary outcomes. It therefore cannot establish whether the groups differed, whether responses changed between solutions, or whether the listed supplement was associated with a change in corneal nerve density or sensitivity. It also does not give estimates with uncertainty that would allow readers to judge precision. A missing result in the registry record should not be interpreted as a null result.

The study is non-randomized, unmasked, and described as a single-group model, with multiple clinically distinct groups listed. These features mean that the record does not support treating the group descriptions as randomized treatment arms. Even if outcome estimates were available, causal claims would need to account for potential group differences and the lack of random allocation. The registry does not report a method for doing so.

The primary endpoint is a behavioral response recorded over a short examination, not a reported diagnosis or a demonstrated screening threshold. The stated rationale is to explore sensitivity as a potential early-detection tool. Establishing whether a measure can serve that purpose would require evidence about its performance and reproducibility, neither of which is reported in this record. Likewise, the treatment objective described in the summary remains an objective rather than a conclusion.

Accordingly, the registry supports a description of the planned questions, groups, and measurement procedure, but not a judgment about efficacy, diagnostic performance, or the size of any association. The completed status indicates administrative completion, not that results are available in the registry entry.

14. Why This Trial Matters Statistically

This study is statistically interesting because it turns a proposed sensory response into a measurable continuous outcome. The eyelid-closure ratio offers a way to quantify a recorded behavior after stimulation, rather than relying only on a participant’s verbal description. The approach also illustrates how a physiological measurement can be framed as a potential screening signal, while requiring evidence that the measure reliably distinguishes relevant groups.

The procedure collects responses to saline and Muro 128 in the same person. In general, repeated measurements can provide useful within-person information because each participant serves as a reference for their own response. At the same time, the fixed sequence and timing make assumptions about order and recovery important. Statistical interpretation depends not just on collecting two readings, but on choosing an analysis that reflects their relationship and the study procedure.

The registry’s non-randomized structure is another important statistical feature. Comparisons across neuropathy categories or with healthy controls can describe patterns, but group differences do not by themselves isolate the effect of neuropathy. The same caution applies to a treatment question when allocation is not randomized. Study design, measurement, and analysis jointly determine what a contrast can mean.

Finally, the record highlights the difference between a research rationale and a reported result. It describes hypotheses about early detection and nerve repair, but does not report outcome estimates that would quantify support for those hypotheses. Reporting estimates and their uncertainty is essential for readers to distinguish a potentially informative pattern from one that is too imprecise or confounded to interpret. In this case, the registry entry leaves that statistical evidence unavailable.

15. 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 main limitation for interpreting the findings is that the registry record does not report numerical results for the primary endpoint. Without group summaries, effect estimates, or uncertainty measures, readers cannot assess the size or precision of a corneal sensitivity difference. The same absence of numerical results applies to the listed secondary outcomes and the proposed fish oil investigation.

The study is non-randomized and unmasked. As a result, comparisons between the listed groups may be affected by differences in participant characteristics, and the record does not report adjustment methods. The record also labels the model as single-group while describing several clinically distinct groups. It does not explain how that model designation relates to the group comparisons or treatment objectives.

The primary measure is a ratio derived from eyelid-closure behavior during video recording. The registry does not report information about measurement reliability, assessor procedures, data quality, or how atypical recordings were handled. It also does not report whether a particular response level was prespecified as clinically meaningful or useful for screening.

The summary describes two phases, but treatment duration, adherence, and the timing of any treatment-related assessments are not reported. The record does not provide a detailed protocol or statistical analysis plan, including the planned handling of missing observations, group differences, or multiple outcomes. The stated examination occurs once per patient, which describes the sensitivity assessment but does not establish the timing or completeness of other outcome assessments.

Finally, the safety listing has different at-risk counts for serious and other events in the normal-subject group, and does not include a corresponding displayed entry for people with type 2 diabetes without neuropathy. These reporting details limit comparisons across groups. The limitations concern what can be interpreted from the registry entry; they do not establish what may be available in other records.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Corneal Nerves Function and Structure — NCT04222660.
• Registry record last updated 2025-05-23; status last verified 2025-05.
• Results first posted 2024-07-03.
• 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.

19. Record Summary

NCT04222660, titled Corneal Nerves Function and Structure, is listed as completed. The official title is Diabetic Neuropathy: Function-Structure of Corneal Nerves to Assess Injury-Repair. The sponsor is the VA Office of Research and Development. Enrollment is listed as 44, with a non-randomized allocation, no masking, and a single-group model.

The study describes corneal sensitivity testing after saline and Muro 128, alongside a broader interest in diabetic neuropathy and a preliminary fish oil investigation. The primary endpoint is the time ratio of eyelids closed versus open during a 150 second recording. Secondary outcomes include sensory assessments, questionnaires, visual acuity, reflexes, and tibial nerve conduction velocity.

Numerical primary and secondary outcome results are not reported in the registry record. The adverse-event listing records zero serious events and zero deaths for the displayed groups, with the at-risk counts described in the safety discussion.