Description

Scientific Rationale

Anterior and posterior approaches to levator aponeurosis advancement differ in the tissues accessed and the surgical exposure required to restore eyelid position. The anterior approach provides access through the skin and orbicularis muscle, whereas the posterior approach accesses the levator aponeurosis through the conjunctival surface. These differences may influence surgical duration, tissue trauma, postoperative recovery, and cosmetic results.

Although both approaches are established surgical options, direct prospective randomized comparisons remain limited. Evidence supporting posterior advancement includes surgical case series, while the anterior approach remains widely used. A randomized comparison may help clarify whether the posterior approach preserves functional effectiveness while offering advantages in recovery or other aspects of the surgical outcome.

Study Hypothesis and Methodological Rationale

The study uses a noninferiority framework for its primary efficacy comparison. This framework addresses whether posterior advancement maintains an acceptable functional result relative to anterior advancement, rather than requiring it to produce a greater postoperative eyelid height. Potential advantages in operative duration, postoperative tissue response, safety, and patient experience will be examined separately through secondary comparisons.

The allocation sequence will be computer-generated using randomly varying block sizes of four and six. A study team member who is not involved in performing the operations will generate the sequence. Variable block sizes are intended to maintain balance between groups during recruitment while reducing the predictability of subsequent assignments.

Using one surgeon experienced in both techniques is intended to limit variation attributable to differences in surgical experience. The surgeon cannot be masked to the assigned approach. An independent healthcare professional will perform the principal efficacy measurements and cosmetic assessments.

Statistical Analysis

Descriptive analyses will characterize the study population and summarize the data. Continuous variables will be reported as means and standard deviations or medians and interquartile ranges, as appropriate. Categorical variables will be reported as frequencies and percentages. The distribution of continuous variables will be assessed using the Shapiro-Wilk test.

The primary comparison will use analysis of covariance, with postoperative upper eyelid height at the primary assessment as the dependent variable, surgical approach as the group factor, and the corresponding preoperative measurement as a covariate. The treatment difference will be calculated as posterior minus anterior approach. Noninferiority will be established if the lower bound of the two-sided 95% confidence interval for the adjusted mean difference is greater than -0.5 mm. This corresponds to a one-sided significance level of 0.025.

Secondary continuous variables will be compared using an independent-samples Student's t-test or the Mann-Whitney U test, according to their distribution. Categorical variables will be compared using the chi-square test or Fisher's exact test, as appropriate. Changes in eyelid height over follow-up will be examined using repeated-measures analysis of variance or a linear mixed-effects model. Secondary comparisons will use a significance threshold of 0.05.

The primary noninferiority conclusion will be considered separately from the secondary comparisons. Demonstrating noninferiority in eyelid height alone will not be interpreted as evidence of superiority in safety, recovery, or cosmetic outcomes.