Statistical analysis
The data were double-typed into Epi-Info 6, and the database was validated and imported into Excel.The mean and standard deviation (SD) were calculated for the descriptive analysis of the continuous quantitative variables. The Student's t-test was used to determine whether there was a statistical difference between the means of the two groups and analysis of variance (ANOVA) with the coefficient of determination for the multiple comparisons of means.Absolute and relative frequencies were calculated for the categorical variables. The test used in the inferential analysis was Pearson's chi-square, and the approximate chi-square test in the Monte Carlo simulation was used in cross-tabulation.In the longitudinal analysis, the generalised linear model (GLM) was employed, with Wald's chi-square test and analysis of the interactions of the effects (group and time or group and tear degree) based on linearly independent pair comparisons between estimated marginal means.The significance level adopted was 