Statistical analysis

The statistical analyses have been performed starting with 2009. All data were analyzed using the Statistical Package for Social Sciences software (version 16.0, SPSS, Inc.) and shown as mean ± standard deviation. Graphs were plotted by Microsoft Excel 2008 (Microsoft Corporation). Means and standard deviations were calculated for all continuous variables. Frequency distribution and percentages were determined for categorical variables. Comparisons between post-operative and pre-operative values, for visual acuity (VA) and foveal thickness (FT) were carried out using the paired sample t-test. Concordance tests (Kolmogorov-Smirnov) have been performed for each data vector in order to determine their normality. For a 0.05 confidence interval, the data have been tested as normally distributed, which allowed the use of parametric methods (for quantitative data). Non-parametric tests have been performed for bivariate categorical data. Differences in the distributions between groups were analyzed using the independent t-test. Differences in the distributions of categorical variables between groups were analyzed using the Chi-squared test. In order to analyze the correlations, both Pearson correlation parametric tests and non-parametric Spearman and Kendall were used. Regression linear curves have been represented to determine the functional dependencies between some characteristics. Their adaptation over the represented point clouds has been appreciated by coefficients of determination. All tests have been performed bilaterally. Two significance thresholds were considered in order to test the statistical significance, α=0,05 and α=0,01, respectively. The statistical significance was set for P-values lower than the significance threshold. The graphic data processing included percentage, comparison diagrams, boxplots and regression functional plots.