Statistical Analysis
We performed a descriptive statistic including the measurement of precision, variance and accuracy of VOG (% error = (alternate cover test - VOG) / alternate cover test *100%). We measured the correlation between conditions calculating the Pearson’s R co-efficient. We calculated the reliability between the two tests using the intraclass correlation coefficient for continuous data. We compared the mean value of the two tests in each condition using a two sided, paired, non-parametric “Wilcoxon test”. We used SPSS for the statistical analysis (IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp.).