Sample size calculation
The number of DE patients was calculated by the popular estimating sample size program; G*power. This calculation was postulated in a conducted pilot study by the manuscript’s authors on 10 DE patients. The result for this calculation marked the sample size = 54 DE patients considering Schirmer’s test was the primary outcome. The value of 0.68 was the resultant effect size which was estimated on the statistical program with type II error = 0.8 and type I error = 0.05. Then, the number increased by 10% due to the estimation of dropout. So the final needed DE elderly were 30 patients in every group.