2.3. Randomization and masking
Stratified random numbers were generated by statisticians using the SAS version 9.3 software (SAS Institute Inc., Cary, NC), which denoted the drug number as a running serial number for the sample size. The investigator administered the corresponding drugs to participants according to the sequence in which they were enrolled.Unified manufacturing of the study drugs (lutein and placebo) was conducted by Santen Pharmaceutical Co. Ltd. Patients in the lutein group were orally administered lutein, 1 capsule, once daily (20 mg/capsule), whereas those in the placebo group were orally administered placebo identical to that in the lutein group daily. The treatment duration was 6 months. There were 2 levels of blinding: first, blinding of each drug to its corresponding group; and second, blinding of the drug was conducted by the blinding staff after the blinding status examination and completion of data locking. The second round of unblinding was performed after the completion of the statistical analysis and unmasking of the placebo and experimental groups. All participants, investigators, and staff members who performed the analyses were blinded to the study protocols.