There was a statistically significant decrease in the IL-1 , IL-6 , IL-12 , and TNF - concentrations and a statistically significant increase in the catalase , peroxiredoxin 2 , superoxide dismutase 2 ( SOD 2 ) , and thioredoxin mean fluorescence intensity ( MFI ) of tears in the preservative-free group at 1 , 2 , and 3 months compared to initial values , respectively ( P < 0.05 ) .