Total RNA will be extracted from the conjunctiva of SLK and control groups with Trizol reagent (Life, Gaithersburg, MD, USA). One microgram of total RNA from each sample will be annealed for 5 min at 70℃ with 500 ng oligo(dT) (Fermentas, Hanover, MD, USA) and reverse transcribed to cDNA by 200u RevertAid™ M-MuLV Reverse Transcriptase (Fermentas, Hanover, MD, USA) per 20 µl reaction for 1 hr at 42℃. The reaction will be stopped by heating for 10 min at 70℃.