Methods
The analysis of the N- glycans was performed using matrix-assisted laser desorption ionization mass spectrometry on single tear samples. Tears from control normal subjects (CTRL), VKC and AKC patients were processed and treated with peptide N-glycosidase F (PNGase F) to deglycosylate N- glycoproteins. Released N- glycans were purified, permethylated and analyzed by Matrix-Assisted Laser Desorption/Ionization-Time Of Flight Mass Spectrometry and tandem Mass Spectrometry (MALDI-TOF MS and MALDI-TOF MS/MS).