Glycoproteins are potentially important biomarkers of disease and therapeutic 
targets. In particular, the N-linked glycoproteins are a focus of interest as 
they can be found in the extracellular environment and body fluids. In this 
study, we have sampled the tears, the extracellular fluid of the epithelial 
cells covering the surface of the eye, of patients with climatic droplet 
keratopathy (CDK) using tears of unaffected normal patients for comparison. 
Prefractionation of the tear sample used a hydrazide-resin capture method, and 
the previously N-glycosylated peptides were then subjected to two-dimensional 
nano-LC-nano-ESI-MS/MS analysis to obtain peptide fragmentation patterns for 
identification through protein database searches. We have identified a total of 
43 unique N-glycoproteins, 19 of which have not previously been reported in tear 
fluid. In addition, we have quantitatively compared N-glycoprotein profiles in 
tear fluid of patients with CDK to tears of nondiseased controls using 
glycopeptide capture, iTRAQ labeling and 2D nano-LC-nano-ESI-MS/MS analysis. In 
tears of CDK patients, increased levels of four N-glycosylated proteins 
including haptoglobin (at sites N207, N211 and N241), polymeric immunoglobulin 
receptor (at sites N83, N90, N135, N186, N421, and N469), immunoglobulin J chain 
(at site N49) and an uncharacterized protein DKFZp686M08189 (at site N470), as 
well as a decrease in the N-glycosylation level of one N-glycosylated protein, 
lacritin (at site N119) were observed. However, the overall levels of these five 
proteins showed no appreciable changes between control and CDK samples. The 
findings could be clinically significant in terms of disease etiology and 
biomarkers.