Diabetic retinopathy is the leading cause of new cases of legal blindness among 
adults in the developed countries. Approximately 40% of all people with diabetes 
have diabetic retinopathy and 5% of these have sight-threatening form. As the 
advanced stage, where there is a high risk for vision loss, can develop without 
any serious symptoms, sometimes it is hard to detect it. A non invasive method 
to detect biomarkers characteristic for diabetic retinopathy from the tear fluid 
was developed. Tear samples from diabetic patients with no retinopathy, non 
proliferative and proliferative stages of diabetic retinopathy were analyzed and 
the protein content of each sample was compared to the protein content of tear 
pool from healthy volunteers. The samples were labeled with iTRAQ fourplex 
labels and were analyzed with nanoHPLC coupled ESI-MS/MS mass spectrometry. The 
lipocalin 1, lactotransferrin, lacritin, lysozyme C, lipophilin A and 
immunoglobulin lambda chain were identified as possible biomarker candidates 
with significantly higher relative levels in the tear of patients with diabetic 
retinopathy.