LCN1 and non-proliferative diabetic retinopathy: Of over 1500 proteins that have been identified in tear fluid [20,21,22] the levels of nerve growth factor, apolipoprotein A1, lipocalin-1, lactotransferrin, lacritin, lysozyme-C, lipophylin A and Ig λ chain have found to be increased in patients with PDR, while lower levels of lipocalin-1, hsp27, β2-microglobulin and increased levels of endothelin and neuron-specific enolase have been found in patients with NPDR [14,23,24,25,26].