APOA1 and non-proliferative diabetic retinopathy: In other studies, NPDR patients had reduced levels of lipocalin-1, HSP27, beta-microglobulin in tears and increased levels of endothelin and neuron-specific enolase, while PDR subjects had increased levels of nerve growth factor, APOA1, lipocalin 1, lactotransferrin, lacritin, lipophilin A and Immunoglobulin lambda chain (21).