Tears have a vital function to protect and lubricate the ocular surface. Tear production, distribution and clearance is tightly regulated by the lacrimal functional unit (LFU) to meet ocular surface demands. The tear film consists of an aqueous-mucin layer, containing fluid and soluble factors produced by the lacrimal glands and mucin secreted by the goblet cells, that is covered by a lipid layer. The array of proteins, glycoproteins and lipids in tears function to maintain a stable, well-lubricated and smooth optical surface. Tear factors also promote wound healing, suppress inflammation, scavenge free radicals, and defend against microbial infection. Disease and dysfunction of the LFU leads to tear instability, increased evaporation, inflammation, and blurred and fluctuating vision. The function of tear components and the consequences of tear deficiency on the ocular surface are reviewed.

眼泪具有保护和润滑眼表的重要功能。泪液的产生、分布和清除受到泪腺功能单元 (LFU) 的严格调控，以满足眼表的需求。泪膜由含水粘蛋白层组成，含有泪腺产生的液体和可溶性因子以及杯状细胞分泌的粘蛋白，被脂质层覆盖。眼泪中的一系列蛋白质、糖蛋白和脂质可维持稳定、润滑良好和光滑的光学表面。撕裂因子还能促进伤口愈合、抑制炎症、清除自由基、抵御微生物感染。LFU 的疾病和功能障碍导致泪液不稳定、蒸发增加、炎症以及视力模糊和波动。