Tear Film and Ocular Surface Surfactants

The hydrophobic surfactant proteins B (SP-B) and C (SP-C) are tightly bound to phospholipids. These proteins play important roles in maintaining the surface tension-lowering properties of pulmonary surfactant. Surfactant protein A (SP-A) and D (SP-D) are extremely hydrophilic and are thought to have a role in recycling surfactant and especially in improving host defense in the lung. Moreover, SP-A supports the hydrophobic surfactant proteins during surfactant subtype assembly and inhibits secretion of lamellar bodies into the alveolar space. During recent years surfactant proteins have also been detected at locations outside the lung such as the lacrimal apparatus. In this review, the latest information regarding SP function and regulation in the human lacrimal system, the tear film and the ocular surface is summarized with regard to mucous epithelial integrity, rheological and antimicrobial properties of the tear film, tear outflow, certain disease states and possible therapeutic perspectives.