Deficiency in tear film quality and quantity are often considered key defining characteristics of dry eye disease (DED). The complex, dynamic multi-component structure, which comprises an underlying aqueous-mucous layer and a superficial lipid layer, synergistically maintains ocular surface homeostasis. Functionally, the aqueous-mucus layer is believed to improve the wettability and support corneal adhesion of the tear film, while the lipid layer tends to form a superficial protective “blanket”, providing an occlusive effect. “Holes” in the blanket (see Fig 1), as typically observed in evaporative DED and especially in meibomian gland dysfunction, can increase exposure of the underlying aqueous layer of the tear fluid to the environment and evaporation, leading to hyperosmolarity of the tear film and epithelial apoptosis. Consequently, artificial tears are frequently used for the management of tear film deficiencies. However, the term “artificial tears” is a misnomer as most products do not mimic the complex composition of human tears and contrary to their name, they typically “supplement” rather than “replace” the tear fluid.
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