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Dartt D. A.
Tears play a critical role in the health of the cells which comprise the ocular surface, namely the corneal and conjunctival epithelia. Tears provide nourishment to and remove cellular waste from these cells as they continuously bathe them. Tears are secreted in response to environmental, mechanical, physical stimulation and infection by organisms. Because of the multitude of functions, the amount and composition of tears is tightly regulated with multiple glands and cell types secreting different portions of the tear film. Secretion of mucus by the conjunctival goblet cells, water, electrolytes, and proteins by the accessory and main lacrimal glands, and lipids by the meibomian glands are under tight neural regulation. As the amount of tears present on the ocular surface is dependent not only upon tear production but also tear drainage, it seems logical to conclude that tear drainage should also be tightly regulated. Indeed, evidence suggests that, like tear production, tear drainage can be modified. Despite the tight regulation of tear production and drainage, alterations in regulation do occur resulting in a large variety of diseases many of which can be deleterious to vision.