The eyes are constantly bombarded by allergens, ultraviolet light, bacteria, and other organic organisms and inorganic materials. Blinking helps to clear the eyes of these toxic materials by creating negative pressure, or a vacuum that suctions tear film away from the eyes and out through the tear ducts. Rear film becomes compromised if the eyes are not sufficiently lubricated or moist, or if the tear ducts become blocked by plugs, cautery, swelling or other factors. Without adequate tear film, the toxic material remains on the eye surface longer than is healthy for the eye. The epithelium and inflammatory cells on the eye surface respond by secreting cytokines, lipid mediators, and matrix metalloproteinases (MMPs), increasing the concentration of irritating factors, which can lead to chronic inflammation of the ocular surface and surrounding tissue, corneal desensitization, and increased aqueous tear deficiency.
Lacrimal Gland, Tear Film and Dry Eye Syndrome 3
page 739. Edited by D. Sullivan et al.
Kluwer Academic/Plenum Publishers.