What is dry eye?
Dry Eye Syndrome is really a misnomer for the truly accepted medical term Ocular Surface Disease (OSD). OSD is a complex interaction involving brain signals, the tear film itself, lacrimal glands, oil glands in the eyelids, and the immune system. The tear film has three layers: the outermost oil layer prevents evaporation of the tear film; the water or aqueous layer is the actual tear film, and the innermost mucin layer which spreads the tear film. The healthy tear film is a delicate balance of the three layers produced by the meibomian oil glands in the eyelids, the lacrimal and accessory lacrimal glands and the conjunctival goblet cells. Electrolytes such as sodium, potassium, calcium, and chloride, proteins such as lactoferrin and albumin, cytokines such as interleukin, transforming growth factor, and mucin, and antibodies such as IgG are all found in a homeostatic balance in a normal healthy tear film. A dry eye tear film typically is depleted of electrolytes (“dehydrated”), lower proteins, less antibodies to fight infection, more inflammation, and activation of destructive enzymes to the ocular surface barrier. OSD is really a triad of three conditions: aqueous deficiency (dry eye), posterior blepharitis (evaporative dry eye), and/or ocular allergy. In the US alone, there are at least 25 million dry eye sufferers.