The term "dry eye" refers to various conditions of the tear film that are associated with damage to the function and protective mechanisms of the outer eye. A healthy ocular surface with an intact tear film results from an optimally coordinated interaction among the tear glands, the ocular surface, the eyelids, and the drainage pathways, as well as their neural and immunological regulation. The balance of this so-called tear functional unit can be disrupted by a variety of factors, ultimately leading to dry eye, or keratoconjunctivitis sicca. According to estimates, 10 million people in Germany, as well as 1 million each in Austria and Switzerland, are affected by this ocular surface disease. The most common symptoms include conjunctival redness, burning eyes, a foreign body sensation, tired eyes, and light sensitivity.