The ocular surface and tear film and their dysfunction in dry eye disease

The ocular surface, tear film, lacrimal glands, and eyelids act as a functi onal unit to preserve the quality of the refractive surface of the eye and to resist injury and protect the eye against changing bodily and environmen tal conditions. Events that disturb the homeostasis of this functional unit can result in a vicious cycle of ocular surface disease. The tear film is the most dynamic structure of the functional unit, and its production and t urnover is essential to maintaining the health of the ocular surface. Class ically, the tear film is reported to be composed of three layers: the mucin , aqueous, and lipid layers. The boundaries and real thickness of such laye rs is still under discussion. A dysfunction of any of these layers can resu lt in dry eye disease. (Surv Ophthalmol 45(Suppl 2):S203-S210, 2001. (C) 20 01 by Elsevier Science Inc. All rights reserved).