Dry eye disease: the scale of the problem.

Dry eye disease, or keratoconjunctivitis sicca, is among the most frequently established diagnoses in ophthalmology; in Germany, one in four patients consulting an ophthalmologist complains of the symptoms of dry eye. Although epidemiological studies investigating the prevalence of dry eye disease are rare, published studies indicate that up to 20% of adults aged 45 years or more experience dry eye symptoms. Recent studies have shown that immunologic changes play a role in the pathogenesis of dry eye, not only in Sjögren's syndrome, but also in postinfectious and age-related conditions. Despite increasing understanding of the pathogenic factors involved in dry eye disease, there has been a lack of consensus on diagnostic criteria, classification of disease states, and the aims and interpretation of specific diagnostic tests. There is a need, therefore, for standardization of disease terminology and diagnostic tests in order to improve the usefulness of epidemiological and clinical investigation of this important ocular disorder.