Tears in health and disease

Purpose A brief review of normal tear function and changes resulting from disease. Methods The factors contributing to normal tear physiological function are considered, and the effect of changes in composition, as reported in the literature, is surveyed, with emphasis on the physical performance of the tears. Major classes of tear tests which would reveal functional changes are listed. Results Where possible, changes of measurable functions in disease are described. Gaps in our current knowledge are indicated. Conclusions Many techniques exist for examination and assessment of both normal and disease tears, but further development is needed to adapt some of these to clinical situations, and to make them more specific diagnostic tests.