What Do You Know About The Composition Of Tears?

The normal tear volume is estimated to be about 6 micro liter in each eye, and the average rate of turnover about 1.2 micro liter/min. When collected with minimal trauma, tear fluid contains a high concentration of proteins. Three fractions are demonstrable by paper electrophoresis: albumin, globulins, and lysozyme. The antimicrobial activity of the tears is in the gamma globulin and lysozyme fractions.

The gamma globulins found in the normal tear fluid are IgA, IgG, and lgE. The IgA predominates and is similar to the IgA found in other body secretions bathing mucous membrane surfaces such as saliva and the bronchial, nasal, and gastrointestinal secretions. The IgA found in tears differs from serum IgA, however, and is more concentrated. In certain allergic conditions such as vernal conjunctivitis, the IgE concentration of tear fluid increases. Lysozyme may act synergistically with IgA in causing lyses of bacteria.

Although lysozyme is known to have a lytic effect on certain bacteria, its absence does not necessarily increase the risk of infection. Reduction in tear lysozyme concentration usually occurs early in the course of Jorgen's syndrome and is considered helpful in the diagnosis of that disorder.

If collection of the tear fluid is traumatic, the normal constituents of the tears may be altered and there may be transudation of substances from the conjunctiva blood vessels. In certain inflammatory conditions of the conjunctiva, there is marked transudation of immunoglobulin directly from the blood to the tear fluid.