The effect of collection technique on tear composition.

Selected proteins were quantitated after collecting samples of the tears by using two sampling techniques. Tears from the same individual were collected via absorption by Schirmer filter paper strip from the unanesthetized, inferior, conjunctival sac and were compared with tears collected by a capillary tube (taking care not to touch the conjunctiva), after stimulation of tearing by irritation of the nasal mucosa with ammonia vapor. Tear samples were quantitated immunochemically for two typical lacrimal proteins, lysozyme and lactoferrin, and three typical serum proteins, albumin, transferrin, and IgG. Tear analysis of all constituents were performed on a single sample of tears collected by each method from the same individual. Normal subjects without ocular pain or discomfort comprised a sample of 12 subjects ranging in age from 19 to 57 years and consisting of 9 men and 3 women. Concentrations of lysozyme and lactoferrin in samples collected by either method were not significantly different. In contrast, the concentration of albumin, IgG and transferrin collected by Schirmer filter paper technique was significantly higher (P < 0.01) than the concentration in tears collected by the capillary tube technique. A highly significant increase in serum proteins was seen when the Schirmer filter paper strip was used to collect tears compared to tears collected without mechanical stimulation of the conjunctiva. Invest Ophthalmol Vis Sci 25:374-377, 1984 The current availability of sensitive analytical techniques has stimulated interest in the identification, characterization, and quantitation of tear proteins. Accurate quantitation of proteins found in tear fluid is not only important in understanding the physiologic properties of tears, but also affords valuable diagnostic opportunities for the clinician. One of the basic requirements in this area of investigation is an appreciation of the effects of collection techniques on the concentration of tear constituents. A number of investigators have measured the total protein concentration and specific components of human tears. Values obtained vary widely, indicating that a number of variables are operative in the release of substances into the tear fluid as well as their concentration. Van Haeringen1 noted in his review of the clinical biochemistry of tears that many contradictory results could be traced back to differences in specimen collection, and he pointed out an essential difference between tear fluid collected by capillary tubes and absorbent material: namely, filter papers and cellulose sponges are more likely to have mucus and epithelial cells sticking to the surface, thus affecting results. Josephson and Lockwood 2 found that mild trauma to