Surface activity of tear fluid in normal subjects.

PURPOSE

The stability of the precorneal tear film is commonly assessed by measurement of its break-up time. An alternative, but less studied, approach is measurement of the surface tension of tear fluid samples. The aim of this study was to develop a clinical method for measurement of the surface activity of tear fluid.

METHODS & RESULTS: Tear fluid was sampled from 20 normal subjects. Surface activity of the samples was measured on a Wilhelmy balance. Maximum and minimum surface tension of tear fluid samples was 71.5+/-1.3 mN/m and 46.6+/-3.8 mN/m, respectively. Surface tension was also recorded on solutions of bovine Meibomian lipids and bovine submaxillary mucin. The area/surface tension tracings obtained from solutions of lipids and mucin were qualitatively similar to those obtained from tear fluid samples. The effects of Meibomian lipids and mucin were additive.

CONCLUSION

The technique for measurement of the surface activity of tear fluid is minimally invasive and easy to use. The inter-individual differences in surface tension of tear fluid are small in normal subjects. The technique may be a useful supplement to measurement of break-up time in the evaluation of patients with dry eyes.