Aim The aim of the study was to examine the possibilities of measuring tear osmolarity in a general clinical setting, and to identify the barriers preventing the uptake of new methodologies for its measurement.
Methods Five non-contact-lens wearers were recruited to evaluate the diagnostic capability of the TearLab. Three osmolarity measurements were taken at 1 min intervals in the morning at 09:00, midday between 12:00 and 13:00 and afternoon at 16:00 for two consecutive days. Forty more osmolarity measurements were carried out at different times on one subject with low and one subject with high tear osmolarity over 4 months. The osmolarity of a standard solution, 290 mOsm/l, was measured 19 times alternatively with the TearLab by two examiners.
Results Consecutive tear osmolarity readings in an individual varied up to 35 mOsm/l, but an average over three readings was found to be a reliable indicator of tear osmolarity at 95% confidence level. For population studies, a power analysis based on the variability of the data showed that three repeat measurements would be required to obtain reliable data for a study with <50 subjects, whereas one measurement would suffice for 490 or more subjects. There were no interobserver or interinstrumental differences, but readings obtained for the standard solution varied up to 89 mOsm/l.
Conclusion Three consecutive readings are required with the TearLab to obtain a reliable measure of tear osmolarity. The variation in recorded tear osmolarity makes it difficult to use the technique for the diagnosis of mild dry eye.
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Part of the work was presented at the 6th International Meeting of Tear Film and Ocular Surface Society, September 2010.
Funding Australian Government linkage project scheme no LP0776482 and the University of Western Sydney Seed Grant.
Competing interests None.
Ethics approval Ethics approval was provided by the University of Western Sydney Australia.
Provenance and peer review Not commissioned; externally peer reviewed.