To assess the interchangeability of tear osmolarity
measurements between electrical impedance and freezing-point depression osmometers and to analyze inter-eye tear osmolarity
variability measured with these osmometers in healthy subjects.
was measured using the TearLab osmometer
(OcuSense Inc., San Diego, CA) and the Fiske 210 microsample osmometer
(Advanced Instruments Inc., Norwood, MA). We randomly selected one eye in 50 subjects (29 women, 21 men; mean age, 33.16 ± 6.11 years) to analyze whether osmolarity
measurements by these osmometers were interchangeable. Both eyes of 25 patients (15 women, 10 men; mean age, 34.32 ± 6.37 years) were included to analyze inter-eye osmolarity
The mean tear osmolarity
values measured with the TearLab osmometer
were higher (305.22 ± 16.06 mOsm/L) than those with the Fiske 210 osmometer
(293.40 ± 12.22 mOsm/L), with the intraclass correlation coefficient being 0.23 (p = 0.051). A Bland-Altman plot showed that the systems were not interchangeable because there was a systematic difference, with the limits of agreement being −17.93 to 41.57 mOsm/L. There were no statistically significant differences (p = 0.5006 and p = 0.6533, respectively) between an individual’s eyes measured with either osmometer
Because the TearLab tear osmolarity
measurements were higher than those of the Fiske 210 measurements and the limits of agreement were too wide, the two osmolarity
values cannot be used interchangeably. In healthy subjects, there is no difference in tear osmolarity
between right and left eyes of the same individual measured with both instruments.