Short-time reproducibility of tearfilm osmolarity measurement assessed with electrical impedance

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There is compelling evidence that increased tearfilm osmolarity is a key pathogenetic mechanism for the development of Dry Eye Syndrom (DES) and its related complications. The current study was performed to assess the short-time and day-to-day reproducibility of an electrical impedance based system for the measurement of tear film osmolarity.


20 patients with moderate DES and a control group of 20 age and sex matched healthy subjects were included in the study. Tear film osmolarity was measured using a commercially available electrical impedance based “lab on a chip” system (TearLab OcuSens). To measure short-time reproducibility 3 consecutive measurements were performed. To assess day-to-day reproducibility this procedure was repeated on three consecutive study days. Schirmer I test and break up time was performed on each study day. Coefficient of variation (CV) was calculated as a measure of reproducibility.


Tear film osmolarity was higher in patients with DES compared to healthy control subjects on all three study days (p<0.05). Short time CV of tearfilm osmolarity on the three study days was 3.18%±2.89%, 2.81%±2.08% and 2.23%±1.85%, respectively. Day-to-day variability based on the CV of the three study days was 3.47%±1.69%. As expected, Schirmer I test and BUT was lower in patients with DES compared to healthy subjects on all three study days (p<0.05).


Electrical impedance based measurements of tear film osmolarity show good short time and day-to-day reproducibility. Whether tear film osmolarity is a suitable clinical parameter to assess severity and to monitor treatment success in patients with DES has yet to be investigated.

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