Accuracy of two osmometers on standard samples: electrical impedance technique and freezing point depression technique

Carlos García-Resúa; Hugo Pena-Verdeal; Mercedes Miñones; Jorge Gilino; Maria J. Giraldez; Eva Yebra-Pimentel

doi:10.1117/12.2030428

18 November 2013 Accuracy of two osmometers on standard samples: electrical impedance technique and freezing point depression technique

Carlos García-Resúa, Hugo Pena-Verdeal, Mercedes Miñones, Jorge Gilino, Maria J. Giraldez, Eva Yebra-Pimentel

Author Affiliations +

Proceedings Volume 8785, 8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications; 8785ET (2013) https://doi.org/10.1117/12.2030428
Event: 8th Ibero American Optics Meeting/11th Latin American Meeting on Optics, Lasers, and Applications, 2013, Porto, Portugal

Abstract

High tear fluid osmolarity is a feature common to all types of dry eye. This study was designed to establish the accuracy of two osmometers, a freezing point depression osmometer (Fiske 110) and an electrical impedance osmometer (TearLab™) by using standard samples. To assess the accuracy of the measurements provided by the two instruments we used 5 solutions of known osmolarity/osmolality; 50, 290 and 850 mOsm/kg and 292 and 338 mOsm/L. Fiske 110 is designed to be used in samples of 20 μl, so measurements were made on 1:9, 1:4, 1:1 and 1:0 dilutions of the standards. Tear Lab is addressed to be used in tear film and only a sample of 0.05 μl is required, so no dilutions were employed. Due to the smaller measurement range of the TearLab, the 50 and 850 mOsm/kg standards were not included. 20 measurements per standard sample were used and differences with the reference value was analysed by one sample t-test. Fiske 110 showed that osmolarity measurements differed statistically from standard values except those recorded for 290 mOsm/kg standard diluted 1:1 (p = 0.309), the 292 mOsm/L H₂O sample (1:1) and 338 mOsm/L H2O standard (1:4). The more diluted the sample, the higher the error rate. For the TearLab measurements, one-sample t-test indicated that all determinations differed from the theoretical values (p = 0.001), though differences were always small. For undiluted solutions, Fiske 110 shows similar performance than TearLab. However, for the diluted standards, Fiske 110 worsens.

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Carlos García-Resúa, Hugo Pena-Verdeal, Mercedes Miñones, Jorge Gilino, Maria J. Giraldez, and Eva Yebra-Pimentel "Accuracy of two osmometers on standard samples: electrical impedance technique and freezing point depression technique", Proc. SPIE 8785, 8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications, 8785ET (18 November 2013); https://doi.org/10.1117/12.2030428

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