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Proceedings Paper

Accuracy of two osmometers on standard samples: electrical impedance technique and freezing point depression technique
Author(s): Carlos García-Resúa; Hugo Pena-Verdeal; Mercedes Miñones; Jorge Gilino; Maria J. Giraldez; Eva Yebra-Pimentel
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Paper 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.

Paper Details

Date Published: 18 November 2013
PDF: 7 pages
Proc. SPIE 8785, 8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications, 8785ET (18 November 2013); doi: 10.1117/12.2030428
Show Author Affiliations
Carlos García-Resúa, Univ. de Santiago de Compostela (Spain)
Hugo Pena-Verdeal, Univ. de Santiago de Compostela (Spain)
Mercedes Miñones, Univ. de Santiago de Compostela (Spain)
Jorge Gilino, Univ. de Santiago de Compostela (Spain)
Maria J. Giraldez, Univ. de Santiago de Compostela (Spain)
Eva Yebra-Pimentel, Univ. de Santiago de Compostela (Spain)

Published in SPIE Proceedings Vol. 8785:
8th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and Applications
Manuel Filipe P. C. Martins Costa, Editor(s)

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