In situ osmometry : validation and effect of sample collection technique

Gokhale, Moneisha, Stahl, Ulrike and Jalbert, Isabelle 2013, In situ osmometry : validation and effect of sample collection technique, Optometry and vision science, vol. 90, no. 4, pp. 359-365, doi: 10.1097/OPX.0b013e31828aaf10.

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Title In situ osmometry : validation and effect of sample collection technique
Author(s) Gokhale, Moneisha
Stahl, Ulrike
Jalbert, Isabelle
Journal name Optometry and vision science
Volume number 90
Issue number 4
Start page 359
End page 365
Total pages 7
Publisher Lippincott Williams & Wilkins
Place of publication Philadelphia, Pa.
Publication date 2013-04
ISSN 1040-5488
Keyword(s) tear osmolarity
in situ osmometer
vapor pressure osmometer
dry eyes
Summary Purpose: To compare tear film osmolarity measurements between in situ and vapor pressure osmometers. Repeatability of in situ measurements and the effect of sample collection techniques on tear film osmolarity were also evaluated.

Methods: Osmolarity was measured in one randomly determined eye of 52 healthy participants using the in situ (TearLab Corporation, San Diego, CA) and the vapor pressure (Vapro 5520; Wescor, Inc., Logan, UT) osmometers. In a subset of 20 participants, tear osmolarity was measured twice on-eye with the in situ osmometer and was additionally determined on a sample of nonstimulated collected tears (3 µL) with both instruments.

Results: Mean (SD) tear film osmolarity with the in situ osmometer was 299.2 (10.3) mOsmol/L compared with 298.4 (10) mmol/kg with the vapor pressure osmometer, which correlated moderately (r = 0.5, P < 0.05). Limits of agreement between the two instruments were -19.7 to +20.5 mOsmol/L. Using collected tears, measurements with the vapor pressure osmometer were marginally higher (mean [SD], 303.0 [11.0] vs 299.3 [8.0] mOsmol/L; P > 0.05) but correlated well with those using the in situ osmometer (r = 0.9, P < 0.05). The mean (SD) osmolarity of on-eye tears was 5.0 (6.6) mOsmol/L higher than that of collected tears, when both measurements were conducted with the in situ osmometer. This was a consistent effect because the measurements correlated well (r = 0.65, P < 0.05).The in situ osmometer showed good repeatability with a coefficient of repeatability of 9.4 mOsmol/L (r = 0.8, P < 0.05).

Conclusions: Correlation between the two instruments was better when compared on collected tear samples. Tear film osmolarity measurement is influenced by the sample collection technique with the osmolarity of on-eye tears being higher than that of collected tears. This highlights the importance of measuring tear film osmolarity directly on-eye. The in situ osmometer has good repeatability for conducting this measurement.
Language eng
DOI 10.1097/OPX.0b013e31828aaf10
Field of Research 111399 Ophthalmology and Optometry not elsewhere classified
Socio Economic Objective 929999 Health not elsewhere classified
HERDC Research category C1.1 Refereed article in a scholarly journal
Copyright notice ©2013, Lippincott Williams & Wilkins
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