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Lionel Sebbag, Shin Ae Park, Philip H Kass, David J Maggs, Christopher J Murphy; Tear film osmolarity measurements using the TearLabTM osmometer in normal dogs and dogs with dry eye disease. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1967.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate utility, repeatability, and reproducibility of tear osmolarity measurements using the TearLabTM osmometer in normal dogs and its diagnostic potential in dogs with dry eye disease (DED).
Eleven beagles were included: six normal and five dogs with DED. At various time points, osmolarity readings were collected with the TearLabTM by two examiners. Normal dogs were examined for diurnal variation, effect of tear dilution with phosphate buffered solution (PBS), and repeatability and reproducibility of measurements, while DED dogs were evaluated for response to therapy using twice-daily topical 2% cyclosporine. Schirmer tear test-1 (STT-1) was performed in all dogs.
Mean ± SD tear osmolarity (mOsm/L) was significantly higher in normal dogs (337.4 ± 16.2) than dogs with untreated DED (306.2 ± 18.0; p < 0.0001), but not compared to treated DED dogs (330.5 ± 13.7; p = 1.00). Osmolarity readings lower than a cutoff value of 325.5 mOsm/L are suggestive of DED (ROC curve; 84.8% sensitivity and 87.1% specificity). In normal dogs, tear osmolarity readings were stable during the daytime (one-way ANOVA, p = 0.99). No significant change in tear osmolarity was detected after PBS instillation (one-way ANOVA, p = 0.11). Repeated measurements revealed high variability and overall poor to moderate repeatability and reproducibility (wide 95% limits of agreement, intraclass correlation coefficients < 0.75), although this was improved by taking three successive measurements at each session. A positive correlation existed between STT-1 and tear osmolarity measurements of all dogs combined (Pearson’s correlation test, p = 0.04, r = 0.62).
The TearLabTM osmometer was easily used and well tolerated by dogs. Testing tear osmolarity may be an effective objective tool in the diagnosis and management of canine DED, although results may be confounded by the large variability in repeated measurements.
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