Performance of tear osmolarity compared to previous diagnostic tests for dry eye diseases.

PURPOSE: Tear osmolarity is considered a key point in dry eye disease (DED) and its measurement is the gold standard in dry eye diagnosis. Tear osmolarity was evaluated in dry eye (DE) patients vs. a control group to assess its diagnostic performance compared to clinical and laboratory tests performed in either clinical or research settings.

METHODS: Tear osmolarity was measured with the TearLab Osmolarity System (OcuSense) in 25 normal subjects and 105 DE patients (severity score 1-4, Dry Eye Workshop (DEWS)). The following tests were also performed: Ocular Surface Disease Index (OSDI) symptoms questionnaire, Schirmer I test, Tear Film Break Up Time (TFBUT), ferning test, lissamine green staining, tear clearance, corneal esthesiometry, and conjunctival cytology by scraping and imprint. Statistical evaluation was performed by unpaired Student's t and Mann-Whitney tests, the Spearman's rho and the Pearson's r correlation coefficients (significance p < 0.05); all variables were also analyzed for sensitivity, specificity, Receiver Operating Characteristics (ROC) curves, likelihood ratio LR+, and positive predictive value (PPV).

RESULTS: Tear osmolarity normal values were 296.5 +/- 9.8 mOsm/L, increasing values were shown stepwise DE severity (mild to moderate to severe dry eye, respectively: 298.1 +/- 10.6 vs. 306.7 +/- 9.5 vs. 314.4 +/- 10.1, p < 0.05). A progressive worsening occurred in all the parameters with DED severity increase. Tear osmolarity exhibited the larger correlation strength vs. tear clearance, TFBUT and clinical score, strength increased with DED severity, mainly to inflammatory score and corneal sensitivity. Tear osmolarity 305 mOsm/L was selected as cut-off value for dry eye, 309 mOsm/L for moderate dry eye, 318 mOsm/L for severe dry eye (Area-Under-the-Curve was 0.737, 0.759, and 0.711, respectively).

CONCLUSIONS: Tear osmolarity can now be considered a test suitable to be performed in a clinical setting. It showed a good performance in dry eye diagnosis, higher than the other tests considered, mainly in severe dry eye. Tear osmolarity values should be interpreted as an indicator of DED evolutionary process to severity.