Assessment of tear film osmolarity using the TearLab osmometer in normal dogs and dogs with keratoconjunctivitis sicca.

OBJECTIVE

To evaluate repeatability and reproducibility of tear osmolarity measured using the TearLab osmometer in normal dogs and to assess its diagnostic potential in dogs with keratoconjunctivitis sicca (KCS).

ANIMALS STUDIED

Beagle dogs; six normal and five with KCS.

PROCEDURES

Tear osmolarity and Schirmer tear test-1 (STT-1) values were obtained at various times. Normal dogs were assessed for diurnal variation and repeatability and reproducibility of measurements. Dogs with KCS were evaluated before and after 5 months' topical twice-daily therapy with 2% cyclosporine.

RESULTS

Mean ± SD tear osmolarity (mOsm/L) was significantly higher in normal dogs (337.4 ± 16.2) than in dogs with KCS before therapy (306.2 ± 18.0; P < 0.0001), but not following therapy with 2% cyclosporine (330.5 ± 13.7; P = 1.00). Osmolarity readings lower than 325.5 mOsm/L were suggestive of KCS (84.8% sensitivity and 87.1% specificity). In normal dogs, tear osmolarity readings were stable during the daytime (P = 0.99). Repeated measurements revealed high variability and typically poor-to-moderate repeatability and reproducibility, although this was improved by taking three successive measurements at each session. Considering combined data from all dogs, a positive correlation existed between STT-1 and tear osmolarity measurements (Pearson's correlation test, P = 0.04, r = 0.62).

CONCLUSIONS

Canine tear osmolarity as determined by TearLab osmometer was variable, required multiple readings to be informative, and differed from values reported for humans. Dogs with KCS had a lower tear osmolarity than did normal dogs, and this increased following cyclosporine therapy.