TEAR FLOW AND EVAPORATION IN PATIENTS WITH AND WITHOUT DRY EYE

Purpose: To evaluate the steady-state tear flow and evaporation from t he ocular surface of patients with and without dry eye. Methods: Two g roups of patients, 21 with dry eye and 34 without dry eye, with simila r age distributions were selected by criteria based on tear osmolarity , Schirmer test, meibomian gland loss, and dry eye symptoms and were c ompared for tear flow, tear volume, percent turnover, and surface evap oration. Results: Tear flow averaged 0.10 +/- 0.08 mu l/minute in pati ents with dry eye versus 0.15 +/- 0.12 mu l/minute in patients without dry eye (P = 0.002), Tear volume averaged 2.13 +/- 1.3 mu l in patien ts with dry eye versus 2.23 +/- 2.5 mu l in patients without dry eye ( P = not significant) and tear turnover averaged 5.3 +/- 2.9% in patien ts with dry eye versus 8.2 +/- 4.3% in patients without dry eye (P = 0 .019). Evaporation averaged 25 +/- 35 X 10(-7) g/cm(2)/second in patie nts with dry eye versus 13 +/- 6 X 10(-7) g/cm(2)/second in patients w ithout dry eye (P = 0.003). Conclusions: Measured tear flow was signif icantly lower than previously determined in patients with and without dry eye. Evaporation was increased in patients with dry eye and accoun ted for the majority of the tear loss in patients with dry eye. Normal tear osmolarity can be maintained, even with low tear flow, if evapor ation is kept within the normal range.