Hyperosmolarity of the tear film in dry eye syndrome

Hyperosmolarity of the tear film is recognized as an important pathogenetic factor in dry eye syndrome (DES). Hyperosmolarity testing has been hampered in the past by difficulties in tear collection and analytic procedures that required laboratory facilities. The Tearlab Osmolarity System is a new user-friendly tool that only needs tiny volumes for analysis and determines hyperosmolarity semi-automatically. We measured tear film osmolarity with the Tearlab in 200 healthy individuals and patients with DES. Dry eye diagnosis was established when > or =3 of the following criteria were fulfilled:(1) Ocular Surface Disease Index > 15; (2) staining of the cornea in the typical interpalpebral area; (3) staining of the conjunctiva in the typical interpalpebral area; (4) tear film break-up time < 7 s; (5) Schirmer test < 7 mm in 5 min; (6) the presence of blepharitis or meibomitis. Tear film osmolarity, as measured by Tearlab, did not show any correlation with the 6 clinical signs of dry eye. Moreover, tear film osmolarity testing could not discriminate between patients with DES (308.9 +/- 14.0 mosm/l) and the control group (307.1 +/- 11.3 mosml/l). Tear film osmolarity did not correlate to artificial tear use. Technical problems with the Tearlab, reflex tearing, or the difficulty in establishing a dry eye diagnosis with the recommended tests may account for these results. Further investigations are necessary before recommending this tool for daily clinical practice.