Oxidative Stress Markers Induced by Hyperosmolarity in Primary Human Corneal Epithelial Cells
PURPOSE To analyze the effects of tear hyperosmolarity on conjunctival cells in mild to moderate dry eye. METHODS Sixty-eight subjects (35 females and 33 males, mean age 43, S.D. 20.3, range 18-87 years) with symptoms of dry eye were enrolled in the study. Patients with severe dry eye or any other condition that induces ocular inflammation were excluded. The sample was divided into two groups according to the tear osmolarity cut-off value of 308 mOsmol L(-1) measured in the right eye of each patient. Impression cytology of the temporal interpalpebral conjunctiva was performed and goblet cell density, nucleus diameter, cytoplasm diameter and nucleus/cytoplasm ratio of epithelial cells quantitatively assessed. A battery of tear tests (ferning test, tear break-up time and Schirmer I test) was also carried out in order to more completely describe the groups and understand the process. Analysis of variance (anova) was applied to establish cytological and tear differences between hyperosmolar and normal tear osmolarity eyes. Pearson's correlation was calculated between the cytological variables and tear osmolarity. RESULTS The normal tear osmolarity group included patients with symptoms of dry eye, grade 1-2 of squamous metaplasia, and a number of positive tear signs of dry eye ranging between 0 and 3. The hyperosmolar tear group included patients with symptoms of dry eye, grade 1-2 of squamous metaplasia with significantly lower values of nucleus diameter (F(1,66) = 4.3, p = 0.040), and a number of positive tear signs of dry eye ranging between 1 (hyperosmolar tear) and 4. Mean reflex secretion of tears was clearly normal in both groups but significantly lower (F(1,66) = 7.2, p = 0.009) in the hyperosmolar tear group. Significant correlations were established for tear osmolarity and goblet cell density (r(33) = 0.45, p = 0.006) and nucleus/cytoplasm ratio (r(33) = -0.44, p = 0.009) in the normal tear osmolarity group but not in the hyperosmolar tear group. CONCLUSIONS Mild to moderate hyperosmolar tear conditions seem to lead to an initial reduction of the conjunctival cell nucleus before the cytoplasm diameter showed a clear tendency to enlarge. The relationship between tear osmolarity and conjunctival cell characteristics seems to be linear only in the normal tear osmolarity group. These results also provide a plausible link between lower reflex secretion of tears and hyperosmolarity.