Sialic Acid in human tear fluid decreases in dry eye

To evaluate the association between tear mucin and dry eye, we compared tear fluid sialic acid concentration in dry eye patients with that in normal volunteers. We also compared the sialic acid concentration with the results of several different types of dry eye examinations.

Subjects comprised 16 age-matched, normal healthy controls and 45 dry eye patients. Dry eye examinations included fluorescein staining, rose bengal staining, Schirmer I test, cotton thread test, and fluorescein breakup time. Tear samples were collected with a micropipette after the instillation of 50 microl saline. The sialic acid concentration was measured by high-performance liquid chromatography.

The sialic acid concentration was significantly lower in the dry eye group (5.3 +/- 4.3 microg/ml) than in the control group (37.1 +/- 28.3 microg/ml) (P < 0.001). Also, the sialic acid concentration correlated significantly with the results of dry eye examinations (P < 0.0002).

The different sialic acid levels in the control and dry eyes may imply differences in the quantity or quality of glycoprotein in tears between these two groups. Thus, sialic acid, a component of mucin, may play a key role in the dry eye condition.