Sialic acid in normal human tear fluid.

PURPOSE We measured the concentration of sialic acid, the terminal component of mucin, in normal diluted human tears. METHODS Twenty-microliter tear samples were collected from 31 healthy volunteers (average age = 50.7 years) using micropipette after 50 microL instillation of saline. We investigated the correlation of concentration between glycoprotein and sialic acid and the difference between the right and the left eyes, as well as the reproducibility of the sampling procedure. RESULTS There was significant correlation of the concentration between glycoprotein and sialic acid (right eye: r = 0.952, P <.0001; left eye: r = 0.976, P <.001). There was no significant difference in concentration between the right and the left eyes. Also, the reproducibility was considered acceptable in three measurements of sialic acid using the present procedure. The sialic acid concentration in normal diluted tears was 37.1 microg/mL on average. CONCLUSION Our data indicates that sialic acid concentration is an indicator for the concentration of glycoprotein and that this method of measurement is applicable to the analysis of mucin-deficient disorders.