Background: The study sought to determine dynamic changes and theoretical bases of a clinical diagnostic test, the tear clearance rate.
Methods: Thirty four healthy subjects ranging in age from 22 to 84 years underwent examination of tear clearance rate, the Schirmer test with anaesthesia, as well as fluorophotometric measurement of tear turnover, tear volume, and tear flow. By applying 0.5% fluorescein into the conjunctival sac and subsequently measuring colour fades on a Schirmer strip, the tear clearance rate for assessing tear drainage was divided into nine grades. The results of the tear clearance rate were compared with those of the basal tear turnover and tear flow obtained from fluorophotometry.
Results: Significant relations were found between the tear clearance rate and the basal tear turnover or tear flow (r = 0.91 and 0.79, respectively, p = 0.0001). Considering the grades of progression from low to high, each grade of tear clearance rate showed a 12.5% increase in basal tear turnover (3.59%/min) and tear flow (0.38 microliter/min). There was no significant correlation between age and the basal tear turnover, tear volume, tear flow, or the tear clearance rate.
Conclusion: The tear clearance rate is proposed as a simple and useful way to estimate basal tear turnover and tear flow, and measure tear drainage indirectly.