Usefulness of Schirmer's tear strips and borosilicate glass tubes in chemical analysis of human tear fluid: A practical check in VEGF detection.

Abstract

Human tears contain a number of agents which may play an important role in diagnosing local eye disorders as well as systemic diseases. The small amount of fluid obtained during the collection and the consequent difficulty in analysing it are the main problems encountered in the diagnostic process. We decided to investigate the practical usefulness of two simple methods of collecting tear fluid for chemical analysis, i.e., glass tubes and Schirmer's strips. The substance analyzed was vascular endothelial growth factor (VEGF), a compound commonly recognized in ophthalmology. We used standard Schirmer's tear test and calibrated glass tubes for tear fluid collection in healthy volunteers. The standard ELISA assay was used to check the effectiveness of the tear sampling by estimating the VEGF level. The results of the study show that Schirmer's tear strip test is a more effective tool of the two. Moreover, using Schirmer's strips to obtain tear fluid was found to be more patient friendly and amounts of the tear fluid collected with that test were enough and better for the VEGF detection. Our study indicates that the widely used Schirmer tear test may be the best method of tear collection for chemical analysis. However, further studies on test calibration are needed.