Purpose: To investigate the influence of gravity and blink rate on lacrimal drainage capacity and to learn whether lacrimal pump function can be measured with the drop test.
Methods: The drop test for lacrimal drainage capacity was performed in 20 test subjects, aged 12 to 30 years. Drops of a known volume of lukewarm saline solution were repeatedly instilled in the tear film for 3 minutes. Excessive saline solution was then removed, and the volume drained by the lacrimal passages was calculated. The drop test was performed both with the nasolacrimal duct in a 45-degree position and with the nasolacrimal duct in a horizontal position. The drop test was performed two times in each position, with the individual reading and not reading. A lower blink rate was induced by reading.
Results: There was a high correlation between blink rate and lacrimal drainage when the nasolacrimal duct was in a horizontal position. The volume drained with each blink was approximately 2 microliters. However, when gravity acted upon the fluid in the lacrimal sac-nasolacrimal duct in the direction of the tear flow, the lacrimal drainage capacity showed a significant but variable increase, and there was no significant correlation between blink rate and lacrimal drainage capacity.
Conclusions: Lacrimal drainage capacity in young individuals was significantly affected by both blink rate and gravity. Lacrimal pump function can be measured quantitatively with the drop test.