Gravity, blink rate, and lacrimal drainage capacity

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.

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.

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.

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.