Abstract
The aim of this project was to increase the knowledge on the function of the lacrimal passages. For this purpose, a quantitative test for the lacrimal drainage function is established: the drop test. Two principal parameters are introduced: the lacrimal drainage capacity and the blink output. In the drop test, drops of lukewarm saline of a known volume, usually 15 microliter, are repeatedly instilled into the tear film. After three minutes, the excess fluid is removed with a blood capillary tube and measured. The drained volume per three minutes can thus be calculated and is termed the lacrimal drainage capacity (drained volume/time). By positioning the nasolacrimal canal in a horizontal position, the influence of gravity can be neutralised and the test focused on the active drainage caused by blinking. Thus, the blink output (drained volume/blink) can be calculated.
The lacrimal drainage capacity was found to be a specific, sensitive and reliable parameter for the lacrimal drainage function. In normal subjects, the lacrimal drainage capacity greatly exceeds the tear production. The lacrimal drainage capacity decreases with increasing age.
With the drop test it could be shown that the principal forces responsible for the lacrimal drainage are blinking and gravity. With each blink approximately 2 microliter of fluid can be drained in young persons. The blink output could be decreased by injection of botulinum toxin A into the medial parts of the eyelids. Botulinum toxin injection increased wetness and eye comfort in patients with dry eyes.
The drop test is useful for evaluation of the lacrimal drainage function and it has provided new insights in the physiology of lacrimal drainage.
