Aspects on the lacrimal drainage function

<p>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.</p><p>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.</p><p>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.</p><p>The drop test is useful for evaluation of the lacrimal drainage function and it has provided new insights in the physiology of lacrimal drainage.</p>