Tear Fluid

Introduction

Tear fluid is a bodily fluid that is continuously produced and secreted by the tear glands located laterally above the two outer corners of the eye. By blinking regularly, the tear fluid is distributed and thus protects the eye from drying out.

Components of the tear fluid

Most of the tear fluid is produced in the lacrimal gland (Glandula lacrimalis), which is located above the eye. From there, it is channelled into the eye via 6 to 12 excretory ducts, where it can spread over the entire cornea through the blinking of the eyelid. It is not easy to say how much tear fluid is produced per day.

The values in the literature vary between 1 and 500 milliliters per day. The difficulty comes from the fact that the amount of tears produced depends on many different factors. Firstly, it varies with age: children and adolescents produce more tear fluid than adults.

There are also some external stimuli that stimulate the production of tears, including foreign bodies, cold and extreme emotions such as laughter and crying. In addition, tear production decreases sharply during the night, and during the day much more tear fluid is needed to be awake, which is why many people experience increased tear secretion even when yawning. The tear fluid that is formed flows through two dots in the inner corner of the eye (one above, one below) via two thin tubes into the lacrimal sac, which is located at the side of the nasal root.

From there, the liquid enters the nasolacrimal duct, which finally leads to the nasal cavity, where the secretion can finally drain away. With the help of the so-called Schirmer test, a doctor can estimate whether the production of tear fluid is occurring in an appropriate amount. For this purpose, a special paper strip is placed in the lower eyelid of the patient. After 5 minutes this is removed and measured again until where it has moistened. Values around 15 mm are normal, everything below 5 mm is considered pathological and should be further clarified.