A person’s tear flow is a natural and important process. The healthy function of tear formation is of considerable importance not only for physical health, but also for mental health.
What is tear flow?
Tear flow is generally understood to be the formation of a mirror-like tear film that stretches protectively over the cornea of the eye. Tear flow is generally understood to be the formation of a mirror-smooth tear film that stretches protectively over the cornea of the eye. Tear fluid is continuously produced by the lacrimal glands and Kraus’ and Wolfring’s glands, which are called accessory glands. The secretion contains enzymes, ions, lipids, ketone bodies, serum proteins, and other components that are distributed over the eyeball by eyelid movements. Removal occurs by flow through the nasolacrimal ducts into the nasal cavity. A much smaller portion of the secretion evaporates. Tear flow is most commonly associated with crying, which reflexively secretes a larger amount of the lacrimal secretion from the lacrimal apparatus. Crying is either triggered by physiological stimuli as a protective measure or occurs in response to a strong emotional stimulus. The normal extent of tear production can be tested by the so-called Schirmer test. A strip of special paper is clamped into the lower crease of the eyelid for five minutes, where it absorbs the fluid. It can then be determined whether the value is within the normal range.
Function and task
The film of tear fluid ensures sharp projection of light rays onto the retina of the eyes and is therefore an important factor in visual acuity. Corneal desiccation is prevented by permanently distributing the secretion over the cornea. This distribution takes place through the blinking of the eyelids, which is colloquially referred to as winking or blinking. A person blinks an average of 10 to 15 times per minute, whereby his or her eyelids usually close and open again reflexively, unnoticed and involuntarily, at a very rapid pace. During this process, the tear fluid prevents the eyelids from rubbing against the eyeballs. When the glands produce more lacrimal secretions, which are flushed over the edge of the eyelid, this serves to protect the body. Foreign bodies and highly irritating substances, such as the essential oils of an onion or a speck of dust, are flushed out of the eye. The signal for increased production of the required tear fluid is reported by the sensory cells on the eye conjunctiva via biochemical messengers to the parasympathetic nervous system. This part of the brain then triggers the glands to massively produce secretion, which disinfects the eye with the lysozyme it contains. The extremely complex process of reflex crying serves to preserve vision. Crying as a form of emotional expression produces tears that are enriched with hormones such as prolactin and endorphins, as well as proteins, potassium and manganese. Numerous studies address the question of whether this should be interpreted as a sign of an attempt by the body to detoxify. There is no consensus on this thesis so far. However, it is a fact that emotional crying is mostly perceived as psychologically relieving. In addition, it serves the social interaction and communication. In this context, the ability of an infant to gain the attention of its caregiver by crying should be mentioned in particular. The extent to which the ability to cry is retained into adulthood depends largely on upbringing, since learned experiences are stored in the cells of the cerebellum.
Diseases and disorders
If the flow of tears is disturbed, this inevitably leads to physical and emotional impairment of well-being. Dry eyes cause irritation of the eye due to friction during blinking. An incessant foreign body sensation can result, which in turn can trigger increased blinking. The protective function is diminished and the eye is susceptible to infection because the germ-killing effect of the tear fluid is missing. Even vision may be impaired if the glands do not produce enough secretion. If the eyes are too dry because the permanent tear production does not work, reflexive crying often sets in, because the conjunctiva perceives the irritated state of the eye and initiates the process of massive tear production. Consequently, dry eyes and excessively watery eyes are not mutually exclusive.The cause of watery eyes should always be sought first. If an ophthalmologist finds an underlying disease or causative injury, it should be treated by a specialist. Common triggers for dry or watery eyes include allergies, the use of certain medications, conjunctivitis, irritants such as cigarette smoke, or excessive screen use. Less frequently, diseases such as gout, asthma, diabetes or thyroid disorders are the cause. Anatomical peculiarities also come into consideration. In rare cases, the lacrimal ducts may be narrowed and have to be opened surgically. The lacrimal glands may even become inflamed or form tumors due to infection or systemic disease. Inflammation can also develop in those lacrimal sacs that are located at the inner corner of the eye and open into the nasolacrimal ducts. Many people who have undergone eyelid correction later suffer from dry eyes. The tear ducts with the so-called lacrimal puncta are extremely sensitive and should not be manipulated if possible. Seeing a specialist in ophthalmology is always advisable when eye complaints occur. The specialist will make the diagnosis and initiate the necessary therapy.
