As far as is known, the human being is the only creature that is capable of crying due to emotions. In so doing, our eyes suddenly produce so much lacrimal fluid that the eyes at first become watery and the fluid then rolls down the cheeks in thick tears.
Why and how often do people cry?
Eye doctors from the German Ophthalmological Society have discovered that, on average, men cry up to 17 times per year, women 64 times. There are also gender-specific differences for the reasons for the emotional tears: women cry more in conflict situations or when they lose something, men out of empathy or in situations of separation. The fact that men cry less frequently probably has its roots in socialisation and culture: while women give expression to their feelings when they cry, men turn their emotions inward and consider strategies for action.
As such, crying due to bereavement, anger or stress provides relief and many people find it to be mood-lifting. However, studies have been unable to prove this to-date: when we cry our bodies are tensed up, the relaxation only starts when the reason for the crying has passed.
Aside from crying, our eyes constantly produce a certain amount of lacrimal fluid. This is necessary for the even lubrication of the eye with fluid and has a different composition from tears which are produced from joy or sadness. For example, emotional tears contain a larger amount of hormones, such as messenger substances (pheromones), which we can unconsciously detect through our sense of smell: Alongside the happy hormone serotonin, female tears have been proven to also contain the milk-forming hormone prolactin.
How tears are formed
Our eyes constantly produce tears which evenly lubricate the surface of our eyes in the form of a tear film. The lacrimal fluid is mainly produced in the lacrimal glands. Together with small glands in the eyelid margin, they cater for the different composition and for the ingredients in the tears. Alongside salts, tears contain oils and protein. Certain enzymes are responsible for the defence against germs which could cause eye inflammation.1
You blink every five to ten seconds, which means that five to seven microlitres of fluid are secreted per minute. The amount of fluid produced increases when crying or in the case of watery eyes (epiphora), caused by eye irritation.
The tear film can break up if the natural production of tears or lubrication of the eye are disrupted. This leads to the typical symptoms of dry eyes such as itching, redness or burning.
What does the tear film consist of?
The tear film, which coats our cornea, can be subdivided into three layers. The innermost layer, which directly coats the eye, is called the mucin layer. It contains proteins and sugars and has a slimy consistency. It enables the adherence of the tear film to the surface of the eye. The mucin layer is produced by the so-called goblet cells, which are located in the conjunctiva of the eye.1
The middle layer, directly on top of that, constitutes 90% of the body of the tear film. This watery layer contains oxygen and nutrients as well as various enzymes. It is formed by the lacrimal glands which are located in the eye socket above the eyeball.
The outermost layer of the tear film is formed by a film of oil which is produced by the so-called meibomian glands. This so-called lipid layer prevents the lacrimal fluid from evaporating and stabilises the tear film.
What tasks does the tear film perform?
The tear film fulfils many important tasks at the same time: it protects the surface of the eye, in particular the cornea, from drying out and supplies it with nutrients and oxygen. In addition to that, blinking cleans the surface of the eye. In addition to that, tears provide a physical barrier against germs and also fight them with special enzymes. The tear film is also very important for our vision as an undamaged tear film is crucial to seeing sharply.
How are tears transported away?
Because new lacrimal fluid is constantly produced, a part of the fluid has to be removed again. For this there are small openings in the skin on the eyelid margins of the upper and lower eyelids, in the inner corner of the eye next to the nose, called the upper and lower lacrimal points. They drain the surplus fluid and guide it through small passages – the tear ducts and the tear sacs – directly into the nasal cavity.1
Ruptures in the tear film and dry eyes
If there is not enough lacrimal fluid or the composition of the tears is not optimal, it can happen that the tear film breaks up. On the one hand, this occurs when there is not enough liquid in the middle, watery layer or if there is a lack of oily elements in the lacrimal fluid which are required for the stable formation of the outer lipid layer.
Ruptures in the tear film lead to the eye being more easily irritated by foreign bodies or natural blinking. The protective function of the tear film is thus suspended and the supply of oxygen and nutrients to the cornea may no longer suffice. The eye does try to counteract it and increases the production of tears. However, the number of additional tears is not always enough or the tear film is unstable because of deficiencies in its composition. Symptoms such as burning, itching or foreign body sensation in the eye can occur.
Reasons for changes in the tear film and dry eyes
Some 40 to 50% of all patients who visit an eye doctor are suffering from dry eyes. Medically speaking, all symptoms which are caused by reduced lubrication of the surface of the eye are called keratoconjunctivitis sicca or sicca syndrome. The reasons for too small an amount of, or a changed composition of, the lacrimal fluid are varied, e.g. an existing general disorder such as diabetes mellitus, chronic rheumatism or inflammatory vascular diseases can lead to dry eyes. Different medicines such as the contraceptive pill, miscellaneous antihistamines and antidepressants can trigger lubrication dysfunctions of the eye.
In the last 20 years, the number of people suffering from dry eyes has doubled. The reasons given are environmental influences such as ozone load, exhaust fumes and dry air from heating. But the individual lifestyle of the patients can also encourage sicca syndrome: smokers and contact lens wearers have to battle significantly more frequently with symptoms such as burning and itchy eyes And: working for hours on end at a PC, tablet and smartphone leads to reduced blinking, which can lead to dry eyes.
This helps with dry eyes
Anyone suffering from dry eyes should try to eliminate the causes as far as is possible. It may be possible that the medication for a pre-existing underlying disease may have to be adjusted, or the position or the material of the contact lenses be checked, as these require a minimum amount of lacrimal fluid in order to be able to move on the tear film when blinking. In difficult sicca syndrome cases, it could therefore make sense to change to soft contact lenses or to stop wearing contact lenses altogether. Your doctor will provide you with a suitable procedure if you consult him. A change in lifestyle can also contribute to an improvement in lubrication of the eye: avoid draughty or over-heated rooms, reduce the amount of work at a monitor and stop smoking.
If your doctor cannot find a reason or if one cannot be eliminated (e.g. due to professional demands), the symptoms of sicca syndrome can be treated in a targeted way. Various artificial tears are available which are applied in the form of eye drops. For occasional symptoms, such as those caused by working at a monitor, strong wind or smoke, eye drops with a low viscosity, such as HYLO FRESH® are recommendable, while patients with constant, severe symptoms should turn to remedies with a higher viscosity like HYLO GEL®. Only artificial tears without preservatives should be used, as these substances can damage the tear film or the surface of the eye. Also, people who wear soft contact lenses should only use eye drops without preservatives, such as the products in the HYLO EYE CARE® family, as preservatives could accumulate in the contact lenses and damage the cornea.
This is what you can do yourself!
You can take some steps yourself to prevent burning and itchy eyes: ventilate several times a day and use air humidifiers to avoid dry ambient air. Avoid switching on the blower in your car and change the filter in your car air-conditioning on a regular basis. Additionally, consumption of sufficient amounts of fluids, at least two litres per day, as well as a vitamin-rich diet and sufficient sleep ensure that the symptoms of dry eyes are alleviated.
1 Augenheilkunde, Grehn, 31st Edition, Springer Verlag