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.
Eye doctors at the Deutsche Ophthalmologischen Gesellschaft (DOG – German Ophthalmological Society) have discovered that on average, men cry up to 17 times a year and women 64 times. There are gender-specific differences in the reasons for the emotional tears: women tend to cry due to conflicts or losses, men due to empathy or splitting up. The fact that men cry less frequently is most probably rooted in socialisation and culture: while women express their feelings through their tears, men hold in their feelings and find ways of coping. They have trained themselves not to cry through self-discipline.
In cases of grief, anger or stress, crying serves as a relief and is found by many people to lift their mood. This has as yet not been confirmed by studies: we are physically tense during crying and the relaxation only starts when the cause of the tears 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.
How tears are formed
Our eyes constantly produce tears which evenly lubricate the surface of our eyes in the form of a tear film. Every minute between five and seven microlitres of fluid are secreted. The amount of fluid produced is increased many times over when crying or with watery eyes (epiphora) caused by eye irritation.
Various glands participate in the secretion of fluid. They take care of the different composition and substances in the tears. Alongside salts, tears contain oils and protein. Certain enzymes are responsible for the defence against germs, which could cause eye inflammation.
The tear film can break up if the natural productsion of tears or lubrication of the eye are disrupted. This leads to the typical symptoms of dry eyes such as itching, redness or burning.
Our tears form a three-layered tear film
The tear film, which coats our cornea, can be subdivided into three layers. The innermost layer, which directly coats the eye, is also 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 specialized cells, so-called goblet cells, which are located in the conjunctiva of the eye.
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 upper eyelid.
The outermost layer of eye lubrication is formed by a film of oil which is produced by the so-called meibomian glands. This oily layer or lipid layer prevents the lacrimal fluid from evaporating and stabilises the tear film.
Tear film performs important tasks
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, hormones and oxygen. Furthermore, it cleans the conjunctival sacs below the eyelid as well as the surface of the eye through the constant movement of fluid. 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 it positively influences eyesight.
The drainage of tears
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 located on the inside of the eye 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 conchae.
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 oily layer.
Ruptures in lubrication 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 is no longer adequate. The eye does try to counteract it and increases the productsion 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. Lubricating eye drops as well as eye ointments can provide relief as, on the one hand, they top up the volume of fluid and, on the other, improve the composition of the tear film.
Reasons for an altered tear film and dry eyes
Some 40-50 per cent of all patients who visit an eye doctor suffer from dry eyes. Medically, all symptoms which are caused by reduced lubrication of the surface of the eye are referred to as keratoconjunctivitis sicca or sicca syndrome. The reasons for too little or an altered composition of lacrimal fluid are many, for example existing general diseases such as diabetes mellitus, chronic rheumatism or inflammatory vascular diseases can lead to dry eyes. Various medicines such as the contraceptive pill, different antihistamines and antidepressants can cause lubrication dysfunctions in the eye.
The number of people who suffer from dry eyes has doubled in the last 20 years. The causes are environmental influences such as ozone exposure, exhaust fumes and dry air from heating. But the individual lifestyle of the patient can also encourage sicca syndrome: smokers and contact lens wearers have to contend more frequently with symptoms such as burning and itchy eyes. Furthermore, working for long hours at a PC, on a tablet or on a smartphone leads to a reduction in blinking which makes the eyes dry.
This helps with dry eyes
Anyone suffering from dry eyes should try to eliminate the causes as far as is possible. Maybe the medication for an existing primary disease needs to be changed. Hard contact lenses can be replaced with soft ones – hard contact lenses require a minimum amount of lacrimal fluid in order to be able to move on the tear film during blinking. In serious cases of sicca syndrome, it can therefore make sense to change to soft contact lenses or to completely forego using contact lenses. Talk to your doctor about this – they will suggest a suitable course of action for you. A change in lifestyle can also lead to an improvement in the lubrication of the eyes: avoid draughty or over-heated rooms, reduce the amount of time you work at a monitor and stop smoking.
If your doctor cannot determine a cause or if the cause cannot be eliminated (for example due to occupational requirements), the symptoms of sicca syndrome can be treated in a targeted way. Various artificial tears are available which can be given in the form of eye drops. For occasional symptoms, for example caused by working at a monitor, strong wind or smoke, eye drops with low viscosity such as HYLO-FRESH® are recommended whereas patients with constant, severe symptoms should use viscous products like HYLO-GEL®. It is imperative that artificial tears without preservatives are used as these substances can also damage the tear film. Wearers of soft contact lenses should also only use preservative-free eye drops such as the products in the HYLO® EYE CARE family as preservatives can build up on the contact lens and damage the cornea.
This is what you can do yourself!
There are some steps which you can take yourself in order to prevent burning or itchy eyes: ventilate your rooms several times a day and use air humidifiers in order to prevent dry room air. Avoid switching on the blower in your car and regularly change the filter in your car’s air-conditioning. In addition to that, sufficient amounts of fluids of at least two litres per day as well as a vitamin-rich diet and enough sleep ensure that the symptoms of dry eyes are alleviated.
1 Augenheilkunde, Grehn, 31st Edition, Springer Verlag