Drops of glaucoma cause dry eyes
Glaucoma and dry eye
Misfortunes never come singly. Unfortunately, this old (truism) wisdom applies to many glaucoma patients. Because numerous people suffering from glaucoma have another eye problem: the dry eye, also called sicca syndrome or lack of tears.
Dry eye is one of the diseases that patients complain about the most in the ophthalmologist's office. Dry eye is common in the elderly and women are generally more likely to suffer from dry eyes than men, which is often hormonally related, for example taking the pill or hormone fluctuations during menopause. Allergies, diabetes, thyroid diseases, acne and neurodermatitis, as well as rheumatic diseases are often associated with this disease.
Compared to glaucoma, it is far safer and is only associated with a slight impairment of visual performance in very extreme cases. Nevertheless, the dry eye is very uncomfortable because it is associated with burning, itching and redness of the eyes. Feelings of dryness and foreign bodies can occur, the eyelids can become heavy and tired, and in some cases eyelid edema and inflamed eyelid margins develop. Paradoxically, it is also sometimes associated with increased tear discharge, something you would not initially expect from this disease because of its name. Tear discharge is due to the fact that the tear fluid is not distributed properly over the eye, but runs off directly.
Why the tear film is so important
The outermost layer of our eyeball is probably the most inconspicuous: the tear film. Its job is to keep the very sensitive cornea moist. When this moisture is lacking, the normally clear cornea becomes cloudy. The blink of an eye distributes the tear film and thus keeps the cornea evenly moist. In addition, the tear film is a first barrier against things that we do not want to see: dust particles, allergens, bacteria. Against the latter, for example, the tear film has a protein, the lysozyme, that can dissolve bacteria - in a more natural way than an antibiotic. If the tear film is disturbed, the eye is threatened with a variety of damage. This can already be the case when the tear film is still present but its composition is disturbed.
Our tears - a difficult composition
Although the tear film is only about 10 micrometers (i.e. only a hundredth of a millimeter) thick, it consists of three very different layers. The outermost layer is very fatty (lipid layer) and is formed by glands in the edge of the eyelid, the so-called meibomian glands. The middle layer makes up the largest part of the tear film, it is watery and is produced by the tear gland. The innermost layer lying directly on the cornea is called the mucin layer - mucins are substances similar to mucus. Cells of the conjunctiva are responsible for their production.
The fact that three different anatomical segments of the eye contribute to the production of the tear film makes it clear how delicate the balance of the individual components is - and gives an idea of how susceptible this fine system is.
The reason and course of this "evil" can be explained quickly and easily: The eye is not sufficiently wetted because either too little tear fluid is produced or the composition of the tear fluid is not as it should be.
The tear fluid is mainly produced by the main lacrimal gland and is primarily used to care for and protect the cornea, which must be cleaned and prevented from drying out from the outside. The cornea is a very special structure that is not supplied directly by blood vessels but from the inside via the aqueous humor.
A tear film is placed on the eye with every blink of the eye. The tear film usually lasts for more than 10 seconds, then it tears, usually not before the next blink of an eye. If the composition of the tear fluid is changed or influenced by other influences, the tear film break-up time is reduced to values that can be less than 5 seconds. There are therefore more situations in which the epithelium is directly exposed to the influences of the outside world and dry spots appear on the cornea, so-called "dry spots".
The ophthalmologist can determine such dry spots through simple tests, e.g. by coloring the tear film with fluorescein, and can also measure the tear film break-up time. The following figure shows an image of the eye, the dry areas (dark) were made visible by staining.
Dry spots visible through staining
The healthy tear film consists of three liquid layers. With the inner thin layer of mucus, the mucin layer, the tear film adheres to the cornea and conjunctiva. The middle layer is the thickest, it is watery and contains antibodies and germicidal substances. A very thin layer of fat floats on top, which is produced by the sebum and sweat glands of the eyelid rims. This stabilizes the tear film and gives it the necessary surface tension. It ensures that the film does not tear open and the tear fluid runs off over the edge of the eyelid and it prevents the watery layer from evaporating too quickly. It can be examined whether the fat layer is too thin or whether there are other impairments of the tear film.
In most cases, however, the cause of dry eye is not found and therapy is limited to symptom relief. Adequate wetting can be restored by closing the tear points, which are two places on the upper and lower edge of the eyelid where the tear fluid drains through channels into the lacrimal sac. On the other hand, tear substitutes, so-called "artificial tears", can be dripped. More or less fluid preparations or ointments are available for different degrees of severity.
In addition, the patient should make sure that he drinks enough, that the living space is well ventilated, that humidifiers are used if possible and that fans and blowers are kept away. Refraining from cigarettes, eating a vitamin-rich diet and getting enough sleep alleviate the symptoms. Filters in car air conditioning systems should be cleaned regularly.
Eye drops that are used several times must contain a preservative in accordance with the legal requirements in order to prevent the drops from being contaminated with germs: Benzalkonium chloride (BAC) is the most common of these preservatives. The fact that it can have a toxic effect on the fine anatomical structures of the eye was first described in the 1940s. Nevertheless, it is usually well tolerated when taken for a short time - for example as a component of anti-inflammatory eye drops, such as those instilled in conjunctivitis for a few days. A glaucoma patient, however, has to use eye drops every day for many years - and until alternatives appear, exposes his conjunctiva, cornea and tear film to permanent contact with this potentially cell-damaging (cytotoxic) substance. Today, many ophthalmologists are certain: whatever discomforts glaucoma patients may have after instilling their drops, whether burning, stinging, redness or a foreign body sensation, does not come from the actual active substance - the beta blocker, the prostaglandin, the carbonic anhydrase inhibitor, but should mostly be due to the preservative.
BAC can have a damaging effect on various cell types on the surface of the eye. Signs of inflammation and swelling of these cells were observed on the epithelial cells of the cornea, and the contacts between these cells can also be loosened by BAC. Laboratory tests on the conjunctiva showed that the number of goblet cells decreased depending on the BAC concentration supplied - i.e. those cells that are responsible for the production of one of the three components of the tear film, the mucin layer. But BAC also has a highly detrimental effect on the aqueous layer, the main component of the tear film: the preservative promotes increased evaporation of this layer.
Regardless of the cell-damaging effects, BAC and the other preservatives in eye drops can trigger an allergic reaction. For ophthalmologists, the problems caused by preservatives are one of the main causes of the Achilles' heel of medical glaucoma therapy: non-compliance. This is understood to mean non-compliance with the doctor's prescription - if glaucoma patients do not instill their drops regularly - or not at all - for fear of symptoms. And thereby endanger your optic nerve.
“Thanks” to preservatives: worse prognosis for surgery
As described elsewhere by glaukom.de, the essential goal of glaucoma therapy, the (possibly permanent) lowering of intraocular pressure, can often be achieved with an operation. However, if an eye has been exposed to preservatives such as BAC for years, chronic damage to the cells of the conjunctiva is often present. However, their function is a prerequisite for good postoperative wound healing, especially after trabeculectomy, which is still the “gold standard” in glaucoma surgery. Some experts see a negative correlation between the duration of a BAC-containing pressure-lowering therapy and the success of the operation. In simple terms: the longer the surface of the eye has been exposed to BAC and other preservatives, the lower the chance of a lasting success of the glaucoma operation. BAC causes chronic inflammatory conditions on the surface of the eye, which after a fistulating glaucoma operation such as trabeculectomy lead to excessive scarring - and thus ruin the success of the operation.
Preservative-free eye drops in glaucoma therapy
A number of studies have now shown that certain glaucoma medications in an unpreserved form are just as good at reducing intraocular pressure as with a preservative. For years the argument in favor of the BAC was used that this preservative makes the penetration of the active ingredient into the eye and thus its therapeutic success possible in the first place - the breaking of the bonds between the cells of the cornea works like a “door opener” and promotes the Penetration of the actual drug into the eye. Prostaglandins are now also available without preservatives.
Those who particularly benefit from not using preservatives
Patients with dry eyes should generally avoid using preservatives. This is especially true if, in addition to the glaucoma drug, you also take artificial tears (of course, if possible, also unpreserved). In addition, preservative-free preparations are also advisable for those patients who are likely to have to take a large number of eye drops over the years. On the one hand, these are patients who apply several different preparations daily and, on the other hand, young patients - for whom it is foreseeable that they will have to drip for many years and for whom damage to the tear film, conjunctiva and cornea should be avoided as far as possible.
How glaucoma patients can live with their dry eye
Since the use of eye drops is the therapy of choice for the majority of glaucoma patients, the use of completely Preservative-free drops are perhaps the greatest chance to get the tear film problem under control and to improve the symptoms.
In addition to doing without BAC and other preservatives, support for the tear film is usually indispensable. There is a large selection of tear substitutes (“artificial tears”) based on various substances such as polyvinyl alcohol, sodium hyaluronate and methyl cellulose. It is also very important here, as with the choice of glaucoma medication: these preparations should be used in a preservative-free version, otherwise you will end up in a vicious circle. For particularly severe cases of dry eye, there are other options such as the use of anti-inflammatory drugs to suppress the inflammatory component of the tear film disorder, which is often present, and the closure of the draining tear ducts with punctum plugs, small plastic plugs that are inserted into the teardrop points.
Meibomian lipid film over an aqueous subphase with BAC 0.1%
Electron microscopic picture of epithelial cell damage
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