Dry eyes (Sicca)
The main function of tear fluid is to keep the eye surface moist. With every blink of the eye, tears are evenly distributed across the eye in a thin layer. This thin layer of moisture is called the “tear film”. This tear film serves to keep the eye surface wetland smooth. A proper tear film will also protect the eye against all kinds of external influences, such as dust and bacteria.
A proper tear film is essential for the forming of a sharp image on the retina. In case of an unstable or bad tear film, vision may become blurred. Blinking more often may temporarily diminish the blurring. In case of an unstable or poor tear film, it is often harder to measure the right lens-strength as results will vary.
What causes dry eyes?
Dry eyes can arise as a result of insufficient moist production due to lacrimal gland issues. Eyes can also dry up because of rapid evaporation of the tear film, usually due to problems with the Meibomian glands in the eyelids. Both forms are common, and often there is a mixed set of causes.
In some cases the eyelids cannot blink or close properly so the tears are not spread across the surface properly or often enough. Sometimes, the eye remains slightly open at night, drying out even more.
In all these situations, the tear film is unstable and moisturizing of the eye hardly happens. The eye surface cannot be kept sufficiently moist and dries out.
My eyes are not dry, they are wet!
We hear this comment quite often. The term dry eyes is actually slightly inaccurate. The proper term would be: eye humidification disorder.
There are 2 types of tears: basal tears and rinsing tears (or reflex tears). Proper basal tears cause the eye to remain moist for at least 10 seconds between blinking movements. Rinsing tears are spring into action whenever something ends up in the eye (such as a fly or a grain of sand), or when the basal tears fail to moisten the eye properly, causing dry spots on the surface of the eye.
At times, dryness of the eye surface can even lead to an excess of tears (produced in a reflex on the dehydration stimuli). However, these reflex tears usually are not composed properly either. As a result, there is a continuing cycle of a drying surface, complaints of a burning sensation etc., followed by reflex tears drying up too fast, etc.
An ophthalmologist can run a number of tests to find the cause of dry eyes:
- Schirmer test: measuring the amount of tears produced by the lacrimal gland. This is done by placing a strip of filter paper in the eyes. After 5 minutes it is checked how far the tears have run into the paper strip. Sometimes this test is repeated after administering anesthetic drops.
- Fluorescein coloring: an orange-yellow coloring strip is placed against the eye. This assesses the degree of damage to the surface due to dehydration (the “dehydration spots”).
- Test assessing quality and stability of the tear film: after administering the fluorescein coloring, the ophthalmologist observes how quickly the tear film evaporates.
- The ophthalmologist gently squeezes your lower eyelid to evaluate its clogging of the Meibomian glands and the sebum composition.
- Additional tests/measurements are carried out occasionally.
- If advisable you may be referred to another specialist, for example an internist or rheumatologist, for further research into possible underlying causes.
Treatment of dry eye is often tough as the cause cannot always be taken away. Where possible, attempts will be made to treat this cause which could be inflammation or position deviation of the eyelids. However, when the cause cannot be found or treated – for example if the lacrimal gland does not work properly or is even damaged beyond repair – then the treatment will be focused on reducing or managing the complaints caused by eye dehydration as much as possible.
In order to increase moisturizing of the eye in the case of a poorly functioning tear film patients often start using artificial teardrops, using “artificial tears” (eye drops) or eye gel, available on the market in a wide range of varieties. It may take a while to find the product that suits you best. If artificial tears alone are not enough, you may also try to retain the existing tears (your own and/or artificial) on the eye surface for as long as possible, by preventing draining and evaporation of the tear film. For example, there are special protective glasses (moisture chamber glasses) to prevent evaporation. Another option is that the tear ducts in the lower eyelid at the side of the nose are (temporarily) sealed with “punctal plugs”. In more severe cases it can sometimes be necessary to use heavier medication in the form of eye drops or even tablets, and in these cases tear ducts are sometimes sealed permanently. Protective contact lenses may also be prescribed in more severe cases.
What can you do yourself?
When you find that your complaints increase under certain circumstances, try to change or reduce these:
- You can prevent tears from evaporating too quickly by improving the humidity in your home or office. This can be done by attaching water tanks to the heating or by installing a humidifier.
- Outside, special (cycling) glasses with closed off sides can keep your eyes from drying out because of the airflow.
- Avoid or try to adjust: factors that cause extra drought or irritation, such as a blow dryer, a fan, air conditioning, or cigarette smoke.
- Apply extra artificial tears or gel to your eyes in advance in situations you cannot avoid, but of which you already know will cause suffering.
- Wearing contact lenses can sometimes cause more complaints in dry eyes. Switching to glasses more often may reduce complaints.
- If the quality of the tear film is poor because the Meibomian glands in the eyelid margin are not working properly or clogged, you can apply warm compresses and then massage the eyelids.
Regular use of eye drops following the ophthalmologist’s instructions, and regular check-ups at the ophthalmologist’s in more serious cases, can prevent complications such as infections.
Any questions? Please contact OMC Amstelland.
Source: NOG patient information – www.oogheelkunde.org