What is dry eye syndrome?
Dry eye syndrome (also known as keratoconjunctivitis sicca, or simply dry eyes) occurs when there is a problem with the tear film that normally keeps the eye moist and lubricated. It can occur as a result of various conditions.
What is the tear film?
The tear film is made up from three layers – the main middle watery layer, the thin outer lipid (oily) layer, and the thin inner mucus layer.
The main middle watery layer is what we may think of as tears. The watery fluid comes from the lacrimal glands. There is a lacrimal gland just above, and to the outer side, of each eye. The lacrimal glands constantly make a small amount of watery fluid which drains onto the upper part of the eyes. When you blink, the eyelid spreads the tears over the front of the eye.
Tiny glands in the eyelids (meibomian glands) make a small amount of lipid (oily) liquid which covers the outer layer of the tear film. This layer helps to keep the tear surface smooth and to reduce evaporation of the watery tears.
Cells of the conjunctiva at the front of the eye and inner part of the eyelids also make a small amount of mucus-like fluid. This allows the watery tears to spread evenly over the surface of the eye.
The tears then drain down small channels (canaliculi) on the inner side of the eye into a tear sac. From here they flow down a channel called the tear duct (also called the nasolacrimal duct) into the nose.
Who gets dry eyes and what causes it?
Dry eyes can affect anyone, but it becomes more common with increasing age. Dry eyes affect about 7 in 100 people in their 50s, and about 15 in 100 people in their 70s. Women are affected more often than men.
The causes include:
- Ageing. You tend to make fewer tears as you get older. In particular, some women notice dry eyes developing after the menopause.
- Medication. Some medicines sometimes have a side-effect of causing dry eyes, or make dry eyes worse. These include: diuretics (water tablets); some antidepressants; antihistamines; some treatments for anxiety and other psychological problems; the contraceptive pill; beta-blockers such as propranolol, atenolol, etc; some eye drops used to treat other eye conditions. This is not an exhaustive list. Tell your doctor if you suspect that a medicine is causing your dry eyes.
- Illness. Some people develop dry eyes as a symptom of a more general disease. For example, dry eyes may occur with rheumatoid arthritis, systemic lupus erythematosus (SLE), and Sjögren’s syndrome. In these situations you would normally have other symptoms in other parts of the body. For example, joint pains.
- Increased evaporation of tears. This may be due to:
- Low humidity. For example, from central heating or air conditioning.
- Low blink rate, often combined with opening your eyes wider than normal. For example, spending a long time looking at a computer, TV or microscope.
- Windy conditions when you are outside.
- Inability to cover the eyes completely when closing the eyelids. For example, due to eye problems that some people have related to thyroid disease. Also, some people sleep with their eyes partly open.
- Damage to the outer part of the eyes, eyelids, etc, from disease, injury or surgery.
- Blepharitis (inflammation of the eyelids), which is often associated with dry eyes.
- Unknown. Some younger people have no apparent cause. They simply produce less than the normal amount of tears.
What are the symptoms of dry eyes?
Both eyes are usually affected. The eyes may not actually feel dry. Symptoms include:
- Irritation in the eyes. The eyes may feel gritty or burning. However, the eyes do not go red. If they do, another eye problem or a complication is usually present.
- Slight blurring of vision from time to time. However, dry eyes do not affect the seeing part of the eye, and dry eyes do not usually cause permanent damage to vision.
- You may not like bright lights.
- If you wear contact lenses, you may find they become uncomfortable.
What are the possible complications of dry eyes?
Complications are uncommon. Inflammation of the conjunctiva (conjunctivitis) or the cornea at the front of the eye (keratitis) sometimes occurs. In severe cases, small ulcers may develop on the cornea. Rarely, the corneal may perforate (puncture).
See a doctor if the eye goes red or if vision becomes affected (more than slight temporary blurring). Also if eye pain develops other than the grittiness or irritation that goes with dry eyes. These are not normally symptoms of dry eyes and may indicate another eye condition or a complication of dry eyes.
How are dry eyes diagnosed?
A doctor can usually diagnose dry eyes from the symptoms. However, as dry eyes can be a symptom of an underlying disease (such as Sjögren’s syndrome), don’t be surprised if your doctor asks about all sorts of other symptoms.
Sometimes a test is done to confirm the diagnosis of dry eyes. This is called Schirmer’s Tear Test. This measures the amount of tears that you form. Special filter paper is placed under the lower lid of your eye and left for five minutes. The amount of tears that you make can be assessed by how wet the filter paper becomes after five minutes.
What is the treatment for dry eyes?
These come as eye drops and gels, and are usually good at relieving symptoms. You can buy them at pharmacies or get them on prescription. At first, you may need to use them every hour or more to improve symptoms. Once symptoms improve, you may then only need to use them three or four times a day. You may need to use them regularly to keep symptoms away.
There are several types of artificial tear drops and gels with different ingredients. Occasionally, some people find one type may irritate. A change to a different preparation may help if the first does not suit.
Note: some types of artificial tears contain preservatives such as benzalkonium hexachloride. If you use drops that contain benzalkonium hexachloride for long periods, they may damage the front of the eye (the cornea). Therefore, if you use artificial tears more than four times per day long-term, it is best to use a preservative-free brand which does not contain benzalkonium chloride.
It may also help to use a soothing and lubricating ointment at bedtime for overnight. You can buy this too at pharmacies, or get it on prescription. You should not use ointment during the day as it may make the artificial tear drops less effective, and can blur vision. (Also, do not use eye ointment if you use other eye drops for other conditions such as glaucoma. The other eye drops may not work so well on top of an ointment.)
Artificial tears and soothing ointments work well in most cases. Other treatments may be advised by a specialist in severe cases not helped by the above. For example, medicines are sometimes used to boost tear production by the tear gland and surgery is sometimes done to block the tears from draining away. Also, some people may need other treatments if they have an underlying cause for their dry eyes.
Contact lens wearers
You should not wear contact lenses whilst using many types of eye drops. Check with your doctor or pharmacist. It is often the preservative in the drops that may cause problems. Some types of drops are available without preservative, which are suitable for contact lens wearers.
You should not wear contact lenses whilst using eye ointment.
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