Dry eye syndrome is a common cause of eye irritation, mainly affecting older people. Artificial tears, gels and soothing ointments usually ease symptoms.
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?
This is made up from three layers - the main middle watery layer, the thin outer oily (lipid) 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. These glands make watery fluid which drains on to the upper part of the eyes. When you blink, the eyelid spreads the tears over the front of the eye.
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 eye syndrome and what causes it?
Dry eye syndrome can affect anyone, but it becomes more common with increasing age. Dry eyes affect about 15 to 33 in 100 people, ie possibly as many as a third of older people. Women are affected much 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:
- 'Water' tablets (diuretics).
- Some antidepressants.
- Some treatments for anxiety and other psychological problems.
- Beta-blockers such as propranolol, atenolol.
- Some treatments for acne, etc.
- Some eye drops used to treat other eye conditions.
- 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 such as 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. Also people with Parkinson's disease can blink less.
- Wearing contact lenses.
- Windy conditions when you are outside.
- Not being able 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.
- Skin rashes such as seborrhoeic dermatitis or rosacea.
- Inflammation of the eyelids (blepharitis), 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.
- Discomfort in your eyes when looking at 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 puncture (perforate).
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. Further examination with an instrument called a slit lamp is sometimes needed. Sometimes eye drops containing special dyes are used to show up dry areas or ulcers in the eye. If these tests are needed, your doctor will usually recommend that you visit an optician. If your dry eyes are more complicated and associated with another disease, your doctor may refer you to an ophthalmologist for tests and treatment.
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. Or, if the artificial tears you are using cause irritation in your eyes, try changing to a type which is preservative-free.
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 raised pressure in the eye (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.
Examples of other treatment options sometimes used for severe cases include:
- Anti-inflammatory eye drops or tablets (for example, steroid eye drops or tetracycline tablets).
- Medicines to boost tear production by the tear gland (for example pilocarpine).
- Surgery to stop the tears from draining away.
- Plugs inserted in your lacrimal ducts to form a temporary block to the tears draining away.
- The fluid contained in your own blood can be used to make special tear drops which are not artificial. These are called autologous serum tears.
- Special lenses or goggles are used to try to keep the moisture in your eyes.
Also, some people may need other treatments if they have an underlying cause for their dry eyes.
It appears that fats from fish oils (omega 3) in the diet, or as supplements, can improve dry eyes. More studies are needed to work out the exact combination and dose. However, meanwhile, including oily fish in your diet once or twice a week may be beneficial. Some groups of people should be careful about the amount of oily fish in their diet, or omega-3 supplements (eg, pregnant women) so check with your doctor or pharmacist.
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.
Dr Tim Kenny
Dr Mary Harding
Dr Helen Huins