Dry eye syndrome - Causes of dry eye syndrome

Dry eye syndrome can occur if your eyes do not produce enough tears or your tears evaporate too quickly.

There are many different reasons why this can happen, although a single identifiable cause is not often found.

About tears

You probably only notice your tears when you laugh or cry. However, the surface of your eye is always covered by a thin layer of liquid known as the tear film that helps to lubricate your eyes, keep them clean and free of dust, and protect them against infection.

The tear film is made up of water, salts, oils, proteins and mucus, which are produced by a number of different glands and cells situated in and around the eyes.

Dry eye syndrome can occur if any part of the tear production process becomes disrupted and the quantity or quality of your tears is affected.

Increased risk

Some of the things that can interfere with the tear production process are described below.

Hormonal changes

Hormones (powerful chemicals produced by the body) and the nervous system play an important part in tear production.

Hormones stimulate the production of tears. Changes in hormone levels in women (for example during the menopause or pregnancy or while using the contraceptive pill) can increase their risk of dry eye syndrome.

Ageing

Dry eye syndrome is more common in older people, possibly because you produce fewer tears as you get older and your eyelids become less effective at spreading tears over your eyes.

Environment and activities

Environmental factors can have a drying effect on your eyes, causing your tears to evaporate. These include:

• sun
• wind
• dry climate
• hot blowing air
• high altitude

Certain activities that require visual concentration – such as reading, writing or working with a computer – can also contribute to dry eye syndrome. This is because people tend to blink less frequently during these activities, which means the tear film evaporates or drains away more quickly than it is replenished.

Certain medications

Several medicines are thought to cause dry eye syndrome as a side effect in some people.

These include antihistamines, antidepressants, beta-blockers and diuretics.

Laser eye surgery

Some people who have had certain types of laser eye surgery find they have dry eye syndrome in the weeks after surgery. The symptoms usually clear up after a few months, but in some cases may continue.

Contact lenses

Sometimes, contact lenses irritate the eye and cause dry eye syndrome. Changing to a different type of lens or limiting their use usually helps resolve the symptoms.

Medical conditions

There are a number of medical conditions that increase your risk of developing dry eye syndrome.

Many people with dry eye syndrome also have blepharitis. This is where the rims of the eyelids become inflamed, which can block the glands that produce oils for the tear film.

Blepharitis can occur at any age and in otherwise healthy people, although it sometimes occurs as the result of a bacterial infection or another condition such as rosacea (a skin condition that causes the face to appear red and blotchy).

Other medical conditions that can increase your risk of dry eye syndrome include:

• allergic conjunctivitis – inflammation of the conjunctiva (the transparent layer of cells that covers the white part of the eyeball and the inner surfaces of the eyelids) caused by an allergy
• contact dermatitis – a type of eczema that causes inflammation of the skin when you come into contact with a particular substance
• Sjögren's syndrome – a condition that can cause excessive dryness of the eyes, mouth and vagina
• rheumatoid arthritis – a condition that causes pain, swelling and inflammation in the joints and can affect any part of the body, including the glands around the eyes
• lupus – a condition where the immune system attacks healthy body tissue, particularly blood vessels
• scleroderma – a condition that causes areas of skin to become hard and thickened
• previous trauma (serious injury) to the eyes – such as burns or exposure to radiation
• Bell's palsy – a condition that causes weakness or paralysis to the muscles of one side of the face
• HIV – a virus that attacks the body's immune system