Causes of dry eye syndrome

Dry eye syndrome can occur ifyour eyes don't produce enough tears or your tears evaporate too quickly.

This may happen ifany part of the tear production process becomes disrupted and the quantity or quality of your tears is affected.

There aremany different reasons why this can happen, althougha single identifiable cause may not be found. Some of the possible causes are described below.

Hormonal changes

Hormones powerful chemicals produced by the bodyand the nervous system play an important part in tear production.

Hormones stimulate the production of tears. Changes in hormone levels in womencan increase their risk of dry eye syndrome. For example:

• during pregnancy
• during the Testosterone deficiency (hypogonadism)
• while using the contraceptive pill

Ageing

Dry eye syndrome is more common in older people. This may be because you produce fewer tears as you get older, and your eyelids become less effective at spreading tears over the surface ofthe 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 can also contribute to dry eye syndrome, such as:

• reading
• writing
• working with a computer

People tend to blink less frequently during activities that require visual concentration. This means the tear film evaporates or drains away more quickly than it's replenished.

Certain medications

Several medicinesare thought to cause dry eye syndrome as a side effect in some people, including:

• antihistamines
• antidepressants
• beta-blockers
• diuretics

Lasereye 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 orlimitinghowoften you use your contact lenses usually helps resolve the symptoms, or you can trychanging cleaning solutions or using preservative-free lubricant eye drops.

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 or meibomian gland dysfunction (MGD). This is where the eyelid margins become inflamed, which can block the glands that produce oils for the tear film.

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

Other medical conditions that canincrease your risk ofdry eye syndrome include:

• allergic conjunctivitis inflammation of the transparent layer of cells that covers the white part of the eyeball and the inner surfaces of the eyelids (conjunctiva) caused by an allergy, usually to pollen and dust mites
• contact dermatitis a type of eczema that causes inflammation of the skinwhen you come into contact with a particular substance you're sensitive to
• Sjgren's syndrome a condition that can cause excessive dryness of the eyes, mouth and vagina, which is also associated with fatigue and arthritis
• rheumatoid arthritis a condition that causes pain, swelling and inflammation in the jointsthat can affect anypart of the body, including the glands around the eyes and inflammation of the white of the eye (scleritis)
• lupus a condition wherethe immune system attacks healthy body tissue, particularly blood vessels
• scleroderma a condition where the immune system causes inflammation of the blood vessels andareas 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