Swollen, itchy eyes are no fun. Dr Sarah Brewer talks you through the causes, diagnosis and solutions.

If your eyes are red, swollen, itchy, watery or sticky and feel uncomfortably gritty, then you probably have conjunctivitis - an inflammation of the conjunctival membrane lining the eye and eye lids. Sometimes just one eye may be involved, but often, both eyes are affected. There are four main causes: allergy, autoimmune, infection and irritation. Some causes of a swollen, red, painful eye can cause permanent damage if left untreated, so it is important to have eye problems diagnosed as soon as possible.

Allergic conjunctivitis
One of the most common causes of allergic conjunctivitis is hayfever, triggered by pollen allergy, but dust mites, animal secretions, cosmetics and even contact lens solutions can cause allergic eye swelling and redness, too. Usual treatment is to avoid the trigger (if known) and to damp down the allergic reaction with antihistamine eye drops or tablets.

Autoimmune eye problems
Some people develop an auto-immune inflammation of the conjunctiva and other parts of the eye as a response to another infection (eg gonorrhoea, Chlamydia) elsewhere in the body. Red, swollen, painful eyes can also accompany an autoimmune condition such as rheumatoid arthritis or an inflammatory bowel disease. This form of red eye occurs when the body makes antibodies aimed against part of the eye. It appears to have a genetic link as it is most common in those inheriting a particular gene known as HLA-B27. It is treated with corticosteroid eye drops and/or tablets, but these are only prescribed where an eye infection has definitely been ruled out. This is because corticosteroids can make eye infections dramatically worse.

Infective conjunctivitis
Eye infections may be bacterial (eg Staphylococci, Streptococci, Haemophilus), viral (eg adenovirus, Herpes simplex) or due to Chlamydia ? a strange cross between a bacterium and a virus. Trachoma ? a Chlamydial eye disease common in some countries ? is one of the most common causes of conjunctival scarring and blindness world-wide. In the UK, it is most commonly seen in newborn babies infected during birth where their mother has undiagnosed Chlamydia (a sexually transmissible infection).

Bacterial and Chlamydial eye infections are treated with antibiotics (creams, drops and tablets). Mild viral conjunctivitis, such as that accompanying the common cold, may need no treatment (but still get it checked out by your doctor). More severe viral conjunctivitis due to the Herpes simplex virus, is treated with antiviral drugs.

Irritative conjunctivitis
Irritation can occur from a foreign body (eg grit, eye lash), exposure to very bright light (eg 'arc' eye in welders) or exposure to chemicals such as chlorine in swimming pools, smoke, fumes, onion juice and overly-concentrated contact lens solutions. All can lead to eye redness, soreness and swelling. Treatment may involve saline irrigation of the eye and removal of any foreign bodies ? this can be difficult where, for example, a piece of metal has flown into the eye with force. Pain can be damped down with analgesic drops, and anti-inflammatory drops. An eye patch may be needed to protect the eye during healing.

Action
All but the most mild cases of conjunctivitis need to be assessed by a doctor, as your eyes are too precious to take for granted. Seek medical advice straight away.

• If eyes are sticky, you may be advised to gently wash away discharge with a warm saline solution. Use a separate compress or eyebath for each eye.
• Stop using contact lenses until the problem has resolved.
• If eyes feel dry, you may be able to use lubricating drops known as artificial tears.
• If symptoms are worse on going out, wear sunglasses

Prevention

• Wash hands thoroughly before touching eyes
• Avoid swimming in murky water
• If conjunctivitis is due to an allergy, stop using make-up, creams, nail polish until symptoms resolve, then gradually re-introduce them one at a time to identify triggers
• Use hypoallergenic toiletries where possible - the gentlest shampoos, soaps and moisturiser are those formulated for new born babies.