Allergic eye disease
	Symptoms and signs
	Investigation
	Treatment
To most people, the term conjunctivitis implies the very common condition that is caused by infection of the conjunctiva, the membrane that covers the front of the eye. Allergic conjunctivitis is, however, almost as common, and the two conditions can be confused.

If conjunctivitis is frequent or persistent, and recurrent infection appears to be the cause, then an allergy investigation should be considered.   There are two main types of allergic conjunctivitis according to whether the symptoms occur for part, or all of, the year.

Seasonal allergic conjunctivitis and perennial allergic conjunctivitis are often associated with a personal or family history of asthma, hay fever, eczema or rhinitis.

Symptoms and signs of allergic conjunctivitis

There is usually an intense itch, a burning sensation, and redness or even swelling of the conjunctiva. Excessive watering (lacrimation) and and intolerance of light (photophobia) are common.

Both eyes will be equally affected and the 'whites' will usually be pink or red. There will be a clear watery discharge and tiny round swellings of the insides of the eyelids may be seen. A generalised swelling of the eyelids may occur, and in severe cases, the conjunctiva overlying the whites of the eyes may appear lifted from the surface of the eye due fluid collecting beneath it.

Investigation of allergic conjunctivitis

A careful history and eye examination will usually establish the correct diagnosis. There is normally a personal or family history of asthma, hay fever, eczema or rhinitis.  Allergy skin tests or allergy blood tests will confirm or exclude, and hopefully define the precise allergen. There may be situations when no commercial extract of the substance under suspicion is available, so that neither kind of test is available. In this case, a conjunctival challenge test may be the only way of confirming the allergy. This approach may be helpful when the allergy suspected is not of the immune-mediated type, and skin prick or allergy blood testing is not valid. Sensitivity to contact lens cleansing solutions comes into this category.

Treatment of allergic conjunctivitis

The feasibility of allergen avoidance will depend on the accurate identification of the responsible allergen(s). When an acute flare-up has occurred, cold compresses can be surprisingly soothing. Contact lenses should not be worn if conjunctivitis is present or during treatment with eye drops or ointments.

Effective drug treatments are available and these can be of considerable help in controlling the symptoms of the condition.

The recent development of a desensitisation treatment that can safely be given at home promises to revolutionise the treatment of allergic rhinitis and conjunctivitis. It is called sublingual immunotherapy.

Complications of allergic eye diseases are rare, but a severe allergic reaction can lead to corneal ulceration. However, the condition can be very uncomfortable and inconvenient, and it can certainly have a bearing on the patient's quality of life.