Eye allergies can vary from mild irritation of the conjunctiva - the membrane that covers the eyeball and extends to the inside of the eyelids - to severe conjunctival inflammation with corneal scarring.'Hay fever eyes'Seasonal allergic conjunctivitis is the eye equivalent of hay fever and affects up to 25 per cent of the general population. The eyes become itchy, watery and red in the summer pollen season - usually from exposure to grass and tree pollen.A more severe form of this disease seen in children is vernal conjunctivitis where the symptoms are more intense. The eyes are very sticky with a stringy discharge and pain occurs especially when opening the eyes on waking. The eyelid inner membranes swell with the conjunctiva developing a cobblestone appearance, corneal damage may even occur if the condition is left untreated. Perennial allergic conjunctivitis tends to occur all year round with house dust mite and cat allergy. The symptoms are usually milder than those in seasonal allergic conjunctivitis. 'Eczema eyes'Atopic keratoconjunctivitis although rare is the most severe manifestation of allergic eye disease occurring predominantly in adult males. It is the eye equivalent of severe eczema. This persistent condition results in constant itching, dry eyes, blurred vision and is associated with corneal swelling and scarring. Eyelid eczema and infection are common and lens cataracts may develop over time.Contact lens allergyContact lens wearers may develop giant papillary conjunctivitis triggered by the constant local irritation of the contact lenses on the conjunctival surfaces. The lining of the upper eyelid is usually most affected. Disposable contact lenses may help settle symptoms but occasionally contact lens wearing has to be suspended.Never use steroid eyedrops unless under the direct supervision of a doctor. Steroid eyedrops although very effective for treating eye allergies can lead to unwanted side effects such as glaucoma, cataract formation and encourage infections of the eye with resultant corneal scarring.What treatment can you get?The treatment for allergic conjunctivitis involves the regular use of eyedrops. Anti-allergy eyedrops such as sodium chromoglycate, nedocromil sodium, olopatidine and lodoxamide help treat mild seasonal disease. Anti-histamine solutions such as levocabastine work for mild to moderate disease. The oral anti-histamines - cetirizine, loratadine, mizolastine and fexofenadine - also help, especially when there is associated nasal allergy. In more severe eye allergies corticosteroid eyedrops occasionally have to be used, but this should be for short periods only.