Several types of allergic reaction are seen on the conjunctiva and some of these also involve the cornea. They may be listed as follows:
This is simply the commonly experienced red and watering eye that accompanies the sneezing bouts of the hay fever sufferer. The eyes are itchy and mildly injected and there might be con-junctival oedema. If treatment is needed, vasoconstrictors, such as dilute adrenaline or naphazoline drops, can be helpful; sodium cromoglycate eye drops can be used on a more long-term basis. Systemic antihistamines are of limited benefit in controlling the eye changes.
Unfortunately, patients with asthma and eczema can experience recurrent itching and irritation of the conjunctiva. Although atopic conjunctivitis tends to improve over a period of many years, it might result in repeated discomfort and anxiety for the patient, especially as the cornea can become involved, showing a superficial punctate keratitis or, in the worst cases, ulcer formation and scarring.
The diagnosis is usually evident from the history but conjunctival scrapings show the presence of eosinophils. Patients with atopic keratoconjunctivitis have a higher risk than normal for the development of herpes simplex keratitis; the condition is also associated with the corneal dystrophy known as keratoconus or conical cornea. They are likely to develop skin infections and chronic eyelid infection by staphylococcus. The recurrent itch and irritation (in the absence of infection) is relieved by applying local steroid drops, but in view of the long-term nature of the condition, these should be avoided if possible because of their side effects. (Local steroids can cause glaucoma in predisposed individuals and aggravate herpes simplex keratitis.)
Vernal Conjunctivitis (Spring Catarrh)
Some children with an atopic history can develop a specific type of conjunctivitis characterised by the presence of giant papillae under the upper lid. The child tends to develop severely watering and itchy eyes in the early spring, which can interfere with schooling. Eversion of the upper lid reveals the raised papillae, which have been likened to cobblestones. In severe cases, the cobblestones can coalesce to give rise to giant papillae (Figure 6.5). Occasionally, the cornea is also involved, initially by punctate keratitis but sometimes it can become vascularised. It is often necessary to treat these cases with local steroids, for example, prednisolone drops applied if needed every two hours for a few days, thus enabling the child to return to school. The dose can then be reduced as much as possible down to a maintenance dose over the worst part of the season. More severe cases can derive some benefit from
topical cyclosporin drops, or eyelid injections of triamcinolone to control the inflammatory response. Less severe cases can respond well to sodium cromoglycate drops; these can be useful as a long-term measure and in preventing but not controlling acute exacerbations. Other medications with a similar modest benefit in symptoms include lodoxamide (a mast cell stabiliser) and emedastine (a topical antihistamine).
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