Allergic Eye Disease
Many people suffer the symptoms of allergic conjunctivitis, either seasonally (seasonal allergic conjunctivitis) or all year round (perennial allergic conjunctivitis). The main symptoms are itching, burning, watering and redness of the eye, and puffiness of the eyelids.
For most of those affected seasonally, these symptoms are part of their hay fever, and the cause is the same. Grass pollens (or other pollens from trees, weeds or shrubs) to which the sufferer has become allergic, land on the eye surface and trigger the release of substances such as histamine, which cause the symptoms. The part of the eye that one sees when looking at someone is not the area mainly affected. The cornea (the transparent window of the eye) is not affected at all, and the surrounding ‘white of the eye’ is affected only slightly. The part that is not seen, a relatively large area that lies beneath the eyelids, is where the reaction mainly takes place.
What is seen under the upper eyelid in allergic conjunctivitis is slight redness, slight swelling (oedema) of the tissues, and perhaps a little bumpiness (papillary hyperplasia). This relative lack of signs, coupled with the typical seasonal history and symptoms, is what helps to distinguish allergic conjunctivitis from other forms of inflammation, including infection.
Perennial allergic conjunctivitis is caused in the same way, but is usually a reaction to house dust mite or pets in the indoor environment, rather than to seasonal pollens. In other countries the same condition is caused by different environmental factors.
The allergy tests normally used to identify the trigger of an allergic reaction (skin prick tests and blood tests) are sometimes unhelpful in finding the triggers for allergic conjunctivitis. The correlation between the allergic antibody (IgE) levels in the tears and those in the blood or skin is limited because the IgE found in tears does not come directly from the blood, but from the lacrimal (tear) gland. The equivalent, in the eye, of the skin prick test is the conjunctival provocation test, in which extremely small amounts of allergen are introduced into the tear film, and the effects noted. This is not often done, but may be helpful in some cases of allergic eye disease.
In addition to seasonal and perennial allergic conjunctivitis, other much rarer but more serious allergic eye diseases are recognised. These are vernal keratoconjunctivitis (VKC), which occurs in some severely allergic children, and the adult equivalent, atopic keratoconjunctivitis (AKC). In both of these conditions, there is usually corneal involvement, which affects, and may even threaten, the sight of the eye, and only the ophthalmologist (eye specialist) is fully equipped to manage them. Some contact lens wearers suffer from a condition (giant papillary conjunctivitis, GPC), which is similar to VKC and AKC, but does not involve the cornea.
Management of allergic eye disease
The first strategy is allergen avoidance, but before allergens can be avoided they must be identified. In many cases the likely triggers can be identified by taking a careful history from the patient. Many allergic people react to common allergens, which are, by definition, difficult to avoid. For more details on avoiding allergens, see our factsheets Avoiding Pollen and Avoiding Indoor Allergens.
Anti-histamine eye drops can be helpful. Some can be bought at pharmacies, whilst others need a prescription. Oral anti-histamines suit many patients whose eye symptoms coincide with other symptoms of hay fever. Again, some of these can be bought over-the-counter while others require a prescription.
Mast cell stabilisers have been used in eye drop form for many years. The first of these was sodium cromoglicate 2%, the effectiveness and excellent safety record of which have earned it ‘gold standard’ status in the management of allergic eye disease. A number of manufacturers produce their own versions of this preparation, some of which can be bought at pharmacies without prescription. Other mast cell stabilisers, and compounds that have both mast cell stabilising and anti-histaminic properties (e.g. olopatadine 0.2%), require prescriptions.
Steroid eye preparations are very effective in allergic eye disease but their unwanted effects can be severe and even sight-threatening. They should therefore be prescribed only by ophthalmologists, or by optometrists registered as Independent Prescribers, as these are the only two professional groups properly trained and equipped to diagnose and manage these complications.
Non-steroidal anti-inflammatory drugs (NSAIDs) are available in eye drop form, but their place in the management of allergic eye disease is not yet fully determined.
Immunosuppressive agents are not needed in simple allergic eye disease, but they may be used in the management of VKC and AKC under the guidance of an ophthalmologist.
In addition to all these active treatments, supportive measures can be very helpful in controlling the symptoms of allergic eye disease. These include cold compresses and the use of artificial tear preparations, some of which are available at pharmacies without prescription.
The management of the contact lens-related disease GPC is a specialist area which is best left to optometrists and ophthalmologists.
A note on the use of eye drops: Eye drops are best instilled with the head well back, or when lying down. The forefinger of one hand is used to gently pull down on the lower eyelid, creating a small recess into which a drop can be made to fall from the bottle held in the other hand. (The ophthalmologist may sometimes recommend the instilling of drops under the upper lid.)
Though the instructions provided with the drops may state that one or two drops should be used, only one is necessary. Indeed the use of more than one drop may be counterproductive. It is important that the top of the bottle (or dropper) should not touch the eye, or the lashes, lids, face or fingers. The hands should be washed before and after use of eye drops. Once opened, the drops should be kept in a cool place (such as in the door of the fridge) and thrown away when they expire (usually one month later). It is not safe to use eye drops that have been open for longer than the recommended interval. Eye drops should never be shared with another person.