Allergic conjunctivitis (AC) is the inflammation of the conjunctiva, the transparent, thin epidermal layer which covers the outer surface of the eye.
The disease is related to the following processes: auto-immune and has an incidence of about 1 / 100.000.
Allergic conjunctivitis (AC) occurs when the eye is exposed to allergens like pollen, mold, household dust and animal dander. The inflammatory reaction is characterized by the classical symptoms of redness, swelling and itching, which in this condition are combined with increased lacrimation. AC is very common among adults as well as children, and is popularly known as “pink eye”.
Conjunctivitis refers to any inflammation of the conjunctiva, which can be triggered by different agents. In the case of allergic conjunctivitis the agent concerned is an allergen, in other words any type of antigen which, although totally innocuous and harmless, is perceived by the body as a threat and fought off through an immune response. This type of conjunctivitis is common in people who already suffer for another allergic condition like hay fever or asthma .
Allergic conjunctivitis is very frequent and affects around 20% of the general population each year. About one-half of these people have a personal or a family history of atopy  which might have a hereditary nature. The occurrence of AC is very common, especially in the areas with high seasonal allergens and tropical and temperate climates, such as the Mediterranean, the Middle East or Africa. Many studies appear to underline the tendency of AC to become more and more frequent with the passing of time, perhaps due to the increased quantities in our environment of substances such as air pollution or cigarette smoke.
Allergic conjunctivitis is usually a type I (immediate) hypersensitivity reaction coordinated by mast cells . The allergen causes cross-linkage of IgE which triggers mast cell degranulation. The mast cells secrete histamine, tryptase, chymase, heparin, chondroitin sulfate, prostaglandins and other inflammatory mediators. Histamines in turn bind both to H1 receptors on the nerve endings, causing pruritus, and to H2 receptors on the blood vessel epithelial cells, causing the classical inflammatory symptoms of vasodilatation, migration of eosinophils and neutrophils and increased vascular permeability.
Certain forms of AC may also be caused be mechanical irritation of the conjunctiva, often in due to contact lenses. The pathophysiological mechanism of vernal keratoconjunctivitis and atopic keratoconjunctivitis are not fully understood.
The condition is frequently acute, but in the worst and most advanced cases it might turn into a chronic state, marked by remodeling of the ocular surface tissues . Furthermore, as conjunctiva is very similar to the nasal mucosa from a molecular point of view, the allergens which trigger rhinitis usually provoke AC as well.
Prognosis of AC is usually very favorable. Symptoms can be easily prevented or relieved with the appropriate medications and measures, and usually go away with treatment unless the subject continues to be exposed to the allergen. Complications are rare, but if left untreated they can cause major problems like keratitis (inflammation and ulceration of the cornea) or even permanent loss of vision which seriously affect the quality of life.
The classical symptoms of allergic conjunctivitis include itching, redness in the white of the eye, eyelid swelling, eye discharge, tearing, photophobia and foreign body sensation often associated with pain  , which usually concerns both eyes without compromising vision. Itching is undoubtedly the most typical of these symptoms, being reported by more than 75% of the people showing signs of AC . Without itching the diagnosis of AC is suspect. Symptoms can sometime be seasonal and usually are marked in patients living in areas with warm and dry weather . In certain situations the symptoms might affect patient’s life, limiting common activities like going outdoor, driving, or reading .
According to the nature of allergen, there are 5 main types of AC:
AC can sometime be passed down from generation to generation in the same families, and might include reactions to some medicines such as eye drops or contact lens solutions.
The clinical diagnosis is based on medical history, signs and symptoms, course of the disease, and physical exam findings. There are three main methodologies for diagnosing AC:
In SAC and PAC, conjunctival scraping might not be sufficient to make the diagnosis of AC, because eosinophils are typically present in the deep layers of the substantia propria and therefore could go undetected with this superficial method. Measuring the levels of IgE in tears and allergen-skin prick testing may be used to test for the offending allergen. Other tear-specific markers such as EPC, IL-4 and IL-5 may also be useful for the diagnosis of AC.
In VKC conjunctival scraping is performed which shows an abundant presence of eosinophils. Through biopsy a marked quantity of mast cells within the substantia propria can also be detected. Eosinophils are numerous in AKC too, although no eosinophilic granule can be seen in this case, and mast cells and IgE can also be detected in greater quantities. Pronounced presence of inflammatory cells as well as elevated tear immunoglobulin levels characterize the diagnosis of GPC.
The treatment of allergic conjunctivitis involves a series of general measures, like avoiding the use of contact lenses until the symptoms have gone or trying not to rub the eyes. Home care can be added, which should be characterized by a combination of preventive strategies and activities to minimize allergen exposure, like closing the windows, keeping home dust-free, using an indoor air purifier or avoiding contact with harsh chemicals such as dyes and perfumes. In any case, it is important to detect the cause of the condition and try to avoid it. In this regard, it is useful to get a detailed history of the patient, which helps finding the cause of reaction or the offending allergen.
In the more severe cases home care might not be enough, and more specialized measures might be needed. The inflammatory symptoms can be reduced by causing vasodilatation through the use of ocular decongestants and ocular steroids, or by blocking histamine action through the use of antihistamines or mast cell stabilizers. Immunotherapy is also gaining momentum as mainstay in ocular allergy management, especially with the sublingual immunotherapy SLIT  which appears to have a moderate effect on the signs and symptoms of this disorder .
Treatment also varies based on the type of allergic conjunctivitis concerned. For example, the use of eye drops is particularly advised in seasonal and perennial conjunctivitis, since it allows to effectively reduce contact with the allergen and alleviate the ocular symptoms. Removal of the foreign body from the eye is the definitive treatment for giant papillary conjunctivitis, along with an improved contact lenses hygiene and a frequent contact lenses change. Permanent relocation to a cooler climate, with an easy management of the air-conditioned environment and dust particle control, is the most effective treatment for VKC and AKC, together with the use of mast cells stabilizers and corticosteroids. Some patients affected by AKC might even benefit from plasmapheresis .
The simplest and most effective measure to prevent allergic conjunctivitis is to limit the exposure to the environmental factors which trigger the inflammation. Identifying the allergens might be difficult, and collecting information about the personal and family history is highly recommended. This allows to pinpoint past allergic and inflammatory episodes which can help recognize the triggering factor. It might also be useful to follow general measures, such as frequently washing hands, not wearing contact lenses or not sharing personal items.
Allergic conjunctivitis (AC) is the inflammation of conjunctiva, the transparent thin epidermal layer which covers the white part of the eye. This inflammation occurs when the eye is exposed to allergens like pollen or mold, and is popularly known as “pink eye.” AC is very frequent and affects around 20% of the general population each year, especially those who already suffer for another allergic condition. The classical symptoms of AC include itching, redness in the white of the eye, eyelid swelling, eye discharge, tearing, photophobia and foreign body sensation, which usually interest both eyes.
According to the triggering factor, AC can be categorized in the following 5 types:
The diagnosis is usually made based on history, signs and symptoms, course of the disease and physical exam findings. Diagnostic tests such as conjunctival scraping, allergen-skin tests or biopsy may be needed to diagnose AC.
The disorder can be treated by following a series of general measures, like closing the windows, or in the worst cases by using more specialized treatments such as using ocular decongestants or ocular steroids. The simplest and most effective AC prevention strategy is to limit the exposure to the environmental factors which trigger the inflammation itself, together with some commonsense measures like frequently washing hands or not sharing personal items.