Seasonal and Perennial Allergic Conjunctivitis

The symptoms and signs of SAC and PAC include burning, itching, watery discharge, conjunctival redness, chemosis and fine follicles. The follicles result from the release of mediators such as histamine, leukotrienes and prostaglandins. This early phase reaction is followed by a late phase reaction in which eosinophils and T lymphocytes are the predominant cells.

Mast cells have been discovered as a source of Th2-type helper cytokines, IL-4, IL-5, IL-6 and IL-13 [12]. MCtc secrete IL-4 and IL-13 while MCT release IL-5 and IL-6 [30]. The latter is the predominant type in ocular allergy. The release of such cytokine mediators from mast cells helps in eosinophil recruitment, activation and inflammatory cell mediator release [30]. High levels of TNF-a upregulate intracellular adhesion molecules on conjunctival epithelial cells, which in turn mediate the epithelial leukocyte interaction with an increase in IL-5. There is also a decrease in IL-10, which has anti-inflammatory properties [27].

Using the presence of the neutral protease tryptase as an immunohisto-chemical marker, mast cell numbers have been found to be raised in SAC and PAC. IgE is the activator of mast cells and is bound to high affinity receptors FceRI on the cell surface. There are raised levels of allergen-specific IgE in patients with a history of atopy [29, 31]. The symptomatology of SAC and PAC relates to the number of mast cells present in the conjunctiva. SCF regulates mast cell growth and maturation. It is a chemoattractant for mast cells and enhances IgE-dependent mast cell mediator release and cytokine generation. Pro-inflammatory cytokines IL-4 and IL-5 are stored in the eosinophils and are essential for the growth and differentiation of eosinophils [29].

As mast cells and eosinophils are the main cells observed in the conjuncti-val allergic response, the role of IL-4 in the allergic response is very important. It is involved in the switching of B cells from IgM to IgE, T cell growth and Th2 differentiation. The IL-4 gene cluster is on chromosome 5 which includes IL-3, IL-4, IL-5 and IL-13 [32].

The medical treatment of SAC and PAC includes topical vasoconstrictors and the H1 receptor blocker, olopatadine. The combined treatment with both of these agents provides greater relief. The mast cell stabilizer sodium cromogly-cate is used for prevention rather than treatment, inhibiting the initial release of inflammatory mediators. The use of steroids remains limited to serious symptoms and its long-term use could result in cataract and glaucoma.

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