The ocular surface may exhibit a wide variety of immunologic responses resulting in inflammation of the conjunctiva and cornea. In the Gell and Coombs classification system for various immunologic hypersensitivity reactions, 5 types of reactions are recognized. The major type I hypersensitivity reactions involving the conjunctiva are commonly referred to as allergic conjunctivitis and are further subclassified into seasonal allergic conjunctivitis (SAC) and perennial allergic conjunctivitis (PAC). Far less common are the more severe forms of allergic conjunctivitis, including atopic keratoconjunctivitis (AKC), giant papillary conjunctivitis (GPC), and limbal and tarsal vernal keratoconjunctivitis (VKC).
Classic signs of allergic conjunctivitis include injection of the conjunctival vessels as well as varying degrees of chemosis (conjunctival edema) and eyelid edema. The conjunctiva often has a milky appearance due to obscuration of superficial blood vessels by edema within the substantia propria of the conjunctiva. Edema is generally believed to be the direct result of increased vascular permeability caused by release of histamine from conjunctival mast cells.
Avoidance of the offending antigen is the primary behavioral modification for all types of allergic conjunctivitis. In other respects, management of allergic conjunctivitis varies somewhat according to the specific subtype (SAC, PAC, GPC, VKC, AKC). Allergic conjunctivitis can be treated with a variety of medications, including topical antihistamines, mast cell stabilizers, nonsteroidal anti-inflammatory drugs (NSAIDs), and corticosteroids. Surgical intervention may be indicated in severe cases of VKC or AKC.
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