Allergic conjunctivitis is irritation of the conjunctiva (the membrane covering the white part of the eye) due to allergy. Although allergens differ between patients, the most common cause is hay fever. Symptoms consist of redness (mainly due to vasodilation of the peripheral small blood vessels), itching and increased lacrimation (production of tears). The conjunctiva is a membrane that covers the sclera (white part of the eye) and lines the inside of the eyelids. ... An allergy or Type I hypersensitivity is a immune malfunction whereby a persons body is hypersensitised to react immunologically to typically nonimmunogenic substances. ... An allergen is any substance (antigen), most often eaten or inhaled, that is recognized by the immune system and causes an allergic reaction. ... Pollen grains from a variety of common plants can cause hay fever. ... The blood vessels are part of the circulatory system and function to transport blood throughout the body. ... An itch (Latin: pruritus) is a sensation felt on an area of skin that makes a person or animal want to scratch it. ... Tears trickling down the cheeks Lacrimation is the bodys process of producing tears, which are a liquid to clean and lubricate the eyes. ... Tears trickling down the cheeks Lacrimation is the bodys process of producing tears, which are a liquid to clean and lubricate the eyes. ...

The symptoms are due to release of histamine and other active substances by mast cells, which stimulate dilation of blood vessels, irritate nerve endings and increase secretion of tears. Histamine is a monoamine chemical involved in local immune responses. ... A mast cell (or mastocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. ...

Treatment of allergic conjunctivitis is by avoiding the allergen (e.g. avoiding grass in bloom during the "hay fever season") and treatment with antihistamines, either topical (in the form of eye drops), or systemic (in the form of tablets). Cromolyn sodium is sometimes used topically. An antihistamine is a drug which serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions, through action at the histamine receptor. ... Categories: Medicine stubs | Pharmacologic agents ... Cromolyn sodium (also called sodium cromoglycate) is a mast cell stabilizing drug. ...