Allergic conjunctivitis is the inflammation of the conjunctiva due to an allergen.
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| Right eye exhibiting characteristic redness |
Allergic conjunctivitis is a Type I hypersensitivity, commonly referred to as an allergic reaction. It is one of the four types of immune responses. The body is "tricked" into thinking an allergen is a threat, such as invading bacteria or viruses. Therefore, the body mounts an immune response to attack and destroy the allergen. The basic pathophysiology is as follows:
- In addition to many other types of cells, the eye contains immune cells called mast cells
- Mast cells have a type of antibody on their surface, called immunoglobulin E (IgE)
- When the conjunctiva is exposed to an allergen, the mast cells' IgE binds to the allergen
- The mast cells become activated and release different mediators to aid in destroying the allergen
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| Process of histamine release from mast cells |
3 Major Mediators Released By Mast Cells
- Histamine: increases vasopermeability or the space between cells of the blood vessels innervating the conjunctiva, so fluid and white blood cells can enter the conjunctiva and destroy the allergen
- Serotonin: increases vasopermeability by the same mechanism as histamine
- Chemotactic Factors: signal the different types of white blood cells to migrate to the site where the allergen was detected, in order to destroy it
*The actions of these mediators and the consequent white blood cells result in the various symptoms associated with allergic conjunctivitis
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