Definition: Allergic keratoconjunctivitis is a group of distinctive clinical disorders that are largely IgE mediated hypersensitivity reactions but have quite similar histopathology (so we group them here). These disorders include "Hay Fever Conjunctivitis," Vernal keratoconjunctivitis (VKC) , and Atopic Keratoconjunctivitis.
Incidence/ Prevalence: Hay Fever Conjunctivitis may occur in patients with asthma and allergic rhinitis. VKC occurs most commonly in boys with a history of atopy, asthma, allergic rhinitis and eczema. Named "vernal" because patients are affected in the spring, VKC can be year round in tropical climates. Atopic keratoconjuncitivitis occurs frequently in patients with atopic dermatitis. It has been written that VKC accounts for about 0.1-0.5% of visits to the eye clinic and allergic conjunctivitis affects about 20% of the world's population.
Etiology: probably a variety of allergens and pollens. However, VKC is not associated with a positive skin test or RAST in 42-47% of patients, suggesting it is not solely an IgE-mediated disease. On the basis of challenge studies as well as immunohistochemical and mediator studies, a Th2-driven mechanism with the involvement of mast cells, eosinophils, and lymphocytes has been suggested. Th2 lymphocytes are responsible for both hyperproduction of IgE (interleukin 4, IL-4) and for differentiation and activation of mast cells (IL-3) and eosinophils (IL-5). Some studies have suggested the involvement of neural factors such as substance P and NGF in the pathogenesis of VKC. The overexpression of estrogen and progesterone receptors in the conjunctiva of VKC patients raises a possible role for sex hormones. Perhaps the pathogenesis of VKC is multifactorial, with the interaction of the immune, nervous, and endocrine systems.
Clinical Findings: VKC is an allergic eye disease that especially affects young boys. The most common symptoms are itching, photophobia, burning, and tearing, irritation, mucoid discharge and eyelid swelling. Most common signs are giant papillae, superficial keratitis, and conjunctival hyperemia. The symptoms are similar in the other forms of allergic conjunctivitis but the time of onset, seasonal nature, chronicity and details of allergen exposure will vary according to the type.
Histopathology: As seen in the photograph the epithelium is thickened and spongiotic (intercellular edema or as seen here separation of epithelial cells).
There is dramatic hyperemia in the substantia propria and a chronic inflammatory infiltrate with numerous eosinophils. However, most important is the exocytosis of eosinophils within the epithelium (green arrow). The surface shows a desquamation of epithelium and inflammatory cells. Limbal papillae may occur in vernal keratoconjunctivitis (Horner-Trantas dots).
Treatment: Many of the treatment regimens are similar in all these forms of allergic conjunctivitis. Removal of the offending allergen and treatment with topical vasoconstrictors, mast cell stabilizers such as cromolyn sodium, topical nonsteroidals, cyclosporin in severe cases, and topical steroids (best avoided if possible) have been used. If steroids are used topically or by lid injection, careful surveillance of intraocular pressure is indicated.
