Purpose of review: To elaborate and review the immunologic spectrum of the five basic types of ocular allergy.
Recent findings: Perennial allergic conjunctivitis (PAC) appears to be an extension of seasonal allergic conjunctivitis (SAC) based on the similarity of clinical symptoms and the immune mechanism involved. T helper type 2 (TH2)-type cytokines, increased ratio of TH1/TH2 cytokines and increased statement of adhesion molecules all appear to play an integral role in the inflammatory process of SAC and PAC. Vernal keratoconjunctivitis (VKC), which is a pediatric disease, differs from SAC and PAC by its more severe and chronic nature. Increased numbers of T cells, eosinophils (along with the products of degranulation), chemokines and their receptors may contribute to the more serious symptoms of VKC. Atopic keratoconjunctivitis (AKC) is similar to VKC by the increased concentration of cytokines involved (i.e. interleukin-4 and -5). Despite clinical similarities with VKC, the presence of atopic dermatitis, along with some differences in clinical signs, make AKC a separate entity, which is sometimes referred to as an adult variant of VKC. Giant papillary conjunctivitis has similar cell involvement as VKC and AKC. However, giant papillary conjunctivitis differs from VKC and AKC by the clinical signs present (i.e. the presence of giant papillae) and the necessary concurrent contact lens wear.
Summary: The important differences and similarities observed in these five types of allergic diseases might help to better treat the patients affected with these disorders.